STABILITY OF SCREW PINCH

A screw pinch, i.e. a finite beta plasma column compressed by a helical magnetic field, has been found to be considerably more stable than follows from existing theories. The reason is that in experiments the magnetic field around the central plasma column carries a strong force-free current, whereas theory usually assumes a vacuum configuration. In this paper a normal-mode stability analysis is given of a cylindrical screw pinch with a uniform-pitch magnetic field in the pressureless plasma. According to this analysis the screw pinch is stable as long a beta does not surpass a critical value beta c.