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Advanced Acceleration Techniques

Office of Science. Advanced Acceleration Techniques. Carl B. Schroeder (LBNL) . 26 th International Symposium on Lepton Photon Interactions at High Energies San Francisco, CA June 24-29, 2013. Outline. Introduction to Advanced Accelerators High gradient structures Plasma

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Advanced Acceleration Techniques

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  1. Office of Science Advanced Acceleration Techniques Carl B. Schroeder (LBNL) 26th International Symposium on Lepton Photon Interactions at High Energies San Francisco, CA June 24-29, 2013

  2. Outline • Introduction to Advanced Accelerators • High gradient structures • Plasma • Dielectrics • High peak power drivers • Laser driven • Particle beam driven • Plasma-based accelerators • Laser driven • Particle beam driven • Electron beam • Proton beam • Dielectric laser accelerators

  3. New accelerator technology needed • “Livingston Plot” Saturation of accelerator tech. • Practical limit reached for conventional accelerator technology (RF metallic structures) • Gradient limited by material breakdown • e.g., X-band demonstration 100 MV/m • Largest cost driver is acceleration • ~ 50 MV/m implies ~ 20 km/TeV • Facility costs scale roughly with facility size (and power consumption) • Any future linear TeV (>TeV) collider is a massive (to ultra-massive) project • Can new approaches and new acceleration concepts reduce the size (and, hence, cost) of a future linear collider? • Demand >order of magnitude increase in acceleration gradient: > GV/m M. Tigner, DOES ACCELERATOR-BASED PARTICLE PHYSICS HAVE A FUTURE? Phys. Today (2001)

  4. Advanced accelerator R&D: High gradient for compact accelerators • Ultra-high gradient requires structures to sustain high fields: • Dielectric structures (higher breakdown limits) ~ 1 GV/m • Plasmas (“already broken down”) ~ 10 GV/m • High gradients require high peak power: • Laser driven • Particle beam driven • There has been a strong Advanced Accelerator R&D effort worldwide for the last 20+ years exploring these concepts. • Critical developments: • Plasma-based acceleration • Development of laser technology for high peak power delivery SLAC Electron beam energy gain (GeV) Beam plasma expts SLAC U.TX LBNL RAL LLNL MPQ Laser-plasma experiments Mich RAL LBNL LOA RAL SM-LWFA UCLA PBWA Year demonstrated

  5. Basic collider requirements: energy and luminosity • Acceleration mechanism must produce ultra-high average (or geometric) gradient for compact linacs: • > 1 GV/m (average or geometric) implies < 1 km/TeV • Beams must achieve sufficient luminosity: • Luminosity requires beam power: • New acceleration technologies must be compatible with reasonable (wall-plug) power: Focusability = low emittance (and energy spread); beam quality preservation High charge / bunch High efficiency (wall-to-driver, driver-to-structure, structure-to-beam)

  6. Basic collider requirements: beamstahlung suppression using short beams • TeV-scale colliders will operate in high-beamstrahlung regime • Beamstrahlung suppressed by using short beams: • Shorter beams save power: • Plasma-based accelerators and laser-driven dielectrics intrinsically produce short (~micron) beams Beamstrahlung background Collider power Short beams!

  7. Laser-driven plasma-based accelerators (Laser-Plasma Accelerators – LPA)

  8. Laser-plasma accelerators: Laser excitation of relativistic electron plasma wave Tajima & Dawson, Phys. Rev. Lett. (1979) Esarey, Schroeder, Leemans, Rev. Mod. Phys. (2009) Ponderomotiveforce (radiation pressure) Plasma wave: electron density perturbation p =2c/p= (re-1/2 ) np-1/2 ~10-100 m Electron plasma density Laser pulse duration ~ p/c ~ tens fs Ti:Sapphirelaser: I~1018 W/cm2

  9. Laser-plasma accelerators: 1-100 GV/m accelerating gradients Electron plasma density vbeam laser bunch plasma wave (wakefield) accelerating field: Ez~102GV/m (for n0~1018 cm-3, IL~1018 W/cm2) (~103larger than conventional RF accelerators: from 10’s of km to 10’s of m) • Higher plasma density yields higher accelerating gradient

  10. Experimental demonstration: 1 GeV beam from 3 cm laser-plasma accelerator H-discharge capillary (1018 cm-3) 3cm 1012 MeV 2.9% 1.7 mrad 30 pC Leemans et al., Nature Phys. (2006); Nakamura et al., Phys. Plasmas (2007)

  11. Limits to Energy Gain: Diffraction, Dephasing, Depletion ZR vbeam laser bunch • Limits to single stage energy gain: • Laser Diffraction (~Rayleigh range) • mitigated by transverse plasma density tailoring (plasma channel) • Beam-Plasma WaveDephasing • mitigated by longitudinal plasma density tailoring (plasma taper) • Laser Energy Depletion: energy loss into plasma wave excitation Scale length of laser energy deposition: • For high energy, laser depletion necessitates staging laser-plasma accelerators

  12. Operational plasma density: 1016 – 1018 cm-3 LBNL 2006 • Laser-plasma interactionlength: • Accelerating gradient: (require > GV/m) • Energy gain (per LPA stage): • For high-energy applications, laser depletion (and reasonable gradient) necessitates staging laser-plasma accelerators • Bunch charge: • Decrease density for reduced power costs: RAL 2009 LLNL 2010 Beam energy (MeV) MPQ 2007 U.Mich 2008 LOA 2006 APRI 2008 RAL 2004 LBNL 2004 plasma density, np(cm-3)

  13. Accelerator length determined by staging technology Laser LPA Number of stages: Lcouple Laccelerator Lstage • total length of linac: plasma density

  14. Laser in-coupling using plasma mirrors enables compact staging • Conventional optics approach: stage length determined by damage on conventional final focus laser optics ~10 m Laser Laser • Plasma mirror in-coupling: • “Renewable” mirror for high laser intensity • Relies on critical density plasma production • Thin liquid jet or foil (tape) • Laser contrast crucial (>1010) plasma mirror ~10 cm • Advantage of laser-driven plasma accelerators: short in-coupling distance for laser driver (high average gradient) • Development of staging technology critical to collider application

  15. Positron acceleration in quasi-linear regime e- accel. Accelerating field • Operate in “quasi-linear” regime: • Quiver momentum weakly-relativistic a ~ 1 • (Intensity ~ 1018 W/cm2) • Region of acceleration/focusing for both electrons and positrons • Stable propagation in plasma channel • Dark current free (no self-trapping) e+ accel. e- accel+focus Plasma density Transverse position e+ accel+focus e- focus e+ focus Focusing field Longitudinal position Direction of laser propagation

  16. Laser driver requirements: 10s of J, 100s of kW p laser Laser spot size ~ p Laser pulse length ~ p/2 • Laser intensity for large plasma wave in quasi-linear regime: a~1 I ~ 1018 W/cm2 for 1 micron laser wavelength • Laser volume: • High repetition rate for luminosity: 10’s kHz • High efficiency (wall to laser) plasma density = n0 ~ 1017 cm-3 p~ 100 micron Tlaser~ 100 fs Ulaser~ 10’s J Plaser~ 100’s kW

  17. Conceptual Laser-Plasma Accelerator Collider • Plasma density scalings (minimize construction and operational costs) indicates:n~ 1017 cm-3 • Quasi-linear wake (a~1): e- and e+ • Staging & laser coupling into tailored plasma channels: • ~30J laser energy/stage required • energy gain/stage ~10 GeV in ~1m Leemans & Esarey, Physics Today (2009) • Laser technology development required: • High luminosity requires high rep-rate lasers (10’s kHz) • Requires development of high average power lasers (100’s kW ) • High laser efficiency (~tens of %)

  18. BELLA: BErkeley Lab Laser Accelerator BELLA Facility: state-of-the-art 1.3 PW-laser for laser accelerator science: >42 J in <40 fs (> 1PW) at 1 Hz laser and supporting infrastructure at LBNL • Critical HEP experiments: • 10 GeV electron beam from <1 m LPA • Staging LPAs • Positron acceleration

  19. 10 GeV Laser-Plasma Accelerator using BELLA WARP simulation (J.-L. Vay, LBNL) • BELLA (BErkeley Lab Laser Accelerator) laser parameters: • 40 J, 1 PW peak power (at max. compression)

  20. Beam-driven plasma-based accelerators (Plasma Wakefield Accelerators – PWFA)

  21. Plasma wakefield accelerator: Plasma wave excitation by space charge forces P. Chen et al., Phys. Rev. Lett. (1985) J. Rosenzweig et al., Phys. Rev. A (1991) • Space charge force of relativistic charged particle beam to excite plasma wave C. Joshi., Scientific American (2006)

  22. SLAC Energy Doubling Experiment Blumenfeld et al., Nature (2007) • Doubled energy of part of 42 GeV beam in 1 m of plasma • First experimental step in demonstration of “afterburner” concept: use plasma to double energy of conventional RF linear collider just before IP

  23. Concept of a PWFA-based Linear Collider • Two-beam accelerator geometry • Ability to generate drive power efficiently (10’s MW) • Benefit from extensive R&D performed on conventional collider designs (e.g., CLIC): conventional technology for particle generation & focusing • Optimize PWFA linac (high gradient): n=1017 cm-3 (set by 30 um driver bunch length) Seryi et al., Proc. PAC (2009) FACET (Facilities for Accelerator Science and Experimental Test Beams at SLAC) designed to address major issues of PWFA for collider applications: • Demonstrate acceleration of witness beam by drive beam • Explore beam quality preservation • Explore positron acceleration

  24. Proton-beam-driven PWFA: TeV in single stage • Drive beam energy and transformer ratio necessitates staging PWFAs • Coupling distance is long for energetic drive beams (~ 10-100 m for ~ 25 GeVe-beams) • Lowers average/geometric gradient • TeV beams available (use proton ring to store tens of kJ of drive beam energy): • Use plasma to convert proton beam energy into lepton beam in a single accelerator stage Caldwell et al., Nature Phys. (2009) • Problem: high acceleration gradients require short bunches (resonant with plasma): • Proton beams difficult to compress (~ 10 cm proton bunch to < 100 micron) • Propose to use a beam-plasma instability to modulate the beam • AWAKE Program at CERN to explore physics of self-modulated proton-beam driven PWFA.

  25. Laser-driven dielectric-based accelerators (Dielectric Laser Accelerators – DLA)

  26. DLA: micron dielectric structures driven by optical lasers • Phase-matching optical EM fields and relativistic particle beam requires novel structure geometries • Several DLA topologies under investigation: • Photonic Crystal Fiber, silica (1890 nm) • E=400 MV/m Lin, Phys. Rev. ST Accel. Beams (2001) • Photonic Crystal “Woodpile”, silicon (2200 nm) • E=400 MV/m Cowan et al., Phys. Rev. ST Accel. Beams (2008) • Transmission Grating Structure, silica (800 nm) • E=830 MV/m Plettner et al., Phys. Rev. ST Accel. Beams (2006)

  27. DLA collider concept: fC bunches at MHz rep rate • 10 TeV collider parameters ICFA Newsletter No. 56 (2011) fC MHz sub-nm emittances • DLA Challenges: • Development of compatible electron and positron (attosec, sub-nm emittance) sources • Development of high average power (low pulse energy) laser systems

  28. Conclusions • Considerable progress in advanced accelerator technology in last 20 years • GeV beams in cm-scale plasmas available using LPA • 10 GeV beams in <1m will be available in next few years • Energy doubling experiment demonstrated using PWFA • Significant efforts world-wide to develop plasma-based acceleration • Extreme Light Infrastructure (ELI): ~700M€ for development application of high power laser systems for particle and radiation generation • CERN AWAKE Program: proton beam-driven PWFA • Many programs in Asia dedicated to advanced accel. research • Laser technology is rapidly advancing, enabling development of advanced acceleration concepts and driving experimental progress • Practical application of technology to colliders poses many technical challenges

  29. When will plasma accelerators be ready to build a collider? TeV ~2035??? • Requires maturity of plasma-based accelerators • LPA: Development of efficient high average (and peak) power laser systems • Many applications along the way, e.g., ultrafast x-ray light sources (compact FEL), gamma ray sources, compact laser-ion sources for medical applications, etc. SLAC Electron beam energy (GeV) SLAC U.TX LBNL RAL LLNL MPQ RAL LBNL LOA Mich RAL SM-LWFA UCLA PBWA 2020 2030 Year demonstrated

  30. Acknowledgments • Many thanks to my colleagues at Berkeley Lab: • Eric Esarey • Carlo Benedetti • Cameron Geddes • CsabaToth • Jean-Luc Vay • WimLeemans

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