Electrostatically driven helical plasma state

A novel plasma state has been found in the presence of a uniformly applied axial magnetic field in periodic cylindrical geometry. This state is driven electrostatically by helical electrodes, providing a driving field that depends on the radius and m θ − n ζ, where θ is the poloidal angle and ζ = z / R is the toroidal angle. We focus on m = n = 1. The radial magnetic field at the wall is taken to be zero. With weak driving, the resulting distortion is very small, but for stronger driving, the mean field of the state has field line safety factor q 0 ( r ) just above the pitch of the electrodes m∕n = 1 except near the edge, where q0 increases monotonically. This state is characterized as a single helicity Ohmic equilibrium with the helical symmetry of the applied field. The plasma appears to be close to force-free in the interior, but current density crosses the magnetic flux surfaces near the edge, where current must enter and exit through the helical electrodes. This perpendicular current density drives l...