THE HARD-CORE PINCH. PART II

The toroidal version of the hard-core pinch tube is created by levitating a ring conductor inside a toroidal shell. The magnitude of induced H/ sub theta / necessary for levi-tation is small in terms of field strengths normally desired for energetic pinches. In a 3-in. glass-and-copper toroid of square cross section a 3/4-in. hollow copper ring has been levitated with a 60- cycle current of 3 kiloamperes. A 12-in stainless steel tube of round cross section is being built. The stability of nearvacuum field hard-core configurations is best investigated in toroidal geometry. At high power levels and low plasma densities, the conventional toroidal stabilized pinch'' is subject to an anomalous plasma energy leakage to the wall, which cannot be explained by the observed ultraviolet radiation alone. A critical question is, therefore, whether the relative stability of some hard-core pinches, as reflected by the smoothness and reproducibility of magnetic probe traces, is reflected by an improved containment of the plasma en-ergy leading to high temperature. A toroidal hard-core tube is also useful in studying the nature of the nonhydromagnetic instabilities observed in the linear inverse stabilized pinch.'' The presence and condition of electrodes appear to have a substantial effect on the magnitude of these instabilities, as would be expected if they were, for instance, of electrostatic origin. In order to complement the plasma study of the hard-core pinch, we have developed an analogue method using sodium tubes to simulate the current-carrying layer. In this way the purely hydromagnetic aspect of the plasma behavior can be isolated. (auth