H-modes under steady-state conditions in JET

Two H-mode regimes have been identified in JET in which edge localized modes (ELMs) maintain steady-state conditions. In the first regime, strong gas puffing was used in combined (ICRF plus NBI) heating experiments at powers of up to 20MW. Rapid ELM activity occurred and at moderate powers ( approximately 8MW) steady-state H-modes with durations of up to 18s and energy confinement times of up to 95% of the JET/D-IIID scaling were established. At high toroidal beta ( beta N>or=1.5) H-mode plasmas were also found to exhibit regular ELM behaviour which resulted in steady-state H-modes with confinement enhancement of approximately 90% of the JET/D-IIID scaling. This paper examines the plasma properties of these regimes and assesses their implications for steady-state H-mode operation in ignited plasmas.