Naval Research Laboratory Electra title page A Repetitively Pulsed, High Energy, Krypton Fluoride Laser Electra Presented by John Sethian & John Giuliani NRL M. Friedman M. Myers S. Obenschain R. Lehmberg P. Kepple JAYCOR S. Swanekamp Commonwealth Tech F. Hegeler Pulse Sciences, Inc D. Weidenheimer SAIC R. Smilgys

Rep-Rate KrF laser (Electra)----NRL Overall Objective…………. Develop technologies for low cost, durable and efficient rep-rate KrF laser. Technologies will be integrated into a 700 J, 5 Hz laser called ELECTRA. Technologies scalable to large ( kJ)systems FY 01 Deliverables………..1. Develop cathode, hibachi and gas recirculator 2. Advanced pulsed power component dev. 3. KrF Physics research to maximize efficiency 4. Optics development (amplifier window) 5. Design Advanced Front End (input laser) PI Experience………………. Leader in e-beam pumped KrF laser R & D. Nike. (POC: J. Sethian) Proposed Amount………….. $ 9,275,000 Relevance of Deliverables [X] NIF……………………High damage optics development [X] Laser RR Facility….Rep-Rate laser [X] Other DP/NNSA……Advanced Pulsed Power, DEW technology [X] Energy………………Potential to meet IFE Driver requirements

Target gain and power plant studies define the laser requirements 1. S.E. Bodner et al,.“Direct drive laser fusion; status and prospects”, Physics of Plasmas 5, 1901, (1998). 2. Sombrero: 1000 MWe, 3.4 MJ Laser, Gain 110; Cost of Electricity: $0.04-$0.08/kWh; Fusion Technology, 21,1470, (1992) $. Sombrero (1992) gave $180/J and $4.00/J 2. Shots between major maintenance (2.0 years) 3. Not Applicable: Different technology 4. Not Applicable: Nike shoots planar targets High Gain Target Design (G >100) 1 Power Plant Study 2 Laser IFE Requirements IFENIKE Beam quality (high mode) 0.2% 0.2% Beam quality (low mode) 2% N/A (4) Optical bandwidth 1-2 THz3 THz Beam Power Balance 2% N/A (4) Laser Energy (amplifier) kJ 5 kJ System efficiency 6-7% 1.4% Cost of entire laser (1) $225/J(laser) $3600/J Cost of pulsed power (1) $5-10/J(e-beam) N/A 3 Rep-Rate 5 Hz.0005 Durability (shots) (2) 3 x Lifetime (shots) DT Vapor DT Fuel Foam + DT

Laser Gas Recirculator The Key Components of a Krypton Fluoride (KrF) Laser Laser Input Output Optics ENERGY + (Kr + F 2 )  (KrF) * + F  (Kr + F 2 ) + h (248 nm) Laser Cell (Kr + F 2 ) Pulsed Power System Electron Beam Foil Support (Hibachi) Amplifier Window Cathode

FY 1999 | FY 2000| FY 2001| FY 2002| FY 2003 | FY 2004| FY2005 FY 1999 | FY 2000| FY 2001| FY 2002| FY 2003 | FY 2004| FY2005 The Electra Program Plan ELECTRA LASER (700 J, 30 cm, 5 Hz KrF Laser ) First Generation Pulsed Power Develop Laser components: Emitter, Hibachi, Gas Recirculator Input Laser Integrated Test ADVANCED PULSED POWER Systems Designs Component R & D, Component test and evaluation Design / Build Advanced System Integrate into Electra ADV FRONT END (pulse shape/zooming) DesignBuild and Test Integrate into Electra OPTICS DEVELOPMENT Amp Window Coating Development Steering/focussing Optics KrF SYSTEMS (architecture for 2 MJ system) Optimum Amplifier SizeArchitecture Optimization KrF PHYSICS (optimize efficiency & develop design tools) Code integration Electron beam propagation & KrF Kinetics/ASE Codes Experimental Validation

The Electra Facility is ready for Laser Component R & D

We are evaluating cathodes for uniformity, turn-on and impedance collapse and durability Velvet (1.0e-01) HC/Ceramic Carbon Fiber Carbon Flock Carbon Foam 100 ppi RHEPP Green Velvet Carbon flock

We are developing the emitter and hibachi as a single system Pattern emitter to miss hibachi ribs Vac.001” Ti Anode HeLaser Gas.001”Al + Main Foil Rib e-beam 1.40 W/cm 2 160º C 40 m/sec Emitter Base Hibachi Emitters Predicted Performance on ELECTRA (1 mil Ti+1 mil Al 500 keV) 61.5% (0.9 atm) Kr 38.3% (1.1 atm) Ar 0.2%F Lost to Foils: 20.6% 1 mil Ti Foil: 10.9% 1 mil Al Foil 7.7% He gas (1.0 atm) 1.4% Transmitted to other foil: 0.6% Absorbed by gas: 78.6% Reflected: 0.0% Radiation: 0.7% 1-D Energy deposition profile

RECIRCULATOR: Textron Systems has installed a system that will allow repetitive amplification of a high quality laser beam Gas recirculator.ppt  /  passes (= 5 Hz) Honeycomb Thermal Equalizers (4) Design based on EMRLD laser--demonstrated1.3 XDL Fan Heat Exchanger Laser Cell Rear Mirror Optical Axis Contraction Muffler Diffuser Muffler Perforated Plate (2) Cross-leg Muffler (4) 6 m Flow 3.75 m/sec

Advanced pulsed power development plan Pick nominal module size of 100 kJ pulsed power = 80 kJ e-beam First design Range Voltage: 800 kV kV Current: kA kA Module size: 100 kJ (electrical) kJ Pulse Length: 600 nsec nsec Evaluated pulsed power concepts that can meet the requirements: Cost: $ /electron beam Joule Efficiency: > 80% Durability: > 3 x 10 8 shots Use systems studies to determine feasibility and define R & D Developed three systems Develop the required components - 3 yrs Integrate into system that demonstrates technology on Electra - 2 yrs Pick nominal module size of 100 kJ pulsed power = 80 kJ e-beam First design Range Voltage: 800 kV kV Current: kA kA Module size: 100 kJ (electrical) kJ Pulse Length: 600 nsec nsec Evaluated pulsed power concepts that can meet the requirements: Cost: $ /electron beam Joule Efficiency: > 80% Durability: > 3 x 10 8 shots Use systems studies to determine feasibility and define R & D Developed three systems Develop the required components - 3 yrs Integrate into system that demonstrates technology on Electra - 2 yrs

We are evaluating three advanced pulsed power systems, and performing R & D to develop the required components TTIMC-1MC-2MC-3 DIODE XFMRS1 TTIMC-1MC-2 DIODE Fast Marx XFMRS1 DIODE PFL Laser-gated switch stack/array 1. $ / e-beam Joule, for 100 kJ system in quantities, NOT Electra; 2. Flat top e-beam/wall plug Transformer + 3 stage Magnetic Compressor Cost 1 Efficiency 2 $11.30/J 81% Fast Marx w/ laser gated switches + 2 stage Magnetic Compressor $ 7.65/J 85% Transformer + PFL + HV laser output switch $ 8.35/J 87%

Meeting the IFE efficiency requirements is a challenge… but achievable Efficiency allocation: How we get there Current status Pulsed power80% Advanced PP design RHEPP 63% Hibachi80% Lattice Hibachi Nike  50% Ancillaries95% Electra + Study 1 N/A Intrinsic 10-12% KrF physics %(small systems) 3,4 12% predicted from Nike kinetics code 5 TOTAL 6-7% 7% Nike (not optimal  ) 1. Electra will validate technology. Efficiency and cost will be established with modeling from Electra results 2.  intrinsic =  formation (25-28%) x  extraction; (40-50%) = (10-14%). Optimize extraction by increasing gain-to-loss 3. “KrF Laser Studies at High Krypton Density” A.E. Mandl et al, Fusion Technology 11, 542 (1987). 4. Characteristics of an electron beam pumped KrF amplifier with atmospheric pressure Kr-rich mixture in strongly saturated region”, A. Suda et al, Appl. Phys. Lett, 218 (1987) 5. M.W. McGeoch et al, Fusion Technology, 32, Efficiency Goal: 6-7%

Electron Beam Propagation - transport in diode & hibachi, - deposition in gas 2-D, 3-D PIC code modeling 2-D simulations Experiments Electron Beam Propagation - transport in diode & hibachi, - deposition in gas 2-D, 3-D PIC code modeling 2-D simulations Experiments KrF Physics: develop science base to meet the requirements for rep-rate, durability and efficiency. Laser Amplifier Physics - e beam to KrF * - laser transport 1-D kinetics, 3-D ASE chemistry & plasma physics Experiments Laser Amplifier Physics - e beam to KrF * - laser transport 1-D kinetics, 3-D ASE chemistry & plasma physics Experiments KrF Physics done on both Nike and Electra

Laser Amplifier Physics code: Kinetics coupled to a 3D, time dependent, radiative transport of the ASE

KrF Kinetics includes a multi-species plasma chemistry

Vibrational Kinetics Model for KrF Vibrational kinetics model for KrF*

data-1 (MW/cm 3 ) (MW/cm 2 ) (MW/cm 2 )

The Kinetics/ASE model compares favorably with experimental data under diverse conditions I out - I in (MW/cm 2 ) (MW/cm 2 )

When the ionization efficiency is constant… R exc /R ion f(u) (eV -3/2 )

Advanced Coatings & Optics are needed in the amps, mirrors and final optic Coatings for KrF amplifier windows * Long life in the amplifier cell: HF, F 2, UV, X-rays, e-beam. High damage threshold * long life, optics: Threshold > 5 J/cm 2 Final optic for IFE power plant (UCSD,LLNL, LANL, etc) Evaluate candidates (optical, debris, x-ray) Neutron testing, if we can establish source TARGET AMPLIFIER WINDOW LASER MIRROR GRAZING INCIDENCE MIRROR

We have developed a test cell to evaluate optic resistance to HF, F 2, and UV 248 nm) 5% F 2 in Ne 2% H 2 0 in Air Lumonics 1/2J KrF Laser (induce UV 1-2 J/cm 2 ) RGA mass spectrometer (measure HF, impurities) Heater & temperature control CELL SAMPLE Mixer Integrated test Can increase exposures to to accelerate damage Test SiO 2 samples Coatings Al 2 O 3 HfO 2 MgF 2 SiO 2 ….? Simulates Environment of KrF Laser Cell Also performing experiments to determine effect of x-rays

Determine Non linear index effect on laser profile ( should affect envelope only, not speckle) >>> Two photon 4 nsec Degradation in transmission Experiments showed profile broadening and degradation of transmission..Probably due to poor materials Will repeat with high quality optics Envelopes of object and image for ~5 XDL with and without self phase modulation Optical Sample (Quartz) (5-10 cm long) Nike Laser beam 10 J / 4 nsec CCD camera focal profile spectrum pulse shape Measure beam with and without optical sample 4.8 cm 2 = 2 J/cm Fluence (arb units) OBJECT  B  = 0  B  = 0.4 We have developed a way to measure the distortion of an ISI-smoothed laser beam in optical materials ( Deniz, Lehmberg, Chan, Pawley, 1999)

10 J, nsec pulse, 5-10 Hz Distortion free amplification of 200 XDL ISI High-contrast pulse shaping Zoomed focal profiles E-Beam pumped Input for Electra AND Nike 10 J, nsec pulse, 5-10 Hz Distortion free amplification of 200 XDL ISI High-contrast pulse shaping Zoomed focal profiles E-Beam pumped Input for Electra AND Nike The Advanced Front End will be sized to drive several ~ 100 kJ Laser Beam lines Front End NS Beam line 1 Beam line 2 Beam line 3 Beam line N

Summary Electra Program is well underway “Platform” for component R & D is finished First generation pulsed power installed Recirculator installed Fully operating facility Electron beam experiments have been started Companion programs in KrF Physics, Optics and Advanced Front End.