Magnetic field measurements in wirearray Z-pinches

Abstract

Summary form only given. Understanding the evolution of the magnetic field topology and magnitude in the high energy density plasmas produced by wire-array Z-pinches is of critical importance for their ultimate application to stockpile stewardship and inertial confinement fusion. A method to determine the magnetic field profile in megampere level wire-array Z-pinches with high spatial and temporal resolution has not yet been developed. An ideal method would be passive and non-perturbing, such as Faraday rotation of laser light or emission spectroscopy. However, Faraday rotation measurements in Z-pinches suffer from severe practical difficulties, including, for example, the fact that there are large density gradients and the plasma appears to develop magnetohydrodynamic turbulence. A technique to measure the magnetic field in high energy density plasmas using magnetic (CoPt) thin films has already been developed. However this technique had insufficient time resolution. Therefore, we are developing a method based on Faraday rotation through a sensing waveguide placed in the vicinity of, and eventually in, a wire-array Z-pinch. We present preliminary theoretical and experimental results. Our ideal device is a "thin film waveguide" coupled to an optical fiber system. While these sensing devices may not survive for long in a dense Z-pinch, they may provide useful information for a significant fraction of the current pulse