Maximizing JET divertor mechanical performance for the upcoming deuterium-tritium experiments

摘要

The next D-T campaign will push the JET ITER-like wall to high divertor power and energy levels. During the 2016 campaign, Strike Point (SP) sweeping permitted relevant H-mode scenarios without exceeding the temperature limits imposed by JET Operation Instructions (JOIs). In the subsequent shutdowns, six outer divertor tungsten-coated 2D carbon fibre composite tiles were found to have inter-laminar cracks.Here we describe the results of a 3D thermo-mechanical analysis aimed at understanding the origin of the cracks. A sensitivity assessment has been carried out on the temperature time-evolution of a realistic tile 3D model during high power pulses, both with fixed and sweeping SPs. Time and space-varying heat flux density loads on the divertor have been calculated using different techniques for reconstructing the power footprint. The results have been benchmarked against the temperature measurements by high resolution infrared diagnostic systems.The study confirmed the source of the cracks and their localization in the upper part of the tile, giving inter-laminar tension higher than the Ultimate Tensile Stress. Plasma input power, radial location of the SP and sweeping amplitude play an important role on the stress field whose maximum value strongly depends on the SP location. Their influence on the maximum stress value has been investigated and optimized to maximize the performance of divertor tiles without exceeding the limits on input energy and maximum surface temperature imposed by the JOIs.