Relaxation Phonomena in the High-Temperature S-1 Spheromak

Abstract

Operation of the S-1 device in a high-current-density ($\frac{j}{n_e}\ge 2\times {10}^{-14\mathrm{}}$ A m) regime has created high-electron-temperature spheromaks ($50 \mathrm{eV}\le T_e\le 130 \mathrm{eV}$). The mechanisms and causes of the periodic relaxation events often observed in these hotter plasmas were made clear. A relationship between the MHD relaxation cycle and confinement was revealed for the first time. Resistive loss at the outer edge causes a departure from the initial force-free minimum-energy Taylor state to an MHD profile unstable to low-$n$ ideal MHD modes; a relaxation event then returns the configuration to a Taylor state.