If you move an air parcel up in a quiet atmosphere its density will be higher than that of the air surrounding it so that it will fall back. The frequency of the resulting oscillation is called the Brunt–Väisälä frequency. The hot ionized plasma, inside the donut-shaped nuclear fusion tokamak, typically rotates around its central axis. The resulting centrifugal forces, similar to the effect of gravity, cause similar oscillations as in the atmosphere.
Through this effect rotation stabilizes and helps to keep the hot plasma confined. See also another post for a second positive effect of rotation.
The Brunt-Väisälä Frequency of Rotating Tokamak Plasmas
J. W. Haverkort, H. J. de Blank, and B. Koren
Journal of Computational Physics,
© 2012 DOI: 10.1016/j.jcp.2011.03.016