Effect of local NH3/CH4 gas injection on the formation of carbon layers on a limiter surface in the SOL of TEXTOR by means of in situ QMB measurements

Ammonia injection in the afterglow region of the divertor plasma has been proposed for the inhibition of tritium/carbon co-deposits in remote areas of ITER when operated with carbon-based divertor targets. Supporting experiments in the PILOT-PSI divertor simulator plasma device and in a RF methane plasma were presented in the last PSI Conference. In this work we address the effect of ammonia injection in TEXTOR, a limiter tokamak. Mixtures of hydrogenated methane and ammonia were puffed into D plasmas at the Quartz MicroBalance (QMB) location, a lock limiter 7cm away from the LCFS. The scavenger effect and erosion of the growing or pre-existing films could play a similar role in the observed behavior. In both mechanisms, eroded carbon is mostly converted into HCN. The observed strong erosion opens up the possibility of controlling T inventory in the plasma-exposed surfaces by direct ammonia seeding in ITER plasmas, implying water-free conditions.