High-Voltage High-Power Resistive Divider for TFTR Neutral-Beam Power Supply

The neutral-beam source at the Tokamak Fusion Test Reactor (TFTR) requires a voltage divider to supply the gradient grid. The requirements are simple, but stringent: it must dissipate 576 kW of peak power at 120 kV dc. Average power is 19.2 kW. A special resistive divider, indirectly water cooled, has been successfully developed for this purpose. The divider is unusually large physically, weighing 1290 kg when filled, and its cooling system is believed to be unique, conferring unusual advantages. The divider consists of an array of 9000 commercial resistors immersed in a plastic tank of inert fluid. The resistors are cooled by subcooled-pool boiling at their surfaces, and the fluid is vigorously circulated by natural convection. A fluid-to-water heat exchanger above the resistors removes the deposited energy and limits the average temperature of the system. The tank is covered by a constant-pressure diaphragm seal. The heat capacity of the system reliably averages the pulse power, and there are no pumps or other moving parts. Operation of the system, which is intrinsically self-regulating, is relatively unaffected by leakage or noncondensible gas.