Demonstration of a Prototype, High Field, Single Turn, Toroidal-Magnet System

Very high toroidal magnetic fields have been produced using a single-turn magnet powered by homopolar generators (HPGs). A design goal of a 20 tesla confinement field has been met by the combination of a low impedance toroidal magnet, a high current, low voltage power supply, and the use of a high strength, high conductivity copper alloy. The Ignition Technology Demonstration (ITD) is a 1/16 scale prototype of the proposed full-scale IGNITEX (Ignition Experiment) toroidal field (TF) magnet. Stresses and temperatures reached in the prototype TF magnet are representative of those that would be experienced in a 1.5-m major radius magnet with a 5 s flat top current profile. Synchronized, parallel operation of multiple homopolar generators into a single-turn toroidal magnet has been realized. The prototype TF magnet has produced toroidal magnetic fields up to 18.1 T on-axis with liquid nitrogen (LN2) precooling and axial preloading of the magnet. Room temperature operation of the magnet has produced on-axis fields up to 11.5 T and with LN2 precooling only, up to 15.4 T. Peak current from the HPG system for the 18.1 T test was 8.14 MA with an open circuit voltage of only 49 V. Generator synchronization is achieved by six, 1.5 MA rated, closing switches with a maximum jitter of 10 μs. A peak current density in the inner leg region of the TF magnet of 750 MA/m2 was experienced during the 18.1 T test. Peak temperature in the inner leg region for this test was measured to be 135°C. The description of the ITD experiment, operational experience, and test results are presented.