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Electra (KrF) Laser Development
16th HAPL Meeting
Princeton, New Jersey
December 12, 2006
Naval Research Laboratory
Plasma Physics Division
Washington, DC
Presented by M. Wolford
Work supported by DOE/NNSA/DP
NRL
J. Sethian
M. Myers
J. Giuliani
M. Wolford
S. Obenschain
Commonwealth
Tech
F. Hegeler
M. Friedman
T. Albert
J. Parrish
K. Gunlicks
RSI
P. Burns
R. Lehmberg
S. Searles
SAIC
R. Jaynes
Summary Since August HAPL Meeting
• Starting Integration of Electra Laser System
– First Stages of Construction
• Pre-Amplifier Laser Energy Measurements
– Increased laser yield to 25 J
– Time-Dependent characterization of laser pulse
– Near-Field Profile
• Cathode & Rep-Rate Durability
– Anode Mesh (1st Implementation 12,363 shots)
Electra Laser System
Main AMP
Pre-AMP
LPX
Electra ISI Source Options
Electra ISI Laser Source Options
Initial experiments and will continue with LPX as is, non ISI
External Cavity
f
Diffuser w/ additional amplifier
f
LPX
Diffuser
A. V. Deniz, S. P. Obenschain Opt. Comm. 106 (1994) 113-122
T. Lehecka et al., Opt. Comm. 117 (1995) 485-491
Amplifier
Pinhole
Focus
See NRL Poster:
Large Aperture KrF
Discharge Amplifier
Electra Laser System
Main AMP
Pre-AMP
Large Amplifier optical architecture
LPX
Double Pass Large Amp Architecture
AMP
Large Concave Mirror
Closely Packed
Convex Mirror Array
Amplifier
Pinhole
Focus
Electra Pre-Amplifier Laser Experiments
Telescope
LPX 305 i
1 cm x 3 cm
Cylindrical lens Pair
3 cm x 3 cm
Input 0.5 J
10 cm x 10 cm
Input
Output
Calorimeter
Review: First light on Electra Pre-Amp
80% Ar, 0.3% Fluorine
30.0
Orestes 0.5 J Input
Measured Input ~0.5 J
Laser Output (J)
25.0
20.0
15.0
10.0
5.0
0.0
8
12
16
Pressure (psi)
20
25 J Electra Pre-Amplifier Output
30.0
Laser Output (J)
25.0
20.0
15.0
Orestes 0.5 J Input
Measured Input ~0.5 J
10.0
Orestes 0.7 J Input
Measured Input 0.6 J
5.0
80% Ar, 0.3% F2
0.0
8
12
16
Pressure (psi)
20
Timing Electron Beam to Laser, 10 J Yield
Input
Output
Voltage
5
Diode Voltage
Diode Power
Output
Input
Voltage (keV)
Power (100 MW)
300
4.5
4
250
3.5
200
3
2.5
150
64.8 ns
2
100
1.5
1
50
0.5
0
-40
-20
0
20
40
60
-50
Time (ns)
80
100
120
0
140
-0.5
Intensity (arb.)
350
Output Time Dependent Intensity
6
1 (-36.3 ns) 3.8 J
4
5
2 (1.3 ns) 10.0 J
5
3
3 (21.5 ns) 15.7 J
Intensity (arb.)
4
Output
2
4 (40.7 ns) 20.0 J
5 (64.8 ns) 10.0 J
6
3
6 (88.0 ns) 2.9 J
1
2
Power (10 GW)
1
0
0
20
40
-1
60
80
100
120
140
120
140
Time (ns)
2
1
3
4
5
6
Input
-40
-20
0
20
40
60
80
100
Pre-Amplifier Energy Function of Input Timing
25
15
80% Ar, 0.3% F2
@ 16 psi
80%Ar, 0.3% F2
@ 18 psi
Orestes 16 psi
10
Orestes 18 psi
Energy (J)
20
5
-30
-10
10
30
Time (ns)
50
70
Cause of
Discrepancy
90
0
-50
0
50
Input Time (ns)
100
150
Progress in realizing long duration laser runs
Previous Limits to Laser Durability
(< 10 k shots)
March 2006 HAPL meeting
primary
emitter
• Gas buildup in the diode
ceramic
honeycomb •
Degradation of the emitter
Solved with new all-carbon emitter.
As much as 25 k shots
(reported at Aug 2006 meeting)
Foil
Screen
Hibachi
• Foil failure due to debris and/or
plasma arcs in A-K gap
MAY have been solved with
high transparency anode screen
One Possible mechanism limiting foil durability
Electron emission from Anode
Hypothesis
Rationale
Micro particles can stick to the foil
Emission is an explosive process.
See marks on foil
Voltage reverses in diode
after the main pulse
Seen on Voltage monitors
Voltage reversal causes micro
particles to emit electrons
See what may be "cathode spots" on
pressure foil
Emission can be an explosive process
Known fact.
Can puncture hole in highly stressed
pressure foil
Experiments with an anode foil show
evolution of this process
First experiments with mesh, (90%-95% effective transmission) show
a) Minimal degradation in laser energy (i.e. transmission OK)
b) First Implementation lasted several multi-thousand shot runs
Summary Since August HAPL Meeting
• Starting Integration of Electra Laser System
– First Stages of Construction
• Pre-Amplifier Laser Energy Measurements
– Increased laser yield to 25 J
– Time-Dependent characterization of laser pulse
– Near-Field Profile
• Cathode & Rep-rate Durability
– Anode Mesh (1st Implementation 12,363 shots)