Experimental comparison of carbon and beryllium as divertor target materials in JET

The performance of carbon (CFC) and beryllium as divertor target materials has been investigated in the JET pumped divertor under a wide range of experimental conditions. In general, the characteristics of L- and H-mode plasmas on the two targets were very similar. The impurity content in the two cases was also similar and it is believed that carbon sputtered from plasma-facing components in the main chamber played a significant role in beryllium target experiments. The success of the target design was confirmed by the absence of carbon blooms and beryllium melting on the edges. However, in a specific melt experiment designed to assess the behaviour of plasmas on molten and melted beryllium, little evidence of vapour shielding of the target was found and melt damage to a depth of 3 mm was observed.