Advanced Acceleration Techniques Carl B Schroeder LBNL 26

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 Office of Science

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 § “Livingston Plot” Saturation of accelerator tech. • Practical limit reached for conventional accelerator technology (RF metallic structures) • Gradient limited by material breakdown - § § M. Tigner, DOES ACCELERATOR-BASED PARTICLE PHYSICS HAVE A FUTURE? Phys. Today (2001) e. g. , X-band demonstration 100 MV/m Largest cost driver is acceleration • ~ 50 MV/m implies ~ 20 km/Te. V • Facility costs scale roughly with facility size (and power consumption) Any future linear Te. V (>Te. V) 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 § Beam plasma expts SLAC U. TX Electron beam energy gain (Ge. V) SLAC § Laser-plasma experiments Mich RAL LBNL LOA RAL SM-LWFA LLNL • 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: LBNL RAL MPQ Ultra-high gradient requires structures to sustain high fields: • Plasma-based acceleration • Development of laser technology for high peak power delivery UCLA PBWA Year demonstrated 4

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/Te. V § 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) 5

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

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

Laser-plasma accelerators: Laser excitation of relativistic electron plasma wave Tajima & Dawson, Phys. Rev. Lett. (1979) Esarey, Schroeder, Leemans, Rev. Mod. Phys. (2009) Plasma wave: electron Ponderomotive force (radiation pressure) 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: Sapphire laser: I~1018 W/cm 2 8

Laser-plasma accelerators: 1 -100 GV/m accelerating gradients Electron plasma density vbeam laser bunch plasma wave (wakefield) accelerating field: Ez ~102 GV/m (for n 0~1018 cm-3, IL~1018 W/cm 2) (~103 larger than conventional RF accelerators: from 10’s of km to 10’s of m) § Higher plasma density yields higher accelerating gradient 9

Experimental demonstration: 1 Ge. V beam from 3 cm laser-plasma accelerator H-discharge capillary (1018 cm-3) 3 cm 1012 Me. V 2. 9% 1. 7 mrad 30 p. C Leemans et al. , Nature Phys. (2006); Nakamura et al. , Phys. Plasmas (2007) 10

Limits to Energy Gain: Diffraction, Dephasing, Depletion ZR vbeam laser bunch Limits to single stage energy gain: § Laser Diffraction (~Rayleigh range) Ø mitigated by transverse plasma density tailoring (plasma channel) § Beam-Plasma Wave Dephasing Ø 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 11

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

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

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 § 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 14

Positron acceleration in quasi-linear regime e- accel. Accelerating field § Plasma density Transverse position e+ accel. Operate in “quasi-linear” regime: • (Intensity ~ 1018 W/cm 2) e- accel+focus e+ accel+focus e- focus Quiver momentum weaklyrelativistic a ~ 1 • Region of acceleration/focusing for both electrons and positrons • Stable propagation in plasma channel • Dark current free (no selftrapping) Focusing field e+ focus Longitudinal position Direction of laser propagation 15

Laser driver requirements: 10 s of J, 100 s of k. W 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/cm 2 for 1 micron laser wavelength § Laser volume: plasma density = n 0 ~ 1017 cm-3 p~ 100 micron Tlaser ~ 100 fs Ulaser~ 10’s J § High repetition rate for luminosity: 10’s k. Hz § High efficiency (wall to laser) Plaser~ 100’s k. W 16

Conceptual Laser-Plasma Accelerator Collider Leemans & Esarey, Physics Today (2009) § 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: ‣ ~30 J laser energy/stage required ‣ energy gain/stage ~10 Ge. V in ~1 m Laser technology development required: § High luminosity requires high rep-rate lasers (10’s k. Hz) § Requires development of high average power lasers (100’s k. W ) § High laser efficiency (~tens of %) 17

BELLA: BErkeley Lab Laser Accelerator BELLA Facility: state-of-the-art 1. 3 PW-laser for laser accelerator science: >42 J in <40 fs (> 1 PW) at 1 Hz laser and supporting infrastructure at LBNL Critical HEP experiments: • 10 Ge. V electron beam from <1 m LPA • Staging LPAs • Positron acceleration 18

10 Ge. V 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) 19

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

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) 21

SLAC Energy Doubling Experiment Blumenfeld et al. , Nature (2007) § Doubled energy of part of 42 Ge. V 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 • 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 23

Proton-beam-driven PWFA: Te. V 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 Ge. V e-beams) • Lowers average/geometric gradient Te. V beams available (use proton ring to store tens of k. J 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 § 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) 26

DLA collider concept: f. C bunches at MHz rep rate § 10 Te. V collider parameters ICFA Newsletter No. 56 (2011) f. C MHz sub-nm emittances § DLA Challenges: • Development of compatible electron and positron (attosec, sub-nm emittance) sources 27

Conclusions § Considerable progress in advanced accelerator technology in last 20 years • Ge. V beams in cm-scale plasmas available using LPA • 10 Ge. V beams in <1 m 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): ~700 M€ 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

When will plasma accelerators be ready to build a collider? Te. V ~2035? ? ? Electron beam energy (Ge. V) SLAC • Requires maturity of plasmabased accelerators • LPA: Development of efficient high average (and peak) power laser systems U. TX LBNL RAL MPQ LLNL Mich RAL LBNL LOA RAL SM-LWFA UCLA PBWA 2020 2030 • 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. Year demonstrated 29

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