Injector Commissioning C Injector Commissioning C. Limborg-Deprey Injector-Linac & Spectrometers Commissioning Plans Oct. 10, 2006 LCLS

Beam Characterization Introduction Beamline Layout & 2007 Baseline Parameters Strategy Beam Characterization 135 MeV Spectrometer 6 MeV Characterization Longitudinal : Spectrometer Transverse : YAGs Risks Mitigation Laser pulse shape Reduced gun voltage Solenoid alignment Matching Conclusion & Discussion

LCLS Injector Klystron Gallery Laser Room BC1 compressor DogLeg Gun 2 linacs 135 MeV Spectrometer 6 MeV Spectrometer

Baseline Parameters Injector Design : 1nC , laser pulse 10ps square ,  < 1 mm-mrad 2007 Commissioning baseline parameters Limits Q ≤ 500pC Repetition rate ≤ 30Hz Gun gradient ≤ 120 MV/m Risk lower than for the design parameters 0.5 nC requires only QE of 10-5 with laser energy of 250 J Getting to  < 1 mm-mrad not as challenging for charges < 0.5 nC laser pulse length of 10 ps ( when radius can be adjusted) Less sensitivity to parameters variation Q objective  Laser Pulse length Laser Pulse radius 0.2 nC 0.85 mm-rad 10 ps Variable [0.35 , 1.5 ] mm 0.5 nC ~ 1 mm-rad Variable [0.55 , 1.5 ] mm

Strategy (Reminder) 1st Pass : beam to 135 MeV Start-up equipment to reach 135 MeV Software checkout 2nd Pass : first order optics Steering Matching 3rd Pass : Characterization: Transverse emittance (slice & projected) Longitudinal phase space (slice energy spread) Optimization : Fine tuning of gun-solenoid Scan of parameters (solenoid fields, phases, voltages …) 135 MeV spectrometer 6 MeV spectrometer 6 MeV transverse

Injector Layout RF Gun L0a RF section L0b RF section gun spectrometer 6 MeV L0b RF section 62 MeV gun spectrometer Transverse RF deflector 135 MeV L1 RF section (21-1b) main SLAC Linac injector spectrometer sector 20 sector 21

Longitudinal Phase Space at TCAV 135 MeV spectrometer Direct Longitudinal Phase Space measurement Transverse deflecting cavity  y / time correlation (with V = 1MV, 0.5mrad over 10ps ) Spectrometer  x / energy correlation Resolution requirements : 7m OTRS1 with 11m resolution ok D = 0.9m ,  = 0.138 m (1) nominal matching  = 0. 069m (2) modified tuning DL1 Longitudinal Phase Space at TCAV 135 MeV Spectrometer Spectrometer Screen

resolution 6 keV for nominal optics resolution 3 keV for modified optics 3keV -> 40 keV will be measurable rms Direct Measurement Projection

6 MeV Spectrometer Energy Correlated Energy Spread QG02 YAG01 QG03 YAGG1 Energy Absolute energy Distinguish rf  Vrf Correlated Energy Spread Slice thermal emittance Relay imaging system from YAG01 to spectrometer YAGG1 Uniformity of line density

Horizontal Projection Linear Scaling of Energy atYAG01 High Charge operation Temporal pulse , … using quadrupoles to project on manageable size screen Tail Horizontal Projection Linear Scaling of Energy atYAG01 8% modulation on laser pulse at YAG01 Location at YAGG1

6 MeV Transverse Measurements QE (charge to laser energy) Charge vs Gun RF phase QE vs x,y position laser on cathode Building thermal emittance model Cathode Uniformity Point-to-Point Imaging Uniformity of emission disk Ellipticity + Slope of Edges Thermal emittance measurement Infinite-to-Point imaging Divergence at cathode Distribution of p Cross-check Energy meas. Using Steerer: beam to YAG02 Rotation angle of mask image YAG01 YAG02 FC01

Cathode Imaging Point-to-point imaging of cathode Cathode Image at DUVFEL Virtual cathode Virtual cathode Direct determination Uniformity of emission Ellipticity Transv. rise/fall slopes e image : hot spot electrons image Getting initial conditions. Use complementary laser image for init distribution. Find image point of ebeam. Measure emitted distribution. Use in simulations. Courtesy W.Graves

Cathode emittance cathode (with appropriate set of Vrf, rf, Bsolenoid) Momentum distribution Assumes cathode = 0.6 mm.mrad Image of divergence of source At YAG2 , with Vrf reduced

Risk : Laser Pulse shape Difficult to meet specifications Rise time 1 ps Uniformity 10% ptp Pulse stacker Pulse with 2-3 gaussians give satisfactory performances Even better for compression (flatter at 135 MeV ) = 1.7 ps = 1.15 ps Dis./  [1nC] p 80 <10,90> (2) Gaussians 1.41 1.23 0.97 (3) Gaussians 1.24 1.11 0.91 “Square” 1.08 0.84

Risk : Gun field if 120MV/m difficult (breakdowns and large dark current) 110 MV/m gives performances very similar to 120 MV/m 100 MV/m is also gives acceptable performances (see next slide) ( for 0.5 nC, 80 < 0.8 mm-mrad ) Q [nC] Laser pulse Gun Field 80 mm-mrad proj.mm-mrad z [mm] 0.2 6.5 ps 120 MV/m 0.35 0.44 0.657 110 MV/m 0.37 0.704 1 10 0.91 1.08 0.948 0.95 1.05 0.97 12 0.92 1.02 14 0.88 1.157

100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.7 mm-mrad Parameters improved by using a 0.6 mm radius beam 80 ~ 0.78 mm-mrad < {10,90} > ~ 0.6 mm-mrad

Risk: Solenoid Alignment Tolerance : 250 m, 250rad w.r.t to gun electrical axis Requires beam based alignment 1) Determine center of cathode 2) Determine error in solenoid position with as few steps of solenoid motion F(X, rf, Vrf, Bsol, Xsol) = Xf 4 unknowns Xsol = (x,x’,y,y’) Center BPM/Screen cannot be determined with beam Angle resolution from BPM2-BPM3 > 100 rad Code Single Particle tracking in Matlab for on-line modeling gun to L0a (including misalignment of components + earth magnetic field) to be extended to DL1 (i.e linacs + quads) Solenoid SC0 SC1 SC2 Gun BPM2 BPM3 L0a BPM5

Risk: Solenoid Alignment 1) Center of cathode Steer laser centroid on 2D grid Scan Gun RF phase Gun YAG02 Centroid on cathode Centroid on YAG01, rf [24,36]

Risk: Solenoid Alignment 2) Mispositioning Solenoid (Position, Angle ) does not vary with strength when the Solenoid aligned Vary Solenoid strength Algorithm A- Assume center cathode known to better than 50 m B- Assume axis gun on screen is known within 50 m C- Requires at least 8 motions of solenoid Issues: Too little light on single pulse when solenoid field small Only explore small Bz range Model based needs to use variation of phase

Risk: Optimization Scan parameters : (rf, Vrf , B solenoid) Large Variation of betatron function while varying Bsolenoid Rematching necessary for emittance measurements 3 screen emittance : best resolution for perfect parabola (with 2 = ½ 1 = ½ 3 )

Matching performed for each point Tuned to matching of -0.6% case

Conclusions 135 MeV spectrometer 6 MeV spectrometer Thermal emittance model Risks : Pulse shaping : stacker with 2-3 gaussians Gun at 100 MV/m Optimization : rematching necessary Solenoid alignment in minimum steps … ? Which other risks are we missing ?

BACK-UP

Imaging source divergence what type of momentum distribution? Momentum at cathode Imaging source divergence what type of momentum distribution?

Injector Diagnostics YAG screen RF Gun trajectory (BPMs) emittance (+ slice) energy spread (+ slice) bunch length (+ dist.) charge (+ dark current) YAG screen YAG screen YAG screen YAG screen gun spectrometer Transverse RF deflector OTR & wire Injector Diagnostics OTR & wire OTR & wire OTR & wire main SLAC Linac injector spectrometer YAG YAG & OTR

Verifications on baseline case Deck updated with all engineering constraints Lost some margin on the emittance growth budget Standard quiet start , 100k With the modified quiet start beam uniform transversally but with ring structure weighted to 1 100k SOL1 had to be increased by +0.5% from above case

Modeling Transverse Profile Apply “quiet start” on square and extract rings Number of particles per square chosen to match transverse charge density

Modeling Transverse Profile Case of ~ 30% peak-to-peak Optimization: scan solenoid 1 Minimum SOL at +1% , p ~1.2 mm-mrad , 80 ~1.0 mm-mrad uses all the error budget But, <10,90> ~0.92 mm-mrad

Modeling Transverse Profile Case of 60% peak-to peak 80 just hardly meets 1.1 mm-mrad <  (10,90) > hardly meets 1mm-mrad

Modeling Transverse Profile Case of 20% peak-to peak 80 ~ 0.94 mm-mrad , <  (10,90) > ~ 0.85 mm-mrad

Summary Transverse profile projected [mm-mrad] 80% <10,90 > Ref. 1.04 0.94 0.85 Modified Quiet Start 0.95 0.86 20% ptp 1.15 (1.07) 0.92 (0.97) 0.84 (0.87) 30% ptp 1.23 (1.15) 0.99 (1.04) 0.92 (0.96) 60% ptp 1.23 1.10 1.03

More Profile measurement Standard “Beer Can” “3D-Ellipsoid”

Cathode Imaging Point-to-point imaging of cathode Cathode Image at DUVFEL Virtual cathode Virtual cathode Direct determination Uniformity of emission Ellipticity Transv. rise/fall slopes e image : hot spot electrons image Result Correlated to E gun Solenoid calibration (from mask image rotation ) Getting initial conditions. Use complementary laser image for init distribution. Find image point of ebeam. Measure emitted distribution. Use in simulations. Courtesy W.Graves

Cathode emittance Direct determination cathode (with appropriate set of Vrf, rf, Bsolenoid) Momentum distribution  Fundamental for initial model + cathode quality Correlated quantities E gun Solenoid calibration Assumes cathode = 0.6 mm.mrad Image of divergence of source At YAG2 , with Vrf reduced

Imaging source divergence what type of momentum distribution? Momentum at cathode Imaging source divergence what type of momentum distribution?

More Profile measurement Standard “Beer Can” “3D-Ellipsoid”

Alignment Procedure Find cathode center first (electrical center of gun) Scan gun phase while scanning laser position Length and curvature of position at screen give cathode center Center found to within +/-100um

Aligning Solenoid Procedure Constraints Assumes RF center on screens are known Scan Bz for different laser pos. on cathode Constraints Need to align with few moves of solenoid 4 parameters to be determined in a 2-D space Many combinations of xs,xs’,ys,ys’ give indistinguishable focus

Model-Based Approach Distinguish overlapping combinations by modeling all possibilities. In examples below, scanning Bz and cathode x position distinguish different cases.

Linearity of Solenoid Misalignment Linear relationship holds throughout spec region

100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.7 mm-mrad Parameters improved by using a 0.6 mm radius beam 80 ~ 0.78 mm-mrad < {10,90} > ~ 0.6 mm-mrad

Gun Characterization QE, thermal, Uniformity Emission , Bunch Length YAG1 YAG2 CR1 YAGG1 CRG1

Courtesy J.Schmerge, GTF QE from Schottky Scan Direct determination of QE RF for a given Vrf Courtesy J.Schmerge, GTF

Solenoid = 98 A Data Parmela Solenoid = 104 A Solenoid = 108 A DUVFEL EXPERIMENT Good match of Slice Emittance and Twiss Parameters Parameters: 200 pC Solenoid = 104 A Solenoid = 108 A

Difficulties of Calibrations  beam at YAG1 varies with Vrf , rf , Gun field balance, charge, Solenoid calibration calibrate Vrf , rf (see slide 18-20) then can possibly detect field unbalanced Fit of DUVFEL measurements

Diagnostics Current Monitors Straight Ahead Spectrometer Wire scanners Cerenkov Radiator OTRs YAGs Gun Spectrometer EO monitor

Including Magnets Treaty Point

1 2 3 4 Linac tunnel ‘Laser Heater’ Straight Ahead Spectrometer 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 Emission thermal Uniformity QE 2 3 4 Gun Spectrometer

3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 6 MeV  = 1.6 m ,un. = 3keV 63 MeV  = 1.08 m ,un. = 3keV 135 MeV  = 1.07 m ,un. = 3keV 135 MeV  = 1.07 m ,un. = 40keV Linac tunnel ‘Laser Heater’ Gun S1 S2 L0-1 19.8MV/m L0-2 24 MV/m DL1 Spectrometer 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 Spectrometer UV Laser 200 J,  = 255 nm, 5-20 ps, r = 0-1.5 mm

Diagnostics Current Monitors EO monitor Cerenkov Radiator YAGs OTRs Faraday Cup EO monitor Cerenkov Radiator YAGs OTRs Wire scanners Gun Spectrometer Straight Ahead Spectrometer

Injector Layout RF Gun L0a RF section L0b RF section gun spectrometer 6 MeV L0b RF section 62 MeV 135 MeV gun spectrometer Transverse RF deflector injector spectrometer main SLAC Linac sector 20 sector 21

Risk: Solenoid Alignment 2) Error of solenoid position F(Xlaser, rf, Vrf, Bsol, Xsol) = Xf Large systematic errors on Xf (reference 0 cannot be determined) F(Xlaser, rf, Vrf, Bsol, Xsol) = Xf - Xf0 Determining Xsol is a very non-linear problem Xsol = (xsol, xp,sol, ysol, yp,sol) Xf reference (Xf0, Xfp0, Yf0,Yfp0)  8 unknowns instead of 4

Risk: Solenoid Alignment 2) Error of solenoid position Single Particle tracking in Matlab for on-line modeling ( similar to V-code) gun to L0a (including misalignment of components + earth magnetic field) to be extended to DL1 (i.e linacs + quads) Algorithm to determine, in minimum steps, mis-positioning of the solenoid F(X, rf, Vrf, Bsol, Xsol) = Xf Issue : 4 unknowns Xsol = (x,x’,y,y’) Center BPM/Screen cannot be determined with beam BPMs too close together for good accuracy on angle Angle resolution from BPM2-BPM3 > 100 rad But Indirect evaluation of angle using BPM5 Only solution: model based analysis for complicated non-linear problem Solenoid SC0 SC1 SC2 Gun BPM2 BPM3 L0a BPM5

100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.6 mm-mrad With 0.6 mm radius beam 80 ~ 0.78 mm-mrad < {10,90} > ~ 0.6 mm-mrad Large margin for emittance increase from errors

Emittance Projected : containing all particles  80 : projected for the 80 central slices <  10,90 > : average of slice emittance for slices from 10 to 90