SLAC Advanced Accelerator Research

accelerators beyond 100 MV/m

Eric R. Colby*

Acting Head of Accelerator Research Division

December 14, 2011

* ecolby@slac.stanford.edu

Outline

• Advances in RF concepts• Novel Acceleration Concepts

• Plasma Wakefield Acceleration• Recent Progress• Towards a PWFA linear collider at 1 TeV

• Laser-Driven Dielectric Accelerators• Recent Progress• Towards a DLA linear collider at 10 TeV

• Thoughts on the Future

RF Accelerators: Prospects for Further Progress

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Sami Tantawi, SLAC

Dual mode accelerating structure

Engineering: Gordon BowdenSolid model: Bob Reed

For details see A.D. Yeremian talk Monday afternoon

• Surface gradients >300 MV/m have been reliably produced in single-cell cavities• Material science to identify the

best materials• Investigation of roles E and H

play in breakdown process• Geometry optimization

• Using high gradient RF requires more efficient, lower cost power sources

• Novel sources using• Photoemission sources• Magnet-free transport• Lower voltages

Plasma Wakefield Acceleration

Progress Demonstrating Key Aspects of Plasma Wakefield Acceleration

• SLAC/UCLA/USC FFTB experiments 1998 - 2006– Plasma Wakefield Acceleration of electrons over meter scales

• 50GeV/m accelerating gradient• Total energy gain of 43GeV

– First plasma acceleration of positrons– Systematic studies of integrated & time dependent focusing

• electrons (extended propagation, emittance preservation @ 10-4m)• positrons (halo formation, emittance growth)

– Refraction of electron beam at plasma boundary– Betatron radiation from strong plasma focusing

• x-rays @ 1014 e-/cc (kT/m)• gammas (e+ production) @ 1017 e-/cc (MT/m)

– Dielectric Wakefield Acceleration• Proof of principle studies of material breakdown threshold

– 14GeV/m induced catastrophic breakdown in 1cm long, 100µm diameter fused Si tubes (we turned the dielectrics into plasmas!)

• 2008 DOE Recognized the need for an ‘Advanced Plasma Acceleration Facility’

Mark Hogan, SLAC

New Installation @ 2km point of SLAC linac:•Chicane for bunch compression•Final Focus for small spots at the IP•Experimental Area (25m)

A Unique Facilityfor Accelerator Science

FACET: Facility for Advanced aCcelerator Experimental Tests

FACET Beam Parameters

Energy 23 GeV

Charge 3 nC

sr 10 µm

sz 20 µm

Peak Current 22 kA

Species e- & e+

Experiments here

Mark Hogan, SLAC

E200: Plasma Wakefield Acceleration5 year targeted R&D on single stage plasma accelerator physics

• Accelerating gradients > 10GeV/m, Focusing fields > 1 MT/m• Meter scale, high density field ionized plasmas (Li, Cs, Rb)• Demonstrate single stage plasma accelerator: meter scale, high gradient, preserved

emittance, low energy spread• First experiments (2012) will quantify head erosion with single high-current bunches• Follow on experiments (2012-2013) will use notch collimator to produce independent

drive & witness bunch• Next phase will use pre-ionized plasmas and tailored profiles to maximize single

stage performance: total energy gain, efficiency• Betatron & Synchrotron radiation, instability studies

Mar

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ogan

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LAC

Several paths are being investigated• Non-linear regime with electrons and positrons

– Majority of activity at SLAC by SLAC/UCLA/MPI collaboration; new program taking shape at DESY• Large wake amplitude, high efficiency, ion column for extended propagation

and emittance preservation• More difficult for positrons• FACET program at SLAC targeted to address many of the issues associated

with applying PWFA to single stage of a PWFA based linear collider

• Linear or quasi-linear regime with electrons– Active experiments at BNL using tailored electron bunch trains to resonantly

drive plasma wave• Potential for larger amplitude and higher transformer ratio• Reduced benefits of ion column: extended propagation, emittance preservation

• Proton Driven Plasmas (PD-PWFA)– Collaboration led by MPI/CERN delivering full proposal to begin experimental

program at CERN staring in 2015. FNAL beginning to evaluate concepts using portions of the Tevatron.• Potential to reach ~TeV e- energy in single long (~400m) plasma stage• Takes advantage of large stored energy in High Energy proton bunches• Reach the energy but difficult to get the beam power needed for luminosity

Mark Hogan, SLAC

Proton Wake Expts

Mark Hogan, SLAC

Key features of a PWFA-LC• Electron drive beam for both electrons and positrons• High current low gradient efficient 25GeV drive linac

– Similar to linac of CERN CTF3, demonstrated performance

• Multiple plasma cells– 20 cells, meter long, 25GeV/cell, 35% energy transfer efficiency

• Main / drive bunches– 2.9E10 / 1E10 PWFA-LC concept will continue to evolve with

further study and simulation

– Bunch charge; Non-gaussian bunch profiles; Flat vs round beams; SC vs NC pulse format; ...

• FACET facility will investigate and iterate these ideas through experiments

Mark Hogan, SLAC

IP Parameter Optimization• Conventional <1TeV LC is typically in low quantum

beamstrahlung regime (when Y=2/3 ωcћ/E <1)– The luminosity then scales as L ~ δB1/2 Pbeam / εny

1/2 (where δB is beamstrahlung induced energy spread)

• High beamstrahlung regime is typical for CLIC at 3TeV• PWFA-LC at 1TeV is in high beamstrahlung regime• Scaling and advantage of high beamstrahlung regime

– L~δB3/2 Pbeam /[σz βy εny]1/2 and δB~σz1/2

– short bunches allow maximizing the luminosity and minimizing the relative energy loss due to beamstrahlung

• Optimization of PWFA-IP parameters performed with high quantum beamstrahlung regime formulae and verified with beam-beam simulations

Mark Hogan, SLAC

Primary Issues for any Plasma-based LC

• Need to understand acceleration of electrons & positrons • Luminosity drives many issues:

– High beam power (20 MW) efficient ac-to-beam conversion – Well defined cms energy small energy spread – Small IP spot sizes small energy spread and small Δε

• These translate into requirements on the plasma acceleration and the experimental programs – High beam loading of e+ and e- (for efficiency) – Acceleration with small energy spread – Preservation of small transverse emittances – maybe flat beams – Bunch repetition rates of 10’s of kHz

• Multiple stages allow better beam control and use of drive-beam – FACET aims to demonstrate single stage before full system test

Mark Hogan, SLAC

A Self-consistent Design of a 1 TeV e-e+ Linear Collider Based on PWFA

• TeV collider design has multiple acceleration stages, each adding ~25 GeV/stage

• FACET PWFA program aims to demonstrate a single stage with needed Q, , efficiency, emittance preservation

• Results will inform designs for future applications (HEP, Photon Science)

see A. Seryi et al., PAC09 Proceedingssee A. Seryi et al., PAC09 Proceedings

E E

Mark Hogan, SLAC

PWFA-LC Efficiency & Power Estimate

• Current design uses Gaussian beams, 35% efficiency

• Tailored current profiles have achieved 90% efficiency in simulation– Better overall efficiency– Improves heat management

problem in plasma cell

• Current design uses Gaussian beams, 35% efficiency

• Tailored current profiles have achieved 90% efficiency in simulation– Better overall efficiency– Improves heat management

problem in plasma cell

127MWModulators 83%Klystrons 65%Distribution 93%.83x.65x.93=50%

127MWModulators 83%Klystrons 65%Distribution 93%.83x.65x.93=50%

90%63.5MW

170MW

Drive Beam57MW

Plasma Wave

Main Beam20MW

Main Beam20MW35%

43MWOther Systems

43MWOther Systems

Mark Hogan, SLAC

1 TeV PWFA LC ParametersEcm = 1 TeV, L = 1034 cm2s-1

Laser-Driven Dielectric Accelerators

Motivation

*28.5 GeV, 1e10 ppp, 1 m x 1 m x 600m (20m for SPPS) beam

**350 MeV, 1e10 ppp, 1m x 1m x 1 mm beam

Source Wavelength

30cm 3cm 3mm 300 m 30 m 3m 300nm

P/l 2

l

Dielectric Damage Threshold

B. C. Stuart, et al, Phys. Rev. Lett., 74, p.2248ff, (1995).

1053nm2 J/cm2 @ 1 ps >2 GV/m

Fused silica, THz range, ~psec exposure

Technion, Israel NTHU,

Taiwan

U. Lancaster, U.K.

Cockcroft Inst, U.K.

Q-Peak Inc.

Stanford

LBNL

SLAC

Tech-X Corp.U. Maryland

DOE

MIT

RadiabeamTechnologies

Incom Inc.

Minotech Engineering

Manhattanville College

Purdue

U. Colorado,UCLA

LLNL

• 51 Participants = 46 US+5 International• 10 Universities• 4 National Labs / Institutes• 5 Companies

• Accelerator

• Laser Science & Technology• Photonics• Novel Materials• Simulations

There is a wealth of concepts being developed…

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cylindrical lensvacuum

channel

electron beam

cylindrical lens

top view

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z

laserbeam

cylindrical lensvacuum

channel

electron beam

cylindrical lens

top view

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top view

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Dielectric Laser Acceleration

Photonic Crystal Fiber

Silica, l=1890 nm, Ez=400 MV/m

Photonic Crystal “Woodpile”

Silicon, l=2200nm, Ez=400 MV/m

Transmission Grating Structure

Silica, l=800nm, Ez=830 MV/m

Structure Candidates for High-Gradient AcceleratorsProjected maximum gradients based on measured material damage threshold data

Much tighter (and all solid-state) coupling means• MW-class not PW-class lasers are needed (Microjoule-class

pulse energies, not 10-100J class laser)• Shot-to-shot reproducibility is better

Waveguiding Structure Waveguiding Structure Phase Mask Structure

Primary challenge for laser acceleration: mode is transverse electromagnetic—must develop longitudinal electric fields to accelerate

Laser Coupling to Structures

~90% power coupling

[courtesy B. Cowan, Z. Wu]

Transverse Coupling to Woodpile Structure

Coupling from transverse waveguide to accelerating mode of the woodpilestructure.>90% coupling from silicon waveguide input couplers to accelerating channel; fabrication R&D of test couplers underway [Z. Wu, D. Xu]

Joel England, SLAC

Benchtop Testing of Structures

Breakdown Strength of Dielectric MaterialsPhase Stability of PBG Structures

1000=Lfor C˚ / phase ̊3

˚/9/..

1

CppmTLn

N

dT

dS

eff

Al2O3 HfO2

Si3N4

SiO2

ZrO2/Y2O3

Si

K. Soong

R. Laouar

2 J/cm2 ~ Epk=5 GV/m

[633 nm HC fiber]

Joel England, SLAC

DLA: The Laser Acceleration Facility at the NLCTA

RF PhotoInjector

Ti:Sapphire LaserSystem

Next Linear Collider Test Accelerator

Cl. 10,000 Clean Room

Counting Room(b. 225)

Optical Microbuncher

Gun Spectrometer

ESB

Next Linear Collider Test Accelerator

E-163

The E163 program has advanced rapidly due to three factors:

• A decade of experience conducting this type of experiment at Stanford

• Extensive NLCTA infrastructure required modest extension to make a functioning facility

• Experienced help from the Test Facilities staff at every step

(Commissioned March 2007)

Experimental Hall

E-Beam Microbunching

C.M.S. Sears, et al. “Production and characterization of attosecond electron bunch trains,” PRST-AB 11, 061301 (2008)].

C.M.S. Sears, et al. “Phase stable net acceleration of electrons from a two-stage optical accelerator.” PRST-AB 11, 101301 (2008).

Net laser acceleration of 1.2 keV demonstrated for 400 attosec microbunches using inverse transition radiation (ITR) at a metal foil.

Joel England, SLAC

First Microaccelerator Demonstration: January 2012

E. Peralta

e-beam

LAS

ER

8 x1mm2 gratingsalignment channels

20x50µm spot

1 mm

Edgar Peralta, Stanford

• Will demonstrate gradient

Multi-Stage Layout Concept

... x 16,000/TeV

Thulium fiber laser =2 l µm

5 modules per wafer1 laser per module (200W per laser)

5 TeV 12.5 km 400,000 lasers

Main Linac (one half)6'' wafer

Loop period=beam repetition rate

Phase control

40 structures per module1 module = 10 cm long1 stage = 750 µm long

Joel England, SLAC

E-Beam Pulse Format

30 attosecN~3e4

=2 mm

159 micropulses per train, 1pC/train

Train length= 1ps300 microns

T_sep=200 nsec

10 TeV DLA LC Parameters

Parameter Units DLA SCRFCM Energy GeV 10000 10000Loaded Gradient MeV/m 400 30Bunch Charge e 3.8E+04 3.0E+10Bunches per train # 159 2820Train Rep Rate MHz 5.00 5e-06Microbunch Length micron 2.6E-03 320.29Design Wavelength micron 1.89 230609.58Normalized Emittance micron 1.0E-04 10.00IP Spot Size nm 0.06 158.00

Disruption Parameter # 1.28E+02 2.06E-01

Beamstrahlung Parameter # 1002.6 5.6Beam Power MW 24.2 339Active Linac Length km 12.5 166.7

Beam Coupling Efficiency # 0.3 0.3

Total Laser/RF Power MW 85.7 1016.5

Wall-plug to Light Efficiency # 0.50 0.60

Total Wall Plug Power MW 171.3 1694.1

Beamstrahlung E-loss % 5.7 91.0

Enhanced Luminosity /cm^2/s 4.09E+36 1.23E+36

Joel England, SLAC

Thoughts for the Future• Electric fields well beyond 100 MV/m have been sustained

reliably in short rf-driven metal accelerators– This remains the nearest-term high gradient technology for a greenfield

TeV-class machine

• Fields beyond 50 GV/m have been sustained in dense plasma wakefield accelerators– Extraordinary gradient has already been demonstrated with respectable

shot-to-shot stability; demonstrations of high quality and high efficiency acceleration are imminent

• Fields well beyond 1 GV/m have been sustained in dielectric accelerator structures in both quasi-CW and broadband – The very small bunch charge, high repetition rate operation of a DLA

offers the only path to multi-TeV accelerators with acceptable beamstrahlung

Power and Efficiency

e-beam

absorption at vacuum box wall

Cherenkov (4%)

200W avg power 2µm wavelength

5% coupling loss

30% coupling to e-beam

(61%)beam dump

Per Module:Accelerator absorption loss: 5 mWCherenkov absorption: 10 mWWaveguide absorption loss: 577 mW(assumes SiO2 substrate, 1e-3 dB/m)

assumes near 100% efficiency of waveguide couplers, splitters

Joel England, SLAC

200W in a fiber? How about 20kW?

http://www.ipgphotonics.com/documents/documents/HP_Broshure.pdf

PWFA-LC Efficiency & Power Estimate

Mark Hogan, SLAC

RESEARCH DEVELOPMENT

Long-Term TimelineGain in performance,Progress towards realization,New scientific knowledge

Concept

Proof-of-PrincipleExperiments

CommunityDevelops

Critical Mass of Experimental Effort Achieved (people+facilities)

Physics Largely Understood

Engineering Tests Underway

Major Project Engineering Begins

Concept implemented as a working machine

Present

OperationalImprovements

compact multistage device

Adapted from AARD SPC report 2011, E. Colby

NLCTA-like test facilityfor DLA technology

5 years 10 years 20 years

Joel England, SLAC

Other Subsystems of PWFA-LC• Design of injectors, damping rings, bunch compressors,

are similar to designs considered for LC and the expertise can be reused– Extensive tests of damping ring concepts at KEK ATF Prototype

Damping Ring and the CESR-TA Test Facility

• Final focus system similar to conventional LC designs– Tested at Final Focus Test Beam and soon at the ATF2 at KEK

• Present design of Final focus and collimation has full energy acceptance of slightly greater than 2%– May need to deal with a factor of two larger energy spread for

PWFA-LC– Further optimization of Final Focus and Collimation will need to

be performed

Mark Hogan, SLAC

Plasma cells & flexibility of the concept• Plasma cell is the heart of the PWFA-LC concept• FACET will be able to produce a wide variety of beams to study the

beam loading and acceleration with different plasmas– The initial tests will be done with lithium plasma

• In the PWFA-LC, the plasma in each cell needs to be renewed between bunches and stability of the plasma parameters is crucial– A high speed hydrogen jet is a possible candidate

• PWFA-LC concept is flexible wrt beam pulse format:– Bunch spacing presently assumed to be typical of NC drive linac: ~4ns

• It can be doubled with the addition of RF separators and delay beamlines that can run along the drive linac

• Increasing the bunch spacing by orders of magnitude could be done with a stretching ring, where the entire drive train would be stored and then bunches would be extracted one-by-one with fast rise kickers

– Alternately could use a SC drive linac for very long spacing

Mark Hogan, SLAC

Wakefield Simulations

beam

Field monitor

[courtesy Cho Ng]

ACE3P simulation of HC-800-1 fiber with axial current excitation. Time domain.

current pulse RMS duration = 0.2 /c[scaled to actual design wavelength]

Optimized PBG Accelerator

Commercial FiberUsed in Experiment

one mode excited many modes excited

blue box= bandgap

blue box= bandgap

Joel England, SLAC

Single-bunch BBU-driven emittance growth is manageable

Misalignments• Xq=Xa=50 nm• X’o=0 rad, Xo=0

nm• Grouping=10Beam• go=1000• s=5/360l• Q=variesAccelerators• Ls=1000l• R=5l• er=2.31• G=500 MV/mQuad Lattice• Leff=2.5 mm• y=90o

• Lq=5 m• Kq=600 T/m

N=234

Fit: de=3.0x10-10 q1.28