Moderation of Target Loads Using Fuelling and Impurity Seeding on JET
Operation with an all-metal, ITER-like wall on JET is scheduled from 2011. Adaptation particularly of baseline ELMy H-mode (q95 3.5) to the new exhaust constraints involved has been explored by systematic scans of deuterium fuelling and seeding with extrinsic impurities neon or nitrogen. Peak heat load between ELMs on the outboard target can be strongly reduced by fuelling (recycling), and approach detachment with either seed species, for only 10% loss of normalised energy confinement. Simultaneously, normalised plasma density and total radiation averaged between ELMs are not simply increased, but at stronger fuelling can actually fall with increasing seeding, indicating some redistribution of efflux power temporally and spatially. At highest nitrogen seeding, ELMs can also be mitigated, even while the electron pedestal and confinement are largely preserved. Charge-exchange recombination spectroscopy indicates a substitution of intrinsic carbon with extrinsic species.