Be Tile Power Handling and Main Wall Protection
In the 2010 shutdown, JET has changed its main chamber limiters and divertor from Carbon Fiber Composite to beryllium and tungsten respectively, to mimic the ITER main chamber and divertor and study the impact of this change in the plasma behaviour as well as to study the power handling of these materials for high power operation. This change required a complete redesign of the limiter tiles and of the protection system to avoid melting since the melting temperature for Be is 1249oC in contrast to the 3500oC sublimation temperature of the CFC. The shaping of the tiles surface for optimisation of the power handling, avoidance of exposed edges over 40µm wetted height and the use of rigorous methods to ensure true implementation allowed us to achieve very good power handling and the expected design values has been achieved. The corroboration of the design was done with a field line following code and experimentally by using limiter plasmas with additional heating (maximum of ~5MW for 7s) with the contact point in both the inner and outer limiter and X-point plasmas with additional power of ~25MW for 3s. The results show good agreement with the calculations and the main chamber power handling has achieved and possibly exceeded the design targets. The wall and divertor protections have also been improved with a vessel temperature map system that collects temperature measurements from near infra-red cameras and computes in real time the temperature in the various wall components. Overall, the "JET ITER-like Wall project" has been very successful.