Design of the TFTR TF coil alternate coolant system

The Tokamak Fusion Test Reactor (TFTR) toroidal field (TF) system consists of twenty coils which when operated with deionized water as the coolant has a maximum pulsed operating current and I²T of 73.3 kA and 5.4 E10 A²-s respectively. With deionized water as the primary coolant, the pulse repetition rate is 300 s, which is dependent upon the cooling system efficiency. Numerous small water leaks in several TF coils occurred which have adversely impacted machine operations. These leaks have resulted in a reduction of the TF coil´s resistance to ground. Various leak repair techniques have been successfully used. However, the leaks which cannot be exactly located have a history of reoccurring after repairs have been made. An alternative approach to coil cooling has been implemented which replaces the deionized water with a nonconductive fluid. This fluid should prevent the degradation of the coil resistance because it will retain its high dielectric strength, even if it wets the coil insulation. Perfluoroheptane was chosen from a number of dielectric fluids because of its compatibility with existing materials in the TF coil circuit, chemical and radiation stability, and environmental acceptability. This fluid has reduced thermal capacity which decreases the TF coil I² T to 4.84 E10 A²-s with an increased repetition rate to 900 s