Numerical Investigation of Higher Order Propagation Modes in High-Power Magnetic Compression Lines

In this article, the influence of higher order propagation modes on pulse transformation in ferrite-filled coaxial nonlinear transmission lines (NLTLs) in multigigawatt pulse compression regime [magnetic compression line (MCL)] is investigated theoretically. A discussion of the application of higher order mode concept to short-pulse time-domain systems is given, which highlights the methodological difficulties associated with such a type of study. A method of dynamical mode analysis in time domain is proposed based on energy considerations and coordinate components of electromagnetic field. Numerical simulations are conducted to study the formation and propagation of modes in a coaxial line partially filled with ferrite, evaluating the influence of nonaxisymmetric modes, axisymmetric TE modes, and axisymmetric TM modes on pulse formation. Such an approach allows to factually demonstrate that the influence of higher order modes on pulse formation in MCLs is negligible, and the main process governing pulse formation is the interaction of nonlinear ferrite material with the fundamental dispersive mode TM₀₀. The presented information deepens the understanding of physical processes occurring in coaxial lines partially filled with ferrite under the application of high-power pulses.