Deposition of ¹³C tracer in the JET MkII-HD divertor

Migration of ¹³C has been investigated at JET by injecting ¹³C-labelled methane at the outer divertor base at the end of the 2009 campaign. The ¹³C deposition profiles on carbon fibre composite divertor tiles were measured by secondary ion mass spectrometry and Rutherford backscattering techniques. ¹³C was mainly deposited near the puffing location on the outer divertor base tiles. High amounts of ¹³C were also found at the outer vertical target: at the bottom of the lower and at the top of the upper plates. Thirty-three percent of puffed ¹³CH ₄ was instantly pumped out by the divertor cryopump, which is close to the pump duct entrance. Global ¹³C transport in the torus was modelled by the EDGE2D/EIRENE and DIVIMP codes, and local ¹³C migration in the vicinity of the injection location by the ERO code. The DIVIMP and EDGE2D simulations show strong prompt deposition of ¹³C directly adjacent to the injection point as well as in the far scrape-off layer (SOL) along both the inner and outer divertor targets. In addition, the measured ¹³C deposition along the outer divertor wall tiles is qualitatively reproduced. However, EDGE2D and DIVIMP do not predict any deposition along the divertor surfaces facing the private plasma on the inner floor tile and inboard of the outer strike point on tile 5. The ERO calculations also indicate that most of the deposition occurs close to the injection location on the vertical face of the LBSRP tile and the horizontal part of tile 6.