A new optimized design concept of the switching network resistors of the large ITER-FEAT tokamak

In the large ITER-FEAT tokamak, resistors are essential electrical components to protect the super-conducting coils but also to produce the needed high voltages in some poloidal field coils during the breakdown and plasma initiation phase to start-up the plasma current. In this specific case, the resistors, called Switching Network Resistors (SNR), must dissipate a large amount of energy but should be also able to provide accurate step resistances within wide ranges of currents and voltages. The step resistances needed in the coil circuits can be precisely determined only during experimentation with the machine. Therefore, a large flexibility has to be foreseen in the design of these resistors. As several SNRs are installed in the large tokamak ITER-FEAT, this paper describes, step by step, a new optimized resistor design concept, with regard to flexibility in operation and cost optimization.