Assessment of the strength of kinetic effects of parallel electron transport in the SOL and divertor of JET high radiative H-mode plasmas using EDGE2D-EIRENE and KIPP codes

Abstract

KInetic code for Plasma Periphery (KIPP) was used to assess the importance of kinetic effects of parallel electron transport in the SOL and divertor of JET high radiative H-mode inter-ELM plasma conditions with the ITER-like wall and strong nitrogen (N2) injection. Plasma parameter profiles along magnetic field from one of the EDGE2D-EIRENE simulation cases were used as an input for KIPP runs. Profiles were maintained by particle and power sources. KIPP generated electron distribution functions, fe, parallel power fluxes, electron-ion thermoforces, Debye sheath potential drops and electron sheath transmission factors at divertor targets. For heat fluxes in the main SOL, KIPP results showed deviations from classical (e.g. Braginskii) fluxes by factors typically ~ 1.5, sometimes up to 2, with the flux limiting for more upstream positions and flux enhancement near entrances to the divertor. In the divertor, at the same time, for radial positions closer to the separatrix, very large heat flux enhancement factors, up to 10 or even higher, indicative of a strong non-local heat transport, were found at the outer target, with heat power flux density exhibiting bump-on-tail features at high energies. Under such extreme conditions, however, contributions of conductive power fluxes to total power fluxes were strongly reduced, with convective power fluxes becoming comparable, or sometimes exceeding, conductive power fluxes. Electron-ion thermoforce, on the other hand, which is known to be determined mostly by thermal and sub-thermal electrons, was found to be in a good agreement with Braginskii formulas, including the Zeff dependence. Overall, KIPP results indicate, at least for plasma conditions used in this modelling, a sizable, but not dominant effect of kinetics on parallel electron transport.

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

“…The profiles were maintained by particle and power sources. This work is a continuation of the previous study carried out for electrons [1].…”

“…The profiles were maintained by particle and power sources. This work is a continuation of the previous study carried out for electrons [1].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 to 4 ('heat flux limiting').…”

“…Details of the setup of the EDGE2D-EIRENE case can be found in [1]. For running KIPP cases, the basic approach, based on the output from EDGE2D-EIRENE, was explained in the previous section.…”

“…Fig. 2, replicated from [1], gives the expanded view of the EDGE2D grid in the divertor region, with positions of slices 1 to 6 indicated. Arrows indicate the direction of counting the parallel distance, from the inner to outer target, projected onto poloidal plane.…”

“…The present work is an extension of the earlier modelling with kinetic electrons [1], where KIPP cases were run using parallel (along magnetic field lines) profiles of plasma parameters calculated by EDGE2D-EIRENE code, which in turn simulated an inter-ELM JET high radiative H-mode plasma with 8 MW of input power and 5 MW of radiated power on nitrogen impurities, with the input power into the computational grid split equally between ion and electron channels. In KIPP runs, macroscopic parameters (density, temperature, parallel velocity) were maintained by particle and power sources, yielding kinetic parallel plasma transport coefficients.…”