Erosion and redeposition experiments in the PISCES facility

Abstract

The modfication of surfaces during exposure to plasma bombardment is a critical issue in the development of limiter and wall materials for fusion confinement experiments. Controlled studies of the erosion and redeposition of materials during high flux and fluence plasma exposure are now possible in the PISCES facility. PISCES is a continuously operating plasma device which has achieved hydrogen plasma densities of over 10 13 cm" 3 and electron temperatures of 5 to 24eV over large areas. Ion fluxes of 10 17 to 10 19 cm" 2 sec 1 and fluences of up to 10 23 cm* 2 have been used to bombard biased samples inserted into the plasma. The plasma parameters can be selected to produce simple sputtering, or redeposition by the ionization and recycling of the sputtered target materials. Collaborative studies on the performance of Cu and Cu-Li alloys (with ANL), stainless steel (with SNLL), and graphite (with IPP at Garching, and SNLL) have been undertaken. Surface topography modification is always observed after a sufficient fluence is achieved-The net erosion rate is significantly lower during redeposition than one would expect from classical sputtering yields. The transport and deposition of different materials by the plasma to the samples during redeposition conditions results in greatly modified surface composition and morphology. Chemical sputtering of graphite during low energy, high flux (>10 18 cm" 2 sec" 1 ) plasma bombardment is observed. Chemically formed hydrocarbons are relatively easily redeposited compared to sputtered carbon. The performance of these materials, the surface morphology evolution, and the characteristics of the redeposited materials are discussed.

Retention behavior in tungsten and molybdenum exposed to high fluences of deuterium ions in TPE

“…Laboratory studies conducted in PISCES-A by Goebel et al in Ref. [7] and in a Penning discharge by Causey et al in Ref. [8], report a retention fraction which varies between 10 À4 and 10 À6 depending on sample temperature.…”