Parallel currents in the scrape-off layer of JET diverted discharges

Abstract

Systematic analysis of currents passing between the two strike zones in the scrape-off layer of JET single-null divertor discharges has been performed. Using a set of Langmuir probes, stretched across the target tiles in poloidal direction, the relation between the asymmetry in plasma parameters at the strike zones and parallel currents has been established. It has been found that the direction of edge currents was entirely determined by the plasma density and electron temperature distributions at the two strike zones, with the thermoelectric current being the major contribution to the net edge current. However, to match the whole set of data, the existing theory of Staebler and Hinton (Nucl. Fusion 29 (1989) 1820), which accounts for the thermoelectric current, had to be extended to comprise the effect of electron pressure imbalance between the two strike zones. The remarkable phenomenon of pressure imbalance in favour of ion strike zone is discussed.