E-169: Wakefield Acceleration in Dielectric

Structures

The planned experiments at FACET

E-169: Wakefield Acceleration in Dielectric

Structures

The planned experiments at FACET

J.B. RosenzweigUCLA Dept. of Physics and

AstronomyAAC 2008 — Santa Cruz — July

30, ‘08

J.B. RosenzweigUCLA Dept. of Physics and

AstronomyAAC 2008 — Santa Cruz — July

30, ‘08

E169 CollaborationE169 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, R. Yoder, D. Walz

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

Lawrence Livermore National LaboratoryManhattanville CollegeEuclid TechLabs, LLC

Collaboration spokespersons

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, R. Yoder, D. Walz

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

Lawrence Livermore National LaboratoryManhattanville CollegeEuclid TechLabs, LLC

Collaboration spokespersons

UCLA

E-169 MotivationE-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 >12 GV/m Complete studies of transformational

technique

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 >12 GV/m Complete studies of transformational

technique

Future colliders: ultra-high fields in

accelerator

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 Scaled beams! Breakdown, dark current Pulsed heating What sources < 1 cm?

High fields in violent accelerating systems

High field implies high Relativistic oscillations… Limit peak power Stored energy

Challenges Scaled beams! Breakdown, dark current Pulsed heating What sources < 1 cm?

€

eE z /mcω ~ 1

Scaling the accelerator in size

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 Reinvent the resonant structure using dielectric

(E163, UCLA; see G. Travish talk)

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

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

(E163, UCLA; see G. Travish talk)

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

Resonant dielectric Structure (HFSS sim.)

Possible new paradigm for high field accelerators: wakefields

Possible new paradigm for high field accelerators: wakefields

Coherent radiation from bunched, v~c e- beam Any impedance environment Also powers more exotic schemes: plasma,

dielectrics Non-resonant, short pulse operation possible Intense beams needed by other fields

X-ray FEL X-rays from Compton scattering THz sources

Coherent radiation from bunched, v~c e- beam Any impedance environment Also powers more exotic schemes: plasma,

dielectrics Non-resonant, short pulse operation possible Intense beams needed by other fields

X-ray FEL X-rays from Compton scattering THz sources

High gradients, high frequency, EM power from wakefields: CLIC @ CERNHigh gradients, high frequency, EM

power from wakefields: CLIC @ CERNCLIC wakefield-powered resonant scheme

CLIC 30 GHz, 150 MV/m structures

CLIC drive beam extraction structure

Power

J. Rosenzweig, et al., Nucl. Instrum. Methods A 410 532 (1998).

The dielectric wakefield accelerator

The 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…

Use wakefield collider schemes CLIC style modular system Afterburner possibility for existing accelerators

Spin-offs V. high power THz radiation source

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…

Use wakefield collider schemes CLIC style modular system Afterburner possibility for existing accelerators

Spin-offs V. high power THz radiation source

Dielectric Wakefield Accelerator

Overview

Dielectric Wakefield Accelerator

Overview

Electron bunch ( ≈ 1) 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 ≈−4Nbremec

2

a8π

ε −1εσ 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 (unshaped beam)

T-481: Test-beam exploration of breakdown

threshold

T-481: Test-beam exploration of breakdown

threshold Leverage off E167 Existing optics Beam diagnostics Running protocols

Goal: breakdown studies Al-clad fused silica fibers

ID 100/200 m, OD 325 m, L=1 cm

Avalanche v. tunneling ionization Beam parameters indicate ≤12

GV/m longitudinal wakes! 30 GeV, 3 nC, σz ≥ 20 m

48 hr FFTB run, Aug. 2005

Leverage off E167 Existing optics Beam diagnostics Running protocols

Goal: breakdown studies Al-clad fused silica fibers

ID 100/200 m, OD 325 m, L=1 cm

Avalanche v. tunneling ionization Beam parameters indicate ≤12

GV/m longitudinal wakes! 30 GeV, 3 nC, σz ≥ 20 m

48 hr FFTB run, Aug. 2005T-481 “octopus” chamber

T481: Beam ObservationsT481: 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… dielectric more robust

Observed breakdown threshold (field from simulations) 13.8 GV/m surface field 5.5 GV/m deceleration field Multi-mode effect?

Correlations to post-mortem inspection

Details in G. Travish talk, PRL

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… dielectric more robust

Observed breakdown threshold (field from simulations) 13.8 GV/m surface field 5.5 GV/m deceleration field Multi-mode effect?

Correlations to post-mortem inspection

Details in G. Travish talk, PRL

OOPIC Simulation StudiesOOPIC Simulation Studies Parametric scans Heuristic model

benchmarking Determine field levels in

experiment Show pulse duration…

Multi-mode excitation – short, separated pulse

Single mode excitation

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 ( )m

E169 at FACET: overviewE169 at FACET: overview Research GV/m acceleration scheme in DWA Push technique for next generation accelerators Goals

Explore breakdown issues in detail Determine usable field envelope Coherent Cerenkov radiation measurements Explore alternate materials Explore alternate designs and cladding Varying tube dimensions

Impedance change Breakdown dependence on wake pulse length

Approved experiment (EPAC, Jan. 2007) Awaits FACET construction

Research GV/m acceleration scheme in DWA Push technique for next generation accelerators Goals

Explore breakdown issues in detail Determine usable field envelope Coherent Cerenkov radiation measurements Explore alternate materials Explore alternate designs and cladding Varying tube dimensions

Impedance change Breakdown dependence on wake pulse length

Approved experiment (EPAC, Jan. 2007) Awaits FACET construction

E-169: High-gradient Acceleration

Goals in 3 Phases

E-169: High-gradient Acceleration

Goals in 3 Phases Phase 1: Complete breakdown study

(when does E169->E168!)

Coherent Cerenkov (CCR) measurement

explore (a, b, σz) parameter space

Alternate cladding

Alternate materials (e.g. CVD diamond)

Explore group velocity effect

σz≥ 20 m

σr< 10 m

U 25 GeV

Q 3 - 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( )

FACET beam parameters for E169: high gradient case

E-169 at FACET: Phase 2 & 3E-169 at FACET: Phase 2 & 3

Phase 2: Observe acceleration

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 length

Ez on-axisBefore & after momentum distributions (OOPIC)

*

Alignment

Group velocity & EM exposureFACET beam parameters for E169: acceleration case

Experimental Issues: THz DetectionExperimental Issues: THz Detection

Conical launching horns

Signal-to-noise ratio

Detectors

Test at Neptune now…

Impedance matching to free space

Direct radiation forward

Background of CTR from tube end

SNR ~ 3 - 5 for 1 cm tube

Pyroelectric

Golay cell

Helium-cooled bolometer

Michelson interferometer for autocorrelation

Neptune THz CCR experiment

Neptune THz CCR experiment

OpticsWaveguide

See presentation by A. Cook

Beam Energy 11 MeV Charge 300 pC

Bunch length 200 um RMS radius 50 - 100 um

Experimental Issues: Alternate DWA design,

cladding, materials

Experimental Issues: Alternate DWA design,

cladding, materials Aluminum cladding used in T-

481

Dielectric cladding

Bragg fiber? Low HOM

Alternate dielectric: CVD diamond Ultra-high breakdown

threshold Doping gives low SEC

Vaporized at even moderate wake amplitudes

Low vaporization threshold due to low pressure

and thermal conductivity of environment

Lower refractive index provides internal reflection

Low power loss, damage resistant

Bragg fiber A. Kanareykin

CVD deposited diamond

Alternate geometry: slabAlternate geometry: slab

Slab geometry suppresses transverse wakes* Also connects to optical

case

Price: reduced wake amplitude

Interesting tests at FACET Diamond example, 600

MV/m

Slab geometry suppresses transverse wakes* Also connects to optical

case

Price: reduced wake amplitude

Interesting tests at FACET Diamond example, 600

MV/m*A. Tremaine, J. Rosenzweig, P. Schoessow, Phys. Rev. E 56, 7204 (1997)

E-169: Implementation/Diagnostics

E-169: 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…Much shared with general SLAC goals, E168

Conclusions/directionsConclusions/directions

Unique opportunity to explore GV/m dielectric wakes at FACET Flexible, ultra-intense beams Only possible at SLAC FACET Low gradient experiments at UCLA Neptune

Extremely promising first run Collaboration/approach validated

Much physics, parameter space to explore

Unique opportunity to explore GV/m dielectric wakes at FACET Flexible, ultra-intense beams Only possible at SLAC FACET Low gradient experiments at UCLA Neptune

Extremely promising first run Collaboration/approach validated

Much physics, parameter space to explore