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Laser R & D plans at Oxford for ILC Laser-wire

Laser R & D plans at Oxford for ILC Laser-wire. Sudhir Dixit , David Howell, Nicolas Delerue, Myriam Qureshi. The John Adams Institute. Two main features of ILC

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Laser R & D plans at Oxford for ILC Laser-wire

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  1. Laser R & D plans at Oxford for ILC Laser-wire Sudhir Dixit, David Howell, Nicolas Delerue, Myriam Qureshi The John Adams Institute

  2. Two main features of ILC • High accelerating gradient – High energy (TeV) & high average power (10s MW) lepton beams 2. Low emittance, very small size lepton beams - High Luminosity (1034 cm-2 s-1) We, at oxford, plans to develop a suitable laser to map the time resolved e-/e+ beam emittance/luminosity within a single ILC pulse of 950 s Method To measure the e-/e+ bunch profiles/sizes within a single ILC pulse with a sub-micron resolution, high-coherence, high average power mode-locked laser all along the 40 km accelerator complex • Damping ring • Linac • Beam delivery section

  3. ILC e-/e+ pulse structure ILC beam sizes

  4. Methodology of Lepton beam size estimation: Laser-wire Vertical scanning: y Horizontal scanning: x

  5. The LASER-WIRE We plan to have about 100 measurements within an ILC pulse by time synchronised laser and e-/e+ pulses and fast, EO/Piezo, laser deflectors

  6. Guidelines on the choice of Laser for the LASER-WIRE 1. Laser repetition rate, flaser flaser = femicrobunch (3 MHz, timing accuracy < 1 ps, Mode locked laser) Tmicro= e- bunch length (0.5 mm) = 2 ps (But may be relaxed to 10 ps) Tmacro = 950 s (Long pulse ML Laser) 2. Laser pulse duration, tmicro and tmacro m2 = e2 + L2 + L jitter2 + e jitter2 + …… We require, jitter < L < e [L  1 m] Gaussian profiles in space and time, TEMoo mode spatial coherence(M2  1) Focussing lens f# = 1.5-2 3. Laser spot size, L L M2  f# NC=P NeC h-1 c-2 -1/2 m-1/2 exp [- 0.5 (/m)2] For good accuracy, NC > 2000 and good energy stability. This requires P  10MW (100 J/10ps) 4. No. of Comptons (NC) & Laser peak power (P) We want, RL = 4 L2/ = x and L < Y Also we know, C reduces as L is reduced 5. Laser wavelength, L & Rayleigh Range, RL The net choice L = 250 nm – 500 nm

  7. Choice on Lasing Materials • Laser-wire output parameters dictates the system to be Laser MOPA • The mature technology dictates one of the following laser materials

  8. Why Oxford ILC Laser-wire to be based on Nd:YLF MOPA at 1.053 m? • 1.053 m (Nd:YLF) is least affected by the thermal effects leading to very high beam quality, good pointing and good energy stability. • 1.053 m (Nd:YLF) has the highest energy storage capability hence the same output energy be achieved in less no. of amplifier stages. • Good mode-locking potential in view of relatively large Nd:YLF gain-bandwidth: upto 1.5 ps mode-locked pulses demonstrated. • Natural Nd:YLF birenfringence leads to polarized output, good for direct frequency conversion and to compensate thermal birenfringence. • Relatively lower 1.053 m (Nd:YLF) gains leads to lower ASE losses • Straightforward pumping with commercially available diodes at 798 nm Nd:YLF has a drawback of low thermal fracture threshold. However mode-locked MOPA operation upto 420 W average laser power and upto 60 kW peak pump power has been reliably demonstrated for round the clock operation. Our average planned power levels upto 350 W and peak pump power of 5 to 10 kW levels are very much within the safety limit.

  9. Technical design of Mode-locked LW system 1 The Laser: Low weight, small size, robust, high beam quality, low maintenance and if possible, the low cost!

  10. Technical design of Mode-locked LW system 2 Fiber delivery between pre and main amplifiers: Much reduced beam pointing, smooth beam profiles and M2=1 Beam pointing before fiber Displacement (rads) 50 rad Time Beam pointing after fiber Displacement (rads) < 1 rad Time

  11. Technical design of Mode-locked LW system 3 Diode pumped amplifier configuration:Much reduced thermal effects, Uniform pumping • All amplifiers modules are exactly identical • Each amplifier is pumped by 16 diode arrays distributed in 4 rings. • Each ring contains symmetrically located 4 diode arrays. • These 4 rings are rotated w. r. t each adjacent one by 45 degree to maintain • excellent uniformity of pumping

  12. Technical design of Mode-locked LW system 4 Pump diodes specifications:Modular design with relatively lower cost • Each diode module --- Standard 1 cm linear bar • Peak power of each bar --- 250 W at 5 to 10 Hz, at 798 nm • Total input power to amplifier --- 5 kW • Diode pulse duration --- 1.4 to 1.5 m-sec • Duty cycle --- 1.5%

  13. Technical design of Mode-locked LW system 5 Frequency conversion options:Choice of a suitable crystal for maximally efficient conversion and good beam quality • For 1053 nm to 527 nm:The best choice is Type I non-critically temperature phase matched LBO crystal • No walk- off - Long interaction lengths, Excellent circular beam • Gaussian profile with good coherence, High • Conversion efficiency > 70% • Large acceptance angle – 100 mrad • Large temperature bandwidth – 40 c at 1500 c • Damage threshold– 20 GW/cm2 at 1053 nm, a factor of 2 to 4 • larger than all other crystals e.g. KDP, KTP, BBO For 527 nm to 263 nm:The choice is limited to Type I critically phase matched BBO crystal Large walk-off, Elliptical output beam (needs correction) Conversion efficiency - 20 to 30%

  14. Plan of work at oxford: Stage 1 To start with:Purchase a commercial mode-locked Nd:YLF oscillator and a preamplifier with following specifications, Oscillator: Mode-locking frequency: 25 to 100 MHz (Variable) Pulse width:5 ps (Option 1) 5 ps to 200 ps (Option 2, Variable) Output beam diameter (1/e2): 5 mm (not-critical) Beam profile: : Gaussian (TEMOO mode) Beam M2: 1 Beam pointing :<5 rad Energy stability :<2% Trigger :External and internal Pre-amplifier: Average power 10 W, M2 1, Power stability < 2%, Pointing <10 rad Timing stabilizer: <0.5 ps timing stabilization system:Closed loop control of ML frequency

  15. Plan of work at oxford: Stage 1 (Contd.) To be developed/studied in house: Pockel cell and its driver, selecting proper time structure Oven design and temperature control of non-linear crystal 2nd/4th harmonic generation All basic beam characterization: M2, beam profiles, output power, energy, pulse-shapes, pointing, energy stability, non-linear conversion efficiencies etc, for all the wavelengths, 1053/527/263 nm

  16. Plan of Laser R & D at Oxford: Stage 2 Purchase of diode arrays, diodes drivers, Nd: YLF rods, Temperature stabilized chillers, delay generators, etc In house R & D: Design of first high power amplifier, assembly, operation and full characterization upto 4th harmonic Complete documentation of stage 1 and 2

  17. Plan of Laser R & D at Oxford: Stage 3 Depending upon the success upto stage 2 and after carrying out corrections, modifications required, we fix the amplifier design Explore commercial vendors for supply of assembled amplifiers Setting up of the full Nd:YLF MOPA system Work on 2nd, 3rd and 4th harmonic of full high power beam ALL the parameters characterization and documentation in the form of internal reports, International publications etc

  18. Cost estimates (Tentative) ML oscillator + pre-amplifier + closed loop rep. rate -stabilizer £100 k Amplifier (x 3) £300 k Optics, crystals, basic lab. Instruments (power/energy meter, CCD, photodiodes, one 500 MHz storage oscilloscope, spatial filters, high speed electronics + ……………………………… £100 k

  19. Conclusions A proposal for ILC mode-locked Laser-wire and R & D plans at Oxford are presented. Thank you

  20. Back up slides

  21. Mode-locked ILC Laser-wire The mode-locked ILC Laser-wire system is very much different from the ILC photo-injector system and has to be developed in a completely different way Photo-injector vis-à-vis Laser-wire The laser beam is imaged on PH with a diameter () of 2 to 6 mm The laser beam is focussed on e-/e+ bunches with a diameter of 1 to 2 µm More emphasis on Flat profiles in space, time and energy Less emphasis on Beam spatial coherence (M2 – Large) Pointing (1% of ): 20 µm– 60 µm at PH We want, Gaussian profile in space and time Good energy stability High beam spatial coherence (M2 1) High pointing < 0.5 µm at IP 266 nm/<20 ps/10 µJ/3 MHz/950 µs/5 Hz 527 nm/2-10 ps/100 µJ/3 MHz/950 µs/5 Hz We propose to build a mode-locked Nd: YLF MOPA for ILC Laser-wire + 2nd HM Architecture: Nd:YAG/Glass/YLF/ Ti:Sapphire Laser MOPA chain + 4th HM Pump sources: A combination of diode and Flash-lamps Pump sources: All diodes

  22. Plot of c for ILC energies for different laser wavelengths and different compton photon energies

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