Analysis of the progress to detachment in the divertor of the MAST tokamak

Abstract

Power handling and erosion of the divertor target plates are critical issues in the design of a next step fusion experimental reactor. Several steps can be taken to mitigate the effect of the plasma interaction with the divertor target, one of the most effective is plasma detachment. In MAST (Mega Ampere Spherical Tokamak) a series of experiments were conducted which aimed to achieve detachment for the first time on a spherical tokamak with rather open divertor geometry. This paper presents the results of these experiments, concentrating on a series of L-mode discharges, additionally heated with 750 kW of NB injection, for which the degree of detachment [Nucl. Fusion 38 (1998) 331] is calculated and discussed. Evidence for deuterium volume recombination in the lower outer divertor is shown and used to estimate with greater accuracy T e (overestimated by the Langmuir probes for detached plasmas) in the divertor region.