A study of the equilibrium phase of the field reversed configuration
A field-reversed configuration (FRC) is a toroidal plasma device presently being investigated as a potential magnetic confinement scheme for a fusion reactor. If the FRC is to be a candidate for use as a fusion reactor it must achieve good confinement of particles and energy. The amount of reversed magnetic flux (trapped flux) that is contained in the FRC is believed to play an important role in the confinement of particles and energy. Under the common assumptions about the internal structure of the FRC, the rate of decay of the trapped flux as inferred from experimental observations exceeds the predictions of classical theory by factors ranging from 3 to 20. This discrepancy suggests a breakdown of the classical model near the reversal point of the FRC. In the present experiments, the ions have orbits that are very large compared to typical gradient scale lengths; thus there is the possibility that fluid descriptions of the plasma are not applicable. In this thesis, an attempt is made to determine whether the anomalous loss of trapped flux is due to kinetic effects. The equilibrium FRC is studied from two points of view. First, the two-dimensional equilibrium FRC is examined to determine (a) whether kinetic equilibrium effects or (b) two-dimensional geometrical effects could be responsible for the observed discrepancy. Second, a kinetic model of the FRC valid on the very long timescales characteristic of a transport problem is developed, to determine whether kinetic processes could be affecting the transport properties of the FRC.^ The first study shows that the experimental observations may be in agreement with the assumption of classical transport at the reversal point. Two-dimensional geometrical effects and the uncertainty about the internal structure of the FRC may be sufficient to explain the observations.^ No predictions can be made from the second study. Although it is shown that the transport model developed is well posed, the algorithm designed to solve the model is poorly posed. The reasons for the failure of the solution scheme are discussed. A modified scheme is proposed. ^
Major Professor: Chan K. Choi, Purdue University.
Physics, Fluid and Plasma