Mechanisms for carbon migration and deuterium retention in Tore Supra CIEL long discharges

A model has been created to examine, in greater detail, co-deposition mechanisms in Tore Supra long discharges with high extracted power. The model couples 1D core, 3D scrape-off layer and detailed 3D wall impurity generation models to follow the C balance in steady state. It describes the complex 3D erosion/deposition zones of the Tore Supra CIEL surface, and includes a description of impurity generation from intra-tile gaps and from the poorly adhered layers of re-deposited material in shadowed areas. Results have been compared with CII/Da spectroscopy for a power scan in a database of 50 discharges. The model reproduces the observed increase in CII emission with power. Sources due to D+ physical sputtering are found to saturate at higher net power levels, while self-sputtering contributions continue to increase. A new mechanism for transport of deposited C to remote areas is suggested from the model: radiant heating of poorly adhered layers, combined with CX bombardment, can cause layer decomposition and further transport. This is relevant to the resolution of questions concerning the observation of large scale deposits (flakes) in areas on JET and in other devices. A scaling for the dependence of total carbon erosion on plasma parameters has been inferred from the spectroscopic database, and used to make a shot-by-shot analysis of 3 sequential Tore Supra annual campaigns in order to establish a direct relation between spectroscopic observation and total erosion..