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 $\left|\mu \right|>\mathrm{}\sqrt{3}$. For the ST and TFR tokamaks, we estimate $1\lesssim \left|\mu \right|\lesssim 5$ at the radius where $q=1\mathrm{}$. For $\left|\mu \right|=3\mathrm{}$, the theoretical growth rate ${\gamma }_{\mathrm{th}}\sim \mathrm{}(2-3)\mathrm{}\times {10}^3$ ${\sec }^{-1\mathrm{}}$ compares well with the experimental value ${\gamma }_{\exp }\sim 3\times {10}^3$ ${\sec }^{-1\mathrm{}}$. The predicted shape of the wave profile is also in qualitative agreement with experiment.