Geodesic acoustic mode induced by toroidal rotation in tokamaks.
The effect of toroidal rotation on the geodesic acoustic mode (GAM) in a tokamak is studied. It is shown that, in addition to a small frequency upshift of the ordinary GAM, another GAM, with much lower frequency, is induced by the rotation. The new GAM appears as a consequence of the nonuniform plasma density and pressure created by the centrifugal force on the magnetic surfaces. Both GAMs in a rotating plasma are shown to exist both as continuum modes with finite mode numbers m and n at the rational surfaces q=m/n as well as in the form of axisymmetric modes with m=n=0.
Wahlberg
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Department of Physics and Astronomy, EURATOM/VR Fusion Association, P.O. Box 516, Uppsala University, SE-751 20 Uppsala, Sweden.