Improved core insulation schemes for multi-terawatt magnetic switches

The operation of multi-terawatt magnetic switches was successfully demonstrated in the Comet 2 pulsed power module in 1984. Those switches, however, had short lifetimes (less than 100 shots) due to inter-lamina dielectric breakdowns at electric-field levels far lower than expected. Since then, experiments have been conducted to gain an understanding of this problem. We found that the breakdowns occurred at low electric-field levels, because the thin dielectric film (Mylar) was abrasively degraded by the relatively rough surface of the magnetic tape (Metglas) during the core winding process. This problem can be solved by modifying the Metglas surface before winding. A factor of 2 improvement in breakdown level, from 0.8 MV/cm to 1.6 MV/cm, has been demonstrated on the MSTF module (a Marx driven, 500 kV, 2 ohm, 50 ns PFN) in 18 in. OD switches wound with Electrodag coated Metglas (nominal coating thickness of approx. 6 microns). Even better performance has been achieved in smaller scale tests with an electrophoretically applied plastic-coated Metglas. A description of these experiments and a discussion of the results will be presented.