Naval Research Laboratory Electra NRL J. Sethian M. Friedman M. Myers S. Obenschain R. Lehmberg J. Giuliani P. Kepple JAYCOR S. Swanekamp Commonwealth Tech F. Hegeler SAIC M. Wolford TITAN-PSD D. Weidenheimer D. Morton MRC-Albuquerque D. Rose D. Welch Electra title page John Sethian Naval Research Laboratory April 9, 2003 Work sponsored by DOE//NNSA/DP

The Key Components of a KrF Laser Input Laser (Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Output Optics

Topics This Time Input Laser (Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Output Optics

Electron Beam transport Input Laser (Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Output Optics

Previous progress/ This time 1. Demonstrated high transmission hibachi by eliminating anode & patterning beam 75% e-beam energy deposited into gas Agrees with LSP modeling Expect >80% on full scale (750 keV) system 2. Delayed onset and reduced magnitude of "Transit Time" instability (on Nike) This Time: 1. Completely eliminated Transit Time instability

Experiments and 2-D models show "Transit Time" Instability in large area, low impedance diodes Experiment (Nike) Theory 2.5 GHz 0 50 100 150 200 Time (ns) V (MV) 0.8 0.4 0.0 f=2.5 GHz dN/dE (Arb. units) 1.0 0.5 0.0 0.5 1.0 E (MeV) Not stopped by gas stopped by foils Theory: mitigate instability by adding resistively tuned slots in cathode CATHODE 0 50 100 150 200 Time (ns) 0.4 0.2 0.0 dN/dE (Arb. units) 0.0 0.5 1.0 E (MeV) 1.0 0.5 Not stopped by gas stopped by foils l/4 e- Slot with Resistive Wire BEFORE AFTER M. Friedman, et al et al Appl. Phys. Lett. 77, 1053 (2000)

Slotting the cathode reduces the transit-time instability in the Nike 60 cm Amplifier 7 current density A/cm2 time (100 ns/div) 14 frequency (GHz) amplitude 1 2 3 .02 .04 current FFT (di/dt) dI/dt side face previous slide, shown to "set the stage" -7 7 14 time (100 ns/div) current density A/cm2 1 9 2 3 .02 .04 amplitude frequency (GHz) side face M. Friedman, S.B. Swanekamp, et al Appl. Phys. Lett. 81, 1597 (2002)

Slotting cathode in both directions eliminates the transit-time instability in the Nike 60 cm Amplifier current .04 14 amplitude FFT (di/dt) current density A/cm2 7 dI/dt 1 2 3 time (100 ns/div) frequency (GHz) 10-6 14 amplitude current density A/cm2 7 1 2 3 time (100 ns/div) frequency (GHz)

Laser Physics Input Laser (Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Full Aperture Calorimeter

Previous progress/ This time 1. First light from Electra operating as an oscillator 400 J single shot 150 J rep rate @ 1 Hz / 10 sec burst This Time: 1. 500 J rep rate @ 1 Hz / 10 sec burst 2. Completed first round of laser physics experiments Higher laser output at lower pressures and Kr concentration, per Orestes code predictions. Laser output peaks at F2 concentrations around 0.25%. Lower than code predictions, but good for an IFE driver. We need the recirculator

8% reflecting output coupler The Electra KrF Laser has produced  500 J of laser light in a 1 Hz, 10 second burst Oscillator Mode; 8% reflecting output coupler 10 shots, 1 Hz burst 600 500 400 300 200 100 Laser Energy per pulse (calc) 5000 4000 3000 2000 1000 Cumulative (measured) Shot # 1 2 3 4 5 6 7 8 9 10 Average Laser Energy; 504 J/shot

Laser output is consistent at 1 Hz Time Measured with a fast photodiode

Temperature of the e-beam pumped laser gas (after e-beam deposition) Laser Output constant during burst, even though gas gets hot.... .....implies KrF kinetics do not depend on temperature 427K 463K 505K 487K Temperature of the e-beam pumped laser gas (after e-beam deposition) Laser Cell E-beam pumped region

Orestes Code being developed to predict KrF Laser behavior (see John Giuliani Poster) 24 species, 122 reactions Neutral Channel Ion Channel Kr,Ar,F2 e-beam e-beam e- Ar* Ar+ ArF* F2 F- Kr Kr Kr* harpoon Kr+ exchange Kr ion-ion rec Good F2 F- GAIN, go KrF* 2Ar 2Kr Bad ArKrF* , Ar, Kr, F2, e- Kr2F* , Ar, Kr, F2, e- , F2, e- Kr,Ar,F absorption,  = F2F2+ F-F- + KrF2 KrF2 + ArF2 ArF2

Orestes predictions of Electra as an oscillator 0.8 atm 1.2 atm 1.6 atm 2.0 atm 0 200 400 600 800 1000 1200 1400 Kr ( Torr ) 1400 1200 1000 800 600 400 200 Ar ( Rosc = 10% Pbeam=800 kW/cc T(t=0) = 300 oK F2= 0.5% 30 x 30 x 100 cc 850 700 600 800 400 40% Kr 60% Kr 100%Kr Higher Laser Output for 1. Lower absolute pressure 2. Lower Kr concentration

Observe higher laser output at both lower absolute pressure and krypton concentration.... as predicted by Orestes. 500 0.3%F2, 39.7% Kr, 60% Ar 400 0.3%F2, 59.7% Kr, 40% Ar 0.3%F2, 99.7% Kr 300 Oscillator Energy (J) 200 100 10 12 14 16 18 20 22 24 26 28 30 32 Laser Cell Pressure (psi)

Fluorine Dependence for 60%Ar, (40-X.XX)% Kr, X.XX% F2 Laser output peaks at a lower fluorine concentration than currently predicted by Orestes.... Fluorine Dependence for 60%Ar, (40-X.XX)% Kr, X.XX% F2 Experiment But less F2 is good! Orestes (Simulation)

Power plant amplifier would be pumped by separate e- beams Power plant amplifier would be pumped by separate e- beams. Operating at lower F2 reduces losses in un-pumped regions 60 kJ Laser Amplifier e-beam un-pumped region Estored 100 kJ x 8 = 800 kJ V, I, : 800 keV, 84 kA x 16, 600 ns Energy in gas: 544 kJ Laser Input: 4 kJ Laser Output: 57.8 kJ ( = 10.8%)

Problems, annoyances, and anomalies which may be cleared up when we re-circulate the laser gas Limited to 10 shot bursts, due to foil and gas warm-up Gas and foils need to be cooled Laser output drops after 7-8 shots when we run at 5 Hz. Gas may be too turbulent (or temperature dependence kicks in) Not due to fluorine burn-up or electron beam Rep-rate operation with Ti foils causes erratic laser output (run to run) Believed to be due to fluorine-Ti reaction (TiFx) that is enhanced at higher temps By-products get on windows, lowers laser output Do not have this effect with SS foils May have to coat Ti foils/ go to other materials/use recirculator to get rid of bad gas JG

Recirculator Input Laser (Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Output Optics

Recirculator to cool and quiet laser gas plus cool hibachi foil is installed and vacuum tested (still need blower) Blower Heat Exchanger Laser Cell Static Pressure Contours varies by 14 Pa (10-4) over laser cell Homogenizers & Turning Vanes

The recirculating laser gas can be used to cool the Hibachi t = 200 ms Louvers closed t =60 ms t =20 ms Foils Rib Foils Rib e-beam e-beam Louvers open t = 0 ms gas flow gas flow Contours of Stream Function Foil Temperature below required 650F Modeling: A.Banka & J.Mansfield, Airflow Sciences, Inc

The louvers and actuator for cooling the hibachi foils have been delivered and are undergoing off-line tests louvers closed louvers open Actuator and motor

Input Laser (aka Front end) Laser Gas Recirculator Bz Pulsed Power System Cathode Electron Beam Foil Support (Hibachi) Amplifier Window Laser Cell (Kr + F2) Output Optics

Pulsed Power for Electra front end is based on expected IFE beam line architecture. Expect Dec 03 delivery Laser in: 1 J @25 nsec Laser out: 40 J @25 nsec Fast Gas Marx (will be retrofitted with solid state switches) Pulse forming line Magnetic switch Laser path Transmission lines E-beam voltage: 150/175 kV E-beam current: 80 kA/68 kA per side E-beam pulse: 40 ns flat-top

SUMMARY-progress in last four months Completely eliminated Transit Time e-beam instability on Nike main amplifier Laser: 500 J rep rate @ 1 Hz / 10 sec burst Completed first round of laser physics experiments Higher laser output at lower pressures and Kr concentration, per Orestes predictions Laser output peaks at a lower fluorine concentration than currently predicted by Orestes....Good for power plant Gas recirculator installed and vacuum tested Louvers for foil cooling delivered, undergoing bench tests. Pulsed power for front end designed and under construction. Expect Dec 03 delivery.

Status of KrF Laser Development for IFE Status of KrF Laser Development for IFE... a "qualitative self assessment " Just starting Ready for Phase II Efficiency Durability Rep-Rate Beam quality Cost