Breakout Sessions SC1/SC2 – Accelerator Physics

1. Breakout Sessions SC1/SC2 – Accelerator Physics E-Beam Diagnostics Overview P. Krejcik

2. Diagnostics Roadmap • Setup • Tuning • Beam size • resolution • Emittance • Energy spread Bunch charge F E E D B A C K • Trajectory • resolution • Position • Angle • Energy • Slice parameters • resolution • Emittance • Energy spread • Bunch length & DT • development • Longit. profile • Single shot rms Noninvasive Invasive • Stabilization • response • Jitter characterization 120 Hz

3. Recent Workshop on Diagnostics and Timing: ICFA Future Light Sources Subpanel Miniworkshop on XFEL Short Bunch Measurement and TimingStanford Linear Accelerator Center, July 26 - 30, 2004 http://www-ssrl.slac.stanford.edu/lcls/xfel2004/index.html

4. 5 Emittance gex,y measurements (Profs, Wire Scanners) : * See also P. Emma talk how optics is optimized for diagnostics 3 prof. mon.’s (Dyx,y = 60°) Accelerator System Diagnostics* • 180 BPMs at quadrupoles and in each bend system 8 Energy (BPM) E, energy spread (Prof) sE measurements : 2 Transverse RF deflecting Cavities for slice measurements 5 Bunch length monitors RF gun L0 L1 L2 L3 X upstream linac BC1 BC2 DL1 DL2 undulator LTU Dump

5. Beam Position Monitoring requirements

6. Linac stripline BPMs • Need to replace old BPM electronics • Commercially available processing units look promising • Beam testing of module as soon as funding available • Test new BPM fabrication techniques http://www.i-tech.si

7. Cavity beam position monitors for the undulator and LTU R&D at SLAC – S. Smith Coordinate measuring machine verification of cavity interior • X-band cavity shown • Dipole-mode couplers • X-band cavity shown • Dipole-mode couplers NLC studies of cavity BPMs, S. Smith et al

8. C-band beam tests of the cavity BPM – S. Smith cavity BPM signal versus predicted position at bunch charge 1.6 nC 25 mm • Raw digitizer records from beam measurements at ATF 200 nm • plot of residual deviation from linear response • << 1 mm LCLS resolution requirement • C-band chosen for compatibility with wireless communications technology

9. Beam Size Measurement • Wire scanners, based on existing SLAC systems • Measures average projected emittance • But is minimally invasive and can be automated for regular monitoring • Profile monitors • Single shot, full transverse profile • YAG screen in the injector for greater intensity • OTR screens in the linac and LTU for high resolution • 1 mm foils successfully tested in the SPPS: • Small emittance increase disrupts FEL, • but no beam loss • -1:1 imaging optics => ~ 9 mm resolution • Used in combination with TCAV • for slice energy spread and emittance • CTR for bunch length measurement OTR image taken in the SPPS Courtesy M. Hogan, P. Muggli et al

10. Bunch length diagnostic comparison

11. Bunch length reconstruction Measure streak at 3 different phases sz = 90 mm Cavity on s s y y Cavity on - 180° (Streak size)2 Cavity off Asymmetric parabola indicates incoming tilt to beam Bunch Length Measurements with the RF Transverse Deflecting Cavity 30 MW 2.4 m

12. Beam centroid [pixels] Cavity phase [deg. S-Band] Calibration scan for RF transverse deflecting cavity • Bunch length calibrated in units of the wavelength of the S-band RF • Further requirements for LCLS: • High resolution OTR screen • Wide angle, linear view optics

13. OTR Profile Monitor in combination withRF Transverse Deflecting Cavity Simulated digitized video image Injector DL1 beam line is shown Best resolution for slice energy spread measurement would be in adjacent spectrometer beam line.

14. BC1 Bunch Length Monitor- based on coherent spectral power detection 400 GHz 1.2 mm CSR Power spectral density signal for bunch length feedback Spectral lines accompanying micro-bunching instability – Z. Huang.

15. BC2 Bunch length monitor spectrum- based on coherent spectral power detection BC2 bunch length feedback requires THz CSR detector Demonstrated with CTR at SPPS 4 THz main peak

16. Interferometer for autocorrelation of CTR- tests at SPPS 12 mm rms Transition radiation is coherent at wavelengths longer than the bunch length, l>(2p)1/2sz Limited by long wavelength cutoff and absorption resonances P. Muggli, M. Hogan

17. Dither feedback control of bunch length minimization at SPPS - L. Hendrickson Bunch length monitor response Feedback correction signal “ping” optimum Linac phase Jitter in bunch length signal over 10 seconds ~10% rms Dither time steps of 10 seconds

18. Bunch length and arrival time from Electro Optic measurements at SPPS A. Cavalieri Principal of temporal-spatial correlation single pulse Line image camera EO xtal analyzer polarizer Er width centroid 30 seconds, 300 pulses: sz = 530 fs ± 56 fs rms Dt = 300 fs rms

19. Electro-Optical Sampling at SPPS – A. Cavalieri et al. <300 fs Single-Shot 200 mm thick ZnTe crystal Ti:Sapphire laser e- Timing Jitter 170 fs rms e- temporal information is encoded on transverse profile of laser beam

20. E E E Φrf(L2) Φrf(L3) Vrf(L1) DL1 sz Φrf(L1) sz E Φrf(L2) Vrf(L0) DL1 Spectr. BSY 50B1 BC2 BC1 DL2 L1 L2 L3 L0 Energy and Bunch Length Feedback Loops 4 energy feedback loops 2 bunch length feedback loops 120 Hz nominal operation, <1 pulse delay More detail given in breakout session SC5 talk on Controls

21. Undulator trajectory launch loop to operate at 120 Hz, <1 pulse delay Damps jitter below 10 Hz Linac orbit loops to operate at 10 Hz because of corrector response time Closed Loop Response of Orbit Feedback Antidamp Damp Gain bandwidth shown for different loop delays - L. Hendrickson

22. Summary • Diagnostics integrated into the LCLS design • All systems require attention to achieve LCLS resolution requirements • New diagnostics are being developed for bunch length and timing • Developmental work at SPPS is critical • Diagnostics being developed hand-in-hand with controls and feedbacks