Transmission Line Code Implementation of Magnetically Insulated Flow Theory

Abstract

Summary form only given. In a magnetically insulated transmission line (MITL) the total current flow is divided between current flowing in the metal and an electron current flowing in the vacuum. As a result of the vacuum electron flow, the impedance of the MITL is reduced below its vacuum value Z0, altering its power coupling to both the generator and the load. The effective impedance is best described by the flow impedance Zf, which is a function of both the geometry and voltage. Before the power pulse reaches the load, the MITL runs at the self-limited impedance, Zf SL. If the load impedance is sufficiently high, the MITL will continue to run at Zf SL after the pulse reaches the load and the system is described as operating in the line-limited regime. If the load impedance is lower than Zf SL, then a retrapping wave flows back up the MITL, reducing the voltage, returning some of the electron flow to the cathode, tightly insulating the remaining electron flow, and increasing Zf to a value close to Z0; in this case the system is described as operating in the load-limited regime. Analytic models of the MITL flow have been developed and predictions compare reasonably well with PIC simulations. These physics models are now being incorporated into transmission line codes so that design studies can be carried more efficiently. A versatile code will ultimately require models for treating impedance transitions and voltage adders. Initial results from the transmission line code model of MITL flow will be presented and compared with PIC simulations and future work will be described