Overview of FEL injectors

Transcription

1 Overview of FEL injectors Massimo Ferrario INFN - LNF VISA-DUV-HGHG 4GLS FLASH-XFEL LEUTL BESSY PAL LCLS Arc en Ciel FERMI SCSS LEG SPARX SDUV 1

2 SASE FEL Electron Beam Requirement: High Brightness B n > 10 5 A/m 2 B n 2I ε n 2 Bunch compressors RF & magnetic Cathode emittance Pulse shaping Emittance compensation 2

3 FEL resonance condition implies that e - slips back in phase w.r.t. photons by λ r per period λ u λ u λ r Nλ r L s Amplification occurs over slippage length L s ==> slice parameters are important Courtesy Paul Emma - SLAC 3

4 13 nm B n [ Am 2 ] 4

5 Emittance Compensation ==> Controlled Damping of Space Charge Effects ρ I=1 ka I=4 ka ε th = 0.6 μm E acc = 25 MV/m I ρ = γ γ I A ε n 2 Potential space charge emittance growth I=100 A ρ = 1 ==> propagation close to the invariant envelope 5

6 5 4 HBUNCH.OUTnew enx_[um] eny_[um] ε th = 0.6μm enx_[um] ka - 1 GeV Z_[m] 6

7 10 15 Achieved Peak Brightness Peak Brightness [A/m^2] ELSA SCSS SCSS BOEING PITZ DESY AFEL FNPL ATF SHI GTF SDL SPARC LEUTL PAL MIT Jlab Frequency [GHz] 7

8 500 kv pulsed thermionic gun for SCSS Stable operation with uniform beam quality Low thermal emittance single crystal CeB 6 (Cerium Hexaborite) Low accelerating gradient ==> Low charge density (10 MV/m) ==> Free from dark current 8

9 Ulta-Low slice emittance gun ==> 0.05 source (0.1 undulator) Field Emitter Array 1 mm gated ZrC tip 9

10 Photo-Injector Test Facility at Zeuthen P I T Z Photo Injector Test Facility Zeuthen Goals of PITZ test facility for FELs: FLASH, XFEL small transverse emittance (1 mm 1 nc) long RF pulses => high average power long laser pulse trains high QE cathode Cs2Te PITZ2 features: higher gun gradient (~60MV/m) flat-top cathode laser profile with shorter rise/fall time emittance conservation with booster cavity Several gun cavities (1.5-cell, L-band, 1.3 GHz) have been conditioned and operated: PITZ-guns1,2,3, BESSY-gun. Currently, gun3 cavity is under characterization 10

11 Emittance measurements of PITZ Gun P I T Z Photo Injector Test Facility Zeuthen PITZ: p = 5.2 MeV/c, Q = 1 nc, The PITZ RF gun is developed for the operation with long RF pulses and long laser pulse trains, e.g. 10 Hz, 800µs, 1 MHz amplified output train pulse train from the oscillator norm. emittance / mm mrad VUV-FEL, 30nm VUV-FEL, 6nm WR XFEL Ex Ey SQRT(Ex*Ey) (100% rms projected emittance) I main, A VUV-FEL(FLASH): p = 127 MeV/c, Q = 1 nc regularly obtain 2.1 mm mrad (100% rms projected emittance) minimum 1.1 mm mrad (90% rms projected emittance) 11

12 LCLS Injector Courtesy : C.Limborg-Deprey, D.Dowell Under Construction Commissioning starts January 2007 Laser Room Klystron Gallery BC1 compressor DogLeg Gun 2 linacs 135 MeV Spectrometer 12

13 LCLS Injector Parameters Parameter Value Peak Current Charge Normalized Transverse Emittance: Projected/Slice 100 A 1 nc < 1.2 / 1.0 micron (rms) Solenoid Beam-to- Linac Repetition Rate 120 Hz Energy 135 MeV Energy Spread@135 MeV: Projected/Slice 0.1 / 0.01 % (rms) Gun Laser Stability 0.20 ps (rms) Booster Mean Phase Stability 0.1 deg (rms) Charge Stability Bunch Length Stability 2 % (rms) 5 % (rms) Gun 13

14 Modified from BNL/SLAC/UCLA version S-Band (2.856 MHz) 1.6 cell LCLS Gun LCLS version RF Dipole suppressed with dual feed Quadrupole suppressed with racetrack shape Solenoid Quadrupole component compensated Laser axial injection Mode separation 15MHz instead of 3.5 MHz 14

15 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 15

16 Ti:Sa LASER system 0.02 nm resolution spectrometer 200 fs resolution UV xcorrelator 30 cm lens CCD 4350 g/mm grating UV beam 16

17 Cu Cathode QE ~ 10-4 improved by laser cleaning 17

18 Coils Current Configuration Beam rotation ~60 Beam rotation ~0 BNL/SLAC/UCLA r = eb () z 2 2γmβc () ϑ = eb z 2γmβc I(A)=+140,+140, +140,+140 I(A)=-140,-140, +140,

19 Movable Emittance-Meter 19

20 Gun and emittance meter in the SPARC bunker 20

21 Beam envelope along the drift 21 This This is is not not a simulation simulation

22 Beam rms norm. emittance along the drift 22

23 Comparison measurements-computations computations:envelopes Q=700 pc σ=4.35 psec y(mm)-measured x(mm)-measured Xrms(mm)-computed Yrms(mm)-computed 1.5 (mm) z(cm) 23

24 Comparison measurements-computations computations:emittance rise time=0 psec rise time=0.5 psec rise time=1 psec rise time=2 psec rise time=3 psec (mm-mrad) Exn(mm-mrad)-computed Eyn(mm-mrad)-computed exn-measured eyn-measured Z(cm) Exn(mm-mrad) Z(cm) 24

25 Velocity bunching concept 25

26 <I> = 860 A ε nx = 1.5 μm 26

27 Rectilinear Bunching Experiments BNL UCLA BNL-DUVFEL UTNL-18L LLNL Methode Ballistic Ballistic Velocity Bunching Velocity Bunching Velocity Bunching Acc. Structure S-band PWT 4 S-band 1 S-band 4 S-band Measurement zerophasing method CTR zero-phasing method Femotsecond Streak Camera CTR Charge 0.04 nc 0.2 nc 0.2 nc 1 nc 0.2 nc Bunch width 0.37 ps (rms) 0.39 ps (rms) 0.5 ps (rms) 0.5 ps (rms) < 0.3 ps Comp. Ratio 6 15 > 3 > Solenoid field No No No Yes Yes 27

28 High average current sources High Average Current Injector Beam Dump LINAC FEL Undulator Radiation 28

29 DC photo-electron source DC Gun Courtesy Ch Sinclair - Cornell Long operating experience High average current Low accelerating gradient ==> Low charge density 29

30 Multivariate Optimization of Cornell Injector 30

31 Superconducting RF photoinjectors Main Advantage: Low RF Power Losses & CW Operation Problems and Open Questions: Emittance Compensation? High Peak Field on Cathode? Cathode Materials and QE? 31

32 FZR (since 1998) IHIP PU (since 2001) f =1.3 GHz Cs 2 Te E RF f =1.3 GHz Cs 2 Te E DC Courtesy of Dietmar Janssen Courtesy of Hao Jiankui BNL (since 2002) BNL/AES (since 2004) f =1.3 GHz f = MHz Nb E RF Alkali+ E RF Courtesy of Triveni Rao Courtesy of Alan Todd 32

33 FZR Rossendorf normal-conducting cathode inside SC cavity Ez(r,+1mm) Er(r,+1mm) Ez, Er [MV/m] r [mm]

34 34

35 Splitting Acceleration and Focusing 1 mm thick µ-metal shield 2K 4K Solenoid (0.3 T) (20 µt) Nb 410 mm (optimum 360 mm) stainless steel The Solenoid can be placed downstream the cavity Switching on the solenoid when the cavity is cold prevent any trapped magnetic field 35

36 sigma_x_[mm] ε n [mm-mrad] HOMDYN HBUNCH.OUT Simulation Q =1 nc R =1.69 mm L =19.8 ps ε th = 0.45 mm-mrad mrad E peak = 60 MV/m (Gun) Eacc = 13 MV/m (Cryo1) B = 3 kg (Solenoid) sigma_x_[mm] enx_[um] I = 50 A E = 120 MeV ε n = 0.6 mm-mrad mrad MeV m Z [m] z_[m] 36

37 Quantum Efficiency of Lead at 300 K BNL QE Pb: vacuum-deposited Pb: bulk Pb: electro-plated Nb: bulk Pb: arc-deposited Pb: magnetron-deposited 248 nm 240 nm 230 nm 210 nm 213 nm 220 nm 200 nm 193 nm 190 nm Ep [ev] 37

38 Schematic diagram of a secondary emission amplified photoinjector 38

39 Conclusions Lot of R&D ongoing on technical issues: Laser and Cathodes, Advanced Diagnostic, High duty, quasi-cw operations, SC RF gun, higher frequencies ultra-high gradients (X and W-band) Within next year more experimental data will be available on RF compression and pulse manipulation for Ellipsoidal Beam and Blow Out Regime Progress in plasma injectors 39