A simulation model for steady-state, lower hybrid current drive is described which incorporates a relativistic, one-dimensional Fokker–Planck calculation and a toroidal ray tracing code. Two-dimensional (v⊥) effects are included in the Fokker–Planck analysis in the form of a large perpendicular electron temperature that results from pitch angle scattering. An increase in the parallel refractive index of the lower hybrid waves, arising from toroidal geometry effects, is proposed as a physical mechanism whereby injected rf waves at high phase velocity (ve≪v∥ ≲c) can interact via the Landau resonance with electrons at low phase velocity (v∥ ≲3ve). Numerical results relevant to the Alcator C [Phys. Rev. Lett. 53, 450 (1984)] and PLT [Phys. Rev. Lett. 49, 1255 (1982)] experiments are presented which demonstrate the dependency of the current drive efficiency on various plasma parameters.

A model for the rate of density rise observed when neutral gas is fed into a plasma-containing chamber is presented for regimes where known collisional transport processes do not provide an adequate explanation. A dense layer of cold plasma produced at the edge of the plasma column and the resulting relatively sharp ion temperature gradient, as compared with the local density gradient, can lead to the excitation of electron temperature fluctuations driven by ion drift modes. The net inflow of electrons and ions that is produced by these modes has been included in a one-dimensional transport code used to simulate experiments performed by the Alcator device. The linear and quasi-linear theories of these modes are given for the regimes of interest. The cold-plasma-layer model is also consistent with the presence of an outflow of impurity ions, due to impurity driven modes, that balance the inflow produced by discrete collisions.

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