Effect of the dynamic ergodic divertor in the TEXTOR tokamak on MHD stability, plasma rotation and transport

With the dynamic ergodic divertor in TEXTOR fundamental effects of the coupling of external magnetic field perturbations to the confined plasma have been studied. The non-linear coupling between external (m/n ≤ 12/4) and internal modes (m/n ≤ 3/1) has been investigated. The critical perturbation field (m/n ≤ 3/1) for the excitation of an m/n ≤ 2/1 tearing mode depends not only on the magnitude but also on the direction of the toroidal angular momentum input by neutral beam injection (NBI). Below the excitation threshold of this mode a toroidal spin-up of the plasma has been observed, which only depends on the strength of the perturbation field. It is independent of both the rotation direction of the external perturbation field and the toroidal angular momentum supplied by the NBI.