Fusion Science and Technology / Volume 49 / Number 4 / May 2006 / Pages 768-772
Technical Paper / Target Fabrication
We have successfully sputter deposited 2 m thick layers of SiO2 on CH mandrels ~ 2 mm in diameter to act as a permeation barrier for deuterium. Such targets can be used for experiments at Sandia's Z facility as well as at the National Ignition Facility (NIF). This permeation barrier has been shown to have a half-life (1/2) of ~2-4 weeks for a thickness of ~ 1.5 m. The sputter coating conditions have been successfully optimized to produce smooth uniform SiO2 coatings with enough integrity to allow routine handling as well as filling to the required pressures (20 atm). The key coating conditions investigated were the agitation mechanism and the coating pressure. We found that an agitation mechanism using gentle rolling produced coatings with a half-life of greater than three weeks, whereas a more vigorous bouncing agitation yielded half-lives of only a few days. Coating pressures of 2, 5, and 10 mTorr were studied and it was found that coatings at 5 mTorr produced coatings free of cracking. Since the sputtering is performed in a background atmosphere of argon, the sputtered SiO2 layer was found to contain trace amounts of argon as measured by x-ray fluorescence (XRF) measurements. Our work has yielded a controllable uniform alternative permeation barrier to the traditionally used poly(vinylalcohol) (PVA).