Analysis of the interaction between plasmas and the graphite first wall in RFX-mod

In the RFX-mod Reversed Field Pinch experiment the wall is entirely covered by graphite tiles. The disadvantage of a graphite wall is that, except after wall conditioning procedures, such as boronization, lithization or glow discharge cleaning, the graphite becomes saturated with trapped Hydrogen, causing that during the discharge the particle recycling factor is approximately one and plasma density is entirely sustained by particle fluxes coming from the wall. In the paper the results of the analyses of graphite samples after their exposure to plasmas or wall conditioning treatments are presented. The topics addressed are: the deposition of Boron during different boronization treatments; the erosion and re-deposition of the Boron layer by Hydrogen plasmas; some remarks about the presence of Lithium in the wall since the beginning of lithization treatments.