Tungsten-coated tiles, manufactured by plasma spray on graphite, were mounted in the divertor of the ASDEX Upgrade tokamak and cover almost 90% of the surface facing the plasma in the strike zone. Over 600 plasma discharges have been performed to date, around 300 of which were auxiliary heated with heating powers up to 10 MW. The production of tungsten in the divertor was monitored by a W I line at 400.8 nm. In the plasma centre an array of spectral lines at 5 nm emitted by ionization states around W XXX was measured. From the intensity of these lines the W content was derived. Under normal discharge conditions W-concentrations around 10 −5 or even lower were found. The influence on the main plasma parameters was found to be negligible. The maximum concentrations observed decrease with increasing heating power. In several low power discharges accumulation of tungsten occurred and the temperature profile was flattened. The concentrations of the intrinsic impurities carbon and oxygen were comparable to the discharges with the graphite divertor. Furthermore, the density and the β limits remained unchanged and no negative influence on the energy confinement or on the Hmode threshold was found. Discharges with neon radiative cooling showed the same behaviour as in the graphite divertor case.
A total of 51 bacterial strains were isolated from fairy shrimps [Branchipus schaefferi (Fisher), Chirocephalus diaphanus (Prévost) and Streptocephalus torvicornis (Waga)] showing signs of 'black disease'. The fairy shrimps showed black nodules on the thoracic appendages, the cercopods, the antennae and sometimes at the back of the head. The infection sites on the thoracic appendages were restricted to the proximal parts of the endopodite, the exopodite and endite I. In order to check Koch's postulates, pure bacterial cultures were administered to healthy fairy shrimps. One bacterial pathogen was identified as Aeromonas hydrophila using BIOLOG and the genotypic fingerprinting technique AFLP.
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