ASTRA Injector Setup 2012 Julian McKenzie 17/02/2012

Baseline: Gun voltage350 kV Bunch charge60 pC Laser spot diameter4 mm flat-top Laser pulse length7 ps Gaussian / 28 ps flat-top ? Sol 1 peak field330 G Sol 2 peak field187 G Buncher power1.6 kW BC1 gradient8 MV/m BC1 phase-20 BC2 gradient5 MV/m BC2 phase+30 Post-booster beam energy6.5 MeV Simulations using ASTRA (07/04/2008 win32) No intrinsic emittance – could expect up to 1.2 mm mrad from photocathode

7 ps Gaussian vs 28 ps flat-top

Buncher power [W] Buncher power scans Bunch length required at entrance to linac to achieve energy spread for FEL ~7ps We still don’t understand booster to linac longitudinal dynamics... Red = 7 ps Gaussian Blue = 28 ps flat-top Yuri reckons 1.6 mm FWHM

BC1 scans Red = 1 kW buncher power Green = 1.6 kW buncher power For 7 ps Gaussian laser pulse

For 1kW buncher power, choose +15 BC1 phase Set SOL-02 to minimise transverse beam size Set BC2 phase to minimise chirp (-13)

But phase space isn’t good: Is RMS bunch length even a good quantity to optimise on? Need to look at phase space plots

Phase space plots (longitudinal) Red = 7 ps Gaussian Blue = 28 ps flat-top -20/ /+10 (as per original model) Using “nominal” setup detailed on slide 1 Looks similar to Bruno’s: Lots of charge at the “crossover point” NB// head to the right. z [m] vs pz (eV/c)

BC1 phase for minimum curvature: BC1 = -6 BC1 = 0 Buncher = 1 kW Buncher = 1.6 kW For 7 ps Gaussian laser pulse

Sol2 scans Red = 1 kW buncher power Green = 1.6 kW buncher power For 7 ps Gaussian laser pulse

BC2 phase? BC1 at -6 SOL-02 at 220G Red = 1 kW buncher power Green = 1.6 kW buncher power For 7 ps Gaussian laser pulse

To do list: Emittance vs SOL-02 for 7/28ps with identical bunch length from buncher At minimum emittance from above, BC2 phase scan to look at minimum energy spread Investigate lowering energy gain from BC1 Anything else?