TOKAMAK DESIGN FOR REACTING PLASMA EXPERIMENT AT IPP NAGOYA

Reacting plasma project (R-Project) aims at studying the reacting plasma physics with relatively small sized tokamak which has a short discharge time of 1.5 sec. A Q-value of 0.3 is expected when additional heating is applied (NBI ≥ 15 MW, RF ≥ 5 MW). In the first phase design of R-tokamak, we adopted stainless steel for structural material. The induced radioactivity of such device caused by one D-T shot is estimated to be several mrem/hr at the machine surface even after a few months. Remote handling technique is, therefore, inevitable in order to perform reasonable number of D-T shots. Alternatively, the use of aluminum alloy for structural material is examined to reduce the induced radioactivity and to ease remote handling technique. The activation can be reduced to a sufficiently low level (roughly 1/100 of that in the first phase design). The following considerations are taken into account in designing the aluminum R-tokamak: a) Optimization of TF and PF coil current waveforms to minimize the induced eddy currents on the vacuum vessel, b) TF coil with a cut in the coil frame to prevent heavy induction current, c) thin vacuum vessel reinforced by ribs in order to keep both high electrical resistance and stiffness against strong electromagnetic forces, d) low operation temperature (~120°) to avoid over-aging of the Al alloy.