Pulse Transformer Operation in Megagauss Fields

Abstract

A flux compression generator operates most effectively when directly coupled to a low impedance load. High impedance loads also can be powered successfully by such generators through impedance matching transformers. The pulse transformer consists of a low inductance primary coil, driven directly by the generator, and a tightly coupled, multi-turn secondary winding. We discuss some of the factors that influence transformer performance when megagauss fields develop in the primary coil. Flux exclusion by the transformer conductors results in severe eddy current heating and compressive stressing. We have found, however, that pulse transformers can operate effectively in fields substantially higher than those predicted for conductor melting and structural yielding, provided the drive-field pulse widths are sufficiently short. Copper-wound secondaries have operated successfully to 110 in fields with 7-µs risetimes and to 165 T, with risetimes of 4–5 µs. Another factor, not normally considered, is the imploding radial motion of the secondary windings. Such motion can be significant when the transformers carry large load currents. Calculations of this motion are compared with data obtained from recovered secondary coils. The effects of the dynamic displacement on transformer coupling is also discussed.

Work supported by the U. S. Department of Energy.