1. 14 th 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 Electra (KrF) Laser Development 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

2. 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

3. Ceramic honeycomb cathode ceramic honeycomb primary emitter: 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

4. 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 copper cooling plate primary emitter: graphite cathode cathode cooling concept Review IB: CERAMIC HONEYCOMB CATHODE: Cathode Action Plan as of March 2006

5. Velvet Carbon 10 k shots...lots of burn marks 31 k shots...no change ESLI (Energy Sciences Laboratories Inc.) SEM New all Carbon Emitter has increased Cathode Lifetime …… 31 k shots total, 24,978 continuous @ 2.5 Hz

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 Time (s) 5 10 30

8. main amp 30 cm x 30 cm seed osc 1cm x 3 cm Focal Profile Floor Layout Aperture May 2006

9. Beam size: 15 cm x 15 cm Schematic of “Pseudo ISI” Essential Optical Elements for focal profile studies Recorded Image NanoStar Camera LPX 305 i Not ISI Source Pinhole Amplifier 6 meter focal length lens 248 nm Lineout Image

10. 500 microns Probe Beam No E-Beam Probe Beam with E-Beam 1 Hz 390 ms after 30 shots 1 Hz Focal Profile Measurement (“Pseudo ISI”) Time (s) 012 3 E-BeamProbe 0.39 1 1.39 2 2.39 Probe

11. 500 microns E-Beam 1 Hz Probe Beam 390 ms after E-Beam 2.5 Hz Probe 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-BeamProbe 0.39 1 1.39 2 2.39 Time(s) E-BeamProbe 0.39.8 22.39

12. Focal Profile Single Shot Lineouts (“Pseudo ISI”) E-Beam Fires at Time Zero Time 1 s 400 ms200 ms 50 ms25 ms 10 s 0

13. Electra Pre-Amplifier Laser Experiments LPX 305 i Input 0.5 J 10 cm x 10 cm Cylindrical lens Pair Telescope 1 cm x 3 cm 3 cm x 3 cm Calorimeter

14. Orestes Prediction (0.5 J input) Measured Output (~0.5 J input) First light on Electra Pre-Amp 80% Ar, 0.3% Fluorine

15. 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

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