Investigating Pellet ELM Triggering Physics Using the New Small Size Pellet Launcher at JET

The power load deposited by type-I ELMs on the first wall and the divertor is a severe concern for ITER plasma facing components. The ELM pellet pacing concept is one of the approaches under investigations to solve this problem. By increasing in a controlled manner the ELM frequency, the energy per ELM can be reduced, as already demonstrated in medium size tokamaks. In order to validate this approach at the largest available tokamak size and demonstrate it under local conditions towards those expected in ITER, a new pellet system was developed at JET. The system is designed to launch fuelling pellets (nominal particle content 21-42.1020 D) at speed adjustable between 100 and 500m/s and injection frequency up to 15Hz and pacing pellets (nominal particle content 0.6-1.2.1020 D) at speed adjustable between 50 and 200m/s and injection frequency between 10 and 60Hz. Pellets can be injected from the Low Field Side (LFS) and from the Vertical High Field Side (VHFS) of the tokamak. This paper describes the experiments on ELM pacing performed at JET over the past two years both with fuelling and ELM pacing pellets and extrapolates the results in view of the ELM pacing system foreseen for ITER.
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