Rotating magnetic field oscillator system for current drive in the translation, confinement, and sustainment experiment

The experimental setup and test results for the ∼125 MW rotating magnetic field current drive system of the Translation, Confinement and Sustainment Experiment at the University of Washington are described. The oscillator system, constructed at Los Alamos National Laboratory, drives two tank circuits $(15 kVpeak$ potential, $8.5 kApeak$ maximum circulating current in each tank to date) operated 90° out of phase to produce a 54 G rotating magnetic field with a frequency of 163 kHz $(ω=1.02×10−6 s−1).$ Programmable waveform generators control “hot deck” totem pole drivers that are used to control the grid of 12 Machlett 8618 magnetically beamed triode tubes. This setup allows the current to be turned on or off in less than 100 ns (∼6°). Both tank circuits are isolated from the current source by a 1:1 air core, transmission line transformer. Each tank circuit contains two saddle coils (combined inductance of 1.6 μH), and radio frequency capacitors (580 nF). Test results are presented for three conditions: no external load, a resistive external load, and a plasma load. A SPICE model of the oscillator system was created. Comparisons between this model and experimental data are given.