JET, the largest fusion device of the European Fusion Programme, has been in operation since June 1983. The inherent flexibility of the machine's original concept and its large plasma volume has permitted a series of engineering upgrades and modifications to be made to improve plasma configuration and machine performance and to allow a large variety of plasma and fusion physics issues to be addressed.

A recent modification, the installation of an axisymmetric single-null pumped divertor (Mark I), operated in the experimental period 1994-95. The design of this divertor ensured that, for the first time in JET, carbon ‘blooms’ were eliminated. The paper reports on the wide range of experimental results during this period including successful studies in the areas of detached plasmas with radiative power exhaust, high performance ELM free H-modes and energy confinement studies. The experimental programme included a comparison between graphite and beryllium as divertor target material, showing that plasma performance with beryllium targets was very similar to that with carbon and that there was little evidence of ‘vapour shielding’. Toroidal asymmetries of vessel forces due to disruptions and halo currents were studied in detail.

A new divertor support structure has now been installed inside the vacuum vessel. It consists of a continuous toroidal structure which forms the base for tile carriers which define the divertor geometry. The first divertor configuration to be installed, the Mark IIA, is designed to enhance neutral particle retention and consists of a more closed configuration than the Mark I divertor as well as exhibiting an increased power handling capability. A key feature of the new components is the possibility to replace divertor target plate structures by full remote handling techniques. D-T operations planned for the end of 1996 and expected to produce ~1020 neutrons will be followed by a remote handling shutdown to replace the Mark IIA target structures by the Mark II Gas Box divertor.