High-β Disruption in Tokamaks

Three-dimensional magnetohydrodynamic simulations of high-β plasmas show that toroidally localized high- $n$ ballooning modes can be driven unstable by the local pressure steepening that arises from the evolution of low- $n$ modes. Nonlinearly, the high- $n$ mode becomes even more localized and produces a strong local pressure bulge that destroys the flux surfaces resulting in a thermal quench. The flux surfaces then recover temporarily but now contain large magnetic islands. This scenario is supported by experimental data.