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 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 ? 05.12.2013 M.Martyanov, CERN
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 05.12.2013 M.Martyanov, CERN
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 05.12.2013 M.Martyanov, CERN
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 to merging point in the proton tunnel Focusing down to 25 meters to the center of the plasma 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. 10-6 Torr “easily” achievable. Pellicle or differential pumping as an option to go better 05.12.2013 M.Martyanov, CERN
Base Line: Merging point Laser + Protons Some measurements of laser room with respect to merging point Merging point Protons and laser towards plasma Thanks to integration team for pictures 05.12.2013 M.Martyanov, CERN
Horizontal connection tunnel 400mm Thanks to integration team for pictures 05.12.2013 M.Martyanov, CERN
Merging point in details p-beam height about 1 m HV volume (10-6 Torr) can be “easily” achieved in the laser pipes UHV volume (10-8 Torr) is supposed to be in the p-beam line 1400 500 p-beam laser beam HV volume last mirror 10002000 1400 500 750 05.12.2013 M.Martyanov, CERN
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 proton beam laser beam gap 6 9 mm Thanks to Chiara Bracco 05.12.2013 M.Martyanov, CERN
Vacuum components Company Product Comments ARUM Microelectronics Stepping motors, translators 1e-10Torr Phytron Stepping motors 1e-11Torr, 10MJ/kg rad.resist. Princeton Research Instruments Stepping motors, translation and rotation stages 1e-09Torr, 4e-10Torr achieved with 190 l/s pumping Tectra NewFocus Picomotors 1e-09Torr SmarAct Picomotors, mirror mounts, translators 1e-09Torr, 2900 Eur per mount Standa Everything… but Mounts 1e-09Torr, Motorized 1e-06Torr 1800Eur 05.12.2013 M.Martyanov, CERN
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 fluence somewhere 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
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 fluence somewhere 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. 0 m, FWHM = 10.6mm, Wmax=0.57J/cm2 cm 20 m, FWHM = 1.6mm, Wmax=5.9J/cm2 25 m, FWHM = 1.9mm, Wmax=6.8J/cm2 05.12.2013 M.Martyanov, CERN
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% 05.12.2013 M.Martyanov, CERN
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 ~100m Aberrations are negligible with respect to diffraction limit (spot size ~1 mm) Telescope footprint is 1000 x 200 mm 05.12.2013 M.Martyanov, CERN
Compressor and Telescope Entire footprint is 2400 x 600 mm Concave mirror 3” Mirrors 2” Convex mirror 2” Launch mirror 3” 05.12.2013 M.Martyanov, CERN
Laser dedicated list of “Things to Do”: Laser Installation System To define / To do Laser room, equipped with a big SAS Air circulation, conditioning, humidity, filters, circuits (electrical, demineralized water, tap water, compressed air, control cables), safety (fire/smoke alarm), shutters, access etc. Connection tunnel 40cm Drilling, coordinates of laser beam to be defined Access to laser room and tunnel AWAKE access concept including Laser Access Modes to p-tunnel and e-gun room, safety shutters Ti:Sa laser Arrangement in a squeezed room, max laser table width is 1m Chillers and electronics are below the tables or in the separate ventilated rack/cabinet or in the big SAS Vacuum pulse compressor and focusing telescope. HV (10-6 Torr) or UHV (10-8 Torr): pellicle or differential pumping Placement is not defined yet Placement in the laser room is a base-line In case of p-tunnel everything must fit between p-beam and wall, “dirty” environment in p-tunnel is not good for compressor/telescope installation and maintenance Transfer line to p-tunnel Merging point chamber HV UHV (only 2 mirrors, possibly without in-vacuum motors) Transfer line to e-gun Separate small compressor 3rd harmonic generation In fore-vacuum Next to the gun 05.12.2013 M.Martyanov, CERN
Laser dedicated list of “Things to Do”: Laser Operation System Issues Ti:Sa laser Controls and diagnostics are provided by the supplier of the laser system Pulse compressor and focusing telescope Diagnostics are provided by the supplier Laser beam in the p-tunnel Steady diagnostics: Focused beam spot monitor (virtual plasma, the same long distance run); near field before merging mirror; screens before and after plasma tube sensitive to “both” beams (laser, electrons, protons) also equipped with fiber-coupling for rough timimg measurements On demand or maintenance diagnostics: Auto-correlator, angular spectrometer, phase-front detector, … Laser beam in the e-gun room (small compressor and 3rd harmonic generation are next to the gun) Virtual cathode CCD, UV energy meter, some IR signal coupled to a fiber for rough timimg measurement Auto-correlator, angular spectrometer, … Delay control between pulses: ionization and e-gun Delay line either on one of 2 beams, proper delay simulation required. Split after RegAmp was proposed by AMPLITUDE with 2.5mJ IR output for e-gun 05.12.2013 M.Martyanov, CERN
Alignment of 3 beams OTR or laser light Imaging (lens system and CCD) 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 plasma p-beam laser-beam e-beam BPM 05.12.2013 M.Martyanov, CERN
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 = 20rad 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) 05.12.2013 M.Martyanov, CERN
AWAKE access modes are under discussion … Preliminary 05.12.2013 M.Martyanov, CERN
Thank you! 05.12.2013 M.Martyanov, CERN