some recent insertion devices on operating third and fourth generation light sources

M. E. Couprie, ICFA Workshop on Future Light Source, Thomas Jefferson Nat. Acc. Facility. March. 5-9, 2012, Invited

Some recent Insertion Device innovations on operating third and

fourth generation light sourcesM. E. Couprie,

C. Benabderrahmane, F. Briquez, O. Marcouillé, F. Marteau, M. Valleau, P.

Berteaud, L. Chapuis, M. Massal, J. Vétéran, H. Abualrob, P. Brunelle, L. Nadolski, R.

Nagaoka, A. Nadji (Synchrotron SOLEIL), O. Chubar, C. Kitegi (BNL), J. M. Filhol (Fusion

to Energy)

Talk dedicated to P. Elleaume (✝ 2011, March 19)

mardi 6 mars 2012


1- In vacuum undulators and wigglersissues (transitions, direct in vacuum measurements..)quest for short period high field, cryogenic systemsin vacuum wigglers as an alternative to superconducting wigglers

2- EPU and fast polarization switchingelectromganetic systemPermanent magnet approachCombined electromagnetic- permanent magnet approach : EMPHU

3- Effect of IDs on the light source operationstrategies to compenstate unwanted effectsdesired effects : A Robinson wiggler as an alternative to the damping wigglercanted undulators

Outline

mardi 6 mars 2012


Introduction

Accelerator type issues for insertion devices

Emittance E2 1/E

Beamsize (µm) 100 (H)-10 (V) 50-10 10-3

vacuum chamber H /V aperture

flatmin gap: 5 mm

round (ex : bore 5 mm), min gap : 3 mm round

charge high 1 nC 10 pC

Pulse duration 10 ps 100 fs 10 fs

impedance very critical critical critical

field integrals very critical very critical very critical

double field integrals very critical very critical very critical

phase errorvery critical for high harmonics

operationcritical critical

multipoles for beam lifetime and injection efficiency less critical not critical

storage ring linac / ERL LWFA

mardi 6 mars 2012


I- In vacuum undulators and wigglers

In vacuum undulatorsMotivation : reach a higher field by placing directly the magnets inside the vacuum chamber

Historical steps :

Sm2Co17 : Br ≤ 1.05T; µHcj = 2.8 T; Nd2Fe14B : Br ≤ 1.4T (1.26T); µoHc = 1.4-1.6 ( resp. 2.4T)

Coercivity to avoid demagnetisation when baking and to resist against irradiation (GeV electrons, high energy photons and gamma-rays, neutrons) => Br<1.26T

• First prototype at BESSYW. Gudat et al. NIMA 246, 1986 50

• First In vac. undulator Installed on TRISTAN AR, Period : 40 mmX90, NdFeB (Br=1.2 T, iHc=21kOe), min gap 10 mm, B=0.82-0.36 T, NEG and sputter ion pumps, magnet stabilization at 125°C and vacuum commissioning at 115°C, S. Yamamoto et al. Rev. Sci. Instr 63, 400 (1992)

• 30 m long in-vacuum undulator at SPring-8 (SLUS-1) : 32 mm x 780, min gap = 12 mm (betaV = 15 m) B=0.59 T5 segments without gaps, very fine adjustments of the gap segments for phase error (11°=> 3.6°)H. Kitamura et al., NIMA 467 (2001) 110; T. Tanaka et al. NIMA 467, (2001) 149

• Revolver in-vacuum undulator (INVRUM) : 6 mm x 133, 10 mmx100, 15 mmX66, 20mmx50; min gap = 3.2 mm, B=0.74, 1.07, 1.32, 1.44 TT. Bizen et al. AIP 705, (2004), 175, 18th International Conference on Synchrotron Radiation Instrumentation, San Franscisco, 2003 417, H.S. Kang et al., EPAC 2006, 2771

Machine protection for the IVU to avoid magnet degradation, cases ESRF, APS

Then, the gap discrepancy between segments, which givesrise to a large phase error, was corrected. Finally, the wholemagnetic distribution has been obtained by combination ofthe fields in five segments and in four junctions.

Figure 10: 25-m long IVU installed in the LSS in SPring-8.

After installation in the LSS, effects on the electronbeam were investigate with the gap closed down to 12 mm,and no serious problems were found except a slight degra-dation of the beam lifetime. After that the radiation spec-trum was measured to estimate the performance of the 25-m IVU as a SR light source and it was found that the band-width was a little wider than expected. After investigationof several factors, it was concluded that the geomagneticfield would be the most probable source, because the direc-tion of the undulator, in which the field corrections werecarried out, differed by 90◦ from the direction of installa-tion in the storage ring. In order to correct it, a uniformfield was applied to cancel the geomagnetic field. As a re-sult, the bandwidth was reduced to ideal one [17]. This factshows that the field measurement and correction carried outfor the 25-m IVU were very precise.

ADVANTAGES IN THE X-RAY FEL

IVUs installed in the storage ring have been describedso far. As a matter of course, the IVU can be utilizedas a driver for the FEL. In fact, the SCSS [18] and PAL-XFEL [19] projects are going to adopt the IVU with pe-riodic length shorter than 20 mm to realize an x-ray FELwith less electron energy, smaller facility scale, and thuslower cost.

Besides the advantage of reducing the electron energy,the IVU has several advantages over the conventional out-vacuum undulator when employed in the X-ray FEL facil-ity where a very long undulator is required for saturation.

Alignment using Optical Laser

An alignment procedure using an optical laser beam isproposed for the SCSS project in order to align the BPMsinstalled in the undulator line [20]. The diffraction pattern

of the laser beam generated by an iris inserted in the BPMpositions is monitored with a CCD camera installed down-stream. For this to be applicable, it is necessary to let theoptical laser pass through the entire undulator line, mean-ing that a wide clearance for the optical path is required. Itis easy for the IVU to realize it because the vacuum gap isvariable unlike the out-vacuum undulators.

Commissioning

The variable vacuum gap is also useful for the initialcommissioning of the electron beam. The wide clearancecreated by fully opening the gap will make it easier. In ad-dition, it is also important for the “FEL commissioning”, orthe on-beam alignment of components installed in the un-dulator line such as the BPMs, undulators, phase shifters,and correction coils. It is to be carried out by monitoringthe spontaneous radiation emitted from one or two adja-cent undulator segments. If the vacuum gap is narrow, thenthe spontaneous radiation emitted near the entrance of theundulator line may be disturbed by the undulator segmentnear the exit.

R&DS UNDER PROGRESS

In SPring-8, a number of R&Ds are under progress forfuture improvement of the IVU and related technology.Two of them are introduced in the following sections.

Cryoundulator

As mentioned in the “Permanent Magnet” section, PMswith high coercivity should be chosen for the IVU toavoid irreversible demagnetization during the bakeout pro-cess and due to radiation damage, which in turn limits theachievable peak field because such PMs have relatively lowremanent field. For example, the remanent field and coer-civity of NEOMAX35EH, which is the PM material nor-mally used for the IVU, are 1.15T and 2000kA/m, respec-tively.

Now let us assume that the magnet arrays are cooleddown to be operated at a cryogenic temperature. Then,outgassing from the PM blocks are reduced considerably;rather, the magnet array may work as a cryopump, mean-ing that the bakeout process is no more necessary. In ad-dition, the PM characteristics are improved a lot becauseboth the remanent field and coercivity normally have a neg-ative temperature coefficient. For example, the remanentfield and coercivity of NEOMAX50BH at a temperature of140K, which has the highest remanent field among the PMmaterials that are commercially available, are found to be1.58T and 3000kA/m, respectively. Compared these valuesto those of NEOMAX35EH, we can expect a 40% increasein peak field and a higher resistance to radiation damage.This is the concept of the cryogenic permanent magnet un-dulator, or the cryoundulator [21].

From the experiments to investigate the temperature de-pendence of PM material, it has been found that the rema-

Proceedings of the 27th International Free Electron Laser Conference

21-26 August 2005, Stanford, California, USA 375 JACoW / eConf C0508213

ION INSTABILITY OBSERVED IN PLS REVOLVER IN-VACUUMUNDULATOR∗

H. S. Kang† , T. Y. Lee, M. G. Kim, C. D. Park, T. Y. Koo, J. ChoiPohang Accelerator Laboratory, POSTECH, Pohang, Kyungbuk, 790-784 KOREA

AbstractRevolver In-Vacuum X-ray Undulator which was de-

signed and fabricated at Spring-8 is under commissioningat PLS. This planar undulator whose permanent magnet ar-ray structure is a revolving type with 90-degree step pro-vides 4 different undulator wavelengths of 10, 15, 20, and24 mm. The minimum gap of the undulator is 5 mm. It wasobserved that the trailing part of a long bunch-train wasscraped off due to ion instability when the undulator gapwas closed down below 6.4 mm. At that time the vacuumpressure in the undulator, which is estimated to be severaltimes lower than that at the undulator gap, increased from1.4×10−10 (gap 20 mm) to 7.9×10−10 Torr (gap 6 mm) atthe stored beam current of 100 mA. This high vacuum pres-sure causes fast beam-ion instability: trailing part of a longbunch-train oscillates vertically. It was also confirmed thatadjusting the orbit along the undulator has improved thesituation appreciably. The ion instability measured with apico-second streak camera and a one-turn BPM as well asthe result of orbit adjustment will be described in this paper.

INTRODUCTIONThe in-vacuum undulator has become popular in the 3-

rd generation light sources because it provides a possibil-ity of hard x-ray experiments in a medium-scale SR facili-ties. Many SR facilities such as SLS, ESRF, KEK, SSRL,SPring-8, NSLS, ALS, and PLS are using in-vacuum un-dulators [1, 2, 3].The stray synchrotron radiation should be blocked by ap-

propriately located photon stops in the storage ring to keepthe vacuum good because the outgassing from the cham-ber surface irradiated by stray synchrotron radiation is veryhuge. But the continuous irradiation of small amount ofstray synchrotron radiation can make the chamber surfaceclean. Under the certain circumstances such as misguidedor badly set orbit, the chamber already cleaned before doesnot cast an outgassing problem.In the out-vacuum undulator the inner surface of the vac-

uum chamber is likely to be continuously cleaned by straysynchrotron radiation so that the surface is very clean andis not weak to beam wake and/or stray synchrotron radia-tion. But, the permanent magnet array of in-vacuum un-dulator which is covered with copper plate is exposed toelectron beam and stray synchrotron radiation. The clean-ing by stray synchrotron radiation is only effective whenthe gap is closed down enough to see the radiation. Thus,

∗Work supported by Korean Ministry of Science and Technology† [email protected]

the surface condition is not good because the cleaning isintermittent depending on the position of the magnet array.That is why the inner surface of the in-vacuum undulator isweak to stray synchrotron radiation.In PLS (Pohang Light Source) there are six insertion

devices in the ring: two out-vacuum undulators, two out-vacuum wigglers, and one in-vacuum undulator. Thein-vacuum undulator is a revolver undulator (RevolverIn-Vacuum X-ray UNdulator) designed and fabricated atSpring-8 [4]. The concept of a revolver undulator is tomount a number of magnet arrays with different periodlengths on a rotary beam, which enables users to select anappropriate one among them for their experiments. Thepermanent magnet array structure of the revolver undulatoris a revolving type with 90-degree step, which provides 4different undulator wavelengths of 10, 15, 20, and 24 mm.The available radiation wavelengths are four times the con-ventional in-vacuum undulator. Figure 1 shows the magnetarray structure. The magnet material is Nd2Fe14B. Theminimum gap of the revolver is 5 mm and its magnet lengthis 1.2 meter.We observed ion instability when the gap of the revolver

was closed down below 6.4 mm. The instability was causedby vacuum degradation in the revolver. It was also foundthat adjusting the orbit along the revolver has improved thesituation appreciably.

Figure 1: Permanent magnet array structure of the in-vacuum revolver (RIVXUN).

ION INSTABILITYWhen the gap size was above 7mm, there was no insta-

bility and no lifetime change at the beam current of 165mA. However, below 6.4mm, transverse ion instability ap-peared and then beam loss occurred. At that time the re-

Proceedings of EPAC 2006, Edinburgh, Scotland THOAFI02

05 Beam Dynamics and Electromagnetic FieldsD04 Instabilities - Processes, Impedances, Countermeasures

2771

mardi 6 mars 2012


Impedance issues : RF transitionsI- In vacuum undulators and wigglers

SPring-8 design, first adopted by SLS(images : courtesy T. Hara)

A. Madur et al., PAC 2009; 333

Cu Taper plates

Sliding contacts

IVID Entrancee! beam

Figure 2: Transition parts between vacuum chamber flangeand IVID gap (from left to right) - Cooling lines are notshown on this picture

and is 80 mm long. Since we could only access the interiorfrom the viewport windows, we inspected the ends region.These regions include the transition plates, the RF fingersand the extremities of the undulator i.e. the conducting foilinstalled on top of the magnets. From the ends we hada global view of the inside of the IVID vacuum chamber.From the inspection we determined the following:

• no discoloration on the sliding contacts: they are notoverheating,

• no discoloration on each part of the transition regions,• some small scratches (order of 1 mm wide) and some

wrinkles on the conductive foil,• an important discoloration around one hole on the

conductive foil; the foil is designed with pairs of 2mm diameter holes distributed longitudinally near theouter edges in order to get a flat surface on the foil (notrapped volume) after its installation,

• some dust deposition; this dust is aligned with thetransverse edges of the magnets.

Figure 3: Pictures from inspection. Left: discolorationand missing copper around a hole. Middle: dust depositedalong magnet edges. Right: Line of dust and a scratch onthe surface (shiny spot)

The left picture from Fig. 3 captured our attention. Ourinterpretation of this picture was that it showed copperpeeling off and cracking due to heat induced stress.

Moreover we collected some samples of the dust in orderto analyze it. The analysis has been performed by EvansAnalytical Group (EAG) [4] using the Energy DispersiveX-ray Spectroscopy method to determine the dust com-position. The dust materials include: aluminum, carbon,

chlorine, chromium, cobalt, copper, iridium, iron, lead,magnesium, molybdenum, nickel, oxygen, potassium, sili-con, sulfur, titanium and zinc. The presence of copper andnickel is consistent with our interpretation from the Fig. 3i.e. deterioration of the conductive foil. After several dis-cussions with Spring8 [2] and colleagues from the insertiondevices community, we decided to replace the conductivefoils.

Replacement of the Cu-Ni FoilsWe replaced the conductive foil in collaboration with

the device manufacturer, Hitachi-Neomax [1] during theSeptember 2008 ALS shutdown. With the help of threequalified technicians from Japan, we managed to removethe IVID from the ALS storage ring, replace the conduc-tive foils and re-install the IVID within four weeks. Theconductive foils replacement also provided an opportunityto directly inspect the IVID.

The main observation from this work is that the conduc-tive foil seemed to be in good shape; the scratches wererelatively small and to be acceptable; they likely occurredduring the initial IVID assembly. The picture of the discol-oration around the hole (Fig. 3) was actually showing anextra layer of nickel. During the plating process, it some-times happens that some nickel material overflows to thecopper side. Consequently no copper was missing at thatlocation and the presence of nickel on the copper side doesnot affect the conductive foil quality.

While inspecting the “old” foils, we also noticed tinybrown spots that were randomly spaced all along the foil.It was not possible to tell if they were the result of the orig-inal fabrication or if they have been generated by vaporizedpieces of dust.

COMMISSIONING AND ACCELERATORPHYSICS SHIFT OBSERVATIONS

CommissioningAfter the foil replacement and the installation of the

IVID back in the ALS storage ring, the IVID was againcommissioned. The result of the commissioning demon-strated that the beam dynamics in term of tune, lifetime,dipole errors and beam size instability were not affectedwith the attempted repair.

We checked the IVID vertical alignment with the elec-tron beam and found an offset of 200 µm which is similarto the one measured before the conductive foil replacement.An alignment of the IVID will be scheduled in the near fu-ture in order to have a balanced beam clearance and heatdeposition between the top and bottom conductive foils.

Following re-installation of IVID in the ALS storagering, it took more than three months to achieve the desiredvacuum performance, 10−11 Torr range (10−9 Pa). Ther-mal outgassing was the result of image current heating andupstream synchrotron radiation dissipating in the conduc-tive foils. This issue has prevented us from operating at

MO6PFP087 Proceedings of PAC09, Vancouver, BC, Canada

334

Magnets

T15 - Undulators and Wigglers

ALS design

T. Nakamura et al. PAC 2001, 1969

s en place

agnétique

mardi 6 mars 2012


Impedance issues : RF transitions

5040

10

60

2030

300

200

100

Températures

Gap


Change of the design at SOLEIL : for SOLEIL storage ring operation at 500 mA

mardi 6 mars 2012


Impedance issues : RF transitions

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⎮Z/n⎮eff = 0.45 Ω, 5 in vacuum ID contribution : 11.6 mΩ

10 taper of middle SS contribution : 9.3 mΩ

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mardi 6 mars 2012


Liner : conductive Ni-Cu foil

Impedance issues : liner


Liner

ESRF/SPring-8 : burned 50 µm stainless steel foil=> demagnetisation of 0.5 % between poles 70-120

=> Cu(10 µm)-Ni(50 µm) foil with better thermal and electric conductivity

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Liner : Conductive foil image current, heat load due to wakefields or up

stream synchrotron radiationSome observations of liner degradation

beam measurements • obstacles with bumps

• outgassing• partial loss

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T. Hara et al., SPring-8 in-vacuum undulator beam test at the ESRF, J. Synchrotron Rad. (1998), 5, 406-408

mardi 6 mars 2012


Some observations of liner degradation

A. Madur et al., PAC 2009; 333

Cu Taper plates

Sliding contacts

IVID Entrancee! beam

Figure 2: Transition parts between vacuum chamber flangeand IVID gap (from left to right) - Cooling lines are notshown on this picture

and is 80 mm long. Since we could only access the interiorfrom the viewport windows, we inspected the ends region.These regions include the transition plates, the RF fingersand the extremities of the undulator i.e. the conducting foilinstalled on top of the magnets. From the ends we hada global view of the inside of the IVID vacuum chamber.From the inspection we determined the following:

• no discoloration on the sliding contacts: they are notoverheating,

• no discoloration on each part of the transition regions,• some small scratches (order of 1 mm wide) and some

wrinkles on the conductive foil,• an important discoloration around one hole on the

conductive foil; the foil is designed with pairs of 2mm diameter holes distributed longitudinally near theouter edges in order to get a flat surface on the foil (notrapped volume) after its installation,

• some dust deposition; this dust is aligned with thetransverse edges of the magnets.

Figure 3: Pictures from inspection. Left: discolorationand missing copper around a hole. Middle: dust depositedalong magnet edges. Right: Line of dust and a scratch onthe surface (shiny spot)

The left picture from Fig. 3 captured our attention. Ourinterpretation of this picture was that it showed copperpeeling off and cracking due to heat induced stress.

Moreover we collected some samples of the dust in orderto analyze it. The analysis has been performed by EvansAnalytical Group (EAG) [4] using the Energy DispersiveX-ray Spectroscopy method to determine the dust com-position. The dust materials include: aluminum, carbon,

chlorine, chromium, cobalt, copper, iridium, iron, lead,magnesium, molybdenum, nickel, oxygen, potassium, sili-con, sulfur, titanium and zinc. The presence of copper andnickel is consistent with our interpretation from the Fig. 3i.e. deterioration of the conductive foil. After several dis-cussions with Spring8 [2] and colleagues from the insertiondevices community, we decided to replace the conductivefoils.

Replacement of the Cu-Ni FoilsWe replaced the conductive foil in collaboration with

the device manufacturer, Hitachi-Neomax [1] during theSeptember 2008 ALS shutdown. With the help of threequalified technicians from Japan, we managed to removethe IVID from the ALS storage ring, replace the conduc-tive foils and re-install the IVID within four weeks. Theconductive foils replacement also provided an opportunityto directly inspect the IVID.

The main observation from this work is that the conduc-tive foil seemed to be in good shape; the scratches wererelatively small and to be acceptable; they likely occurredduring the initial IVID assembly. The picture of the discol-oration around the hole (Fig. 3) was actually showing anextra layer of nickel. During the plating process, it some-times happens that some nickel material overflows to thecopper side. Consequently no copper was missing at thatlocation and the presence of nickel on the copper side doesnot affect the conductive foil quality.

While inspecting the “old” foils, we also noticed tinybrown spots that were randomly spaced all along the foil.It was not possible to tell if they were the result of the orig-inal fabrication or if they have been generated by vaporizedpieces of dust.

COMMISSIONING AND ACCELERATORPHYSICS SHIFT OBSERVATIONS

CommissioningAfter the foil replacement and the installation of the

IVID back in the ALS storage ring, the IVID was againcommissioned. The result of the commissioning demon-strated that the beam dynamics in term of tune, lifetime,dipole errors and beam size instability were not affectedwith the attempted repair.

We checked the IVID vertical alignment with the elec-tron beam and found an offset of 200 µm which is similarto the one measured before the conductive foil replacement.An alignment of the IVID will be scheduled in the near fu-ture in order to have a balanced beam clearance and heatdeposition between the top and bottom conductive foils.

Following re-installation of IVID in the ALS storagering, it took more than three months to achieve the desiredvacuum performance, 10−11 Torr range (10−9 Pa). Ther-mal outgassing was the result of image current heating andupstream synchrotron radiation dissipating in the conduc-tive foils. This issue has prevented us from operating at

MO6PFP087 Proceedings of PAC09, Vancouver, BC, Canada

334

Magnets


Solution : liner tensor

ALS

SOLEIL : burned thermocouple (U20 n°4), beam heating (U20 n°5)

Impedance issues : LinerI- In vacuum undulators and wigglers

Section

SDC

SDM

Position T L T L Type RS CS RS CS

Pt RS CS RS CS

Pt

4 /4 1.2 9.8 3 13.1 27.1 2.4 9.8 3.4 13.1 28.7 3 /4 1.2 13.2 3 17.5 34.8 2.4 13.2 3.4 17.5 36.5 hybrid 1.2 13.3 3 18 35.5 2.4 13.3 3.4 18 37.1 8 b 120 0.3 2.6 0.7 21.4 25 0.6 2.6 0.8 21.4 25.4 8 b 80 0.2 2.3 0.5 9.5 12.5 0.4 2.3 0.5 9.5 12.7 1 bunch 0.05 2.57 0.1 4.7 7.4 0.09 2.57 0.14 4.7 7.5

Section

SDL9

SDL13

Position T L T L Type RS CS RS CS

Pt RS CS RS CS

Pt

4/4 6.4 9.8 3.4 13.1 32.7 17.6 9.8 1 13.1 41.5 3 /4 6.4 13.2 3.4 17.7 40.5 17.6 13.2 1 17.5 49.3 hybrid 6.4 13.3 3.4 18 41.1 17.6 13.3 1 18 49.9 8 b 120 1.5 2.6 0.8 21.4 26.3 4.2 2.6 0.24 21.4 28.5 8 b 80 1 2.3 0.5 9.5 13.3 2.8 2.3 0.16 9.5 14.8 1 bunch 0.26 2.57 0.14 4.7 7.7 0.7 2.57 0.04 4.7 8

0.7mm off axis, 0.4 mm excitation

mardi 6 mars 2012


Magnetic measurementsI- In vacuum undulators and wigglers

Chamber installationIn vac. und. Bench

3D Hall probe, flipping coils

• Use of a conventional bench based on the displacement of the magnetic sensor (Hall

probe, flopping coil) by an actuation stage of high precision

- without in situ magnetic measurements

mardi 6 mars 2012



- without in situ magnetic measurements, for no lateral access• Use of the pulsed wire technique

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Pulse 4.5 A ∆t=10 µs, Signal/Noise :

26.02 dB

CuBe wire : 125 µm diameter, 10 N, sag : 65 µm5 A 2 µs bipolar pulse generator

developed in house

Photodiode for vibration detection

SOLEIL : 1 T, 18 mm period, 2 m long undulator

Measurements of SOLEIL Insertion Devices using Pulsed Wire Method , M. Valléau, C. Benabderrahmane, M.-E. Couprie, O. Marcouillé, F. Marteau, J. Vétéran , IPAC2011, San Sebastián, Spain, 3242-3244

SOLEIL

INTRODUCTIONPRÉSENTATION DE LA MÉTHODE

DISPOSITIF EXPÉRIMENTALRÉSULTATS

CONCLUSIONANNEXES

ObjectifLa chaîne d’acquisition

But : optimiser le rapport signal sur bruit

Aug. sensibilité Aug. impulsion Filtrage Aug. tension Pointcapteurs de courant numérique mécanique d’attention

Fréq. de résonnance X Effet JouleVibrations externes X Effet Joule

Déformations X ! aux BFBruit X X ! aux BFFlèche X Déflexion diminuée

Figure 12: Courbe d’intégrale simple

- Paul Sherrer Institute a :Impulsion : I � 5 A, �t� 10 �sOnd. : �0 � 19 mm�B0 � 1 TS/N = 9.54 dB

- Soleil :Impulsion : I � 4�5 A, �t� 10 �sOnd. : �0 � 18 mm�B0 � 1 TS/N = 26.02 dB

a. T. SCHMIDT et al.,The pulsed wire

magnetic measurement system, Internatio-nal Magnetic Measurements Workshop 16,

2009

M. VALLÉAU La méthode du fil pulsé

The Pulse wire magnetic measurement system, T. Schmidt, International Magnetic Measurements Workshop 16, 2009

Swiss Light Source : 1 T, 19 mm period, Signal/Noise = 26.02 dB

R.W. Warren, ”Limitations on the use of the pulsed-wire field measuring technique”, Nucl. Instr. and Meth. A272 (1988) 257

Measurements of SOLEIL insertion devices using pulsed wire method

M. Valleau�, C. Benabderahmane, M.E. Couprie, O. Marcouille, F. Marteau And J. VeteranSynchrotron-SOLEIL, Saint-Aubin, FRANCE

AbstractSOLEIL permanent magnets insertion devices are usu-

ally measured with a Hall probe in order to evaluate theelectron angular deflexion, their deviation and the opti-cal phase error [1]. A pulsed wire bench is developed atSOLEIL for reducing the measurement time of an undula-tor and for providing a measurement method without lateralaccess. A current pulse injected in a stretched wire insidethe magnetic field area generates an acoustic wave. Thewire motion is detected by optical sensors whose signalsare proportional to the local integral value. The signal-to-noise ratio of this method is often reduced due to severaleffects such as acoustic noises, external and wire vibra-tions. However, following some hardware optimization itwas possible to increase it up to almost 26 dB, making themethod accurate and reproducible in order to realize effi-cient corrections. Measurements of first and second fieldintegral performed with Pulsed wire and Hall probe arecompared on two different types of insertions: an ��APPLE-II undulator and a �� in vacuum wiggler [2].

INTRODUCTIONSOLEIL storage ring is equipped of �� permanent

magnets undulators of various kinds [3] (�� APPLE II, �planar in-vacuum and � in-vacuum wiggler) with a periodranging from �� to �� . Some can also provideelliptical or quasi-periodic field with a magnetic lengthvarying from �� to � �. Measuring the magnetic fieldpoint by point with Hall probe is necessary to evaluatethe trajectory of the electron and the optical performancesas phase errors, but is time-consumming even if it maybe one of the most accurate and reliable method. Thepulsed wire method has been developed in �� [4] asan alternative technique to characterize narrow gaps orlateral accessless insertion devices. The advantage of thismethod is to measure in few �� the first or second fieldintegral of an undulator reducing the time to correct mag-netic field errors. However, it suffers from a lot of effectswhich tends to add noise and distortions to the main signal.

Figure 1 shows the set-up of the bench consistingin a thin wire stretched along the magnetic axis of theinsertion device. A current pulse excites acoustic waves,generated by to Laplace forces, which travel at bothextremities. Optical sensors measure the wire transverseand vertical deflection which allows to calculate the first

�[email protected]

Figure 1: Set-up of the pulsed wire bench.

or second field integral point by point. Sending a pulseshorter than the time spent by the wave to propagatealong a single period of the insertion enables to measurethe angular deflection according to equation (1) (resp.equation (2)) in the vertical (resp. horizontal) plane [4].

��

��

� ��

�� (1)

��

��

� ��

�� (2)

with �� and �� the intensity and duration of the pulse, �the wire linear mass density, � the wave speed, �� (resp��) the horizontal (resp. vertical) magnetic field. The sec-ond integral, obtained by injecting a pulse longer than thetime spend by the wave to propagate along all the insertiondevice is given by equation (3) (resp. equation (4)) in thevertical (resp.horizontal) plane. This quantity representsthe electron beam path along the insertion device.

��

� ��

� (3)

��

� ��

� (4)

THE PULSED WIRE MEASUREMENTBENCH AT SOLEIL

Signal to noise ratio improvementsEven if the major drawback of the method is the low sig-

nal to noise ratio, the set-up developed at SOLEIL aims at

mardi 6 mars 2012



- in situ magnetic measurementsex : SAFALI (Self aligned field analyzer with laser instrumentation)

T. Tanaka et al, FEL 2007, Novosibirsk, 468;T. Tanaka et al. FEL 2008, Gyeonju, 371; T. Tanaka, et al., . Phys. Rev. Spec.Topics 12, 120702 (2009)

O-ring reciprocating seal

4axis-stage(remote 2axis)

xy linearguide

Top View

Side View

θz rotarystage

θx,y stage

x,y stage

to TMP

to TMP

SUS pipe

Figure 4: Schematic illustration of the SAFALI system forthe CPMU prototype.

cating seals have been installed to insert the SUS tube to fixthe cantilever of the Hall probe, which is actuated by meansof pushing or pulling the end of the tube. The Hall probeposition feedback is performed by the multi-axis stage sup-porting the vacuum duct including the O-ring seal. Thevariation of the Hall probe position during actuation wasslightly worse than the system for IVU24 described in thepreceding section, however, the reproducibility was simi-lar. For details, refer to [3].

RESULTS OF MEASUREMENT

IVU24We measured the magnetic distribution at the gap values

of 6, 8, 10, 14, and 20 mm and compared the magnetic per-formances with those measured by a conventional methodin July 2000, just after the field correction and before in-stallation in the SLS ring. The results are shown in Fig. 5in terms of the electron trajectory (2nd field integral) andphase error distribution.

We find negligible difference between the two measure-ments in terms of the electron trajectory, while a small dis-crepancy in the phase error distribution suggests that themagnetic field distribution has changed slightly. It shouldbe emphasized, however, that the variation is very smalland less than 0.5 degree in r.m.s. So we can concludethat no significant demagnetization took place in the IVU24during operation.

CPMU PrototypeWe measured the field distribution of CPMU prototype

at different temperatures and found that the peak field be-came maximum at a temperature of 130 K. During the mea-surement, the gap was fixed at 5 mm by measuring directlythe distance between the top and bottom magnet arrays bymeans of a laser scan micrometer. From the point of viewof field correction, what is important is the phase error vari-ation due to temperature change. Figure 6 shows the mag-netic performances measured at room temperature and 130K in terms of the electron trajectory and phase error. Wefind negligible difference between the performances at two

-800 -400 0 400 800

-3

0

3

6

-3

0

3

6

-3

0

3

6

-3

0

3

6

-3

0

3

6

6mm

z (mm)

8mm

20mm

10mm

2nd

Fie

ld In

tgeg

ral (

103 G

.cm

2 )

14mm

0 10 20 30 40 50 60 70 80 90 100 110

-8

-4

0

4

8

-8

-4

0

4

8

-8

-4

0

4

8

-8

-4

0

4

8

-8

-4

0

4

8

Pole Number

Pha

se E

rror

(de

gree

)

March 2007 (SAFALI) July 2000 (Conventional)

Figure 5: Comparison of magnetic performances of IVU24between July 2000 and March 2007. Note that measure-ment in July 2000 was done by a conventional method.

different temperatures, suggesting that cooling the perma-nent magnets did not induce a large change in the errormagnetic components that could affect the undulator per-formance. This is a very encouraging result toward realiza-tion of CPMUs.

-300 -200 -100 0 100 200 300

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2nd

Fie

ld Int

egra

l (10

3 G.c

m2 )

z(mm)

300K 130K

0 10 20 30 40 50 60 70

-10

-8

-6

-4

-2

0

2

4

6

Pha

se E

rror

(de

gree

)

Pole Number

300K (3.3o)

130K (3.2o)

Figure 6: Variation of magnetic performances of CPMUprototype at room temperature and 130 K.

SUMMARY

We have described the SAFALI system as a new schemeof undulator field characterization and its practical appli-cation. It should be also stressed that the SAFALI sys-tem is portable: the magnetic performance of IVUs can bechecked at any time without moving to the laboratory or fa-cility for the field measurement. Such a portability is veryimportant especially in X-ray FEL facilities where a num-ber of undulators will be installed. The SAFALI system canbe used not only for the final check after assembly but alsoto monitor the magnetic performance as the FEL driver. Wealso note that most undulators nowadays have a C-shapedframe, but not a O-shaped frame, in order to ensure open-ings for field mapping with Hall probe scanning, whetherthey are in-vacuum or out-vacuum. This imposes a severerestriction on the undulator design, because C-shape frame

WEPPH052 Proceedings of FEL 2007, Novosibirsk, Russia

FEL Technology II

470

Light Source (SLS) as a collaboration to aim at utilizationof angstrom x rays in the medium-sized SR facility. After3-year operation, IVU24 has been replaced with anotherIVU and returned to SPring-8. It is important to measurethe magnetic field of IVU24 and compare with the initialstate, and to check the variation of magnetic performancesfrom the point of view of demagnetization due to electronirradiation during operation.

Top View

Side View

steppermotor

laser diode

undulator magnet Hall probeiris

2-axis stagecarriage

corner cube

rail

laser scale

PSD

Figure 1: Schematic illustration of the SAFALI system forthe CPMU prototype.

Figure 1 shows a schematic illustration of the SAFALIsystem for IVU24. We have installed a rail and carriage toactuate the Hall probe by means of a tensioned loop wiredriven by a stepper motor. The Hall probe cantilever wasattached to the carriage together with the cubic mirror toreflect the laser beam of the laser scale to measure the lon-gitudinal position of the Hall probe. In addition, two irisesare attached at the both ends of the Hall probe cantileverwith a diameter of 2 mm. In order to measure the transverseHall probe position during actuation, two laser beams wereintroduced to irradiate the irises and create laser spots atthe opposite side. The positions of the laser spot were mea-sured with position sensitive detectors (PSDs), the averageof which defines the position of the Hall probe.

-1000 -800 -600 -400 -200 0 200 400 600 800 1000

-0.1

0.0

0.1

0.2

0.3

with feedbackσ

x=4.9µm,σ

y=3.9µm

Tra

nsv

ers

Posi

tion (m

m)

z (mm)

Horizontal Vertical

without feedbackσ

x=51µm,σ

y=79µm

Figure 2: Variation of the Hall probe position with andwithout feedback.

The feedback of the Hall probe position is done by mov-ing the rail with the three sets of 2-axis stages supporting

the rail. Figure 2 shows the variation of the Hall probe po-sition measured with and without the feedback procedure.We can clearly find the effects due to the feedback. Themagnetic error due to the positional deviation of 5 µ is just5×10−6 for an undulator with a magnetic period of 10 mm,and smaller for a longer period.

As a field measurement system for undulators, the re-producibility is the most important. We measured the mag-netic field distribution of IVU24 four times under the samecondition to examine the reproducibility. The results areshown in Fig. 3 in terms of the phase error as a functionof the pole number, where we find quite a good agreementbetween the measurement results.

0 10 20 30 40 50 60 70 80 90 100 110

-10

-8

-6

-4

-2

0

2

4

6

1st 2nd 3rd 4th

Phase

Err

or (d

egre

e)

Pole Numbere

Figure 3: Reproducibility of the field measurement in termsof the phase error distribution.

As described above, the developed SAFALI system hasbeen found to have a performance good and reliable enoughto measure the magnetic field of IVU24.

SAFALI FOR CPMU PROTOTYPE

The CPMU is a novel undulator proposed at SPring-8in 2004 [1]. The permanent magnets in the IVU is cooleddown to improve the magnetic property in terms of the re-manence and coercivity. The operation temperature will bearound 100∼150K where the remanence becomes maxi-mum, and much higher than liquid helium, so the operationwill be much more feasible than superconducting undula-tors composed of NbTi wires. We have constructed a pro-totype of CPMU with a magnetic length of 600 mm and amagnetic period of 15 mm and made experiments to inves-tigate the feasibility of CPMUs such as the cooling capa-bility, variation of the magnetic gap and tapering during thecooling process [2]. Although promising results have beenobtained in these experiments, we have to establish a fieldmeasurement technique to be adapted to the CPMUs. So,we have developed a system based on the SAFALI methodto measure accurately the magnetic performance at a cryo-genic temperature [3].

Figure 4 shows a schematic illustration of the SAFALIsystem for the CPMU prototype. A pair of O-ring recipro-

Proceedings of FEL 2007, Novosibirsk, Russia WEPPH052

FEL Technology II

469

SACLA undulators

T. Tanabe, et al., . Design concept for a modular in vacuum probe mapper for use with CPMU convertible in vacuum undulators of varying magnetic length, PAC 2011, 2534

mardi 6 mars 2012


Magnetic correctionsI- In vacuum undulators and wigglers

Shimming In Situ Sorting, Swapping

Change of the undulator inner gap

ex : 5.5 mm => 5.15 mm

Shim

T. Tanaka et al, Undulator field correction by in situ sorting, NIMA 465 (2001) 600ex : phase error 16° to 2.2°

stretched-wire system and the phase errors areobtained from the magnetic distribution along thez- axis measured with a Hall probe. The essence ofin-situ sorting consists in rearrangement of mag-nets not according to the magnetic field of eachmagnet measured before assembly but to the fieldof the total device measured after assembly.

3.1. Data processing

First of all, how the magnetic data measuredwith a Hall probe is processed is described. We canobtain from this measurement many character-istics such as the electron velocity and position,electric field formed by the electron, and thespectral intensity. In particular, the first fieldintegral over the range of a specific magnet poleis important for the in-situ sorting, which isdefined as the deflection caused by the nth magnetpole given by

I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ

where zn ¼ %L=2þ nlu=2 is the boundary betweenthe nth and ðnþ 1Þth poles and BðzÞ is themagnetic field as a function of z. We can obtainfrom I1n two important functions to determine therearrangement of magnets for the in-situ sorting.

The first function is called an error storage ESn

defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ

where hIi is the mean value of jI1nj. We havefound that ESn has a strong correlation with thephase error [3] as shown in Fig. 1.

The second function is called a field storage FSn

defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with

fn ¼ I1n % ð%1ÞnhIi: ð6Þ

Here, the peak field at odd poles are assumed to bepositive. The quantity fn shows an error deflectionat the nth pole and FSn the accumulation of fn. Theerror deflection means an extra kick in addition tothe normal deflection corresponding to the K valueof the device, therefore, FSn is expected to be agood approximation of the electron orbit as shownin Fig. 2. We have to suppress the orbit deviationbecause it causes a rapid oscillation of the phaseerror as the function of the magnet pole. Reduc-tion of the field storage is important for thispurpose.

3.2. Multipole reduction

After measuring the field integral as a functionof the horizontal position, we can determine thepolynomial representing the I–X curve by a leastsquare fitting to obtain the multipole componentsof the total device (total multipole). Because thefield integral corresponds to the summation of I1nover all poles, we can improve the total multipole

Fig. 1. Comparison of the error storage (top) and phase error(bottom) as functions of the magnet pole number.

T. Tanaka et al. / Nuclear Instruments and Methods in Physics Research A 465 (2001) 600–605602

by correcting the field of the pole which has thelargest contribution to the total multipole. For thispurpose, the magnetic distributions along z-axis asfunctions of the horizontal positions are measuredto obtain I1nðxÞ, where the argument x means thehorizontal position. Now we can obtain themultipole components for the nth pole by theleast square fitting of I1nðxÞ and look for the polewith the largest contribution to the total multipole(the worst pole). In order to reduce the contribu-tion of the worst pole, the magnets forming it areflipped.

How the magnet is to be flipped is schematicallyshown in Figs. 3(a)–(c). The arrows indicatedbetween the magnets show error fields to becorrected and those indicated in the magnets showthe direction of the magnetization causing the

error field. If the direction of the field integral to becorrected is vertical, we can expect that flipping themagnet vertically as shown in Fig. 3(a) reduces thetotal multipole, however, it has no effect on thehorizontal field. We have to flip horizontally asshown in Fig. 3(b) to reduce the horizontal dipole,sextupole, and higher multipoles of even numbers.As for the horizontal multipoles of odd numbers,we have to flip the magnet itself to change thesurface facing the undulator axis as shown inFig. 3(c). We have to select the magnet to beflipped so that the effects on the total multipole islarge for the components to be corrected andnegligible or small for others.

Fig. 2. Comparison of the field storage as a function of themagnet pole number (top) and the electron orbit in terms of the2nd field integral (bottom). The pole number of 140 corre-sponds to the z position of 0, or the center of the undulator.

Fig. 3. How to flip the magnets to reduce the total multipole:(a) vertical, (b) horizontal, and (c) surface flip, respectively. Thehatched area shows the plane with respect to which the magnetsare flipped. If the main polarity of the magnet is reversed byflipping, the location of the magnets should be changed so thatthe undulator sinusoidal field is not disturbed. In the case of thesurface flip (c), only the magnet is flipped to change the surfacefacing the undulator axis.

T. Tanaka et al. / Nuclear Instruments and Methods in Physics Research A 465 (2001) 600–605 603




I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with










I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with










I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with






T. Tanaka et al. / Nuclear Instruments and Methods in Physics Research A 465 (2001) 600–605602stretched-wire system and the phase errors areobtained from the magnetic distribution along thez- axis measured with a Hall probe. The essence ofin-situ sorting consists in rearrangement of mag-nets not according to the magnetic field of eachmagnet measured before assembly but to the fieldof the total device measured after assembly.



I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with










I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with










I1n ¼Z znþ1

zn

BðzÞ dz; ð2Þ



defined as

ESn ¼X

n

m¼1

im ; ð3Þ

with

in ¼jI1nj% hIi

hIi; ð4Þ



defined as

FSn ¼X

n

m¼1

fm ; ð5Þ

with







exchange (phase error), rotation (multiple components)

mardi 6 mars 2012


Genetic algorithm based ID Builder

Evaluation:

1 2 3 4 5 6 7 8

5 4 8 1 7 2 6 3 7 2 6 35 4 8 11 3 5 7

2 4 6 8

Variation Operators for Permutations:

Mutation : - e.g. swap items (magnets) at two randomly chosen positions - [ 5 4 8 1 7 2 6 3 ]

Crossover : - e.g. «order 1» - [ 1 2 3 4 5 6 7 8 ]

[ 3 5 6 8 1 2 7 4 ][ ? ? ? 4 5 6 7 ? ]

Ordered Magnet Sequence(s)

«Decoded» Undulator Structure

Magnetic Measurements Dataon Individual Magnets (/Modules) & Partly Assembled Undulator

Mathematical Model / Total Field Calc. Method

Undulator Magnetic Field (/ Field Integrals)

Characteristics/ Fitness Terms

Electron Trajectory Straightness

Radiation Phase Error

Field Integral deviation from zero

Integrated Multipoles

. .

.

“GA”

Advantages : object function, arbitrary search space, search from ap population, mutation and cross-over => global optimum, multi-modal/multi-objet

Efficient Computation of Coherent Synchrotron Radiation taking into account 6D Phase space distribution of emitting electrons, O. Chubar, M. E. Couprie, International Conference on Synchrotron Radiation Instrumentation Daegu (KO) 28 May-2 June 2006, AIP Conference Proceedings 2007, 879, 259-362

2- EPU and fast polarisation switching

mardi 6 mars 2012


• Configuration : Pure Permanent magnet (magnet configuration) to Hybrid technology

Towards short period high field in vacuum undulators

SmCo magnets => NdFeB magnetsVanadium Permendur poles =>Dysprosium poles

RADIA design


• Magnet and poles choices

Proposed alternative to superconducting undulators : cryogenic undulators

T. Hara, T. Tanaka, H. Kitamura, T. Bizen, X. Maréchal, T. Seike, T. Kohda, Y. Matsuura, Phys. Rev. Spc. Topics 7, 050702 (2004)

- increase of remanent field and coercivity at low temperature

- operation at liquid nitrogen temperature => manageable heat budget

- easy operation on synchrotron light sources

Prototype of Cryoundulator

Undulator period 15 mm

Type halbach ppm

Legnth ~ 0.6 m

Material NdFeB 50BH

Temperature control by heaters

Cryocooler

Heaters

• Cryocooler installation with flexible Cu plate.

• Enforcement of thermal isolation at magnet beam supports.

K. Halbach, Jour. Physics, 44 (1983) 211

Cryogenic undulator with high Tc superconductorsT. Tanaka et al. PRSTAB 7, 090794 (2004)

mardi 6 mars 2012


Magnetic characterisation on sample magnets

=> Variation of the susceptibility vs T


PrFeB

PrFeB

In-vacuum undulator technology, widely used to produceshort period small gap undulators, the permanent magnet arraysare mounted on beams inside the vacuum chamber to eliminatethe physical limitation of the magnetic gap due to the vacuumchamber [8]. The permanent magnets used in undulators areNd2Fe14B or Sm2Co17. Nd2Fe14B magnets have a higher rema-nence magnetisation Mr; however Sm2Co17 magnets have ahigher coercivity Hcj and show better radiation resistance againstelectron beam [9]. In-vacuum undulators are built either withSm2Co17 [10] or with Nd2Fe14B [11]. It is necessary to choose alarge coercivity material in order to prevent demagnetisation dueto electron beam losses and vacuum baking [12]. In general largecoercivity Nd2Fe14B magnets show small remanence magnetisa-tion. Therefore, the undulators cannot take full advantage of themagnetic performance of Nd2Fe14B. In order to shift further theemitted radiation toward higher energies, the peak magnetic fieldof the in-vacuum undulators can be increased while operating atcryogenic temperature. When cooling down RE2Fe14B permanentmagnets (Rare Earth based magnets), the remanent magnetisationMr increases up to a certain temperature at which the process islimited by the appearance of the Spin Reorientation Transition(SRT) phenomenon [13,14]. The easy magnetisation axis is tilted

from the crystallographic c-axis [001], the tilted angle increaseswhen lowering the temperature [13,15]. The coercivity is notaffected by the SRT phenomenon and keeps increasing at lowtemperature. Initially proposed at SPring-8 [16], Cryogenic Per-manent Magnet Undulators (CPMU) are one of the future evolu-tions of in-vacuum undulators.

At ESRF a 2 m cryogenic undulator has been built using abaked Nd2Fe14B grade [17,18], SPring-8 and Danfysik built a nonbaked Nd2Fe14B grade CPMUs, respectively, for SLS and DiamondStorage rings [19,20], HZB [21], UCLA [22] and BNL [23] built andtested a Pr2Fe14B CPMU prototype, BESSY [24] built and tested a(Nd0.2 Pr 0.8)2Fe14B CPMU prototype.

In this paper, different RE2Fe14B samples (Nd and Pr) arecharacterised for temperatures between 300 K and 80 K, andcompared to the behaviour of the magnet in a four periodundulator.

2. RE2Fe14B magnet characterisation versus temperature

2.1. Permanent magnet samples

Table 1 presents the characterisation of RE2Fe14B samplemagnets under study for the SOLEIL cryogenic undulator.RE2Fe14B magnets with a very high remanence cannot beemployed for the construction of room temperature in-vacuumundulator because of their weak coercivity at this temperature.However, when these magnets are cooled down at cryogenictemperatures, not only their remanence but also their coercivityincrease and consequently these magnets present a high resis-tance to demagnetisation (up to 5 T external field) similar to thematerial generally used at room temperature. Hence, RE2Fe14Bappears very attractive for the construction of cryogenic undu-lator. The samples have been characterised with a fully automaticsystem magnetometer of Neel Institute (CNRS Grenoble) [25],operating in a magnetic field range of 710 T and at temperaturesbetween 1.5 and 300 K. The magnetic field H is produced by asuperconducting magnet located in a liquid Helium cryostat andthe temperature is regulated within 0.1 K by a He flow-througharrangement. The measurement is based on flux extractionmethod. The sample is fixed on a rod allowing a vertical move-ment. The magnetisation is measured with three sets of pick upcoils placed around the sample.

2.2. Measurement results

The magnetic properties of the five samples have been mea-sured at different temperatures between 300 and 80 K. Fig. 2presents the measured hysteresis cycle of BH50 Nd2Fe14B magnet.With the sample located in the homogeneous volume of theexternal magnetic field H, its magnetic moments get rapidlyoriented in the applied H direction. In the first magnetisationcurve, the magnetisation M increases with the field and reaches

Fig. 1. Permanent magnet undulator configuration: a) pure permanent magnetundulator, (b) hybrid undulator.

Table 1Characteristics of different magnet samples at 20 1C: Br remanence, Hcj coercivity. VAC stands for Vacuumschmeltze.

Characteristics CR53 BH50 CH49 VAC764 495T N50Company Hitach-Neomax VAC Neorem Atlas-Yunshen

Type of magnet Pr2Fe14B Nd2Fe14B Nd2Fe14B Nd2Fe14B Nd2Fe14B Nd2Fe14B

Remanence Br (T) 1.35 1.40 1.39 1.37 1.18 1.40Coercivity Hcj (T) 1.65 1.39 1.63 1.63 2.81 1.38Temp. Coef. DBr (%/1C) 0.11 0.11 0.11 0.12 0.11 0.11Temp. Coef. DHcj (%/1C) 0.58 0.58 0.58 0.70 0.58 0.60Dimensions (mm3) 4!4!4 4!4!4 4!4!4 4!4!4 4!4!4 4!4!4

C. Benabderrahmane et al. / Nuclear Instruments and Methods in Physics Research A 669 (2012) 1–62

C. Benabderrahmane et al, NIM A 669 (2012) 1-6K. Uestuener et al., Sintered (Pt,Nd)FEB permanent magnets with (BH)max of 520 kJ/m3 at 85 K for cryogenic applications, 20th Workshop on Rare Earth Permanent Magnets 2008, Crete

M. Sagawa et al. J. Magn. Magn. Mater. 70, 316 (1987)T. Hara et al. APAC2004, Gyeongju, Korea, 216

Spin Transition ReorientationNdFeB strong Magneto-Crystalline Anisotropy (MCA) => orientation along [001] Magneto-cristalline orientation given by the energy : E(T) = K1sin2(θ)+ K2sin4(θ) , θ angle between the magnetisation and [001]at room temperature : magnetisation // cFe MCA independant of T, Nd : K1 // [001] dominant at room T and K2//[110] at low T

D. Givord et al. Solid State Comm. 51 (1984) 857L. M. Garcia et al. Phys. Rev. Lett. 85 (2) 429

mardi 6 mars 2012


CPMU cooling strategy


undulator technology, the performance of the magneticfield can be drastically improved.

II. CRYOGENIC PERMANENT MAGNETUNDULATORS

NdFeB magnets with high coercivity or Sm2Co17 mag-nets are generally used in in-vacuum undulators becauseof their resistance against demagnetization due to elec-tron beam irradiation. In addition, when installed in astorage ring, thermal stabilization and vacuum bakeout athigh temperatures around 420 K are necessary for themagnets; high coercivity magnets are also favored tominimize thermal demagnetization during these pro-cesses [12]. However, if the undulator is operated at acryogenic temperature, the outgassing rate from the mag-nets becomes very low or the magnets are even expectedto work as cryopumps, so that it is no more necessary toexpose the magnets to high temperatures. Supposing acryogenic temperature operation, NdFeB magnets withhigh remanent fields, normally showing low coercivity atroom temperature, are expected to have sufficiently highcoercivity and resistivity against electron beam irradia-tion. This gives us an opportunity to create a new undu-lator concept called the cryogenic permanent magnetundulators (CPMUs).

Since the magnet arrays of an in-vacuum undulator areplaced under good thermal isolation with vacuum, theundulator operation at the cryogenic temperature ofliquid nitrogen or higher simply needs some additionalrefrigerant channels or cryocoolers. Figure 1 shows two

examples of the CPMU design, both of which resemblethe ordinary in-vacuum undulator design [12] excepthaving refrigerant channels 1(a) or cryocoolers 1(b) at-tached to the magnet beams.

The most important advantage of the CPMUs is toallow a very high heat load of several hundred watts,which can be covered by a compact cryocooler of aGifford McMahon type. In case of a 1.5 m CPMU, theestimated amount of heat flowing in through the shafts ofthe magnet beams is about 100 W and thermal radiationfrom the inner surface of the vacuum chamber is about15 W. The heat generated by the resistive wall effect andsynchrotron radiation from upstream bending magnets isnormally smaller, for instance about 10 W in the case ofthe 203-bunch operation in SPring-8 at a 3 mm gap. Theseheat loads can be covered by one cryocooler, for example,the Suzuki Shokan RF90S having a cooling capacityhigher than 200 W at 80 K.

The CPMUs offer further advantages over SCUs, withthe saving of electricity and a stable operation withoutany quench. In addition, all techniques of magnetic fieldcorrection developed for permanent magnet undulatorscan be applied to the CPMUs without any significantmodification.

III. CHARACTERISTICS OF NdFeB MAGNETS ATCRYOGENIC TEMPERATURES

Sintered NdFeB magnets exhibit negative dependenceof remanent fields against temperature, typically!0:1%=K around room temperature. According to this

FIG. 1. (Color) Design examples of a CPMU with refrigerant channels (a) or with cryocoolers (b).

PRST-AB 7 CRYOGENIC PERMANENT MAGNET UNDULATORS 050702 (2004)

050702-2 050702-2

Cryocoolers Cryo Cooler: Power 2000 W (<300 W), Liquid LN2, Pump : 30 to 90 Hz (40 Hz), Flow : 1 to 30 l/mn (5 l/mn)

SPring-8T. Hara et al. Phys. Rev. Spc. Topics 7, 050702 (2004)

SOLEILC. Benabderrahmane et al 7, 050702 (2004)

Cooling to He temperature at BNL

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Nd2Fe14B and Pr2Fe14B magnets characterisation and modelling for cryogenic permanent magnet undulator applications, C. Benabderrahmane, P. Berteaud, M. Valléau, C. Kitegi, K. tavakoli, N. Béchu, A. Mary, J. M. Filhol, M. E. Couprie, Nucl. Instrum. Methods A 669 (2012) 1-6

U20-NdFeB

U10-PrFeB


at SOLEILat NSLS-II

at BESSYValidation of magnetic model at low temperature

PRASEODEMIUM IRON BORON UNDULATOR

Magnet Arrays and Measurement System The first room temperature (RT) IVU was developed at KEK in 19922. Since then, RT-IVUs have become the

de-facto standard for short period devices in synchrotron light sources around the world. Various attempts to employ superconducting undulators (SCUs) have been made. However, it appears that more R&D is needed before SCUs can be reliably used at user facilities. The concept of a CPMU was proposed in 2004 to enhance the performance of a RT-IVU3. Since it is based on the fundamental characteristics of a NdFeB permanent magnet, it is considered a much more realistic option than SCUs to achieve higher performance from an ID. Unfortunately, a NdFeB magnet starts to exhibit spin reorientation below 150K, which limits the maximum enhancement of its remanent field.

The PrFeB, a “twin” of NdFeB, was originally developed for space applications. does not show such deterioration at lower temperature. Its remanence continues to increase monotonically all the way to 4°K. Test arrays having eight full periods of 14.5mm period length have been constructed with PrFeB magnets (NEOMAX Type 53CR)4 and Vanadium Permendur poles. No elaborate shimming was done except for trajectory optimization by magnet sorting. The test undulator was installed in the VTF5 at the NSLS for field measurement with either liquid nitrogen or liquid helium as cryogens. The magnetic gap was set to 4.85mm which is determined by the thickness of the aluminum guide tube in which the Hall probes move. Hall probe calibration in LHe was done in-situ with SC calibration coils. Figure 1 shows the Radia model for the SC calibration coils, photographs of the PrFeB undulator arrays and the SC calibration coils enclosure.

(a) (c) FIGURE 1. (a) PrFeB arrays installed in the VTF; (b) Radia model of the calibration coils; (c) Photograph of the coil enclosure in the VTF.

Measurement in LN2 Bath First, a number of measurements were conducted in liquid nitrogen. The Hall probe elements were calibrated

separately against an NMR probe in a conventional electromagnet dipole ,while they were immersed in a small LN2 dewar. Figure 2-(a) shows the comparisons between predicted field by Radia6 and measurement results at both room temperature and at 77K. Br in the simulation was varied to achieve the closest fit to the measured peaks. The fitted results indicate that the magnet’s Br increased from 1.37T at RT to 1.64T at 77K. The discrepancy in the extremities is mainly due to the imperfection of the magnet machining. Hall probe data show that the average period length has decreased from 14.503mm at RT to 14.489mm at 77K due to thermal contraction of the aluminum array holder. Linear expansion of 6061-T6 aluminum alloy is supposed to contract by approximately 4!10-3 from 293K to 77K which translates 0.8mm contraction for 20cm arrays. It is known that NdFeB magnet has negative thermal expansion perpendicular to the magnetized direction. More investigation is needed to understand the reason for smaller reduction of the period length. Phase error plots for both cases are shown in Fig. 2-(c) for RT and Fig. 2-(d) for 77K. No significant change in the pattern of phase errors have been observed, but the RMS phase error exhibits

(b)

T. Tanabe, et. al., AIP Conference Proceedings, Vol. 1234, p.29 (2010). 4.85 mm gap

Notice: This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH1-886 with the U.S. Department of Energy. The United States Government retains, and the publisher, by accepting the article for publication, acknowledges, a world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes.

FIGURE 3. (a) Hall probe element output voltage for two adjacent positive peaks at various temperatures. The measurement started at 4.2K and data at higher temperatures were measured as the array temperature increased. (b) Phase error plot in the full period region for a LHe temperature scan. RMS phase error is 6.8 degrees.

OTHER OPTIONS The rare-earth metal dysprosium (Dy) has one of the largest magnetic moments. In the ferromagnetic ordered

state, it could exhibit the a saturation inductance of 3.8T at 4.2K. Dy orders ferromagnetically at 90K, therefore, it could be used as pole material only in CPMU designs. The peak field of U20 at a 5mm gap assuming Br=1.50T is found to increase from 1.29T with permendur to 1.36T with textured Dy poles. The comparison was done with Radia using measured µH v.s. M data for crystallized Dy9.

Low temperature SCUs have been tested at several laboratories in the world. Heat shield problems demand increased effective magnetic gap, which in turn diminishes the advantages of SCUs. SCUs with high temperature superconductor tapes is another possibility for the future R&D. However, further increase of maximum engineering current density is required to be compete with CPMU field performance.

SUMMARY The magnetic field characteristics of PrFeB undulator arrays of 14.5mm period length have been measured at LN2

and LHe temperature. The operation at 77K was found to be very promising. Not much performance gain was observed at 4.2K. A combination of PrFeB magnets and textured Dy poles may give further performance gain compared to conventional CPMU consisting of NdFeB and permendur poles.

ACKNOWLEDGMENTS The authors wish to thank Dr. Vyacheslav Solovyov of the Material Science Department at BNL for providing

measurement data for PrFeB magnet and Dy materials, Dr. Tsutomu Kohda and Dr. Yutaka Matsuura of Hitachi Metal, NEOMAX company for their support.

REFERENCES 1. T. Tanabe, et. al., " X-25 Cryo-ready In-vacuum Undulator at the NSLS" AIP Conference Proceedings, Volume 879, pp. 283-

286 (2007). 2. S. Yamamoto, et. al., Rev. Sci. Instrum. 63, pp400 (1992) 3. T. Hara, et. al., “Cryogenic permanent undulators”, Phys. Rev. ST, Acc. and Beam, Vol. 7, p.050720 (2004). 4. http://www.hitachimetals.com/product/permanentmagnets/ 5. D. Harder, et. al., “Magnetic measurement system for the NSLS superconducting undulator vertical test facility”, Proceeding

of PAC05, pp. 1730-1732 (2005). 6. O. Chubar, P. Elleaume, and J. Chavanne, J. Synchrotron Rad. 5, pp.481 - 484 (1998). 7. http://www.cryomech.com/ 8. S. G. Sankar, in private communication. 9. Vyacheslav (Slowa)Solovyov, in private communication.

(a) (b) J. Bahrdt et al. IPAC10, 3111

fixed gap=2.5 mm

mardi 6 mars 2012

http://www.springer.com/series/3849



In vacuum low temperature measurements

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• Gap opening due to thermal contraction of the supporting rods to be compensated

Measurement :Capacitance type displacement monitors

(Nantex Corp.) SPring-8Wire resistivity : ESRF, SOLEIL

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New Journal of Physics 8 (2006) 287 (http://www.njp.org/)

T. Tanaka et al., New Journal of Physics, Development of cryogenic permanent magnet undulaotrs operating around liquid nitrogen temperature, New Jour. Physics 6, 2011, 287

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2414Light Sources and FELs


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WE5RFP067 Proceedings of PAC09, Vancouver, BC, Canada

2416Light Sources and FELs


J. Chavanne et al., First operational experience with a cryogenic permanent magnet undualtor at the ESRF, PAC09, 2414

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Proceedings of IPAC’10, Kyoto, Japan WEPD026

02 Synchrotron Light Sources and FELsT15 Undulators and Wigglers 3149

T. Tanaka et al., in situ magnetic c o r r e c t i o n f o r c r y ogen i c undulators, IPAC 2010, 3147

Tanaka, et al., . Phys. Rev. Spec.Topics 12, 120702 (2009)

mardi 6 mars 2012



SOLEIL Cryo U18 PrFeB operation at 77 K, Non baked, B= 1.16 T @5.5 mm gap

Cryogenic undulators on operation

Thermal gradient on the magnetic system < 1.2 K/mTotal temperature variation due to electron beam (500 mA) and gap variation < 2.5 K

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WEPD006 Proceedings of IPAC’10, Kyoto, Japan

309402 Synchrotron Light Sources and FELs

T15 Undulators and Wigglers

NdFeB, operation at 157 K, Non baked, B= 1.04 T@ 4 mm gap

C. W. Ostenfeld et al. , Cryoegnic in vacuum unduator at Danfysik, IPAC2010, 3093J. Schouten et al, Electron beam heating and operation of the cryogenic undulator and superconducting wigglers at DIAMOND, IPAC 2011, 3323

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Proceedings of IPAC2011, San Sebastián, Spain THPC179


T15 Undulators and Wigglers 3325 Co

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mardi 6 mars 2012

M. E. Couprie, ICFA Workshop on Future Light Source, Thomas Jefferson Nat. Acc. Facility. March. 5-9, 2012, Invited!

Test RP : 13 décembre 2011

I- In vacuum undulators and wigglersCryogenic undulators radiation

U18 cryo

U20

SOLEIL

mardi 6 mars 2012


Choice of an in vacuum wiggler rather than a superconducting wigglerIn vacuum wiggler


performance magnet (remanent field 1.17 T, coer-cive force 12 kOe) compatible with the hightemperature bake-out process required for ultra-high vacuum operation.

The wiggler has just been delivered to theSPring-8 insertion device magnetic measurementlaboratory, and is now being characterized (field,field integrals). Fig. 2 shows the variation of thevertical peak magnetic field measured as a functionof the gap. At 7mm, the vertical peak magneticfield is 1.95 T (corresponding to a critical energyec=83 keV for the 8GeV SPring-8 electron beam).At 5mm, the minimum gap set for the operation ofin-vacuum undulators, the peak field increases upto 2.3 T (ec=98 keV). The uniformity of thevertical magnetic field in the orbit plane has alsobeen measured (Fig. 3). In a ! 5mm rangearound the wiggler axis (i.e., around the main axisof the electron trajectory), the vertical field variesby less than 0.2% for gaps between 5 and 20mm.In a ! 2mm range around the wiggler axis, theroll-off is below 0.06% (0.03% at gap 7mm).

Field integrals and their transverse distributions,which characterize the transparency of an inser-tion device to the electron beam (i.e. the ID mustnot generate any beam losses or any significantmodification of the ring optic), are now beingmeasured and corrected. The results of the fieldcorrections will be presented in a future paper.

3. Effective parameters and performances

The well-know formulas (see Ref. [3] forexample) using the value of the peak field tocalculate the deflection parameter, the total powerPT and the power density Pd are not validanymore: they assume a pure sinusoidal field,while high field wigglers, such as the in-vacuum

Fig. 1. The in-vacuum wiggler during magnetic field measure-ments and correction.

Table 1In-vacuum wiggler main parameters

Period length 90mmNumber of period 10Peak field @ 7mm 1.95TTransverse roll-off ! 5mm @ 7mm 0.17%Magnet H"W"L 30" 80" 19mm3

Pole H"W"L 25" 60" 7mm3

Fig. 3. Transversal homogeneity of the magnetic field at gaps 5,7, 15, 20 and 40mm.

Fig. 2. Peak magnetic field as a function of the gap.

X.-M. Marechal et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 138–140 139

SPring-8 : 1.95T, gap=7 mm, 10x90 mm

SOLEIL : 2.1T, gap=5.5 mm, 10x150 mm

X.M. Marechal et al, NIMA 4676-468 (2001) 138-140

O. Marcouillé et al., SRI 09

mardi 6 mars 2012


Spectral Flux per Unit Horizontal Angle (Far-Field Estimation)

In vacuum wiggler


O. Chubar

mardi 6 mars 2012



Electromagnetic undulators

Radia code: http://www.esrf.fr

Bz(s)=BB.cos[2πs/λo]+BR.sin[2πs/λo]=Bzo.cos[2πs/λo+f]

Fast switching : 1 Hz : 270 ms for switching -±600 A on PS1, 300 ms flat top for data acquisition

SOLEIL conception- Realisation Danfysik, Magnetic measurements SOLEIL

Ex of the SOLEIL 10 m HU640

Design, Construction and Magnetic Measurements of the DESIRS Undulator at SOLEIL, O. Marcouillé et al., International Conference on Synchrotron Radiation Instrumentation Daegu (KO) 2006, AIP Conference Proceedings 2007, 879, 396-399

mardi 6 mars 2012


Electromagnetic undulators

Linear H, V, + Quasi periodic, Circular

Coll. BINP

27 Bz dipoles (Symmetric field)

28 Bx dipoles (Asymmetric field)

A

P

MCurrent

Field

P→M

M→P

Zone usable to produce photons

Reference for theintegral corrections

Ex of the SOLEIL 526

Magnetic design and manufacture of elliptical undulators HU256A. Batrakova, F. Briquez, O. Chubar, I. Churkin, M.-E. Couprie, A. Dael, I. Ilyin, Yu. Kolokolnikov, G. Roux, E. Rouvinski, E. Semenov, A. Steshova, M. Valleau, P. Vobly, Nuclear Instruments and Methods in Physics Research A 575 (2007) 29–32


mardi 6 mars 2012



Permanent magnets EPU: Crossed undulators

Onuki undulators

Undulator : Period : 30 mm Minimal gap : 15,5 mm

Magnets : NdFeB Size : 8 x 15,5 mm Br : 1,26 T

Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,4

Linear V. 0,4

Circular 0,280,28

H. Onuki, Nucl. Instr. Meth., A246, 94, (1986)H. Onuki et al, Appl. Phys. LeB., 52, 173, (1988)

H. & V. field values in circular polarisaLon. H. & V field roll-‐off at minimal gap

o Crossed and overlapped type polarizing undulator

M. Moissev et al. Sov. Phys. J. 21, 332, 1978K. J. Kim NIMA219, 426 (1986)

mardi 6 mars 2012



Permanent magnets EPU: HELIOS

P. Elleaume, A flexible planar / helical undulator design for synchrotron radiaLon sources, Nucl. Instr. Meth., A291, 371 (1990)P. Elleaume, J. Synch. Rad.,1, 19 (1994)

Helios undulatorsUndulator :

Period : 30 mm Minimal gap : 15,5 mm

Magnets : NdFeB Size : 30 x 30 mm Br : 1,26 T

Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,173

Linear V. 0,125

Circular 0,10,1

H. & V. field values versus gap at 0 mm shi[. H. & V field roll-‐off at minimal gap,

mardi 6 mars 2012



Permanent magnets EPU: Diviacco/WalkerDiviacco/Walker undulators



Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. -‐

Linear V. -‐

Circular 0,130,13

H. & V. fields at minimal gap

o No phase shiJo No longitudinal component

H. & V. fields roll-‐off at minimal gap

B. Diviacco and R. P. Walker, Nucl. Instrum. Meth., A292, 517 (1990)

mardi 6 mars 2012



Permanent magnets EPU : APPLE I

Apple I undulatorsUndulator :



Θmag = 45 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,456

Linear V. 0,21

Circular 0,1350,135

H. & V. field values versus gap at 0 mm shi[. H. & V. field values versus shi[ at minimal gap H. & V field roll-‐off at minimal gap,

S. Sasaki et al, A new undulator for generaLng variably polarized radiaLon, Jpn. J. Appl. Phys., 31, L194 (1992) S. Sasaki et al, Nucl. Instr. Meth., A331, 763 (1993)S. Sasaki et al, Nucl. Instr. Meth., A347,87 (1994)

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Permanent magnets EPU : APPLE II

Apple II undulatorsUndulator :



Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,421

Linear V. 0,247

Circular 0,1450,145


R. Carr , Nucl. Instr. Meth., A306, 391 (1991) R. Carr et al , Rev. Sci. Instrum., 63, 3564 (1992)R. Carr, Proceedings of 1992 EPAC, p489 (1992)

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Apple III undulatorsUndulator :


Magnets : NdFeB Size : 40 x 40 mm Br : 1,13 T & 1,19 T

Θmag = 45 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 1,29

Linear V. 0,83

Circular 0,520,52



Permanent magnets EPU : APPLE III

[1] J. Bahrdt et al, Proceedings of the 2004 FEL Conference, Triestre, ITALY, p610 (2004)

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Permanent magnets EPU : APPLE IIIApple III undulators(SOLEIL model)



Θmag = 33 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,463

Linear V. 0,23

Circular 0,160,16


J. Bahrdt et al, Proceedings of the 2004 FEL Conference, Triestre, ITALY, p610 (2004)

mardi 6 mars 2012



Permanent magnets EPU : DELTA

Delta undulatorsUndulator :

Period : 30 mm Minimal gap : 5 mm

Magnets : NdFeB Size : 25 x 9 x 9 mm Br : 1,26 T

Θmag = 0 °

Xdist = 0,5 mm

Modes Bz [T] Bx [T]

Linear H. 1,04

Linear V. 1,04

Circular 1,041,04

H. & V. fields at 0 mm shi[. H. & V field roll-‐off at minimal gap,

A. B. Temnykh, Phys. Res. Spec. Topics AB, 11,120702 (2008)

Quater of period shi[

Without phase shi[

mardi 6 mars 2012


to copper holders without demagnetization [8]. This tech-nique was used in the construction.

It should be mentioned that the conceptual idea for sucha PPM undulator was presented in 2006 [9]. Encouraged byinterest from the Cornell x-ray users’ community, this ideaevolved into a detailed design and recently a prototype wasbuilt and tested.

II. MODEL DESCRIPTION

A. General information

A picture of the Delta undulator prototype is shown onFig. 1. The prototype is !30 cm long, !15 cm high, and!15 cmwide. The magnetic structure consists of two pairsof magnetic arrays as depicted in the computer generatedFig. 2 with major components numbered. One pair pro-vides vertical field and another horizontal. Magnet arrays(1) are assembled on baseplates (2). To provide longitudi-

nal displacement for the field strength and polarizationcontrol, these plates are mounted on miniature rails (3)attached to the thick plates forming a rigid frame. In linearpolarization mode, the pairs will be in phase, so the re-sulted field will be planar and will be

ffiffiffi2

pstronger than

from a single pair. In circular polarization mode, the pairswill be shifted relative to each other by 1=4 period or 90",so the resultant field will be helical. To change the fieldstrength, two arrays forming the pair should be shiftedlongitudinal in opposite directions. The prototype has a5 mm diameter bore. Gas conductance from the centralregion is provided by four 0.5 mm wide slits betweenmagnetic arrays. From the following discussion it will beseen that these slits have enough conductance to providesatisfactory vacuum conditions on the beam axis. Note thatthe picture on Fig. 1 shows the prototype without magneticarray driving mechanisms. These mechanisms are de-signed and are in the process of construction. They willbe added latter.

B. Magnetic field properties

A 3D model of one period of the Delta-type magneticstructure used in the magnetic field calculation by codeVECTOR FIELDS is shown in Fig. 3. As a real structure themodel had 24 mm period, 5 mm diameter bore, and 0.5 mmwide slits between magnetic arrays, permanent magnetmaterial characteristics of NdFeB (40SH) material (Br ¼1:26 T) used in prototype construction. We calculated afield distribution along the beam axis as well as a fieldvariation across the bore for both helical and planar modes.Field distributions have been used for calculation of thex-ray spectrum and the field variation will be used forevaluation of the requirement on undulator alignment andfor beam dynamics study.Plots on Fig. 4 characterize the helical mode. They

depict magnetic field components on beam axis versusFIG. 1. (Color) Delta undulator prototype view.

FIG. 2. (Color) Computer generated view. Left plot—magnetic arrays providing vertical field. Here (1)—magnetic arrays, (2)—baseplates, (3)—rails providing longitudinal motion, (4)—plates forming the rigid frame. Right plot—arrays providing horizontalfield.

ALEXANDER B. TEMNYKH Phys. Rev. ST Accel. Beams 11, 120702 (2008)

120702-2

to copper holders without demagnetization [8]. This tech-nique was used in the construction.

It should be mentioned that the conceptual idea for sucha PPM undulator was presented in 2006 [9]. Encouraged byinterest from the Cornell x-ray users’ community, this ideaevolved into a detailed design and recently a prototype wasbuilt and tested.

II. MODEL DESCRIPTION

A. General information

A picture of the Delta undulator prototype is shown onFig. 1. The prototype is !30 cm long, !15 cm high, and!15 cmwide. The magnetic structure consists of two pairsof magnetic arrays as depicted in the computer generatedFig. 2 with major components numbered. One pair pro-vides vertical field and another horizontal. Magnet arrays(1) are assembled on baseplates (2). To provide longitudi-

nal displacement for the field strength and polarizationcontrol, these plates are mounted on miniature rails (3)attached to the thick plates forming a rigid frame. In linearpolarization mode, the pairs will be in phase, so the re-sulted field will be planar and will be

ffiffiffi2

pstronger than

from a single pair. In circular polarization mode, the pairswill be shifted relative to each other by 1=4 period or 90",so the resultant field will be helical. To change the fieldstrength, two arrays forming the pair should be shiftedlongitudinal in opposite directions. The prototype has a5 mm diameter bore. Gas conductance from the centralregion is provided by four 0.5 mm wide slits betweenmagnetic arrays. From the following discussion it will beseen that these slits have enough conductance to providesatisfactory vacuum conditions on the beam axis. Note thatthe picture on Fig. 1 shows the prototype without magneticarray driving mechanisms. These mechanisms are de-signed and are in the process of construction. They willbe added latter.

B. Magnetic field properties

A 3D model of one period of the Delta-type magneticstructure used in the magnetic field calculation by codeVECTOR FIELDS is shown in Fig. 3. As a real structure themodel had 24 mm period, 5 mm diameter bore, and 0.5 mmwide slits between magnetic arrays, permanent magnetmaterial characteristics of NdFeB (40SH) material (Br ¼1:26 T) used in prototype construction. We calculated afield distribution along the beam axis as well as a fieldvariation across the bore for both helical and planar modes.Field distributions have been used for calculation of thex-ray spectrum and the field variation will be used forevaluation of the requirement on undulator alignment andfor beam dynamics study.Plots on Fig. 4 characterize the helical mode. They

depict magnetic field components on beam axis versusFIG. 1. (Color) Delta undulator prototype view.

FIG. 2. (Color) Computer generated view. Left plot—magnetic arrays providing vertical field. Here (1)—magnetic arrays, (2)—baseplates, (3)—rails providing longitudinal motion, (4)—plates forming the rigid frame. Right plot—arrays providing horizontalfield.

ALEXANDER B. TEMNYKH Phys. Rev. ST Accel. Beams 11, 120702 (2008)

120702-2

Cornell ERL ‘‘Coherence’’ mode operation. Results areplotted on Fig. 15. The upper plot shows the spectrum ofcircular polarized photon flux corresponding to a helicalfield. There is only one peak at !1650 eV photon energy.The absence of the other peaks confirms the magnetic fieldquality. The bottom plot gives the spectrum for linear x-ray

polarization corresponding to a planar field distribution.The lowest peak at !1650 eV matches the first undulatorharmonic. Other peaks correspond to higher order odd andeven harmonics. Even harmonics appeared because of thefinite slit size. The well-defined narrow peaks up to 15thorder indicate small phase errors in the field distributionand confirm the field quality.

IV. NEXT STEPS

Prior to the full scale Delta undulator design and con-struction, the following steps will be taken.In order to verify magnetic field properties inside the

5 mm diameter undulator gap we will build a specialmagnetic field measurement setup. In this setup a smallsize Hall probe will be inserted in the bore and movedalong the beam axis. This project is now under way.To provide the smooth flow of the beam image current

between 24 mm (1 in) diameter ERL beam pipe and 5 mmdiameter undulator bore, we have to design special tran-sition pieces. They will be carefully examined for the beamimpedance and beam induced power dissipation.In Ref. [18] we measured demagnetization of the NdFeB

permanent magnets induced by high energy elector radia-tion. The obtained data allowed us to roughly estimate IDdemagnetization rate caused by the beam losses expectedat ERL, see [19]. A more detailed analysis will be doneafter finalizing of ERL optics and beam halo collimationscheme and will be presented in a subsequent paper.Because we are going to use the Delta undulators for in-

vacuum operation, we will develop and test vacuum clean-ing techniques suitable for all undulator components.Traditional in-vacuum high temperature baking at 140"Ccan be applied to all components except magnet arrays.Magnetic arrays can be stabilized against demagnetizationat 120"C by attaching ferromagnetic plates as described inRef. [20]. We also will exam the vacuum properties of the

FIG. 15. (Color) Spectrum of the photon flux calculated for thecomposite field distributions corresponding to the helical (upper)and planar (bottom) mode of operation.

FIG. 14. (Color) Prototype field obtained as a combination of the individual array fields. The left plot shows vertical and horizontalfield components for magnet arrays in helical mode configuration. The right plot gives two orthogonal field components for magneticarrays in planar mode position. For latter rms phase errors !2:2".

DELTA UNDULATOR FOR CORNELL . . . Phys. Rev. ST Accel. Beams 11, 120702 (2008)

120702-9


Permanent magnets EPU : DELTA

A. B. Temnykh, DELTA undulator for Cornell Energy Recovery Linac, Phys. Res. Spec. Topics AB, 11,120702 (2008)

mardi 6 mars 2012



Permanent magnets EPU: 6 arrays

Kitamura undulators

Undulator : Period : 30 & 60 mm Minimal gap : 15,5 mm

Magnets : NdFeB Size : 30 x 30 mm

10 x 50 mm Br : 1,26 T

Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,424

Linear V. 0,06

Circular -‐-‐

H. Kitamura et al, J. Electron Spectr. Relate Phenom., 80 ,437, (1996)A. Hiraya et al, J. Synchr. Rad., 5, 445, (1998)

H. & V. field at minimal gap Flux density for a 400mA, 275 GeV beam without emiBance an energy spread

o Degree of circular polar. maintained while changing the photon energy

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3- EPU and fast polarisation switchingPermanent magnets EPU

Polarisa4on modes LH LV C Remarks

Apple I 0,45 0,21 0,135

Apple II 0,42 0,24 0,14

Apple III 0,46 0,23 0,16

Delta (Apple IV?) 1,04 1,04 1,04 5mm round gap

Helios 0,173 0,125 0,1

Diviacco-‐Walker -‐ -‐ 0,13 Circular only

Kitamura 0,424 0,06 -‐ Low field strength in circular

Onuki 0,4 0,4 0,28

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Quasi periodic PM EPU: QP APPLE II

Apple II undulatorsUndulator :



Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,421

Linear V. 0,247

Circular 0,1450,145

H. & V. field values in linear Horizontal (red line) and linear verLcal (blue one)

H. & V. trajectories in linear Horizontal (red line) and linear verLcal (blue one)

o Magnets creaXng aperiodicity are moved verXcally

J. Chavanne et al, Proceedings of the European ParLcle Accelerator Conference, Sweden (1998)B. Diviacco et al, Proceedings of the European ParLcle Accelerator Conference, Sweden (1998)

mardi 6 mars 2012



Quasi periodic PM EPU: Figure 8

Figure8 undulatorsUndulator :



Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H.

Linear V.

Circular

o Low on-‐axis power density in linear modeo CombinaXon of different period length

MagneLc fields at minimal gap and 0 mm shi[

Orbit projected in X-‐Y plane

T. Tanaka, H. Kitamura, Nuclear Instruments And Methods, A364, 368 (1995)

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Spatial d&i&ions of the power density of the planar and figuure-8 undulaton are shown in Figs. 7a and 7b. respectively. the undulator parameters are the same as those in Figs. 6a and 6b. in case of the planar undulator. tiu ,pocver density has a maximum of 98 kW/mnd? on axis. @I the other hand. the distribution of the figun-8 unduiator is asymmetric with respect to 8, and iuoks like a V figure. since j?, is asymmetric with respect to & as shown in Rg. 3d. Since most of the r&i&d power of the figure-8 tttt&iator distributes on the V figure. much kss heat load falls on axis than in case of the planar undulat0f. TIE on-axis pawa density is as low as 1.4 kW/nxadZ. which is impo?tam benefit for the soft x-ray optics.

3.2. lm-fefd case {K “r I )

Nex~.tkbw-fieMcasc(K - II iscomidendTbt petiodlengthisassumedtobe3.2cmandthCnanbn@f periods 140.

T. Tanaka, H. Kitamura, J. Synchrotron Radiation (1998), 5, 412-413T. Hara et al. Nucl. Instrum. Methods A 467-468 (2001) 165-168

• odd (LH), integer (LH), and half integer harmonics (LV)

In vac helical

0,42

0,22

mardi 6 mars 2012


Permanent magnets EPU carriages

HU64 at SOLEIL : 4 arrays and gap movement


J. Bahrdt et al., "APPLE Undulator for PETRA III", Proc. EPAC08, 2219 (2008)

phase and gap variationaperiodicitytapercorrection coils

or longitudinally) and a minimum stiffness in another direction allowing for a girder tapering and thermal expansions without generating additional strong forces or torques (figure 7).

All four magnet rows can be moved which permits a rotation of the linear polarization vector in the inclined mode by 180°. Due to the large longitudinal force on the magnet rows of up to 58kN the rows are split longitudinally and each subassembly is driven by an individual screw. Both screws are connected to a common motor via a gear box (figure 8). Table 2: Magnetic forces and torques (Fi and Ti) on one magnet girder for row phase = 0mm and for the inclined mode with row phase = 16.4mm. The coordinates are given in figure 8. The reference points for Tx and Tz are the centre between the two transverse flexible joints (Tx) and the longitudinal flexible joint (Tz), respectively.

units: kN, kNm Fx Fy Fz Tx Ty Tz hor. linear 0 73 0 0 0 0 inclined, 16.4 mm 54 0 12 6.4 0.75 22.5

Figure 7: Flexible joints for transverse (right) and longitudinal (left) guiding of the magnet girder.

Figure 8: Mechanical Layout of the UE65.

The displacements and rotations of the two magnet girders can be separated into parallel and opposite movements (figure 9). These movements have different influences on the performance of the undulator [5].

The expected girder movements are summarized in table 3. They cause systematic field variations over the length of the undulator. The field variations perpendicular to the undulator axis depend quadratically on y and z :

2)( )(/ zyaBB zyeffeff ⋅=∆ eq. 1

where the coefficients )( zya are given in table 4. The field variations are small and will not degrade the

spectral performance of the undulator. These data may

even be acceptable for FEL applications which require tighter tolerances on B-field variations. This topic is subject to further investigations. Table 3: Calculated movements of the two magnet girders under maximum load in inclined mode. The relative displacements !x1, !y1, !z1 and relative angles 2 1, 2 1, 2 1 are given. The red numbers are achievable only with the described feedback systems.

units: m, rad fig. 8 x / y / z / same displacement b 12 4 5 opposite displacement a 257 1 30 same rotation d 100 17 7 opposite rotation c 20 10 0.4

Figure 9: Girder misalignment.

Table 4: Scaling factors for evaluating the transverse field variations of the UE65 at smallest gap of 11mm (eq. 1).

operation mode ay [0.001/mm**2]

az [0.001/mm**2]

hor. linear 2.0 0.4 circular 4.6 11.5 vert. linear 12.7 16.9 inclined 45° 5.1 8.6

REFERENCES [1] PETRA III Technical Design Report, DESY 2004-

035; http://petra3.desy.de. [2] K. Balewski, these proceedings. [3] M. Tischer et al., Proceedings of the EPAC,

Edinburgh, Scotland, 2006, pp 3565 3567. [4] M. Tischer et al., AIP Proceedings of the

Synchrotron Radiation Conference, Daegu, South Korea, 2006, pp 343-346.

[5] J. Bahrdt, Proceedings of the FEL-conference, Berlin, Germany, 2006, pp 521-528.

[6] J. Bahrdt et al., Nucl. Instr. and Meth. in Phys. Res. A, 516 (2004) 575-585.

[7] F.-J. Boergermann et al., these proceedings. [8] J. Bahrdt et al., Proceedings of the FEL Conference

2004, Trieste, Italy, pp 610-613.

x

z

y

! x 2

! y 2

1 1 1

! y = gap 1

! z 1 ! x 1

a

c

b

d 2

2 2

! z 2

Proceedings of EPAC08, Genoa, Italy WEPC096

02 Synchrotron Light Sources and FELs T15 Undulators and Wigglers

2221

if the main dipole component points perpendicular to the wire. The inhomogeneities as measured with the stretched wire contribute significantly to the field integrals even at large gaps (figure 3).

-0.04

-0.02

0

0.02

0.04

-40 -20 0 20 40 60

gap = 12mm

-0.01

0

0.01

-40 -20 0 20 40 60

gap = 39mm

field

inte

gral

[Tm

m]

-0.005

0

0.005

-40 -20 0 20 40 60

gap = 79mm

z [mm] Figure 3: Transverse distribution of vertical field integrals measured at two opposite sides of magnet AN 53 (black solid and black dashed (sign reversed)). The average (blue) reproduces the data extrapolated from dipole data (magenta) as measured with the Helmholtz coil.

A statistical analysis demonstrates that the field integral contributions from the dipole moments alone and from the inhomogeneities (dipole contributions are subtracted) have roughly the same strength (figures 4 and 5). It is essential to use both data sets for an effective sorting and a reliable prediction of the undulator performance [5].

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

-30 -20 -10 0 10 20 30

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

-30 -20 -10 0 10 20 30

z [mm]

inho

mog

enei

ty [T

-mm

]

AN By side 1

AN By side 2

AS By side 1

AS By side 2

Magnet AN 53

z [mm]

dipo

le c

ontr

ibut

ion

[T-m

m]

AN By(My)

AN By(Mz)

AS Bz(Mz)

AS Bz(My)

Figure 4: Field integrals averaged over all A-magnets of one type originating from the block inhomogeneities alone, excluding the dipole components (top) and by the dipole components alone (bottom). The error bars indicate twice the rms value of the distribution at each z-value. The green curve represents the individual data of magnet AN 53 (see figure 3).

-0.1-0.08-0.06-0.04-0.02

00.020.040.060.08

0.1

-30 -20 -10 0 10 20 30

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

-30 -20 -10 0 10 20 30

z [mm]

inho

mog

enei

ty [T

-mm

] BN By side 1

BN By side 2

BS By side 1

BS By side 2

z [mm]

dipo

le c

ontr

ibut

ion

[T-m

m]

BN By(∆My)

BN By(Mz)

BS By(∆My)

BS By(Mz)

Figure 5: Field integrals averaged over all B-magnets of one type originating from inhomogeneities alone, excluding the dipole components (top) and by the dipole components alone (bottom). See also figure caption 4.

MECHANICAL LAYOUT The UE65 forces and torques are about a factor of two

higher as compared to the BESSY UE112 (table 2). The support structure is made from a single piece of cast iron (figure 6). The Al-girders for the magnetic structure are milled from solid blocks in order to avoid the welding of aluminium. The magnet girders are supported at four locations using two cross bars inside each of the girders to minimize the deflection under magnet load. The residual bending is only ±2 m.

Figure 6: Cast iron support structure: result from bionic optimization (left) and final shape (right).

Without any compensation the girders would tilt in the inclined mode by about 168 rad which would cause an unacceptable increase of the minimum gap of 0.84mm. Therefore, four instead of two servo motors are used: two motors which are moving the lower girder are controlled by two linear encoders mounted to the stiff support structure. The other two motors move the upper girder and use the gap measurement system [8] for the feed back loop.

Each magnet girder is attached to the support structure with four transverse flexible joints and one longitudinal flexible joint. These joints have been optimized for a maximum stiffness in one specific direction (transversally

WEPC096 Proceedings of EPAC08, Genoa, Italy


2220

T15 Undulators and Wigglers

mardi 6 mars 2012


Gap : 11.6 mm (min . 8 mm)Period : 26 mmLength : 4.5 mBz=0.728 T @ 8 mmBx= 0.31 T @ 8 mm22k W

T. Tanaka, H. Kitamura, J. Synchrotron Radiation (1998), 5, 412-413T. Hara et al. Nucl. Instrum. Methods A 467-468 (2001) 165-168

TiN coating on the magnetsCu Ni foil, baking 145 °C

no phasing mechanics

front end slit aperture. At the front end ofBL40XU, a cylindrical mask eliminates the off-axis undulator radiation and further bandwidthreduction is obtained with an adjustable rectan-gular x2y slit. Compared with a conventionalX-ray undulator beamline of SPring-8 with amonochromator (10!4 resolution), the availablephoton flux is higher by two orders.

2. In-vacuum helical undulator

Since the polarization state is not an importantparameter for the present user experiments ofBL40XU, there is no phasing mechanics on theundulator. However, variable polarization can beeasily obtained using a phase retarder with aswitching rate up to 100Hz at energies above5 keV, and it does not affect the electron beam[2,3]. Therefore, the undulator phasing is lessimportant than for soft X-ray devices.

A magnet structure is newly designed based onthe SPring-8 type soft X-ray helical undulator [4](Figs. 1 and 2). The undulator has three magnetarrays each on top and bottom planes. Two centerarrays produce the vertical magnetic field and fourside arrays add the horizontal field. Grooves at the

center of the magnet surface improve fielduniformity at small undulator gaps [4,5]. Anapparent change from the old helical design isthat the center arrays are hidden under the sidearrays at horizontal field poles (see top cross-section in Fig. 1). Thus, a further enlargement ofthe horizontal field uniformity at small undulatorgaps can be realized. Between the old and newmagnet designs, the good field region (roll off lessthan 0.5%) of the horizontal field is increased fromDx ¼ #0:6 to # 5mm with the same peak field at8mm gap, while keeping that of the vertical field at

Fig. 2. Photograph of the undulator magnet arrays.

Fig. 1. Magnet structure of the in-vacuum helical undulator.Top and bottom cross-section is displaced by a quarter of theundulator period.

T. Hara et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 165–168166

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! 3mm. The horizontal and vertical field ratio(Bx=By) is kept within 0.97–1.0 for the gapbetween 8 and 40mm.

In order to reduce electron beam impedance, thegrooves on the magnet surface are filled up withcopper pieces to keep the surface flat, and a Cu(10 mm) plated Ni (50 mm) foil covers the wholemagnet surface [6]. Since the magnet blocks areinstalled in an ultra-high vacuum (10"9 Pa), eachmagnet block is plated with 5 mm-thick TiN toprevent out gassing and baked out at 1458C beforeassembling into the magnet arrays. Main para-meters of the in-vacuum helical undulator aregiven in Table 1.

3. Spectral width

The whole energy range (7.6–16.5 keV) of thebeamline is covered by the fundamental radiation,since higher harmonics are completely eliminatedby the horizontal and vertical focusing mirrors.Available flux and spectral bandwidths are deter-mined by the physical aperture of the front end. At23m away from the undulator center, a cylindricalmask with a fixed aperture of j42.7 mrad isinstalled, and a rectangular adjustable x2y slit isplaced at 10m downstream of the mask to scrapefurther off the photon beam. A smaller aperturesharpens the spectrum but reduces the flux. Thecalculated undulator flux for 8 keV radiation isshown in Fig. 3. When the x2y slit is fully openedand the mask limits the aperture, the photon fluxreaches the order of 1015 with a bandwidth

(DEphoton=Ephoton) of 5.2% (FWHM). When weclose the front end slit to 10 mrad# 10 mrad, abandwidth of 1.7% (FWHM) can be obtained.Comparing with the total radiated power of3.5 kW, the power passing through the front endmask is reduced to 140W and that coming outfrom the 10 mrad# 10 mrad slit is about 10W.

The concept of the high flux beamline is verifiedby the measured spectrum at 12.6 keV. Fig. 4shows a good agreement of the spectral band-widths (1.6% FWHM) between the measurementand expectation. The high flux beamline has beenopen to public use since April 2000.

Table 1Main parameters of the in-vacuum helical undulator forBL40XU at SPring-8

Type Pure magnet type (NEOMAX-32EH)Period length 36mmNumber of periods 125Phase FixedMinimum gap 7mmMaximum K Kx; y ¼ 1:1Fundamental radiation 7.6–16.5 keVPhase error 9.88 at 8mm gap

Fig. 3. Photon flux calculated for the cases FE x2y slit fullyopened (dotted line) and closed by 10 mrad# 10 mrad (solidline).

Fig. 4. Measured and calculated spectrum of the undulatorradiation at 12.6 keV with a 15 mrad# 5 mrad FE x2y slitaperture.

T. Hara et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 165–168 167

Central arrays : vertical fieldside arrays : horizontal field

In vacuum Fig8 type helical undulator


mardi 6 mars 2012


ElectroMagnetic Permanent magnet Helical Undulator


Vertical field : coil and laminated yoke, horizontal field : array of permanent magnets

ESRF19 x 80 mm, B=0.2T

flippling the current in the coil in 20 ms, ploarisaiton switching in 1 HzSmCo magnets

DSP card for real time synchronisation (eddy currents)

J. Chavanne, P. Elleaume, P. VanVaerenbergh, “A novel fast switching linear/helical undulator”, Proceedings of EPAC 98, p. 317 (1998).

field integral as a function of the horizontal coordinate.The shimming of the Yoke consisted in fixing thinpieces of steel with screws on the horizontal outer sideof some poles . Figure 5 presents an hysteresis cycle ofthe measured field integral as a function of the maincurrent in the coil for a magnetic gap of 16 mm.

-1.5

-1.0

-0.5

-200 -100 0 100 200Main Current [Amp]

0.3 Gm

Gap = 16 mm

Figure 5 Hysteresis cycle of field integral vs. Current inthe coil for a magnetic gap of 16 mm.

The current is cycled between -250 A and +250 A. Themaximum thickness of the hysteresis cycle is 0.3 Gm .Thinner cycles have been observed for larger gaps andlower currents. As a result, a vertical field integralcorrection is applied as a function of the magnetic gapand current but no correction is made for the hysteresiseffect. Figure 6 presents the vertical field integralsobserved as a function of current and averaged overthe hysteresis cycle.

-3

-2

-1

0

1

-200 -100 0 100 200Main Current [Amp]

Gap = 16 mm Gap = 25 mm Gap = 40 mm Gap = 60 mm Gap = 100 mm

Figure 6 : Average vertical field integral measured asa function of the main current and magnetic gap.

The horizontal field integral variations with current andgap measured in the laboratory are smaller than 0.1Gm and no correction is applied. Nevertheless, due tothe different ambient field in the storage ring tunnelcompared to the laboratory, one may need a furthertuning of both the horizontal and vertical field integralcorrection tables when the device is operated on thestorage ring. Such phenomena has been observed on allhybrid permanent magnet insertion devices [4].As one suddenly flips the vertical field to flip thepolarization, one observes some time dependent fieldintegrals during the transition. They originates mainlyfrom eddy currents. The shorter the flipping time, the

larger the field integral during the transient. They arecorrected by applying a vertical field integralproportional to the derivative of the main current with a25 ms exponential delay. The results are illustrated onFigure 7 for the worst case corresponding to the highestcurrent (250 A) and minimum gap (16 mm). Theresidual field integral excursions peaks around 0.5 Gm(0.2 Gm) for a 20 ms (200 ms) flipping time. The eddycurrent in the stainless steel vacuum chamber accountsfor a 0.3 Gm for a 20 ms flipping time. These periodicchange of field integrals will be seen by the users of theESRF beamlines as a small growth of the horizontalemittance. Some limitations will be placed on theflipping time that will be determined following the firstoperation in the storage ring in July 98.

-2

-1

0

1

2

1.21.00.80.60.40.2Time [seconds]

-0.2

-0.1

0.0

0.1

0.2

Vertical FieldField Integral without Correction

Field Integral with Correction

Figure 7 : Vertical field and field integrals as functionof time for a 1 Hz repetition rate. The current is flippedbetween -250 A and 250 A within 20ms. The magneticgap is 16 mm.

ACKNOWLEDGMENTSThe authors wants to thank B. Cottin for performing

the field measurement and shimming , C. Penel fordeveloping the control system and J.M. Hasselsweilerand J.F. Bouteille for the help provided in setting upand tuning the power supply.

REFERENCES[1] M. Stampfer, P. Elleaume, A 4T Superconducting

Wiggler for the ESRF, EPAC94 p 2316-2318, WoldScientific Pub. Co, London

[2] P. Elleaume, HELIOS a New Type ofLinear/Helical Undulator, J. Synchr. Rad. (1994). 1,10-26

[3] The Radia code is freely available for downloadfrom« http://www.esrf.fr/machine/support/ids/Public/welcome.html ». Details have been published in :P. Elleaume, O. Chubar, J. Chavanne, PAC97Conference May 1997, Vancouver. see also O.Chubar, P. Elleaume, J. Chavanne, proceedings ofthe SRI97 Conference August 1997, Himeji, Japan.

[4] J. Chavanne, P. Elleaume, P. VanVaerenbergh, "TheESRF Insertion Devices ", proceedings of the SRI97Conference August 1997, Himeji, Japan.

319

current flipping in 20 ms, gap 16 mm

A NOVEL FAST SWITCHING LINEAR/HELICAL UNDULATOR

J. Chavanne, P. Elleaume, P. Van VaerenberghESRF, B.P. 220, F-38043 GRENOBLE Cedex France

AbstractA new fast switching linear/helical undulator has been

built and its field has been measured . It consists of 19periods of 80 mm with a field slightly less than 0.2 T .The vertical sinusoidal field is produced by a coil andlaminated yoke while the horizontal field is producedby an array of permanent magnets. A fast reversal ofthe circular polarization rate is induced by flipping thecurrent in the coil within a time which can be a short as6 ms. The magnetic design of the central section andextremities is presented. The result of local field aswell as field integral as a function of the magnetic gapand coil current are detailed. The field integrals arecorrected in real time using a DSP I/O board operatingwith a 5 kHz cycle.

1 INTRODUCTIONThe production of circularly polarized radiation from

insertion devices has always been a high priority at theESRF. The hard X-ray range (20-500 keV) is coveredby three asymmetric wigglers installed on ID15A (1.8T, 7 poles) , ID15B (4 T, 1 pole)[1] and ID20 (1 T, 8poles) while the low energy range (0.5-10 keV) iscovered by three variable polarization helical undulatorsinstalled on ID12A, ID12B and ID16. These undulatorsare made of permanent magnets and allow anindependent setting of the vertical and horizontal fieldcomponents and of their phase allowing any ellipticalpolarization to be produced[2]. During the four years ofuser operation of these undulators , it appears that themost frequent adjustment is a phase inversion whichflips the circular polarization between left and right.Such a flip takes a few seconds which is too long if onewants to detect a dichroism signal as low as 10-4. Toovercome this limit a new variable polarization helicalundulator has been built. It will be installed very soonon the ID12 beamline dedicated to dichroismmeasurement. It is described in this paper.

2 MAGNETIC DESIGNFigure 1 presents a 3D view of the undulator. The

vertical field is produced by a coil and a laminatediron structure. The horizontal field is produced by anarray of Sm2CO17 permanent magnets located betweenthe poles. The spatial period is 80 mm and its length is1600 mm. The horizontal magnetic field is varied bychanging the magnetic gap between the upper andlower magnet arrays placed on both side of the vacuum

chamber. At the minimum magnetic gap of 16 mm andfor the highest current of 250 A , an almost purelyhelicoidal field is generated. The flipping of the helicityof the magnetic field is obtained by inverting the currentin the coil.

magnet blocks

laminated poles

coil layer

Figure 1: 3D view of the termination of the undulator.

The magnetic design is largely dictated by theoperation of the vertical field at the highest frequency aspossible (up to 100 Hz). The choice of Sm2CO17 asopposed to NdFeB magnets was made to avoid anypossible thermal demagnetization of the magnets dueto the eddy current.

ConductorLaminated yokeSm2C017

Figure 2: Longitudinal cut of the yoke and coils aroundthe extremity.

The yoke is made of 0.35 mm laminations of SiliconIron (STABOCOR V270-35A) similar to those used in

317

mardi 6 mars 2012


Permanent magnets

Steel : core and poles

Cu foils

SOLEIL26 x 64 mm, B=0.24T

flippling the current in 100 msNdFeB magnets

Coils: 25 layers of copper sheets stacked together 516 with current and 9 with

cooling) SPI controller for real time

synchronisation (eddy currents)

G. Biallas et al. an 8 cm period electromagnetic wiggler magnet with coils made from sheet copper“, Proceedings of PAC 2005, Knoxville, 4093 ; FEL04, 554-557

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G. H. Biallas et al. / Proceedings of the 2004 FEL Conference, 554-557 555

FEL Technology

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G. H. Biallas et al. / Proceedings of the 2004 FEL Conference, 554-557 555

FEL Technology

Jefferson Lab28 x 80 mm, B=0.134T

EMPHU @ SOLEIL


F. Marteau et al., Description of a EMPHU for fast polarisation switching , Proceedings MT, Marseille, Sept. 2011

mardi 6 mars 2012


3- Effect of the ID on the light source operation

Multipolar terms Dipolar terms: field integral

Comparison magnetic measurement/ electron beam => FFWD tables

+ Fast/slow orbit feedback to keep to source position and divergence in 10% of the electron beam size

Dynamic field integral compensation

HU60 ANTARES

Quadrupolar terms: normal quadrupoles => tune shift => feedback on

the tunes, or FFWD tablesSkew quadrupoles => coupling

Compensation : current sheet for APPLE-II devices

J. Bahrdt, et. al., “Active shimming of the dynamic multipoles of the BESSY UE112 Apple Undulator”, Proceedings of EPAC’08, p. 2222 (2008).

Sextupolar terms=> chromaticity

General approachMagnetic field maps (RADIA; measurements)

introduced on TRACY electron beam simulation (on and off momentum) for injection efficiency and lifetime study

0,200

0,202

0,204

0,206

0,208

0,210

0,212

0,214

0 1 2 3 4 5 6 7 8 9 10

Ho

rizo

nta

l tu

ne

Single bunch current [mA]

December 2006

Four invacuum IDs at 10 mm

Four invacuum IDs at 5.5 mm

J. Safranek et al, Phys. Rev. Special Topics (2002), Vol. 5, 010701, pp. 1-7O. Marcoullé et al, IPAC 2011, 3236

mardi 6 mars 2012


Simulation of the effect of the HU36 undulator located in a short straight section (betax=17.8 m)

Bare machine

11.5 mm minimum gapPhase = 0

On-momentum dynamic aperture

2nd order kick map from RADIA

2nd order kick map from RADIA+ magnetic measurement map

Injection rate : bare machine, 88% => 80%

RP configuration 52% => 55%

Modelisation with field maps


mardi 6 mars 2012


Measured lifetime : bare machine, 19.4 h@400 mA => 14.3 h

RP configuration 7.8 h => 6.6 h

Simulation of the effect of the HU36 undulator located in a short straight section

Bare machine

11.5 mm minimum gapPhase = 0

Off-momentum horizontal aperture

2nd order kick map from RADIA

2nd order kick map from RADIA+ magnetic measurement map

Modelisation with field maps3- Effect of the ID on the light source operation

mardi 6 mars 2012


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1013

1014

1015

1016

Flu

x [p

ho

ton

s/se

c/0.

1%b

w]

101

102

103

104

105

Photon Energy

EPU100 VUV undulator100 mm, L=4 m, Kmax=14.0

EPU45 SXU45 mm, L=4.0 m, Kmax=4.33

U14 SCU14 mm, L=2.0 m, Kmax=2.2

U19 CPMU19 mm, L=3.0 m, Kmax=2.03

W60 SCW,B=6.0 T, 60 mm,L=1.0 m, K=33.6

Damping Wiggler DW100B=1.8 T, 100 mm,L=7 m, K=16.8

25m-radius bend,B=0.4 T, Ec=2.39 keV

3-pole wiggler,B=1.0 T, Ec=5.98 keV

Figure 2. Flux vs. photon energy for various devices at NSLS-II.

A**

*

H. Wiedemann / An ultra-low emittance mode 29

Table 2 Parameters for the PEP damping wigglers

Wiggler field sinusoidal Maximum field strength Bw 12.6 kG Period length ~.,~ 12.0 cm Gap height G~ _< 30.0 mm Wiggler parameter K 14.12 Deflection angle/pole 20~ 2.40 mrad Average bending radius P~, 25.0 m

Obviously for this example the quantum excitation is much smaller than the damping effect and we can expect a significant reduction in the beam emittance. It is asst~med that the damping wigglers are installed as 16.2 m long devices at each end of the six interaction region straight sections.

Using such damping wigglers, the resulting theoreti- cal beam emittance is shown in fig. 4 as a function of the total installed wiggler length L w. To obtain these parameters, the focusing effect of the wigglers has been

140

120

IO0

2 80 60:

4O

20

0

0 25 50 75 160 "125 140 175 Distance from Interaction Point (m)

Fig. 3. Horizontal betatron function in the PEP lattice.

5O

4 O

.< v

3o

E Lu

E 2 0

' 6o 0 5JO 100 Total Length of Damping Wigglers (rn)

Fig. 4. PEP beam emittance as a function of the total wiggler length.

compensated in the lattice by proper adjustments of the quadrupoles to keep the tunes off resonances. From fig. 4 it is obvious that a significant emittance reduction can be obtained from the first wiggler sections installed. For very long wiggler length, the effectiveness is reduced and at some point does not justify the cost anymore.

For the case considered, and a total length of installed wiggler magnets of Lw = 194.4 m, we get from eq. (25) %,,! 1 + 0.0325

- 0 . 1 1 3 . ( 2 6 ) %0 1 + 8.165

At this point it is interesting to check how this method of reducing the beam emittance would work in other synchrotron radiation sources, specifically the newly proposed advanced synchrotron light sources [7,8]. Al- though this method is applicable to any electron storage ring, the effectiveness is greatly determined by the bending radius of the ring magnets, P0. The damping effect scales proportionally with the bending radius of the ring bending magnets and, therefore, it is easier to reduce the beam ernittance with damping wigglers in large storage rings, like PEP, than in smaller rings.

For the newly proposed radiation sources like the APS or the ESRF the beam emittance could be simi- larly reduced. Using the proposed insertion devices for the ESRF, an emittance reduction by a factor of about two [9] is expected. With damping wigglers of equal parameters as assumed here for PEP, an emittance reduction factor of two can be achieved in the APS with a total wiggler length of Lw = 80 m and with L,v = 157 m for the ESRF. Since the quantum excitation is very small, stronger (superconducting?) wiggler magnets could be used to reduce the beam emittance. For the same total length of wiggler magnets as quoted above, but using wigglers twice as strong, the beam emittance could be reduced by a factor fo 4.5 for both the APS and the ESRF.

Intense radiation is produced from these wiggler magnets. For PEP at 6 GeV the synchrotron radiation power is 3.6 kW per 100 mA circulating beam and per meter of wiggler length, In the extreme case of 194.4 m of wiggler magnets, the radiation power would be 58 kW in each of the 12 wiggler magnet beam lines or a total of 700 kW for all wigglers. Since the wiggler action in PEP may occur in both the horizontal and vertical planes, it is possible to spread out the radiation over a large cooling area to avoid excessive heating problems.

The method of reducing the beam emittance by wiggler magnets has the appearance of a brute force approach. Attempts to reduce the beam emittance to such low levels by other means, such as proper choice of a low emittance lattice, however, have been limited so far by the inability to correct for the chromatic and geometric aberrations caused by the focusing lattice. Thus the usual problem of obtaining a large dynamic

l(c). FUTURE FACILITIES

Example for PEP

NSLSII (3 GeV):Horizontal emittance : 0.55 nm.radVertical emittance : 0.008 nmrad

2x3.4 mperiod 9 cm, gap 12.5 mm, K=15.2

H. Wiedemann, An ultra-low emittance mode for PEP using damping wigglers, Nucl. Instr. Meth. A266 (1988) 24-31.T. Raubenheimer et al. SLAC PUB 4808, 1988

Desired ID effects: damping wiggler3- Effect of the ID on the light source operation

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)<<:2()+2:26=$;5$ 6.,$<;:,$36-,*76.$ 64*2*7S$<-)(62()+2:26=$;5$

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)33,&+:=$ ;5$ 6.,$ 9277:,-$ .):L,3$ 5;-$ 2*3,-62;*$ ;5$ 6.,$

L)(44&$(.)&+,-0$$

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&)7*,62($ &;&,*63$ )*/$ :;():$ 2*.;&;7,*,262,3$ 2*$ )*$

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Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee

0-7803-8859-3/05/$20.00 c�2005 IEEE 2448

M. Tischer et al. Damping wigglers for the PETRA III light source, PAC 2005, Knoxville, 2446; EPAC08, 2317

magnet positions [5]. Superposition of different corrector signatures allowed to model any transverse field integral dependence and to find the appropriate configuration (Fig.6).

RESULTS Figures 7–10 present the transverse dependence of 1st

and 2nd horizontal and vertical field integrals of all wigglers. For most devices, the horizontal and vertical 1st field integral is within a range of ±50Gcm and ±30Gcm, respectively. Horizontal and vertical 2nd field integrals are within ±30kGcm2. Note, that the total vertical 1st integral, produced by the 40 positive and negative poles, sum up to ±1,800kGcm.

Horizontal field 1st integral

-100

-50

0

50

100

-2 -1 0 1 2X, cm

Bl, Gs*cm

Figure 7: Transverse dependence of horizontal 1st field integral for all damping wigglers.

Vertical field 1st integral

-100

-50

0

50

100

-2 -1 0 1 2X, cm

Bl, Gs*cm

Figure 8: Transverse dependence of vertical 1st field integral.

Horizontal field 2nd integral

-40000

-20000

0

20000

40000

-2 -1 0 1 2X, cm

Bll, Gs*cm*cm

Figure 9: Corresponding horizontal 2nd field integral.

Vertical field 2nd integral

-40000

-20000

0

20000

40000

-2 -1 0 1 2X, cm

Bll, Gs*cm*cm

Figure 10: Corresponding vertical 2nd field integral.

TEST INSTALLATION An assembly test with two wigglers has been performed

in one of the damping sections (Fig. 11). A special appliance can be mounted at the wiggler to separate the two wiggler halves manually. In the opened state, the wiggler can be moved on the support unit over the vacuum chamber once the damping wigglers shall go into operation. It has been proven that the field integral measurements can be reproduced within about ±30Gcm after opening and closing the wiggler halves.

Figure 11: Damping wiggler test installation at tunnel.

REFERENCES [1] K. Balewski, “Status of PETRA III”, these

proceedings; http://petra3.desy.de [2] M. Tischer et al., “Damping Wigglers for the

PETRA III Light Source”, Proceedings of PAC, Knoxville, 2005, p.2446

[3] A. Batrakov, S. Zverev, I. Ilyin, et al., “The new VME – based system for magnetic measurements with Hall sensors”, Proceedings of RuPAC, 2006.

[4] A. Batrakov, V. Sazansky, D. Shichkov, P. Vagin. “Hardware and software for magnetic measurements with movable coils”, Proceedings of RuPAC, 2006.

[5] A. Dubrovin, “Mermaid User’s guide”, Novosibirsk, 2006

Proceedings of EPAC08, Genoa, Italy WEPC132

02 Synchrotron Light Sources and FELs T15 Undulators and Wigglers

2319

NLSLII website

MAX-IV (3 GeV):Horizontal emittance : 0.24 nm.rad

More damping with additional synchrotron radiation through installation of strong wiggler magnets placed in a dispersion free location (for the equilibrium orbit to

be independant of the particle energy) => emittance reductionPETRAIII:Horizontal emittance : 1 nm.rad, Vertical emittance : 0.01 nmrad

mardi 6 mars 2012


Desired ID effects: Robinson wiggler


D: partition number due to radiation damping

D=-1 => εx/2 and energy spread x√2

Generally, D ~ 0 and Jx ~ 1Robinson theorem : Jx + Jz + Js = 4

B*dB/dx ≠0 and ηx≠0

2

Emittance in Electron Storage Rings

!  Horizontal (natural) Emittance:

Jx= Horizontal damping partition number

! !"#$%&#'()*!+,%-)'.+!%/!0+(+$,%'+0!12!(3+!+45%*%1$%5,!1+(6++'!(3+!45)'(5,!+7.%()8#'!!!!!05+!(#!(3+!+,%//%#'!#9!:3#(#'/!)'0!(3+!0),:%';!05+!(#!(3+!<=!)..+*+$)8#'!>+*0!5/+0!!!!!(#!.#,:+'/)(+!(3+!+'+$;2!*#//!#9!(3+!/2'.3$#($#'!$)0%)8#'?!

xx

dipoleqx J

HC

!"

#2

=

DJx !=1! Jx is related to the damping partition D by :

D =

12!

"x (s)#x!! 1

!x2 + 2K(s)

"

#$

%

&'ds

ds!x2!!

where

(the integral is to be evaluated only in dipoles). !"#$%&'()*(+",-./012(3)!)(4542(+-6%78%$(9:';2(9<==2(>"$;#/(

D=-1 =>

Type B(T) g (mm) dB/dx (T/m)out of

vacuum1.4 11 140

In vacuum 1.0 5.5 182

Application to SOLEILhorizontal emittance : 3.7 nmrad⇒1.85 nmrad

Short straight section : ηx = 0.28 m

- Js=1 damping in longitudinal plane- high gradients?- field homogeneity (injection, lifetime)- radiation properties

mardi 6 mars 2012







ηx= dispersion function

ρx = radius of curvature due to BB*dB/dx ≠0 and ηx≠0

2




! !"#$%&#'()*!+,%-)'.+!%/!0+(+$,%'+0!12!(3+!+45%*%1$%5,!1+(6++'!(3+!45)'(5,!+7.%()8#'!!!!!05+!(#!(3+!+,%//%#'!#9!:3#(#'/!)'0!(3+!0),:%';!05+!(#!(3+!<=!)..+*+$)8#'!>+*0!5/+0!!!!!(#!.#,:+'/)(+!(3+!+'+$;2!*#//!#9!(3+!/2'.3$#($#'!$)0%)8#'?!

xx

dipoleqx J

HC

!"

#2

=


D =

12!

"x (s)#x!! 1

!x2 + 2K(s)

"

#$

%

&'ds

ds!x2!!

where


D=-1 =>


vacuum1.4 11 140

In vacuum 1.0 5.5 182




mardi 6 mars 2012







ηx= dispersion function

ρx = radius of curvature due to BB*dB/dx ≠0 and ηx≠0

2




! !"#$%&#'()*!+,%-)'.+!%/!0+(+$,%'+0!12!(3+!+45%*%1$%5,!1+(6++'!(3+!45)'(5,!+7.%()8#'!!!!!05+!(#!(3+!+,%//%#'!#9!:3#(#'/!)'0!(3+!0),:%';!05+!(#!(3+!<=!)..+*+$)8#'!>+*0!5/+0!!!!!(#!.#,:+'/)(+!(3+!+'+$;2!*#//!#9!(3+!/2'.3$#($#'!$)0%)8#'?!

xx

dipoleqx J

HC

!"

#2

=


D =

12!

"x (s)#x!! 1

!x2 + 2K(s)

"

#$

%

&'ds

ds!x2!!

where


D=-1 => ≈ 89 T2/m


vacuum1.4 11 140

In vacuum 1.0 5.5 182




mardi 6 mars 2012


CERN PS (1983)damping of horizontal betatron oscillationsJx=3 et D = -2



9

One of the Robinson Wiggler used on the PS (CERN)

!"#$%&'()*(+",-./012(3)!)(4542(+-6%78%$(9:';2(9<==2(>"$;#/(

Y. Baconnier et al. / The PS wiggler 251

1.2

1.1

1

.9

.6

.7

.6

2.4 2.2

2

1.B

1.6

1.~

1.2

'~'x (Iv)

'9"x (Iw:ol } 1 1 1 1 1 1 1 1 1

0 100 200 :300 ~O0 500 600 700

ta) lw tA)

Jx (Iv)

Jx (M=o)

.6 i I I 1 I I I I I I t t I

0 100 200 300 600 506 600 700

(b) iw (A) Fig. 10. Expected and measured relative variations of (a) rms horizontal bunch width o x (b) damping partition number Jx as functions of the wiggler current.

where h = 8 (the harmonic number), Z/n = 7 12 (the broad band coupling impedance), V = 100 kV (the peak RF voltage), %--16.3 ° (the stable phase angle), R = 15.056 m (the ring mean radius), and I o = 10 mA (the circulating beam current, constant during the experi- ment). The beam energy spread was then evaluated as

O E Q s ~-(Iwl=°sO(Iw) Rap ,

where ap -- 0.078 is the horizontal momentum compaction and

ehapVcos qPs ]1/2 Q~=L T~g j the synchrotron tune. The longitudinal partition number was evaluated as

jE([w)mCq( gl2[-~.~, (Iw)] -2, p3 \ t~0/ LZ~ J

where Cq = 3.83 ! 10 -13 m and P3 = 3.87 m as defined in ref. [61. Figs. 9a and 9b show the values of

o~0(Iw) and &(Iw) Os0(I w = 0) JE(Iw = 0) ' respectively, deduced from bunch length measurements, together with the expected values.

The horizontal rms beam size ox(Iw) was worked out from the width A X at half height of the beam profile.

ox~ (Iw) =AXi(Iw)/2.36, where the indexes are related to the two different measurement locations Yt and H 6.

The horizontal partition number was deduced:

H E 1 2

where B~ is the horizontal betatron function at the measurement location and /-/= 0.82 m is a machine lattice invariant.

wiggler was progressively raised up to 640 A with simultaneous compensation of betatron tune changes to keep the beam away from resonances.

For various wiggler excitations, two characteristics of the beam were measured:

(i) The bunch length, by means of the digitized signal from a PU electrode.

(ii) The horizontal profile, by means of synchrotron light monitors placed in two different locations of the ring (called Yt and He).

From the measured bunch length o~(Iw) a bunch length without potential well effect Oso (Iw) was deduced through the relationship [5]:

Oso(i , )[o2( iw)= _ 2 ~ ] Z / n [ ~ I 0 R3 X 106]1/2 h Vcos rp s Os(Iw)

Fig. 11. Horizontal positron beam profile in DCI (a) without the wiggler and (b) when the wiggler is excited.

Test in DCI

Y. Baconnier et al, Emittance control of the PSe± beamas using A Robinson wiggler, Nucl. Instr. Meth. A 234 (1985) 244-252 Nucl. Instr. Meth. A266 (1988) 24-31.

Lee SY Kolski J Review of Scientific Instruments 78, 075107 (2007)

Z. W Huang et al. IPAC 2010, 3186, PAC 2011, 1265

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Accelerator Technology

Tech 15: Insertion Devices (Undulators and Wigglers)

mardi 6 mars 2012


B<0 B>0 B>0 B<0

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CERN PS (1983)damping of horizontal betatron oscillationsJx=3 et D = -2



9

One of the Robinson Wiggler used on the PS (CERN)

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Y. Baconnier et al. / The PS wiggler 251

1.2

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1

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'~'x (Iv)

'9"x (Iw:ol } 1 1 1 1 1 1 1 1 1

0 100 200 :300 ~O0 500 600 700

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(b) iw (A) Fig. 10. Expected and measured relative variations of (a) rms horizontal bunch width o x (b) damping partition number Jx as functions of the wiggler current.

where h = 8 (the harmonic number), Z/n = 7 12 (the broad band coupling impedance), V = 100 kV (the peak RF voltage), %--16.3 ° (the stable phase angle), R = 15.056 m (the ring mean radius), and I o = 10 mA (the circulating beam current, constant during the experi- ment). The beam energy spread was then evaluated as

O E Q s ~-(Iwl=°sO(Iw) Rap ,

where ap -- 0.078 is the horizontal momentum compaction and

ehapVcos qPs ]1/2 Q~=L T~g j the synchrotron tune. The longitudinal partition number was evaluated as

jE([w)mCq( gl2[-~.~, (Iw)] -2, p3 \ t~0/ LZ~ J

where Cq = 3.83 ! 10 -13 m and P3 = 3.87 m as defined in ref. [61. Figs. 9a and 9b show the values of

o~0(Iw) and &(Iw) Os0(I w = 0) JE(Iw = 0) ' respectively, deduced from bunch length measurements, together with the expected values.

The horizontal rms beam size ox(Iw) was worked out from the width A X at half height of the beam profile.

ox~ (Iw) =AXi(Iw)/2.36, where the indexes are related to the two different measurement locations Yt and H 6.

The horizontal partition number was deduced:

H E 1 2

where B~ is the horizontal betatron function at the measurement location and /-/= 0.82 m is a machine lattice invariant.

wiggler was progressively raised up to 640 A with simultaneous compensation of betatron tune changes to keep the beam away from resonances.

For various wiggler excitations, two characteristics of the beam were measured:

(i) The bunch length, by means of the digitized signal from a PU electrode.

(ii) The horizontal profile, by means of synchrotron light monitors placed in two different locations of the ring (called Yt and He).

From the measured bunch length o~(Iw) a bunch length without potential well effect Oso (Iw) was deduced through the relationship [5]:

Oso(i , )[o2( iw)= _ 2 ~ ] Z / n [ ~ I 0 R3 X 106]1/2 h Vcos rp s Os(Iw)

Fig. 11. Horizontal positron beam profile in DCI (a) without the wiggler and (b) when the wiggler is excited.

Test in DCI

Y. Baconnier et al, Emittance control of the PSe± beamas using A Robinson wiggler, Nucl. Instr. Meth. A 234 (1985) 244-252 Nucl. Instr. Meth. A266 (1988) 24-31.

Lee SY Kolski J Review of Scientific Instruments 78, 075107 (2007)

Z. W Huang et al. IPAC 2010, 3186, PAC 2011, 1265

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Accelerator Technology

Tech 15: Insertion Devices (Undulators and Wigglers)

mardi 6 mars 2012


Conclusion Conclusion

Interesting prospects with the advanced permanent magnet based insertion devicesNew technological develpments towards short period high fields

Superconducting undulators and wiggler are also quickly developing :Thermal budget (resistance wall and synchrotron radiation) =>with (larger gap) /without

thermal shieldprocedure of magnetic field correction

mardi 6 mars 2012


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the sorting results have been found to be some-what different from the expected values in the caseof long undulators. Even in such a case, we canmake field corrections by sorting magnets with themagnetic data measured for the total device. Wecall it an ‘‘in-situ’’ sorting technique because themagnets are rearranged according to the situationof the undulator field, which enables us step-by-step improvements of the undulator performance.

The purpose of this article is to describe thedetails of the in-situ sorting technique andpractical results of field corrections. A Cartesiancoordinate with the photon propagation axis asthe z direction, the horizontal axis as the xdirection and the vertical axis as the y directionis used in the following discussions. The undulatorcenter is assumed to be at z ¼ 0.

2. Requirements on undulator fields

Because the undulator field not only affects theelectron beam but also determines the perfor-mances of the photon beam, it should satisfy manyrequirements. We can classify the requirementsinto two types. One is the requirement from theviewpoint of a stable operation of the storage ringand the other from the photon-beam performance.

2.1. Effects on the electron beam

In order to obtain a stable operation of thestorage ring, the undulator field is required to betransparent for the electron beam. In other words,the magnetic field integrated over the total lengthof the undulator should be negligible. The fieldintegral ðIÞ is measured as a function of thehorizontal position ðXÞ of the electron beam toestimate the effects of the undulator field. Bydifferentiating the I–X curve at the electron beamaxis (X ¼ 0) several times, the multipole compo-nents are obtained. They are called the dipole,quadrupole, sextupole, octupole and so on accord-ing to the number of differentiation. The dipoleinduces a closed orbit distortion (COD) followed bya variation of the photon-beam axis, the quadrupolethe tune shift and increase of the coupling, thesextupole degradation of the dynamic aperture.

Higher order multipoles should also be suppressedfor a stable operation of the storage ring.

2.2. Photon-beam performance

For SR users, the most important performanceof the undulator is that the available photon flux isas high as possible. The energy spectrum ofundulator radiation has sharp peaks at the multi-ples of the fundamental energy determined by theperiodic length and magnetic fields of the un-dulator and the electron energy. These sharp peaksare called harmonics of undulator radiation andthe peak photon intensities are degraded due toseveral factors such as the emittance and energyspread of the electron beam, the finite acceptanceof the optics, and so on. In the case of realundulators, error magnetic fields due to imperfec-tions of magnets also degrade the peak intensity.Because the degradation is more pronounced asthe harmonic number increases, the error fieldshould be corrected more accurately to utilizehigher harmonic radiations.

A simple method of the field correction torecover the spectral intensity is to reduce peak-fielddeviations. It is, however, pointed out by manyauthors [4,5] that the practical meaningful prop-erty that determines the spectral intensity is not thepeak-field deviation but the phase error, or thedeviation of the relative phase between radiationsemitted at different positions of the electron orbit.The relative phase fðzÞ is given by

fðzÞ ¼2pl

z

2g2þ

Z z

%L=2

b2xðz0Þ þ b2yðz

0Þ2

dz0" #

; ð1Þ

where g is the Lorentz factor of an electron movingin the undulator field, l the wave length ofradiation, bx;y the horizontal=vertical relativevelocity of the electron and L the length of theundulator. The phase error should be reduced toobtain sufficiently high intensity at high harmonics.

3. Principle of in-situ sorting

The field integral distribution along the hor-izontal axis are measured with a flipping-coil or

T. Tanaka et al. / Nuclear Instruments and Methods in Physics Research A 465 (2001) 600–605 601

In vac NSLS P. Stefan et al. J. Synchrotron Rad. (1998)

H. Hsieh et al. NIM A246, 1983, 79

mardi 6 mars 2012



Quasi periodic PM EPU: PERA undulators

PERA undulators



Θmag = 0 °

Xdist = 1 mm

S. Sasaki, B. Diaviacco and R. P. Walker, Synchrotrone Triestre Internal Report, ST/MTN-‐98/8S. Sasaki, B. Diaviacco and R. P. Walker, Proceedings of EPAC 2008

Modes Bz [T] Bx [T]

Linear H. 0,2

Linear V. 0,26

Circular -‐-‐

o No phase moXono Linear polarizaXon onlyo CombinaXon of different period length

o Magnets creaXng aperiodicity have reduced height and opposite direcXon of magneXsaXon.

H. & V. field values in linear mode H. & V. trajectories in linear Horizontal (red line) and linear verLcal (blue one) Spectrum calculated for 400 mA, 2,75 GeV

and zero emiBance and energy spread,

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Quasi periodic PM EPU: APPLE VIII

Apple VIII undulatorsUndulator :

Period : 30 & 60 mm Minimal gap : 15,5 mm

Magnets : NdFeB Size : 30 x 30 mm

50 x 50 mm Br : 1,26 T

Θmag = 0 °

Xdist = 1 mm

Modes Bz [T] Bx [T]

Linear H. 0,42

Linear V. 0,24

Circular 0,210,21


S. Sasaki, B. Diviacco and R. P. Walker, Proceedings of European ParLcle Accelerator Conference, Sweden (1998)S. Saski, Nuclear Instruments and Methods A347, 83 (1994)

mardi 6 mars 2012



Quasi periodic PM EPU: APPLE VIII

Fig. 1 : MagneLc fields at minimal gap and 0 mm shi[ Fig. 1 : MagneLc fields at minimal gap and λ/4 mm shi[

Fig. 1 : MagneLc fields at minimal gap and λ/2 mm shi[ Fig. 1 : MagneLc fields at minimal gap and λ mm shi[Fig. 1 : MagneLc fields at minimal gap and 3λ/4 mm shi[

o Complex structure o Aperidodicity o Low on-‐axis power density

Apple VIII undulators

mardi 6 mars 2012


0.1 - 10 keV(2.6 keV)

Bh = 0.22 TBv = 0.8 Tλ0 = 16 cm

Modification of the polarisation at 100 Hz

Five full-field and two half-field poles produce a mirror-symmetric magnetic field distribution with a period length of16.0 cm. A peak field magnitude of 0.8 T at a minimum gapgo of 28.0 mm was achieved. The nonsteering terminationwas realized with the magnetic gap g1 increasing by 2 mm atthe half-field poles. The upper and lower hybrid assemblies areattached to independent drive trains, providing a continuouslyvariable gap motion from a minimum of 28.0 mm to amaximum of 160 mm. At an extreme AC regime, when theelectromagnet is energized with 100 Hz alternating currentwith an amplitude of 550 A, the computed total losses due toeddy currents induced in the vanadium-permendur poles, thepermanent magnets, and the iron "neutral" poles can reachabout 60 W per wiggler period.

III. ELECTROMAGNETIC STRUCTURE The electromagnetic structure generates a periodicalternating horizontal magnetic field of antisymmetricconfiguration in order to provide the periodic vertical beamtrajectory deflection along the wiggler. The electromagnetincludes six uniform poles with a magnetic gap of 54 mm andend structures consisting of two poles at each side. The currentexcitation is provided by means of two water-cooled, "snake-type" coils [6] with a copper cross section of about 140 mm2.The magnetic gaps of the end structure poles and number ofturns around the first and last poles are different from those inthe main periodic structure. This end structure performancewas designed to attain a nonsteering {first field integral, Eq.(1)} and a displacement-free {second field integral, Eq. (2)}termination provided that the pole strength pattern is close totheoretical 1/4 : 3/4 : 1. The iron cores of the first and lastpoles are separated from the main yoke and are provided withadjusting systems to vary their magnetic gaps. To reduce thegeneration of eddy currents, the yoke of the electromagnet wasconstructed from 0.5-mm-thick laminations of transformeriron with a silicon content of 3.5%. At the extreme regime(I=0.55 kA and fmod=100 Hz), the computed power loss doesnot exceed about 5 W per wiggler period.

g1= 89 mm =80mm! /2g2 =64 mm g0 =54 mm

Figure 2. Electromagnetic structure design.

IV. VACUUM CHAMBER The vacuum chamber of the EMW was manufactured bythe deformation of a stainless steel circular pipe to anelliptical cross section of inner dimensions: major axis of 50mm and minor axis of 25 mm. To decrease the eddy currentlosses in the vacuum chamber, a wall thickness of 0.6 mmwas chosen as the minimum possible from a mechanicalcollapse point of view. The power dissipation computed byELECTRA does not exceed 0.8 W per wiggler period at theextreme AC regime.

V. POWER SUPPLY FOR ELECTROMAGNET The principle of forced DC current commutation is used inthe power supply for the electromagnetic structure. It consistsof a thyristor-stabilized DC power supply as an initial currentsource and a commutator based on the fast thyristor bridge-inverter. The bridge-inverter output is connected to theelectromagnet coil in parallel with capacitor. This scheme isdesigned to supply the electromagnet by direct current or bytrapezoidal shape alternating current with a switchingfrequency range from 0 up to 100 Hz. The switching time(current polarity reversing time) does not exceed 2 msec, and itretains the same duration up to the upper limit of switchingfrequencies. The power supply can provide an output currentrange of 0.2 - 1.2 kA with the current magnitude differencebetween both polarities less than 0.5%.

hybrid wiggler ball-bearing supports

vanadium-permendur pole

electromagnet core

coilcoil

electromagnet holder

vacuum chamber

Fig. 2. Side sectional view of the elliptical multipole wiggler.

VI. TIME-DEPENDENT WIGGLER FIELD INTEGRALS The electromagnet design includes some nonuniformitiesrelated mostly to anti-symmetric locations of the coil currentleads. In turn, these nonuniformities give rise to a disturbanceof the ideal antisymmetric magnetic field configuration at bothends of the electromagnetic structure. This effect has beencorrected easily for DC operation by means of the passive gapadjusting systems at the end poles. However, duringswitching, periodic time-dependent components arise for boththe first and second field integrals. Due to the slightly differentgeometry of the electromagnet ends, the eddy currents inducedin the copper turns, the iron elements of hybrid structure, andthe vacuum chamber lead to different magnetic field timedelays along the wiggler, hence, to different conditions of fieldintegral compensation at each time moment. On the other hand, the surroundings of the electromagnetinclude some conductive elements with a thickness a fewtimes the skin depth at frequencies corresponding to theswitching time (0.5 kHz). As the switching frequency isincreased, the time of magnetic field diffusion through thesematerials becomes comparable or greater than a half-period ofcurrent pulse. It is obvious that the time-dependent

Gluskin et al.

ElectroMagnetic Permanent magnet Helical Wiggler


mardi 6 mars 2012


Introduction

Light Source Context

generation

3

4

few undulators, ε~few 10nm.rad

1

2

parasitic use of synchrotron radiation

Synchrotron radiation used as spontaneous emission for the production of coherent intense radiation (emittors in phase)

Higher harmonics

B: Nber of photons / phase space cell

diffraction limit: ∆x. ∆x’ ∼ λ/2π

Fourier limit : ∆ω. ∆τ ∼1Gaussian beams case :

c ∆t.∆λ/λ2=0.44

5

fs pulses, ε~εn/E longitudinal coherence for FEL

Long straight sections for ID, ε~few nm.radUltimate storage ring

accelerator

storage ring

storage ring

storage ring

LinacERL

LWFA LWFA based FEL

mardi 6 mars 2012


2




! !"#$%&#'()*!+,%-)'.+!%/!0+(+$,%'+0!12!(3+!+45%*%1$%5,!1+(6++'!(3+!45)'(5,!+7.%()8#'!!!!!05+!(#!(3+!+,%//%#'!#9!:3#(#'/!)'0!(3+!0),:%';!05+!(#!(3+!<=!)..+*+$)8#'!>+*0!5/+0!!!!!(#!.#,:+'/)(+!(3+!+'+$;2!*#//!#9!(3+!/2'.3$#($#'!$)0%)8#'?!

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mardi 6 mars 2012


3

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DJx !=1

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!  <&:$('&-+$$

=3-0$%($>$?@$A$?B$A$?($8$C$$/0+#+$?B$8$D$%&:$?($8$E$$

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mardi 6 mars 2012


4

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DJx !=1

Jx = 2

And the horizontal emittance can be divided by a factor 2!

xx

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HC

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mardi 6 mars 2012


5

!  Note that D depends on the dispersion function !(s) and the quadrupole strength K(s)

!

!! ""#

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x

xxx

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A magnetic element introducing the product B*dB/dx in a straight section where the dispersion !x is non zero contributes to the modification of D.

!"#$%&'()*(+",-./012(3)!)(4542(+-6%78%$(9:';2(9<==2(>"$;#/(

mardi 6 mars 2012


SOLEIL energy acceptance

Calculated

The energy acceptance of the bare machine is large : +/- 4%

Measured

Off-momentum (dp/p, x) map

Vacuum chamber at 12 mm


mardi 6 mars 2012


Effect on injection efficency

Bare machine 5xU20 at minimum gap + HU640 LV mode at maximum field

Reduction of the on-momentum dynamic aperture and the energy acceptance in the presence of IDs => reduction of the injection rate

Measured on-momentum (x, z) map

Measured off-

momentum (dp/p, x)

map


mardi 6 mars 2012


Rare Earth Magnet behaviour versus temperature


M. Sagawa et al. J. Magn. Magn. Mater. 70, 316 (1987)T. Hara et al. APAC2004, Gyeongju, Korea, 216

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Spin Transition ReorientationNdFeB strong Magneto-Crystalline Anisotropy (MCA) => orientation along [001] Magneto-cristalline orientation given by the energy : E(T) = K1sin2(θ)+ K2sin4(θ) , θ angle between the magnetisation and [001]at room temperature : magnetisation // cFe MCA independant of T, Nd : K1 // [001] dominant at room T and K2//[110] at low T

D. Givord et al. Solid State Comm. 51 (1984) 857L. M. garcia et al. Phys. Rev. Lett. 85 (2) 429

mardi 6 mars 2012



Lab. Tech. Period (mm) Magnet Br (T) Hcj (kA/

m) Installation Length (m) Reference

SPring-8 PPM 15 Nd2Fe14B, 1.41 1114 Lab 0.6 T. Hara, et al., . Phys. Rev. Spec.Topics 7, 050702 (2004)

NSLSII Hybrid 14.5 Nd2Fe14B 1.37 Lab 0.11

SLS/SPring-8 Hybrid 14 Nd2Fe14B 1.33 1670 3G 1.7 T. Tanaka, et al., . Phys. Rev. Spec.Topics 12, 120702 (2009)

ESRF n°1 Hybrid 18 Nd2Fe14B 1.16 2400 3G 2

ESRF n°2 Hybrid 18 Nd2Fe14B 1.16 2400 3G 2 J. Chavanne et al. , IPAC 2008, 2011 3245

DIAMOND/Danfysik

Hybrid 17.7 Nd2Fe14B 1.31 1670 3G 2

SOLEIL Hybrid 20 Nd2Fe14B 1.41 1114 0.08

SOLEIL Hybrid 18 Pr2Fe14B 1.35 1355 0.072

SOLEIL Hybrid 18 Pr2Fe14B 1.35 1355 3G 2 C. Benabderrahmane et al. IPAC 2011

BESSY/UCLA Hybrid 9 Pr2Fe14B 5G 2 J. Bahrdt et al. IPAC10, 3111 fixed gap=2.5 mm

NSLSII/ADC Hybrid 18 Nd2Fe14B 3G 2 T. Tanabe, et al.

NSLSII Hybrid 17 3G 2.7 T. Tanabe, et. al., PAC 2011, 2090

SOLEIL/LUNEX5

Hybrid 12-15 Nd2,xPr2,1-xFe14B 4-5G 3-5

Examples of CPMU

T. Tanabe, et. al., AIP Conference Proceedings, Vol. 1234, p.29 (2010). 4.85 mm gap

J. Chavanne et al., PAC09,

C. Benabderrahmane et al. NIMA A 669 (2012) 1-6

C. Benabderrahmane et al. NIMA A 669 (2012) 1-6

mardi 6 mars 2012






High Tc Tanaka PRST et New Journal of Physics

13 Institute of Physics !DEUTSCHE PHYSIKALISCHE GESELLSCHAFT

Electromagnet

Cryocooler

Hall probe

Linear actuator

Bellows

HTSC ring

Figure 10. Experimental setup. The HTSC ring is mounted on a copper plateattached to the cryocooler head to be cooled down to 25 K and inserted in the gapof an electromagnet that can apply an uniform magnetic field of up to 2.0 T. Ahall probe mounted on a cantilever is inserted from the opposite side to measurethe magnetic field generated by the HTSC ring.

1.8 T1.6 T1.2 T0.8 T0.4 T

0.22 T

00.10.20.3

0.40.50.60.70.8

0.9

Figure 11. Spatial profiles of the magnetic field generated by the HTSC ringsample A (no treatment for reinforcement) for different values of the externalfield strength applied by the electromagnet. See text for details.

It is worth noting that two peaks of magnetic field were found when Bext was higher than 1.6 Tand that they remained even after the ring HTSC sample was broken. Paying attention to thegeometrical structure of the ring HTSC shown in figure 9(b), we can conclude that the two peakswere generated by local current loops in the sections indicated by the red circles.

Figure 12 shows the results for the sample B, in which profiles similar to the sample A wereobserved, and it was found that the sample was broken at Bext = 1.6 T. Thus the resin impregna-tion is not enough for reinforcement of the ring HTSC for realization of cryoundulator plus.

New Journal of Physics 8 (2006) 287 (http://www.njp.org/)

mardi 6 mars 2012



Permanent magnets EPU

Cross undulators :

M. Moissev et al. Sov. Phys. J. 21, 332, 1978K. J. Kim NIMA219, 426 (1986)

Onuki et al.

Sasaki et al.Helios et al.

mardi 6 mars 2012


Compensation of the dynamic integral by magic fingers


Dynamic field integral compensation

J. Safranek et al, Phys. Rev. Special Topics (2002), Vol. 5, 010701, pp. 1-7O. Marcoullé et al, IPAC 2011, 3236

mardi 6 mars 2012


Desired ID effects: damping wiggler


emittance : equilibrium between quantum excitation and radiation

damping (loss of transverse momentum)Jx : horizontal partition number

More damping with additional synchrotron radiation through installation of strong wiggler magnets places in a dispersion free location (for the equilibrium orbit to

be independant of the particle energy)

26 H. Wiedemann / An ultra-low emittance mode

3.1. Effects of wiggler magnets on beam parameters

Much larger changes in the beam emittance can be obtained using regular wiggler magnets. They can be used in storage rings to either increase or decrease the beam emittance; here we are interested in minimizing the beam emittance. The effect of wiggler magnets on the beam emittance and energy spread will be described.

The particle beam ernittance in a storage ring is the result of two competing effects. First, the quantum excitation caused by the quantized emission of photons contributes to a continuous increase of the beam emittance. Second, a damping effect, resulting from the loss of some transverse momentum of the particles during photon emission, compensates the quantum excitation. Both effects lead to the equilibrium beam emittance observed in electron storage rings.

Independent of the value of the equilibrium beam emittance in a particular storage ring, that beam emittance can be further reduced by increasing the damping without also increasing the quantum excitation. More damping can be established by causing additional synchrotron radiation through the installation of deflecting dipole magnets, such as strong wiggler magnets. In order to avoid quantum excitation of the beam emittance, however, the placement of the wiggler magnets must be chosen carefully. An increase of the beam emittance through quantum excitation is caused only when synchrotron radiation is emitted at a place in the storage ring where the beam orbits are dispersed due to the energy of the particles. The emission of a photon causes a sudden energy loss, and thereby also a sudden change of a particle's equilibrium trajectory, which generally causes a corresponding increase in the betatron oscillation amplitude about the new equilibrium orbit. This increase of the betatron amplitude for all particles constitutes the increase of the beam emittance. Emit- tance reducing wiggler magnets, therefore, must be placed in areas around the storage ring where the dispersion vanishes and the equilibrium orbit is independent of the particle energy.

The quantum excitation can be expressed by

d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)

c is the speed of light, E is the particle energy, P0 is the bending radius of the ring magnets and

1 .*= {,," +

The average ( ) is to be taken for the whole ring and the index 0 indicates that the average (,gff/p 3)o be taken only for the ring proper without wiggler magnets. The parameters/3 =/~(s) and "q = ~(s) are the betatron and dispersion functions of the lattice. If there is a wiggler magnet installed in the storage ring we get an additional excitation term to give

( d % ) =cCqES{(jg,/O3)o+(jg,/O3)w}. (3) dt ]Q~

Both the ring magnets and the wiggler magnets produce synchrotron radiation and contribute to damping of the transverse particle oscillations given by

dt }o ,

where C re - 2 . 1 1 X 1 0 3 m 2 GeV 3 s - i (5)

CD 3 ( m c 2 ) 3

and Jx is the horizontal damping partition number. An equilibrium beam emittance including the effect

of the wiggler magnets is obtained by adding eqs. (3) and (4) and solving for %w:

e 2 <~/O3>o + <~/P>w "xw = Ca Jx <1/02>0 q- <l/p2>w (6)

where C a = cCq/(2Ct~ ) = 1.463 ! 10 -6 m GeV -2. With %o being the unperturbed beam emittance (Pw--' m) we get for the relative emittance change

%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)

We can make use of the definition of the averaged parameters. With C = 2~rR the circumference and R the average radius of the storage ring we have

e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R

Here L w is the total length of the wiggler magnets, 0w is the bending radius of the wiggler magnet, for simplicity assumed to be constant, (-/g')w = (1/C)¢w -/t° ds and







d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)


1 .*= {,," +




dt }o ,


CD 3 ( m c 2 ) 3





%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)


e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R








d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)


1 .*= {,," +




dt }o ,


CD 3 ( m c 2 ) 3





%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)


e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R








d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)


1 .*= {,," +




dt }o ,


CD 3 ( m c 2 ) 3





%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)


e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R








d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)


1 .*= {,," +




dt }o ,


CD 3 ( m c 2 ) 3





%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)


e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R








d% ] Oo = cCqES(~/O3)°' (1) ~ t

where

55 rehc 10_11 m2 Cq 48V~ ( m £ 2 ) 6 -- 2.06 ! GeV 5, (2)


1 .*= {,," +




dt }o ,


CD 3 ( m c 2 ) 3





%w 1 + <~/p3)w/<~/O3)o %o 1 + <1/02 )w/<1/02 )0 (7)


e Tds= <*>o.

( ) ) l ~ w ~ Lw 1 w=~ as - c ,:,~'

1 ) 1 1 "

~ d s = 1 7 Po R


H. Wiedemann / A n ultra-low emittance mode 27

( J r ) 0 = 1/C9~0 aft ds. With these expressions we finally get from eq. (7):

1 + ( Po ]3 ( ' ~ ) w % w = \ ~ w ] (aft)0 (9)

,x0 Lw (p012 1 + ~ ~ i

Concurrent with a change in the beam emittance we also have a change in the energy spread o E due to the wiggler radiation:

Lw ( Po ] 3 o2 w = 1 + ~ \ O 7 I . (10)

°20 1 + 2~00 \Ow]

From this derivation we conclude the following: - If the dispersion function is finite in the wiggler

section we have (-"ff)w =~ 0 which can lead to strong quantum excitation depending on the choice of Ow.

- If wiggler magnets are placed into a storage ring lattice where the dispersion function vanishes, *i --- 0, we have (o~'°)w = 0 and therefore no quantum excitation occurs. In this case we can reduce the beam emittance, since the wiggler radiation always contributes to the damping term in the denominator of eq. (9).

- Whenever wiggler magnets are used and P0 > Ow the energy spread in the beam is increased. This is true for virtually all cases of interest.

Thus, we have developed a potential way to reduce the beam emittance in a storage ring by creating strong additional radiation damping while minimizing the quantum excitation effects. The circumstances necessary to achieve this will be derived in the next section.

3.2. Reduction of the beam emittance by damping wigglers

The general effects of wiggler magnet radiation on the beam emittance have been derived and we found that the beam emittance can be reduced if the wiggler is placed where *i = 0 since, then, also ()ff)w = 0. This latter assumption, however, is not quite correct.

Even though we have chosen a place where *i = 0, the quantity aft w will not be exactly zero once the wiggler magnets are turned on because they create (like any dipole magnet) their own dispersion function.

We will calculate this part of the dispersion function for a wiggler period as shown in fig. 2. The magnet period is subdivided into four segments of equal length l w. Again we use a model where the wiggler fields are constant with alternating signs. In short period wiggler magnets the actual fields assume a more sinusoidal distribution along the axis and the result must be mod- ified accordingly.

~(~)

Fig. 2. Dispersion function in a wiggler magnet.

The dispersion function in the first of the four magnet sections of a wiggler period can be expressed for small deflection angles by:

1 s 2 *i1 ( s ) 2 Pw' (11)

t *i,(s) - - s Pw

where 0 _< s _< l w within this section and where we have assumed that *i0 = ~/o = 0 at the beginning of the wiggler magnet. In the second magnet section we have:

1 (I 2 + 2 l w s - s 2) * i 2 ( S ) = - - 2 Pw '

l w - s *i~(s) - - , (12)

Pw

where 0 < s < l w. For the other two wiggler magnet sections the *l-function is similar to eqs. (11) and (12) for symmetry reasons.

The integral

1 / *

(')ff)w = ~JwO~'w ds

now can be calculated, but for simplicity we set here fix = constant and fl" = 0. The contributions of the first and second wiggler magnet sections to the integral 9~w~/p 3 ds in eqs. (8) are

Sw ' ,'w ,x,.w a I - - s 20fl, p~ + 305 "~ 3p 5 '

a 2 / ' . / f d s = 43 15w + flx l~ = flx l aw (13) Jwd- 60~xCw 2¢w 2¢w' where we have assumed that I w << fix- For the whole wiggler system with N w periods we have

~w 1---ds = Nw4/~ - . (14) p 2 P w

Using eqs. (8) and (14) in eq. (7) we finally get for

I(c). FUTURE FACILITIES

H. Wiedemann / A n ultra-low emittance mode 27

( J r ) 0 = 1/C9~0 aft ds. With these expressions we finally get from eq. (7):

1 + ( Po ]3 ( ' ~ ) w % w = \ ~ w ] (aft)0 (9)

,x0 Lw (p012 1 + ~ ~ i

Concurrent with a change in the beam emittance we also have a change in the energy spread o E due to the wiggler radiation:

Lw ( Po ] 3 o2 w = 1 + ~ \ O 7 I . (10)

°20 1 + 2~00 \Ow]

From this derivation we conclude the following: - If the dispersion function is finite in the wiggler

section we have (-"ff)w =~ 0 which can lead to strong quantum excitation depending on the choice of Ow.

- If wiggler magnets are placed into a storage ring lattice where the dispersion function vanishes, *i --- 0, we have (o~'°)w = 0 and therefore no quantum excitation occurs. In this case we can reduce the beam emittance, since the wiggler radiation always contributes to the damping term in the denominator of eq. (9).

- Whenever wiggler magnets are used and P0 > Ow the energy spread in the beam is increased. This is true for virtually all cases of interest.

Thus, we have developed a potential way to reduce the beam emittance in a storage ring by creating strong additional radiation damping while minimizing the quantum excitation effects. The circumstances necessary to achieve this will be derived in the next section.

3.2. Reduction of the beam emittance by damping wigglers

The general effects of wiggler magnet radiation on the beam emittance have been derived and we found that the beam emittance can be reduced if the wiggler is placed where *i = 0 since, then, also ()ff)w = 0. This latter assumption, however, is not quite correct.

Even though we have chosen a place where *i = 0, the quantity aft w will not be exactly zero once the wiggler magnets are turned on because they create (like any dipole magnet) their own dispersion function.

We will calculate this part of the dispersion function for a wiggler period as shown in fig. 2. The magnet period is subdivided into four segments of equal length l w. Again we use a model where the wiggler fields are constant with alternating signs. In short period wiggler magnets the actual fields assume a more sinusoidal distribution along the axis and the result must be mod- ified accordingly.

~(~)

Fig. 2. Dispersion function in a wiggler magnet.

The dispersion function in the first of the four magnet sections of a wiggler period can be expressed for small deflection angles by:

1 s 2 *i1 ( s ) 2 Pw' (11)

t *i,(s) - - s Pw

where 0 _< s _< l w within this section and where we have assumed that *i0 = ~/o = 0 at the beginning of the wiggler magnet. In the second magnet section we have:

1 (I 2 + 2 l w s - s 2) * i 2 ( S ) = - - 2 Pw '

l w - s *i~(s) - - , (12)

Pw

where 0 < s < l w. For the other two wiggler magnet sections the *l-function is similar to eqs. (11) and (12) for symmetry reasons.

The integral

1 / *

(')ff)w = ~JwO~'w ds

now can be calculated, but for simplicity we set here fix = constant and fl" = 0. The contributions of the first and second wiggler magnet sections to the integral 9~w~/p 3 ds in eqs. (8) are

Sw ' ,'w ,x,.w a I - - s 20fl, p~ + 305 "~ 3p 5 '

a 2 / ' . / f d s = 43 15w + flx l~ = flx l aw (13) Jwd- 60~xCw 2¢w 2¢w' where we have assumed that I w << fix- For the whole wiggler system with N w periods we have

~w 1---ds = Nw4/~ - . (14) p 2 P w

Using eqs. (8) and (14) in eq. (7) we finally get for

I(c). FUTURE FACILITIES

+ corrections due to the own dispersion created by the wiggler

H. Wiedemann, An ultra-low emittance mode for PEP using damping wigglers, Nucl. Instr. Meth. A266 (1988) 24-31.K. Robinson, Radiation effects in Circular electron accelerators, Phys. Rev. 111 (2), 1958, 373

mardi 6 mars 2012


HU36 undulator : Measured vertical field integrals at 11.5 mm minimum gap

HU36 undulator : Measured horizontal field integrals at 11.5 mm minimum gap

Modelisation with field maps


mardi 6 mars 2012


Figure8 or bi-periodic undulator


Figure 8V. und. period = 2X H und. period

• Linear polarised soft X ray: on axis power density lower than for an ordinary undulator• odd (LH), integer (LH), and half integer harmonics (LV)

T. Tanaka, H. Kitamura, Nucl. Instrum. Methods A 346, 368-373

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Spatial d&i&ions of the power density of the planar and figuure-8 undulaton are shown in Figs. 7a and 7b. respectively. the undulator parameters are the same as those in Figs. 6a and 6b. in case of the planar undulator. tiu ,pocver density has a maximum of 98 kW/mnd? on axis. @I the other hand. the distribution of the figun-8 unduiator is asymmetric with respect to 8, and iuoks like a V figure. since j?, is asymmetric with respect to & as shown in Rg. 3d. Since most of the r&i&d power of the figure-8 tttt&iator distributes on the V figure. much kss heat load falls on axis than in case of the planar undulat0f. TIE on-axis pawa density is as low as 1.4 kW/nxadZ. which is impo?tam benefit for the soft x-ray optics.

3.2. lm-fefd case {K “r I )

Nex~.tkbw-fieMcasc(K - II iscomidendTbt petiodlengthisassumedtobe3.2cmandthCnanbn@f periods 140. On axis radiation, 8 GeV K=4.72

planar, Fig.8 Kx=Kz=3.34

H1

H3H5

H1

H2H1.5

mardi 6 mars 2012


Correctorr CHE-CHS: field integral adjustment

Correctorr IP50 : adjustment of the exit position

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

0 50 100 150 200 250

CVE (A) CHE (A) CVS (A) CHS (A)

Static measurements

Corrector HUE-HUS : pointing adjustment

EMPHU @ SOLEIL


Dynamic measurements

-1

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90 100

reponse impulsionnelle de 1A pdt 2ms fit

-400

-300

-200

-100

0

100

200

300

400

-300

-200

-100

0

100

200

300

0 50 100 150 200 250 300 350 400 450 500

IT0 IT1 IBP

Pulse response

Matlab iterative correction

mardi 6 mars 2012






=>

D=-1 => Type B(T) g (mm) dB/dx (T/

m)out of vacuum

1.4 11 140

In vacuum 1.0 5.5 182

Questions : - Js=1 damping in longitudinal plane- high gradients?- field homogeneity (injection, lifetime)- radiation properties

mardi 6 mars 2012





(ρ0B0 = 9.138 Tm for SOLEIL)


=>


m)out of vacuum

1.4 11 140

In vacuum 1.0 5.5 182


mardi 6 mars 2012






Bw = wiggler peak field, Lw = wiggler length (2m) , g= wiggler gap


=>


m)out of vacuum

1.4 11 140

In vacuum 1.0 5.5 182


mardi 6 mars 2012






Bw = wiggler peak field, Lw = wiggler length (2m) , g= wiggler gap


=>

D=-1 => ≈ 89 T2/m


vacuum1.4 11 140

In vacuum 1.0 5.5 182


mardi 6 mars 2012

some recent insertion devices on operating third and fourth generation light sources

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