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Abstract

The plasma-neutral gas balance is considered for the boundary layer of a magnetically confined plasma being near the density (Murakami) limit. It is found that, due to the high rate of charge separation by the guiding centre drifts in an inhomogeneous toroidal magnetic field, Pfirsch-Schlueter particle diffusion can prevail, even in the presence of magnetic disturbances which perturb the magnetic surfaces and strongly enhance the electron heat conductivity. In the boundary layer the Nernst and Ware effects become negligible in a first approximation. The characteristic plasma pressure and density gradients in this layer are independent of the plasma diffusion rate, whereas the ratio between the average plasma density and the neutral density at a surrounding wall (limiter) depends on the same rate. The deduced plasma density and pressure gradients and the plasma-neutral density ratio are of the same order as those obtained from tokamak experiments. Finally, the heat losses from plasma-neutral gas interaction can in some cases become comparable to the ohmic heating power, thereby affecting the energy containment time.

Additional information

Authors: LEHNERT B ROYAL INSTITUTE OF TECHNOLOGY, STOCKHOLM (SWEDEN), ROYAL INSTITUTE OF TECHNOLOGY, STOCKHOLM (SWEDEN)
Bibliographic Reference: WRITE TO DEPARTMENT OF PLASMA PHYSICS AND FUSION RESEARCH, ROYAL INSTITUTE OF TECHNOLOGY, S-10044 STOCKHOLM 70 (SWEDEN), MENTIONING REPORT TRITA-PFU-8402, 1984
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