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An investigation into the characteristics of magnetohydrodynamic instabilities (MHD modes) in the ASDEX tokamak is reported. For this purpose the Mirnov diagnostic technique (measuring fluctuations in the magnetic field) was used and further developed. In analysing MHD mode behaviour of the tokamak, emphasis is placed on the physics of mode locking, i.e. the process by which rotating modes are subject to braking; this often precedes the interruption of the current, which is so dangerous for a fusion reactor. The theory developed in the course of the project provides an interpretation of the experimental results consistent with results obtained using other diagnostic methods. A particularly interesting experimental observation was the loss of angular momentum by rotating plasmas through mode locking. Experiments into mode stabilisation and prevention of current breakdowns build upon the knowledge thus far gained. Several other MHD phenomena occurring under a variety of plasma conditions are discussed on the basis of the theoretical models developed. It is shown that the main part of the plasma in the tokamak can be described well using one-dimensional models with cylindrical geometry, whereas the boundary zone of the plasma requires more complex analysis.

Additional information

Authors: ZOHM H, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/254 DE (1990) 108 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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