P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 LCLS - Accelerator System Overview Patrick Krejcik on behalf of the LCLS Team Stanford Linear Accelerator Center LCLS

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Ti:Sa laser RG Gun Laser Heater Upstream linac L0 Linac1 RF PhotoInjector 135 MeV  x,y = 1mm mrad, q=1 nC    0.05 %  z = 3ps,    0.05 % RF PhotoInjector 135 MeV  x,y = 1mm mrad, q=1 nC    0.05 %  z = 3ps,    0.05 % Linac2 Linac3 BC1 chicane 250 MeV  z = 0.63 ps BC1 chicane 250 MeV  z = 0.63 ps Existing SLAC structure warm, copper linac S-band 2856 MHz 120 Hz Existing SLAC structure warm, copper linac S-band 2856 MHz 120 Hz X-band harmonic cavity BC2 4.5 GeV  z = 0.07 ps BC2 4.5 GeV  z = 0.07 ps Undulator L =130 m Undulator L =130 m X-rays 1.5 Å LTU 14.1 GeV    0.01 %  z = 0.07 ps,    0.01 % LTU 14.1 GeV    0.01 %  z = 0.07 ps,    0.01 % 1 km LoLa transverse cavity

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Accelerator Issues in the SLAC Design Issues Low emittance injector Cold beam, low    0.05 % Bunch compression Coherent Synchrotron Radiation Longitudinal space charge Beam stability Issues Low emittance injector Cold beam, low    0.05 % Bunch compression Coherent Synchrotron Radiation Longitudinal space charge Beam stability Design solutions RF photoinjector Laser heater Two magnetic chicanes RF linearization with higher harmonic X-band cavity Diagnostics Fast feedback Design solutions RF photoinjector Laser heater Two magnetic chicanes RF linearization with higher harmonic X-band cavity Diagnostics Fast feedback

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 V rf Electron bunch S-band  rf = -25º Electron bunch S-band  rf = -25º energy time Electron bunch with higher energy tail …tail begins to catch up …fully compressed additional X-band  rf = -160º additional X-band  rf = -160º Bunch Compression Dynamics Longitudinal tracking with litrack – P. Emma Remove spike in distribution with addition of X-band

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Diagnostic challenges Measurement Measurement of ultra- short bunch profiles Shot-by-shot measurement of bunch length Bunch timing measurement Measurement Measurement of ultra- short bunch profiles Shot-by-shot measurement of bunch length Bunch timing measurement Devices RF transverse deflecting cavity “LOLA” Terahertz coherent spectral power measurement Coherent radiation autocorrelation Electro-optic bunch profiling Devices RF transverse deflecting cavity “LOLA” Terahertz coherent spectral power measurement Coherent radiation autocorrelation Electro-optic bunch profiling

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Bunch Length Measurements with the RF Transverse Deflecting Cavity   y y  Asymmetric parabola indicates incoming tilt to beam Cavity on Cavity off Cavity on - 180° Bunch length reconstruction Measure streak at 3 different phases  z = 90  m (Streak size) m 30 MW LoLa* An S-band DLW structure with a TM 11 transverse deflecting mode at 2856 MHz *Loew, Larsen 1964

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Accelerator Issues in the SLAC Design Issues Low emittance injector Cold beam, low    0.05 % Bunch compression Coherent Synchrotron Radiation Longitudinal space charge Beam stabilityIssues Low emittance injector Cold beam, low    0.05 % Bunch compression Coherent Synchrotron Radiation Longitudinal space charge Beam stability Design solutions RF photoinjector Laser heater Two magnetic chicanes RF linearization with higher harmonic X-band cavityDiagnostics Fast feedback Design solutions RF photoinjector Laser heater Two magnetic chicanes RF linearization with higher harmonic X-band cavityDiagnostics Fast feedback

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Limitation from Coherent Synchrotron Radiation r  z radiation coherent r  z radiation coherent Energy spread from CSR increases  x P. Emma With CSR:  /  0  14 no CSR: Limits compression hypothetical 1  m bunch CSR instability CSR instability amplifies noise in initial charge distribution S. Heifets, S. Krinsky, G. Stupakov, SLAC-PUB-9165, March 2002    3  10  6 Microbunching* and further emittance growth * First observed by M. Borland (ANL) in LCLS Elegant tracking

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Two-stage bunch compression approach – P. Emma Issues At low energies if bunch is compressed too much space charge spoils emittance At high energies if bunch is compressed too hard synchrotron radiation adds large energy spread Issues At low energies if bunch is compressed too much space charge spoils emittance At high energies if bunch is compressed too hard synchrotron radiation adds large energy spread Design solutions Compress in two stages Limit low energy compression so space charge not a limit Second compression to final bunch length at higher energy, but with weaker bends to limit synchrotron radiation. Design solutions Compress in two stages Limit low energy compression so space charge not a limit Second compression to final bunch length at higher energy, but with weaker bends to limit synchrotron radiation.

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Transition radiation is coherent at wavelengths longer than the bunch length, >(2  ) 1/2  z SLAC SPPS measurement: P. Muggli, M. Hogan Limited by long wavelength cutoff and absorption resonances  z  9  m Diagnosing Coherent Radiation 1. autocorrelation

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Diagnosing Coherent Radiation 2. spectral power Smooth Gaussian bunch spectrum from BC1 With 5% microbunching Measure bunch length Detect microbunching Measure bunch length Detect microbunching Fixed BW detector Signal prop. 1/  z Bunch length signal for RF feedback  - J. Wu

P. Krejcik LINAC 2004 – Lübeck, August 16-20, keV rms ‘Laser Heater’ for Landau Damping Z. Huang et al. PR ST AB, June 2004 Z. Huang et al. PR ST AB, June 2004 Ti:Sa 800 nm 1.2 MW Injector e- 135 MeV ‘Laser heater’ suggested by Saldin et al. heater ON 0.01 % heater OFF 0.1% Final energy distribution: Microbunch instability Damped IFEL energy modulation chicane energy mixing

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Electro-Optical Sampling at SPPS – A. Cavalieri et al. eeee Ti:Sapphire laser Single-Shot <300 fs 170 fs rms Timing Jitter ErEr Line image camera polarizer analyzer 200  m thick ZnTe crystal Pol. Laser pulse Electron bunch

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Energy and Bunch Length Feedback Loops 4 energy feedback loops 2 bunch length feedback loops 120 Hz nominal operation, <1 pulse delay 4 energy feedback loops 2 bunch length feedback loops 120 Hz nominal operation, <1 pulse delay Feedback model (J. Wu) PID controller (proportional, integral, derivative) Cascade control for sequential loops (off-diagonal matrix elements) Feedback model (J. Wu) PID controller (proportional, integral, derivative) Cascade control for sequential loops (off-diagonal matrix elements) L0 L1 DL1 Spectr. BC1 BC2 L2L3 BSY 50B1 DL2 V rf (L0) Φ rf (L2) V rf (L1) Φ rf (L3) EEE Φ rf (L2) zz Φ rf (L1) zz E

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Bode Plot (  E/E) P:0.2; I:0.5 P:0.2 Ø 3 different settings of the PID controller ØIntegral term dominant Ø 3 different settings of the PID controller ØIntegral term dominant I:0.5 Energy feedback loop response - J. Wu P. Emma

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Bode Plot (  I/I) P:0.2; I:0.5 P:0.2 Ø 3 different settings of the PID controller ØIntegral term dominant Ø 3 different settings of the PID controller ØIntegral term dominant I:0.5 Bunch length feedback loop response - J. Wu P. Emma

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Summary Design optimized for emittance preservation Minimize disruption from strong self-fields of the bunch Two-stage compression Laser heater reduces instabilities Diagnostics and feedback integral part of design Future expansion to multiple sase beamlines New possibilities include enhanced sase and ultra- short bunches! Design optimized for emittance preservation Minimize disruption from strong self-fields of the bunch Two-stage compression Laser heater reduces instabilities Diagnostics and feedback integral part of design Future expansion to multiple sase beamlines New possibilities include enhanced sase and ultra- short bunches!

P. Krejcik LINAC 2004 – Lübeck, August 16-20, 2004 Acknowledgements R. Akre A. Cavalieri E. Bong D. Dowell P. Emma Z. Huang C. Limborg-Duprey J. Wu And many others! R. Akre A. Cavalieri E. Bong D. Dowell P. Emma Z. Huang C. Limborg-Duprey J. Wu And many others! and thank you to the LINAC 2004 organization