Microporosity of carbon deposits collected in the Tore Supra tokamak probed by nitrogen and carbon dioxide adsorption

Nitrogen and carbon dioxide adsorption experiments have been used to investigate the porosity of carbon deposits formed in the Tore Supra tokamak as a consequence of the erosion of the plasma-facing components. We compare BET, α_s-, and Dubinin-Raduskevich methods to distinguish between micropore volume (∼0.04 cm³ g⁻¹) and external surface (∼90 m² g⁻¹). Consistent results have been obtained for nitrogen and carbon dioxide, and the smallest pores are shown to be reversibly closed and opened under air exposure and outgassing at 600 °C, respectively, probably due to blocking of pore entrances by surface oxides. Pore size distribution is calculated using the non-local density functional theory: a novel and straightforward method is used to fit the experimental isotherms by Lorentzian distributions of pores centered in some relevant pore size regions. We thus show that the tokamak sample micropores are mainly ultra-micropores (∼75%) whose widths are centered at 0.6 nm. This latter result is in good qualitative agreement with the outgassing effect and in good quantitative agreement with what is deduced from α_s-plot.