A New ‘Wedge’ Type Instability Observed in a ‘Theta’ Pinch

Abstract

The phenomena of trapped magnetic fields were observed in theta pinches during the first half-cycle of the discharge. The parameters of the experiment were such that a cylindrically converging shock wave was obtained on the first half-cycle with trapped magnetic field parallel to the driving field. Photographs of the discharge show bright radial wedges with less luminous plasma filling their interstices. The number of wedges seems to be determined by the irregularities in the system since it can be varied by deliberately introducing irregularities in the external conductors. The effect of reducing the trapped magnetic field by a considerable factor was also studied. Next a reversed trapped magnetic field was produced during the first halfcycle of the discharge. When the externally produced field was at a maximum, the theta discharge was initiated and the plasma produced had a reversed trapped magnetic field. The experimental evidence suggests that the radial wedges are only formed when there is a trapped magnetic field in the same direction as the driving field when the azimuthal currents on the shock front and the current sheet have opposite directions of rotation. more » (P.C.H.) sions for the force contain then a term in W/r which represents a corrective force, attractive or repulsive according to the sign of the charge, which can contribute to the contraction of the current, to the production of the pinch effect. It also describes, at the same time, the case of toroidal installations. (tr-auth) « less