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Laser System Commissioning for Injector with Spectrometer at 135MeV

This document outlines the commissioning plans for the laser system in the injector with spectrometer at 135MeV, including parameters, tuning, diagnostics, start-up, and alignment. It also discusses critical measurements and the key software and data analysis tools used.

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Laser System Commissioning for Injector with Spectrometer at 135MeV

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  1. Injector Commissioning PlansC.Limborg-Deprey Parameters nominal tuning 1nC 0.2nC Diagnostics Start-Up and Alignment Calibrations + Critical Measurements Gun : Spectrometer 135MeV : Emittance, Spectrometers Key Softwares Data Analysis Softwares On-Line Modeling Tools

  2. Preinjector:

  3. Injector-Linac Installation • Laser System June 2006 • Gun Region April 2006 • Accel Region March 2006 • Heater Region January 2006 • Wall Region October 2005 • Injection Region August 2006 • Spect Region August 2006 Commissioning starts Jan07  August07

  4. Alcove : feet underground Sector 20 Alcove Laser Bay Drive Laser Drive Laser System Transport Tubes Transport Tube Laser Heater RF Gun Laser Heater UV Launch and Condition. Photocathode Gun & Launch System Electron Diagnostic Courtesy J.Mitchell

  5.  Critical parameters assessed at GTF thermal = 0.6 mm.mrad per mm laser spot size measured for S-Band copper cathode (discrepancy to theoretical thermal value is under investigation) E peak = 120MV/m QE = 3.10-5 Alternate tuning 0.2 nC Performances demonstrated at GTF (slice~ 1mm.mrad without laser shaping) With laser pulse shaped, much better performances expected Tuning easier for whole LCLS (reduced wakefields …) Parameters

  6. 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’ DL1 Gun S1 S2 L0-2 24 MV/m L0-1 19.8MV/m Spectrometer 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 Spectrometer UV Laser 200 J,  = 255 nm, 5-20 ps, r = 0-1.5 mm

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

  8. Start-Up Steering + Stability + Shape Temporal Transverse • Laser Commissioning • Deliver laser to linac vault • Steer beam through transport tubes and set up alignment fiducials • Set up laser BPM and measure laser beam spatial jitter • Test laser energy diagnostic and vary laser energy from 1-100 mJ at cathode • Test laser timing diagnostic (ns diode or comparable detector) • Set up and test the laser virtual cathode • Measure laser pulse length with streak camera • Measure at cathode position without cathode. • Test ability to adjust pulse length from 2-10 ps • Vary laser beam diameter at cathode from 100 microns to 2 mm. • Gun Commissioning • RF processing • Measure following parameters as a function of rf field (power) at 10 Hz stop when the field on axis as measured with the field probes is 130 MV/m. • Gun Probe amplitude signals • Gun forward power signals • Gun Probe phase signals • Dark current • Vacuum levels • Gun Temperature • Reflected power pulse shape • klystron voltage • Decrease field to 120 MV/m and increase rep rate slowly while monitoring gun probe signals (amplitude and phase) and reflected power signal for change in shape or amplitude • Laser and RF Timing • Measure the gun Probe RF amplitude signal and photodiode signal vs time • Add delay as necessary to trigger laser at desired time during rf signal RF Processing Laser Timing Courtesy J.Schmerge

  9. BBA • BBA of solenoid • align centers of • laser beam – Gun – solenoid – linac • Steerers in solenoid + SC1 (0.8m)+SC2(1.5m) • Do we need remote control ? • still under discussion in our group • hope to get information from M.Krasilnikov presentation • BBA • BPMs offsets (Quad Shunt)

  10. Including Magnets Treaty Point

  11. 1 2 4 3 Linac tunnel ‘Laser Heater’ Straight Ahead Spectrometer 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 Emission thermal Uniformity QE Gun Spectrometer

  12. 2 1 Thermal emittance Uniformity Emission Spot YAG1 YAG2 CR1 Energy Energy Spread Temporal uniformity Time-Space correlation Slice thermal emittance YAGG1 rf Vrf Bsolenoid CRG1

  13. 1 Emission • QE • Cathode imaging • Point-to-Point Imaging • Transverse uniformity of emission disk • Ellipticity + Slope of Edges • Thermal emittance measurement • Infinite-to-Point imaging • Divergence at cathode • Model thermal emittance • Future “optimal pulse shaping” (3D-ellipsoid) • Measure time-radius correlation • Dephasing of RF Gun • Good thermal emittance model is fundamental for experiment/simulations

  14. Schottky Scan J.Schmerge, GTF

  15. Laser masking of cathode image at DUVFEL Above: Laser cathode image with mask removed showing smooth profile. Below: Resulting electron beam showing hot spot of emission. Above: Laser cathode image of air force mask in laser room. Below: Resulting electron beam at pop 2. Courtesy W.Graves

  16. Thermal emittance • At YAG2 • With low accelerating gradient Good resolution Assumes th = 0.6 mm.mrad Good resolution (better than at YAG1) YAG2 == Image of divergence of source

  17. Imaging source divergence what type of momentum distribution?

  18. Difficulties of Calibrations •  beam atYAG1 varies with Vrf , rf , Gun field balance, charge, Solenoid calibration • calibrate Vrf , rf (see slide 21-22) • rotation of L-shape mask • then can possibly detect field unbalanced Fit of DUVFEL measurements

  19. 2 Gun Spectrometer • Energy • Absolute energy • alignment using laser • spectrometer field calibration • Lifts-up rf  Vrf • 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 • 3D-ellispoid Emission pulse

  20. Calibrations, Orthogonality of knobs Rotation of L-shape mask Vrf Steering coil (2), offset at YAG1/YAG2 Spectrometer calibration Shottky scan (for short bunch ~2ps) rf Shottky scan at different gun fields Energy spread at low/high current in spectrometer Solenoid Beam size compared at YAG1 / YAG2 Waist vs charge Gun Balance Offset in solenoid scan curve Direct field measurement from probes

  21. Orthogonality rf  Vrf • Energy vs Phase (for different Vrf) • Current vs charge Operating point = 2 from minimum E Zero Current

  22. Orthogonality rf  Vrf • With finite bunch length

  23. Direct measurement of E vs rf Low Charge operation Gun spectrometer with all quadrupoles off Referenced to nominal = 32 Referenced to nominal = 32

  24. 1nC Nominal tuning – no quadrupole on - High Charge operation Longitudinal at YAG1 YAGG1 YAGG1

  25. High Charge operation • Correlated Energy spread vs rf • Calibration rfrepeated At YAG1 At YAGG1 PARMELA Simulations for 1 nC Good Linearity

  26. High Charge operation 1nC, temporal pulse … at YAG1 location 8% modulation Nominal phase Quadrupoles off YAG1

  27. Temporal pulse , … using quadrupoles to project on manageable size screen High Charge operation RF  Quadrupoles on Resolves modulation at YAG1 location

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

  29. Laser Heater Transverse RF Cavity OTR Emittance Screens 3 DL1 Bend Straight Ahead Spectrometer Straight Ahead Spectrometer

  30. Longitudinal Phase Space at waist • Transverse deflecting cavity  y / time correlation • (0.5mrad over 10ps ) • Spectrometer  x / energy correlation • Direct longitudinal Phase Space representation rms From PARMELA simulations (assuming 1m emittance), resolution of less than 10 keV

  31. Straight Ahead Spectrometer • Tuned to possibly be used in pulsed mode • Laminated magnet + ceramic chamber Dx ~ 1m x ~0.1 Same tuning

  32. 4 sy bunch length RF-deflector at 1 MV Slice-Emittance Measurement Simulation slice OTR 10 times quad scanned Courtesy P.Emma

  33. = meas. sim. = calc. = y distribution = actual (slice-y-emittance also simulated in BC1-center) Slice-Emittance Measurement Simulation Injector at 135 MeV with S-band RF-deflector at 1 MV (same SLAC slice-ecode used at BNL/SDL) slice-5 Courtesy P.Emma

  34. Conclusions • Diagnostics were designed to provide • Tools for performing correctly emittance compensation • 6D characterization of beam at end of injector • Diagnostics for degraded beam started • Temporal Modulation laser • Large emittance => Energy spread measurement ok • On-line simulations tools to be chosen • Fast-tracker (Homdyn, Trace3D, PARMELA …??…) • MP tracker (PARMELA, ASTRA, IMPACT, GPT …??…)

  35. Including Magnets Treaty Point Straight Ahead Spectrometer 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1 Gun Spectrometer

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

  37. Low Charge Operations 1 nC 2.8 kA • Need 20% smaller emittance (0.8 mm), but with 1/5 charge & 1/3 gun current (30 A) • No more transverse wakes in linac • Almost no CSR in BC’s • 2-times less peak-current jitter • No undulator wakes • 3-times shorter X-ray pulse • 1-nC still OK, but only ~twice the photons, and a much more challenging machine 0.2 nC 2.0 kA no spikes 1.11012 photons no resistive wake W. Fawley, LBNL Z. Huang

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