Accurate modeling of the proximity effect in helical flux-compression generators

Two-dimensional (2-D) modeling 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 three-dimensional (3-D) phenomena, and their influence is represented approximately by either existing formulae or a one-dimensional (1-D) 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 new detailed approach that has been developed for use with an existing 2-D model which forms the first element of an overall more detailed modeling code. It is shown that the scale of the proximity effects in a helical coil carrying a pulsed current can be many times greater than those predicted by the conventional formulae.