Two-dimensional measurement of heat load on the first wall due to fast ion ripple loss in JT-60U with near-perpendicular NBI

Toroidal field ripple produced by a finite number of toroidal field coils can lead to enhancement of fast ion excursions in a tokamak. The ripple-induced fast ion loss has an impact on the realization of fusion tokamak reactor because of its serious heat deposition on the first wall. In order to predict the local heat load due to fast ion ripple loss, several simulation codes have been developed. Recently heat load to the first wall was one-dimensionally measured in JT-60U using toroidal/poloidal thermocouple arrays. The experimental result has been compared with the orbit-following Monte Carlo (OFMC) code, and it showed good agreement. This suggests that our understanding of single particle behaviour of fast ions in non-axisymmetric field is reasonably good and that the OFMC code is useful for predicting ripple-induced alpha loss in a burning plasma. At present, we are performing a further investigation on ripple-induced fast ion loss by introducing infrared thermography. This paper describes the latest results on the two-dimensional measurement of heat deposition on the first wall due to ripple loss and comparison between the experiment and the OFMC computation. (author) 5 refs., 4 figs