1. 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

2. 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

3. LCLS CDR 1 nC FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

4. LCLS CDR 1 nC FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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