Superconducting ohmic-heating coil simulation

Superconducting coils have been proposed for use as ohmic-heating coils in the conceptual designs of most tokamak and reverse field pinch fusion reactors because of their high energy efficiency. Lack of detailed knowledge about the behavior of superconducting coils performing the required bipolar flux swings may delay their application in future fusion reactors. The Los Alamos Scientific Laboratory has undertaken a study to show how such coils can be constructed. This program includes both theoretical and experimental phases. The work is based to a large extent on the experience gained during the fast discharge (1 ms) magnetic energy transfer and storage (METS) program. A series of experiments in which a typical ohmic-heating current waveform is simulated have been undertaken using the 300-kJ, 10-kA METS superconducting coil, a 500-kW, 250-V, 2-kA dc motor generator set used as a capacitor, and a rectifier power supply. The coil has undergone full bipolar flux swings to greater than rated current (± 12-kA, 430 kJ) and remained superconducting. The commutator dc machine has functioned successfully as a capacitor up to 12 kA. We describe the test circuits and discuss the components. Terminal characteristics are presented. Coil energy losses are presented as a function of the terminal current. These tests support the viability of bipolar pulsed superconducting coils for use in tokamaks and other fusion concepts.