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Overview

Laser Beam Transport and Integration AWAKE Collaboration meeting Mikhail Martyanov Christoph Hessler CERN, EN-STI-LP Valentin Fedosseev CERN, 04-06.12.2013. Overview. Short intense laser pulse is needed for : to create a 100% ionized plasma

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Overview

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  1. Laser Beam Transport and IntegrationAWAKE Collaboration meetingMikhail Martyanov ChristophHessler CERN, EN-STI-LPValentin FedosseevCERN, 04-06.12.2013

  2. Overview • Short intense laser pulse is needed for: • to create a 100% ionized plasma • moving ionization front is a source of perturbation for proton-laser instability (micro-bunching and wake-field with a stable phase) • Plan for the Laser system: • First it is delivered to MPP Munich for plasma experiments - mid 2014 • Then it goes to CERN - end 2015 ? M.Martyanov, CERN

  3. AWAKE Area: Zones - doors to laser room, local access control - doors with central access control - safety “shutters” with central control Access tunnel AWAKE gallery laser SAS e-gun room laser room e-gun Laser laser beam 2 connection tunnel 400mm to be drilled… p-tunnel electron beam laser beam 1 proton beam plasma chamber M.Martyanov, CERN

  4. Overview • Laser system comprises: - laser with 2 beams (for plasma and for the e-gun) - delay line is possible in either one of these beams - optical compressor - focusing telescope - small optical compressor and 3rd harmonics generator for e-gun • Laser parameters for plasma: - energy 450 mJ - pulse duration 120 fs after compression - beam diameter 40 mm (smoothed flat-top) Only reflective optics on the way Rule of thumb (B<1): I[GW/cm2]L[cm]<36 M.Martyanov, CERN

  5. Laser system base-line • Laser, Compressor and Telescope are in the laser room • Focusing down to 35 meters to the center of the plasma • Question is if this possible? • Back solution: Compressor and Telescope are next tomerging point in the proton tunnel • Focusing down to 25 meters to the center of the plasma • Question is if this possible? Crucial points are: • Focusability of the laser beam down to 25 or 35 meters • No detailed information on the laser system yet (beam quality) • The placement of the optical compressor and the focusing telescope has an impact on the position of the anew drilled connection tunnel • Availability of vacuum components for the compressor and telescope is under study. • 10-6Torr “easily” achievable. Pellicle or differential pumping as an option to go better M.Martyanov, CERN

  6. Base Line: Merging point Laser + Protons Some measurements of laser room with respect to merging point Protons and laser towards plasma Merging point Thanks to integration team for pictures M.Martyanov, CERN

  7. Horizontal connection tunnel 400mm Thanks to integration team for pictures M.Martyanov, CERN

  8. Merging point in details • p-beam height about 1 m • HV volume (10-6Torr) can be “easily” achieved in the laser pipes • UHV volume (10-8Torr) is supposed to be in the p-beam line laser beam 500 1400 HV volume last mirror 500 1400 750 p-beam 500 10002000 M.Martyanov, CERN

  9. Merging point in details • Distance from p-beam envelope to optical axis is 14 mm • Assuming laser beam  10 to 16 mm • Gap between beams is 6 to 9 mm • Tough but manageable • Possible issue: mirror charging and destruction laser beam gap 6  9 mm proton beam Thanks to Chiara Bracco M.Martyanov, CERN

  10. Vacuum components M.Martyanov, CERN

  11. Compressor and Telescope are in the laser room • Flat-top beam focusing profiles Focusing of a 430 mJ flat-top beam 35 m downstream to the middle of the plasma. At the ideal Gaussian waist Wmax= 6.84 J/cm2 and FWHM = 2.35 mm. Flat-top beam focusing has been optimized to obtain the same maximum fluencesomewhere in the plasma and equal fluence on both sides. Flat-top beam d=14 mm , f=52 m looks like a Gaussian beam and considered as an optimum. 0 m, FWHM=14mm, Wmax=0.32J/cm2 cm 35 m, FWHM=2mm, Wmax=6.6J/cm2 • 10 m - last mirror, beam size 16 mm, no peak in the middle for reasonably smooth beams, Wmax ~ 0.5J/cm2

  12. Compressor and Telescope are at the merging point • Flat-top beam focusing profiles Focusing of a 430 mJ flat-top beam 25 m downstream to the middle of the plasma. At the ideal Gaussian waist Wmax= 6.84 J/cm2 and FWHM = 2.35 mm. Flat-top beam focusing has been optimized to obtain the same maximum fluencesomewhere in the plasma and equal fluence on both sides. Flat-top beam d=10.6 mm , f=47 m looks like a Gaussian beam and considered as an optimum. 20 m, FWHM = 1.6mm, Wmax=5.9J/cm2 25 m, FWHM = 1.9mm, Wmax=6.8J/cm2 0 m, FWHM = 10.6mm, Wmax=0.57J/cm2 cm M.Martyanov, CERN

  13. Compressor predesign Two gold coated gratings 1700 lines/mm, 100x140 and 120x140 mm Damage threshold ~ 250 mJ/cm2 (in AWAKE less then 100 mJ/cm2) Efficiency per 1 reflection @ 800nm and 10deg deviation – 92% Gratings supplier – SPECTROGON, Sweden Acceptance: compress 160 ps to 120 fs, bandwidth 24nm, beam size 50mm Compressor fits to 1200 x 400 mm footprint, 400 mm high, 2 view-ports for alignment Max efficiency of the compressor – 70% M.Martyanov, CERN

  14. Telescope predesign Around 3-fold mirror telescope, detuned to provide 25 meter focusing, flat geometry Concave mirror R=2400mm, incident angle 2 Convex mirror R=800mm, incident angle -3.54 in the same plane Mirrors displacement 806mm Beam size 40mm, ray focal spot size ~100m Aberrations are negligible with respect to diffraction limit (spot size ~1 mm) Telescope footprint is 1000 x 200 mm M.Martyanov, CERN

  15. Compressor and Telescope Entire footprint is 2400 x 600 mm Convex mirror 2” Mirrors 2” Launch mirror 3” Concave mirror 3” M.Martyanov, CERN

  16. Laser dedicated list of “Things to Do”: Laser Installation M.Martyanov, CERN

  17. Laser dedicated list of “Things to Do”: Laser Operation M.Martyanov, CERN

  18. Alignment of 3 beams Just started … • OTR or laser light • Imaging (lens system and CCD) • Capture and measure with photodiode or streak-camera • (coupling to a fiber or lens system) • Other techniques laser-beam p-beam BPM BPM plasma e-beam M.Martyanov, CERN

  19. Alignment of 3 beams • 3 beams (protons, electrons and laser) have to be align in space and time • Transverse accuracy ~ 0.2mm • Angular accuracy ~ 0.2mm / 10 m = 20rad • Timing electrons-laser ~ 100fs – alignment by response? Rough alignment is needed anyway • Timing protons-laser ~ 100ps – alignment with fast photodiode and scope possible, 1pJ of light is required. Streak-camera. For robust alignment of 3 beams we need an optical signal which comes from the same screen sensitive to 3 beams (the power of laser beam can be reduced for the measurements not to damage the screen) M.Martyanov, CERN

  20. AWAKE access modes are under discussion … Preliminary M.Martyanov, CERN

  21. Thank you! M.Martyanov, CERN

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