Scaling Study of ELMY H-Mode Global and Pedestal Confinement at High Triangularity in JET

In ELMy H modes in JET, high triangularity (δ≅0.47) is found necessary to achieve H98=1 at ne/ nG ≥0.85, the ITER requirements. This paper reports on experiments in JET to study the scaling with plasma current and edge safety factor of the global and pedestal confinement at high triangularity (δ≥0.40). It is shown that high confinement quality (H98=0.9-1) at high density (ne/ nG ≥1) is linked with access to the mixed Type I/II ELMy regime. This regime is characterized by higher pedestal pressure at high density than with Type I ELMs, and, so far, has been observed up to 3MA. The variation in behaviour in the mixed I/II regime with δ and q95 is described. At the ITER q95 of 3, the ρ* dependence of the global confinement scaling is confirmed up to 3.5MA (where ρ*≅1.7 ρ* ITER, ν*≅5.3 ν*ITER at ne/nG≅0.8). In the entire range of Ip and q95 explored (Ip from 1 to 3.5MA, q95 from 3 to 5), the pedestal pressure is found to scale with Ip or slightly weaker, as expected from ideal ballooning stability. The ratio between the thermal stored energy (Wth) and pedestal energy (Wped) is similar with both Type I and mixed Type I/II ELMs, such that variations in pedestal with density, plasma current and edge safety factor are reflected in the core thermal energy.