Electra title page

1
Electra title page
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
John Sethian Naval Research Laboratory April 9,
2003
Work sponsored by DOE//NNSA/DP
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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
3
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
4
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
5
Previous progress/ This time
Previous 1. Demonstrated high transmission
hibachi by eliminating anode patterning
beam 75 e-beam energy deposited into gas
Agrees with LSP modeling Expect gt80 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
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Experiments and 2-D models show "Transit Time"
Instability in large area, low impedance diodes
Experiment (Nike)
Theory
2.5 GHz
Theory mitigate instability by adding
resistively tuned slots in cathode
CATHODE
l/4
e-
Slot with Resistive Wire
BEFORE
M. Friedman, et al et al Appl. Phys. Lett. 77,
1053 (2000)
AFTER
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Slotting the cathode reduces the transit-time
instability in the Nike 60 cm Amplifier
current
FFT (di/dt)
dI/dt
previous slide, shown to "set the stage"
M. Friedman, S.B. Swanekamp, et al Appl. Phys.
Lett. 81, 1597 (2002)
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Slotting cathode in both directions eliminates
the transit-time instability in the Nike 60 cm
Amplifier
current
.04
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FFT (di/dt)
amplitude
current density A/cm2
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dI/dt
0
0
3
2
0
1
time (100 ns/div)
frequency (GHz)
10-6
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amplitude
current density A/cm2
7

0
0
3
2

0
1

time (100 ns/div)
frequency (GHz)
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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
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Previous progress/ This time

• Previous
• 1. First light from Electra operating as an
  oscillator
• 400 J single shot
• 150 J rep rate _at_ 1 Hz / 10 sec burst
• This Time
• 1. 500 J rep rate _at_ 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

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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
Average Laser Energy 504 J/shot
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Laser output is consistent at 1 Hz
Measured with a fast photodiode
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Laser Output constant during burst, even though
gas gets hot.........implies KrF kinetics do not
depend on temperature
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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
Kr
exchange
ion-ion rec
Good
F2
F-
GAIN, go
KrF
2Ar
2Kr
Bad
?, Ar, Kr, F2, e-
Kr2F
ArKrF
?, F2, e-
Kr,Ar,F
absorption, ? ?F2?F2 ?F-?F- ?KrF2 ?KrF2
?ArF2 ?ArF2
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Orestes predictions of Electra as an oscillator
Rosc 10 Pbeam800 kW/cc T(t0) 300 oK F2
0.5 30 x 30 x 100 cc
Higher Laser Output for 1. Lower absolute
pressure 2. Lower Kr concentration
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Observe higher laser output at both lower
absolute pressure and krypton concentration....
as predicted by Orestes.
500
400
300
Oscillator Energy (J)
200
100
0
10
12
14
16
18
20
22
24
26
28
30
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Laser Cell Pressure (psi)
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Laser output peaks at a lower fluorine
concentration than currently predicted by
Orestes....
Fluorine Dependence for 60Ar, (40-X.XX) Kr,
X.XX F2
Experiment
But less F2 is good!
Orestes (Simulation)
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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)
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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
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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
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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
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The recirculating laser gas can be used to cool
the Hibachi
gas flow
gas flow
Contours of Stream Function
Foil Temperature below required 650?F
Modeling A.Banka J.Mansfield, Airflow
Sciences, Inc
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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
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Input Laser (aka Front end)
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
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Pulsed Power for Electra front end is based on
expected IFE beam line architecture. Expect Dec
03 delivery
Laser in 1 J _at_25 nsec Laser out 40 J _at_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
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SUMMARY-progress in last four months

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

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