Under the assumption of long axial length of a double theta pinch, a radial one-dimensional configuration of equilibrium which permits the high βp plasma is shown. The equilibrium configuration astisfies the Suydam criterion. Typical examples of the equilibrium configuration, corresponding to the double theta pinch operation, are shown.
As a secondary closed confinement system, a device of a cusp-torus with toroidal plasma current and lost particle feedback fields is described. The device consists of even number cusp-fields so that the point cusps are connected to be on a circle and the toroidal plasma current flows along the circle. The lost particles from the ring cusps are fed back into the confinement region through lost particle feedback fields which connect the couples of the neighboring ring cusps, so that the device is approached to the closed confinement systems. A simple calculation of a displacement of the plasma column by the hoop force of the toroidal plasma current is shown.
Analysis of the filamentation instability presented by P. Kaw et al. is extended to apply in a plasma with relatively high densities. It is found that the spatial growth rate increases with the plasma density. This result enables us to expect a possibility for detecting the instability in laboratory plasmas. Experimental conditions to verify the instability are discussed in some detail.