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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

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

layout
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

hardware consideration
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

chicane setup
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

basic consideration
Basic consideration

Generic two bunch compressors system: after BC2

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

optimization
optimization

Jitter model: normal distribution for the LINAC phases

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

optimization1
optimization

Objective function: including de-chirping in L3

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

optimization2
optimization

Analytically complete the integrals

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

optimization3
optimization

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

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

layout1
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

profiles
Profiles

BC1

Final

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

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

layout2
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

profiles1
Profiles

BC1

Final

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

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

emittance
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

layout3
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

profiles2
Profiles

BC1

Final

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

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

tolerance
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

tolerance1
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

slide19

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