EFFECTS OF LIMITERS ON REVERSED-FIELD PINCH CONFINEMENT

This paper documents the effects on confinement of introducing discrete limiters into the edge plasma of the ZT-40M reversed-field pinch (RFP) [Fusion Technol. 8, 1571 (1985)]. RFP confinement is not significantly degraded by appropriately designed single limiters inserted to a sufficient depth for effective local vacuum vessel wall protection. Inserting limiters too deeply into the plasma results in excess limiter heating, and a consequent increase in the impurity content of the plasma. Under these conditions the plasma loop voltage increases. The heating of the limiters is observed to be asymmetric, with the majority of the heat flux in ZT-40M being attributable to suprathermal electrons [T(supra) approximately 2-3 X T(e) (0)] reaching the edge moving almost unidirectionally along magnetic-field lines.