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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 Overview 1. Final optic program summary 2. New mirror fabrication and testing 3. Larger scale testing 4. Contaminant transport modeling 5. Gas puff modeling 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 • Key Issues: • Shallow angle stability • • Laser damage resistance • goal = 5 J/cm2, 108 shots • 85Þ Contamination Optical quality Fabrication Radiation resistance ~50 cm 2. Characterize threats to mirror: LIDT, radiation transport, contaminants 3. Perform research to explore damage mechanisms, lifetime and mitigation Bonding/coating Al: 20-500 nm q”=10 mJ/cm2 SiC: 10 m Microstructure Fatigue Ion mitigation 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) 5. Develop fabrication techniques and advanced concepts ion accelerator neutron modeling and exposures 6. Perform mid-scale testing Diamond-turned, electroplated mirrors survived 105 shots at 18 J/cm2 on a small scale (mm2) 1. Relatively small grains (10-20 m) 2. Relatively dense, thick coating Still, these mirrors ultimately fail due to grain motions, ... ... and we would like to improve the high-cycle fatigue behavior Post-processing after thick (35-50 m) thin-film deposition should provide good optical quality with a damage-resistant microstructure rough substrate polish/turn 35 m “thick thin-film” mirror, turned at Schafer Corp. and exposed to 104 shots at 5 J/cm2 coat final polish/turn no damage to elecroplated mirror (turned at GA) under the same exposure conditions Ringdown reflectometry (now @266 nm) indicates somewhat high absorption at 85˚ reflectivity of 35 m Schafer mirror photodiode polarizer lens output coupler test specimen output coupler QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. <1 ns nanolaser Diamond turning lines are too deep – 50 nm rms – (A new Pacific Nanotechnolgy AFM has been added to our surface analysis capabilities) Peaks grow during exposure (unlike earlier results which exhibited etching) etching observed previously in diamondturned polycrystalline foils It’s time to start making smoother mirrors MRF systems are popping up all over the place (this one is at Edmund Optics) Larger mirrors are being fabricated with increasing emphasis on surface quality 1. Mid-scale 4” optics • Thick e-beam coatings • Electroplated Al 2. Other improvements under consideration • MRF surface finishing • Hardening techniques • nanoprecipitate, solid solution hardening • friction stir burnishing (smaller grains) 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 Experimental Layout Beam Dump Wave Plate UV Window Beam Profiler Cube Lens Beam Sampler Mirror Window Camera 43” 12” Laser energy measurements showed dramatic energy loss along the beam path 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 1/2 waveplate p-polarized Electra oscillator 3.9 J Nike mirror telescope 10 cm 0.14 J 0.57 J 1” aperture 1.04 J vacuum chamber 12.8 J (measured with a 30cm x 30 cm calorimeter) 14.2 – 15.3 J (measured with a 30 cm x 30 cm calorimeter) 13.2 J with a 2” dia. aperture We don’t see this with our Compex laser 1 = 86 mJ 2 = 84 mJ 1 1 3 = 86 mJ 4 = 85 mJ 2 3 3 4 4 5 1 = 228 mJ 2 = 119 mJ 3 = 95 mJ 4 = 92 mJ 5 = 13 6 = 75 7 = 58 8 = 56 mJ mJ mJ mJ 6 2 7 8 An alternative idea for scaled testing: large-aperture uncoated FS window @56˚ 700 J blunderbuss 12” FS window ($5250) beam dump 34˚ 30 cm square aperture 10” round aperture 10” diameter, 6-m fl Nike lens 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 8” port 6.7” 10” chamber 30 cm Another alternative idea for scaled testing: Contrast is >100:1 over a 7˚ range 700 J blunderbuss 10” diameter, 6-m fl Nike lens 30 cm square beam with 9” round aperture beam dump 32˚ 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 6” 12” chamber Contamination transport from the chamber to the final optic was explored using Spartan Displacement field after 1st shot • 160 MJ NRL target • 50 mTorr Xe @RT • Bucky hand-off at 500 s • Net flow toward chamber • center is predicted – we need to include rad-hydro displacements Net flow toward optic? Particles transport rapidly toward the final optic Test particle trajectories 4 Pressure at 100 ms Pa 3 2 1 • We need to run multiple shots to establish the long-term behavior 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 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 3m Number of ducts 64 Orifice conductance 44 l/s/cm2 Target mass 4 mg Rep rate 5 Hz Chamber radius 7m It doesn’t look promising! 5-yr plan and progress to date 2001 start 2002 KrF initial promising results at 532 nm 2003 2004 electroplate success lower limits at 248 nm, chemistry control larger optics new lab, cryopump attempts at thin film optics 2005 2006 Phase I evaluation extended database, mid-scale testing, radiation damage, mirror quality, design integration