Speaker: Brian Nelson, University of Washington, Seattle
Abstract: Steady inductive helicity injection (SIHI) current drive produces spheromaks with up to 90 kA toroidal current, and plasma current to injector current ratios of up to 3.8, in the Helicity Injected Torus-Steady Inductive (HIT-SI) experiment. Unlike most helicity injection methods, SIHI directly applies a periodic non-axisymmetric distortion, called Imposed Dynamo Current Drive (IDCD). IDCD eliminates the need for the plasma itself to produce non-axisymmetric relaxation mechanisms, and furthermore can be used to sustain a kink-stable equilibrium. HIT-SI creates and sustains spheromaks with equilibrium reconstructions (fitting to internal magnetic field measurements) that are ideally n=1 kink-stable. Furthermore, at injector frequencies greater than the inverse sound transit time, equilibrium fits to internal magnetics show pressure confinement with high beta, as well as exhibiting both an outward shift of the magnetic axis and improved toroidal symmetry. The high efficiency of IDCD sustaining stable equilibria with high beta, enables spheromak reactor designs with overnight capital costs competitive with present power-generating plants.