Engineering experience in JET operations

The inherent flexibility of JETʹs original concept has permitted several engineering upgradings and modifications, to address a large variety of plasma and fusion physics issues. The most recent major modification has been the installation of an axisymmetric single-null pumped divertor (Mark I), successfully operated in the experimental period 1994–1995. Following the divertor optimization programme a new, more closed, divertor configuration has now been installed (Mark II), which has shown a better power handling capability and substantially improved neutral particle retention. A key feature of the new design is the possibility to replace the divertor target plate structure using full remote handling techniques following extended D-T operations. Toroidal asymmetries of vessel forces due to Vertical Displacement Events (VDE) and halo currents were experienced since 1994, leading in some cases to sideways movements of the vessel of 7 mm. This has required modification and upgrading of the vacuum vessel support system. Gap control of plasma position and shape and machine protection systems have been developed further, leading to increased experimental availability. Future development foresees the installation of a Mark II Gas Box divertor structure, while studies are underway to increase the toroidal field capability from 3.45 to 4 T and the additional heating power by increasing the NB injector output from 80 kV, 60 A to 120 kV, 60 A and by using wide band matching for ICRF.