Power Handling of the JET ITER-Like Wall
The ITER-like wall (ILW) at JET is a unique opportunity to study the combination of material (beryllium and tungsten) that will be used for the plasma facing components (PFC) in ITER. Both the limiters (Be) and divertor (CFC W coated and bulk W) have been designed to maximise their power handling capability. During the last experimental campaign (October 2010 to July 2011) this capability has been assessed and even challenged in the case of the beryllium wall. The Be limiters are composed of highly shaped, castellated tiles. They are optimised for a range of scrape-off layer (SOL) power decay length 5 < lq,design < 20mm. Its power handling capability (19MW/m2s1/2), predicted with a simple model, has been proven to be robust by the experiments despite unexpected power loads pattern. However, this capability has been pushed to its limit leading to Be melt events, which revealed that the power load is toroidally asymmetric. The toroidal asymmetry could be explained by a misalignment of the limiters by 1mm. The protection system of the ILW has now been partially commissioned and the main chamber protection was operational. It did not prevent melt events mainly because the protection. The bulk W divertor target performed as predicted. Operations were constrained by: 1) an energy load limit of 60MJ per stack ( 60MJ/m2), and 2) the limited number of cycles of the surface temperature above 1200oC in order to prevent thermal fatigue. This latter limit has been exceeded about 300 times and no signs of damage or thermal fatigue have been observed by the photogrammetric survey.