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Naval Research Laboratory Plasma Physics Division Washington, DC 20375 13 th HAPL Meeting November 8, 2005 University o

NRL J. Sethian M. Myers J. Giuliani R. Lehmberg S. Obenschain SAIC M. Wolford R. Jaynes Commonwealth Tech F. Hegeler M. Friedman RSI P. Burns S. Searles. KrF Lasers: Electra Laser Overview. Naval Research Laboratory Plasma Physics Division Washington, DC 20375

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Naval Research Laboratory Plasma Physics Division Washington, DC 20375 13 th HAPL Meeting November 8, 2005 University o

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  1. NRL J. Sethian M. Myers J. Giuliani R. Lehmberg S. Obenschain SAIC M. Wolford R. Jaynes Commonwealth Tech F. Hegeler M. Friedman RSI P. Burns S. Searles KrF Lasers: Electra Laser Overview Naval Research Laboratory Plasma Physics Division Washington, DC 20375 13th HAPL Meeting November 8, 2005 University of Rochester (LLE) Work supported by DOE/NNSA/DP

  2. Electra KrF Laser Layout pre-amp 10 cm x 10 cm main amp 30 cm x 30 cm seed osc 1cm x 3 cm

  3. Electra 30 cm x 30 cm Amplifier stage Electra title page 730 J Plano-Parallel Oscillator ~100 ns FWHM

  4. Laser gas recirculates (provides cooling and quiescent flow) Capacitor charging to +/- 43 kV (>160 ms) E-Beam KrF Pump Source 500 kV, 110 kA 140 ns pulse Discharging through the 1:12 step-up transformer Charging of the PFL to 1 MV (3-4 ms)

  5. Currently in use Gas Velocity Foils Rib Rib gas flow “V” plate mimics “ideal” closed louvers optimum gas flow velocity at foil Rep-rated oscillator laser output was not influenced by fixed “V” plate More Far-Field Experiments needed Electra Foil Cooling Concepts Foil Cooling concepts being examined See Georgia Tech Poster on “Investigation of Mist Cooling for the Electra Hibachi“ Demonstrated 5 Hz at full power for 10,000 shots continuous in module See John Giuliani Poster “Foil Cooling for electron beam pumped KrF lasers “ Louvers Thermal Conduction Mist Cooling

  6. Laser resonator and Rep-Rate Diagnostics All Optics Standard Grade Fused Silica 1F Photodiodes Pump Source (electrons) Output Coupler Mirror Pickoff Window Graphite Beam Dump E-Beam Pumped Region (Gain Media) 1 m Tilted Windows Rear Mirror Photodiode Pump Source (electrons) Calorimeter Positions Real Time F2 monitor with Nitrogen laser attached to recirculator

  7. Electra KrF laser is very consistent in long duration, repetitively pulsed, runs 300 J @ 1 Hz (300 W) 10,000 shots continuous (2.5 hrs) 700 J @ 1 Hz (700 W) 400 shots continuous 400 J @ 5 Hz (2000 W) 500 shots continuous Notable results: 7700 shots @ 5 Hz four back to back runs 9600 shots @ 2.5 Hz in a multiple segmented run

  8. Efficiency (9.6%)= PLaser (5.75 GW)/ PE-Beam (60.2 GW) Intrinsic Efficiency 730 J Laser Shot E-Beam Power PLaser (GW) PE-beam (GW) Time (ns) E-Beam Power = (Pressure Rise (E)*Radiation Correction (105%)) + Laser Energy (E) Distributed over the pulse width measured in the diode

  9. How we project an amplifier intrinsic efficiency of ~11-12% based on oscillator results of 9.6% • Better windows (>99% transmitting vs. measured 93% transmission in oscillator) Anti-Reflection coating on both side windows (currently single sided) KrF or ArF grade (currently standard grade fused silica) Utilization of Rigrod analysis implies an expected increase of 17% in efficiency( ) A properly designed amp would have: • Lower laser light absorption due to fluorine, less passes through e-beam unpumped regions (~2%) • Full laser extraction of the created gain media, data here is 31.5 cm deposition in electron beam propagation direction and utilization of a 30 cm laser extracting (~4-5%) • Amplification from input laser, no oscillator build-up time (~1%)

  10. Intrinsic Efficiency Data (optimal conditions highlighted)

  11. TC TN 1” CN CC Gain Media Uniformity Measurements(Single Pass Gain) 248 nm bandpass filter Parasitic Light Attenuators Neutral Density Filter KrF output 12” Photodiode (1 ns risetime) Iout Iin PD2 PD3 ND E-Beam Pumped Region KrF input PD1 PD4 Beam Cube Polarizer Gas Composition: 60% Ar, 39.7% Kr, 0.3% F2

  12. Oscillator Yield 730 J TC TN TC TN CN CN CC CC g0 = 6%/cm α = 0.6%/cm Isat = 10 MW/cm2 Rigrod Analysis Uniform Amplification Gain Across the entire 30 cm x 30 cm aperture @ 20 psi

  13. CC Addition of He does not significantly reduce output …. Increases foil cooling Single Pass Gain (Amplifier) results and Oscillator results

  14. KrF Laser Calculations (Orestes) e-beam: ionization and excitation from Boltzmann analysis. plasma: 1D axially resolved, separate electron and gas temperatures, enthalpy balance. kinetics: 24 species, 144 reactions, Includes KrF vibrational structure. lasing: method of characteristics. ASE: 3D, discrete ordinates, time dependent, ASE gain narrowing.

  15. Kinetics Change Explains Fluorine Concentration e e e e

  16. KrF Kinetics Calculations (Orestes) Agree with Experiment 9 8 7 6 5 4 3 2 1 0 Pe-beam (expt) ILaser (expt) ILaser (Orestes) Shot OSC080404_11 ELaser = 731 Joules Pe-beam (100 kw/cc) ILaser (MW/cm2) 0 50 100 150 200 250 time (ns)

  17. Orestes has been used to predict the performance of a 25 kJ amplifier four e-beams per side 800 kV 200 kA 225 nsec 100 x 50 cm each 40 cm 100 x 100 cm window 10 cm 1.1 atm, 40% Kr, 0.35% F2 TWIN = 99%, RMIR = 100% 210 kJ e-beam deposition flat (250 kJ total) PEB = 526 kW/cc (105 J/liter) in flat portion Laser EIN(t1 to t2) = 1.0 kJ Laser EOUT(t1 to t2) = 27.4 kJ (32.4 kJ total) Intrinsic Efficiency(t1 to t2) = 13.0%

  18. Key stresses in the 25 kJ KrF amplifiers are within existing Electra and Nike parameters 25 kJ Laser Amplifier Marx 1st stage 1st Mag Switch 2nd stage (PFL) TTI 2nd Mag Switch Laser Cell 25 kJ Nike Electra E-beam voltage (kV) 800 640-750 500 E-beam pulse (ns) 225 225 140 Cathode size (cm) 50 x 100 60 x 200 30 x 100 5 Hz Foil Load (W/cm2) 4.1 N/A 4.1 Pump Power (kW/cc) 526 326-430 700 Window Load (J/cm2) 2.5 1.0 0.78

  19. Summary • Measured flat-top intrinsic efficiency of 9.6% with an oscillator yield of 731 J Yield, plus advances in pulsed power and hibachi gives a basis for the projection of 7% wall plug efficiency in amplifier configuration • Orestes Code agrees with Electra Oscillator measurements over wide range of parameter space (F2 concentration, pressure dependence, absolute yield) • 3) 2.5 hour operation rep-rate (durability, with high reproducibility) at 1 Hz with 5 Hz capability • 4) Gain Media Uniformity over entire 30 cm x 30 cm has been measured

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