Advanced Acceleration Techniques Carl B. Schroeder (LBNL) Office of Science 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 -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 2

New accelerator technology needed M. Tigner, DOES ACCELERATOR-BASED PARTICLE PHYSICS HAVE A FUTURE? Phys. Today (2001)  “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 3

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 LBNL UCLA PBWA RAL SM-LWFA LOA LBNL RAL MPQ Mich LLNL U.TX SLAC RAL Year demonstrated Electron beam energy gain (GeV) Laser-plasma experiments Beam plasma expts 4

 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: Basic collider requirements: energy and luminosity Focusability = low emittance (and energy spread); beam quality preservation High charge / bunch High efficiency (wall-to-driver, driver-to-structure, structure-to-beam) 5

 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 Basic collider requirements: beamstahlung suppression using short beams Collider power Short beams! Beamstrahlung background 6

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

Laser-plasma accelerators: Laser excitation of relativistic electron plasma wave Ti:Sapphire laser: I~10 18 W/cm 2 Plasma wave: electron density perturbation Ponderomotive force (radiation pressure) Laser pulse duration ~ p /c ~ tens fs p =2  c/  p = (  r e -1/2 ) n p -1/2 ~  m Tajima & Dawson, Phys. Rev. Lett. (1979) Esarey, Schroeder, Leemans, Rev. Mod. Phys. (2009) Electron plasma density 8

plasma wave (wakefield) accelerating field: E z ~10 2 GV/m (for n 0 ~10 18 cm -3, I L ~10 18 W/cm 2 ) (~10 3 larger than conventional RF accelerators: from 10’s of km to 10’s of m) Laser-plasma accelerators: GV/m accelerating gradients laser bunch v beam Electron plasma density 9  Higher plasma density yields higher accelerating gradient

Experimental demonstration: 1 GeV beam from 3 cm laser-plasma accelerator Leemans et al., Nature Phys. (2006); Nakamura et al., Phys. Plasmas (2007) H-discharge capillary (10 18 cm -3 ) 3 cm 1012 MeV 2.9% 1.7 mrad 30 pC 10

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

 Laser-plasma interaction length:  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: Operational plasma density: – cm -3 plasma density, n p (cm -3 ) Beam energy (MeV) LBNL 2006 RAL 2009 LLNL 2010 MPQ 2007 LOA 2006 APRI 2008 LBNL 2004 RAL 2004 U.Mich

L stage LPA Laser L accelerator L couple Number of stages:  total length of linac: Accelerator length determined by staging technology plasma density 13

Laser in-coupling using plasma mirrors enables compact staging  Conventional optics approach: stage length determined by damage on conventional final focus laser optics Laser ~10 m  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 (>10 10 ) ~10 cm plasma mirror  Advantage of laser-driven plasma accelerators: short in-coupling distance for laser driver (high average gradient)  Development of staging technology critical to collider application 14

Positron acceleration in quasi-linear regime Accelerating field Plasma density Focusing field e- accel. e+ accel. e- focus e+ focus e- accel+focus e+ accel+focus Direction of laser propagation Transverse position Longitudinal position  Operate in “quasi-linear” regime: Quiver momentum weakly- relativistic a ~ 1 (Intensity ~ W/cm 2 ) Region of acceleration/focusing for both electrons and positrons Stable propagation in plasma channel Dark current free (no self- trapping) 15

laser Laser spot size ~ p Laser pulse length ~ p /2 p a~1 I ~ W/cm 2 for 1 micron laser wavelength plasma density = n 0 ~ cm -3 p ~ 100 micron T laser ~ 100 fs U laser ~ 10’s J Laser driver requirements: 10s of J, 100s of kW  Laser volume:  High repetition rate for luminosity: 10’s kHz  High efficiency (wall to laser)  Laser intensity for large plasma wave in quasi-linear regime: P laser ~ 100’s kW 16

Conceptual Laser-Plasma Accelerator Collider Leemans & Esarey, Physics Today (2009)  Plasma density scalings (minimize construction and operational costs) indicates: n ~ 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 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 %) 17

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

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

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

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

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 22

Concept of a PWFA-based Linear Collider Seryi et al., Proc. PAC (2009) 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=10 17 cm -3 (set by 30 um driver bunch length) Demonstrate acceleration of witness beam by drive beam Explore beam quality preservation Explore positron acceleration FACET (Facilities for Accelerator Science and Experimental Test Beams at SLAC) designed to address major issues of PWFA for collider applications: 23

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 (~ m for ~ 25 GeV e-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. 24

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

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

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

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 28

UCLA PBWA RAL SM-LWFA LOA LBNL RAL MPQ LLNL RAL U.TX SLAC LBNL When will plasma accelerators be ready to build a collider? Mich Year demonstrated Electron beam energy (GeV) ~2035??? TeV 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. 29

Acknowledgments Many thanks to my colleagues at Berkeley Lab: Eric Esarey Carlo Benedetti Cameron Geddes Csaba Toth Jean-Luc Vay Wim Leemans 30