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