Generation of High Toroidal Magnet Fields Using Single-Turn Magnet Technology
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The production of very high magnetic fields in a toroidal configuration has been accomplished using single-turn magnet technology coupled with low voltage, high current homopolar generators (HPGs). Single-turn, toroidal field magnets are an attractive alternative to conventional multi-turn coils because of the elimination of turn-to-turn insulation and complicated case structures. A20 T, single-turn toroidal magnet has been designed, built, and tested to demonstrate the high-field technology necessary for a fullscale fusion ignition experiment (IGNITEX). Six, 10 MJ HPGs, operated in a parallel circuit configuration, have powered the 1/16 scale (9 cm major radius) toroidal magnet to an on-axis field density of 20 T. The nominal peak current in the magnet is 9 MA while the open circuit voltage of the generators for a full current test is only 57 V. Each generator drives a 60° section of magnet circuit consisting of multiple wedge-shaped conductor plates. Stresses and temperatures within the magnet are managed by the use of a high strength beryllium copper conductor precooled to liquid nitrogen temperature and axially preloaded to produce an isostatic stress condition at peak electromagnetic loading. The stresses and temperatures produced in the scale TF magnet are representative of those that would be produced in a full-scale device with a 5 s flat top. Generator synchronization is accomplished by one explosively driven closing switch per generator that experiences an action of 1.24 x 1011 A2s per switch. Magnet instrumentation includes magnetic field density, temperature and strain measurements. A description of the experiment, operation and test results are presented in this paper.