A Model of Tokamak Locked Mode Disruptions

Abstract

Locked modes are precursors to major disruptions. During locked modes, the temperature decreases in the plasma edge region. This causes the current to contract. A model is given to analyze the MHD stability of contracted current equilibria. If there is sufficient current contraction, resistive wall tearing modes are destabilized. This requires that the q = 2 surface be sufficiently close to the wall. The threshold conditions obtained in the model are consistent with experimental observations of the conditions for a thermal quench in a disruption.

arXiv comment7 pages, 3 figures