Advanced Acceleration Techniques

Carl B. Schroeder

(LBNL)

Office of Science

26th 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-LWFALOA

LBNLRAL

MPQ

Mich

LLNL

U.TXSLAC

SLAC

RAL

Year demonstrated

Electro

n b

eam en

ergy g

ain (G

eV)

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

€

Pwall ∝ η −1Pbeam = η −14πσ x

*σ y*

Ne

⋅ E⋅ L

€

L ∝ 1 E 2

€

Pbeam =4πσ x

*σ y*

Ne

⋅ E⋅ L

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

€

L

E 2 ∝nγ

2 / 3ηPwall

σ *σ z1/ 2

€

nγ ≈ 3.5δE ∝Ne

2 / 3

σ *1/ 3 σ z

1/ 3 ∝ L1/ 3σ z1/ 3

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~1018 W/cm2

€

∂2

∂t 2+ ωp

2 ⎛

⎝ ⎜

⎞

⎠ ⎟n

n0

= c 2∇ 2 1

4

eELaser

mc 2ω

⎛

⎝ ⎜

⎞

⎠ ⎟2

Plasma wave: electron density perturbation

Ponderomotive force (radiation pressure)

€

n n0Laser pulse duration ~ p/c ~ tens fs

€

vwave ≈ vg ≈ cp =2c/p= (re-1/2 ) np

-1/2 ~10-100 m

Tajima & Dawson, Phys. Rev. Lett. (1979)Esarey, Schroeder, Leemans, Rev. Mod. Phys. (2009)

Electron plasma density

8

€

E z ~mcω p

e

⎛

⎝ ⎜

⎞

⎠ ⎟≈ 96V/m( ) n0[cm-3]

plasma wave (wakefield) accelerating field:

Ez ~102 GV/m (for n0~1018 cm-3, IL~1018 W/cm2)

(~103 larger than conventional RF accelerators: from 10’s of km to 10’s of m)

Laser-plasma accelerators: 1-100 GV/m accelerating gradients

laser

bunch

€

vphase wave ≈ vgroup laser

vbeam

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 (1018 cm-3)

3 cm

1012 MeV2.9%1.7 mrad30 pC

10

laser

bunch

ZR

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

€

vphase wave ≈ vgroup laser

€

Ldeplete ∝ n−3 / 2Scale length of laser energy deposition:

vbeam

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:

€

Ldeplete ∝ n−3 / 2

Operational plasma density: 1016 – 1018 cm-3

plasma density, np (cm-3)B

eam

ene

rgy

(MeV

)

€

E z ~ mecω p e( ) ∝ n

€

E z ⋅ Lint ∝ 1 n

€

Δγ∝1

n

LBNL 2006

RAL 2009

LLNL 2010

MPQ 2007

LOA 2006

APRI 2008

LBNL 2004

RAL 2004

U.Mich 2008

€

Ne ∝ 1 n

€

P ∝ n 12

Lstage

LPA

Laser

LacceleratorLcouple

€

Nstage =E cm

Wstage

∝ nNumber of stages:

€

Ltotal = NstageLstage

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

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 (>1010)

~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 application14

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

Tra

nsve

rse

posi

tion

Longitudinal position

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)

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laserLaser spot size ~ p

Laser pulse length ~ p/2

p

a~1 I ~ 1018 W/cm2

for 1 micron laser wavelength

plasma density = n0 ~ 1017 cm-3 p~ 100 micron Tlaser ~ 100 fs€

a ≈ 8.6 ×10−10 λ[μm]I1/ 2[W /cm2]

Ulaser~ 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)

€

~ λ p3

Laser intensity for large plasma wave in quasi-linear regime:

Plaser~ 100’s kW

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:

‣ ~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 <40 fs (> 1PW) at 1 Hz laser and supporting infrastructure at LBNL

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➡ 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

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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=1017 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:

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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 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. €

E z,max ≈ 3 GeV/m Nb

1010

⎛

⎝ ⎜

⎞

⎠ ⎟100 μm

σ z

⎛

⎝ ⎜

⎞

⎠ ⎟

2

ln σ z σ r( )

€

σ z ~ λ p ∝ n−1/ 2

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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-nmemittances

10 TeV collider parameters ICFA Newsletter No. 56 (2011)

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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

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UCLA PBWA

RAL SM-LWFALOA

LBNLRAL

MPQ LLNL

RAL

U.TXSLAC

SLAC

LBNL

When will plasma accelerators be ready to build a collider?

Mich

Year demonstrated

Electron beam

energy (GeV

)

20302020

~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.

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Acknowledgments

Many thanks to my colleagues at Berkeley Lab: Eric EsareyCarlo BenedettiCameron GeddesCsaba TothJean-Luc VayWim Leemans

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