Observation of Nonlinear Neoclassical Pressure-Gradient–Driven Tearing Modes in TFTR

A detailed comparison is made between the tearing-type modes observed in TFTR supershot plasmas and the nonlinear, neoclassical pressure-gradient–driven tearing mode theory. Good agreement is found on the nonlinear evolution of single helicity magnetic islands $(m/n=3/2\mathrm{}$, $4/3$, or $5/4$, where $m$ and $n$ are the poloidal and toroidal mode numbers, respectively). The saturation of these neoclassical tearing-type modes requires ${\Delta }^{\prime }<0\mathrm{}$ (where ${\Delta }^{\prime }$ is the well-known parameter for classical current-driven tearing instability), which is also consistent with the numerical calculation using the experimental data.