Analysis of the Spatial Variation and Time Dependence of the Current Distribution in a Single-Turn Coil for Megagauss Fields

Due to the semi-destructive character of the single-turn coil, this technique is especially useful for reproducible experiments in megagauss fields. Theoretically, geometry, the skin effect, and resistivity changes due to inhomogeneous Joule heating determine the current distribution within the coil. To calculate the current and temperature distribution, the cross section of the coil is divided into small rectangular filaments according to Nakao et al. The dimensions of these sections have to be comparable or smaller than the skin depth in order to get realistic results. These results show that the time dependence of the magnetic field values on the coil axis are different for different distances from the coil center. This result implies that the zero in the magnetic field at a given position on the coil axis does not necessarily agree with the zero of the total current. This effect has been observed for the first time experimentally with our equipment using a twin pick-up system for special analysis of the spatial distribution of the magnetic field on the coil axis.