Transport studies of compact torsatron reactors

An efficient transport survey code that uses the spectral collocation method was developed and is being used to study ignition in low-aspect-ratio torsatron reactors. A transport model dominated by helical-ripple-induced neoclassical heat fluxes is used to show that ignition is possible for a range of radial electric fields and plasma aspect ratios even when the loss of trapped alpha particles is considered. However, control of the density profile near the plasma boundary is necessary. The sensitivity of the results to anomalous electron transport is considered. Some initial investigations of the role played by off-diagonal terms in the neoclassical transport matrix in determining reactor performance are also presented, and a potentially attractive operating regime is found when these additional terms are considered.