## A model of plasma rotation in the regimes of good confinement in compact toroids

Author: Dmitri D. Ryutov

Requested Type: Consider for Invited

Submitted: 2006-12-17 16:52:51

Co-authors:

Contact Info:

Lawrence Livermore National Laboratory

7000 East Avenue

Livermore, CA 94551

USA

Abstract Text:

A model is suggested that predicts the velocity and geometrical characteristics of the plasma rotation in spheromaks and FRCs. The model addresses the “good confinement” regimes in these devices, where the typical length of magnetic field lines before their intersection with the wall (this length is called “connection length” below) becomes large enough to make the parallel heat loss insignificant. In such regimes, the heat flux is determined by the transport across toroidally-averaged flux surfaces. The model is based on the assumption that, entering the good confinement regime, does not automatically mean that the connection length becomes infinite, and perfect flux surfaces are established. We hypothesize that connection length remains finite, albeit large in regard to the parallel heat loss. The field lines are threading the whole plasma volume, although it takes a long distance for them to get from one toroidally-averaged flux surface to another. It turns out that the parallel electron momentum balance then uniquely determines the distribution of the electrostatic potential between these surfaces. An analysis of viscous stresses allows one to conclude that poloidal flow is slow, whereas the toroidal flow can be significant. Applicability conditions for this model are analyzed and it is concluded that, for a very large connection length, the model breaks down. Assuming that applicability conditions are satisfied, we obtain rotation profiles and the rotation shear for several profiles of the plasma parameters. It turns out that the shear of the rotation velocity can be higher than the typical growth rate of drift-type instabilities, thereby creating a possibility for formation of transport barriers with respect to anomalous transport associated with drift turbulence. Work performed for the U.S. DoE by UC LLNL under contract # W-7405-Eng-48

Characterization: A1,E5

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