Non-ideal ballooning modes in a tokamak

Hybrid two-fluid and kinetic equations have been used to study ballooning modes in a tokamak. These modes separate into two branches: a modified ideal magnetohydrodynamic (MHD) ballooning mode and a toroidally induced ion temperature gradient (etasub(i)) mode. Using both model and actual high beta equilibria we find that the etasub(i) mode (etasub(i)=deltalnTsub(i)/deltalnNsub(i)) may dominate the ideal MHD mode for moderate etasub(i)(etasub(i)> or approx. 1), leading to substantially lower beta thresholds. (author)