1. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Accelerator Issues and Design Paul Emma, SLAC Dec. 12, 2003 Accelerator Issues and Design Paul Emma, SLAC Dec. 12, 2003 Design of Compression and Acceleration Systems Technical Challenges Full System Simulations Design of Compression and Acceleration Systems Technical Challenges Full System Simulations LCLS

2. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC ‘Slice’ versus ‘Projected’ Emittance collision integrates over bunch length — ‘ projected’ emittance is important ‘ ‘ For a collider… …FEL integrates over slippage length: ‘ slice’ emittance is important For an FEL… u u r r e  slips back w.r.t. photons by r (  1.5 Å) per period N r  0.5  m

3. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC SASE X-ray FEL is very sensitive to electron ‘slice’ emittance Instead of mild luminosity loss, power nearly switches OFF. However, longer wavelength, such as 15 Å (4.5 GeV), is much easier (  N  6  m ). courtesy S. Reiche P  10 GW  N = 1.2  m P  0.1 GW  N = 2.1  m r = 1.5 Å r = 1.5 Å

4. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC 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.) 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

5. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Nominal System Design Constraints Use existing SLAC linac compatible with PEP-II operation Undulator located beyond research yard Constraints Use existing SLAC linac compatible with PEP-II operation Undulator located beyond research yard 1 km

6. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC 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  m < 4/40  m) Emittance more critical (>2  m 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 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  m < 4/40  m) Emittance more critical (>2  m 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

7. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Design Strategy Design longitudinal optics first Set proper compression in two stages Minimize final energy spread Minimize I pk and E f 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 Design longitudinal optics first Set proper compression in two stages Minimize final energy spread Minimize I pk and E f 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

8. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Nominal LCLS Linac Parameters for 1.5-Å FEL Single bunch, 1-nC charge, 1.2-  m slice emittance, 120-Hz repetition rate… (RF phase:  rf = 0 at accelerating crest) SLAC linac tunnel research yard Linac-0 L =6 m Linac-1 L  9 m  rf   25° Linac-2 L  330 m  rf   41° Linac-3 L  550 m  rf   10° BC-1 L  6 m R 56   39 mm BC-2 L  22 m R 56   25 mm LTU L =275 m R 56  0 DL-1 L  12 m R 56  0 undulator L =125 m 6 MeV  z  0.83 mm    0.05 % 135 MeV  z  0.83 mm    0.10 % 250 MeV  z  0.19 mm    1.6 % 4.54 GeV  z  0.022 mm    0.71 % 14.1 GeV  z  0.022 mm    0.01 %...existing linac new rfgun 21-1b21-1d X Linac-X L =0.6 m  rf =  21-3b24-6d25-1a30-8c

9. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC RMS Bunch Length and Energy Spread sector-21sector-25sector-30FFTB++  zzzz

10. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC after BC1 after X-RF after L1 after DL1 after BC2 after L3 at und. after L2  z = 830  m  z = 190  m  z = 23  m  z = 190  m energy profile phase space time profile FINAL

11. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC  1   40°  x =  Slope linearized x = s /4 X-band RF used to Linearize Compression ( f = 11.424 GHz ) S-band RF curvature and 2 nd -order momentum compaction cause sharp peak current spike X-band RF at decelerating phase corrects 2 nd - order and allows unchanged z-distribution avoid! 0.6-m section, 19 MV available at SLAC (200-  m alignment)

12. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Transverse Wakefields and Component Misalignments L3 phase adv/cell optimized  z = 22  m wakeson wakesoff also misaligned quads/BPMs generate dispersion   x L2 phase adv/cell optimized  z = 195  m wakes off wakeson Choose  -phase adv/cell for each linac to minimize emittance dilution:

13. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Transverse Optics from Cathode to e  Dump LCLS MAD Deck  Cathode to e  Dump (2200 elements) Thanks to M. Woodley  x,y  75º  x,y  30º

14. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC RMS Transverse Beam Sizes from Cathode to e  Dump 100  m 10  m 1 mm undulator 4.0 mm (BC1) 2.6 mm (BC2)

15. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Alignment and Roll Tolerances (most > 1 mm, > 1 deg)

16. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Linac RF Section Modifications If modulators on 20-6, -7, and -8 used for injector, lose another 670 MeV (1.56 GeV total)

17. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Injector to Linac Interface “Linac” Responsibility Starts Here (21-1b) courtesy L. Bentson

18. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Linac-1 Through BC1 21-1b21-1c21-1d21-3b

19. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC BC2 Area 24-6d 25-1a

20. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Moveable Chicanes (BC1 shown) BPM screen collimator quadrupole BPM critical for energy feedback (20  m resolution) offset: 17 to 30 cm (24 cm nominal) 3 cm contraction BPM screen collimator

21. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Field quality requirement too tight with fixed chicane... SPPS dipoles: |b 2 /b 0 | < 0.010% @ 2 cm (just barely met) |b 2 /b 0 | < 0.002% @ r = 2 cm  requires: |b 2 /b 0 | < 0.002% @ r = 2 cm (moveable chicane requires 0.070%) Also needed: BPM res. 20  mBPM res. 20  m BPM linearityBPM linearity profile monitorprofile monitor collimatorcollimator x 12 mm 45 mm 80 mm

22. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Future Multiple Undulators +4º +2º N S 2º2º2º2º

23. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Linac-To-Undulator (LTU) 4  -wires, 6 collimators energy centroid & spread meas. (3  10  5 & 10  4 ) + collimation vertical bend 4.7 mradvertical bend 4.7 mrad horizontal jog 1.25 mhorizontal jog 1.25 m energy diagnosticsenergy diagnostics emittance diagnosticsemittance diagnostics collimatorscollimators CSR cancellationCSR cancellation branch points for future undulatorsbranch points for future undulators spontaneous undulator possiblespontaneous undulator possible vertical bend 4.7 mradvertical bend 4.7 mrad horizontal jog 1.25 mhorizontal jog 1.25 m energy diagnosticsenergy diagnostics emittance diagnosticsemittance diagnostics collimatorscollimators CSR cancellationCSR cancellation branch points for future undulatorsbranch points for future undulators spontaneous undulator possiblespontaneous undulator possible vertical bends

24. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Collimation for Undulator Protection  2.5 mm well shadowed in x, y, and E Coll.  x mm  y mmCE1  5.0 - CE2 - CX1  2.0 - CY1- CX2 - CY2-

25. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Electron Dump e →e →e →e → e →e →e →e → x-rays → quad soft bend quads powered vert. bends screen (  E /E = 10  5  5  m) permanent vert. bends yyyy yyyy dump

26. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Specification Sheets on Every New Magnet BX01 DL1 dipole: z-locationz-location fieldfield currentcurrent trim info.trim info. alignment tol.’salignment tol.’s lengthlength max/min strengthmax/min strength etc...etc...

27. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Technical Challenges Coherent Synchrotron Radiation in Bends projected emittance growth micro-bunching instability (+ LSC — see Z. Huang talk) Coherent Synchrotron Radiation in Bends projected emittance growth micro-bunching instability (+ LSC — see Z. Huang talk) LCLS Emittance Preservation in Linacs transverse wakefields misalignments & chromaticity Machine Stability gun and rf system jitter energy and bunch length feedback

28. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC zz zz   1/3 coherent power incoherent power vacuum chamber cutoff N  6  10 9 Coherent Synchrotron Radiation

29. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC 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) Powerful radiation generates energy spread in bends Induced energy spread breaks achromatic system Causes bend-plane emittance growth (short bunch is worse)  R e–e– zzzz coherent radiation for  z overtaking length: L 0  (24  z R 2 ) 1/3 L0L0L0L0   s xxxx  x = R 16 (s)  E/E bend-plane emittance growth

30. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Coherent Synchrotron Radiation (CSR) in SPPS Chicane ON Chicane OFF  x = 27.6  0.6  m  x = 34.2  0.7  m

31. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Bend-plane emittance is consistent with calculations and sets upper limit on CSR effect Coherent Synchrotron Radiation (CSR) in SPPS

32. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC CSR Micro-bunching* CSR amplifies small modulations on bunch current  Successive bend-systems cause micro-bunching  Growth of slice-energy spread & emittance. * First observed by M. Borland (ANL) in LCLS Elegant tracking without heater    3  10  6 avoid! 230 fsec S. Heifets, S. Krinsky, G. Stupakov, SLAC-PUB-9165, March 2002 energy spread damps bunching    3  10  5 Add slice energy spread to Landau damp instability. ‘Laser-Heater’ see Z. Huang talk

33. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Misalignments, Steering, and Emittance Correction BPM, quad, and RF misalignments: (each at 300  m rms)... then steered in Elegant BPM, quad, and RF misalignments: (each at 300  m rms)... then steered in Elegant  x  5  m  y  2  m  x  5  m  y  2  m trajectory after steering

34. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Emittance Correction with Trajectory ‘Bumps’  x  1.02  m  y  1.09  m  x  1.02  m  y  1.09  m steering coils  /   15% Thanks to M. Borland (ANL/APS) 100 seeds

35. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Jitter Budget (<1 minute time-scale) klystron phase rms  0.07° (20 sec) klystron ampl. rms  0.06% (60 sec) measured RF performance X-band X-X-X-X-

36. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Start-to-End Tracking Simulations Track entire machine to evaluate beam brightness & FEL Track machine many times with jitter to test stability budget (M. Borland, ANL) Track entire machine to evaluate beam brightness & FEL Track machine many times with jitter to test stability budget (M. Borland, ANL) ParmelaParmelaElegantElegantGenesisGenesis space-charge compression, wakes, CSR, … SASE FEL with wakes LCLS

37. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Sliced e  Beam to Evaluate FEL (  z  0.7  m) After full system tracking (also studied by S. Reiche) L g < 4 m  x  y yy xx mismatch amplitude variation slice 4D centroid osc. amplitude

38. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Machine Stability Simulations Track LCLS 230 times with Parmela  Elegant  Genesis Include wakes, CSR, etc. + jitter budget (M. Borland, ANL) Track LCLS 230 times with Parmela  Elegant  Genesis Include wakes, CSR, etc. + jitter budget (M. Borland, ANL) LgLgLgLg I pk  x P out

39. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Emittance and Energy Spread Diagnostics* 5 energy spread meas. stations (optimized for small  x ) * see also P. Krejcik talk...existing linac L0 rfgun L3L1 X L2 3 prof. mon.’s (  x,y = 60°)  x,y EEEE EEEE EEEE EEEE 5 emittance meas. stations designed into optics (  x,y ) slice measurements possible with transverse RF (L0 & L3) EEEE

40. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC Transverse RF deflector as diagnostic* eeee zzzz V(t)V(t)V(t)V(t) S-band xxxxRF‘streak’ long. phase space * see P. Krejcik talk Built & used at SLAC in 1960’s V 0 = 0 230 fsec LCLS simulation meas. bunch length & slice emittance V 0 = 20 MV meas. longitudinal phase space y = kt [mm] x =  E/E [mm]

41. Accelerator Issues and Design Emma@SLAC.Stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Internal Review, Dec. 12, 2003 Paul Emma, SLAC 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. 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!