Observation of Resistive Wall Modes in JT-60U

Abstract

Resistive wall modes (RWM) associated with ideal magnetohydrodynamic current-driven (β_N < 0.2) and pressure-driven (β_N > 2.4) kink modes with low toroidal mode number n (n = 1) have been identified in JT-60U. The pressure-driven RWM occurs at the plasma toroidal rotation of about 1% the Alfvén speed without clear continuous slowing down of the plasma toroidal rotation. Occurrence of n = 1 RWMs result in thermal quench accompanied by higher n (n ≥ 2) modes. In the case of current-driven (˜ zero β) RWMs, a thermal quench occurs only at the peripheral region just after the RWM. In contrast, a thermal quench occurs in the whole plasma region following a drastic increase in the growth rate of the RWM from the order of τ_w^-1 (τ_w is the resistive diffusion time of the wall) to larger than 10² τ_w^-1in the case of pressure-driven (high β) RWMs.