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

E-169: Wakefield Acceleration in Dielectric Structures The proposed experiments at FACET. J.B. Rosenzweig UCLA Dept. of Physics and Astronomy FACET Review — February 19, 2008. E169 Collaboration.

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

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  1. 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

  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, 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

  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 >10 GV/m • Complete studies of transformational technique

  4. Colliders and the energy frontier • Colliders uniquely explore energy frontier • Exp’l growth in equivalent beam energy w/time • Livingston plot: “Moore’s Law” for accelerators • We are now falling off plot! • Challenge in energy, but not only…luminosity as well • How to proceed to linear colliders? • Mature present techniques • Discover new approaches

  5. 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…

  6. 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 < 1 cm? • Approaches • Superconducting • High frequency, normal conducting • Lasers and/or plasma waves, or…

  7. Resonant dielectric structure schematic 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, loading • Reinvent the structure using dielectric (E163, Neptune) • To jump to GV/m, only need mm-THz • Must have new source…

  8. Possible new paradigm for high field accelerators: wakefields • Coherent radiation from bunched, v~c 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

  9. CLIC wakefield-powered resonant scheme CLIC 30 GHz, 150 MV/m structures CLIC V.O.: High gradients, high frequency, EM power from wakefields CLIC drive beam extraction structure Power

  10. 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)

  11. Peak decelerating field • Mode wavelengths Extremely good beam needed • Transformer ratio 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

  12. 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 

  13. Tunable permittivity 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 <50 MV/m by available beam

  14. 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, L=1 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

  15. 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

  16. Breakdown Threshold Observation X-ray data yields bunch length, current

  17. 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

  18. Striking conclusions • Observed breakdown threshold (field from simulations) • Esurf >13 GV • Eacc>5 GV/m! • Much higher than laser data (1.1 GV/m for 100 psec) • Tunneling ionization dominant • Multi-mode excitation gives effective shorter pulses?

  19. E169 at FACET • Approved by SLAC EPAC 12/06 • Research >GV/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)

  20. 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 • Total energy gives field measure • Harmonics are sensitive zdiagnostic

  21. 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 • Phase 3: Scale to 1 m fibers • Alignment • Group velocity & EM exposure • Transverse BBU Before & after momentum distributions (OOPIC) Ez on-axis

  22. 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

  23. 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

  24. 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

  25. 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

  26. E169 Game Plan and Timeline 1 m multi-GeV design study Design, initial construction Slab structures Cerenkov production 1 m multi-GeV acceleration experiments (witness beam) Go Alternate materials 10 cm module acceleration FACET beam commissioning Breakdown studies Novel cylindrical structures 10 cm module BBU studies UCLA Neptune experiments Path to staging 2008 2009 2010 2011 2012

  27. 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…

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