Particle and Radiation Source Physics: Status and Opportunites at ORION

1. Particle and Radiation Source Physics:Status and Opportunites at ORION J.B. Rosenzweig UCLA Department of Physics and Astronomy SLAC, 2/23/2000

2. Outline • Challenges in high-brightness electron beam generation • Beam manipulation experiments • Bunching • Focusing of ultra-dense beams • Ultra-fast measurements • Computational modeling issues • Exotic electron beam source schemes • Beam-radiation interaction • Opportunities in FEL and Thomson scattering sourcery ORION II Workshop

3. Electron source: a critical enabling technology • High brightness for radiation production • High peak current for wake (NLC, adv.acc.) work • Ultra-low emittance beams for laser acceleration • HEP specific NLC beam attributes • Beam production is relativistic, one-component, violently accelerating, cold-plasma problem • Some aspects solved in generation, some in compression (sourcery and chicanery…) ORION II Workshop

4. Attributes of RF Photogun System • Very high gradient 1.6 cell S-band gun • State-of-art after many iterations • Excellent emittance • Pulse length preservation • Emittance compensation • Ferrario scenario • High bandwith photocathode drive laser • High QE, uniform emission photocathode ORION II Workshop

5. Experimental challenges for ORION in high brightness beam production • High quality photocathodes • Emittance compensation with X-band high gradient linacs • Demonstration of charge-scaled performance • Beam-plasma frequency (density) controls dynamics • Small=>large charge optimized beams can be made in same system • Generate longitudinally tailored pulse (and train) distributions using laser… O.25 nC design simulations (HOMDYN) ORION II Workshop

6. Laser-based pulse shaping • “Flat-topping” for low emittance • Witness beam generation • Pulse stacking • Longitudinal Fourier plane • Do these shapes survive acceleration and transport? Neptune laser Fourier plane manipulations (autocorrelation) Witness beam generation (UCLA/AWA) ORION II Workshop

7. NLC e- source requirements • How does ORION pay the rent at NLCTA? • Wavelength specific to driving polarized source (~800 nm) • Stringent gun vacuum • Challenging pulse train requirements • ~100 bunches/train, ~ nC level • 1.4-2.8 nsec separation • Can this be mimicked at ORION (beam splitting, high QE, thermionic) NLC laser layout (J. Frisch) ORION II Workshop

8. New photoinjectors scalable to short RF wavelength (X-band) • Physics indicates high advantage in moving to high frequency photoinjector • Large technical challenges • Laser • Cooling (lower gradient integrated structure) • RF handling (klystron isolation) • New S-band hybrid structure under development w/industry+UCLA • Initial SW cells coupled to waveguide • Long TW section downstream • X-band at ORION? ORION II Workshop

9. Pulse compression I: chicane • Chicanes have enabled/will enable enormous strides in wakefield physics and FELs • Chicanes have cutting edge collective physics (diseases) in their own right… Vertical chicane gives artifacts in data… 4 nC compressed beam nearly stopped in plasma (FNAL/UCLA experiment) ORION II Workshop

10. Collective physics in chicane • Noninertial space-charge • Transverse phase space bifurcation from folding in x-z • Coherent transition radiation • Emittance growth • Microbunching instability • Understanding critical to LC and FEL future… • Many experiments <100 MeV Transverse phase space bifurcation observed at Neptune (S. Anderson) BNL SDL measurement of Microbunchin (W. Grave) ORION II Workshop

11. Opportunities in chicane physics • Add chicane to ORION? • Full longitudinal tuning flexibility in tandem with negative R56 dogleg • Studies at >300 MeV most interesting niche • New physics? • Coherent edge radiation • Sort out radiative v. velocity field effects 1 mm 1 mm Coherent edge radiation (simulation of UCLA/BNL ATF exp.) ORION II Workshop

12. Velocity Bunching: a Cure for “The Bends”? • Proposed by Serafini, Ferrario; tool for SASE FEL injector, avoids magnetic compression • Inject emittance-compensated beam at 5-7 MeV into slow-wave linac • Effectively compresses at low energy — good for energy spread control • Perform one-quarter of synchrotron oscillation to compress beam • Gentle, low gradient option • Also “thin-lens” option for ORION • May need for obtaining ultra-small energy spread a la LEAP Longitudinal phase space schematic for velocity bunching ORION II Workshop

13. Velocity bunching optimization and implementation at ORION • Serafini-Ferrario proposal: long slow-wave structure from tuning w (new source) or k (structure)? • Expensive in structure and real estate • Alternative for ORION: use only short bunching section to split functions of bunching and acceleration • Example buncher: PWT (Neptune model, 14 MW) Simulation of proposed ORION system First linac “catches”beam, second removes energy spread (accel. + phase). 10 pC case. ORION II Workshop

14. PARMELA simulation of ORION case • Study at nominal design (0.25 nC) Tailored magnetic field for emittance compensation Velocity bunching induces little emittance growth until longitudinal “cross-over” ORION II Workshop

15. ORION opportunities • Experiments now at • BNL SDL • UCLA Neptune • LLNL PLEIADES • ORION has: • Need! • Robust emittance compensation • Solenoids • Full test of transverse phase space control with “thin-lens” approach Neptune measurements (PWT “thin lens”, no post acceleration) ORION II Workshop

16. Ramped beam pulses • Uses negative R56 dogleg • Optimum for wakefield acceleration • Plasma wakefields at high density • Small beams, better at high energy • Correction of T566 and other 2nd order terms a must • Studies ongoing at Neptune laboratory (also ATF for VISA experiment) ORION II Workshop

17. Neptune example • 45 degree bends • Simple FDF quad configuration • Sextupoles next to F quads Without Sextupoles (T566 = -1.9 m) RAMPED BEAM WITH Sextupoles (T566 = 0) ORION II Workshop

18. Preliminary ORION dogleg analysis More, better, from E. Colby and Joel England 60 ps with the dogleg and high energy spread Simple momentum collimation Sextupole corrected Ramped beam Witness beam from collimation as well! ORION II Workshop

19. Focusing to very small beam sizes • Thomson experiments • Matching to PWFA (esp. ramped pulses) • Large (huge) momentum acceptance needed • Developing at UCLA for LLNL very strong (>300 T/m) PM-based quadrupole array, tuned by long. position. Elegant simulation of sub-10 micron spot Permanent magnet quad (Radia simulation) ORION II Workshop

20. Ultra-fast beam diagnostics: ORION must go beyond the streak camera • Streak camera a mainstay at the picosecond level (see Hogan talk) • Ultra-short beams • Radiation based diagnostics • CTR for macro- and micro-bunching • Very short time structure, no time-resolved “anything else” • Using the beam as a streak camera • RF deflector (LCLS) • Use of linac chirping (T. Smith) Hi-res Michelson for CTR T. Smith method time profile L2 phase varies, amplitude constant L1 phase = 0, amplitude constant L3 off L4 phase = -90, amplitude ~ 1/R56 Chicane set for R56 ~ 9 cm ORION II Workshop L4 L3 L2 L1

21. Exotic sourcery: PWFA transition wavebreaking • Automatically synchronized source for plasma acceleration • Rephasing by density droop to achieve low energy spread • Proof-of-principle experiment at FNAL A0 (low energy) • High emittance (>30 mm-mrad) • Scale plasma at ORION: beat LCLS injector brightness! ORION II Workshop

22. Beam-radiation interaction: Electron beam-based sources • SASE FEL and Thomson are strong drivers of high brightness beam development • ORION is cousin of LCLS • Other coherent radiation sources of interest • Cerenkov (DWFA, etc.) • Transition (collective field emittance growth from foils!) • Synchrotron (explore relationship between CSR instability and FEL) • Plasma-based (hard photons from focusing) ORION II Workshop

23. Computational physics: start-to-end simulation for VISA • In order to understand • Anomalous gain • Strange spectra In VISA, we needed to study the beam from the cathode onwards • Suite of codes: • PARMELA • ELEGANT • GENESIS • Benchmarked to • beam measurements post-linac • Beam measurements post-dogleg • FEL! • Applicable to many situations at ORION (see E. Colby talk) Data and simulation of far-field radiation pattern ORION II Workshop

24. Frontiers of SASE FEL at ORION? 0% 0.5% • UV to DUV photons • Interest from users (TTF) • Harmonics to extend wavelength range • Basic physics • Not so many places • Ultra-short pulse generation • Beam chirping • Inverse process for acceleration… 4% 2% 0% 0.5% 2% 4% ORION II Workshop Chirped beam experiment for VISA

25. Thomson scattering sources • Thomson scattering can produce high intensity incoherent x-rays (LCLS spectrum at 20-40 MeV w/IR) • Example: PLEIADES • Very interesting to universities • At full ORION energy, obtain multi-MeV photons • Test-bed for g-g collider • Polarized positron sources • Nuclear physics LLNL PLEIADES Data (F. Hartemann reports) ORION II Workshop

26. Conclusions • ORION has the potential to be a path-breaking laboratory in: • electron source physics • Manipulations at the sub-psec level • Fast diagnostics • Electron beam-based radiation sources • Rapid progress has been made in the field since ORION I. • Complementarity and leverage between ORION and existing programs at SLAC (NLC, LCLS) • Let’s make sure we have envisioned the most capable facility… ORION II Workshop