Effects of a Conducting Wall on Z-Pinch Stability

Abstract

The stabilizing effect of a conducting wall on Z-pinch stability has been investigated through a systematic experimental and numerical study. Numerical simulations of a Z-pinch with a cylindrical conducting wall are compared with a case that modeled perforations in the conducting wall. The conducting wall also acts as the return current path for these investigations. Plasma conditions with various pinch sizes were studied numerically to better understand the effect of wall stabilization in Z-pinches. A study using the ZaP Flow Z-Pinch was performed by inserting a 0.35-m perforated section of electrode that has eight longitudinal slots cut from the outer electrode, reducing the conducting wall material by \(\approx 70\%\) . This modification prevents currents from flowing freely along the azimuthal distance of the outer electrode required to stabilize the \(m = 1,2,3\) modes, which are experimentally monitored. Operating with identical experimental parameters with and without the perforated electrode was assumed to produce similar equilibrium and flow shear conditions in the pinch. Comparing the stability characteristics isolated the potential effects of the conducting wall. Magnetic data, interferometry, and optical images indicate that the conducting wall does not have a discernible effect on stability in the ZaP experiment. This result agrees with simulations with similar ratios of conducting wall radius to pinch radius.