Plasma facing materials have been selected for the ITER first wall on the basis of experiments in tokamaks, plasma simulators, ion beams and high heat flux test beds but none of these have replicated the actual ITER configuration. It is clear that it is difficult to predict the material migration pattern, the associated tritium retention and the impact of the materials on ITER operation without a test of the materials in a realistic geometry in a large device such as JET. The current objective of the ITER-like Wall (ILW) Project is to install in JET, a beryllium (Be) wall and an all tungsten (W) divertor (the favoured back-up materials solution for ITER). This choice is technically more demanding than the ITER-reference combination which has carbon fibre composite (CFC) tiles at the divertor strike point where the heat load is highest but leaves open the option to remotely replace specific rows of divertor tiles with CFC at a future date. The ILW and combined with other JET upgrades will enable development of ITER relevant plasma conditions which are compatible with the wall materials, thus accelerating the early phases of ITER.
The main constraints on the ILW project are cost, schedule and the need to preserve the power, energy handling and force limits (due to disruptions where there is a rapid plasma termination) currently set for the CFC wall whilst providing a scientifically relevant materials configuration for ITER. These constraints have led to Be tile designs which are inertially cooled (cost/complexity), segmented (eddy forces) and castellated (thermal stress cracking) with hidden bolts (maximum power handling). The recessed areas of the inner wall are either Be coated inconel (cost/eddy forces) or W-coated CFC (NBI shinethrough). For the divertor, R&D tasks have been completed to evaluate W coating of CFC tiles (driven by cost/schedule) and the design of a single row of bulk W tiles for the outer divertor. To meet the schedule, a major upgrade of remote handling systems to allow co-operative working with two booms at once and new tooling are required to install the novel tile designs.
The ITER-like Wall Project represents a significant step by EFDA in preparing for ITER operation. Although the new wall will not be operational before the end of 2009, it is already shaping the programmes of the JET Task Forces by making the materials driven operational constraints predicted for ITER a more immediate reality for JET.
Submitted for the for the ITER-like Wall Project Team.
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