Radial thermal stability of the radiative mantle

Sufficient conditions for the thermal stability against radial excursions of a cylindrical equilibrium temperature distribution in a plasma with a strongly radiative edge, or mantle, are established in terms of the minimum allowable ratio of the core heating power density to the edge radiation power density. A positive dependence of the thermal conductivity upon temperature is found to be stabilizing, and a divertor separatrix boundary condition for the temperature is found to be destabilizing relative to a fixed separatrix temperature condition. The stability conditions are consistent with the conditions extant in a stable radiative mantle experiment and in a stable radiative mantle simulation. Expressions are developed for a radiation edge density limit and for the maximum fraction of the plasma heating power which can be radiated from the mantle.