LCLS Injector Commissioning
J.F. Schmerge
2-11-2005
1. Laser Commissioning
1.1. Deliver laser to linac vault
1.1.1. Steer beam through transport tubes and set up alignment fiducials
1.1.2. Set up laser BPM and measure laser beam spatial jitter
1.1.3. Test laser energy diagnostic and vary laser energy from 1-100 J at
cathode
1.1.4. Test laser timing diagnostic (ns diode or comparable detector)
1.1.5. Set up and test the laser virtual cathode
1.1.6. Measure laser pulse length with streak camera
1.1.6.1.
Measure at cathode position without cathode.
1.1.6.2.
Test ability to adjust pulse length from 2-10 ps
1.1.7. Vary laser beam diameter at cathode from 100 microns to 2 mm.
2. Gun Commissioning
2.1. RF processing
2.1.1. 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.
2.1.1.1.
Gun Probe amplitude signals
2.1.1.2.
Gun forward power signals
2.1.1.3.
Gun Probe phase signals
2.1.1.4.
Dark current
2.1.1.5.
Vacuum levels
2.1.1.6.
Gun Temperature
2.1.1.7.
Reflected power pulse shape
2.1.1.8.
klystron voltage
2.1.2. 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
2.2. Laser and RF Timing
2.2.1. Measure the gun Probe RF amplitude signal and photodiode signal vs time
2.2.2. Add delay as necessary to trigger laser at desired time during rf signal
2.3. Schottky scan
2.3.1. Measure current at FC01 as a function of RF gun phase.
2.3.1.1.
With laser off measure dark current on FCO1 to test FC01.
2.3.1.2.
Turn laser on and vary rfphase to maximize measured photocurrent emitted from the gun
2.3.1.3.
Scan over 720 degrees to verify the Schottky scan is periodic with
360 degree period
2.3.1.4.
Verify the current is emitted only over approximately 120 degrees
2.3.1.5.
Test for satellite laser pulses and laser timing jitter
2.4. Test YAG01 screen
2.4.1. Find beam on YAG01 screen
2.4.2. Turn on-off laser to verify photo-current and dark current
2.4.3. Test solenoid by varying current and looking at image size variation on
screen
2.5. Center laser on the cathode
2.5.1. measure beam centroid position with BPM
2.5.1.1.
Move laser until beam centroid independent of solenoid field
2.5.1.2.
Move laser until beam centroid independent of rf field amplitude
and/or phase
2.5.2. Verify laser position nearly identical for two previous steps
2.6. Measure beam size at YAG01 and YAG 02 with camera as a function of solenoid
strength
2.6.1. Verify round beam over all solenoid values
2.6.2. Compare electron beam and laser beam profiles
2.6.3. Measure electron beam size versus laser beam size and compare with
theory
2.6.4. Measure electron beam size versus solenoid field and compare with theory
2.6.5. Try to image Air Force Target (assumes Air Force Target has been imaged
on virtual cathode camera)
2.7. Measure QE vs laser energy
2.7.1. Measure photo-charge from 10-500 pC on FC01 vs laser energy
2.7.2. Verify QE linearity and no abnormalities
2.8. Measure QE spatial profile
2.8.1. Focus laser to approximately 100-200 microns spot size
2.8.2. Limit laser fluence to values less than or equal to values used in step 6 to
prevent damage to cathode
2.8.3. Scan laser across 2.5 X 2.5 mm array and measure photo-charge on FC01
2.9. Measure gun exit energy
2.9.1. Measure energy using spectrometer as a function of RF phase and
amplitude
2.9.2. Compare spectrometer energy measurement with solenoid steering coil
energy measurement if desired
2.9.3. Can also compare with solenoid rotation energy measurement if desired
2.10. Measure energy spread vs injection phase
2.10.1. Set up beamline for energy spread measurement on spectrometer screen
2.10.2. Verify laser pulse length less than 2 ps FWHM
2.10.3. Measure beam size on spectrometer screen as a function of RF phase and
amplitude
3. Injector L0 commissioning
3.1. Turn QG01 and BXG and S2 off
3.2. Center beam on BPM 2
3.3. Increase field in L0-A to > 10 MV/m
3.4. Look for beam on screen? As a function of L0-A rf phase
3.5. Adjust QA01 and QA02 and verify effect on beam
3.6. Increase S2 and verify no steering effect on beam
3.7. Increase field in L0-B to > 10 MV/m
3.8. Look for beam on screen? As a function of L0-B rf phase