Electron thermal confinement in the edge plasma of a field-reversed configuration

The electron energy loss rate along the open field lines in the edge layer of field-reversed configurations (FRC’s) can be inferred from experiments using a simple model. Since FRC edge layers resemble θ pinches a similar model can be applied to θ pinches. Collecting results from a large number of FRC and θ-pinch experiments, it is shown that the electron energy loss is convective, with 3–7kTe lost per electron escaping from the plasma. This stands in marked contradiction to the conclusions of two previous papers, which claimed that the electron energy loss could be explained by thermal conduction. Convective electron thermal loss is well established as the loss mechanism in low-collisionality plasmas such as mirrors. However, thermal conduction (a diffusive mechanism) was expected in the dense, collisional plasmas of typical FRC’s and θ pinches. The thermal conduction mechanism (which applies for sufficiently high collisionality) is shown here to fail at a higher level of collisionality than expected. Consequently, in collisionality ranges where thermal conduction applies, its rate is comparable to or less than the convective loss rate.