14th HAPL Meeting

1
NRL J. Sethian M. Myers J. Giuliani M.
Wolford R. Lehmberg S. Obenschain M.
Levy Commonwealth Tech F. Hegeler M.
Friedman RSI P. Burns SAIC R. Jaynes
Electra (KrF) Laser Development
14th HAPL Meeting San Diego, CA August 8th ,
2006 Naval Research Laboratory Plasma Physics
Division Washington, DC Presented by M.
Wolford Work supported by DOE/NNSA/DP
2
Summary Since Last HAPL Meeting

• Cathode Rep-rate Durability
• Installed Carbon Emitter
• 2.5 Hz 24,978 shots (continuous)
• Beginning Rep-Rate Focal Profile Experiments
• Single shot Recovery of Recirculator less than
  200 ms (Necessary Time for 5 Hz Operation)
• First Light Electra Pre-Amplifier
• 23 J laser output

3
Review IA CERAMIC HONEYCOMB CATHODEPlacing a
ceramic honeycomb slab above the emitter
significantly improves the cathode performance
and lifetime
HAPL Meeting March 2006
Present Limit of Laser Durability

• The continuous shot number is limited by gas
  buildup in the vacuum diode (forces us to briefly
  break up long runs)
• Laser run duration is ultimately limited by foil
  failure.
• (due to cathode debris and/or excess plasma in
  the A-K gap)

Cathode lifetime was limited to 10,000 continuous
shots
4
Review IB CERAMIC HONEYCOMB CATHODECathode
Action Plan as of March 2006

• Conditioning of the cathode
• Replace velvet primary emitter with graphite
  emitter
• Cool the cathode
• Modify the cathode construction to eliminate weak
  spots
• Replace cordierite ceramic with more robust SiC
  or YZA (yttria stabilized zirconia-alumina)
• Eliminate cathode shroud

high voltage feedthrough for water cooling
primary emitter graphite cathode
cathode cooling concept
copper cooling plate
5
New all Carbon Emitter has increased Cathode
Lifetime 31 k shots total, 24,978 continuous
_at_ 2.5 Hz
Velvet
Carbon
31 k shots...no change ESLI (Energy Sciences
Laboratories Inc.)
10 k shots...lots of burn marks
SEM
SEM
6
Motivation for Beginning Focal Profile Experiments

• Nike Laser System (Single Shot)
• ISI smooth focal profiles
• Rep-Rate Considerations
• Possible Additional Phase Aberrations
• Recirculator baseline gas flow
• Leftover energy (pressure gradients) from last
  shot
• Foil Temperature (Boundary Layer)
• Gas Temperature after one roundtrip of
  recirculator

7
Focal Profile after E-Beam Single Shot with NO
RECIRCULATOR FLOW
E-Beam Fires at Time Zero
0
5
10
30
Time (s)
8
Focal Profile Floor Layout
Aperture May 2006
main amp 30 cm x 30 cm
seed osc 1cm x 3 cm
9
Schematic of Pseudo ISI Essential Optical
Elements for focal profile studies
Beam size 15 cm x 15 cm
Amplifier
Pinhole
NanoStar Camera
Recorded Image
LPX 305 i Not ISI Source
Lineout Image
6 meter focal length lens 248 nm
10
30 shots 1 Hz Focal Profile Measurement (Pseudo
ISI)
Probe Beam with E-Beam 1 Hz 390 ms after
Probe Beam No E-Beam
Probe
500 microns
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1 Hz and 2.5 Hz Rep-Rate Focal Profile Lineouts
(Pseudo ISI)
30 shot measurement bursts (gas cycle time of
recirculator 5 secs)
E-Beam
Probe
0
2
2.39
.39
.8
Time(s)
E-Beam 1 Hz Probe Beam 390 ms after
E-Beam 2.5 Hz Probe Beam 390 ms after
500 microns
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Focal Profile Single Shot Lineouts (Pseudo
ISI)
E-Beam Fires at Time Zero
400 ms
200 ms
10 s
1 s
50 ms
25 ms
0
Time
13
Electra Pre-Amplifier Laser Experiments
Input 0.5 J 10 cm x 10 cm
LPX 305 i
1 cm x 3 cm
Cylindrical lens Pair
3 cm x 3 cm
Telescope
Calorimeter
14
First light on Electra Pre-Amp
80 Ar, 0.3 Fluorine
Orestes Prediction (0.5 J input) Measured Output
(0.5 J input)
15
Summary Since Last HAPL Meeting

• Cathode Rep-rate Durability
• Installed Carbon Emitter
• 2.5 Hz 24,978 shots (continuous)
• Beginning Rep-Rate Focal Profile Experiments
• Single shot Recovery of Recirculator less than
  200 ms (Necessary Time for 5 Hz Operation)
• First Light Electra Pre-Amplifier
• 23 J laser output

16
Next Steps Based on Results

• Cathode Rep-rate Durability
• Cool the cathode
• Modify the cathode construction to eliminate weak
  spots
• Replace cordierite ceramic with more robust SiC
  or YZA (yttria stabilized zirconia-alumina)
• Eliminate cathode shroud
• Rep-Rate Focal Profile Experiments
• Interferometer
• Examine all of Aperture
• Pre-Amplifier Laser
• Integrate into the full laser system