Azimuthal magnetic field distribution in gas-puff Z-pinch implosions with and without external magnetic stabilization.

Abstract

An experimental study of the magnetic field distribution in gas-puff Z pinches with and without a preembedded axial magnetic field (B_{z0}) is presented. Spatially resolved, time-gated spectroscopic measurements were made at the Weizmann Institute of Science on a 300 kA, 1.6 μs rise time pulsed-power driver. The radial distribution of the azimuthal magnetic field, B_{θ}, during the implosion, with and without a preembedded axial magnetic field of B_{z0}=0.26T, was measured using Zeeman polarization spectroscopy. The spectroscopic measurements of B_{θ} were consistent with the corresponding values of B_{θ} inferred from current measurements made with a B-dot probe. One-dimensional magnetohydrodynamic simulations, performed with the code trac-ii, showed agreement with the experimentally measured implosion trajectory, and qualitatively reproduced the experimentally measured radial B_{θ} profiles during the implosion when B_{z0}=0.26T was applied. Simulation results of the radial profile of B_{θ} without a preembedded axial magnetic field did not qualitatively match experimental results due to magneto-Rayleigh-Taylor (MRT) instabilities. Our analysis emphasizes the importance of MRT instability mitigation when studying the magnetic field and current distributions in Z pinches. Discrepancies of the simulation results with experiment are discussed.