HIGH-BETA DISRUPTION IN TOKAMAKS

Three-dimensional magnetohydrodynamic simulations of high-beta plasmas show that toroidally localized high-n ballooning modes can be driven unstable by the local pressure steepening that arises from the evoluti on of low-n modes. Nonlinearly, the high-n mode becomes even more loca lized and produces a strong local pressure bulge that destroys the flu x surfaces resulting in a thermal quench. The flux surfaces then recov er temporarily but now contain large magnetic islands. This scenario i s supported by experimental data.