Plasma Containment in the Theta Pinch

An experimental investigation of the containment time of plasma in a theta pinch is described. Observations of changes in the plasma diamagnetism have been made, analysis of which leads to a determination of the field trapping conditions in the plasma and of the variations in line density of the plasma which take place during a discharge. The results show that in parallel field discharges the containment time of the plasma depends on the flux trapped within the plasma, in agreement with theoretical predictions. In particular, the containment time increases as the flux approaches zero. In reversed field discharges the plasma containment is limited by an axial contraction instability, which is slower the lower the amount of reversed trapped flux. At very low values of this flux, the plasma appears to stay contained and stable in a closed reversed field configuration for the period of observation (6 μsec).