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Study on the BC1 Energy Set Point

Study on the BC1 Energy Set Point . J. Wu working with T.O. Raubenheimer, J. Qiang (LBL), LCLS-II Accelerator Physics meeting April 11, 2012. Layout. Previously BC1 @ 250 MeV for LCLS Pros and Cons of setting BC1 @ 300 ~ 350 MeV for LCLS-II

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Study on the BC1 Energy Set Point

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  1. Study on the BC1 Energy Set Point J. Wu working with T.O. Raubenheimer, J. Qiang (LBL), LCLS-II Accelerator Physics meetingApril 11, 2012 LCLS-II Accel. Phys. , J. Wu, SLAC

  2. Layout • Previously BC1 @ 250 MeV for LCLS • Pros and Cons of setting BC1 @ 300 ~ 350 MeV for LCLS-II • Hardware consideration: cost and future 360 Hz operation • Macroscopic: chicane strength • Stability and tolerance • Microbunching instability: CSRTrack/IMPACT simulation indicating emittance growth during the compression, higher BC1 energy helps (example: Swiss XFEL moved BC1 from 256 MeV to 350 MeV) LCLS-II Accel. Phys. , J. Wu, SLAC

  3. Hardware consideration • Cost benefit for locating BC1 @ 300 ~ 350 MeV • Gird 11-3 is now the positron source, and it will be either replaced by a chicane or accelerator structure • Putting BC1 on gird 11-3 and keep RF cavities for gird 11-2 will be cost effective • Future 360 Hz operation will be running with unSLEDed cavities • Setting BC1 @ 300 ~ 350 MeV for 120 Hz will make it possible to still have the option of having BC1 @ 250 MeV for 360 Hz operation • Setting BC1 @ 250 MeV for 120 Hz operation will make it necessary to have cavities on gird 11-1 be SLEDed. LCLS-II Accel. Phys. , J. Wu, SLAC

  4. Chicane setup • Assuming adding 200 MeV, so that the peak energy gain of is about 345 MeV between DL1 to BC1 (recall that for LCLS, it is about 145 MeV) • Keep setting the X-band at -160 degree, but vary the amplitude • One Example: setting BC1 energy @ 380 MeV and cancelling the second order curvature • L1S @ -21.8 degree (compared to ~ -22 degree) • L1X peak energy gain is 32.5 MeV (compared to ~ 20 MeV for LCLS) LCLS-II Accel. Phys. , J. Wu, SLAC

  5. Basic consideration Generic two bunch compressors system: after BC2 LCLS-II Accel. Phys. , J. Wu, SLAC

  6. optimization Jitter model: normal distribution for the LINAC phases LCLS-II Accel. Phys. , J. Wu, SLAC

  7. optimization Objective function: including de-chirping in L3 LCLS-II Accel. Phys. , J. Wu, SLAC

  8. optimization Analytically complete the integrals LCLS-II Accel. Phys. , J. Wu, SLAC

  9. optimization Close form for the objective function with weight function: Wi,0 LCLS-II Accel. Phys. , J. Wu, SLAC

  10. Layout • BC1 @ 250 MeV • Set points • BC1: R56 = 45.5 mm, Energy 250 MeV, peak current 250 Amp • L1S: – 22 degree • L1X: – 160 degree; 20 MeV • L2: – 35.6 degree • BC2: R56 = 25.2 mm, Energy 4.3 GeV, peak current 3 kA wire scanner 4 wire-scanners L0 L1X L1S gun DL1 135 MeV BC1 250 MeV BC2 4.3 GeV TCAV3 5.0 GeV BSY 14 GeV L3-linac L2-linac LCLS-II Accel. Phys. , J. Wu, SLAC

  11. Profiles BC1 Final CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008] LCLS-II Accel. Phys. , J. Wu, SLAC

  12. Layout • BC1 @ 335 MeV • Set points • BC1: R56 = 39.5 mm, Energy 335 MeV, peak current 220 Amp • L1S: – 19.5 degree • L1X: – 160 degree; 30 MeV • L2: – 31.8 degree • BC2: R56 = 26.2 mm, Energy 4.3 GeV, peak current 3 kA wire scanner 4 wire-scanners L0 L1X L1S gun DL1 135 MeV BC1 335 MeV BC2 4.3 GeV TCAV3 5.0 GeV BSY 14 GeV L3-linac L2-linac LCLS-II Accel. Phys. , J. Wu, SLAC

  13. Profiles BC1 Final CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008] LCLS-II Accel. Phys. , J. Wu, SLAC

  14. emittance Example for BC1 @ 335 MeV: Impactsimulation BC1 compressing to 250 Amp peak current does not see much slice emittance growth LCLS-II Accel. Phys. , J. Wu, SLAC

  15. Layout • BC1 @ 380 MeV • Set points • BC1: R56 = 36.2 mm, Energy 380 MeV, peak current 300 Amp • L1S: – 21.8 degree • L1X: – 160 degree; 32.5 MeV • L2: – 29.6 degree • BC2: R56 = 25.7 mm, Energy 4.3 GeV, peak current 3 kA wire scanner 4 wire-scanners L0 L1X L1S gun DL1 135 MeV BC1 380 MeV BC2 4.3 GeV TCAV3 5.0 GeV BSY 14 GeV L3-linac L2-linac LCLS-II Accel. Phys. , J. Wu, SLAC

  16. Profiles BC1 Final CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008] LCLS-II Accel. Phys. , J. Wu, SLAC

  17. Tolerance Assuming L1S has 0.06 degree rms phase jitter BC1 @ 250 MeV BC1 @ 380 MeV 1.36 % 3.95 % LCLS-II Accel. Phys. , J. Wu, SLAC

  18. Tolerance Assuming injector has 200 fsrms timing jitter BC1 @ 250 MeV BC1 @ 380 MeV 5.04 % 2.77 % LCLS-II Accel. Phys. , J. Wu, SLAC

  19. discussion • Linear compression study with optimization for BC1 @ 300 -- 350 MeV up to bypass line • Longitudinal profile up to bypass line • Tolerance study: peak current on timing and LINAC phase jitter up to bypass line • Transverse emittance degradation and microbunching instability with BC1 @ 335 MeV up to @ BC1 do not show much difference compared to the previous design with BC1 @ 250 MeV • Full machine lattice in Impact code is on going • Strong focusing on sec. 11-2 • BC1 dipole strength: keeping same R56 will increase the B-field by 40 %, assuming same angle, same length • More tolerance study is needed: centroid energy, chirp, etc. LCLS-II Accel. Phys. , J. Wu, SLAC

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