Determining the Magnetic Field Near X-Pinch Plasma Discharges using Magnetic (COPT) Thin Films

Abstract

Summary form only given. An important question in improving our understanding of wire-array Z-pinch physics lies in studying magnetic field topologies and strengths in high energy density plasma regimes. We present a novel technique to determine a lower limit of the maximum magnetic field at a particular point near an X-pinch plasma discharge using CoPt thin films with a high coercivity. The X-pinch configuration involves two or more wires that cross and touch at a single point, in the form of an X. They are then exploded by a large current pulse, which produces a hot, dense plasma at the original cross-point of the wires. This plasma is then compressed by a magnetic field that is generated by the current. For the experiments presented herein, the ~450 kA, 100 ns XP pulser at Cornell University was used to power four-wire X pinches. The CoPt film's magnetic hysteresis was examined using a superconducting quantum interference device (SQUID) and a vibrating sample magnetometer (VSM). The structure and ordering of the atomic planes in the thin films were determined using an X-ray diffractometer and a general area detector diffraction system (GADDS) instrument. The magnetic domain alignments of the films were examined using magnetic force microscopy (MFM). Using the SQUID, two thin films were initialized with remnant magnetization along a specified direction. The two were then placed about 2 cm from the X-pinch plasma column with magnetizations in opposite directions. As a result of the current driven through the X pinch, the films were exposed to a magnetic field of at least 4 T parallel and anti-parallel to the initial magnetization directions. The induced change in the magnetization of the films was then determined using the SQUID. This change implied a lower bound on the order of 2 T for the magnitude of the maximum magnetic field to which the film was exposed. Films with higher coercivity will be used in further tests possibly enabling us to probe closer to the X-pinch plasma column as well as inside a wire-array Z-pinch