Feng Zhou LCLS-II AP meeting 02/23/2017 Tuning Procedures for Early Injector Commissioning (EIC) Feng Zhou LCLS-II AP meeting 02/23/2017

Technical scope for EIC Pre-beam checkout Baking for gun/buncher and CW RF conditioning RF baking 150-200C for the gun (80kW peak, 3-4% duty cycle: ~3kW average) ~3 days Tape baking ~150C for the buncher ~3 days CW RF conditioning for gun/buncher Study for ‘quick’ gun power-turn on Major parameters to be characterized: Bunch charge, QE, and QE lifetime for different repetition rate Dark current vs. different gun energy/repetition rate Thermal emittance Beam energy Phase and amplitude calibration for gun/buncher BBA for the components

~1 MeV LCLS-II injector source in EIC RF gun, buncher, 2 solenoids, 5 pairs of x/y correctors Diagnostics: 1 ICT, 2 BPMs, 1 YAG screen, and one 300-W temporary dump w/ a Faraday cup

Pre-beam checklist for EIC First cut for the checklist, 10 pages in total for EIC. May add more details for the gun including pumps/gauges/RTDs in the gun body, two couplers and loadlock system

‘Quick’ gun power-turn on ~half an hour for every gun-turn on, which may become an issue for user operations (availability) New frequency push-pull tuner may help (x2 tuning range, about 250kHz) but … How to shorten RF gun turn-on time (~ a few minutes?): Block the gun water flow? Increase the heater power? How to slow down the temperature drop due to trips caused by vacuum or temperature or reflected power Block the gun water flow after the trip? Developing a plan for the study in the EIC To discuss with LBL experts

Dark current, bunch charge, QE & QE lifetime, and thermal emittance Dark current can be characterized with the Faraday cup for different gun energy Will borrow FC electronics from Diag0 Bunch charge can be measured with the ICT/faraday cup and the calibrated two BPMs TMIT BPM electronics ready for EIC QE and, QE lifetime for different repetition rate Thermal emittance can be measured by scanning the solenoid strength to record the beam size at the YAG screen (simple matrix: solenoid + drift) The method used at the LCLS1 and Apex

Assume gun phase is fixed, similar to LCLS1 Laser launch phase Assume gun phase is fixed, similar to LCLS1 Scan the charge (w/ ICT) vs. laser phase to determine zero- crossing laser phase w.r.t. RF reference Set laser phase to on- crest Zero-crossing

Buncher phase Buncher’s zero-crossing phase: Beam energy with buncher’s zero-crossing phase  gun energy On-crest phase at -3 due to phase slippage at <1MeV energy The -3 accuracy is not important for the optimized performance Bunching vs. debunching at zero-crossing : Beam size at YAG screen much larger beam size for bunching than debunching Debunching Bunching Zero-crossing Bunching Debunching

Buncher phase calibration steps Measure gun energy Scan the energy with the gun and buncher vs. buncher phase to determine zero-crossing phases Determine the zero-crossing phase for bunching through comparison of the beam size at the YAG screen Set buncher to desired phase w.r.t. zero-crossing at bunching side

Gun/buncher RF amplitude calibration (beam energy measurement) Assume the gun/buncher RF power has been pre- calibrated by RF experts. We are to discuss gun/buncher RF calibration with beam energy measurement: w/ a corrector: to measure the beam displacement at a viewing screen or BPM vs. corrector strength (slope) d: the distance between corrector and screen/BPM x/BL: the slope

Gun amplitude calibration Calibration steps: Turn off buncher and adjust SOL1 strength to focus the beam at YAG screen Scan the XC01 corrector and measure corresponding beam’s x-displacement (slope) Extract the gun beam energy with the measured slope Calibrate gun energy for different gun RF amplitude May resolve ~10 keV beam energy SOL1= 0.078 kG.m 10 keV energy difference

Buncher amplitude calibration Measure gun energy Turn on the buncher, set its phase on-crest with nominal RF power, and focus the beam at the YAG screen with adjustment of SOL1 strength Scan XC03 corrector and measure corresponding beam’s x- displacement at YAG (slope) Obtain net energy gain from the buncher by subtracting the gun energy from the total Calibrate different buncher RF amplitude @nominal RF power

Requirement for transverse alignment Misalignment -growth Cathode 100 µm <2% Solenoid 0.5mm or 2mrad <2.5% Buncher 1mm or <3% CM01 0.5 or 0.5mrad <1% And also alignment is crucial for subsequent emittance tuning with optimization of the solenoid strength

BBA for cathode APEX experience: Steps for the cathode alignment Cathode plug is aligned well with the gun (~10 m level) Only central 5mm of the cathode is doped with Cs Steps for the cathode alignment Map QE with scanning the laser mirror in x-plane and record laser mirror setting when QE starts dropping to zero on both sides of the central area, x1 and x2 Set laser mirror in x-plane = (x1+x2)/2 and repeat same step as above but for y-plane Cathode center =[(x1+x2)/2, (y1+y2)/2] Could align ~100m level according to APEX experience

BBA for solenoids Method: given the initial offset x0, x0’, y0, y0’ for solenoid, the beam’s x- and y-displacement at downstream BPM can be calculated with the matrix (a solenoid + a drift): where C=cos(KL) S=sin(KL) KL=BL/(2B) K=B/(2B) B: solenoid strength L: solenoid length d: distance between solenoid exit and BPM

BBA procedures for SOL1/2 Alignment steps: Record beam’s x- and y-displacement at BPM1 for >3 different SOL1 strength Directly solve the SOL1 misalignments (x0, x0’, y0, y0’) according to the equation Correct the misalignments through moving the solenoid actuators (x, y, x’, and y’), Check beam alignment again after the correction with different SOL1 strength; more iterations if still not fully aligned Replace SOL1/BPM1 with SOL2/BPM2 then can align for SOL2

BBA for buncher Set buncher to debunching zero-crossing Eliminated the effect of dispersion due to the stray fields Smaller beam size (extra focusing from debunching phase) Turn on SOL1 and adjust its strength to focus the beam at YAG screen Correct the offset using pairs of correctors xc01/02 through measuring difference of centroid beam at YAG for buncher on/off; may align <100 m.

HLAs requested Gun and buncher RF turn-on process (apex scripts available) Laser phase scan (migrated from LCLS1) Buncher phase calibration (new) Beam energy (apex script available) Thermal emittance (apex script available) Cathode alignment (new) Solenoid alignment (new) Buncher alignment (new)

Beam performance with one cavity failure Nominal (grad/phase) Cav1 failure Cav4 failure Cav5 failure Cav1 Cav2 Cav3 Cav4 Cav5 Cav6 Cav7 Cav8 7.9/-4 14/0 16/0 16/1 16/6 7.1/-8 15/-4 16/13 15/0  (µm) I (A) E (MeV) @100pC 0.29 12 94 0.54 7.5 0.4 96 0.39 95