The frequently interrupted regime of neoclassical tearing modes (FIR-NTMs): required plasma parameters and possibilities for its active control

Abstract

The plasma parameters required for the occurrence of (3, 2) FIR-NTMs and thus good confinement properties at high normalized plasma pressure (βN) are investigated. Both on ASDEX Upgrade and on JET it is found that, with remarkable consistency between the devices, for a variety of plasma parameters in conventional current profile scenarios, this regime establishes itself for discharges with sufficient high normalized plasma pressure at mode onset, βN,onset > 2.3. An active triggering of this regime has been achieved by lowering the magnetic shear at the q = 4/3 rational surface. That way an ideal (4, 3) MHD mode is being destabilized, forcing the required three-wave coupling between the (3, 2) NTM, (1, 1) and (4, 3) mode activity.