Eddy Current Decay and Resistivity Measurements on Longitudinally Grooved High-Purity Aluminum Bars

Abstract

The eddy current decay (ECD) method for determining electrical resistivity uses a relationship between the time constant of magnetic flux diffusion and resistivity. This method is shown to be valid for determining the resistivity of solid high-purity aluminum cylinders with eight equally spaced longitudinal grooves machined into the surface. The effects of changes in groove dimensions for a 25.4-mm-diameter, superconducting magnetic energy storage (SMES) conductor stabilizer are reported. Observations of machining, heat treatment, and material inhomogeneity effects are discussed. It is found that the ECD time constant is dependent primarily on groove depth and that groove width has only a minor influence. An empirical equation relating groove dimensions with the time constant and with resistivity is presented.