E-169: Wakefield Acceleration in Dielectric

StructuresThe proposed experiments at

FACETJ.B. Rosenzweig

UCLA Dept. of Physics and Astronomy

FACET Review — February 19, 2008

E169 Collaboration

H. Badakov, M. Berry, I. Blumenfeld, A. Cook, F.-J. Decker, M. Hogan, R. Ischebeck, R. Iverson, A. Kanareykin, N. Kirby, P. Muggli, J.B. Rosenzweig, R. Siemann, M.C. Thompson,

R. Tikhoplav, G. Travish, D. Walz

Department of Physics and Astronomy, University of California, Los AngelesStanford Linear Accelerator CenterUniversity of Southern California

Lawrence Livermore National LaboratoryEuclid TechLabs, LLC

Collaboration spokespersons

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

UCLA

QuickTime™ and a decompressor

are needed to see this picture.

E-169 Motivation Take advantage of unique experimental

opportunity at SLAC FACET: ultra-short intense beams Advanced accelerators for high energy frontier Very promising path: dielectric wakefields

Extend successful T-481 investigations Dielectric wakes >10 GV/m Complete studies of transformational

technique

Colliders and the energy frontier

Colliders uniquely explore energy frontier

Exp’l growth in equivalent beam energy w/time Livingston plot: “Moore’s

Law” for accelerators We are now falling off plot!

Challenge in energy, but not only…luminosity as well

How to proceed to linear colliders? Mature present techniques Discover new approaches

Meeting the energy challenge

Avoid gigantism Cost above all Higher fields implied

Higher fields give physics challenges Linacs: accelerating fields

Enter world of high energy density (HED) physics Impacts luminosity

challenge…

HED in future colliders: ultra-high fields in

accelerator High fields in violent accelerating systems

High field implies high Relativistic oscillations… Limit peak power, stored energy

Challenges Breakdown, dark current Pulsed heating Where is source < 1 cm?

Approaches Superconducting High frequency, normal conducting Lasers and/or plasma waves, or…

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

€

eE z /mcω ~ 1

Scaling the accelerator in size

Lasers produce copious power (~J, >TW) Scale in size by 4 orders of magnitude < 1 m gives challenges in beam dynamics, loading Reinvent the structure using dielectric (E163,

Neptune)

To jump to GV/m, only need mm-THz Must have new source…

Resonant dielectric structure schematic

Possible new paradigm for high field accelerators: wakefields Coherent radiation from bunched, v~c e- beam

Any impedance environment Powers next generation or exotic schemes Plasma, dielectrics…

Non-resonant, short pulse operation possible High fields without breakdown?

Intense beams needed by other fields X-ray FEL, X-rays from Compton scattering THz sources for imaging with chemical signature

CLIC V.O.: High gradients, high frequency, EM power from wakefields

CLIC wakefield-powered resonant scheme

CLIC 30 GHz, 150 MV/m structures

CLIC drive beam extraction structure

Power

Simpler approach: Collinear dielectric wakefield

accelerator

Higher accelerating gradients: GV/m level Dielectric based, low loss, short pulse Higher gradient than optical? Different breakdown

mechanism No charged particles in beam path… field configuration

simpler Wakefield collider schemes

Modular system Afterburner possibility

Spin-offs THz radiation source Imaging, acceleration…

"Towards a Plasma Wake-field Acceleration-based Linear Collider", J.B. Rosenzweig, et al., Nucl. Instrum. Methods A 410 532 (1998)

Dielectric Wakefield Accelerator

Electromagnetic characteristics Electron bunch drives Cerenkov wake in cylindrical dielectric structure

Variations on structure featuresMultimode excitation

Wakefields accelerate trailing bunch Mode wavelengths

€

n ≈4 b − a( )

nε −1

Peak decelerating field

€

eE z,dec ≈ −4Nbremec2

a 8πε −1

εσ z + a ⎡

⎣ ⎢

⎤

⎦ ⎥

Design Parameters

€

a,b

€

σ z

€

Ez on-axis, OOPIC

*

Extremely good beam needed

€

R =E z,acc

E z,dec

≤ 2

Transformer ratio

OOPIC Simulation Studies Parametric scans Heuristic model

benchmarking Analyze experiments:

Field values Beam dynamics Radiation production

Multi-mode excitation (short bunch)

Single mode excitation (longer bunch)

Example scan, comparison to heuristic model Fundamental

0

5 109

1 1010

1.5 1010

40 60 80 100120140160

E_dec,max (OOPIC)E_acc max (OOPIC)E_dec,theory

Ez (V/m)

a ()

Experimental BackgroundArgonne / BNL experiments

Proof-of-principle experiments (W. Gai, et al.)

ANL AATF Mode superposition (J. Power, et al. and S. Shchelkunov, et al.)

ANL AWA, BNL Transformer ratio improvement (J. Power, et al.)

Beam shaping Tunable permittivity structures

For external feeding (A. Kanareykin, et al.)

Tunable permittivity

E vs. witness delay

Gradients limited to <50 MV/m by available beam

T-481: Test-beam exploration of breakdown

threshold Leverage off E167 Existing optics, diagnostics, protocols

Goal: breakdown studies Al-clad fused silica fibers

ID 100/200 m, OD 325 m, L=1 cm Multi-photon v. tunneling ionization Beam parameters predict ≤12 GV/m

longitudinal wakes 30 GeV, 3 nC, σz ≥ 20 m

48 hr FFTB run, Aug. 2005 Follow-on planned, no FFTB time PRL on breakdown threshold

producedT-481 “octopus” chamber

T481: Beam Observations Multiple tube assemblies Alignment to beam path Scanning of bunch lengths for

wake amplitude variation Excellent flexibility: 0.5-12

GV/m Vaporization of Al cladding…

use dielectric, more robust Breakdown monitored by light

emission Correlations to post-mortem

inspection

View end of dielectric tube; frames sorted by increasing peak current

1.00 107

1.20 107

1.40 107

1.60 107

1.80 107

2.00 107

2.20 107

2.40 107

0 50 100 150 200

08170cs

Breakdown Camera Pixel Sum

Bunch Length Variable[rms XRAY]

Breakdown Threshold Observation

X-ray data yields bunch length, current

T-481: Inspection of Structure Damage

ultrashortbunch

longerbunch

Aluminum vaporized from pulsed heating!

Laser transmission test

Bisected fiber

Damage consistent with beam-induced discharge

Striking conclusions Observed breakdown threshold (field from

simulations) Esurf >13 GV Eacc>5 GV/m!

Much higher than laser data (1.1 GV/m for 100 psec) Tunneling ionization dominant Multi-mode excitation gives effective shorter pulses?

E169 at FACET Approved by SLAC EPAC 12/06 Research >GV/m acceleration scheme in DWA Push technique for next generation accelerators Goals:

Explore breakdown issues in detail Varying tube dimensions

Change impedance, mode content Breakdown dependence on wake pulse length

Determine usable field envelope Coherent Cerenkov radiation measurements: Explore alternate materials (diamond, etc) Observe acceleration Explore alternate structure designs Examine deflecting modes, transverse BBU Push to modular DWA demonstration (1 m section)

E-169 at FACETHigh-gradient acceleration research

Goals in 3 Phases Phase 1: Complete breakdown study

Coherent Cerenkov (CCR) measurement

explore (a, b, σz) parameter space

Alternate cladding

Alternate materials (e.g. diamond)

Explore group velocity effect

σσzz≥ ≥ 20 20 mm

σσrr< 10 < 10 mm

UU 25 GeV25 GeV

QQ 3 - 5 nC3 - 5 nC

€

UC ≈ eNb E z,decLd

2

€

Un ≈π 2nNb

2remec2σ z

2Ld

2a b − a( )2 8π ε −1( )εσ z + ε −1( )a[ ]

exp −nπσ z

2 b − a( ) ε −1

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2 ⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

Total energy gives field measure

Harmonics are sensitive σz diagnostic

€

T = Ld / c − vg( ) ≤ εLd / c ε −1( )

E-169 at FACET: Phase 2 & 3 Phase 2: Observe acceleration, explore new designs

10 cm tube length

longer bunch, σz ~ 150 m

moderate gradient, 1 GV/m

single mode operation

σz150 m

σr< 10 m

U 25 GeV

Q 3 - 5 nC Phase 3: Scale to 1 m fibers

Ez on-axis

Before & after momentum distributions (OOPIC)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Alignment

Group velocity & EM exposure

Transverse BBU

Experimental Issues: THz Detection

Conical launching horns

Signal-to-noise ratio

Detectors

Impedance matching to free space

Direct radiation forward

Fabrication, test at UCLA Neptune

Background of CTR from tube end

SNR ~ 3 - 5 for 1 cm tube

Pyroelectric

Golay cell

Helium-cooled bolometer

Michelson interferometer for autocorrelation

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Autocorreation of coherent edge radiation at BNL ATF, 120 fsec beam

Experimental Issues: Alternate DWA design, cladding, materials

Aluminum cladding used in T-481

Dielectric cladding

Alternate dielectric: CVD diamond High breakdown threshold Doping gives low SEC Available for Phase I (Euclid)

Phase 2 Bragg fibers 2D photonic band gap

structures?

Vaporized at even moderate wake amplitudes

Low threshold from low pressure, thermal environment

Lower refractive index provides internal reflection

Low power loss, damage resistant

Bragg fiber

A. Kanareykin

CVD deposited diamond

Alternate design: Slab structure

Slab structure familiar from resonant laser idea

Suppresses BBU! Ultra-short bunch means

~GV/m fields still obtainable

Example: Ez~ 700 MV/m

E-169 at FACET: Implementation/Diagnostics

New precision alignment vessel Upstream/downstream OTR

screens for alignment X-ray stripe CTR/CCR for bunch length Imaging magnetic spectrometer Beam position monitors and

beam current monitors Controls…

Heavy SLAC involvement

Much shared with E168

Path tostaging

E169 Game Plan and Timeline

Go

2008 2009 2010 2011 2012

Design, initial construction

UCLA Neptune experiments

Cerenkov production

FACET beamcommissionin

g

Breakdown studies

Alternate materials

Novel cylindrical structures

10 cm module BBU studies

Slab structures

10 cm module acceleration

1 m multi-GeV acceleration experiments

(witness beam)

1 m multi-GeV design study

Conclusions/directions Extremely promising initial run

Collaboration/approach validated Physics tantalizing; new regime for dielectric

acceleration must be explored Unique opportunity to explore GV/m dielectric

wakes at FACET Flexible, ultra-intense beams Only possible at SLAC FACET

Complementary low gradient experiments at Neptune Conceptual, experimental, and personnel synergies

with E168…