MHD studies of magnetic relaxation

Summary form only given, as follows. The tendency of plasmas to relax toward a minimum energy state while satisfying the constraint of constant helicity has been confirmed in spheromak and RFP experiments. This tendency is exploited in the coaxial helicity injection current drive technique that is the central feature of the helicity injected tokamak (HIT) experiment. In HIT, current is initially driven on outer (open) flux surfaces, and then relaxation toward the minimum energy state leads to rearrangement of the magnetic configuration so that the current is driven throughout the plasma and is amplified. In this study, we attempt to gain a better understanding of how the plasma evolves during this relaxation process by doing high-resolution, numerical MHD simulations of several simple plasma configurations, including planar and cylindrical current sheets. The MHD simulations are done using a new implicit MHD code based on an approximate Riemann solver technique.