cesrta e-cloud activities (jan. 2009)

CesrTA E-cloud Activities(Jan. 2009)

J.W. Flanagan, KEK

Organization

• CesrTA meeting slides from 2009.2.11 WebEx, provided by Mark Palmer– Have tried to attribute original authors correctly.

• Supplemental slides on some contributions from KEK

February 11, 2009 CesrTA-KEK Update 3

CesrTA Run & Down Recap• Completed experimental run 2/2/2009

– Low emittance correction in 2.085 GeV baseline optics– X-ray Beam Size Monitor (xBSM) commissioning– EC Measurements

• RFA & TE wave measurements• Dynamics

– General instrumentation/feedback tests/commissioning• 13 visitors

– LET - J. Jones, A. Wolski – xBSM – J. Flanagan, H. Sakai– EC – S. De Santis, R. Holtzapple, K. Shibata, L. Wang– Feedback – D. Teytelman, M. Tobiyama– CLIC – H. Schmickler– Instrumentation – A. DellaPenna, I. Pinayev

• 2nd upgrade down is underway…– Installation of PEP-II experimental hardware– Installation of photon stop chamber for 5GeV operation of the CesrTA L0 wiggler straight– Replacement of SRF cavity that failed during summer 2008– Installation of xBSM beam line front end for electron beam– Continue with instrumentation upgrade for 4ns bunch train operation– Contingency item: Repair of 15BW dipole coils

M. Palmer (CesrTA Mtg.)


Optics and LET• Low emittance 2.085 GeV optics loaded and corrected

– Correction methods tested– Beam-based alignment measurements– Coupling and dispersion bumps created for tuning

• Emittance measurements begun…– Touschek lifetime measurements initially used to characterize

beam size– xBSM measurements as detector and optics were characterized

• Ongoing program of magnet alignment to improve emittance– Alignment work continued throughout the run– 2 anomalous locations in the ring have been identified which

are being scrutinized.

D. Rubin (CesrTA Mtg)


Measured energy acceptance = 0.7% v ~ 32pmFrom xBSM v ~ 155 m v ~ 38pmAppear to be within a factor of 2 of the 20pm target

First Detailed Optics Correction Touschek Study xBSM Measurement (Preliminary)

Wolski

A. Wolski (CesrTA Mtg.)


xBSM Snapshots (Preliminary)

• Scan of coupling knob• Coded aperture measurements• Smallest recorded size:

~15 m (but further calibrationwork needed)

Simulations

Measurement

Fresnel Zone Plate

CodedAperture

<20mbeam size

J. Alexander (CesrTA Mtg.)


EC Data-Simulation Updates• Simulations of tune shifts in POSINST at Cornell and LBNL, using a new option in

POSINST for offseting the bunches, have shown that the tune shifts of a single bunch are different if the whole train is oscillating coherently, than if just the single bunch is oscillating. – Horizontal tune shifts in a dipole are much smaller when the whole train is oscillating

coherently. This is particularly relevant for the tune shift measurements at CesrTA, since we kick the whole train coherently to do the measurement.

– Tune shifts calculated for a coherently oscillating beam give better agreement with measurements: see following three slides.

• January run– Studies of systematic effects in the tune shift measurements were carried out.– Measurements of tune shift vs. current for long trains (10, 20, 45 and 116 and 145

bunches) were carried out (evidence of instability developing at the end of the 116 and 145 bunch trains)

– RFA and TE wave measurements to characterize EC density in drifts, dipoles and wigglers

– Work on comparisons between RFA and TE wave measurements as well as systematics checks for both

G. Dougan(CesrTA Mtg.)


10 Bunch Train with Trailing Witness Bunch(es) Data-POSINST Comparison (Preliminary)

Positron Beam

Blue Vertical QRed Horizontal QSquares SimulationCircles Data

G. Dougan(CesrTA Mtg.)


Electron Beam

10 Bunch Train with Trailing Witness Bunch(es) Data-POSINST Comparison (Preliminary)


G. Dougan (CesrTA Mtg.)


Drift vs Dipole Contributions• Comparison of drift (red) and dipole (blue)

contributions to tune shifts in each dimension

Horizontal Vertical



Positron Beam

45 Bunch Train: Data-POSINST Comparison (Preliminary)




L0 RFA Data

2/3/08

Wiggler with RFAsand uncoated Cu VC

Wiggler with RFAsand TiN-coated VC

e+

e-

2E Segmented RFA

2W Segmented RFA



Electron-Positron Comparisons (1x45 Current Scans)Segmented driftCu wiggler (pole center)

Positrons

Electrons

2W detectordownstream of

wigglers for e+ beam

2E detectordownstream of

wigglers for e- beam

Cu wiggler (pole center)Segmented drift



Cu wiggler, pole center

Drift (Cu VC)

Dipole (Al VC)

Long Train Data• 1x145 e+

– 14 ns spacing 79% of ring filled– Multipacting stripe

• Strongly visible in dipole• Weaker in L0 wiggler and

drift regions



Plans

15E/W testchamber design for coating tests

Segmented RFA

Shielded Pickups

• CESR layout modifications to be completed by March 1– 4 Experimental areas for EC build-up and mitigation studies

• L0 wiggler straight– Configured for RFA and TE Wave measurements of EC build-up– 4 wiggler comparisons planned (CU-KEK-LBNL-SLAC collab.)

» Cu vacuum chamber (installed)» TiN coated vacuum chamber (installed)» Grooved vacuum chamber ( summer ’09 installation)» Clearing electrode vacuum chamber ( fall ’09 installation)

• L3 straight w/PEP-II chicane and SEY sample station– Sample station tests (CU-FNAL-SLAC collab.)– Grooved chamber tests (CU-SLAC collab.)

• 15E/W – Flexible location for testing chambers with dipole synchrotron radiation– Presently planned comparisons (summer/fall ’09)

» Al vacuum chamber» carbon coated VC (CERN-CU collab.)» Enamel chamber with electrode

(Project X collab.)» TiN-coated Al vacuum chamber

– Detailed beam dynamics studies at ultralow emittance

• Mid-2009 end of program• Characterize instability thresholds• High resolution bunch-by-bunch beam size

measurements to characterize incoherent emittance growth

• Witness bunch studies for flexible control of EC interaction with beam

M. Palmer (CesrTA Mtg.)

KEK Participation in CesrTA• Several members of KEKB are participating in CesrTA:

– K. Ohmi (electron cloud instability dynamics studies and simulation)– M. Tobiyama (instrumentation and feedback)– K. Kanazawa, Y. Suetsugu, K. Shibata (vacuum group: electron cloud

mitigation measures)– J. Flanagan (e-cloud studies and diagnostics, x-ray beam size monitor)– +H. Fukuma, N. Ohuchi, …– Note: Funding provided by US-Japan Cooperation Program (Nichibei)

• ATF members also participating:– H. Sakai (U. Tokyo): X-ray beam size monitor– K. Kubo: Low emittance tuning

– Reverse direction (from Cornell):– Jim Alexander -> KEK for x-ray monitor readout tests– Jim Shanks -> ATF for low emittance tuning

– Others likely not listed

Bunch-by-bunch Feedback

• Longitudinal feedback at 4 ns successfully demonstrated in January 2009 by Dmitry Teytelman (Dimtel, formerly SLAC) using iGp– iGp: Next generation digital feedback system

developed by collaboration of SLAC (J. Fox, D. Teytelman), KEK (M. Tobiyama), INFN (A. Drago), Dimtel

– Transverse feedback also demonstrated.

Mitigation methods:PRELIMINARY results from KEKB

• Techniques also being tested at CesrTA– Clearing Electrode (Suetsugu, Fukuma et al.

design)• Design being worked on for CesrTA

– Grooved Chamber (Pivi et al. design)• Being installed at CesrTA for testing in summer run

Clearing Electrode 1Study on clearing electrode also started for mitigation of electron cloud in magnets.

Clearing electrode and electron detector were installed in wiggler magnet of LER. (placed at the center of pole)

To demonstrate the effect of electrode, the electron density was measured by the electron detector with 7 strips.

Sustainability for high beam current was also tested.

19The 14th KEKB Review on 9-11 February 2009 at KEK

Very thin electrode (0.1 mm, Tungsten) and insulator (0.2 mm, Al2O3) were developed. (Thermal Spray)

7 strips can measure the horizontal spatial distribution of the electron cloud.

440 mm

Stainless steel

Tungsten

Al2O3

40 m

m

Feed-through

Y. Suetsugu et al., NIM-PR-A, 598 (2008)

372

K. Shibata (KEKB Review)

Clearing Electrode 2


Electrode [W] (~ +1 kV)

Collector (7 strips, w5 mm)

Cooling channel

Insulator [Al2O3](t~0.2 mm)

Grid (~ 1 kV)

Vacuum seal by metal O-ring

Cooling Water paths

Shield

MonitorBlock

ElectrodeBlock

2 mm holesR47

Limited by magnet aperture

(w40, l440, t~0.1)

Beam

Cross-section

Test chamber

Wiggler magnet Magnetic filed : 0.77 TEffective length : 346 mmAperture (height) : 110 mm

Electron detector

Clearing electrode


372


Clearing Electrode 3Drastic decrease in electron density was demonstrated by applying positive voltage.

21

[8ns]

[6ns]

[4ns]

[16ns]I e [

A]

Velec [V]

Number of electrons was reduced to 1/10 1/100 if applied voltage of clearing electrode was more than 300 V for any bunch spacing.

The 14th KEKB Review on 9-11 February 2009 at KEK

Vr = 1.0 kVB = 0.77 T

I e [A] V el

ec [V

]

Collectors

1 x 10-5

1 x 10-6

1 x 10-7

1 x 10-8

1 x 10-9

1585 bunches(Bs ~ 6 ns)~1600 mA

Collector : #4

Velec = 0

posit

ive

nega

tive


372


Clearing Electrode 5Electrode was very effective, but modification of the feed-through connection part is required for high beam current.

Insulation resistivity decreased from 2 M to several 10 k during the trial period due to discharge at feed-through connection part.

Connection part

Improved clearing electrode will be installed this winter.

22

electrodeinsulator


Y. Suetsugu


Clearing electrode for CesrTA

Groove Surface 1Effect of groove surface was also studied last autumn. (collaboration with SLAC)

Electrode was replaced by groove surface.Same setup for clearing electrode was utilized.Groove structure was designed and manufactured in SLAC.

TiN~200 nm

Flat surface with TiN coating was also tested for reference.

R47

Beam

[Groove]

[Monitor]

Mag

neti

c field

Y. Suetsugu, ILCDR2008

Groove surface [SUS + TiN]

Flat surface [SUS + TiN]

TiN~200 nm



Groove Surface 2Electrons for groove surface was reduced to 1/5 1/10 the number for flat surface (3 buckets spacing).

1x10-61x10-6

Flat surface Groove surface

25

Y. Suetsugu

Preliminary result

Further R&D will be carried out toward the practical use of groove surface.



Mitigation Performance Comparison

~1x1012 e-/m3

~1x101 １

~1x1010

~1x109

Vr = -1 kV(1/1585/3.06)

Ranking of estimated performance in magnet is ;

Clearing electrode is much more effective than groove surface and TiN coating.

Electrode >> TiN+Groove >> TiN(Flat) > Cu(Flat)10 510 23

26

Preliminaryresult

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

0 2x105 4x105 6x105 8x105 1x106 1.2x106

Ele

ctro

n C

urr

en

t [A

]

Beam Dose [mA Hours]

TiN

Groove+TiN

W electrode(V

elec = 0 V)

W electrode(V

elec > 300 V)

Ib = 1450 - 1550 mAV

r = 1 kV,

1/1585/3.06


Electrode and groove surface are very promising, but more studies are required to achieve the practical use of them.


X-ray monitor: Coded Aperture Imaging

Simulated detector response for various beam sizes

Example of beam size measurement at CesrTA (y =~

45 m)

Uniformly Redundant Array (URA) mask being tested at CesrTA

•Technique developed by x-ray astronomers using a mask to modulate incoming light.

•Resulting image must be de-convolved through mask response (including diffraction and spectral width effects) to reconstruct object.

•Open aperture of 50% gives high flux throughput for bunch-by-bunch measurements.

•A heat-sensitive monochromator not needed.

red : datagreen : simulation

preliminary

A*G : system point-spread function ~ function

ˆ O P *G O*(A *G)P=O*A

A : mask or aperture, G: post processing array

ˆ O : reconstructed object, P: picture, O: object,

* : convolution

Coded Aperture.1/28/2009CESR condition same as for the 18um case on previous page

X-ray Beam Size Monitor

• X-ray beam size monitor results:– Beam size = 15-20 um (using both Fresnel Zone

Plate and Coded Aperture Mask)• Corresponds to emittance of ~38 pm.

• Touschek lifetime measurements indicate an emittance of ~30 pm.

cesrta e-cloud activities (jan. 2009)

Documents

wolski cesrta mtg

palmer cesrta mtg

tune shift measurements

measurements of tune

cesrta ecloud activitiesjan

wolski xbsm

beam sizexbsm measurements

horizontal tune shifts