STABILITY OF A Z PINCH WITH RISING CURRENT

A two-dimensional resistive magnetohydrodynamic (MHD) code is used to examine the stability of a Z pinch to m = 0 perturbations under conditions of rising current. The current waveform is chosen to keep the unperturbed radius of the pinch constant in time. At low current the perturbations oscillate without growing, or grow only weakly, contrary to the predictions of ideal MHD theory. At high current, the perturbations grow at a rate consistent with ideal MHD. The point of transition can be described in terms of a critical Lundquist number; this increases with the wavelength of the perturbation, and is about 160 for ka = 0.3, where k is the wavenumber and a is the pinch radius. These results may explain recent experimental observations of anomalously stable dense Z pinches.