Chirality-dependent Plasma Density Profile Changes from Helicon Wave Ponderomotive Forces

Abstract

It is shown that nonresonant helicon-wave-induced transport may result in significant changes in the plasma density radial profile; this is illustrated using parameters appropriate to the cylindrical experiment BASIL and the toroidal experiment SHEILA. Whereas m = +1 helicon waves induce an inward-directed transport and change the density profile to a more centrally peaked one with a higher density on the axis, m = −1 helicon waves induce an outward-directed transport velocity and change the density profile to a hollow one. This may be the clue to the puzzle as to why m = −1 helicon waves are frequently difficult or impossible to excite, as the plasma column is effectively blown off to the discharge chamber walls by the ponderomotive force density of the waves with this chirality (sense of rotation of the wavevector with respect to the axial or toroidal magnetic field).