14th HAPL MeetingSan Diego, CA

August 8th , 2006

Naval Research LaboratoryPlasma Physics Division

Washington, DC

Presented by M. Wolford

Work supported by DOE/NNSA/DP

Electra (KrF) Laser Development

NRLJ. SethianM. MyersJ. GiulianiM. Wolford

R. LehmbergS. Obenschain

M. Levy

Commonwealth Tech

F. HegelerM. Friedman

RSIP. Burns

SAIC R. Jaynes

• 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

Summary Since Last HAPL Meeting

Ceramic honeycomb

cathode

ceramic honeycomb

primaryemitter:velvet

Review IA: CERAMIC HONEYCOMB CATHODE:Placing a ceramic honeycomb slab above the emitter significantly

improves the cathode performance and lifetime

• 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)

Present Limit of Laser Durability

Cathode lifetime was limited to 10,000 continuous shots

HAPL Meeting 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 feedthroughfor water cooling

copper cooling plate

primary emitter:graphite cathode

cathodecoolingconcept

Review IB: CERAMIC HONEYCOMB CATHODE:Cathode Action Plan as of March 2006

Velvet Carbon

10 k shots...lots of burn marks31 k shots...no change

ESLI (Energy Sciences Laboratories Inc.)

SEM SEM

New all Carbon Emitter has increased Cathode Lifetime …… 31 k shots total,

24,978 continuous @ 2.5 Hz

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

Focal Profile after E-Beam Single Shot with NO RECIRCULATOR FLOW

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E-Beam Fires at Time Zero

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main amp 30 cm x 30 cm seed osc 1cm x 3 cm

Focal Profile Floor Layout

ApertureMay 2006

Beam size:15 cm x15 cm

Schematic of “Pseudo ISI” Essential Optical Elements for focal profile studies

Recorded Image

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NanoStarCamera

LPX 305 iNot ISI Source

PinholeAmplifier

6 meter focal length lens 248 nmLineout Image

500 microns

Probe Beam No E-Beam Probe Beam with E-Beam 1 Hz390 ms after

30 shots 1 Hz Focal Profile Measurement (“Pseudo ISI”)

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500 microns

E-Beam 1 HzProbe Beam 390 ms after

E-Beam 2.5 HzProbe Beam 390 ms after

1 Hz and 2.5 Hz Rep-Rate Focal Profile Lineouts (“Pseudo ISI”)

30 shot measurement bursts (gas cycle time of recirculator ~5 secs)

Time(s)

E-Beam Probe

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E-Beam Probe

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Focal Profile Single Shot Lineouts (“Pseudo ISI”)

E-Beam Fires at Time Zero

Time

1 s400 ms200 ms50 ms25 ms 10 s0

Electra Pre-Amplifier Laser Experiments

LPX 305 i Input 0.5 J10 cm x 10 cm

Cylindrical lens Pair

Telescope

1 cm x 3 cm

3 cm x 3 cm

Calorimeter

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Orestes 0.5 J Input

Measured Input ~0.5 J

Orestes Prediction (0.5 J input)Measured Output (~0.5 J input)

First light on Electra Pre-Amp

80% Ar, 0.3% Fluorine

• 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

Summary Since Last HAPL Meeting

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