Refurbishment of the JET halo current diagnostics

During the 2001 shutdown the new halo coils were installed together with other modular based components, in order to minimise the impact on the in-vessel activities. The refurbishment includes two sets of diagnostics: one at the bottom (in the divertor) and one at the top of the vessel. The divertor set consists of two toroidal field pick-up coils, each embedded in a carrier of the septum replacement plate (SRP). The top set is integrated with new discrete wall protection plates. It consists of three subassemblies, which can be fully installed or removed by Remote Handling (RH). Each subassembly encompasses a toroidal field pick-up coil and a Rogowski coil embracing the plate support posts. Signals from the three toroidal locations are brought to a single feedthrough by a conduit running 180° in the toroidal direction. The first results (April–May 2002) are presented, and indicate an increased halo current fraction. This work was performed under the European Fusion Development Agreement.