Long pulse fusion physics experiments can be performed economically via resistive electromagnets designed for thermally steady-state operation. Possible fusion experiments using resistive electromagnets include long pulse ignition with DT fuel.1,2,3,4 Long pulse resistive electromagnets are alternatives to today's delicate and costly superconductors.5 At any rate, superconducting technology is now evolving independent of fusion, so near-term superconducting experience may not ultimately be useful.

High magnetic field copper coils can be operated for long pulses if actively cooled by subcooled liquid nitrogen, thermally designed for steady state operation. (Optimum cooling parameters are characterized herein.) This cooling scheme uses the thermal mass of an external liquid nitrogen reservoir to absorb the long pulse resistive magnet heating. Pulse length is thus independent of device size and is easily extended. This scheme is most effective if the conductor material is OFHC copper, whose resistivity at liquid nitrogen temperature is small. Active LN2 cooling also allows slow TF ramp-up and avoids high resistance during current flattop; these factors reduce power system cost relative to short pulse adiabatic designs.