KINETIC AND CURRENT PROFILE EFFECTS OF ALFVEN WAVES IN THE TCA TOKAMAK
Recent Alfv'en wave experiments in the TCA tokamak show new experimental evidence of the importance of kinetic effects and analysis of the results reveals the influence of plasma conditions on the Alfv'en wave. The importance of kinetic effects is demonstrated by comparing the measurements with a 1-D cylindrical code in which kinetic effects could be included or excluded. The RF magnetic field measured at the plasma edge reflects unambiguously the resonance of the kinetic wave eigenmodes in the plasma centre. In particular, when the kinetic wave propagates radially inwards from the Alfv'en resonance layer, standing waves due to reflection at the axis are detected by the presence of satellite peaks. These occur at slightly higher density than the principal eigenmode and can only be modelled with kinetic effects included. The experimentally measured values of the resonance Q- factor of the principal eigenmodes are lower than predicted by the code by a factor of three to 20, although all expected damping mechanisms are included in the code. Alternative damping mechanisms are discussed and the best candidates proposed after quantitative evaluation. Many experimental observations indicate that the coupling to the eigenmodes does not only depend on the plasma current and density. The coupling tends to increase with RF power and, even at constant RF power, the coupling can be modified. Obviously, the RF itself modifies the plasma in such a way that the coupling strength can change very strongly. The experimental observations and the results of the code show that the current profile is certainly the best candidate which can affect the coupling in this way, implying that the RF is able to influence the plasma current profile.
Bibliographic Reference: 15TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA HEATING, DUBROVNIK (YUGOSLAVIA), MAY, 16-20, 1988, AVAILABILITY: CEC-LUXEMBOURG, DG-XIII-C-3, POB 1907, MENTIONING PAPER EN 34067 ORA
Availability: Can be ordered online
Record Number: 1989126118400 / Last updated on: 1989-06-01
Available languages: en