2. E-169: Wakefield Acceleration in Dielectric Structures A proposal for experiments at the SABER facility J.B. Rosenzweig UCLA Dept. of Physics and Astronomy SLAC EPAC - December 4, 2006 J.B. Rosenzweig UCLA Dept. of Physics and Astronomy SLAC EPAC - December 4, 2006

3. 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 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

4. Proposal Motivation  Take advantage of unique experimental opportunity at SLAC  SABER: ultra-short intense beams  Advanced accelerators for high energy frontier  Promising path: dielectric wakefields  Extend successful T-481 investigations  Dielectric wakes >10 GW  Complete studies of revolutionary technique  Take advantage of unique experimental opportunity at SLAC  SABER: ultra-short intense beams  Advanced accelerators for high energy frontier  Promising path: dielectric wakefields  Extend successful T-481 investigations  Dielectric wakes >10 GW  Complete studies of revolutionary technique

5. 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  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

6. Meeting the energy challenge  Avoid gigantism  Cost above all  Higher fields give physics challenges  Linacs: accelerating fields  Enter world of high energy density (HED) physics  Impacts luminosity challenge…  Avoid gigantism  Cost above all  Higher fields give physics challenges  Linacs: accelerating fields  Enter world of high energy density (HED) physics  Impacts luminosity challenge…

7. Linear accelerator schematic HED in future colliders: ultra-high fields in accelerator  High fields in violent accelerating systems  High field implies small  Relativistic oscillations…  Limit peak power  Limit stored energy  Diseases  Breakdown, dark current  Pulsed heating  Where is source < 1 cm?  Approaches  High frequency, normal cond.  Superconducting  Lasers and/or plasma waves  High fields in violent accelerating systems  High field implies small  Relativistic oscillations…  Limit peak power  Limit stored energy  Diseases  Breakdown, dark current  Pulsed heating  Where is source < 1 cm?  Approaches  High frequency, normal cond.  Superconducting  Lasers and/or plasma waves

8. Scaling the accelerator in size  Lasers produce copious power (~J, >TW)  Scale in size by 4 orders of magnitude  < 1  m challenge in beam dynamics  Reinvent the structure using dielectric  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 challenge in beam dynamics  Reinvent the structure using dielectric  To jump to GV/m, only need mm-THz  Must have new source… Resonant dielectric structure schematic

9. Possible new paradigm for high field accelerators: wakefields  Coherent radiation from bunched, v~c e - beam  Any impedance environment  Non-resonant, short pulse operation possible  Also powers more exotic schemes  Plasma, dielectrics…  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  Non-resonant, short pulse operation possible  Also powers more exotic schemes  Plasma, dielectrics…  Intense beams needed by other fields  X-ray FEL, X-rays from Compton scattering  THz sources

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

11. 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  Afterburner possibility for existing accelerators  CLIC style modular system  Spin-offs  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  Afterburner possibility for existing accelerators  CLIC style modular system  Spin-offs  THz radiation source

12. 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

13. Experimental Background Argonne / BNL experiments  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.)  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.) Tunable permittivity  E vs. witness delay Gradients limited to <50 MV/m by available beam

14. 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  Follow-on planned, no time  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  Follow-on planned, no time 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… dielectric more robust  Observed breakdown threshold (field from simulations)  4 GV/m surface field  2 GV/m acceleration field!  Correlations to post-mortem inspection  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)  4 GV/m surface field  2 GV/m acceleration field!  Correlations to post-mortem inspection View end of dielectric tube; frames sorted by increasing peak current

16. Breakdown Threshold Observation

17. OOPIC Simulation Studies  Parametric scans  Heuristic model benchmarking  Determine field levels in experiment Multi-mode excitation Single mode excitation Example scan, comparison to heuristic model Fundamental

18. T-481: Inspection of Structure Damage ultrashort bunch longer bunch Aluminum vaporized from pulsed heating! Laser transmission test Bisected fiber Damage consistent with beam-induced discharge

19. Proposal: E169 at SABER  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  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

20. Proposal: E-169 at SABER High-gradient Acceleration Goals 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 < 10  m U 25 GeV Q 3 - 5 nC A. Kanareykin Total energy gives field measure Harmonics are sensitive  z diagnostic CVD deposited diamond

21. E-169 at SABER: Phase 2 & 3  Phase 2: Observe acceleration 10 cm tube length longer bunch,  z ~ 150  m moderate gradient Single mode  z 150  m  r < 10  m energy25 GeV Q 3 - 5 nC  Phase 3: Scale to 1 m fibers E z on-axis Before & after momentum distributions (OOPIC) * Alignment Group velocity….

22. Experimental Issues: THz Detection  Conical launching horns  Signal-to-noise ratio  Detectors 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

23. THz in Wider Use  Screening/remote sensing  Atmosphere spectroscopy  Defect analysis  Synergy with LCLS Many chemical and organic molecules have distinct absorption spectra in THz Transparency of many materials Safe for living tissue UCLA Detection of chemical and biological hazards Mittelman, et al.

24. Experimental Issues: Alternate DWA design, cladding, materials  Aluminum cladding used in T-481  Dielectric cladding  Bragg fiber?  Alternate dielectric: CVD diamond  High breakdown threshold  Doping gives dow 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 resistatn Bragg fiber

25. E-169 at SABER: 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. E-169 Timeline SABER operational January 2007 January 2008 January 2009 3-week run 3-week run Phase 3 ? Phase 1: 3 weeks @ SABER Phase 2: 3 weeks @ SABER Phase 2+: + 6 months

27. Conclusions/directions  Unique opportunity to explore GV/m dielectric wakes at SABER  Flexible, ultra-intense beams  Only possible at SLAC SABER  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 SABER  Flexible, ultra-intense beams  Only possible at SLAC SABER  Low gradient experiments at UCLA Neptune  Extremely promising first run  Collaboration/approach validated  Much physics, parameter space to explore

28. Marx panel recommendation July 2006 “ A major challenge for the accelerator science community is to identify and develop new concepts for future energy frontier accelerators that will be able to provide the exploration tools needed for HEP within a feasible cost to society. The future of accelerator-based HEP will be limited unless new ideas and new accelerator directions are developed to address the demands of beam energy and luminosity and consequently the management of beam power, energy recovery, accelerator power, size, and cost. ”