Accelerator Issues and Design LCLS Design of Compression and Acceleration Systems Technical Challenges
Download ReportTranscript Accelerator Issues and Design LCLS Design of Compression and Acceleration Systems Technical Challenges
Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Accelerator Issues and Design Paul Emma, SLAC Dec. 12, 2003 Design of Compression and Acceleration Systems Technical Challenges Full System Simulations LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design LCLS Paul Emma, SLAC [email protected] ‘ Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center ‘Slice’ versus ‘Projected’ Emittance For a collider… collision integrates over bunch length — ‘projected’ emittance is important For an FEL… e- slips back w.r.t. photons by lr (= 1.5 Å) per period lu …FEL integrates over slippage length: ‘slice’ emittance is important LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design lr Nlr 0.5 mm Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center SASE X-ray FEL is very sensitive to electron ‘slice’ emittance eN = 1.2 mm eN = 2.1 mm P 10 GW P 0.1 GW lr = 1.5 Å courtesy S. Reiche Instead of mild luminosity loss, power nearly switches OFF. However, longer wavelength, such as 15 Å (4.5 GeV), is much easier (eN 6 mm). LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Nominal System Design 1.5-Å SASE FEL Linac: Requirements Acceleration to 14.1 GeV (~3 GeV min.) Bunch compression to 3.4 kA Emittance preservation (<20% ‘slice’ of 1-mm-mrad) Final energy spread (0.01% ‘slice’, <0.1% ‘projected’) Minimal sensitivity to system ‘jitter’ (charge, phase, voltage, ...) Diagnostics integrated into optics Flexible operations (1.5 Å →15 Å, low-charge, chirp, etc.) use 2 compressors, 3 linacs LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Nominal System Design Constraints Use existing SLAC linac compatible with PEP-II operation Undulator located beyond research yard 1 km LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS versus SLC LCLS Advantages Shorter linac (1 km < 3 km) Shorter bunch in linac (1 mm → 0.2 mm → 0.02 mm) Lower charge (1 nC < 7 nC) ‘Slice’ emittance important, not projected No positrons, no sextupoles, no rolls, no DR’s, no RTL’s, no arcs Round beams (no x-y coupling issues) Disadvantages Lower initial linac energy (135 MeV < 1.2 GeV) Smaller emittance (1/1 mm < 4/40 mm) Emittance more critical (>2 mm kills FEL power) Tighter RF, charge, & timing jitter tol’s (~0.1 deg) CSR is new issue RF gun less stable platform than damping ring LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Design Strategy Design longitudinal optics first Set proper compression in two stages Minimize final energy spread Minimize Ipk and Ef sensitivity to gun charge and timing jitter Design transverse optics second Minimize transverse wakefields, CSR, and chromatic effects Build in emittance, energy spread, bunch-length diagnostics Track entire system Iterate design LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Nominal LCLS Linac Parameters for 1.5-Å FEL Single bunch, 1-nC charge, 1.2-mm slice emittance, 120-Hz repetition rate… 6 MeV z 0.83 mm 0.05 % 250 MeV z 0.19 mm 1.6 % Linac-X L =0.6 m rf= -160 4.54 GeV z 0.022 mm 0.71 % 135 MeV z 0.83 mm 0.10 % rf gun Linac-1 L 9 m rf -25° Linac-0 L =6 m ...existing linac 21-1b 21-1d DL-1 L 12 m R56 0 X Linac-2 L 330 m rf -41° Linac-3 L 550 m rf -10° 21-3b 24-6d 25-1a 30-8c BC-1 L 6 m R56 -39 mm SLAC linac tunnel BC-2 L 22 m R56 -25 mm 14.1 GeV z 0.022 mm 0.01 % undulator L =125 m LTU L =275 m R56 0 research yard (RF phase: frf = 0 at accelerating crest) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center RMS Bunch Length and Energy Spread sector-21 sector-25 sector-30 FFTB++ z LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center after L2 energy profile phase space time profile after DL1 z = 830 mm after L1 z = 190 mm after BC2 z = 830 mm after X-RF z = 23 mm after L3 z = 830 mm after BC1 z = 23 mm at und. z = 190 mm LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design FINAL z = 23 mm Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center X-band RF used to Linearize Compression (f = 11.424 GHz) S-band RF curvature and 2nd-order momentum compaction cause sharp peak current spike X-band RF at decelerating phase corrects 2ndorder and allows unchanged z-distribution lx = ls/4 1 -40° Slope linearized x = p avoid! 1 ls2T566 E0 1 - 2 1 - z z0 3 R56 2p eVx = ls lx 2 - 1 LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design 2 - Ei 0.6-m section, 19 MV available at SLAC (200-mm alignment) Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Transverse Wakefields and Component Misalignments Choose b-phase adv/cell for each linac to minimize emittance dilution: L2 phase adv/cell optimized L3 phase adv/cell optimized z = 195 mm z = 22 mm x also misaligned quads/BPMs generate dispersion De wakes on wakes on wakes off wakes off LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Transverse Optics from Cathode to e- Dump LCLS MAD Deck Cathode to e- Dump (2200 elements) Dyx,y 75º Dyx,y 30º Thanks to M. Woodley LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center RMS Transverse Beam Sizes from Cathode to e- Dump 4.0 mm (BC1) 2.6 mm (BC2) 1 mm 100 mm undulator 10 mm LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Alignment and Roll Tolerances (most > 1 mm, > 1 deg) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac RF Section Modifications If modulators on 20-6, -7, and -8 used for injector, lose another 670 MeV (1.56 GeV total) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Injector to Linac Interface courtesy L. Bentson “Linac” Responsibility Starts Here (21-1b) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac-1 Through BC1 21-1b LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design 21-1c 21-1d 21-3b Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center BC2 Area 24-6d LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design 25-1a Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Moveable Chicanes (BC1 shown) BPM critical for energy feedback (20 mm resolution) collimator BPM offset: 17 to 30 cm (24 cm nominal) quadrupole screen 3 cm contraction collimator BPM screen LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Field quality requirement too tight with fixed chicane... b2 x 2 B y = b0 1 2 b0 r 45 mm Also needed: • • • • 80 mm 12 mm BPM res. 20 mm BPM linearity profile monitor collimator x requires: |b2/b0| < 0.002% @ r = 2 cm (moveable chicane requires 0.070%) SPPS dipoles: |b2/b0| < 0.010% @ 2 cm (just barely met) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Future Multiple Undulators +4º +2º N S -2º LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac-To-Undulator (LTU) vertical bends energy centroid & spread meas. (310-5 & 10-4) + collimation 4 e-wires, 6 collimators LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design • • • • • • • vertical bend 4.7 mrad horizontal jog 1.25 m energy diagnostics emittance diagnostics collimators CSR cancellation branch points for future undulators • spontaneous undulator possible Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Collimation for Undulator Protection CE1 Dx mm 5.0 Dy mm - CE2 5.0 - CX1 2.0 - CY1 - 2.0 CX2 2.0 - CY2 - 2.0 Coll. 2.5 mm well shadowed in x, y, and E LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Electron Dump x-rays → quads soft bend permanent powered vert. bends vert. bends hy quad by screen (E/E = 10-5 5 mm) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Specification Sheets on Every New Magnet BX01 DL1 dipole: • z-location • field • current • trim info. • alignment tol.’s • length • max/min strength • etc... LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Technical Challenges Coherent Synchrotron Radiation in Bends projected emittance growth micro-bunching instability (+ LSC — see Z. Huang talk) Emittance Preservation in Linacs transverse wakefields misalignments & chromaticity Machine Stability gun and rf system jitter energy and bunch length feedback LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design LCLS Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Coherent Synchrotron Radiation coherent power N 6109 ~l-1/3 incoherent power z LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design vacuum chamber cutoff Paul Emma, SLAC [email protected] Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Coherent Synchrotron Radiation (CSR) Powerful radiation generates energy spread in bends Induced energy spread breaks achromatic system Causes bend-plane emittance growth (short bunch is worse) coherent radiation for l > z z bend-plane emittance growth l L0 e– s DE/E = 0 Dx DE/E < 0 R overtaking length: L0 (24zR2)1/3 LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Dx = R16(s)DE/E Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Coherent Synchrotron Radiation (CSR) in SPPS Chicane OFF gex = 27.6 0.6 mm LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Chicane ON gex = 34.2 0.7 mm Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Coherent Synchrotron Radiation (CSR) in SPPS Bend-plane emittance is consistent with calculations and sets upper limit on CSR effect LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source CSR Micro-bunching* CSR amplifies small modulations on bunch current Successive bend-systems cause micro-bunching Growth of slice-energy spread & emittance. Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center S. Heifets, S. Krinsky, G. Stupakov, SLAC-PUB-9165, March 2002 without heater 310-6 avoid! 230 fsec Add slice energy spread to Landau damp instability. energy spread damps bunching 310-5 ‘Laser-Heater’ see Z. Huang talk * First observed by M. Borland (ANL) in LCLS Elegant tracking LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Misalignments, Steering, and Emittance Correction trajectory after steering BPM, quad, and RF misalignments: (each at 300 mm rms)... then steered in Elegant gex 5 mm gey 2 mm LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Emittance Correction with Trajectory ‘Bumps’ steering coils 100 seeds De/e 15% gex 1.02 mm gey 1.09 mm Thanks to M. Borland (ANL/APS) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Jitter Budget (<1 minute time-scale) measured RF performance klystron phase rms 0.07° (20 sec) X-band X- klystron ampl. rms 0.06% (60 sec) LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Start-to-End Tracking Simulations Track entire machine to evaluate beam brightness & FEL Parmela space-charge Elegant Genesis compression, wakes, CSR, … SASE FEL with wakes Track machine many times with jitter to test stability budget (M. Borland, ANL) LCLS LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected] Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Sliced e- Beam to Evaluate FEL (Dz 0.7 mm) After full system tracking gex (also studied by S. Reiche) gey z 12 b 0g - 2 0 g 0 b 1 mismatch amplitude variation zx 2 2 2 x x x xb x y y y yb y R4 b e b ye y x x 2 1 2 zy slice 4D centroid osc. amplitude LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Lg < 4 m Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Machine Stability Simulations Track LCLS 230 times with Parmela Elegant Genesis Include wakes, CSR, etc. + jitter budget (M. Borland, ANL) Lg Ipk gex LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Pout Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Emittance and Energy Spread Diagnostics* 5 energy spread meas. stations (optimized for small bx) 5 emittance meas. stations designed into optics (Dyx,y) slice measurements possible with transverse RF (L0 & L3) 3 prof. mon.’s (Dyx,y = 60°) rf gun gex,y ...existing linac L1 E * see also P. Krejcik talk LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design gex,y gex,y gex,y L2 X E L3 E gex,y E Paul Emma, SLAC [email protected] E Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Transverse RF deflector as diagnostic* e- RF ‘streak’ V(t) x S-band long. phase space 230 fsec z y = kt [mm] V0 = 0 LCLS simulation Built & used at SLAC in 1960’s * see P. Krejcik talk l Es z rf 2p eV0 sin Dy cos 2 y - y20 V0 = 20 MV x = hDE/E [mm] bd bs meas. bunch length & slice emittance LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design meas. longitudinal phase space Paul Emma, SLAC [email protected] Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Summary Linac design optimized for nominal 1.5-Å operation Design is flexible to accommodate 15-Å, low-charge, & chirp CSR growth of projected emittance – not slice Much experience on SLAC linac with wakefield control Beam diagnostics built into design Full system tracking to… Evaluate e- brightness preservation, Calculate SASE gain, Simulate pulse-to-pulse stability. LCLS Full tracking with errors shows FEL saturation at 1.5 Å, but a very challenging machine! LCLS Internal Review, Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC [email protected]