DEUTERIUM TRAPPING AND IMPURITY COLLECTION ON A 1990 JET BE BELT LIMITER

From a tile of the JET toroidal belt limiter installed during the 1990 operation period, samples were cut from the plasma-facing side along the poloidal direction and the surface layers were analysed by SEM and by the ion beam techniques NRA, PIXE, RBS and HIERD. The poloidal distribution of D is fairly uniform with values of up to 2 X 10(17) cm-2. The contamination of the Be by metallic impurities from the vessel wall is typically up to 2 X 10(16) Ni cm-2, 5 X 10(15) Cr cm-2 and 2 X 10(16) Fe cm-2, giving totally about 0.2 g of metals deposited on the upper limiter. Other impurities amount up to 3 X 10(17) C cm-2, 7 X 10(17) O cm-2, 2 X 10(17) Cl cm-2, 2 X 10(16) K cm-2, 4 X 10(15) Ca cm-2, 3 X 10(15) Ti cm-2 and 1 x 10(15) Zn cm-2. The D deposition is about a factor of 4 smaller than on the C limiter of the previous discharge period, while the deposition of the Inconel components is about one order of magnitude smaller than on the C limiter. O is found to be trapped in the Be at depths up to several micrometers, which may be caused by segregation of pure Be through the oxide to the surface of oxide layers on the limiter. This would improve the O gettering of the Be. The lower D concentration is consistent with the observed degassing of D in the time between discharges.