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Abstract
Previous theoretical studies have shown that a poloidal potential variation of order $\epsilon$ (=r/R), which is likely to be produced during high power electron and ion cyclotron wave heating (ECRH and ICRH), can significantly enhance neoclassical transport in a simple plasma model consisting of one ion species and electrons in the low collisionality regime. The more realistic case of a plasma model with one or more impurity ion species present, in which the effects of a poloidal potential variation are likely to be more significant, has not been investigated previously.
In this thesis, the effects of a poloidal electric field of order $\epsilon$ upon particle transport and current in a tokamak plasma with a significant impurity content are studied theoretically. A kinetic theory approach is used to obtain the neoclassical transport coefficients for a large aspect ratio ($\epsilon$ $\ll$ 1) tokamak in the low collisionality regime.
Calculations indicate that, in an impure plasma, a poloidal electric field can significantly enhance (by a factor of $\sim$3) ion diffusion, while its effect on the electron transport is similar to that obtained in the previous studies for a simple plasma. The magnitude of the ion transport enhancement is found to depend upon the impurity content, impurity species, and the magnitude of the poloidal electric field.
Enhancement of the neoclassical conductivity is found to be similar to that obtained in the previous studies; however, in the presence of a large impurity concentration, results of the present work can sometimes differ from those in the previous studies by $\sim$20%. A poloidal electric field causes a significant enhancement (a factor of $\sim$2) of the bootstrap current coefficients. However, the nature of density and temperature profiles seem to be important in determining the change in the bootstrap current. With parabolic profiles and carbon impurity, there is a decrease in the bootstrap current in most cases. The bootstrap current increases only when the potential on the outside is greater than that on the inside of the tokamak (as during ICRH) and the density profile is more peaked than roughly the square root of the temperature profile.
