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Temporal characterization of laser accelerated electron bunches using coherent THz

Temporal characterization of laser accelerated electron bunches using coherent THz. Wim Leemans and members of the LOASIS Program Lawrence Berkeley National Laboratory. BIW 2006 May 1-4, 2006. Website: http://loasis.lbl.gov/. plasma. d=2 mm. LWFA: two regimes for bunch production

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Temporal characterization of laser accelerated electron bunches using coherent THz

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  1. Temporal characterization of laser accelerated electron bunches using coherent THz Wim Leemansand members of the LOASIS ProgramLawrence Berkeley National Laboratory BIW 2006 May 1-4, 2006 Website: http://loasis.lbl.gov/

  2. plasma d=2 mm • LWFA: two regimes for bunch production • Large-energy-spread bunch (unchanneled) • Quasi-mono-energetic bunch (channeled) Laser wakefield acceleration Ionization of gas by laser Ponderomotive push of plasma electrons Restoring force from due to charge separation Density oscillation: strong electric fields (100 GV/m) Sprangle et al. (92); Antonsen, Mora (92); Andreev et al. (92); Esarey et al. (94); Mori et al. (94)

  3. Tool: LOASIS multi-terawatt laser 100 TW-class Ti:sapphire Shielded target room 10 TW Ti:sapphire LOASIS laser system Three main amplifiers (Ti:sapphire,10 Hz): - Godzilla: 0.5-0.6 J in 40-50 fs (10-15 TW) ===> main drive beam (to date) - Chihuahua: 20-50 mJ in 50 fs ===> ignitor beam 250-300 mJ in 200-300 ps ===> heater beam 100-200 mJ in 50 fs ===> colliding beam - T-REX: 2-3 J in 30-40 fs ===> capillary experiments } guiding

  4. CCD Phosphor Phosphor vacuum Magnet Laser beam Gas Jet e-beam on phosphor screen Electron beam e-beam spectrum Jet Energy spectrum obtained with a magnetic spectrometer Charge Detector ~10 mrad Magnet OAP Mid 90’s -2003: short pulse laser systems generate electron beams with 100 % energy spread LWFA experiments produce electrons with: 1-100 MeV, multi-nC, ~100 fs, ~10 mrad divergence Modena et al. (95); Nakajima et al. (95); Umstadter et al. (96); Ting et al. (97); Gahn et al. (99); Leemans et al. (01); Malka et al. (01)

  5. Dominates if sz < l How short are the bunches ? Simulations predict 10-20 fs Can we measure them? (Is the linac stable enough?) Coherent emission

  6. Diagnostic relies on coherent transition radiation from the plasma-vacuum boundary Laser-Wakefield Accelerator Schematic for Transition Radiation Leemans et al., Phys. Rev. Lett. (2003); Schroeder et al., Phys. Rev. E (2004); Van Tilborg et al., Phys. Rev. Lett. (2006) Diagnostic implementation: • Use radiated field • Couple out of vacuum chamber Boundary size 

  7. In detail: CTR from Plasma-vacuum boundary

  8. CTR (THz) in spectral and temporal domain Diffraction function (boundary size ) • Intense THz source • 0.01-10 MV/cm at focus (up to 10’s of J in THz pulse) • ‘traditional’ laser-based sources deliver <100 kV/cm Form factor Single electron TR CTR spectrum CTR in time Schroeder et al., Phys. Rev. E (04) van Tilborg et al., Laser Part. Beams (04) van Tilborg et al., Phys. Plasmas, submitted

  9. Temporal THz measurement: electro-optic sampling Valdmanis (82); Yariv (88); Gallot (99); Yan (00); Fitch(01); Wilke(02); Berden(04); Cavalieri(05) Phase shift  is proportional to THz field

  10. Electro-Optic measurement of Coherent Transition Radiation yields information on laser accelerated electron beam: < 50 fs bunches W.P. Leemans et al., PRL2003 C.B. Schroeder et al., PRE2004 J. Van Tilborg et al., Laser and Particle Beams 2004; PRL 2006

  11. Choice of EO-material affects temporal resolution • CTR based on 50 fs (rms) Gaussian electron bunch • ZnTe vs GaP: • ZnTe cutoff ~ 4 THz • GaP cutoff ~ 8 THz

  12. Scanning technique provides bunch duration: Resolution limited by crystal properties Scanning technique (takes 1.5 hours) • < 50 fs bunches • Synchronization • Charge and bunch stability Van Tilborg et al., PRL2006, Phys. Plasmas06

  13. Single-Shot Technique for EO detection of THz pulses: Information on every bunch 3 ps 50 fs • < 50 fs bunches • peak E-field of ECTR≈150 kV/cm J. van Tilborg et al., submitted to PRL G. Berden et al., Phys. Rev. Lett. 93, 114802 (2004)

  14. Shot A Spectrum A Shot B Spectrum B Experiments show double THz pulse Red curves are double-THz-pulse-based waveforms and spectra • Use GaP instead of ZnTe • Higher bandwidth • Observation • Temporal waveform: double pulse • Spectral modulation • Why? • Double bunch e-beam ?

  15. Single-shot 2D EO imaging provides spatial profile of THz beam Shot 1 =546 fs 5 mm Shot 2 =796 fs Shot 3 =1154 fs 7 mm • Measure 2 D THz profile • Focused THz beam • Collimated laser beam • Step laser beam in time Van Tilborg et al., to be published

  16. ‘Ray Optics’ approach to analyze spatio-temporal effects of coma Shot 3 =1154 fs

  17. with coma t=0 t=-0.3 t=+0.3 t=-0.6 t=+0.6 Propagation of a single-cycle pulse through focus no coma t=0 t=-0.3 t=+0.3 t=-0.6 t=+0.6

  18. No coma With coma ‘Ray optics’ model for waveform and spectrum

  19. 2004 Results: High-Quality Bunches • Large spot size, no channel (ZR order of gas jet length) • RAL/IC: (Mangles et al.) • No Channel: 21019 cm-3 • Laser: 12 TW, 40 fs, 0.5 J, 2.51018 W/cm2, 25 m • E-bunch: 1.4108 (22 pC), 70 MeV, E/E=3%, 87 mrad • LOA: (Faure et al.) • No Channel: 0.5-2x1019 cm-3 • Laser: 30 TW, 30 fs, 1 J, 18 m • E-bunch: 3109 (0.5 nC), 170 MeV, E/E=24%,10 mrad • Controlled laser guiding with channel • LBNL: (Geddes et al.) • Plasma Channel: 1-4x1019 cm-3 • Laser: 8-9 TW, 8.5 m, 55 fs • E-bunch: 2109 (0.3 nC), 86 MeV, E/E=1-2%, 3 mrad

  20. 2w probe Cylindrical Mirror Main beam <500mJ >50fs Pre ionizing Beam 20mJ H, He gas jet e- Heater beam 100mJ 250ps Interferometer CCD & Spectrometer Plasma Channel Production: Hydrodynamic Ignitor-Heater in H2 Gas Jet Plasma channel Ti:sapphire * P. Volfbeyn, E. Esarey and W.P. Leemans, Phys. Plasmas 1999 C.G.R. Geddes et al., Nature 431, p. 543 (2004), Phys.Rev.Lett. (2005).

  21. At laser power of 8-9 TW: e-beam with %-level energy spread, 0.3 nC, 1-2 mm-mrad Beam profile Spectrum Unguided Guided 2-5 mrad divergence Charge~100 pC C.G.R. Geddes et al., Nature 431 (2004); PRL (2005); Phys. Plasmas 2005

  22. Group velocity of laser < speed of light causes particle dephasing which causes momentum bunching gv Momentum z-vgt Phase • Dephasing distance: • Control via density and a0 (laser intensity) • Optimum acceleration requires Lacc = Ldeph: channel or large ZR

  23. Wake Evolution and Dephasing Yield Low Energy Spread Beams in PIC Simulations 200 WAKE FORMING Longitudinal Momentum 0 Propagation Distance 200 INJECTION Longitudinal Momentum 0 Propagation Distance 200 DEPHASING DEPHASING Longitudinal Momentum 0 Propagation Distance Geddes et al., Nature (2004) & Phys. Plasmas (2005)

  24. 1-2 GeV e- beam Next step: GeV laser driven accelerator Capillary L'OASIS 100 TW laser • Lower density needed: capillary discharges Increasing beam energy: cm-scale capillary discharge + 100 TW laser Capillary TREX Laser Plasma injector 40-100 TW 40 fs 3-5 cm

  25. Capillary channel guiding: set-up

  26. Hydrogen based capillary discharge produces suitable density profile for guiding • Mach-Zehnder interferometer CCD • 209 m diameter capillary • 85 mbar initial pressure • n0 = 8.5x1017 cm-3 • 32 micron matched spot A. Gonsalves et al., submitted to PRL

  27. Input Output 40 TW power guided over > 3 cm P = 0.1-40 TW in 40 fs, 10 Hz wx,in=wy,in= 26 m wx,out=wy,out= 33 m

  28. LOASIS GeV Spectrometer Forward view: 0.16 - 1GeV moderate resolution - Maximum resolving energy: ~1.1 GeV Yoke - Large momentum acceptance (factor 25) Pole - High resolution (bottom: <1%, forward: 2~4%) Chamber Interaction point Capillary Beamline 1GeV Mirror and cameras Phosphor 40MeV Bottom view: 40-160 MeV high resolution(under const.) 160MeV Chamber Shielded mirror and cameras

  29. Up to 1 GeV achieved with 40 TW laser pulses 25 TW E<0.6 GeV Q~50-300 pC DATA UNDER PRESS EMBARGO 40 TW E< 1.1 GeV Q~50-100 pC

  30. Summary • Single shot EO-based methods of CTR THz radiation measures < 50fs laser-wakefield accelerated e-bunches • Single cycle THz detected, 0.4 MV/cm • Spatio-temporal coupling from aberrations in imaging can lead to apparent double bunches • GeV electron beam generated in 3.3 cm with 40 TW laser pulses • THz based bunch profile measurements underway • Novel diagnostics needed with fs and sub-fs resolution for slice energy spread and emittance • Next steps are on staging modules towards 10 GeV

  31. Scientists and Techs of LOASIS team Staff: Exp’t: C. Geddes, W. Leemans, C. Toth Theory: E. Esarey, C. Schroeder, B. Shadwick, Postdocs:E. Michel*, P. Michel, B. Nagler Students: K. Nakamura, J. van Tilborg, G. Plateau,T. Wolf Techs: D. Syversrud, N. Ybarrolaza Collaborators: D. Bruhwiler, D. Dimitrov, J. Cary--TechX Corp T. Cowan, H. Ruhl -- University of Nevada, Reno* S. Hooker, A. Gonsalves--Oxford University, UK R. Ryne, J. Qiang--AMAC, LBNL R. Huber, R.Kaindl, J. Byrd, M. Martin--LBNL W. Mori--UCLA D. Jaroszynski-University of Strathclyde, UK M. Van der Wiel-TUE, Eindhoven, NL G. Dugan--Cornell University D. Schneider, B. Stuart, C. Barty, C. Bibeau--LLNL

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