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

LAYOUT

Previously BC1 @ 250 MeV for LCLSPros and Cons of setting BC1 @ 300 ~ 350 MeV for LCLS-II

Hardware 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, SLAC

HARDWARE CONSIDERATION

Cost 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 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 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, SLAC

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 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, SLAC

BASIC CONSIDERATION

Generic two bunch compressors system: after BC2

LCLS-II Accel. Phys. , J. Wu, SLAC

OPTIMIZATION

Jitter model: normal distribution for the LINAC phases

LCLS-II Accel. Phys. , J. Wu, SLAC

OPTIMIZATION

Objective function: including de-chirping in L3

LCLS-II Accel. Phys. , J. Wu, SLAC

OPTIMIZATION

Analytically complete the integrals

LCLS-II Accel. Phys. , J. Wu, SLAC

OPTIMIZATION

Close form for the objective function with weight function: Wi,0

LCLS-II Accel. Phys. , J. Wu, SLAC

LAYOUT

BC1 @ 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 kA

LCLS-II Accel. Phys. , J. Wu, SLAC

BC24.3 GeV

BSY14 GeV

TCAV35.0 GeV

BC1250 MeV

L1S

wirescannerL1X

4 wire-scanners

L2-linac L3-linacDL1135 MeV

L0gun

PROFILES

BC1

LCLS-II Accel. Phys. , J. Wu, SLAC

Final

CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]

LAYOUT

BC1 @ 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 kA

LCLS-II Accel. Phys. , J. Wu, SLAC

BC24.3 GeV

BSY14 GeV

TCAV35.0 GeV

BC1335 MeV

L1S

wirescannerL1X

4 wire-scanners

L2-linac L3-linacDL1135 MeV

L0gun

PROFILES

BC1

LCLS-II Accel. Phys. , J. Wu, SLAC

Final

CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]

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

LAYOUT

BC1 @ 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 kA

LCLS-II Accel. Phys. , J. Wu, SLAC

BC24.3 GeV

BSY14 GeV

TCAV35.0 GeV

BC1380 MeV

L1S

wirescannerL1X

4 wire-scanners

L2-linac L3-linacDL1135 MeV

L0gun

PROFILES

BC1

LCLS-II Accel. Phys. , J. Wu, SLAC

Final

CSR, LSC included in LiTrack, good agreement with Elegant [Bosch, Kleman, Wu, PRSTAB, 2008]

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 %

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 %

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.

DISCUSSION

LCLS-II Accel. Phys. , J. Wu, SLAC