Toroidal field coil thermal analysis for fast tokamak

A new facility for fusion, the Fusion Advanced Studies Torus (FAST), has been proposed to prepare ITER scenarios and to investigate non linear dynamics of energetic particles, relevant for the understanding of burning plasmas behavior, using fast ions accelerated by heating and current drive systems [1]. This new facility is considered an important tool also for the successful development of the demonstration/prototype reactor (DEMO), because the DEMO scenarios can take valuable advantage by a preparatory activity on devices smaller than ITER with sufficient flexibility and capable plasma conditions, before to testing them on ITER itself. To keep the cost of this new facility low enough was chosen to use the copper as main conductor material for the toroidal and poloidal fields coils. So FAST is a compact (Ro = 1.82 m, a = 0.64 m, triangularity ? = 0.4) and cost effective machine consisting of 18 Toroidal Field Coils (TFC), 6 Central Solenoid (CS) coils, 6 External Poloidal coils (3 + 3), adiabatically heated during the plasma pulse and cooled down at cryogenic temperatures (30 K) by helium gas between two consecutive pulses [1], [2]. Then a careful consideration of thermal loads due to the high density currents circulating in the coils is mandatory to establish the limiting performances of this tokamak. Moreover FAST is a very demanding machine because of the large number of scenarios foreseen on it and this strong flexibility in operation capability doesn´t allow to choose the more demanding scenario on a simple B²t criterion. In fact several scenarios are to be investigated to ascertain the more onerous conditions on the machine not only because of the non linear copper resistivity growth with the temperature but also due to its non linear variation with the applied magnetic fields. In this work the thermal analysis carried on the toroidal magnet are presented with particular regard to the role of the magneto-resistive effect and taking in account als- o the copper specific heat variation with temperature. The analysis are performed by F.E.M. (Finite Elements Method) models realized with a commercial multi-physics code (by COMSOL^?) and comparing its results with the ones obtained using an axisymmetric integral code developed in ENEA.