Tearing Modes Driven by 3-Wave Coupling

Nathan J. Richner
Oak Ridge Associated Universities
Tuesday, January 30, 2024
11:00 am
FRH 4135


Abstract: Tearing modes (TMs) degrade plasma confinement and can lead to disruptions in tokamaks. As such, stabilization strategies are crucial to the successful operation of future fusion devices. In ITER-relevant scenarios on DIII-D, rotationally coupled m/n=1/1 and 3/2 modes have been observed to drive 2/1 neoclassical tearing modes (NTMs) through three-wave coupling [L. Bardoczi et al. Phys. Rev. Lett. 127, 055002.]. The frequency of the driven 2/1 daughter mode is set by the parent frequencies. When the driven mode frequency matches the local plasma rotation frequency, for 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, a sufficiently large frequency mismatch was found to prevent destabilization of disruptive 2/1 NTMs by this mechanism. This work implicates differential rotation as a useful actuator in the prevention of NTMs from nonlinear three-wave coupling and can help inform the development of stabilization strategies and scenarios.

Laszlo Bardoczi