Search

The new full-metal ITER-like wall at JET was found to have a deep impact on the physics of disruptions at JET. In order to develop disruption classification, the 10D operational space of JET with the new ITER-like wall has been explored using the generative topographic mapping method. The 2D map has been exploited to develop an automatic disruption classification of several disruption classes manually identified. In particular, all the non-intentional disruptions have been considered, that occurred in JET from 2011 to 2013 with the new wall. A statistical analysis of the plasma parameters describing the operational spaces of JET with carbon wall and JET ITER-like wall has been performed and some physical considerations have been made on the difference between these two operational spaces and the disruption classes which can be identified. The performance of the JET- ITER-like wall classifier is tested in real-time in conjunction with a disruption predictor presently operating at JET with good results. Moreover, to validate and analyse the results, another reference classifier has been developed, based on the k-nearest neighbour technique. Finally, in order to verify the reliability of the performed classification, a conformal predictor based on non-conformity measures has been developed. [ABSTRACT FROM AUTHOR]

Recent studies dedicated to the characterisation of in-vessel dust in JET with the new ITER-like wall (ILW) show that dust levels are orders of magnitude lower compared with the latter stages of the carbon-wall (CW) period and are decreasing with operational time. Less than 1 g of dust was recovered in a recent inspection, compared with more than 200 g of material recovered at the end of the JET-CW life. Recent inspection of the ILW shows low rates of re-deposition with only small areas of damage of a type likely to create particulate matter. Quantifiers from laser scattering techniques also indicate an order of magnitude reduction in dust relative to the JET-CW and show that the amount of dust mobilized after a disruption is proportional to the dynamic vessel forces. It is not possible to infer what fraction of dust (if any) might be created by disruptions. However, disruption mitigation is found to reduce the amount of dust seen after moderate disruptions by a factor of 4. Analysis of the transient impurity events (TIEs) associated with dust show that tungsten dominates. A significant contribution to TIEs is also seen from iron, nickel and chromium (probably from steel and Inconel components). The incidence of severe negative effects on operations from TIEs is found to be relatively rare, with <1% of ILW disruptions linked to TIEs. The evolution of the TIE rate closely follows changes in the laser scattering dust quantifiers; both trend downwards in time but peak during periods of higher disruption rate (thought to be primarily driven by the mobilization of existing dust). [ABSTRACT FROM AUTHOR]