H-MODE CONFINEMENT AND FUSION PERFORMANCE IN JET

JET has conducted extensive experiments in H-mode plasmas focusing on two broad aims. The first, involving the characterization of reactor-r elevant aspects of the regime, encompasses the study of steady-state H -modes at plasma currents of up to 6 MA. In these plasmas, energy conf inement is typically a factor of 1.8-2 greater than predicted by L-mod e scalings and local transport varies with the ion Larmor;radius, at l east for input powers well above the II-mode threshold power. Using ni trogen impurity seeding, it regime has been developed in which good co re confinement, with an enhancement of 1.5 relative to L-mode scaling, is combined with radiated power fractions of up to 80%. The second ma jor goal is to optimize fusion power production by exploiting high-con finement ELM-free H-modes, which exhibit energy confinement enhancemen t factors of three or more relative to L-mode plasmas. In this regime, fusion power quotients Q(DT) similar to 1 have been achieved, though the highest fusion performance is transient.