Mitigation of low-frequency oscillations by parallel inhomogeneous flow

Abstract

A fundamental reality throughout the space and laboratory plasmas is the existence of magnetic field-aligned flows. It is usually believed that the spatial transverse shear in the parallel flow destabilizes many low-frequency instabilities and this may be the origin of low-frequency oscillations in the ionosphere. Here we show that this notion of the destabilizing influence of the shear in the parallel flow can be changed altogether if one takes the effect of the flow curvature (second spatial derivative) into account. The transverse curvature in the parallel flow can overcome the destabilizing influence of the shear and can render the low-frequency ion temperature gradient-type instabilities stable.

Effects of a sheared ion velocity on the linear stability of ITG modes

“…With reference to a tokamak plasma configuration, a sheared poloidal rotation has a non-linearly stabilizing effect against modes producing radially elongated vortices [6]. The role of the toroidal component of the plasma rotation is however more intriguing, as it is shown from the results of several theoretical studies where either slab [7][8][9][10][11][12][13] or toroidal [14][15][16] ITG stability issues have been investigated. In addition, the stability properties of the ITG modes with a toroidal sheared velocity are of particular interest as a first principle approach to the determination of the anomalous momentum transport observed in tokamak plasmas.…”