Influence of Variable Impedance Terminations and Input Voltages on the Operating Conditions of an Under-Matched Magnetically-Insulated Transmission Line

Abstract

Summary form only given. Termination of a magnetically-insulated transmission line (MITL) with an impedance that is less than the matched MITL operating impedance launches a re-trapping wave back up the MITL toward the source. A previous investigation obtained the relationship for the MITL operating conditions (voltage and current) after the passage of the re-trapping wave that depended on the input voltage, the termination impedance, and the MITL operating conditions based on parapotential flow at minimum current. The relationship was in agreement with detailed particle-in-cell (PIC) simulations and experiments of the re-trapping wave process for large area diodes. The scaling law and simulations however were only applied to a constant input (forward going) voltage and termination impedance. This work extends those PIC simulations and wave analyses to MITL operating conditions for termination impedances and input voltages that are functions of time. We first examine the case in which the input voltage is constant and the impedance changes in a staircase manner. These results are then extended to termination impedances that are continuously varying functions of time. The complementary case of fixed termination impedances and a variable input or forward going voltage will also be presented. The MITL operating conditions after the passage of the re-trapping will be examined as a function of the time history of the termination impedance and input voltage. Particle-in- cell simulations will be used extensively in the analyses and compared with linear and non-linear wave analyses. The objective of the work is to determine if the operating conditions of an under-matched magnetically insulated transmission line can be represented by a simple state function or do the final operating conditions depend on the previous time history of the termination impedance and input voltage.