Spectra and growth rates of resistive wall modes in a reversed-field pinch

The Reversatron II [IEEE Trans. Plasma Sci. PS-16, 667 (1988)] reversed-field pinch has been operated with shells having magnetic penetration time comparable to and shorter than the discharge duration. The spectra and growth rates of the resistive wall modes have been measured and compared for the two cases. The growth rates of modes are typically in the expected range γτs=0.5–2 where γ is the growth rate and τs is the magnetic penetration time of the shell. The spectra, however, are broader than expected from linear theory and there are indications that both the growth rates and the mode spectra are affected by nonlinearities.