1. 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

2. 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
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

6. Experiments and 2-D models show "Transit Time" Instability in large area, low impedance diodes
Experiment (Nike)
Theory
2.5 GHz
Time (ns)
V (MV)
0.8
0.4
0.0
f=2.5 GHz
dN/dE (Arb. units)
1.0
0.5
E (MeV)
Not stopped
by gas
stopped by foils
Theory: mitigate instability by adding resistively tuned slots in cathode
CATHODE
Time (ns)
0.4
0.2
0.0
dN/dE (Arb. units)
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)

7. Slotting the cathode reduces the transit-time instability in the Nike 60 cm Amplifier7
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)

8. 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)

9. 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

10. Previous progress/ This time
1. First light from Electra operating as an oscillator
400 J single shot
150 J rep 1 Hz / 10 sec burst
This Time:
J rep 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

11. 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 #
Average Laser Energy; 504 J/shot

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

13. 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

14. 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

15. Orestes predictions of Electra as an oscillator
0.8 atm
1.2 atm
1.6 atm
2.0 atm
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

16. 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)

17. 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)

18. 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%)

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. Pulsed Power for Electra front end is based on expected IFE beam line architecture. Expect Dec 03 delivery
Laser in: nsec
Laser out: 40 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

26. SUMMARY-progress in last four months
Completely eliminated Transit Time e-beam instability on Nike main amplifier
Laser: 500 J rep 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.

27. 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