Moderation of divertor heat loads by fuelling and impurity seeding in well-confined ELMy H-mode plasmas on JET

In anticipation of revised operational limits accompanying upgrade of the JET tokamak to an all-metal, ITER-like wall, systematic studies have been conducted of moderating divertor heat load in type I ELMy H-mode by enhanced deuterium fuelling and seeding with the extrinsic impurities neon or nitrogen. These were found to differ mainly in the roughly ten times higher level of nitrogen than neon presently required to approach outboard detachment, and in their effects upon ELMs. With either species up to input power of ≈17 MW, strongly reduced target loads between ELMs, compatible with the new wall, were sustained for longer than 10 energy confinement times while losing <10% of normalized energy confinement and keeping density above 90% of the Greenwald value. At the highest nitrogen levels, ELMs were also markedly decreased in size, yielding a regime still with reasonable confinement plus attenuated exhaust both between and during ELMs.