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The LCLS energy jitter: sensitivities and tolerance. J. Wu Meeting on “reduction of LCLS linac energy jitter” October 24, 2012. Outline. Sensitivities are different for different charge, different compression Original CDR was devoted to 1 nC Operation is for 150 pC

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the lcls energy jitter sensitivities and tolerance

The LCLS energy jitter: sensitivities and tolerance

J. Wu

Meeting on “reduction of LCLS linac energy jitter”October 24, 2012

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

outline
Outline
  • Sensitivities are different for different charge, different compression
    • Original CDR was devoted to 1 nC
    • Operation is for 150 pC
    • Self-seeding is for 40 pC

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

lcls cdr
LCLS CDR

1 nC

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

lcls cdr1
LCLS CDR

1 nC

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

lcls cdr2
LCLS CDR

L1s -21.9o

L1s -22o

L1s -22.1o

150 pC: compressed to 3 kA

DE/E ~ 2.1E-04

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

lcls cdr3
LCLS CDR

L1s -27.9o

L1s -28o

L1s -28.1o

40 pC: compressed to 2 kA

DE/E ~ 2.8E-04

Ipk: 1-1.5 -2 kA

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

electron bunch profile
Electron bunch profile

L1s -21.9o

L1s -22o

L1s -22.1o

Elegant for LCLS (L1S RF phase jitter by ±0.1o)

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

electron bunch profile1
Electron bunch profile

Tail

Head

Elegant for LCLS (L1S RF phase jitter by ±0.1o)

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

electron bunch profile2
Electron bunch profile

Tail

Head

Elegant for LCLS (L1S RF phase jitter by ±0.1o)

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

40 pc
40 pC

Electron profile @ FEL operation point: vary from shot-to-shot

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

rf phase fluctuation
RF phase fluctuation

Taper starts @ 30 m with 0.4 %;

Seed: 1 MW

Different bunch compression, energy fixed

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

rf phase fluctuation1
RF phase fluctuation

Taper starts @ 30 m with 0.4 %;

Seed: 1 MW

Temporal profile

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

rf phase fluctuation2
RF phase fluctuation

Taper starts @ 30 m with 0.4 %;

Seed: 1 MW

spectrum

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

summary
Summary
  • In general, a seeded FEL tolerance on the seed properties, the RF jitter, the details of the current profile coupled to the collective effects, taper tolerance, etc. are much more demanding
  • Intrinsic fluctuation in power due to the SASE process in the seed generation
  • Other sources of seeded FEL jitter arise from energy, energy chirp, and beam distribution changes
  • Sensitivities can be measured, benchmark the existing measurement against simulation to validate the model
  • With this model, find a stable operation point given the hardware constraints.

FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu