1. Laser Beam Transport and Integration AWAKE Collaboration meeting Mikhail Martyanov Christoph Hessler CERN, EN-STI-LP Valentin Fedosseev CERN,

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 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
M.Martyanov, CERN

6. 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
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 (10-6 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
10002000
1400
500
750
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
proton beam
laser beam
gap 6  9 mm
Thanks to Chiara Bracco
M.Martyanov, CERN

10. 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 Eur
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 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

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 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
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 800nm and 10deg deviation – 92%
Gratings supplier – SPECTROGON, Sweden
Acceptance: compress 160 ps to 120 fs, bandwidth 24nm, beam size 50mm
Compressor fits to 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
Concave mirror 3”
Mirrors 2”
Convex mirror 2”
Launch mirror 3”
M.Martyanov, CERN

16. 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
M.Martyanov, CERN

17. 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
M.Martyanov, CERN

18. 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
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