Overview of the second stage in the comprehensive mirrors test in JET

The first mirror test for ITER in JET with carbon walls has been completed. Thirty polycrystalline Mo mirrors including four coated with a 1 μm rhodium (Rh) film were exposed to plasma in the divertor region and in the main chamber. The mirrors were installed in eight cassettes of pan-pipe shape. The reflectivity of all mirrors exposed in the divertor has been degraded by 80–90% because of the formation of thick (>20 μm) flaking co-deposits on surfaces. Only small reflectivity losses (5–10%) occurred on mirrors located at the channel mouth of the cassettes from the main chamber wall. This is due to the in situ removal of deposited species by charge exchange neutrals. Deuterium, ¹²C and ⁹Be are the main isotopes detected on surfaces, but other isotopes (¹³C) are also found in some locations, thus indicating differences in the material migration. Rhodium coatings with an initial reflectivity that is 30% better than that of pure Mo survived the test without detachment, but their resultant reflectivity was the same as that of the exposed Mo surfaces.