E-169: Wakefield Acceleration in Dielectric Structures The planned experiments at FACET J.B. Rosenzweig UCLA Dept. of Physics and Astronomy AAC 2008 — Santa Cruz — July 30, ‘08 J.B. Rosenzweig UCLA Dept. of Physics and Astronomy AAC 2008 — Santa Cruz — July 30, ‘08

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 , R. Yoder , D. Walz   Department of Physics and Astronomy, University of California, Los Angeles  Stanford Linear Accelerator Center  University of Southern California  Lawrence Livermore National Laboratory  Manhattanville College  Euclid 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 Angeles  Stanford Linear Accelerator Center  University of Southern California  Lawrence Livermore National Laboratory  Manhattanville College  Euclid TechLabs, LLC Collaboration spokespersons UCLA

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 >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  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?

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  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: CERN CLIC 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 (1998).

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  Electron bunch (  ≈ 1) drives Cerenkov wake in cylindrical dielectric structure  Variations on structure features  Multimode excitation  Wakefields accelerate trailing bunch  Mode wavelengths  Peak decelerating field  Design Parameters Ez on-axis, OOPIC * Extremely good beam needed  Transformer ratio (unshaped beam)

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,  z ≥ 20  m  48 hr FFTB run, Aug  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,  z ≥ 20  m  48 hr FFTB run, Aug T-481 “octopus” chamber

T481: Beam Observations  Multiple tube assemblies  Alignment to beam path  Scanning of bunch lengths for wake amplitude variation  Excellent flexibility: 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: 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 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

E169 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  Phase 1: Complete breakdown study (when does E169->E168!)  Coherent Cerenkov (CCR) measurement explore (a, b,  z ) parameter space Alternate cladding Alternate materials (e.g. CVD diamond) Explore group velocity effect  z ≥ 20  m  r < 10  m U 25 GeV Q nC Total energy gives field measure Harmonics are sensitive  z diagnostic FACET beam parameters for E169: high gradient case

E-169 at FACET: Phase 2 & 3  Phase 2: Observe acceleration 10 cm tube length longer bunch,  z ~ 150  m moderate gradient, 1 GV/m single mode operation  z 150  m  r < 10  m U 25 GeV Q nC  Phase 3: Scale to 1 m length E z on-axis Before & after momentum distributions (OOPIC) * Alignment Group velocity & EM exposure FACET beam parameters for E169: acceleration case

Experimental 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 ~ for 1 cm tube Pyroelectric Golay cell Helium-cooled bolometer Michelson interferometer for autocorrelation

Neptune THz CCR experiment Optics Waveguide See presentation by A. Cook Beam Energy 11 MeVCharge 300 pC Bunch length 200 um RMS radius um

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: 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  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/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