Three-dimensional modelling of helical flux-compression generators

Two-dimensional modelling techniques using a filamentary-mesh approach are very well established for use in helical flux-compression generator design, and provide results that have been verified experimentally. However, none of the published numerical codes appear to describe adequately certain details involved in calculating the resistance of the helical stator coil. In particular, the skin and proximity effects that arise from diffusion of the magnetic field into the conductor are clearly 3-dimensional phenomena, and their influence is only very approximately represented by either existing formulae or a 1-dimensional description. In most published codes, the formulae that are used provide merely a steady-state approximation to the proximity effect. The present paper outlines a 3-dimensional approach that has been developed for use with an existing 2-dimensional model, and which forms the first element of an overall 3-dimensional modelling code. It is shown that the scale of the 3-dimensional proximity effects in a helical coil carrying a pulsed current can be many times greater than those predicted by the conventional formulae.