INTERACTIONS OF BULK-BORONIZED GRAPHITES WITH DEUTERIUM PLASMAS IN THE PISCES-B FACILITY

Newly developed bulk-boronized graphites and boronized carbon-carbon composites, with a total boron concentration ranging from 3 to 30 wt%, have been bombarded with steady-state deuterium plasmas at temperatures between 200 and 1600-degrees-C in the PISCES-B facility. The erosion yield of bulk-boronized graphite is smaller than that of pyrolytic graphite by a factor of 2 to 3 in regimes of chemical sputtering, physical sputtering, and radiation-enhanced sublimation (RES). Plasma bombardment at elevated temperatures does not noticeably alter the near-surface composition of bulk-boronized graphite. A chemical pinning effect of boron on the migration of interstitial carbon atoms is the key to the reduction of erosion due to RES. Postbombardment thermal desorption spectroscopy indicates that bulk boronization enhances recombinative desorption of deuterium. The enhanced deuterium desorption is responsible for the suppressed chemical sputtering. Deuterium retention in bulk-boronized graphite at temperatures from room temperature to 800-degrees-C has been measured, and it is maximized at temperatures around 300-degrees-C. The maximized deuterium retention increases by a factor of 2 as the boron concentration changes from 0 to 90%.