M. S. Tillack

1. Final Optic Research – Progress and Plans M. S. Tillack with contributions from: Z. Dragojlovic, F. Hegeler, E. Hsieh, J. Mar, F. Najmabadi, J. Pulsifer, K. Sequoia, M. Wolford HAPL Project Meeting, PPPL 27-28 October 2004

2. Overview • Final optic program summary • New mirror fabrication and testing • Larger scale testing • Contaminant transport modeling • Gas puff modeling

3. The steps to develop a final optic for a Laser IFE power plant (1 of 2) 1. “Front runner” final optic – Al coated SiC GIMM: UV reflectivity, industrial base, radiation resistance • Contamination• Optical quality• Fabrication• Radiation resistance Key Issues:• Shallow angle stability• Laser damage resistance goal = 5 J/cm2, 108 shots • 2. Characterize threats to mirror: • LIDT, radiation transport, contaminants 3. Perform research to explore damage mechanisms, lifetime and mitigation Bonding/coating Microstructure Fatigue Ion mitigation

4. The steps to develop a final optic for a Laser IFE power plant (2 of 2) 4. Verify durability through exposure experiments 10 Hz KrF laser UCSD (LIDT) XAPPER LLNL (x-rays) ion accelerator neutron modeling and exposures 5. Develop fabrication techniques and advanced concepts 6. Perform mid-scale testing

5. Diamond-turned, electroplated mirrors survived 105 shots at 18 J/cm2 on a small scale (mm2) • Relatively small grains (10-20 mm) • Relatively dense, thick coating Still, these mirrors ultimately fail due to grain motions, ... ... and we would like to improve the high-cycle fatigue behavior

6. 35 mm “thick thin-film” mirror,turned at Schafer Corp. and exposed to 104 shots at 5 J/cm2 no damage to elecroplated mirror (turned at GA) under the same exposure conditions Post-processing after thick (35-50 mm) thin-film deposition should provide good optical quality with a damage-resistant microstructure rough substrate polish/turn coat final polish/turn

7. Ringdown reflectometry (now @266 nm) indicates somewhat high absorption at 85˚ reflectivity of 35 mm Schafer mirror

8. Diamond turning lines are too deep – 50 nm rms – (A new Pacific Nanotechnolgy AFM has been added to our surface analysis capabilities)

9. Peaks grow during exposure (unlike earlier results which exhibited etching) etching observed previously in diamond-turned polycrystalline foils

10. It’s time to start making smoother mirrors MRF systems are popping up all over the place(this one is at Edmund Optics)

11. Larger mirrors are being fabricated with increasing emphasis on surface quality • Other improvements under consideration • Mid-scale 4” optics • Thick e-beam coatings • Electroplated Al • MRF surface finishing • Hardening techniques • nanoprecipitate, solid solution hardening • friction stir burnishing (smaller grains)

12. Scaled testing was initiated at Electra during late August we spent 1 week assembling the optical path, developing test procedures, and exploring issues for large scale testing

13. Beam Dump UV Window Wave Plate Beam Profiler Cube Beam Sampler Lens Mirror Window Camera 43” 12” Experimental Layout

14. Laser energy measurements showed dramatic energy loss along the beam path Electra oscillator 2” graphite aperture 3” lead aperture 0.14 J to 5.2 J (measured with a 2” calorimeter) 80 cm periscope 10 cm 5.2 J polarizer cubes Nike mirror telescope 1/2 waveplate 3.9 J p-polarized 10 cm 0.14 J 14.2 – 15.3 J (measured with a 30 cm x 30 cm calorimeter) 13.2 J with a 2” dia. aperture 12.8 J (measured with a 30cm x 30 cm calorimeter) 1” aperture 0.57 J 1.04 J vacuum chamber

15. 1 3 4 5 6 2 7 8 1 2 3 4 We don’t see this with our Compex laser 1 = 86 mJ 2 = 84 mJ 3 = 86 mJ 4 = 85 mJ 1 = 228 mJ 2 = 119 mJ 3 = 95 mJ 4 = 92 mJ 5 = 13 mJ 6 = 75 mJ 7 = 58 mJ 8 = 56 mJ

16. An alternative idea for scaled testing: large-aperture uncoated FS window @56˚ 12” FS window($5250) beam dump 700 J blunderbuss 34˚ 30 cm squareaperture 10” roundaperture 10” diameter, 6-m fl Nike lens 6.7” 8” port 10” 30 cm assume 700 J in 900 cm2 ~ 0.75 J/cm2 ~25% of s-light reflected = 0.09 J/cm2 10” round on 6x12 rectangle ~ 362 cm2 35 Joules (polarized) available chamber

17. 6” 12” Another alternative idea for scaled testing:Contrast is >100:1 over a 7˚ range 10” diameter, 6-m fl Nike lens beam dump 700 J blunderbuss 32˚ 30 cm squarebeam with 9” round aperture 12” FS window 8” port • assume 700 J in 900 cm2 ~ 0.75 J/cm2 • ~25% of s-light reflected = 0.09 J/cm2 • 9” round ~ 410 cm2 • 37 Joules (polarized) available chamber

18. Contamination transport from the chamber to the final optic was explored using Spartan • 160 MJ NRL target • 50 mTorr Xe @RT • Bucky hand-off at 500 ms Displacement field after 1st shot • Net flow toward chamber center is predicted • – we need to include rad-hydro displacements • Net flow toward optic?

19. Particles transport rapidly toward the final optic Test particle trajectories Pressure at 100 ms Pa 4 3 2 1 • We need to run multiple shots to establish the long-term behavior

20. Gas puffing was examined as a posssible optic protection technique • ~1 Torr-m may help reduce ion and x-ray damage • Fast gas puff could be used immediately preceding implosions • Might also help cool chamber gas

21. A gas puff sufficient to protect optics would increase the base pressure beyond 100 mTorr Pump speed per duct 1.5x105 l/s Duct diameter 75 cm Duct length 3 m Number of ducts 64 Orifice conductance 44 l/s/cm2 Target mass 4 mg Rep rate 5 Hz Chamber radius 7 m It doesn’t look promising!

22. 5-yr plan and progress to date 2001 2002 2003 2004 2005 2006 start KrF larger optics Phase I evaluation electroplatesuccess initial promising results at 532 nm new lab,cryopump extended database,mid-scale testing,radiation damage, mirror quality, design integration lower limits at 248 nm, chemistry control attempts at thin film optics