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Changes w.r.t LBL simulations

Changes w.r.t LBL simulations. Set gun phase for minimum energy spread S et on-crest phases for all cavities after buncher Turned off 2 nd cavity (~5MV/m amplitude for LBL versions for 2 nd cavity) Optimized cavity field amplitude & solenoids

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Changes w.r.t LBL simulations

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  1. Changes w.r.t LBL simulations • Set gun phase for minimum energy spread • Set on-crest phases for all cavities after buncher • Turned off 2nd cavity (~5MV/m amplitude for LBL versions for 2nd cavity) • Optimized cavity field amplitude & solenoids • Emittance improved ~10% - LBL simulations have been good in general. Feng Zhou, 12/18/2013

  2. Independent control for 1st 9 cells (APEX gun, 300pC) • Slice emittance & bunch shape stay similar. • More knobs help to improve the slice matching, which improve projected emittance ~20%. • Further look into dc gun as well Same phase/amp different phase/amp

  3. Concerns for charge production • Current laser sizes need 2-3 times additional laser energy for the required charge as they work at the space charge limited charge production region. • Does laser energy have enough headroom?

  4. Cornell vs. LBL injector layout Cornell, Ez Cornell, Bz • 300pC Cornell: • Laser pulse 28 ps • Laser size 3mm • Thermal emittance 0.48um/mm-rms APEX, Ez APEX, Bz • 300pC APEX: • Laser pulse 56 ps • Laser size 1.2mm • Thermal emittance 1um/mm-rms

  5. Observations from Cornell simulations • Reproduced Cornell results but found the bunch shapes are asymmetry from the charge 50pC to 500pC • Asymmetry may be improved after tweaking the phases but most likely it will be similar to APEX in the end.

  6. Summary • Independent control for 1st 9 cells: • For APEX: only improve projected emittace 20%. Slice emittance/bunch shape stays similar. • For Cornell dc gun: is under study. • Current design with APEX gun requires extra 2-3 times laser energy as charge production is in space charge limited regime. • Have to enlarge laser size thus sacrifice emittance if laser is not capable to produce enough energy-headroom • A little more simulations for Cornell DC gun are needed to improve the asymmetry bunch.

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