Asymmetry of peripheral plasma diffusion in a tokamak

The asymmetry of the diffusion of the peripheral plasma in a tokamak in the poloidal angle, which corresponds to the dominant plasma flux to the wall through the outer part of the torus, is studied. It has been shown experimentally that in the T-10 tokamak this asymmetry is most apparent in regimes with a low peripheral electron temperature and is apparently determined by the parameters of the plasma, rather than by a contact of the plasma with the limiter. The development of a combination of drift-dissipative and gravitational-dissipative instabilities is studied with reference to the tokamak periphery. It is shown in the linear approximation that initial perturbations which are very extended along the magnetic field can grow rapidly and go into a nonlinear stage. The resulting transverse plasma diffusion coefficient is highly asymmetric with respect to poloidal angle, in the direction of the outer part of the torus. It is on the order of magnitude of the Bohm diffusion coefficient. The perturbations which are most effective in causing turbulence in the plasma are localized in the outer part of the torus. Their length scale in the poloidal direction is larger than that in the radial direction