Impact of the ITER-like wall on divertor detachment and on the density limit in the JET tokamak

L-mode and H-mode density limits with the ITER-like wall (ILW) have been investigated in the recent experimental campaign and compared with experiments in the JET carbon material configuration. The density limit is up to 40% higher in the JET-ILW than in the JET-CFC machine. This is linked to the formerly higher radiation fraction and, correspondingly, to earlier divertor detachment in the JET-CFC. In the ILW configuration, the discharge demonstrates a stable operation with a completely detached outer divertor in L-and H-mode. In contrary to the well-known `` heating power independent'' Greenwald limit, the Lmode densities limit increases moderately with rising heating power (similar to P-heat(0.4)) independently of the wall material. The H-L transition constitutes an effective undisruptive density limit for an H-mode plasma. Detachment itself does not trigger the H-L back transition and does not present a limit on plasma density. In the range of neutral beam heating 8-10.5 MW, no dependence of the H-mode density limit on the heating power was observed. (C) 2013 Euratom. Published by Elsevier B. V. All rights reserved.