Basic Performance Of Flux Compression/Expansion Converters

Flux-compression generators are used when high current-pulses are needed in applications as diverse as the establishment of high magnetic fields, fusion research, electromagnetic launchers, welding, metal forming, and geological mapping. Because of the reversibility of the electromechanical energy conversion process, the analysis of flux compression in generators also applies to flux expansion in electromagnetic launchers. The aim of this paper is to study a simple case that is amenable to closed-form formulas, in order to establish the relations among the parameters of the generator circuit, to predict the important aspects of performance, and to provide guidelines for the design. The cycle of performance of these generators involves three phases: (1) build up of the flux interlinked initially with the collapsible inductor, (2) flux compression and accompanying current rise, and (3) current decay. Each phase is dealt with separately for the two most common cases of voltage sources: (a) a self-excited generator operating at constant speed and (b) a constant voltage source which approximates the output of a self-excited generator operating with retrieval of the kinetic energy of the rotating masses.