Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 The LCLS Injector C.Limborg-Deprey Emittance compensation linear emittance compensation for ideal laser beams limits of emittance? thermal emittance 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

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun Solenoid Linac Emittance Compensation Photocathode RF gun adequate to generate coldest electron beam photoemission produces some transverse momentum px  “thermal 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 = Compensate for the mismatch between slices

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Single Particle Dynamics defocusing focusing defocusing focusing Single particle dynamics in gun Gun

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Single Particle Dynamics defocusing focusing defocusing focusing Electric field effects RF effects are non linear RF Kicks are time dependent: so vary along the bunch Are not be compensated for Very small contribution to  total ~ 0.1 mm.mrad in our S-Band Gun Magnetic field effects

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun Solenoid Single Particle Dynamics Solenoid focusing focal length energy dependent Gun Solenoid Linac Focusing kick at entrance of Linac Time dependent Used in emittance Compensation process

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun Solenoid Linac Simulations Diverging: Space charge RF kick at exit cell Converging: Solenoid RF kick at entrance cell

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Emittance Compensation

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Linac Gun S1 S2 Movie 1Movie 2 Movie 3 Movie 4 Movies 1,2,3 :  thermal = 0.72 mm.mrad Movie 4 :  thermal = 0 mm.mrad 3D Ellipsoid Space Charge linear with r,  optimal shape for perfect emittance compensation

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Movie 1Movie 2 Movie 3 Movie 4

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Preinjector: SLAC Main Linac Beamline SECTOR 20 VAULT

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 ParameterValue Peak Current100 A Charge1 nC Normalized Transverse Emittance: Projected/Slice < 1.2 / 1.0 micron (rms) Repetition Rate120 Hz Energy135 MeV Energy MeV: Projected/Slice 0.1 / 0.01 % (rms) Gun Laser Stability0.50 ps (rms) Booster Mean Phase Stability 0.1 deg (rms) Charge Stability2 % (rms) Bunch Length Stability5 % (rms) Goal parameters

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun S1S2 L MV/m L MV/m ‘Laser Heater’ ‘RF Deflecting cavity’ TCAV1 3 screen emittance measurement 6 MeV  = 1.6  m  ,un. = 3keV 63 MeV  = 1.08  m  ,un. = 3keV 135 MeV  = 1.07  m  ,un. = 3keV DL1 135 MeV  = 1.07  m  ,un. = 40keV Spectrometer Linac tunnel UV Laser 200  J,  = 255 nm, 10ps, r = 1.2 mm Spectrometer

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004  ~19 parameters to optimize Gun E (MV/m)  Balance Solenoid Position Length Field Solenoid 2 Position Length Field Linac0-a Position E(MV/m) Linac0-b Position E(MV/m) 1- Analytic formula  emittance compensation 2- Envelope equation code (Homdyn, Trace3D) define components 3- Fine tuning + sensitivity studies (multiparticle tracking code: PARMELA, ASTRA …) Laser Parameters Longitudinal (length, rise time, flatness) Transverse(r, uniformity, pointing spot) Energy  charge

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Nominal tuning Rise/fall0.7 ps1.0ps1.5 ps  projected [mm.mrad]  80% [mm.mrad] [mm.mrad] [mm.mrad]  proj = 0.954,  80 = 0.89 mm.mrad

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Tolerance as a function of single parameter variation Solenoid 1  0.3%  gun  2.5  Solenoid 2 20% Linac Field 12 % (E Final = 150 MeV ) E gun  0.5% Balance~ 3% is ok

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Param.Nom.UnitsStability Requirements Sol kG  0.02 % Sol20.748kG  1 % Gun Phase  /0-X  0.1  Gun Field 120MV/m  0.5% Charge1nC  5% L01 Field 18MV/m  2.5% Defined after combining errors  Small margin left for laser parameters variation Stability Requirements Stability requirements

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Tolerances – Alignment and Laser Uniformity (*) combined with uniformity of QE Param.TypeToleranceUnits Solenoid 1Transverse Position500 mm Angular Position1.5mrad LaserTransverse Position100 mm Laser UniformityTransverse (Slope)  10 % NA Transverse (Cross)  10 % NA Longitudinal30% ptpFreq.> 1THz (1ps) Longitudinal20% ptpFreq.< 1THz Linac 1Transverse Position150 mm Angular Position120  rad Linac 2Same as Linac 1 Solenoid 2Same as Solenoid 1

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Requirements on Laser Pulse - Summary Transverse  10 % ptp maximum on emission uniformity Longitudinal =480  m =240  m =120  m 5% ok for emittance But too much for LSC

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd nC, long pulse Alternate tunings for cylindrical bunch  th = 0.6 mm.mrad per mm laser spot size reduce r laser to 0.85 mm BUT to keep charge density same order lengthen bunch Start with  th = 0.51 mm.mrad

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Alternate tunings for improving  NameQ (nC) Laser pulse (ps) r (mm)  th (  m.rad)  80 (  m.rad)  RF (  )   80  5% Nominal nC, 17.5 ps nC,10ps nC,5ps  th = 0.6 mm.mrad per mm laser spot size minimum r best, BUT limit on minimum radius = space charge limit (ignoring Shottky) E sc = Q / (  r 2  o ) example: for 1nC, r = 1.2mm, E sc = 25 MV/m (  12  ) for 1nC, r = 0.85 mm, E sc = 50 MV/m (  25  ) for 0.2 nC, r = 0.3mm, E sc = 80 MV/m (  42  ) for 0.2 nC, r = 0.42mm, E sc = 40 MV/m (  20  )

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd nC A 5ps laser pulse improves dramatically the peak current compared to the 10ps laser pulse case without damaging too much the slice emittance

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Ellipsoid emission bunch

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Ellipsoid emission bunch

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Ellipsoid emission bunch square ellipsoid Exit gunEntrance L01 Exit L01Exit L02 Longitudinal Phase Space Ek [MeV] vs T [ps]

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun S1S2 L MV/m L MV/m ‘Laser Heater’ ‘RF Deflecting cavity’ TCAV1 3 screen emittance measurement 6 MeV  = 1.6  m  ,un. = 3keV 63 MeV  = 1.08  m  ,un. = 3keV 135 MeV  = 1.07  m  ,un. = 3keV DL1 135 MeV  = 1.07  m  ,un. = 40keV Spectrometer Linac tunnel UV Laser 200  J,  = 255 nm, 10ps, r = 1.2 mm Spectrometer

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 LSC observed at the DUVFEL Courtesy of Timur Shaftan Also observed at TTF Longitudinal Space Charge Instability Simulations and theoretical studies Z.Huang et al. PhysRev. SLAC-PUB J.Wu et al. LCLS Tech Note, SLAC-PUB G.Geloni. Et al. DESY The self-consistent solution is the space charge oscillation Current Density Energy

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 ENERGY CURRENT GUN EXIT 6 MeV ASTRA/ PARMELA Simulations, Amplitude = +/- 5%,  = 100  m

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 ENERGY CURRENT End L MeV Microstructure at the end of the injector Laser Heater provide enough energy spread (40keV) for “Landau damping” preventing -further amplification of the microbunching - the increase an energy spread (as it needs to remain < the FEL parameter  )

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 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 , ,  projected,  slice - 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

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 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 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 = 104 A Solenoid = 98 A

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 DUVFEL Measurements Thermal emittance experiment Confirms the 0.6 mm.mrad per mm radius of laser spot size

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 R&D Status: GTF Measurements  longitudinal emittance GTF measurements mm.mrad for 130A Peak Current (A) Instantaneous Peak Current Spectrometer Image of Slice Quad Scan Data Slice Emittances head tail Time (ps)  n (mm mrad)  slice = 1.5 mm.mrad for 130 A ~ close to LCLS requirements Similar measurements at the DUVFEL facility (Spring 2002) Slice number 300pC

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 ‘Laser Heater’ ‘RF Deflecting cavity’ TCAV1 3 screen emittance measurement Gun Spectrometer Linac tunnel Straight Ahead Spectrometer Uniformity + Thermal emittance 1243 Commissioning Diagnostics YAG1YAG2

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Above: Laser cathode image of air force mask in laser room. Below: Resulting electron beam at pop 2. Above: Laser cathode image with mask removed showing smooth profile. Below: Resulting electron beam showing hot spot of emission. Laser masking of cathode image at DUVFEL Courtesy W.Graves Point-to-point imaging of cathode on YAG1 Emission uniformity 1

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 YAG2 == Image of divergence of source Assumes  th = 0.6 mm.mrad Very good resolution of divergence Infinite-to-point imaging what type of momentum distribution? Thermal Emittance 1

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun Spectrometer Energy Absolute energy Alignment using laser Spectrometer field calibration 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 Energy Absolute energy Alignment using laser Spectrometer field calibration 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 YAG01 Spectrometer YAGG1 YAGG2 Quadrupoles 2

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 High Charge Operation : 1nC Nominal tuning – no quadrupole on – Very good linearity Longitudinal at YAG1 YAGG1

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Resolves line density uniformity at high charge YAG1  RF + 25  / nominal Quadrupoles on for manageable image size Resolves modulation +/- 8% modulation on laser beam

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Laser Heater Transverse RF Cavity OTR Emittance Screens DL1 Bend Straight Ahead Spectrometer 135MeV Diagnostics Point-to-point imaging of the 75  m waist (OTR5) Horizontal slice emittance Vertical deflecting cavity + 3screen Vertical slice emittance Quad scan + spectrometer Quad Scan + Dogleg bend  Verification of thermal emittance Longitudinal Phase space Vertical deflecting cavity + spectrometer Efficiency of laser heater (spectrometer has 10 keV resolution) Horizontal slice emittance Vertical deflecting cavity + 3screen Vertical slice emittance Quad scan + spectrometer Quad Scan + Dogleg bend  Verification of thermal emittance Longitudinal Phase space Vertical deflecting cavity + spectrometer Efficiency of laser heater (spectrometer has 10 keV resolution) 6D beam measurements

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Longitudinal Phase Space at waist Transverse deflecting cavity  y / time correlation (  1mrad over 10ps ) Spectrometer  x / energy correlation From PARMELA simulations (assuming 1  m emittance), resolution of less than 10 keV rmsfwhm Spectrometer + Vertical deflecting cavity  Direct longitudinal Phase Space representation

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 RF Gun – Racetrack in full cell 2d-: no port = benchmark omega3p/sf 3d-cylin: with coupling ports- cell cylindrical 3d-rtrack: with coupling ports- cell racetrack Full : with laser ports + racetrack Full retuned: with laser ports + racetrack+ retuned From L.Xiao, ACD/SLAC bb d  x =  y =0.88   x = 0.96  y =1.01  x =  y =  0.90  x = 0.97,  y = 0.99  x = 0.91,  y = 0.915

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 RF Studies- L01 coupler Dipole moment Quadrupole moment From Z.Li, L.Xiao, ACD/SLAC for 10 ps Single feed Dual feed Dual feed +rtrack

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Injector Schedule

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Conclusion Gained confidence in PARMELA/ASTRA vs experiment vs other codes Injector computations based on large thermal emittance (Twice the theoretical one for copper) Discrepancy remains to be understood Mitigation : running at 0.2 nC Laser Pulse shaping and uniformity is critical to reach parameter goals

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 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, M.Cornacchia, J.Galayda

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Slice-Emittance Measurement Simulation RF-deflector at 1 MV slice OTR 10 times  y  bunch length quad scanned 4

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Slice-Emittance Measurement Simulation slice-5 Injector at 135 MeV with S-band RF-deflector at 1 MV = meas. sim. = calc. = y distribution = actual (same SLAC slice-  code used at BNL/SDL) (slice- y -emittance also simulated in BC1-center)

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 RF Gun – Mode 0 studies dF3.4 MHz8 MHz 3  s, V cath. in 0 mode MV/m4.96 MV/m 0.82  s, V cath. in 0mode 10 MV/m5.7 MV/m 3.4MHz mode separation 8MHz mode separation From Z.Li, ACD/SLAC Solution : Klystron Pulse shaping Study of 12 MHz mode separation 120MV/mNon-negligeable effect Study suggested by T.Smith

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Full Cell “Half” Cell Electron Beam Exit Photocathode Laser Port Currently using a single crystal (100) Cu cathode GTF 1.6 cell S-band gun

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 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 GTF 1.6 cell S-band RF gun Waveguide Feed Full Cell Power Monitor

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Gun Solenoid Single Particle Dynamics defocusing focusing defocusing Solenoid focusing

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Search for better tuning for the 2.8 FHWM case With 1ps rise/fall time, assuming r = 0.42 mm & Retuning

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 E gun  0.5% Gun S1S2 L MV/m L MV/m Solenoid 1  0.3% E gun  0.5%  gun  2.5  … Tolerance and stability as a function of single parameter variation

Cecile Limborg-Deprey Theory Club: The LCLS December 3rd 2004 Solenoid = 98 A Solenoid = 108 A Solenoid = 104 A Slice emittance vs solenoid strength. Charge = 200 pC. Solenoid Eyn Alpha Beta 98 A 3.7 um (3.2) 0.4 (1.0) 1.3 m (1.3) 104 A 2.1 um (2.8) -6.9 (-3.6) 9.8 m (6.8) 108 A 2.7 um (2.7) -9.0 (-9.6) 45 m (36) Projected Values (parmela in parentheses) Data Parmela