E-169: Wakefield Acceleration in Dielectric Structures The proposed experiments at FACET

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E-169 Wakefield Acceleration in Dielectric
StructuresThe proposed experiments at FACET

• J.B. Rosenzweig
• UCLA Dept. of Physics and Astronomy
• FACET Review February 19, 2008

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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 Angeles
• ?Stanford Linear Accelerator Center
• ?University of Southern California
• ?Lawrence Livermore National Laboratory
• ?Euclid TechLabs, LLC
• Collaboration spokespersons

UCLA
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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 gt10 GV/m
• Complete studies of transformational technique

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Colliders and the energy frontier

• Colliders uniquely explore energy frontier
• Expl growth in equivalent beam energy w/time
• Livingston plot Moores Law for accelerators
• We are now falling off plot!
• Challenge in energy, but not onlyluminosity as
  well
• How to proceed to linear colliders?
• Mature present techniques
• Discover new approaches

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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

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HED in future colliders ultra-high fields in
accelerator

• High fields in violent accelerating systems
• High field implies high w
• Relativistic oscillations
• Limit peak power, stored energy
• Challenges
• Breakdown, dark current
• Pulsed heating
• Where is source lt 1 cm?
• Approaches
• Superconducting
• High frequency, normal conducting
• Lasers and/or plasma waves, or

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Scaling the accelerator in size

• Lasers produce copious power (J, gtTW)
• Scale in size by 4 orders of magnitude
• ? lt 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

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Possible new paradigm for high field
accelerators wakefields

• Coherent radiation from bunched, vc 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

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CLIC V.O. High gradients, high frequency, EM
power from wakefields
CLIC drive beam extraction structure
Power
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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)
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Dielectric Wakefield AcceleratorElectromagnetic
characteristics

• Electron bunch drives Cerenkov wake in
  cylindrical dielectric structure
• Variations on structure features
• Multimode excitation
• Wakefields accelerate trailing bunch

• Design Parameters

Ez on-axis, OOPIC
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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 ?
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Experimental BackgroundArgonne / BNL experiments
?E vs. witness delay

• 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.)

Gradients limited to lt50 MV/m by available beam
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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, L1 cm
• Multi-photon v. tunneling ionization
• Beam parameters predict 12 GV/m longitudinal
  wakes
• 30 GeV, 3 nC, ?z 20 ?m
• 48 hr FFTB run, Aug. 2005
• Follow-on planned, no FFTB time
• PRL on breakdown threshold produced

T-481 octopus chamber
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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
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Breakdown Threshold Observation
X-ray data yields bunch length, current
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T-481 Inspection of Structure Damage
Damage consistent with beam-induced discharge
ultrashort bunch
Bisected fiber
longer bunch
Aluminum vaporized from pulsed heating!
Laser transmission test
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Striking conclusions

• Observed breakdown threshold (field from
  simulations)
• Esurf gt13 GV
• Eaccgt5 GV/m!
• Much higher than laser data (1.1 GV/m for 100
  psec)
• Tunneling ionization dominant
• Multi-mode excitation gives effective shorter
  pulses?

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E169 at FACET

• Approved by SLAC EPAC 12/06
• Research gtGV/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)

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E-169 at FACETHigh-gradient acceleration
researchGoals in 3 Phases

• Phase 1 Complete breakdown study
• Coherent Cerenkov (CCR) measurement

• explore (a, b, ?z) parameter space
• Alternate cladding
• Alternate materials (e.g. diamond)
• Explore group velocity effect

?z 20 ?m
?r lt 10 ?m
U 25 GeV
Q 3 - 5 nC

• Total energy gives field measure
• Harmonics are sensitive ?z diagnostic

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E-169 at FACET Phase 2 3

• Phase 2 Observe acceleration, explore new
  designs

• 10 cm tube length
• longer bunch, ?z 150 ?m
• moderate gradient, 1 GV/m
• single mode operation

?z 150 ?m
?r lt 10 ?m
U 25 GeV
Q 3 - 5 nC

• Phase 3 Scale to 1 m fibers

• Alignment
• Group velocity EM exposure
• Transverse BBU

Before after momentum distributions (OOPIC)
Ez on-axis
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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

Autocorreation of coherent edge radiation at BNL
ATF, 120 fsec beam
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Experimental Issues Alternate DWA design,
cladding, materials
A. Kanareykin

• 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

CVD deposited diamond
Bragg fiber
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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
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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
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E169 Game Plan and Timeline
Design, initial construction
Go
UCLA Neptune experiments
2008
2009
2010
2011
2012
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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