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

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 2. Characterize threats to mirror: LIDT, radiation transport, contaminants Key Issues: Shallow angle stability Laser damage resistance goal = 5 J/cm 2, 10 8 shots Contamination Optical quality Fabrication Radiation resistance 3. Perform research to explore damage mechanisms, lifetime and mitigation MicrostructureBonding/coatingFatigueIon mitigation

6. Perform mid-scale testing5.Develop fabrication techniques and advanced concepts 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 acceleratorneutron modeling and exposures

Diamond-turned, electroplated mirrors survived 10 5 shots at 18 J/cm 2 on a small scale (mm 2 )... and we would like to improve the high-cycle fatigue behavior Still, these mirrors ultimately fail due to grain motions,... 1.Relatively small grains (10-20  m) 2.Relatively dense, thick coating

35  m “thick thin-film” mirror, turned at Schafer Corp. and exposed to 10 4 shots at 5 J/cm 2 no damage to elecroplated mirror (turned at GA) under the same exposure conditions Post-processing after thick (35-50  m) thin-film deposition should provide good optical quality with a damage-resistant microstructure rough substratepolish/turncoatfinal polish/turn

Ringdown reflectometry nm) indicates somewhat high absorption at 85˚ reflectivity of 35  m Schafer mirror

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 diamond- turned 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 2.Other improvements under consideration MRF surface finishing Hardening techniques nanoprecipitate, solid solution hardening friction stir burnishing (smaller grains) 1.Mid-scale 4” optics Thick e-beam coatings Electroplated Al

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 43” 12” Lens Beam Dump Wave Plate Cube Mirror Beam Sampler Beam Profiler UV Window Window Camera

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

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

An alternative idea for scaled testing: large-aperture uncoated FS 10” diameter, 6-m fl Nike lens 700 J blunderbuss 8” port 12” FS window ($5250) 30 cm square aperture 34˚ 10” round aperture 30 cm 6.7” 10” assume 700 J in 900 cm 2 ~ 0.75 J/cm 2 ~25% of s-light reflected = 0.09 J/cm 2 10” round on 6x12 rectangle ~ 362 cm 2 35 Joules (polarized) available beam dump chamber

Another alternative idea for scaled testing: Contrast is >100:1 over a 7˚ range 10” diameter, 6-m fl Nike lens 700 J blunderbuss 8” port 12” FS window 30 cm square beam with 9” round aperture 32˚ 12” 6” assume 700 J in 900 cm 2 ~ 0.75 J/cm 2 ~25% of s-light reflected = 0.09 J/cm 2 9” round ~ 410 cm 2 37 Joules (polarized) available beam dump chamber

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

Particles transport rapidly toward the final optic We need to run multiple shots to establish the long-term behavior Test particle trajectoriesPressure at 100 ms Pa

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 duct1.5x10 5 l/s Duct diameter75 cm Duct length3 m Number of ducts64 Orifice conductance44 l/s/cm 2 Target mass4 mg Rep rate5 Hz Chamber radius7 m It doesn’t look promising!

electroplate success 5-yr plan and progress to date startKrF larger optics initial promising results at 532 nm attempts at thin film optics Phase I evaluation lower limits at 248 nm, chemistry control new lab, cryopump extended database, mid-scale testing, radiation damage, mirror quality, design integration 2004