The plasma-sheath equation for a collisionless plasma with arbitrary ion temperature in plane geometry is formulated. Outside the sheath, this equation is approximated by the plasma equation, for which an analytic solution for the electrostatic potential is obtained. In addition, the ion distribution function, the wall potential, and the ion energy and particle flux into the sheath are explicitly calculated. The plasma-sheath equation is also solved numerically with no approximation of the Debye length. The numerical results compare well with the analytical results when the Debye length is small.

The two-dimensional effect of plasma flow along the field lines in the scrape-off zone of a poloidal divertor has been modelled phenomenologically in a one-dimensional tokamak transport code. Some results for the density and temperature profiles in the scrape-off zone, as well as in the main plasma, are given in this paper. These calculations suggest some approximations, which have been used to develop a zero dimensional model of the divertor; this model can be used to make estimates of divertor performance without having to make detailed numerical calculations.

A one-dimensional (1-D), multifluid transport model is used to investigate the effects of particle fuelling profiles on plasma transport in an ignition-sized tokamak. The neutral-beam injection power required to reach ignition is used as a measure of the conduction and convection energy losses. Normal diffusive properties of plasmas are likely to maintain the density at the centre of the discharge even if no active fuelling is provided there; this significantly relaxes the requirements for fuel penetration. Not only is lower fuel penetration easier to achieve, but it may have the advantage of reducing or eliminating density-gradient-driven trapped-particle microinstabilities. Simulation of discrete pellet fuelling indicates that relatively low-velocity (∼ 103 m·s−1) pellets may be sufficient to (1) fuel a device of this size (∼ 1.25m minor radius), (2) produce a relatively broad, and cool edge region of plasma which should reduce the potential for sputtering, and (3) reduce the likelihood of trapped-particle-mode-dominated transport. Low-penetrating pellets containing up to 10–20% of the total plasma ions can produce fluctuations in density and temperature at the plasma edge, but the pressure profile and fusion alpha production remain almost constant.