The effect of BT reversal on the asymmetries between the strike zones in single null divertor discharges: experiment and theories

Abstract

Asymmetries in power and particle fluxes to the strike zones in single null divertor configuration are strongly affected by the toroidal field direction. In the present paper we review experimental data and examine physical mechanisms which redistribute density between the inner and outer divertor branches and, consequently, affect temperature and power deposition asymmetries between the two strike zones. Amongst these is the radial E*B drift caused by the Te drop along the field lines towards the target and recently proposed mechanism of momentum transfer into the SOL due to edge toroidal rotation. These two mechanisms compress the plasma at the inner side in the normal BT configuration (ion Del B drift towards the target), and at the outer side-when the BT is reversed. Since they do not supply additional power to the target apart from convective energy fluxes, the increased recycling and radiation at the side where the plasma is compressed should lead to a decrease in Te. The combined effect of the above mechanisms allows one to explain qualitatively experimental observation that plasma parameters at the target become more symmetric when the BT is reversed.