An investigation of the theta pinch using magnetic pick-up loops

This paper presents an account of the investigation of the behaviour of the plasma in a thetapinch device using a magnetic pick-up loop system. The technique has been developed to determine the current in the plasma from measurements made outside the plasma. Experimental results are presented to show the extent to which this determination contributes to an understanding of the phenomena of magnetic field trapping, radial and axial motion and containment which occur in the Thetatron. Specific measurements can be made of the strength of trapped field when it is reversed. Observations can also be made of the variation of the plasma line density with time, and this has enabled a study of axial contraction and expansion to be made. It is found that the rate of axial contraction decreases as the strength of the reversed trapped field decreases. Near the transition region between the trapping of reversed and like magnetic field the line density is observed to be constant in time suggesting good containment.