Erosion, redeposition and boronization lifetime in RFX

In this paper the boronization lifetime in the reversed field pinch experiment RFX is discussed. It is found that the redeposition of carbon-rich layers, which grow during plasma exposure, cover the boron containing layers preventing the getter effect through formation of stable boron oxides. Enhanced localized erosion on graphite tiles, which constitute the first wall of the experiment, due to magnetic disturbances or held errors is identified as the source of carbon which codeposits together with hydrogen over the boronized layers. Samples covered with different boron containing layers have been exposed to the plasma, analyzed by surface techniques and compared. The redeposition process is confirmed to be the main cause determining the boronization lifetime. (C) 1999 Elsevier Science B.V. All rights reserved.