1 of 11 John Pulsifer and Mark Tillack with help from Patrick Rye and Matt Aralis HAPL Project Meeting October 2007 Washington DC Progress in fabrication and testing of grazing-incidence metal mirrors

2 of 11 Trials and Tribulations in GIMM Testing TrialTribulationOutcome No vendor could fabricateWe had to learn to make3x higher damage obtained in high-quality custom mirrorsour own mirrors1%Cu solid solution coatings High shot count requires highA custom beam homogenizerStable, smooth irradiations rep rate and multiple gas fills,had to be designed and testedare now possible creating unpredictable profiles High shot count requires aOur LPX is anything butIt’s working now; we’ve reliable light sourcereliable; <50% up timeacquired over 1.6 x 10 7 shots Chamber contamination hasMaximum fluence isTBD returned to haunt us compromised; absorption on specimen a problem

3 of 11 1%Cu solid-solution Al alloy coatings have been fabricated and tested at UCSD Small alloy additions can have a large enhancement to mech. props. (10 X hardness) Precipitates are dangerous for a mirror, so solid solution films were fabricated. 5-µm Al-1%Cu sputtered on 4” Si wafers, polished by CMP to < 1 nm RMS, < 10 nm PV Much smaller grains than pure Al, and smoother finish as coated. Magnetron coater, UCSD fabrication lab E (GPa)H (MPa)Y s (MPa) Alumiplate %Cu alloy 15110,556- Pure Al %-Cu alloy* --65 *Mechanical Behavior of Contact Aluminum Alloy David T. Read, Yi-Wen Cheng, J. David McColskey, and Robert R. Keller Mat. Res. Soc. Symp. Proc. Vol. 695 © 2002 Materials Research Society Evidence suggests a 3 X increase in Y s Nano-indentation performed on: Alumiplate, D-T UCSD sputtered 1%Cu alloy, 5 microns thick

4 of 11 Beam homogenization is used to create a more uniform intensity distribution homogenized MLA1MLA2 Fourier lens relay plane (homogenized) focus lens relayed, demagnified target plane A custom homogenizer design was needed to provide standoff and low divergence across the shallow target GIMM 1 m new gasold gas

5 of 11 Both beam and specimen are more uniform resulting in more uniform damage Footprint: 0.4 x 4 mm Footprint: 1 x 10 mm Beam NOT homogenizedBeam homogenized Mirror #111 (D-T Al) Location #3: 2 to 4 J/cm 2 1,596,164 shots

6 of 11 Contamination on mirrors and chamber window is evident at high shot counts Location #1 is a 129,000 shot test at 4.8 J/cm 2 (no visible layer) Locations #2 and #3 are both ~1.5 million shots each with fluence ranging from 4.6 to 2.2 J/cm 2 Absorption on surface increases due to contamination. Fluence on specimen falls as chamber window is being coated during testing. Will this happen in a power plant? Chamber pressure is < 2 x Torr for all tests. Electron spectroscopy will be performed to identify the contaminant so the source can be eliminated. Possible suspects: Translation stage grease Epoxy on electrical feedthrough Pump oil from rough pumping

7 of 11 High cycle data is our top priority, with a goal of >10 8 shots We have acquired 1.65 x 10 7 shots so far without specimen failure. Current homogenizer limits fluence to < 5 J/cm 2 ; A better homogenizer can allow us to collect data in the 1-to-2 x 10 6 range to fill out the curve.

8 of 11 The LPX laser seems to be failing more than the mirrors these days… Borrowed from Roundel, Nov

9 of 11 Plastic strain accumulation, extrapolation revisited Contamination on the specimen surface could be affecting our high-cycle data more negatively than low-cycle data. * Laser-induced damage on single-crystal metal surfaces Yong Jee, Michael F. Becker, and Rodger M. Walser J. Opt. Soc. Am. B/Vol. 5, No. 3/March 1988 Empirical model: F n = F 1 N (s-1) s = 0.89, Jee et al * pure Al Surface preparation and material composition, however, can also affect the value of s.

10 of 11 Summary Alloy mirrors fabricated at UCSD show a 3-fold improvement in damage fluence that suggests a 3-fold improvement in yield strength over pure Al. The homogenizer produces a smooth beam that eliminates doubt about the local fluence on target and produces uniform damage. Contamination (activated by UV light) is a problem for high-cycle data collection and may be a problem in a fusion power plant x 10 7 shots is the longest test performed so far, and the specimen has not failed. The laser fails more often these days… Provided that surface absorption remains constant, plastic strain accumulation theory may accurately predict long term damage. “Effect of laser pulse duration on damage to metal mirrors for laser-IFE” was presented at the 39th Boulder Damage Symposium on 24 September. “Development of damage-resistant metal mirrors for laser-IFE” was presented at the 22nd Symposium on Fusion Energy on 21 June.

11 of 11 Future plans 1. Achieve more fluence with a different homogenizer (larger aperture, AR-coated) Current homogenizer limitations: Small aperture (1 cm x 1 cm) limits energy input Non AR-coated surfaces cause more energy loss Max fluence on target is 4.8 J/cm 2 2. Chamber contaminant source to be identified and eliminated. Throughput to target is reduced up to 50% after millions of shots due to window contamination Absorption at specimen surface is likely changing drastically due to contamination and negatively affecting high-cycle data. 3. Continue shooting to achieve 10 8 shots