Oil as an alternative coolant for use in the TFTR toroidal field coils

The Tokamak Fusion Test Reactor (TFTR) has twenty toroidal-field (TF) coils with a maximum current rating of 73 kA for 3.6 s when cooled with water. Operation of the TF array at this maximal current produces a 5.2-T magnetic field at a major radius of 2.48 m. Repetition rate is dependent upon the efficiency of the cooling system for the array. An alternative approach to the water cooling would be to circulate a silicate ester (oil) in the coils. This technique would improve the electrical insulation of a leaking coil because, unlike water, the oil will not dissolve electrolytes and, therefore, retains a high dielectric strength as it wets the insulation. The oil cooling system is composed of a pump, heat exchanger and piping, and associated control and protective action circuits. Due to higher viscosity and lower heat capacity than water, oil removes 0.89 MW (maximum) at 12 L/s for each coil (1.4 MW at 12 L/s for water). This decreases the repetition rate to one maximum power pulse every 900 s, as opposed to one every 300 s for water. A thermal analysis is presented, and the equipment and controls are described. A flow diagram for the system is provided