Nitrogen implantation into carbon: retention, release and target-erosion processes

Abstract

The interaction of nitrogen ions with carbon films is investigated in view of the nitrogen recycling behavior on carbon divertor targets during plasma operation with nitrogen gas puffing. Nitrogen ion implantation is carried out in the energy range between 0.75 and 20 keV and at irradiation temperatures between room temperature and 800°C. Nitrogen retention and release are analyzed in situ, using elastic recoil detection and time-resolved residual gas analysis, respectively. It is found that the nitrogen contents inside the implanted near-surface layers saturate at large fluences, and that the temperature and energy dependence of the saturation level is qualitatively different from the behavior found for the bombardment of graphite surfaces with hydrogen ions. The different behavior is mainly attributed to the formation of N 2 bubbles in the implanted near-surface layers. The N 2 formation is also identified as the driving force for nitrogen saturation and release at large fluences. It is concluded that nitrogen interacting with carbon surfaces cannot be regarded as a non-recycling gas under high-dosage irradiation conditions.