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Naval Research Laboratory Plasma Physics Division Washington, DC 20375 12 th HAPL Meeting June 20-21, 2005 Lawrence Livermore National Laboratory Livermore,

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Presentation on theme: "Naval Research Laboratory Plasma Physics Division Washington, DC 20375 12 th HAPL Meeting June 20-21, 2005 Lawrence Livermore National Laboratory Livermore,"— Presentation transcript:

1 Naval Research Laboratory Plasma Physics Division Washington, DC 20375 12 th HAPL Meeting June 20-21, 2005 Lawrence Livermore National Laboratory Livermore, CA Work supported by DOE/NNSA/DP KrF Lasers NRL J. Sethian M. Myers J. Giuliani R. Lehmberg S. Obenschain Commonwealth Tech F. Hegeler M. Friedman T. Albert SAIC M. Wolford RSI P. Burns MRC Albuquerque D. Rose Titan PSD, Inc D. Weidenheimer Georgia Tech S. Abdel-Khalik D. Sadowski

2 Why KrF lasers for IFE? Short wavelength (248 nm) maximizes Target gain (increases absorption and rocket efficiencies) Target stability (minimizes risk from laser plasma instabilities) Laser-plasma interactions (threshold scales roughly with I 2 ) Demonstrated outstanding spatial uniformity and large bandwidth (2 THz) on NIKE laser Decreases imprint (hydrodynamic instabilities) Straightforward zooming Pulsed power based (low cost, industrial technology) High laser system efficiency (predict 7% wall plug to laser light)

3 Electra title page Electra’s main amplifier Two-sided e-beam pumping: 500 kV, 100 kA, 140 ns FWHM

4 Pulsed power system Pulsed forming line Diode Laser gas recirculator Operation of Electra’s main amplifier (oscillator) Capacitor charging to +/- 43 kV (>160 ms) Charging of the PFL to 1 MV (3-4  s) Laser triggered switch Matched diode provides 500 kV, 110 kA 140 ns pulse Discharging through the 1:12 step-up transformer

5 Diode Magnet Diode Operation of Electra’s main amplifier (oscillator) Velvet strip cathode Ceramic cathode still needs to be partitioned into strips Cathode generates electron beam e-beam Laser Gas Kr + F 2 + Ar 1 mil SS pressure foil e-beam Electron beam ionizes laser gas hibachi

6 Operation of Electra’s main amplifier (oscillator) Laser cell Laser gas recirculates (provides cooling and quiescent flow) e + Kr Kr + e Kr + F KrF + F KrF + h (248 nm) Kr + F + 2 h (248 nm) 2 * -- ** *

7 Planned Electra laser system layout

8 Accomplishments of the Electra KrF Laser Program 300 J @ 1 Hz for 10,000 continuous shots 700 J @ 1 Hz for 400 continuous shots 400 J @ 5 Hz for 500 continuous shots monolithic cathode strip cathode

9 intrinsic eff.: 9.8%...expect ~12% as an amplifier Electra’s oscillator achieved an intrinsic efficiency of 9.8%

10 Lower laser light absorption due to fluorine, less passes through e-beam unpumped regions Amplification from input laser, no oscillator build-up time A properly designed amp would have: 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 ( ) How we project an amplifier intrinsic efficiency of ~12% based on oscillator results of 9.8%

11 Demonstrated high e-beam transmission into the laser gas using velvet strip cathodes 70% e-beam energy into gas @ 500 keV with 1 mil stainless steel (SS) pressure foil 700 J of laser energy Agrees with LSP models by MRC Expect 80-82% @ 800 keV – 1 MeV with 1 mil SS (full scale system) cathode e-beam Hibachi pressure foil

12 p n+ n- n++ p++ Diode Laser D Laser Silicon Thyrsitor CONCEPT: Diode lasers flood entire thyristor with photons ultra fast switching times (< 100 nsec) Continuous laser pumping reduces losses PROGRESS: > 4,000,000 shots @ 5 Hz many 1 M shot runs Required specs (5 Hz, 16.4 kV) current rate of rise of 88 kA/  sec/cm 2 (3 x needed) current density of 14.7 kA/cm 2 (3 x needed value) shot 220,000 vs shot 1,000,000 top view Laser gated and pumped thyristor (LGPT) principal has been demonstrated Power and Energy

13 Second Generation Pulsed Power: All solid state Electron beam Fast Marx LGPT switched Pulse Forming Line Magnetic Switch Transit Time Isolator This pulsed power architecture is being evaluated with the new Electra front end p n+ n- n++ p++ Diode Laser D Laser Silicon Thyrsitor LGPT PROJECTEDIFE Req 2 Rep rate:5-10 Hz(5-10 Hz) Efficiency:85%(85%) Durability:3 x 10 8 shots(3 x 10 8 ) Cost:$7.25/J 1,3 (< $10/J) 1.800 kV/600 nsec/175 kA 2.SOMBERO Study 3.For 100 kJ systems in quantities

14 Pulsed PowerAdvanced Switch 85% Hibachi StructureNo Anode, Pattern Beam80 - 82% KrFBased on Electra expt’s11 - 12 % Optical train to targetEstimate 95% AncillariesPumps, recirculator 95% Global efficiency6.8 - 7.5% > 6 % is adequate for fusion target gains > 100......and latest designs have 2D gains ~ 160 Based on our research, an IFE-sized KrF system is projected to have a wall plug efficiency of ~7% (meets goal)

15 PD1 PD2PD3 PD4 KrF input ND Beam Cube Polarizer E-Beam Pumped Region I in I out 12” KrF output Neutral Density Filter 248 nm bandpass filter Parasitic Light Attenuators Photodiode (1 ns risetime) Single pass gain set-up 1” TC CN CC TN Gas Composition: 60% Ar, 39.7% Kr, 0.3% F 2

16 Spatial dependence @ 20 psi laser gas pressure TC CN CC TNTC CN CC TN Oscillator Yield 730 J Increased pressure to 28 psi Lowers Oscillator Yield 665 J OutputGas Composition 715 J80% Ar, 19.7% Kr 715 JAdded 10% He 690 JAdded 20% He

17 We are developing three techniques to cool the foil Convection cooling by the laser gas Pro: Successful operation @ 1 Hz (foil temp < 200°C) Con: Foil temperature rises to 350-500°C @ 5 Hz operation Mist cooling of the foil (developed by Georgia Tech) Pro: Successful demonstration @5 Hz (foil temp < 140°C) Con: More complex system, lower e-beam transport efficiency Conduction cooling to hibachi ribs Pro: Simple cooling system Con: Requires close rib spacing, challenging e-beam transport through hibachi (may be reduced with advanced materials)

18 Louvers enhance convective cooling of the pressure foil 480°C no gas flow 430°C louvers are open 325°C 100 ms 265°C louvers are closed gas flow 7.5 m/s 1 mil SS foil 50 shots @ 5 Hz

19 Increased current density of strip cathode leads to higher foil temperatures 430°C 169 shots @ 5 Hz 155°C 50 shots @ 1 Hz 200°C @ 1 Hz 380°C @ 2.5 Hz 530°C @ 5 Hz 50 shots strip cathode monolithic cathode 100% Ar in the laser cell, 5 m/sec gas velocity, louvers actuated

20 Foil temperature depends on laser gas mixture 410°C: 8 psi Kr, 12 psi Ar 50 shots @ 5 Hz 7.5 m/sec gas velocity, louvers actuated 330°C: 8 psi Kr, 12 psi Ar + 2.3 psi He 310°C: 8 psi Kr, 12 psi Ar + 4 psi He Thermal conductivity: He > Ar > Kr Electron backscattering: He < Ar < Kr Foil temperature with 100% Ar: 325°C

21 The Electra Front End a) Platform to develop advanced solid state pulsed power system b) Provide 30-50 J of laser light input to the main amplifier Has operated in e-beam mode @ 5 Hz, with very low jitter (<1000 ps) Pulsed power runs > 100,000 shots without maintenance

22 The Electra Front End E-beam diode performance at 5 Hz is reliable

23 Electron deposition (1D) Plasma Chemistry ----- >>> 22 species 130 reactions Laser Transport (3D) Amplified Spontaneous Emission (3D) Combines relevant physics into single “First Principles” code Predicts KrF Laser under wide range of conditions Orestes kinetics code combines relevant KrF physics and chemistry (22 species, 130 reactions) into a single "First Principles" code

24 0 50 100 150 200 250 P e-beam (expt) I Laser (expt) I Laser (Orestes) Shot OSC080404_11 E Laser = 731 Joules 98765432109876543210 Orestes simulation are in good agreement with experimental results of the Electra oscillator time (ns) Amplitude (arb. unit)

25 Next generation KrF laser e-beam mirror 3 meters 40 laser cell window 100 cm x 100 cm independent pulsed power systems laser light 10 100 flat-top laser energy: 60.9 kJ intrinsic efficiency: 12%

26 Main points of this talk We like KrF lasers for fusion energy Wavelength (248 nm), smooth profiles, large bandwidth helps target physics KrF architecture allows straightforward zooming Pulsed power inherently robust, cost efficient, industrial technology Can scale to energies, cost, efficiency, rep-rate needed for fusion energy Efficiency: predict can meet goal of > 7% total based on R&D Pulsed power, electron beam physics, KrF kinetics Durability & cost: Pulsed power: new switch to meet cost & durability Foil durability: 300 J @ 1 Hz for 2.5 hrs (10,000 shots) 700 J @ 1 Hz and 300-400 J @ 5 Hz (500 shots) Developing advanced hibachis for sustained high energy @ 5 Hz 40-60 kJ power plant beam line based on Electra R&D

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