A study is made of the effects on ion transport of collisions and of finite drift excursions for a variety of guiding centre drift orbit shapes. The drift excursions Δx, where x denotes a normalized flux surface label, are calculated by solving the guiding centre drift equation for individual orbits. Collisions are described by a Fokker–Planck operator valid in all collisionality regimes. The operator describes the interaction between a test particle and a thermal plasma. The test particles represent the thermal ions of the plasma such that the collision operator is made to conserve particle number, momentum and energy. The momentum conservation leads to a new formulation of the ion heat flux from test particle calculations. General Monte Carlo type equations are derived from moments of the collision operator. These equations are solved in a two step computational approach. A plasma equilibrium based on a JET configuration is used in computations which scan a phase space of three dimensionless variables which characterize the guiding centre orbits. The time–space dependent contributions from the drifts across flux surfaces, as well as along field lines, are accumulated to yield the ion heat flux profile qi(x) characterizing a thermal, Ohmically heated plasma. The profile of this ion heat flux is different from those predicted by conventional neoclassical theories as it vanishes on the magnetic axis. The edge value is approximately a third of the experimental value determined from the total Ohmic heating rate. The electron heat flux qe(x), can in principle also be evaluated by the model, but requires a two order of magnitude increase in computing resources.
Variational calculation of neoclassical ion heat flux and poloidal flow in the banana regime for axisymmetric magnetic geometry