Energy and particle confinement in JET H-mode plasma

Abstract

This work describes the behaviour of the global energy and particle confinement on JET observed in a massive database of H-mode plasmas covering almost the whole lifetime of JET operations, both with the carbon and metal wall. The analysis is focused on type I ELMy H-modes in stationary phases. It is shown that plasma density in that regime is determined mainly by the plasma current, edge safety factor, triangularity of the last closed flux surface and the hydrogenic isotope mass. Behaviour is consistent for the whole database regardless of divertor configuration or the plasma facing materials. On average, thermal energy confinement time in JET with the carbon wall (JET-C) is accurately predicted by the IPB98(y,2) scaling. For JET with the ITER-like wall (JET-ILW), the energy confinement is found to be lower than expected from the scaling. The difference is found to be much stronger in a divertor configuration with the outer strike point at a vertical target and the pumping throat at the private flux. Observed lower confinement in JET-ILW can partially be attributed to the additional operational constraints of the metal wall machine, i.e. the avoidance of heavy impurity accumulation via additional gas dosing, but not fully. The isotope effect on the energy confinement in the Meff = 1–2 range is found to be the same in JET-C and JET-ILW, thus is independent of the wall material, if correlation with plasma density is accounted for. The effect of the toroidal magnetic field on the confinement is between zero and slightly negative. Triangularity has a generally favourable effect on the energy confinement, but the magnitude changes across the database. The effect of triangularity on plasma density is always much stronger than on energy confinement however, therefore plasmas with high triangularity are in general more dense and colder than at lower triangularities. The work described in this paper is completed under the EUROfusion global confinement database project, and the data shown here will be available to EUROfusion collaborators shortly. The data are also either already included in the international H-mode confinement database, or will be in the future updated version.