Scaling of the critical plasma rotation for stabilization of the n = 1 resistive wall mode (ideal kink) in the DIII-D tokamak

Abstract

Experiments in the DIII-D tokamak show that the n = 1 ideal kink can be stabilized by a resistive wall if the plasma is rotating fast enough. A database of the onset of the n = 1 resistive wall mode as a function of the equilibrium toroidal magnetic field, the plasma density and the toroidal rotation has been assembled for plasmas with beta between the theoretically predicted no wall and ideal wall stability limits. The critical rotation frequency is found to scale as the inverse of the Alfvén time with ω ϕ τA ≈ 0.02 (evaluated at the q = 2 surface at ρ ≈ 0.6) or ωϕ τS ≈ 0.7, where τS is the sound time. The dependence of ωϕ τ A or ωϕ τS on βN/βN,no wall from 1–2 is weak and suggests the plasmas are in the ‘intermediate dissipation’ regime.