1. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Comments from LCLS FAC Meeting (April 2004): J. Roßbach:“How do you detect weak FEL power when the gain is very low (few hundred)?” K. Robinson:“Can you modulate the laser heater in some way to help FEL signal detection?” Comments from LCLS FAC Meeting (April 2004): J. Roßbach:“How do you detect weak FEL power when the gain is very low (few hundred)?” K. Robinson:“Can you modulate the laser heater in some way to help FEL signal detection?” Laser-Heater Modulation P. Emma, Z. Huang, J. Wu

2. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004  P   370 kW (not 10 GW) 1.5-Å LCLS, but  x,y  3.6  m  Gain   470 LCLS with poor gain (large emittance, jitter, M. Xie model)

3. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 modulate laser power (1.2 to 19 MW @ 7 Hz) Kem Robinson idea… modulated slice energy spread (0.01% to 0.04% rms at 14 GeV) laser heater Laser Heater at 135 MeV

4. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Simulate LCLS (Linac + M. Xie) with linac jitter, large emittance (3  m), spontaneous radiation background, and laser-heater modulated at 7 Hz (or other unique frequency << 120 Hz) 1.5-Å LCLS, except  x,y = 3.6  m 2% rms charge jitter 0.5 ps rms gun-timing jitter 0.1-deg rms RF phase jitter (each of 4 linacs) 0.1% rms RF amplitude jitter (each of 4 linacs) 2% rms emittance jitter includes small emittance growth in laser-heater 10-MW spontaneous power (1% BW cut)* 10% rms radiation energy measurement noise fast, accurate 2 nd -order linac model in Matlab, with jitter

5. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Modulate Slice Energy Spread with Heater (Square-wave suggested by Gennady Stupakov) 7 Hz

6. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Effects of linac jitter & modulation bunch length energy spread peak current e  relative energy bunch arrival time

7. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 P < P sat : P > P sat : 1-D startup power: Use ‘Ming Xie’ model to calculate gain length, L g, then calculate power as: Assume 1% BW cut to get 10-MW spontaneous power (none)

8. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Red:Total power + meas. noise Magenta:Spontaneous power Green:FEL power

9. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004  x,y = 3.6  m 14.7 ± 4.1 m 0.029 ± 0.013 % 4.2 ± 0.6 kA 0 ± 0.088 % 1.0 ± 0.02 nC 21 ± 3.0  m L g  13-29 m

10. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 7 Hz FFT of total power + noise

11. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Enhanced Self-Amplified Spontaneous Emission A. Zholents b P. Emma a, W. Fawley b, Z. Huang a, S. Reiche c, G. Stupakov a, a) SLAC, b) LBNL, c) UCLA First proposed by A. Zholents (LBNL) Submitted to PRL LCLS study published in FEL’04 proc.

12. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Only one optical cycle is shown ESASE: “nuts and bolts” Energy modulation in wiggler at 4 GeV Laser peak power ~ 10 GWLaser peak power ~ 10 GW Wiggler with ~ 10 periodsWiggler with ~ 10 periods BunchingAccelerationModulation Peak current, I/I 0 z / L 50 fs laser pulse L = 2 microns L = 2 microns Electron beam after bunching at optical wavelengthElectron beam after bunching at optical wavelength 20-25 kA

13. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 The output x-ray radiation from a single micro- bunch Each spike is nearly temporally coherent and Fourier transform limited Each spike is nearly temporally coherent and Fourier transform limited Pulses less than 100 attoseconds may be possible with 800 nm laser Pulses less than 100 attoseconds may be possible with 800 nm laser ~200 as -200 -100 0 100 200

14. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 A schematic of the LCLS with ESASE SLAC linac tunnel research yard BC1BC2 LTU DL1 undulator L =130 m 6 MeV  z  0.83 mm 135 MeV  z  0.83 mm 250 MeV  z  0.19 mm 4.3 GeV  z  0.022 mm 13.6 GeV  z  0.022 mm...existing linac Linac-0 rfgun Linac-1 X Linac-2Linac-3 laser wiggler

15. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Beta and dispersion functions in the LCLS 3-m wiggler existing buncher

16. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Peak current, emittance and energy spread after linac  x  y

17. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 At undulator entrance: E = 14 GeV

18. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 FEL Simulations Genesis Ginger laser wavelength of 0.8 or 2.2 nm

19. P. Emma LCLS FAC Emma@SLAC.Stanford.edu 12 Oct. 2004 Summary Shorter gain length, higher power, ~same average power Adjustable x-ray pulse duration by changing laser pulse Nearly temporally coherent and transform limited radiation within spike with random carrier phase between spikes - solitary attosecond x-ray pulse Absolute synch. between laser pulse and x-ray pulse Relaxes emittance requirement Shorter x-ray wavelengths possible Better with smaller  (and closer und. quad spacing) Work on impedance issues ongoing (see FEL’04 proc.)