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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.

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