1. J. Wu J. Wu working with T.O. Raubenheimer, J. Qiang (LBL), LCLS-II Accelerator Physics meeting April 11, 2012 Study on the BC1 Energy Set Point 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 BC 2 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: W i,0 LCLS-II Accel. Phys., J. Wu, SLAC

10. LAYOUT BC1 @ 250 MeV Set points BC1: R 56 = 45.5 mm, Energy 250 MeV, peak current 250 Amp L1S: – 22 degree L1X: – 160 degree; 20 MeV L2: – 35.6 degree BC2: R 56 = 25.2 mm, Energy 4.3 GeV, peak current 3 kA LCLS-II Accel. Phys., J. Wu, SLAC BC2 4.3 GeV BSY 14 GeV TCAV3 5.0 GeV BC1 250 MeV L1S wirescanner L1X 4 wire-scanners L2-linac L3-linac DL1 135 MeV L0 gun

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

12. LAYOUT BC1 @ 335 MeV Set points BC1: R 56 = 39.5 mm, Energy 335 MeV, peak current 220 Amp L1S: – 19.5 degree L1X: – 160 degree; 30 MeV L2: – 31.8 degree BC2: R 56 = 26.2 mm, Energy 4.3 GeV, peak current 3 kA LCLS-II Accel. Phys., J. Wu, SLAC BC2 4.3 GeV BSY 14 GeV TCAV3 5.0 GeV BC1 335 MeV L1S wirescanner L1X 4 wire-scanners L2-linac L3-linac DL1 135 MeV L0 gun

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

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

15. LAYOUT BC1 @ 380 MeV Set points BC1: R 56 = 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: R 56 = 25.7 mm, Energy 4.3 GeV, peak current 3 kA LCLS-II Accel. Phys., J. Wu, SLAC BC2 4.3 GeV BSY 14 GeV TCAV3 5.0 GeV BC1 380 MeV L1S wirescanner L1X 4 wire-scanners L2-linac L3-linac DL1 135 MeV L0 gun

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

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

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

19. Linear compression study with optimization for BC1 @ 300 -- 350 MeV up to bypass line Linear compression study with optimization for BC1 @ 300 -- 350 MeV up to bypass line Longitudinal profile up to bypass line Longitudinal profile up to bypass line Tolerance study: peak current on timing and LINAC phase jitter 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 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 R 56 will increase the B- field by 40 %, assuming same angle, same length  More tolerance study is needed: centroid energy, chirp, etc. DISCUSSION LCLS-II Accel. Phys., J. Wu, SLAC