The LCLS Injector C.Limborg-Deprey Emittance compensation Nominal and alternate tunings
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The LCLS Injector C.Limborg-Deprey Emittance compensation Minimum emittance thermal emittance Linear emittance compensation for ideal laser beams Nominal and alternate tunings Beamline layout 1nC, 0.2 nC last year modifications Laser heater RF structures How much can we believe PARMELA GTF, DUVFEL PARMELA vs experiment Code comparison What could we be missing? Commissioning measurements Spectrometers Emittance measurement 6D measurements December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Emittance Compensation Photocathode RF gun adequate to generate coldest electron beam photoemission produces some transverse momentum px “cathode emittance” ~ x px also called “intrinsic emittance” or “minimum” emittance We want to preserve at best the beam emittance along the transport line (space charge, wakefield, CSR …) Space charge very strong at low energy generates large energy spread Appropriate choice and tuning of components allow to compensate for variation in transverse dimension (size, divergence) due to chromatic effects Gun Solenoid Linac = Compensate for the mismatch between slices December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Emittance Compensation 0.7 e n rms (m/mm) 0.6 0.3m 0.5 10 0.4 0.3 0.2 0.1 0.0 250 Cu flat Cu rough 255 260 UV Wavelength (nm) 265 270 Courtesy J.Schmerge Theory (perfect surface) ~ 0.3 mm.mrad /mm radius December 3rd 2004 Measured Theory Club: The LCLS Injector Cecile Limborg-Deprey ~ 0.6 mm.mradlimborg@slac.stanford.edu /mm radius = ½(o-2o+o) e = 1.16 mm.mrad December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Single Particle Dynamics Single particle dynamics in gun Gun focusing defocusing defocusing focusing December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Single Particle Dynamics RF effects are non linear Electric field effects RF Kicks are time dependent: so vary along the bunch Are not be compensated for Very small contribution to etotal ~ 0.1 mm.mrad in our S-Band Gun focusing defocusing defocusing Magnetic field effects focusing December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Single Particle Dynamics Gun Solenoid Gun Solenoid Linac Solenoid focusing focal length energy dependent Focusing kick at entrance of Linac Time dependent Used in emittance Compensation process December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Simulations Gun Solenoid Linac Diverging: Space charge RF kick at exit cell December 3rd 2004 Theory Club: The LCLS Injector Converging: Solenoid RF kick at entrance cell Cecile Limborg-Deprey limborg@slac.stanford.edu Emittance Compensation December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Gun S1 S2 Movies 1,2,3 : ethermal = 0.72 mm.mrad Movie 4 : ethermal = 0 mm.mrad Linac Movie 3 Movie 1 Movie 4 Movie 2 3D Ellipsoid Space Charge linear with r , optimal shape for perfect emittance compensation December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Movie 1 December 3rd 2004 Theory Club: The LCLS Injector Movie 2 Movie 3 Cecile Limborg-Deprey limborg@slac.stanford.edu Movie 4 Movie 1 Movie 3 Movie 4 e = 0.75 mm.mrad e = 2.34 mm.mrad Movie 2 e = 1.16 mm.mrad December 3rd 2004 Theory Club: The LCLS Injector e = 0.2 mm.mrad Cecile Limborg-Deprey limborg@slac.stanford.edu Preinjector: VA TR EA TM CU UM EN MP S HA MB ER PU T C LO A SS NG EM B EL BL LO Y WS SP SE O OL AL S SECTOR 20 FR O M VA H LV E CA TH OD E UH G ATV A E LL VA ME LV TA ES L PO RC OL U DE PIN R E VAULT SLAC Main Linac Beamline December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Goal parameters Parameter Value Peak Current 100 A Charge 1 nC Normalized Transverse Emittance: Projected/Slice < 1.2 / 1.0 micron (rms) Repetition Rate 120 Hz Energy 135 MeV Energy Spread@135 MeV: Projected/Slice 0.1 / 0.01 % (rms) Gun Laser Stability 0.50 ps (rms) Booster Mean Phase Stability 0.1 deg (rms) eN = 1.2 m Charge Stability 2 % (rms) Bunch Length Stability 5 % (rms) eN = 2.0 m December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu P = P0 P = P0/100 6 MeV e = 1.6 m ,un. = 3keV Gun S1 S2 L0-1 63 MeV e = 1.08 m ,un. = 3keV L0-2 135 MeV e = 1.07 m ,un. = 3keV ‘Laser Heater’ 135 MeV e = 1.07 m ,un. = 40keV DL1 19.8MV/m 24 MV/m Spectrometer ‘RF Deflecting cavity’ TCAV1 3 screen emittance measurement UV Laser 200 J, = 255 nm, 10ps, r = 1.2 mm December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Nominal tuning eproj = 0.954 , e80 = 0.89 mm.mrad Rise/fall 0.7 ps 1.0ps 1.5 ps eprojected [mm.mrad] 0.954 1.028 1.141 e80% [mm.mrad] 0.894 0.935 0.986 <eslice >10..90[mm.mrad] 0.849 0.877 0.901 <eslice >1..100[mm.mrad] 0.906 0.953 1.004 December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Tolerance as a function of single parameter variation Solenoid 1 0.3% Egun 0.5% gun 2.5 Balance~ 3% is ok Solenoid 2 20% Linac Field 12 % (EFinal = 150 MeV ) December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Stability Requirements Stability requirements Defined after combining errors Param. Nom. Units Stability Requirements Sol1 2.7235 kG 0.02 % Sol2 0.748 kG 1% Gun 27.25 /0-X 0.1 Gun Field 120 MV/m 0.5% Charge 1 nC 5% L01Field 18 MV/m 2.5% Phase Small margin left for laser parameters variation December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Tolerances – Alignment and Laser Uniformity Param. Type Tolerance Units Solenoid 1 Transverse Position 500 m Angular Position 1.5 mrad Laser Transverse Position 100 m Laser Uniformity Transverse (Slope) 10 % NA Transverse (Cross) 10 % NA Longitudinal 30% ptp Freq.> 1THz (1ps) Longitudinal 20% ptp Freq.< 1THz Transverse Position 150 m Angular Position 120 rad Linac 1 Linac 2 Same as Linac 1 Solenoid 2 Same as Solenoid 1 December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Requirements on Laser Pulse - Summary Transverse 10 % ptp maximum on emission uniformity Longitudinal =120 m =240 m =480 m 5% ok for emittance But too much for LSC December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Longitudinal Space Charge Instability LSC observed at the DUVFEL Courtesy of Timur Shaftan Also observed at TTF Simulations and theoretical studies Current Density Energy Z.Huang et al. PhysRev. SLAC-PUB-10334 J.Wu et al. LCLS Tech Note , SLAC-PUB-10430 G.Geloni. Et al. DESY 04-112 The self-consistent solution is the space charge oscillation December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu ASTRA/ PARMELA Simulations , Amplitude = +/- 5%, = 100 m GUN EXIT 6 MeV ENERGY CURRENT December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu End L02 135 MeV ENERGY CURRENT Microstructure at the end of the injector Laser Heater provide enough energy spread (40keV) for “Landau damping” preventing -further amplification of the microbunching -December the increase an energy spread (as it needs to remain < the FEL parameter) 3rd 2004 Cecile Limborg-Deprey Theory Club: The LCLS Injector limborg@slac.stanford.edu Alternate tunings for cylindrical bunch 1nC, long pulse eth = 0.6 mm.mrad per mm laser spot size reduce rlaser to 0.85 mm BUT to keep charge density same order lengthen bunch Start with eth = 0.51 mm.mrad December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Alternate tunings for improving e Name Q (nC) Laser pulse (ps) r (mm) eth (m.rad) e80 RF (m.rad) () e80 5% Nominal 1 10 1.2 0.72 0.9 32 2.5 1 nC, 17.5 ps 1 17.5 0.85 0.5 0.75 33 1.5 0.2nC,10ps 0.2 10 0.39 0.234 0.38 37 2.5 0.2nC,5ps 0.2 5 0.42 0.25 0.37 32 5 • eth = 0.6 mm.mrad per mm laser spot size • minimum r best , BUT limit on minimum radius = space charge limit (ignoring Shottky) Esc = Q / ( r2 eo) example: for 1nC, r = 1.2mm, Esc = 25 MV/m ( 12) for 1nC, r = 0.85 mm, Esc = 50 MV/m ( 25) 42)Limborg-Deprey December 3rd 2004 for 0.2 nC, r = 0.3mm, Esc = 80 MV/m ( Cecile Theory Club: The LCLS Injector limborg@slac.stanford.edu for 0.2 nC, r = 0.42mm, Esc = 40 MV/m ( 20) 0.2nC A 5ps laser pulse improves dramatically the peak current compared to the 10ps laser pulse case without damaging too much the slice emittance December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Ellipsoid emission bunch December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Ellipsoid emission bunch December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Ellipsoid emission bunch square ellipsoid Exit gun Exit L01 December 3rd 2004 Theory Club: The LCLS Injector Longitudinal Phase Space Ek [MeV] vs T [ps] Entrance L01 Exit L02 Cecile Limborg-Deprey limborg@slac.stanford.edu 6 MeV e = 1.6 m ,un. = 3keV Gun S1 S2 L0-1 63 MeV e = 1.08 m ,un. = 3keV L0-2 135 MeV e = 1.07 m ,un. = 3keV ‘Laser Heater’ 135 MeV e = 1.07 m ,un. = 40keV DL1 19.8MV/m 24 MV/m Spectrometer ‘RF Deflecting cavity’ TCAV1 3 screen emittance measurement UV Laser 200 J, = 255 nm, 10ps, r = 1.2 mm December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Can we believe PARMELA? • Sensitivity studies fine since relative evolution • Meshing : by hand in PARMELA , automated in ASTRA criteria well understood • Benchmarks - w.r.t experiences Proved importance of data on initial distribution Fitted the slice parameters such as , , eprojected , eslice - w.r.t other codes Seems that extraction agree with PIC codes (experiment to be revisited for low accelerating voltage) Still need to compute fields for lossy copper December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu DUVFEL measurements 200 pC Good Agreement Slice Emittance and Twiss Parameters for the various solenoid fields After including thermal emittance, gun field balance between the two cells, transverse non-uniformity and longitudinal profile Solenoid = 98 A December 3rd 2004 Theory Club: The LCLS Injector Solenoid = 104 A Cecile Limborg-Deprey limborg@slac.stanford.edu DUVFEL Measurements Thermal emittance experiment Confirms the 0.6 mm.mrad per mm radius of laser spot size December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu R&D Status: GTF Measurements GTF measurements - 1.5 mm.mrad for 130A Peak Current (A) Instantaneous Peak Current head tail for 130 A ~ close to LCLS requirements 150 100 50 Similar measurements at the DUVFEL facility Time (ps) 0 en (mm mrad) -1.5 Slice Emittances eslice = 1.5 mm.mrad 300pC Spectrometer Image of Slice Quad Scan Data Theory Club: The LCLS Injector -0.5 0 0.5 1 2 1 0 December 3rd 2004 -1 (Spring 2002) longitudinal emittance Slice number 5 10 Cecile Limborg-Deprey limborg@slac.stanford.edu Commissioning Diagnostics 1 Uniformity + Thermal emittance ‘Laser Heater’ YAG1 YAG2 2 Gun Spectrometer December 3rd 2004 Theory Club: The LCLS Injector ‘RF Deflecting cavity’ TCAV1 Straight Ahead Spectrometer 3 screen emittance measurement 3 4 Cecile Limborg-Deprey limborg@slac.stanford.edu 1 Emission uniformity Point-to-point imaging of cathode on YAG1 Laser masking of cathode image at DUVFEL Above: Laser cathode image of air force mask in laser room. Below: Resulting electron beam at pop 2. December 3rd 2004 Theory Club: The LCLS Injector Above: Laser cathode image with mask removed showing smooth profile. Below: Resulting electron beam showing hot spot of emission. Cecile Limborg-Deprey limborg@slac.stanford.edu Courtesy W.Graves 1 Thermal Emittance Infinite-to-point imaging what type of momentum distribution? Very good resolution of divergence YAG2 == Image of Assumes eth = 0.6 mm.mrad December 3rd 2004 Theory Club: The LCLS Injector divergence of source Cecile Limborg-Deprey limborg@slac.stanford.edu 2 Gun Spectrometer YAG01 Spectrometer Energy Quadrupoles Absolute energy Alignment using laser Spectrometer field calibration YAGG1 YAGG2 Correlated Energy Spread for all charges Uncorrelated energy spread for low charges Introducing a time-energy correlation (varying injection phase) Slice thermal emittance Relay imaging system from YAG1 to spectrometer screens Point-to-point imaging in both planes Uniformity of line density December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu High Charge Operation : 1nC Nominal tuning – no quadrupole on – Very good linearity Longitudinal at YAG1 YAGG1 December 3rd 2004 Theory Club: The LCLS Injector YAGG1 Cecile Limborg-Deprey limborg@slac.stanford.edu Resolves line density uniformity at high charge +/- 8% modulation on laser beam YAG1 RF + 25 / nominal Quadrupoles on for manageable image size Resolves modulation December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu 135MeV Diagnostics 6D beam measurements Horizontal slice emittance Laser Heater Vertical deflecting cavity + 3screen Transverse RF Cavity OTR Emittance Screens DL1 Bend Vertical slice emittance Quad scan + spectrometer Quad Scan + Dogleg bend Verification of thermal emittance Longitudinal Phase space Straight Ahead Spectrometer Point-to-point imaging of the 75 m waist (OTR5) December 3rd 2004 Theory Club: The LCLS Injector Vertical deflecting cavity + spectrometer Efficiency of laser heater (spectrometer has 10 keV resolution) Cecile Limborg-Deprey limborg@slac.stanford.edu Spectrometer + Vertical deflecting cavity Direct longitudinal Phase Space representation Longitudinal Phase Space at waist • Transverse deflecting cavity y / time correlation (1mrad over 10ps ) • Spectrometer x / energy correlation rms fwhm From PARMELA simulations (assuming 1m emittance), resolution of less than 10 keV December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu RF Gun – Racetrack in full cell 2d-: no port = benchmark omega3p/sf 3d-cylin: with coupling ports- cell cylindrical ex = 0.96 ey =1.01 d b ex = ey =0.88 3d-rtrack: with coupling ports- cell racetrack ex = ey = 0.90 b Full : with laser ports + racetrack ex = 0.97 , ey = 0.99 Full retuned: with laser ports + racetrack+ retuned ex = 0.91, ey = 0.915 Quadrupole r (1/m) cylindrical cavity (lc=2.475cm) 8 6 4 2 0 -2 -4 -6 -8 -180 -130 racetrack cavity (lc=2.413cm) with d=0.315cm racetrack cavity (lc=2.413cm) with d=0.356cm -80 -30 20 70 120 170 rf phase (degree) From L.Xiao, ACD/SLAC December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu RF Studies- L01 coupler Dipole moment From Z.Li, L.Xiao, ACD/SLAC for 10 ps Dual feed Single feed Quadrupole moment December 3rd 2004 Dual feed Dual feed Theory Club: The LCLS Injector +rtrack ()/m Head-tail angle (rad/m) SLAC Single feed 0.78 0.078 Symmetric dual 0.63 0.063 Race-track dual 0.04 0.004 Cross Dual Cecile Limborg-Deprey 0.20 limborg@slac.stanford.edu 0.020 Injector Schedule December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Conclusion Gained confidence in PARMELA/ASTRA vs experiment vs other codes Injector computations based on large thermal emittance Discrepancy on thermal emittance by a factor of 2 between exp. and simulations remains to be understood If that value is confirmed: probably too large e at 1nC so run 0.2 nC Laser Pulse shaping and uniformity is critical to reach parameter goals December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Acknowledgements Many thanks to S.Gierman, J.Schmerge, J.Lewellen, D.Dowell, W.Graves, T.Shaftan, Z.Huang, J.Wu, P.Emma, S.Lydia, J.Qi, M.Ferrarrio, K.Floetmann, L.Serafini, P.Bolton, P.Krejcik, HD Nuhn, S.Reiche, M.Cornacchia, J.Galayda December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu 4 Slice-Emittance Measurement Simulation RF-deflector at 1 MV y bunch length slice OTR 10 times quad scanned December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Slice-Emittance Measurement Simulation (slice-y-emittance also simulated in BC1-center) Injector at 135 MeV with S-band RF-deflector at 1 MV (same SLAC slice-e code used at BNL/SDL) = meas. sim. = calc. = y distribution = actual slice-5 December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu RF Gun – Mode 0 studies 120MV/m Non-negligeable effect Study suggested by T.Smith dF 3.4 MHz 8 MHz 3s, Vcath. in 0 mode 11.77 MV/m 4.96 MV/m 0.82s, Vcath. in 0mode 10 MV/m 5.7 MV/m 3.4MHz mode separation December 3rd 2004 Solution : Klystron Pulse shaping Theory Club: The LCLS Injector Study of From Z.Li, ACD/SLAC 8MHz mode separation Cecile Limborg-Deprey limborg@slac.stanford.edu 12 MHz mode separation GTF 1.6 cell S-band gun Laser Port Photocathode Currently using a single crystal (100) Cu cathode “Half” Cell Electron Beam Exit Full Cell 0 1" 2" 3" Scale December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu GTF 1.6 cell S-band RF gun Waveguide Feed LCLS Modifications: Dual rf feed Cathode plate with brazed cathode plug Load lock 120 Hz cooling Full and ½ cell power monitors and remote tuners Full Cell Power Monitor December 3rd 2004 Theory Club: The LCLS Injector 0 1" 2" Scale Cecile Limborg-Deprey limborg@slac.stanford.edu 3" Single Particle Dynamics Gun Solenoid focusing defocusing defocusing Solenoid focusing December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Search for better tuning for the 2.8 FHWM case With 1ps rise/fall time, assuming r = 0.42 mm & Retuning December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Tolerance and stability as a function of single parameter variation Egun 0.5% gun 2.5 Egun 0.5% Solenoid 1 0.3% Gun S1 S2 L0-1 L0-2 … 19.8MV/m 24 MV/m December 3rd 2004 Theory Club: The LCLS Injector Cecile Limborg-Deprey limborg@slac.stanford.edu Data Slice emittance vs solenoid strength. Charge = 200 pC. Solenoid = 98 A Parmela Projected Values (parmela in parentheses) Solenoid 98 A 104 A 108 A Eyn 3.7 um (3.2) 2.1 um (2.8) 2.7 um (2.7) Alpha 0.4 Beta 1.3 m (1.3) (1.0) -6.9 (-3.6) -9.0 9.8 m (6.8) 45 m (-9.6) (36) Solenoid = 104 A December 3rd 2004 Theory Club: The LCLS Injector Solenoid = 108 A Cecile Limborg-Deprey limborg@slac.stanford.edu
