Plasma differential rotation is found to be capable of preventing disruptive neoclassical tearing modes (NTMs) seeded by nonlinear three-wave coupling. As tearing modes degrade confinement and can lead to disruptions, stabilization strategies are crucial to the successful operation of future devices. In ITER-relevant scenarios on DIII-D, rotationally coupled = 1/1 and 3/2 modes have been observed to drive 2/1 islands through three-wave coupling. The frequency of the driven 2/1 mode is set by matching conditions and the frequencies of the driving modes. When the driven mode frequency matches the local plasma rotation frequency, e.g. at low differential rotation, the driven 2/1 island can grow into a disruptive NTM. Using neutral beam torque as an actuator to scan the differential rotation, these experiments demonstrate that a sufficiently large frequency mismatch prevents destabilization of disruptive 2/1 NTMs by three-wave coupling. This work indicates that differential rotation can be used as an actuator to prevent NTMs seeded by three-wave coupling.
This paper shows that differential plasma rotation can be used to prevent disruptive neoclassical tearing modes (NTMs) caused by nonlinear three-wave coupling. NTMs can degrade confinement and lead to disruptions, so stabilization strategies are crucial for future fusion devices like ITER. The experiments demonstrate that a large enough frequency mismatch between the driven 2/1 mode and the local plasma rotation prevents the destabilization of disruptive 2/1 NTMs.