MODIFIED MERCIER CRITERION

The ideal magnetohydrodynamic Mercier criterion for the stability of l ocalized interchange modes is easily violated by modest pressure gradi ents in the central region of a tokamak plasma where the magnetic wind ing index q drops below unity. However, kinetic effects can substantia lly modify this criterion, allowing for stable peaked pressure profile s. In this paper, we discuss the modifications to the Mercier criterio n brought about by high-energy particles and by the thermal trapped io ns in the collisionless Kruskal-Oberman regime.