an fel oscillator: performance, challenges ... - desy

An FEL Oscillator: Performance, Challenges, & Implementations

Kwang-Je Kim

ARD SeminarDESY

September 2, 2014Hamburg, Germany

Evolving bright & coherent x-ray sources

ARD Seminar DESY XFELO KJK

29/2/2014

Hard X-Ray FELs in Operation & Under Construction

SACLA 20118.5 GeV, 60 Hz NC

PAL XFEL 201610 GeV, 100 Hz NC

SWISS FEL 20175.8 GeV, 100 Hz NC


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LCLS‐I, II 2009, 201814.5 GeV, 120 Hz NC

Euro‐XFEL 201617.5 GeV, 3000 x 10 Hz SC

9/2/2014

EuroFEL Activities in Main Tunnel XTL

Empty Tunnel

Installed Ancors

Installed Support Frames

Test Installation of (empty) CryostatsAdjustable Supports

SASE and Seeded spectra recorded on single shots. The left panels are SASE with 150 pC, 3kA peak current, un-seeded. The FWHM of the SASE spectrum is 0.2 % Bandwidth. The right panels are the seeded beam with the same electron beam parameters. The FWHM of the seeded beam is 0.5 eV (5x10-5 bandwidth)

• Concept developed by Geloni, Kocharyan and Saldin, DESY 10‐053 (2010).

• The mean seeded FEL power is 8 GW with a 2.5 GW SASE background at 8 keV for 40 pC bunch charge.

• Peak seeded power is in excess of 15 GW, comparable to SASE but with a spectral bandwidth reduction by the factor of 40.

• Pulse energy jitter : SASE+ 10‐3 e‐beam energy jitter

Pulse energy (mJ)

Single shot pulse energy from the gas detectors with 40pC charge

SASE SeededSASE FEL spectrum Seeded FEL spectrum

~ 20 eV ~ 0.5 eVNear Fourier Transform limit

Self-seeding demonstration at LCLS

Slide 5ARD Seminar DESY XFELO KJK

9/2/2014

Star application: Making molecular movies (from J. Pflüger)Eadward Muybridge1892

European XFEL2017

9/2/2014


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FEL can also operate in an oscillator configuration

An intra-cavity pulse is formed by low-gain amplification over several hundred passes stability due to averaging

Stability also from CW operation X-ray FEL oscillator will provide full coherence, high

spectral purity with storage ring-like stability Applications complementary to high-gain XFEL

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ARD Seminar DESY XFELO KJK8

X-Ray FEL Oscillator

A hard x-ray FEL oscillator is feasible by using an optical cavity with Bragg mirrors – R. Collela and A. Luccio, 1983; KJK, Y. Shvyd’ko, and S. Reiche, 2008– Tuning scheme by R.M.J. Cotterill in 1968

Fully coherent, ultra-high spectral resolution(~meV) with storage-ring like stability: A real laser!

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Diamond is the best material (R, D, ). Tolerances on optical element placement (10 nr) and figure error for focusing mirrors appear feasible.


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Null feedback on HRM to 50 nr

High heat diffusivity at < 100K

Yamauch, JTEC, R~ 99%, fig error< 1 r

9/2/2014

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Test of possible diamond damage

Planning for a new test at the APS: 34-E ( Diff) or 35 ID ( Dynamic Comp)

Monte-Carlo /Molecular-dynamics simulation of nano /mesoscopicdiamond (P. Ho and C. Knight)

9/2/2014


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J. Als‐Nielsen, A.K. Freund, M. Wulff, M. Hanfland, and D. Häusermann. Nucl. Instrum. Methods Phys. Res. B 94, 348 (1994)

ARD Seminar DESY XFELO KJK12

XFELO applications

High resolution spectroscopy– Inelastic x-ray scattering

Mössbauer spectroscopy – 103/pulse, 109/sec Moessbauer s (14.4 keV, 5 neV BW)

X-ray photoemission spectroscopy– Bulk-sensitive Fermi surface study with HX-TR-AR PES

X-ray imaging with nm resolution– Smaller focal spot with the absence of chromatic aberration

picosecond time resolution A second user WS was held at POSTECH in Feb 2013

9/2/2014

Ultra-high-resolution (< meV) inelastic scattering will be revolutionized: from ~109 to 1015 photons /sec

9/2/2014


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The XFELO output pulses are identical copies of the circulating intra-cavity pulse

Inter-pulse coherence is possible, for example by FB referenced to a narrow nuclear resonance(57Fe)– X-ray spectral combs & the field of experimental x-ray quantum

optics for fundamental physics, x-ray metrology, etc (Bernhard Adams, KJK, 2012)

9/2/2014


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Advances in CW e-gun technology is promising for XFELO application

DC gun at Cornell/KEK/JAEA Low frequency, normal

conducting RF gun at LBNL SCRF gun at Rossendorf

9/2/2014


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V=0.14‐0.29 (20‐80)pC

100 ms

t

Electron bunch trains (with up to 2700 bunches à 1 nC)

100 ms

t = 220 ns

t

600 s

t

188 fs

t

100 fsPhoton pulses

FELprocess

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Euro‐XFEL linac can drive a pulsed XFELO(J. Rossbach, J. Zemella, Ch. Maag)

9/2/2014


Options for CW SCRF linac

EuroXFEL can in principle be operated in CW at a reduced E-beam energy of 7 GeV ( J. Sekutowicz)– Need new modulators and power couplers

Eith higher harmonic, the E-beam energy could be significantly lower than 7 GeV ( H.-X. Deng & Z.-M. Dai)

9/2/2014


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LCLS-II Concept by August 2013 (J. Galayda)

Accelerator Superconducting linac: 4 GeVUndulators in existing LCLS‐I Tunnel

New variable gap (north) New variable gap (south), replaces existing fixed‐gap und.

Instruments Re‐purpose existing instruments (instrument and detector upgrades needed to fully exploit)

South side source:1.0 ‐ 25 keV (120 Hz, copper” linac )1.0 ‐ 5 keV (≥100 kHz, SC Linac)

4 GeV SC Linac In sectors 0‐10

NEH FEH14 GeV LCLS linac still usedfor x‐rays up to 25 keV

North side source:0.2‐1.2 keV (≥ 100kHz)

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Harmonic XFELO performance (R. Lindberg, with a new code with exact total energy conservation)

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Electron beam

γmc2 4 GeV

σγ/γ 0.0125%

I 120 A

εx,n 0.2 μmUndulator

λu 2.6 cm

K 1.69

Nu 2500Cavity

ZR 11 m

R 75%Radiation

λrad 1

harmonic 5

Parameter Value

Power 0.42 MW

# photons 1.6 x 108

ΔTFWHM 265 fs

ΔEFWHM 6.8 meV

Input Output

9/2/2014


Full potential of x-ray FEL will be realized iffoscillators & amplifiers are both available Amplifiers & XFELO separately or low power

XFELOs seed high-gain amplifiers We have begun a modest 3 year R&D program, with

emphasis on crystal damage issues. If we find that diamond crystals can withstand the

intense intra-cavity x-ray exposure, the only real issue with an XFELO construction is the high-cost of a SCRF linac.

Implementation options (almost realistic):– Pulsed XFELO with the EuroXFEL linac– CW XFELO with EuroXFEL running at 7 GeV– CW XFELO (Harmonic) with LCLS II 4 GeV linac

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an fel oscillator: performance, challenges ... - desy

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