ALFVEN WAVE HEATING AND ITS EFFECT ON THE TOKAMAK CURRENT PROFILE
The link between Alfv'en wave (AW) excitation and the subsequent global reaction of the plasma is crucial to the understanding of AW heating in tokamaks. The present understanding of the physics of AW launching into a tokamak plasma accounts for many detailed experimental observations of the AW spectral evolution, wavefield and density fluctuations. The spectrum excited also has a strong influence on global plasma parameters such as the level of MHD activity, X-ray flux profile, sawtooth frequency, density and loop voltage. However, although these global effects have been well documented on TCA, they have so far defied a consistent explanation in terms of plasma heating simply due to power deposition associated with the AW resonance surfaces. The connection between the well-established physics of AW launching and the phenomenology of the tokamak plasma therefore remains to be explained. In this paper, we defend the hypothesis that AW heating indirectly causes these global phenomena by modification of the ohmic current profile. It is proposed that the kinetic AW, associated with its shear AW resonance surface, drives current by electron Landau damping as predicted. The required asymmetric for driving a net current with a symmetric antenna is due to the plasma gyrotopy (omega-"ci" effect). In the low current density outer region of the plasma, where negative helicity AW resonance surfaces are located, an rf-driven anti-parallel current would strongly modify the ohmic current gradient, li, and hence the MHD activity as observed. During the AW-induced density rise, resonance surfaces move outwards as new surfaces and global AW modes appear in the plasma. It is demonstrated that many global phenomena can be explained in terms of the consequent changes in current profile, thus providing a more complete picture of tokamak AW heating.
Bibliographic Reference: 15TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA HEATING, DUBROVNIK, (YUGOSLAVIA), MAY, 16-20, 1988 AVAILABILITY: CEC-LUXEMBOURG, DG-XIII-C-3, MENTIONING POB 1907, MENTIONING PAPER EN 34071 ORA
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Record Number: 1989126118800 / Last updated on: 1989-06-01
Available languages: en