Magnetic relaxation in coaxial helicity injection

The Helicity Injected Torus (HIT-II) (Jarboe T R 1998 Phys. Plasmas 5 1807) is operated with either cathode or anode central column (CC) during coaxial helicity injection (CHI). The CC polarity has a strong effect on tokamak behaviour. For cathode CC operation, the magnetic profile is inferred from surface data to be more relaxed, and the n = 1 mode is stronger and more slowly rotating than for anode CC operation. Mode toroidal rotation follows the applied E×B direction. Ion toroidal spin-up in the core is consistent with electromotive action. Apparently, some type of mode asymmetry, effected by the plasma flow and mode rotation, is integral to the current drive observed. This is discussed in terms of electromotive effects, and the picture is shown to be consistent with observations. Some possible implications are outlined, including those concerning parallel fluid velocity shear and other magnetic confinement configurations.