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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. Rosenzweig UCLA Dept. of Physics and Astronomy AAC 2008 — Santa Cruz — July 30, ‘08. E169 Collaboration.

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

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

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

  3. 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

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

  5. 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… Resonant dielectric Structure (HFSS sim.)

  6. 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

  7. CLIC wakefield-powered resonant scheme CLIC 30 GHz, 150 MV/m structures High gradients, high frequency, EM power from wakefields: CLIC @ CERN CLIC drive beam extraction structure Power J. Rosenzweig, et al., Nucl. Instrum. Methods A 410 532 (1998).

  8. 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

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

  10. 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. 2005 T-481 “octopus” chamber

  11. 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… 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

  12. 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 

  13. 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

  14. E-169: High-gradient AccelerationGoals 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 • Total energy gives field measure • Harmonics are sensitive zdiagnostic FACET beam parameters for E169: high gradient case

  15. 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 • Phase 3: Scale to 1 m length • Alignment • Group velocity & EM exposure FACET beam parameters for E169: acceleration case * Before & after momentum distributions (OOPIC) Ez on-axis

  16. 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 ~ 3 - 5 for 1 cm tube • Pyroelectric • Golay cell • Helium-cooled bolometer • Michelson interferometer for autocorrelation

  17. Neptune THz CCR experiment Beam Energy11 MeV Charge 300 pC Bunch length200 um RMS radius50 - 100 um Waveguide Optics See presentation by A. Cook

  18. 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 Bragg fiber • Lower refractive index provides internal reflection • Low power loss, damage resistant A. Kanareykin CVD deposited diamond

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

  20. 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

  21. 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

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