MHD mode structure and propagation in the ASDEX device
The Mirnov oscillations observed in the ASDEX tokamak are analysed with regard to the generally accepted interpretation scheme, according to which (1) Mirnov oscillations are caused by currents flowing parallel to B on rational magnetic surfaces and (2) the field perturbation is frozen within the plasma. If the second statement holds, the frequency is obtained from the profiles of the electron density, the ion temperature and an eventual toroidal or poloidal rotation velocity. It is shown that there are modes which follow this prediction. On the other hand, mode coupling is observed, which is also invoked to reconcile the experimental findings with the predictions of a theory based on statement (1), according to which there is a poloidal variation of both the phase velocity and the amplitude of the Mirnov oscillations. While the observed phase velocity fits well into this picture, the poloidal variation of the amplitude cannot be ascribed to only one mode in the majority of cases. In addition, the possibility of coherent MHD activity due to currents in the scrape-off layer is discussed.
Bibliographic Reference: Report: IPP III/140 EN (1989)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199010721 / Last updated on: 1994-12-01
Original language: en
Available languages: en