Kinetic modelling of parallel ion transport in the scrape-off layer and divertor of inter-edge localised mode JET high radiative H-mode plasma

KInetic code for Plasma Periphery (KIPP) was used to assess the importance of kinetic effects of parallel ion transport in the scrape-off layer (SOL) and divertor of JET high radiative H-mode inter-edge localised mode plasma conditions with strong nitrogen (N₂) injection, leading to partial detachment at divertor targets. Plasma parameter profiles along the magnetic field from one of the EDGE2D-EIRENE simulation cases were used as an input for KIPP runs. The profiles were maintained by particle and power sources. This work is a continuation of the previous study carried out for electrons (Chankin et al 2018 Plasma Phys. Control. Fusion 60 115011).

In this modelling KIPP calculated ion distribution functions and ion parallel power fluxes. In the main SOL kinetic effects lead to a reduction of heat (conductive power) fluxes compared to Braginskii fluxes by factors 3−4 ('heat flux limiting'). In the divertor, on the contrary, a strong 'heat flux enhancement', by up to two orders of magnitude above Braginskii's, was found. Similar to cases for electrons, high ion heat flux enhancement factors, in particular near targets, are attributed to a non-local transport of super-thermal ions originating from positions along field lines with the highest ion temperature, resulting in the appearance of bump-on-tail features on ion heat flux density profiles. Despite ion heat flux enhancement factors at the target being much higher than for electrons, total power fluxes, ion plus electron, were dominated by ion and electron convection and electron conduction, with ion conductive fluxes playing a secondary role. This must be attributed to lower ion (than electron) velocities (factor ∼$\sqrt{m_e/m_i}$ reduction), which are not compensated by kinetic effects of lower ion upstream collisionality. (paper)