JET Confinement Studies and their Scaling to High bN, ITER Scenarios

The ITER Hybrid scenario aims to exploit bootstrap current to enable burn times in excess of 1000s. To achieve this, and optimise fusion performance, requires high bN (the plasma pressure normalised to a stability scaling) and energy confinement equal to or greater than that predicted for the baseline scenario. This paper discusses results from the JET candidate Hybrid scenario, where bN, MHD 3.6 plasmas have been produced. Despite a different initial phase, confinement relevant plasma parameters evolve rapidly towards those of equivalent ELMy H-modes and are well described by IPB98(y,2). In contrast to previous ELMy H-mode studies, a dedicated b scan experiment in the JET Hybrid candidate scenario shows a strong negative dependence of global confinement on bN. Analysis indicates that the core transport remains consistent with weakly dependent electrostatic transport, whilst the edge confinement decreases strongly with increasing bN. By combining global confinement data from ASDEX Upgrade, DIII-D and JET Hybrid scenario discharges, a multi-machine database is produced. In contrast to the JET case, confinement in ASDEX Upgrade and DIII-D is is shown to be inconsistent with IPB98(y,2) and alternative dependencies are explored.
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