Erosion and transport of Sn and In in the SOL of MAST plasmas

A satisfactory method for monitoring the erosion of vessel wall tiles in a fusion power plant remains an important missing diagnostic in the fusion program. Spectroscopic observation of embedded impurity layers may provide such a capability. In a preliminary experiment, Sn and In have been introduced to the scrape off layer of MAST plasmas by erosion from a target mounted on the reciprocating probe system, and have been successfully observed spectroscopically in the core and at the edge. The atomic transitions corresponding to each observed spectral line and feature have been predicted and then identified, with those in the visible region being used to estimate the erosion/influx rate. The confined plasma emission has been measured and modelled using the impurity transport code UTC-SANCO. The results show that eroded Sn and In emission is observable and distinguishable in MAST, and shows that the technique has promise for use in future devices.