1. Doe FACET Review February 19, 2008 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

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. 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 RAL LBL Osaka UCLA E164X/E-167 ILC Current Energy Frontier ANL LBL

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

5. Charge

6. Particle Accelerators Requirements for High Energy Physics High Energy High Luminosity (event rate) L=fN 2 /4  x  y High Beam Quality Energy spread  ~.1 - 10% Low emittance:  n    y  y << 1 mm-mrad Low Cost (one-tenth of $10B/TeV) Gradients > 100 MeV/m Efficiency > few %

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

8. Linear Plasma Wakefield Theory Large wake for a laser amplitude a beam density n b ~ n o Requirements on I,  require a FACET-class facility Ultra-high gradient regime and long propagation issues not possible to access with a 50 MeV beam facility  Q/  z = 1nCoul/30  (I~10 kA) For  z of order c  p -1 ~ 30  (10 17 /n o ) 1/2 and spot size  =c/  p ~ 15  (10 17 /n o ) 1/2 :

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

10. E+ E- Beam propagation Head erosion (L=    Hosing Transformer Ratio: driver load Limits to Energy Gain

11. PIC Simulations of beam loading Blowout regime flattens wake, reduces energy spread Unloaded wake EzEz Beam load U C L A Loaded wake N load ~30% N max 1% energy spread

12. Emittance Preservation Plasma focusing causes beam to rotate in phase space Emittance  n = phase space area: 1/4 betatron period (tails from nonlinear F p ) Several betatron periods (effective area increased) x pxpx  Matching: Plasma focusing (~2  n o e 2  ) = Thermal pressure (grad p    /  3 ) No spot size oscillations (phase space rotations) No emittance growth FpFp F th

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

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

15. Path to a TeV Collider from 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 Drive Beam Accelerator 12 usec trains of e- bunches accelerated to ~25 GeV Bunch population ~3 x 10 10, 2 nsec spacing 100 trains / second Main Beam e+ Source:500 nsec trains of e- bunches Bunch population ~1 x 10 10, 2 nsec spacing 100 trains / second DR PWFA Cells: 25 GeV in ~ 1 m, 20 per side ~100 m spacing DR Main Beam e- Source: 500 nsec trains of e- bunches Bunch population ~1 x 10 10, 2 nsec spacing 100 trains / second Beam Delivery System, IR, and Main Beam Extraction / Dump ~2 km ~60 MW drive beam power per side ~20 MW main beam power per side ~120 MW AC power per side ~ 4 km 1TeV CM

17. Drive Beam Source DC or RF gun Train format: With 3 x 10 10 /bunch @ 100Hz: ~2.3 mA average current, ~2 A beam current, similar to beam successfully accelerated in CTF3 Compress bunches to ~30  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 100ns kicker gap mini-train 1 mini-train 20 500ns: 250bunches 2ns spacing 12  s train

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 10  (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 R 56. Assuming that another ~50 m needed for combiner, each PWFA cell needs ~100 m of optics around it.

22. TeV Beam Parameter Summary IP Parameters* e+ e- h.e. bunch gamepsX [m]2.0E-06 h.e. bunch gamepsY [m]5.0E-08 beta-x [m]5.0E-02 beta-y [m]2.0E-04 sigx [m]3.2E-07 sigy [m]3.2E-09 sigz [m]1.0E-05 Dy5.6E-01 Uave2.81 delta_B0.14 P_Beamstrahlung [W]2.9E+06 ngamma0.79 Hd1.2 Lum. [cm-2 s-1]2.4E+34 Int. Lum. [fb-1 per 2E7s]474 Coherent pairs/bc2.2E+07 E CM at IP [GeV]1000 N, drive bunch2.9E+10 N, high energy bunch1.0E+10 n h.e. bunch/sec [Hz]25000 Main beam train length [nsec]500 Main beam bunch spacing [nsec]2 Main beam bunches / train250 Repetition rate, Hz100 PWFA voltage per cell [GV]25 PWFA Efficiency [%]35 # of PWFA cells20 n drive bunch/sec [Hz]500000 Drive bunch energy [GeV]25 Power in h.e. beam [W]2.0E+07 Power in drive beam [W]5.7E+07 Avg current in h.e. beam [uA]40.05 Avg current in drive beam [mA]2.29 Modulator-Drive Beam Efficiency [%]54 Site power overhead [MW]71 Total site power [MW]283 Wall Plug Efficiency 14% *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/  ) needs to increase by 10 2 -10 4

24. Critical Issues System Req.IssueTech Drivers N Load 2nd bunchChicane+chirp photocathode  Load 2nd bunchBunch shape Phase control nn Matching hosing Scattering Ion motion Plasma sources Plasma channels plasma matching sections Combiner/separators e+ Gradients Nonlinear focusing Accel on e- wake Plasma channels e+ sources phase control E Beam propagation Synchrotron losses Staging or shaping Simulation modeling to guide designs Laser jitter stabilization f Power coupling RF stability w/ hi load, short bunch (CSR) Gas removal & replenish Klystron power CLIC DoD Gas laser program L Final Focus-Plasma lens’ Pointing stability Plasma sources Ultra-fast feedback Red=FACET only Blue=FACET Green=Facet partial

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  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  y *=0.1mm

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