Slide 1

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, SLAC1LayoutPreviously BC1 @ 250 MeV for LCLSPros and Cons of setting BC1 @ 300 ~ 350 MeV for LCLS-IIHardware consideration: cost and future 360 Hz operationMacroscopic: chicane strengthStability and toleranceMicrobunching 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, SLACHardware considerationCost benefit for locating BC1 @ 300 ~ 350 MeVGird 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 cavitiesSetting BC1 @ 300 ~ 350 MeV for 120 Hz will make it possible to still have the option of having BC1 @ 250 MeV for 360 Hz operationSetting 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, SLACChicane setupAssuming 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 amplitudeOne 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, SLACBasic considerationGeneric two bunch compressors system: after BC2LCLS-II Accel. Phys. , J. Wu, SLAC

optimizationJitter model: normal distribution for the LINAC phasesLCLS-II Accel. Phys. , J. Wu, SLAC

optimizationObjective function: including de-chirping in L3LCLS-II Accel. Phys. , J. Wu, SLAC

optimizationAnalytically complete the integralsLCLS-II Accel. Phys. , J. Wu, SLAC

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

LayoutBC1 @ 250 MeV

Set pointsBC1: R56 = 45.5 mm, Energy 250 MeV, peak current 250 AmpL1S: 22 degreeL1X: 160 degree; 20 MeVL2: 35.6 degreeBC2: R56 = 25.2 mm, Energy 4.3 GeV, peak current 3 kALCLS-II Accel. Phys. , J. Wu, SLACBC24.3 GeVBSY14 GeVTCAV35.0 GeVBC1250 MeVL1SwirescannerL1X4 wire-scannersL2-linacL3-linacDL1135 MeVL0gunProfilesBC1LCLS-II Accel. Phys. , J. Wu, SLAC

FinalCSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]LayoutBC1 @ 335 MeV

Set pointsBC1: R56 = 39.5 mm, Energy 335 MeV, peak current 220 AmpL1S: 19.5 degreeL1X: 160 degree; 30 MeVL2: 31.8 degreeBC2: R56 = 26.2 mm, Energy 4.3 GeV, peak current 3 kALCLS-II Accel. Phys. , J. Wu, SLACBC24.3 GeVBSY14 GeVTCAV35.0 GeVBC1335 MeVL1SwirescannerL1X4 wire-scannersL2-linacL3-linacDL1135 MeVL0gunProfilesBC1LCLS-II Accel. Phys. , J. Wu, SLACFinalCSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]

emittanceBC1 compressing to 250 Amp peak current does not see much slice emittance growthLCLS-II Accel. Phys. , J. Wu, SLACExample for BC1 @ 335 MeV: Impact simulation

LayoutBC1 @ 380 MeV

Set pointsBC1: R56 = 36.2 mm, Energy 380 MeV, peak current 300 AmpL1S: 21.8 degreeL1X: 160 degree; 32.5 MeVL2: 29.6 degreeBC2: R56 = 25.7 mm, Energy 4.3 GeV, peak current 3 kALCLS-II Accel. Phys. , J. Wu, SLACBC24.3 GeVBSY14 GeVTCAV35.0 GeVBC1380 MeVL1SwirescannerL1X4 wire-scannersL2-linacL3-linacDL1135 MeVL0gunProfilesBC1LCLS-II Accel. Phys. , J. Wu, SLACFinalCSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]

ToleranceBC1 @ 250 MeVLCLS-II Accel. Phys. , J. Wu, SLACBC1 @ 380 MeV3.95 %Assuming L1S has 0.06 degree rms phase jitter1.36 %

ToleranceBC1 @ 250 MeVLCLS-II Accel. Phys. , J. Wu, SLACBC1 @ 380 MeV2.77 %Assuming injector has 200 fs rms timing jitter5.04 %Linear compression study with optimization for BC1 @ 300 -- 350 MeV up to bypass lineLongitudinal profile up to bypass lineTolerance study: peak current on timing and LINAC phase jitter up to bypass lineTransverse 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 MeVFull machine lattice in Impact code is on goingStrong focusing on sec. 11-2BC1 dipole strength: keeping same R56 will increase the B-field by 40 %, assuming same angle, same lengthMore tolerance study is needed: centroid energy, chirp, etc.discussionLCLS-II Accel. Phys. , J. Wu, SLAC19