an fel oscillator: performance, challenges ... - desy
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An FEL Oscillator: Performance, Challenges, & Implementations
Kwang-Je Kim
ARD SeminarDESY
September 2, 2014Hamburg, Germany
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
ARD Seminar DESY XFELO KJK
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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
ARD Seminar DESY XFELO KJK
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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
9/2/2014
ARD Seminar DESY XFELO KJK
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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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9/2/2014
Diamond is the best material (R, D, ). Tolerances on optical element placement (10 nr) and figure error for focusing mirrors appear feasible.
ARD Seminar DESY XFELO KJK
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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
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
ARD Seminar DESY XFELO KJK
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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
ARD Seminar DESY XFELO KJK
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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
ARD Seminar DESY XFELO KJK
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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
ARD Seminar DESY XFELO KJK
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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
ARD Seminar DESY XFELO KJK
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
ARD Seminar DESY XFELO KJK
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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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9/2/2014
ARD Seminar DESY XFELO KJK
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
ARD Seminar DESY XFELO KJK
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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