Magnetic Field Measurements in Wire-Array Z- Pinches and X Pinches

We are investigating novel techniques to obtain time-dependent magnetic field measurements in wire-array Z-pinches and X-pinches. An ideal method would be emission spectroscopy (Zeeman splitting of lines, for example, in the visible or VUV spectrum), as it would be entirely passive and non-perturbing. However, a spectroscopic method to determine the high magnetic fields present in megampere level wire-array Z-pinches with high spatial resolution has not yet been identified. Determining the Faraday rotation of laser light passing through wire-array Z-pinches suffers from severe difficulties precisely where the measurements are most interesting, namely inside of the array where density gradients are large and the plasma is thought to be magnetohydrodynamically turbulent. We are looking into using “remote sensing” methods whereby a very small sensor material is placed in the plasma and then is investigated to extract useful information. Faraday rotation of polarized laser light traversing a small area through thin film waveguides coupled to a fine optical fiber is a possibility. While these films may not survive for long in a dense z-pinch, they may provide useful information for a significant fraction of the current pulse. Details of these two methods along with preliminary results from one or both of them will be discussed. We will also discuss results of experiments conducted using magnetic CoPt thin films to obtain the maximum magnetic field seen by the film near the end of the load current pulse.