Naval Research Laboratory Electra title page A Repetitively Pulsed, High Energy, Krypton Fluoride Laser Electra 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
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Naval Research Laboratory Electra title page A Repetitively Pulsed, High Energy, Krypton Fluoride Laser Electra Presented by John Sethian & John Giuliani.
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Naval Research Laboratory
Electra title page
A Repetitively Pulsed, High Energy, Krypton Fluoride Laser
and efficient rep-rate KrF laser.• Technologies will be integrated into a 700 J, 5 Hz laser called ELECTRA.• Technologies scalable to large (50-150 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 definethe 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)
1. 1999 $. Sombrero (1992) gave $180/J and $4.00/J2. Shots between major maintenance (2.0 years)3. Not Applicable: Different technology4. Not Applicable: Nike shoots planar targets
High Gain Target Design (G >100) 1
Power Plant Study 2
Laser IFE Requirements
IFE NIKE
Beam quality (high mode) 0.2% 0.2%
Beam quality (low mode) 2% N/A(4)
Optical bandwidth 1-2 THz 3 THz
Beam Power Balance 2% N/A(4)
Laser Energy (amplifier) 30-150 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/A3
Rep-Rate 5 Hz .0005
Durability (shots) (2) 3 x 108 200
Lifetime (shots) 1010 104
DT Vapor
DT Fuel
Foam + DT
Laser GasRecirculator
The Key Components of a Krypton Fluoride (KrF) Laser
LaserInput
OutputOpticsENERGY + (Kr + F2) (KrF)* + F (Kr + F2) + h (248 nm)
1. Electra will validate technology. Efficiency and cost will be established with modeling from Electra results2. 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, 610 1997
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 physicsExperiments
Laser Amplifier Physics- e beam to KrF*
- laser transport 1-D kinetics, 3-D ASE chemistry & plasma physicsExperiments
KrF Physics done on both Nike and Electra
Laser Amplifier Physics code: Kinetics coupled to a 3D, time dependent, radiative transport of the ASE
e-beam..........presently uniform, change to 3D w/ e-beam code.
plasma..........1-D axially resolved complete energy accounting Te and Tg, ne, species, ...
lasing.............method of characteristics for laser transport.
The Kinetics/ASE model compares favorably with experimental data under diverse conditions
Iin (MW/cm2)
The kinetics/ASE model compares favorably withexperimental data under diverse conditions.
McGeoch, et al.,Fusion Tech., 32, p.610 (1997)
Suda, et al.,Appl. Phys. Lett., 51, p.218 (1987)
P(beam) (kW/cc)
Kr/F2/Ar=99.4/0.6/0%1 bar
Kr/F2/Ar=10/0.4/89.6%1 bar
Kr/F2/Ar=35/0.4/64.6%1.1 bar
no vib no ASE
full
single pass amp at Keio Univ. NIKE double pass amp at NRL
Pbeam =1730 kW/cc
1000 kW/cc
Iin=62 kW/cm2
I out -
Iin (
MW
/cm
2 )
(M
W/c
m2 )
When the ionization efficiency is constant…
Rex
c /R
ion
NRL
Radiation Hydrodynamics
Laser Physics
100 101 102 1030.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 2010-7
10-6
10-5
10-4
10-3
10-2
10-1
100
103
102
101
100
Kr
Ar
used forAr & Krsince '76
Pdep (kW/cm3)
Pdep (kW/cm3)
u (eV)
While the ionization efficiency is constant,the excitation efficiency depends on theelectron distribution function resultingfrom the e-beam deposition..
f(u)
(e
V-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, F2, UV, X-rays, e-beam.
High damage threshold*
long life, optics:
Threshold > 5 J/cm2
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 WINDOWLASER
MIRROR
GRAZING INCIDENCEMIRROR
We have developed a test cell to evaluate optic resistance to HF, F2 , and UV (@ 248 nm)
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 absorption @ 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 beam10 J / 4 nsec
CCD camera• focal profile• spectrum• pulse shape
Measure beam with and without optical sample
4.8 cm2 = 2 J/cm2
1.2
1.0
0.8
0.6
0.4
0.2
0
Flu
en
ce
(a
rb u
nit
s)
-100 1000 50- 50
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, 20-30 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, 20-30 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 sizedto 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 finishedFirst generation pulsed power installedRecirculator installedFully operating facility
Electron beam experiments have been started
Companion programs in KrF Physics, Opticsand Advanced Front End.