Interpretation of Precursors of Internal Disruptions

A collisional instability driven by electron temperature gradients is described which appears to explain the major characteristics of the precursors of the internal disruptions. The threshold is reached when a certain parameter |μ|>√3. For the ST and TFR tokamaks, we estimate 1|μ|5 at the radius where $q=1$. For |μ|=3, the theoretical growth rate γₜₕ~(2-3)×10³ sec^-1 compares well with the experimental value γₑₓₚ~3×10³ sec^-1. The predicted shape of the wave profile is also in qualitative agreement with experiment.