Finite pressure effects on sawtooth oscillations

Nonlinear 3-D simulation of sawtooth oscillations shows that the helically twisted hot spot has a prominent toroidal bulge at the large major radius side, characteristic of a high-εβp instability. This bulge drives other m/n islands just outside the mixing radius resulting in a stochastic annular region. A similar effect is also found in shaped plasmas, even at low beta. These effects agree with experimental data, giving detailed support to the Kadomtsev reconnection model. This effect can also be used to explain the experimental sawtooth heat pulse ‘‘anomaly.’’ At high εβp, the stochastic region can essentially fill the whole plasma, and can result in a ‘‘high-beta disruption.’’