Particle-in-cell-simulation resealing of magnetically insulated flow theory

Abstract

Summary form only given. In a magnetically insulated transmission line (MITL) the total current flow I/sub a/ is divided between current flowing in the metal I/sub c/ and electron current flowing in the vacuum, i.e., I/sub a/-I/sub c/. As a result of the vacuum electron flow, the impedance of the MITL is altered and, thus, the power coupling between it and both the generator and the load changes. The effective impedance is best described by the flow impedance Z/sub f/, which is a function of both the geometry and the voltage. Before the power pulse reaches the load the MITL runs at the self-limited impedance Z/sub f//sup SL/. If the load impedance is sufficiently high, the MITL will continue to run at Z/sub f//sup SL/ after the pulse reaches the load. Thus, the properties of self-limited flow are particularly important. Here, an assumption on the electron density distribution in the flow layer used in existing MITL theory is relaxed by introducing a space-charge scaling factor. Values for the scaling factor are determined by matching to particle-in-cell (PIC) simulations, effectively rescaling the MITL theory. Any polarity differences found in the PIC simulations can be accommodated by scaling differently for positive and negative polarity. Finally, analytic expressions are derived for the first time for Z/sub f//sup SL/ and the self-limited currents I/sub c//sup SL/ and I/sub a//sup SL/. Expressions are also obtained for Z/sub f/(I/sub a/) when the anode current I/sub a/ is known and Z/sub f/(I/sub c/) when I/sub c/ is known. Theoretical results are presented and compared with PIC simulations.