Experimental study of the compatibility of beryllium limiters with a tokamak plasma

Abstract

Beryllium rail limiters were inserted into the plasma of the tokamak Unitor to study the behaviour of this material. The power load onto the limiter surface was about 2 kW-cm" 2 . The occurrence of heavy (Cr) and light (O) impurities was monitored spectroscopically. It was found that the contamination by heavy impurities stemming from the first wall (Cr) was reduced by a factor of ten in the course of a few subsequent shots. In comparison with other limiter materials (graphite, TiC, spinel, Ni, AI2O3) the number of disruptive discharges was considerably reduced. After breaking the vacuum and opening the vessel, the beryllium deposition on the wall and the various components (pumps, mass spectrometer, etc.) was studied. No volatile beryllium dust could be detected by samplers. The released beryllium was found to be quantitatively condensed on the torus wall with a thickness of ten monolayers after 1000 tokamak shots.

Impurity fluxes and concentrations in the ISX-B beryllium limiter experiment

“…Since Be-gettering reduces the low-Z impurity density in the plasma core, it is of interest to determine if the intermediate-Z elements are also diminished, because of deposited beryllium shielding the structural wall from sputtering as implied by the Unitor experiment [5]. It is somewhat difficult to compare data from the first IXS-B beryllium limiter experiments to previous observations in this machine.…”

“…Thus, attention is being paid to the possible use of beryllium inside the vacuum chambers of fusion devices. A beryllium limiter was first tested with promising results in the Unitor tokamak [5]. Most notably, discharges operated for a longer time than when using other materials, and the frequency of disruptions was reduced below previous rates.…”

The beryllium limiter experiment in ISX-B

“…To test the suitability of beryllium as a limiter material for JET, experiments were carried out in the Unitor [2] and Impurity Study Experiment-B (ISX-B) tokamaks. Results from the latter experiment are reported here.…”

Release of beryllium from poloidal limiters in UNITOR

“…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).…”

“…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).…”