Workshop Summary: Accelerator Physics for Future Light Sources

1. Workshop Summary:Accelerator Physics for Future Light Sources William A. Barletta Director, United States Particle Accelerator School Dept. of Physics, MIT John N. Corlett Lawrence Berkeley National Laboratory Berkeley, CA 94720 BESAC Meeting November 5th, 2009

2. Purpose: Provide a technical basis for BES investment in accelerator R&D • Evaluate the state of readiness of machine architectures to building the next major X-ray science user facility • What will be ready in 5 years? In 10 years? • Provide peer-reviewable scientific manuscripts describing • Potential of approach (not wavelength specific) • Physics & technological challenges • Technical readiness of light source architectures • Describe research steps & directions toward a new generation of photon sources • Explicit R&D roadmap • Smaller-scale architectures were considered for context and long term potential

3. What was not part of the workshop • The workshop did not consider project-specific proposals • We did not consider the scientific justifications for various architectures / operating parameters • Areas of interest were guided by, but not limited to, the those described • In the BESAC (Crabtree) report • In CMMP 2010

4. Workshop structure & areas of interest • Opening plenary session presentations (1/2 day) • FELs, ERLs, Ultimate Storage Rings, Laser-driven sources • Working group meetings (11/2 day) • 5 groups (we added an Instrumentation & Detector group) • Focus on drafting detailed outline of paper & writing assignments • Close-out preparation (1/2 day) • Limited to ~50 participants (machine experts only) • Balance participation in each working group • Balance institutional participation • Add group in instrumentation & detectors • Papers to be submitted to Nuclear Instruments & Methods -A in mid-December

5. Readiness of Architectures: FELs • FELs now proven from IR to hard X-ray range • Success of LCLS commissioning and early operations • High brightness injector • e < 1 mm-mrad @ ~1 nC • Saturation in 60 m • Peak brightness ~1x1033 @ 1.5 Å • ~2x1012 photons/pulse • Average brightness ~2x1022 @ 1.5 Å • Ultrashort pulse ~5 fs (low charge mode, 20 pC) • Laser heater tames microbunching • Experiment verifies theory and simulations • Advances in R&D • Velocity bunching, HGHG, HHG seeding

6. Directions for FEL Developments • Increase average flux & brightness • High repetition rate photocathode gun • High repetition rate RF or CW SCRF systems • Enhance temporal coherence • Seeding, self-seeding • X-ray oscillators • Control pulse duration and pulse energy • Laser manipulations and seeding • Ultrashort electron bunches • Extend photon energy range • Short-period undulators • High-gradient RF • Novel acceleration schemes

7. FEL: Peak Brightness LCLS LCLS FLASH 1010 FLASH ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

8. FEL: Average Brightness LCLS LCLS Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917 FLASH single bunch ~1016–1017

9. FEL: BW & Pulse Length FLASH LCLS LCLS Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

10. FEL: Rep Rate & Pulse Length FLASH Future directions LCLS ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

11. FEL Physics & Technology: R&D Priorities • Photocathodes • High efficiency • Low intrinsic emittance • High current • Robust • Injectors • High brightness • Flexibility to incorporate beam manipulations • High repetition rate (10s kHz – MHz and beyond) • Laser manipulations & seeding techniques • High harmonic upshift efficiency • X-ray oscillators and self-seeding • High average power laser systems • High repetition rate • Short wavelength for seeding (HHG) • Dependent on developments in photocathodes and seeding techniques Cross-cutting technologies Cross-cutting technology

12. FEL Physics & Technology: RD&D Needs • Medium risk • RF structures & power • Optimized CW SCRF • Optimized high frequency, high gradient in pulsed mode (≤1 kHz) • Undulators • Short-period for resonance at lower energy / extended photon wavelength reach • Collective effects • Compression & transport • Diagnostics & Instrumentation • X-ray optics • Fast kickers • Simulation tools • Detectors • Beam stability Cross-cutting technology Cross-cutting technology Cross-cutting technology

13. FEL Physics & Technology: Test Beds • Make full use of existing facilities • BNL SDL, SPARC, LCLS, FLASH, FERMI@elettra, SCSS, … • Ready now to build dedicated test beds to develop critical concepts: • Low repetition-rate • Test coherent emission from laser manipulations, seeding, self-seeding, and oscillator, and short bunch techniques • Beam energy ~2 GeV to reach soft X-ray range • Low emittance gun, ≤1 mm-mrad, ≤1 nC • High repetition-rate • Test high-brightness photocathode, gun, and injector designs • Flexibility in bunch parameters • Repetition rate kHz to MHz • Beam energy ~100 MeV (set by emittance freezing)

14. Readiness of Architectures: Timescales for FEL Developments • Increase average flux & brightness • Injector and RF developments • 1 kHz soft X-ray ready to build today • 10–100 kHz soft X-ray facility ready to build within 3–5 years • Enhance temporal coherence • Control pulse duration (<1 fs to 100s fs) and pulse energy • Ultra-short bunches ~coherence length (~1 fs) ready today • Laser manipulations for soft X-ray, 10+ kHz within 3–5 years • Self-seeding and oscillators for hard X-rays ~5–10 years • Extend photon energy (to 10s keV) • Undulator technology, factors of few in 3 years • High-frequency, high-gradient RF structures ~3–5 years • Novel acceleration methods available 10+ years

15. Energy Recovery Linac X-ray Source High-brightness, high average current 10 MeV injector “Merger” Multi-GeV output beam Multi-GeV Superconducting Linac ID ~10 MeV energy-recovered beam Multi-GeV return beam Turn-around arc with undulator beamlines

16. Readiness of Architectures: ERLs Today’s status Demonstrated 9 mA CW two-pass at 30 MeV (BINP) Demonstrated 9 mA CW at 150 MeV (Jlab FEL) Demonstrated 70 µA CW at 1 GeV (JLab CEBAF) Promise of high spectral brightness in hard X-ray range Goal is for ~100 mA, and with beam emittance ~10–100 smaller than demonstrated Multi-GeV ~100 MW beam power

17. Directions for ERL Developments High peak brightness for hard X-rays Approach diffraction limit for hard X-rays High brightness, high energy beam (several GeV) Small energy spread High average flux & brightness High brightness, high repetition rate photocathode gun and injector Optimized CW SCRF systems Energy recovery physics High beam power Reduce bandwidth Maintain small energy spread in single-pass machine Reduce pulse duration High brightness injector

18. ERL: Spatial Coherence Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

19. ERL: Average Brightness Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

20. ERL: BW & Pulse Length Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

21. ERL: Rep Rate & Pulse Length Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

22. ERL Physics & Technology: R&D Priorities • Photocathodes • High efficiency • Low intrinsic emittance • Robust • Injectors • High brightness • Flexibility to incorporate beam manipulations • High repetition rate (GHz) • Drive laser • Recirculation and energy recovery • Multi-pass physics, halo, collimation, wakefields • ~100 mA, 7 GeV = 700 MW • RF structures & power • Optimized CW SCRF Cross-cutting technologies

23. ERL Physics & Technology: RD&D Needs • Medium risk • Simulation tools • Undulators • Short-period for resonance at lower energy / extended photon wavelength reach • Collective effects • Compression & transport • Diagnostics and Instrumentation • X-ray optics • Beam stability • Detectors Cross-cutting technology Cross-cutting technology Cross-cutting technology

24. Make full use of existing facilities CEBAF, Jab FEL, Cornell R&D ERL , BNL R&D ERL Injector test facility Test photocathode, gun, and injector designs, drive laser, beam merger Very high repetition-rate, up to GHz Beam energy ~100 MeV (set by emittance freezing) Multi-pass ERL with characteristics of a full scale facility Test multi-bunch instabilities, emittance preservation in arcs, halo & collimation, hardware 600 MeV, 2-pass acceleration/deceleration 200 pC, 1 mm-mrad injector, ~ 5 MHz CW repetition rate Incorporates recirculation & energy recovery (600 kW) ERL Physics & Technology: Test Beds

25. Readiness of Architectures: Timescales for ERL Developments • High brightness injector ready ~3–5 years • ERL test facility demonstrates critical hardware and physics ~10 years

26. Readiness of Architectures: Storage Rings • Well developed & understood technology • High average brightness & flux • High average current: ~0.5A • High repetition rate • High average brightness & lower peak brightness desirable for many experiments • Very stable • Position, angle, beam size, current, energy • Easily & rapid tunable • Wide photon spectrum from IR to hard X-rays • Polarization control • Simultaneously serves many users with multiple requirements • High reliability (>90%) • Cost shared by many beamlines

27. Approach diffraction limit for hard X-rays 8 pm-rad at 1 Å High average flux & brightness High energy beam Several GeV Large ring with very small emittance (horizontal & vertical) Few km cirmumference Frequent injection Off-axis accumulation On-axis (swap out / replacement) Partial lasing at longer wavelengths Directions for Ultimate Storage RingsDevelopments

28. Ultimate Rings: Spatial Coherence Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

29. Ultimate Rings: Average Brightness Future directions ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917

30. Ultimate Rings Physics & Technology: RD&D Needs • Medium risk • Code development and simulation • Dynamic Aperture • Lifetime • Injection • Ring with larger dynamic aperture allows for accumulation • Pulsed multipole kickers • Ring with smaller dynamic aperture requires on axis injection • Fast dipole kickers • Bunch manipulations • Crab cavities • Tailored time structure • Instrumentation & Diagnostics • Short-period undulators • RF cavities and power • Detectors Cross-cutting technology Cross-cutting technology Cross-cutting technology

31. Readiness of Architectures: Timescales for Ultimate Rings Developments • RD&D to reduce costs and optimize performance • Almost all required accelerator physics & technologies to realize an ultimate storage ring are in hand • Complete an integrated design that optimizes the performance • Design mature in ~5 years

32. Readiness of Architectures: Other Sources • Lasers generating EUV/XUV radiation • HHG • Ultrafast pulses extending into XUV, ~mW level • Potential use as seed for SXR FEL • Lasers as alternates to “conventional” technologies • Laser-plasma accelerators • Compact electron source and extremely high fields of 10–100 GVm-1 • Electron beams demonstrated 10 pC, <50 fs, few % energy spread, <1 mrad divergence, ~1 GeV • Laser-driven vacuum structures • All-optical accelerator and undulator • Up to 1 GVm-1 accelerating gradient • Intrinsic ultrafast timescales, TW peak power • Inverse Compton sources • Compact integration of laser/accelerator technologies • Broadband incoherent hard X-ray source 1-100 keV

33. Other Sources: RD&D Priority High power lasers ~100 W in IR Enable unique HHG based XUV sources Stand alone source or for FEL seed E.g. seed pulse ~5 nJ in ~25 fs, ~30 nm Source for testing equipment & preparation for measurements at FELs Essential for laser plasma acceleration and laser-driven vacuum structures Experimental lasers to match FEL rep-rate Diode pumped amplifier performance Ceramics New crystals Fiber multiplexing Optical cooling & damage issues Cross-cutting technology

34. Laser-plasma accelerators Tailored plasma channels Injection and acceleration schemes Diagnostics 3D simulation codes Short period undulators Laser-driven vacuum structures Basic proof-of-principle experiments for key concepts Sub-fs synchronization, materials damage, charging of structures, diagnostics for as beams Inverse Compton sources High brightness, high beam power injectors Laser build-up cavity Integration of laser and CW SCRF accelerator Other Sources: R&D Needs

35. Readiness of Architectures: Timescales for Other Sources Developments • HHG • Optimize laser/gas interaction, extraction, transport, tunability, establish theoretical limits of HHG efficiency and approach them, characterize HHG beam • Reliable (95% up time) drive laser with ~2 mJ, 5–20 fs, • 1–10 kHz within 5 years • Extend rep rate to MHz over 10 years • Laser-plasma accelerators • Demonstration of soft X-ray production pursued by several groups • LPA-driven SXR FEL user facility expected within ~10 years • Laser-driven vacuum structures • R&D required for 10+ years to realize potential capabilities • Inverse Compton scattering • Laser and accelerator R&D ~5 years, systems integration ~5 years • 10 year horizon

36. Enabling Instrumentation & Technology • Cathodes • Photocathode, thermionic, advanced materials • Photocathode, drive laser shaping (3D) • Ultrafast beam instrumentation • Timing and synchronization • Electron/photon bunch length • Electron/photon arrival time • Photon optics bandwidth • Optics damage issues • Photon detectors • Smart detectors • Improved readout rates, radiation hardness • Time resolved (streak cameras,etc.) • Insertion Devices • High power lasers Cross-cutting technologies