LCLS FEL Parameters Heinz-Dieter Nuhn, SLAC / SSRL April 23, 2002 SASE Introduction Overview of Main LCLS Components Gun Linac (Bunch Compression) Undulator (Structure, Focusing) Baseline Parameters FEL Performance LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

SASE FELs SASE FEL theory well developed and verified by simulations FEL radiation starts from noise in spontaneous radiation Transverse radiation electric field modulates the energy and bunches the electrons within an optical wavelength Exponential build-up of radiation along undulator length Saturation Exponential Gain Regime Undulator Regime 1 % of X-Ray Pulse Electron Bunch Micro-Bunching LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Operational Range Operation will take place at any wavelength in the range 1.5 Å – 15 Å This will be accomplished by an adjustment of electron beam acceleration to values in the range 14.35 GeV – 4.54 GeV LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Relevance of Slice Emittance Primary FEL interaction between electrons and radiation field is local. Each electron is affected only by radiation field at electron’s current location. New radiation field is produced at electron’s location and travels with the electron. “Slippage” between electrons and radiation field in the undulator extend interation interval. “Slippage” causes the electrons to fall behind one optical wavelength for every undulator traveled Electrons are affected by radiation produced earlier by electrons closer to the tail of the bunch Maximum interaction interval not larger than maximum “slippage” in undulator length Lu Lslip = ( Lu / lu ) × lr (0.5 mm at 1.5 Å, 5 mm at 15 Å) Interaction interval reduced In exponential gain regime to cooperation length LC, i.e., to “slippage” in power gain length LG LC = ( LG / lu ) × lr (0.02 mm at 1.5 Å, 0.2 mm at 15 Å) Amplitude of earlier radiation becomes neglegible compared to more recent radiation. FEL performance for an interaction interval (or slice) only dependent on slice parameters Slice emittance, Slice energy spread, Peak Current in a slice, Average slice energy Distant slices might produce different radiation characteristics. Slices will saturate over the length of the undulator if slice parameters are sufficient. LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Goal Values for LCLS Beam Parameters Parameter Location LCLS Goal Values* Normalized Slice Emittance Injector (@150 MeV) 1.0 mm mrad (RMS) Undulator Entrance 1.2 mm mrad (RMS) Normalized Projected Emittance Injector (@150 MeV) 1.2 mm mrad (RMS) Undulator Entrance 1.5 mm mrad (RMS) Slice Energy Spread Injector (@150 MeV) <0.01 % (RMS) Undulator Entrance <0.01 % (RMS) Projected Energy Spread Undulator Entrance 0.06 % (RMS) *At a peak current of 3400 A at the undulator LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS: System Components SLAC linac tunnel Undulator Hall Linac-0 L =6 m Linac-1 L =9 m Linac-2 L =330 m Linac-3 L =550 m BC-1 BC-2 L =22 m DL-2 L =66 m DL-1 L =12 m Undulator L =121.8 m 7 MeV z  0.83 mm   0.2 % 150 MeV   0.10 % 250 MeV z  0.19 mm   1.8 % 4.54 GeV z  0.023 mm   0.76 % 4.54-14.35 GeV   0.02 % ...existing linac new RF Gun 25-1a 30-8c 21-1b 21-1d X Linac-X L =0.6 m 21-3b 24-6d Beam Dump Exp Halls 1.5 Å 8 GW 15 Å 17 GW => Talk by P. Emma LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

=> Talks in Breakout Session for Subgroup 1./2. RF Photo-Cathode Gun “Half” Cell Laser Port Normalized Slice Emittance: 1 mm rad (rms) Max Bunch Charge: 1 nC Bunch Length: 0.8 mm => Talks in Breakout Session for Subgroup 1./2. Full Cell Electron Beam Exit Photocathode LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Linac Acceleration and Magnetic Bunch Compression Initial Energy: 7 MeV Final Energy: 4.54 – 14.35 GeV Initial Bunch Length: 0.8 mm Final Bunch Length: 0.023 mm Number of Compressors: 2 Total Compression Factor: 35 DE/E z 2sz0 DE/E z DE/E z 2sz Under-compression Over-compression => Talk by P. Emma V = V0sin(wt) RF Accelerating Voltage Dz = R56DE/E Path Length-Energy Dependent Beamline LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

=> Talk by E. Gluskin Breakout Session for Subgroup 2. LCLS Undulator Space for X-Ray Diagnostics QD QF Beam Position Monitor (BPM) Undulator Segment Length 3.42 m Vacuum Pump Vacuum Chamber 5 mm ID / 5.6 mm OD 121 m Length Electron an X-Ray Beams Magnet Gap 6 mm => Talk by E. Gluskin Breakout Session for Subgroup 2. Va Permendur NdFeB LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Basic Undulator Parameters Undulator Type planar hybrid Magnet Material NdFeB Gap 6 mm Period Length 3 cm Peak On-Axis Field 1.32 T K 3.71 Segment Length 3.42 m Number of Segments 33 Segment Break Lengths 0.187-0.421 m Undulator Magnet Length 112.8 m Undulator Device Length (incl. Breaks) 121.1 m Undulator Filling Factor 93 % LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS Optimum b-Function at Short Wavelength Energy = 14.35 GeV Operational <b > = 18.0 m lr = 1.5  Å lu = 3.0 cm Bu = 1.32 T Optimum Beta-Function LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS Average b-Function <b> < b > predicted for LCLS < b > for minimum saturation length LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS Optimum b-Function at Long Wavelength Energy = 4.54 GeV Operational <b > = 7.3 m lr = 15.0  Å lu = 3.0 cm Bu = 1.32 T Optimum Beta-Function Reduced at the Longer Wavelength End LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

=> Talk by E. Gluskin and Undulator Breakout Session FODO Optics Break Lengths S S L S S L => Talk by E. Gluskin and Undulator Breakout Session Energy 14.35 GeV <b > = 18.0 m bmax = 21.9 m bmin = 14.0 m (bmax- bmin)/(bmax+ bmin)= 0.22 Superperiod LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

FODO Optics Energy 4.54 GeV <b > = 7.3 m bmax = 12.4 m Break Lengths S S L S S L Energy 4.54 GeV <b > = 7.3 m bmax = 12.4 m bmin = 2.5 m (bmax- bmin)/(bmax+ bmin)= 0.66 Superperiod LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Start-to-End Tracking Simulations => Talks by P. Emma and S. Reiche LCLS Simulations No Undulator Wakefields Including Undulator Wakefields Energy = 14.35 GeV Wavelength = 1.5  Å Start-to-End Tracking Simulations => Talks by P. Emma and S. Reiche Parmela Elegant Genesis space-charge compression, wakes, CSR, … SASE FEL with wakes LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Selected LCLS Baseline Design Parameters Fundamental FEL Radiation Wavelength 1.5 15 Å Electron Beam Energy 14.3 4.5 GeV Normalized RMS Slice Emittance 1.2 1.2 mm-mrad Peak Current 3.4 3.4 kA Bunch/Pulse Length (FWHM) 230 230 fs Relative Slice Energy Spread @ Entrance <0.01 0.025 % Saturation Length 87 25 m FEL Fundamental Saturation Power @ Exit 8 17 GW FEL Photons per Pulse 1.1 29 1012 Peak Brightness @ Undulator Exit 0.8 0.06 1033 * Transverse Coherence Full Full RMS Slice X-Ray Bandwidth 0.06 0.24 % RMS Projected X-Ray Bandwidth 0.13 0.47 % * photons/sec/mm2/mrad2/ 0.1%-BW LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS Working at the Short Wavelength End Extendable Undulator Length Available Undulator Length 2.0 mm mrad 1.7 mm mrad 1.2 mm mrad Nominal Working Point Saturation predicted 30 m before undulator end Space for Undulator Extension Available if needed. Length of Dogleg 2 65.518 m Length of Extension Space 30.969 m Length of Undulator 121.045 m LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

LCLS Working at the Long Wavelength End Nominal Working Point Strongly reduced requirements for electron beam parameters to achieve saturation before end of undulator. LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL

Summary A consistent reference set of LCLS parameters is the basis of the CDR. The LCLS reference parameters describe a light source that exceeds existing devices by many order of magnitude in brilliance and that produces x-ray pulse with sub-picosecond pulse length. LCLS DOE Review, April 23, 2002 Heinz-Dieter Nuhn, SLAC / SSRL