A Plasma Wakefield Accelerator-Based Linear Collider

1. A Plasma Wakefield Accelerator-Based Linear Collider Vision for Plasma Wakefield R&D at FACET and Beyond e-e+Colliding Plasma Wakes Simulation, F. Tsung Beyond 10 GeV: Results, Plans and Critical Issues T. Katsouleas University of Southern California Doe FACET Review February 19, 2008

2. Outline • Brief History and Context • Introduction to plasma wakefield accelerators • Path to a high energy collider • Critical issues, milestones and timeframe • What can and cannot be addressed with FACET

3. ILC Current Energy Frontier E164X/E-167 LBL RAL LBL Osaka UCLA ANL Plasma Accelerators -- Brief History • 1979 Tajima & Dawson Paper • 1983 Tigner Panel rec’d investment in adv. acc. • 1985 Malibu, GV/m unloaded beat wave fields, world-wide effort begins • 1989 1st e- at UCLA • 1994 ‘Jet age’ begins (100 MeV in laser-driven gas jet at RAL) • 2004 ‘Dawn of Compact Accelerators’ (monoenergetic beams at LBL, LOA, RAL) • 2007 Energy Doubling at SLAC

4. Acceleration, Radiation Sources, Refraction, Medical Applications Research program has put Beam Physics at the Forefront of Science

5. Charge

6. Particle AcceleratorsRequirements for High Energy Physics • High Energy • High Luminosity (event rate) • L=fN2/4psxsy • High Beam Quality • Energy spread dg/g ~ .1 - 10% • Low emittance: en ~ gsyqy << 1 mm-mrad • Low Cost(one-tenth of $10B/TeV) • Gradients > 100 MeV/m • Efficiency > few %

7. E 1-D plasma density wave Simple Wave Amplitude Estimate Vph=c Gauss’ Law

8. Linear Plasma Wakefield Theory Large wake for a laser amplitude a beam density nb~ no For sz of order cpwp-1 ~ 30m (1017/no)1/2 and spot sizes=c/wp ~ 15m (1017/no)1/2 : • Q/ sz = 1nCoul/30m (I~10 kA) Requirements on I, t, s, g require a FACET-class facility Ultra-high gradient regime and long propagation issues not possible to access with a 50 MeV beam facility

9. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + - - - - - - - - - drive beam + - - + + + + + - + + + + + - + + + + + + + - - - - + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + - - - - - - + + + + + + + + + + + + - - - - - - - + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - + + + + + + + + - - - - - - - - - Ez Nonlinear Wakefield Accelerators (Blowout Regime) Rosenzweig et al. 1990 • Plasma ion channel exerts restoring force => space charge oscillations • Linear focusing force on beams (F/r=2pne2/m) • Synchrotron radiation • Scattering

10. Limits to Energy Gain • Beam propagation • Head erosion (L=ps2/e) • Hosing • Transformer Ratio: E- load driver E+

11. U C L A PIC Simulations of beam loading Blowout regime flattens wake, reduces energy spread Beam load Ez Unloaded wake • Loaded wake • Nload~30% Nmax • 1% energy spread

12. px x s Several betatron periods (effective area increased) 1/4 betatron period (tails from nonlinear Fp ) Emittance Preservation • Emittance en = phase space area: Plasma focusing causes beam to rotate in phase space • Matching: Plasma focusing (~2pnoe2s) = Thermal pressure (grad p~e2/s3) • No spot size oscillations (phase space rotations) • No emittance growth Fp Fth

13. e- e+ Positron Acceleration -- two possibilitiesblowout or suck-in wakes e+ load • • Non-uniform focusing force (r,z) • Smaller accelerating force • Much smaller acceptance phase for acceleration and focusing Ref. S. Lee et al., Phys. Rev. E (2000); M. Zhou, PhD Thesis (2008)

14. Accelerator Comparison On ultra-fast timescales, relativistic plasmas can be robust, stable and disposable accelerating structures • No aperture, BBU TESLA structure l ~ 30cm 2a Plasma l ~ 100mm

15. Path to a TeV Colliderfrom present state-of-the-art* • Starting point: 42 --> 85 GeV in 1m • Few % of particles • Beam load • 25-50 GeV in ~ 1m • 2nd bunch with 33% of particles • Small energy spread • Replicate for positrons • Marry to high efficiency driver • Stage 20 times * I. Blumenfeld et al., Nature 445, 741 (2007)

16. CLIC-like PWFA LC Schematic ~120 MW AC power per side 12 usec trains of e- bunches accelerated to ~25 GeV Bunch population ~3 x 1010, 2 nsec spacing 100 trains / second ~2 km Drive Beam Accelerator ~60 MWdrive beam power per side ~20 MW main beam power per side PWFA Cells: DR 25 GeV in ~ 1 m, 20 per side ~100 m spacing DR Beam Delivery System, IR, and Main Beam Extraction / Dump Main Beam e- Source: ~ 4 km 500 nsec trains of e- bunches Bunch population ~1 x 1010, 2 nsec spacing 100 trains / second Main Beam e+ Source: 1TeV CM 500 nsec trains of e- bunches Bunch population ~1 x 1010, 2 nsec spacing 100 trains / second

17. mini-train 20 mini-train 1 500ns: 250bunches 2ns spacing 100ns kicker gap 12ms train • Drive Beam Source • DC or RF gun • Train format: • With 3 x 1010 /bunch @ 100Hz: • ~2.3 mA average current, ~2 A beam current, similar to beam successfully accelerated in CTF3 • Compress bunches to ~30 m RMS length • SPPS achieved much smaller RMS lengths • Accelerate to 25 GeV • Fully-loaded NC RF structures, similar to CLIC / CTF 3 • Inject into “Drive Beam Superhighway” with pulsed extraction for each PWFA cell • Both e+ and e- main beams use e- drive beam See slide notes for additional background

18. Drive Beam Superhighway • Based on CLIC drive beam scheme • Drive beam propagates opposite direction wrt main beam • Drive mini-train spacing = 2 * PWFA cell spacing i.e, ~600 nsec

19. Drive Beam Distribution • Format options • Mini-trains < 600 nsec • NC RF for drive beam • Duty cycle very low • Individual bunches > 12 μsec • SC RF for drive beam • Duty cycle ~100 %

20. Main Beam Source and Plasma Sections • Electron side: • DC gun + DR • Compress to 10m (achieved in SPPS) • 20, +25GeV plasma sections, each 1E17 density, <1.2 meters long • Gaussian beams assumed -shaped beam profiles => larger transformer ratio, higher efficiency • Final main beam energy spread <5% • Positron side: • conventional target + DR • Positron acceleration in electron beam driven wakes (regular plasma or hollow channel) • Will have tighter tolerances than electron side

21. Matching / Combining / Separating Main and Drive Beams • Must preserve bunch lengths • Preserve emittance of main beam • ~100 μm spacing of main and drive bunches • Time too short for a kicker – need magnetostatic combiner / separator • Need main – drive bunch timing at μm level • Different challenges at different energies • High main beam energy: emittance growth from SR • Low main beam energy: separation tricky because of ~equal beam energies • Need ~100 m between PWFA cells “First attempt” optics of 500 GeV / beam separator. First bend and first quad separate drive and main beam in x (they have different energies); combiner is same idea in reverse. This optics needs some tuning and ~2 sextupoles. System is isochronous to the level of ~1 μm R56. Assuming that another ~50 m needed for combiner, each PWFA cell needs ~100 m of optics around it.

22. TeV Beam Parameter Summary *If DR emittance is preserved

23. Other Paths to a Plasma-based Collider • Hi R options --> 100 GeV to TeV c.m. in single stage • Ramped drive bunches or bunch trains • Plasma question: hose stability • RF Driver questions: pulse shaping techniques, drive charge is 5x larger • SRF Driven Stages • 5 stage example of Yakimenko and Ischebeck • Plasma question: extrapolate to 2m long 100 GeV • SRF questions: 3x5 +1 times the power/m and loading of ILC, wakes and BBU • Laser drivers • Extrapolate 1 GeV experiments to 25 GeV • Scale up laser power x25, pulse length x5, density x0.04, plasma length x125 • 20 Stages • Plasma questions: channel guiding over 1m; injected e-; e+ behind bubble • Laser questions: Avg. laser power (20MW/h) needs to increase by 102-104

24. Red=FACET only Blue=FACET Green=Facet partial Critical Issues

25. R&D Roadmap for a Plasma-based Collider

26. Summary • Recent success is very promising • No known show stoppers to extending plasma accelerators to the energy frontier • Many questions remain to be addressed for realizing a collider • FACET-class facility is needed to address them • Lower energy beam facilities cannot access critical issues in the regime of interest • FACET can address most issues of one stage of a 5-20 stage e-e+ TeV collider

27. Backup and Extra

28. Future upgrade or alternative paths • PWFA can be an upgrade path of e-e- or gg options • The following flow corresponds to the afterburner path

29. Beam delivery • NLC style FF with local chromatic correction can be a starting point • ~TeV CM required just ~300m • Energy acceptance (full) was about 2% –within a factor of two from what is needed for PWFA-LC (further tweaking, L* optimization, etc) • Beam delivery length likely be dominated by collimation system (could be +1.0-1.5km/side) – methods like crystal collimation and nonlinear collimations to be looked at again An early (2000) design of NLC FF L* =2m by*=0.1mm

30. 1 TeV Plasma Wakefield Accelerator PWFA Modules P ~10 µs+ ~1 ns Trailing Beam Trailing Beam 5, 100 GeV drive pulses, SC linac Ref.:V. Yakimenko and R. Ischebeck, AIP conference proceedings 877, p. 158 (2006).