Investigations of the magnetic structure and the decay of a plasma‐gun‐generated compact torus

The results of a series of experimental measurements of compact toroidal (CT) plasmas produced by a magnetized coaxial plasma gun injecting into a flux‐conserving metallic liner are reported. The experiments were performed on the Beta II facility at Lawrence Livermore National Laboratory. The magnetic equilibria are well described by a force‐free eigenmode structure that results from an extension of Taylor’s theory of the reversed‐field pinch. Consideration of helicity conservation during relaxation of the composite plasma‐gun flux‐conserver system to the final state equilibrium yields theoretical expressions that are compared with the experiment. In particular the CT poloidal flux (ψpol) and the overall electrical efficiency for producing the CT are predicted to be functions of the plasma gun inner‐electrode flux (ψgun) and the volt‐seconds input to the gun discharge (∫∞0 V dt). Away from a cutoff at too low values of ∫∞0  V dt or too high values, ψgun ,ψpol scales linearly with the square root of the pr...