Release of beryllium from poloidal limiters in UNITOR

Abstract

The release of beryllium from poloidal limiter tiles was investigated by laser-induced Auorescence. The measured beryllium fluxes are in the range 10'9-1020 m-2 s-', depending on the proton flux and heat load onto the limiters. Evaluation of the data shows that besides physical sputtering by protons sublimation becomes iniportant at elevated surface temperatures. The density of neutral metastables in front of the limiter was found to be two times higher than the ground-state density.BERYLLIUM as limiter and first wall material in Tokamak devices has been successfully tested during the last years (MIODUSZEWSKI et al., 1986 ;HACKMANN and UHLENBUSCH, 1984; VON HELLERMAY et al., 1989). The use of beryllium leads to a considerable reduction of metallic and light impurities (0, C). In this work the beryllium flux, released from a limiter surface, was measured by laser-induced fluorescence. The advantage of this method is its high spatial and temporal resolution and its ability to distinguish between the different species, i.e. neutral ground-state, metastable and singly ionized beryllium atoms.