Plasma Experiments with a 570-kJ Theta-Pinch

Abstract

Initial measurements on the plasma produced in the Scylla IV theta‐pinch of its electron density, soft x‐ray emission, neutron emission, plasma shape and motion have been carried out as a function of the initial deuterium pressure and bias magnetic field. Interferograms establish electron densities in the range 4 to 7×10¹⁶ cm⁻³ for the plasma at peak compression and give azimuthally symmetric plasma shapes, which show the absence of the ``rotating flute'' instability as well as the absence of large trapped magnetic fields at peak compression. Streak photographs also indicate gross plasma stability. Shadowgraphs in conjunction with deflection mapping of a grid pattern show sharp plasma boundaries. Soft x‐ray absorption measurements yield plasma electron temperatures in the range 400 to 1200 eV, which are dependent on the magnitude of the reversed bias field and have a gross correlation with the neutron emission. Neutron emissions in the range 10⁷ to 2×10⁹ per discharge are observed and depend upon the magnitude of the reversed bias field. Neutron collimation experiments yield a plasma length of approximately 70 cm in the 1‐m mirrorless compression coil. The observed electron temperature, neutron emission, and electron density as functions of the bias magnetic field and filling pressure are consistent with the product of the plasma particle energy and the plasma density being a constant, as required for a β=1 plasma.