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Compact FEL Based on Dielectric Wakefield Acceleration

Compact FEL Based on Dielectric Wakefield Acceleration. J.B. Rosenzweig UCLA Dept. of Physics and Astronomy Towards a 5 th Generation Light Source Celebration of Claudio Pellegrini Catalina Island — October 2, 2010 . FELs are Big Science. Size=$. Creating a compact FEL.

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Compact FEL Based on Dielectric Wakefield Acceleration

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  1. Compact FEL Based on Dielectric Wakefield Acceleration J.B. Rosenzweig UCLA Dept. of Physics and Astronomy Towards a 5th Generation Light Source Celebration of Claudio Pellegrini Catalina Island — October 2, 2010

  2. FELs are Big Science Size=$

  3. Creating a compact FEL • High brightness beam • Very low charge (pC) • Attosecond pulse • Few 10-8 norm. emittance • High field, short lundulator • With HBB, large r, short Lg • Lowerse- energy needed • 2 GeV hard X-ray FEL J.B. Rosenzweig, et al., Nucl. Instruments Methods A, 593, 39 (2008) F.H. O’Shea et al, PRSTAB 13, 070702 (2010) FEL w/1 pC driver at 2.1 GeV Hybridcryo-undulator: Pr-based, SmCo sheath9 mm l, up to 2.2 T

  4. Scaling the accelerator in size • Lasers produce copious power (~J, >TW) • Scale in by 4 orders of magnitude • challengesin beam dynamics • Reinvent resonant structure using dielectric • GV/m fields possible, breakdown limited… • GV/m allows major reduction in size, cost of FEL, LC • To jump to GV/m, mm-THz may be better: • Beam dynamics, breakdown scaling • Need newpower source… Resonant dielectric laser-excited structure (with HFSS simulated fields)

  5. New paradigm for high field acceleration: wakefields • Coherent radiation from bunched, v~c,e- beam • Any slow-waveenvironment • Powers exotic schemes: plasma, dielectrics • Resonant or non-resonant (short pulse) operation • THz regime easily w/in reach • High average power beams can be produced • Tens of MW, beats lasers… good for FEL, LC • Intense beams needed, synergy with many fields • X-ray FEL, ICS X-ray source, intense THz sources Wakefields in dielectric tube

  6. Schematic of wakefield-based collider J. Rosenzweig, et al., Nucl. Instrum. Methods A 410 532 (1998). (concept borrowed from W. Gai…) • Similar to original CLIC scheme • Study for plasma wakefield accelerator • gg due to charge asymmetry in PWFA • Not a problem for DWA… • FEL can avoid all this complexity, use one module

  7. The dielectric wakefield accelerator Cerenkov scaling Coherent Cerenkov scaling • High accelerating gradients: GV/m level • Dielectric based, low loss, short pulse • Higher gradients than optical possible • Unlike plasma, no charged particles in beam path… • Use wakefield collider schemes • CLIC style modular system • Afterburner (energy multiplier) possible for existing linacs • Spin-offs • High power CCR THz source

  8. Peak decelerating field • Mode wavelengths (quasi-optical) Extremely good beam needed • Transformer ratio (unshaped beam) Dielectric Wakefield AcceleratorHeuristic View • Electron bunch ( ≈ 1) drives wake in cylindrical dielectric structure • Dependent on structure properties • Generally multi-mode excitation • Wakefields accelerate trailing bunch * • Design Parameters Ez on-axis, OOPIC

  9. T-481: Test-beam exploration of breakdown threshold • 1st ultra-short, high charge beams • Beyond pioneering work at ANL… • Much shorter pulses, small radial size • Higher gradients… • Leverage off E167 PWFA • 48 hr FFTB run • Excellent beam 3 nC, z≥ 20 m, 28.5 GeV • Goal: breakdown studies • Al-clad fused SiO2 fibers • ID 100/200 m, OD 325 m, L=1 cm • Avalanche v. tunneling ionization studies • Prediction: beam can exciteEz≤12GV/m T-481 “octopus” chamber

  10. Beam Observations, Analysis longer bunch ultrashort bunch Post mortem images View end of dielectric tube; frames sorted by increasing peak current Breakdown determined by benchmarked OOPIC simulations Breakdown limit: 5.5 GV/mdecel. Field (10 GV/maccel.?) Multi-mode excitation – 100 fs, pulses separated by ps — gives better breakdown dynamics?

  11. 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

  12. E169 at FACET: overview • Research GV/m acceleration scheme in DWA • Goals • Explore breakdown issues in detail • Determine usable field envelope • Coherent Cerenkov radiation measurements • Varying tube dimensions • Impedance, group velocity dependences • Explore alternate materials • Explore alternate designs and cladding • Slab structure (permits higher Q, low wakes) • Radial and longitudinal periodicity… • Observe acceleration • Awaits FACET construction • Reapproval recently submitted • Add AWA group to collaboration CVD deposited diamond Already explored At UCLA, BNL Bragg fiber Slab dielectric structure (like optical)

  13. Observation of THz Coherent Cerenkov Wakefields @ Neptune • Chicane-compressed (200 mm) 0.3 nC beam • Focused with PMQ array to sr~100 mm (a=250 mm) • Single mode operation • Two tubes, different b, THz frequencies • Extremely narrow line width in THz • Higher power, lower width than THz FEL

  14. Transverse wakes and slab-symmetric structures • Slab symmetric structures: why? • Can accelerate more charge • Mitigate transverse wakes • Transverse wakes at FACET • Observable BBU with >10 cm Simulated BBU @ FACET, Initial, 10.7 cm distribution (courtesy AWA group) 4 GV/m simulated wakes for FACET experiment

  15. E-169 at FACET: Acceleration • Observe acceleration • 10-33 cm tube length • longer bunch, acceleration of tail • “moderate” gradient, 1-3 GV/m • single mode operation • Phase 3: Accelerated beam quality • Witness beam • Alignment, transverse wakes, BBU • Group velocity & EM exposure • Positrons. Breakdown is different? FACET beam parameters for E169: acceleration case Momentum distribution after 33 cm (OOPIC) Witness beam, acceleration and BBU

  16. A High Transformer Scenario using Dielectric Wakes Symmetric beam R<2 • How to reach high energy with DWAs? • Enhanced transformer ratio with ramped beam • Does this work with multi-mode DWA? • Scenario: 500-1000 MeV ramped driver; 5-10 GeV X-ray FEL injector in <10 m Ramped beam R>>2

  17. A FACET test for light source scenario • Beam parameters: Q=3 nC, ramp L=2.5 mm,U=1 GeV • Structure: a=100 mm, b=100 mm, e=3.8 • Fundamental f=0.74 THz • Performance: Ez>GV/m, R=9-10 (10 GeV beam) • Ramp achieved at UCLA. Possible at ATF, FACET? Ramped beam using sextupole-corrected dogleg compression Longitudinal phase space after 1.3 m DWA (OOPIC) Longitudinal wakefields R. J. England, J. B. Rosenzweig, and G. Travish, PRL 100, 214802 (2008)

  18. Multipulse operation: control of group velocity • Multiple pulse beam-loaded operation in linear collider • Needs lowvg • Low Q, e beams shorter, smaller • Can even replace large Q driver • Use periodic DWA structure in ~p-mode, resonant excitation Example: SiO2/diamond structure Accelerating beam Driving beam

  19. Standing wave wakes in periodic dielectric structures • 4 pulse train excitation, 2-l separation • Rms pulse length l/4, suppresses HOM

  20. Initial multi-pulse experiment: uniform SiO2 DWA at BNL ATF • Exploit Muggli pulse train slicing technique • 400 mm spacing, micro-Q=25 pC, sz=80 mm • DWA dimensions: a=100 mm, b=150 mm

  21. BNL multi-pulse experiments • Array of 1 cm tubes • Si02, also diamond • 325-660 mm l • Large aperture 490 mm case first • Use PMQs later… • Operation of pulse train with both chirp signs • Sextupole correction used • CTR autocorrelation 4-drive + witness in spectrometer CTR autocorrelation and FFT

  22. 2nd harmonic 1st deflecting mode Fundamental (@noise level) Recent results from BNL multi-pulse experiments • Single, multi- bunch wakes observed • Wakes without mask give fundamental resonant l • ~490 mm, per prediction • Resonant wake excitation, CCR spectrum measured • Excited with 190 mm spacing (2nd harmonic) • Misalignments yield l~300mm, 1st deflecting mode CCR autocorrelation Frequency spectrum

  23. Towards GV/m: multiple pulse DWA experiment at SPARC/X • Uses laser comb technique • Bunch periodicity: 190 mm (0.63 ps) • 0.5 of BNL case • Scaled structure • 125 pC/pulse @ 750 MeV • 4 pulses + witness • 1 GV/m, energy doubling in <70 cm >1.1 GV/m wakes in scaled DWA@SPARX

  24. Honey, I shrunk the FEL (not quite yet…CP’s 80th) • FEL itself gets small with small Q, high brightness beams; innovative undulators • Lower energy needed • Ultimate limit in optical undulators? • Wakefields give very high field • DWA gives a credible path • Booster for hard X-ray FEL in few m • Scaling to low Q synergistic, hard • Expect rapid experimental progress • 1st ATF; then FACET, SPARC/X, etc. TV/m simulated PWFA using LCLS 20 pCbeam

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