BERTHA Circuit Model of the HERMES III Induction Voltage Adder and Magnetically Insulated Transmission Line

HERMES III is a pulsed power accelerator that operates at 18 MV, with a full-width half-maximum (FWHM) of 30 ns, and peak current of 650 kA. This work describes modifications made to the BERTHA¹ circuit model of HERMES-III to better represent the pulsed power system and optimize power delivery to a load. In addition, impedance changes to a magnetically insulated transmission line (MITL) are prescribed across a tapered transition section to a higher impedance MITL extension. The low-to-high impedance taper increases voltage and decreases current on the downstream side, results are being compared to EM PIC simulations and experimental data. Deviations from experiment are expected to be accounted for by incorporating an improved model of electron emission, which includes dynamic change to the operating impedance of the MITL once magnetic insulation occurs. BERTHA is being used to test a redesign (staggered tapers) of the HERMES MITL to increase the impedance of the standard 34-Ohm line. Results show increased voltage delivery and less sensitivity to the lack of an electron flow correction, further refinements to be presented.

* Sandia National Laboratories is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

1. D. Hinshelwood, BERTHA—A versatile transmission line and circuit code, Naval Research Laboratory, Washington, DC, Technical Report No. 5185, 1983.