Excitements and Challenges for Future Light Sources Based on X-Ray FELs

Transcription

1 Excitements and Challenges for Future Light Sources Based on X-Ray FELs 26th ADVANCED ICFA BEAM DYNAMICS WORKSHOP ON NANOMETRE-SIZE COLLIDING BEAMS Kwang-Je Kim Argonne National Laboratory and The University of Chicago Lausanne, Switzerland September 2-6, 2002

2 SASE FELs Saturation Saturation Exponential Gain Exponential Gain Regime Regime Undulator Regime Undulator Regime 1 % of X-Ray Pulse 1 % of X-Ray Pulse Electron Bunch Electron Bunch Micro-Bunching Micro-Bunching

3 Transverse Coherence Z=25 m Z=37.5 m Z=50 m Z=62.5 m Z=75 m Z=87.5 m m Courtesy of Sven Reiche, UCLA

4 Peak Brightness Enhancement From Undulator To SASE B = #of photons (Ÿ i - phase space area) Ÿ x Ÿ y Ÿ z Undulator SASE Enhancement Factor # of photons αν e αν e N lc N lc ~ 10 6 Ÿ x Ÿ y ε x ) (2 ε y ) ( λ 2) Ÿ Z ω ω σ Z = ps c ω ω σ Z = fs 10 2 c compressed l c -coherence length

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6 Projects: TESLA 400 m X-ray Laser Laboratory 4.5 km 3.9 km Main tunnel

7 /,1$&,1$& &2+(5(172+(5(17 /,*+7,* &( 285&( 0 Km 2 Km 3 Km

8 LCLS: Parameters & Performance FEL Radiation Wavelength Å Electron Beam Energy GeV Repetition Rate (1-bunch) Hz Single Bunch Charge 1 1 nc Normalized rms Emittance mm-mrad Peak Current ka Coherent rms Energy Spread <2 < Incoherent rms Energy Spread <0.6 < Undulator Length m Peak Coherent Power GW Peak Spontaneous Power GW Peak Brightness * * photons/sec/mm 2 /mrad 2 /0.1%-BW

9 Performance Characteristics Peak and time averaged brightness of the LCLS and other facilities operating or under construction TTF FEL LEUTL LCLS Spontaneous

10 Self Seeding Scheme for Full Longitudinal Coherence Seed No Seed

11 Energy E FW /E = 1.0% Two-stage undulator for shorter pulse Energy FW = time 230 fsec t FW x-ray pulse Also a DESY scheme which emphasizes line-width reduction (B. Faatz) Si monochromator (T = 40%) FW < time 10 fsec t FW Mitigates e e energy jitter jitter and and undulator wakes time time e 8&/$ 43 m SASE gain (P( sat sat /10 30 m 52 m /10 3 ) SASE Saturation (23 GW)

12 LCLS - The First Experiments Team Leaders: Absorption t0 t1 t2 t3 t4 t5 Femtochemistry Dan Imre, BNL Resonance Raman t=w t=0 Nanoscale Dynamics in Condensed Matter Brian Stephenson, APS e 1 as Atomic Physics Phil Bucksbaum, Univ. of Michigan classical plasma Aluminum plasma G=1 dense plasma G =10 G =100 Plasma and Warm Dense Matter Richard Lee, LLNL Report developed by international team of ~45 scientists working with accelerator and laser physics communities high density matter Density (g/cm -3 ) Structural Studies on Single Particles and Biomolecules Janos Hajdu, Uppsala Univ.

13 Accelerator System RF Photo-cathode gun Emittance Preservation in Linacs transverse wakefields CSR microbunching instability misalignments & chromaticity Machine Stability jitter tolerance budget simulation of budget

14 LCLS: System Components 7 MeV σ z 0.83 mm σ δ 0.2 % Linac-0 L =6 m RF Gun new new 150 MeV σ z 0.83 mm σ δ 0.10 % Linac-1 L =9 m Linac-X L =0.6 m 250 MeV σ z 0.19 mm σ δ 1.8 % Linac-2 L =330 m 4.54 GeV GeV σ z mm σ z mm σ δ 0.76 % σ δ 0.02 % Linac-3 Undulator L =550 m L =121.8 m 1.5 Å 8 GW σ z mm 15 Å 17 GW σ z mm...existing linac 21-1b 1b 21-1d 1d X 21-3b 24-6d 25-1a 30-8c DL-1 L =12 m BC-1 L =6 m BC-2 L =22 m DL-2 L =66 m Beam Dump SLAC linac tunnel Undulator Hall Exp Halls

15 RF Photo-Cathode Gun Half Cell Laser Port Normalized Normalized Slice Slice Emittance: Emittance: (rms) (rms) Max Max Bunch Bunch Charge: Charge: Bunch Bunch Length: Length: 11 Pm Pm rad rad 11 nc nc mm mm Full Cell Electron Beam Exit Exit Photocathode 0 1" Scale 2" 3"

16 X-band RF used to Linearize Compression (f = GHz) S-band RF curvature and 2 nd -order momentum compaction cause sharp peak current spike X-band RF at decelerating phase corrects 2 nd order and allows unchanged z-distribution E/ E /% σ E / E =1.761 % ϕ E/ E /% E = GeV, N e = λ x = λ s / ϕ x = π I /ka σ z = mm Slope linearized nd σ E / E =1.761 % E = GeV, N 4 e = σ z = mm avoid! E/ E /% 2 0 E/ E /% 2 0 I /ka n/ z /mm z /mm ev x = E 1 ( 1 σ σ 0 ) 2 1 λs T π R 56 ( λ λ ) s x z z Ei 0.6-m m section, 22 MV available at SLAC (200-µm m alignment)

17 e Coherent Synchrotron Radiation (CSR) Induced energy spread breaks achromatic system Causes bend-plane emittance growth (short bunch is worse) Powerful radiation generates energy spread in bends bend-plane emittance growth σ z θ L 0 R λ s Ε/Ε = 0 Ε/Ε < 0 x overtaking length: L 0 (24σ z R 2 ) 1/3 coherent radiation for λ > σ z x x = R 16 (s) E/E

18 CSR Micro-bunching and Projected Emittance Growth 14.3 GeV at undulator entrance 230 fsec x versus z without SC-wiggler projected emittance growth is simply steering of bunch head and tail 0.5 µm x versus z with SC-wiggler Workshop Workshop in in Berlin, Berlin, Jan. Jan to to benchmark benchmark results results ( ( Courtesy Courtesy Paul Paul Emma, Emma, SLAC SLAC slice emittance is not altered

19 &HOOVWUXFWXUHRIWKH/&/6XQGXODWRU OLQH UNDULATOR mm Horizontal Steering Coil Vertical Steering Coil Beam Position Monitor X-Ray Diagnostics Quadrupoles

20 Start-to-End Tracking Simulations Track entire machine to evaluate beam brightness & FEL space-charge charge Parmela compression, wakes, CSR, Elegant SASE FEL with wakes Genesis Track machine many times with jitter to test stability budget (M. Borland, ANL)

21 Magnetic Measurement of the Prototype +RUL]RQWDOÃ7UDMHFWRU\ 2.0 Horizontal Trajectory(µ) 1.0 V Q R U0.0 LF Z(mm)

22 Potential for Damage to X-Ray Optics LLNL undulator FEE exit experimental Hall A hall Be C Si W Au Photon energy (ev) experimental hall Hall BB In Hall A, low-z materials will accept even normal incidence. The fluences in Hall B are sufficiently low for standard optical solutions. Even in the Front End Enclosure (FEE), low Z materials may be possible at normal incidence above ~4 kev, and at all energies with grazing incidence. In the FEE, gas is required for attenuation at < 4 kev

23 SASE Demonstration Experiments at Longer Wavelengths IR wavelengths: UCLA/LANL (O = 12P, G = 10 5 ) LANL (O = 16P, G = 10 3 ) BNL ATF/APS (O = 5.3P, G = 10, HGHG = 10 7 times S.E.) Visible and UV: TESLA Test Facility (DESY): E e = 390 MeV, L u = 15 m, O = 42 nm VISA (BNL-LANL-LLNL-SLAC-UCLA): E e = 70 MeV, L u = 4m, O = 0.8 P APS LEUTL: E e d 700 MeV, L u = 25 m, 120 nm dod530nm All successful!

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25 Optical Intensity Gain Intensity [arb. units] I peak bunch length charge emittance 266 A 0.3 ps 200 pc 8.5 µm 1 energy spread 0.1% L g, theor m 0.1 L g, meas m Distance [m] Science, v. 292, pp (2001)

26 Properties of SASE FEL radiation: 1) transv. coherence 2) long. coherence 3) fluctuations 1) Transverse coherence should be almost 100 % at saturation Observation of diffraction pattern at TTF FEL: Y [mm] after double slit after cross Intensity [arb.units] X [mm] X [mm]

27 TTF2: Soft-X ray User Facility / Overview BC 3 BC 2

28 Future Light Sources based on X-ray FELs A leap in electron beam and photon beam technology A leap in x-ray science Proposals around the world for UV and x-ray facilities LCLS turns on in 98

29 Acknowledgement I thank my colleagues at SLAC, DESY, and ANL for making these excellent VGs available to me!