E-169: Wakefield Acceleration in Dielectric Structures A proposal for experiments at the SABER facility J.B.
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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 E169 Collaboration Qu i c k T i m e ™ a n d a T I F F (U n c o m p re s s e d ) d e c o m p re s s o r a re n e e d e d t o s e e t h i s p i c t u re . UCLA 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 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 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 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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… HED in future colliders: ultra-high fields in accelerator High fields in violent accelerating systems d Linear accelerator schematic eE z /mc ~ 1 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 Qu i c k T i m e ™ a n d a Ph o t o - J P EG d e c o m p re s s o r a re n e e d e d to s e e th i s p i c t u re . z 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 Resonant dielectric structure schematic To jump to GV/m, only need mm-THz Must have new source… 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 High gradients, high frequency, EM power from wakefields: CLIC @ CERN CLIC drive beam extraction structure Power CLIC 30 GHz, 150 MV/m structures CLIC wakefield-powered resonant scheme 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 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 Design Parameters a,b z n 4 b a 1 n Peak decelerating field Ez on-axis, OOPIC 4N b re mec 2 eEz,dec 8 a z a 1 Transformer ratio E R z,acc 2 E z,dec Extremely good beam needed Experimental Background Argonne / 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.) Tunable permittivity Gradients limited to <50 MV/m by available 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. 2005 Follow-on planned, no time T-481 “octopus” chamber 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 QuickTime™ and a H.264 decompressor are needed to see this picture. 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 Breakdown Threshold Observation Breakdown Camera Pixel Sum 2.40 10 7 08170cs 2.20 10 7 2.00 10 7 1.80 10 7 1.60 10 7 1.40 10 7 1.20 10 7 1.00 10 7 0 50 100 Bunch Length Variable [rms XRAY] 150 200 OOPIC Simulation Studies Parametric scans Heuristic model benchmarking Determine field levels in experiment 1.5 10 Multi-mode excitation 10 E_dec,max (OOPIC) E_acc max (OOPIC) E_dec,theory 10 E (V/m) 1 10 z Single mode excitation 5 10 9 0 40 60 80 100 120 140 160 a (m) Example scan, comparison to heuristic model Fundamental 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 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 Proposal: E-169 at SABER High-gradient Acceleration Goals in 3 Phases Phase 1: Complete breakdown study explore (a, b, z) parameter space Alternate cladding Alternate materials (e.g. diamond) Explore group velocity effect T Ld /c vg Ld / c 1 Coherent Cerenkov (CCR) measurement z r ≥ 20 m U 25 GeV Q 3 - 5 nC < 10 m A. Kanareykin Total energy gives field measure Harmonics are sensitive z diagnostic eNb E z,dec Ld 2 2 2 nN b re me c 2 z 2 Ld UC Un 2ab a 2 2 n z exp 2b a 1 8 1 z 1a CVD deposited diamond E-169 at SABER: Phase 2 & 3 Phase 2: Observe acceleration z r 10 cm tube length longer bunch, z ~ 150 m moderate gradient Qu i c k T i m e ™ a n d a T I F F (L Z W ) d e c o m p re s s o r a re n e e d e d to s e e t h i s p i c t u re . Single mode Phase 3: Scale to 1 m fibers Alignment Group velocity…. * Before & after momentum distributions (OOPIC) Ez on-axis 150 m < 10 m energy 25 GeV Q 3 - 5 nC Experimental Issues: THz Detection Conical launching horns Impedance matching to free space Direct radiation forward Signal-to-noise ratio Background of CTR from tube end SNR ~ 3 - 5 for 1 cm tube Detectors Pyroelectric Golay cell Helium-cooled bolometer Michelson interferometer for autocorrelation Qu i c k T i m e ™ a n d a T I F F (L Z W ) d e c o m p re s s o r a re n e e d e d to s e e th i s p i c t u re . UCLA THz in Wider Use Screening/remote sensing Many chemical and organic molecules have distinct absorption spectra in THz Transparency of many materials Safe for living tissue Atmosphere spectroscopy Detection of chemical and biological hazards Defect analysis Synergy with LCLS Mittelman, et al. Experimental Issues: Alternate DWA design, cladding, materials Aluminum cladding used in T-481 Vaporized at even moderate wake amplitudes Low vaporization threshold due to low pressure and thermal conductivity of environment Dielectric cladding Lower refractive index provides internal reflection Low power loss, damage resistatn Bragg fiber? Alternate dielectric: CVD diamond High breakdown threshold Doping gives dow SEC Bragg fiber 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 E-169 Timeline SABER operational January 2007 3-week run 3-week run January 2008 Phase 1: 3 weeks @ SABER Phase 2: 3 weeks @ SABER Phase 2+: + 6 months Phase 3 ? January 2009 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 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.”