Search

The plasma background and impurity transport in the scrape-off layer (SOL) of the WEST tokamak are modeled for three discharges over a Psep power scan ranging between 1.5 and 2.35 MW. An extended modeling grid is used to investigate far-SOL sourcing from the WEST baffle and lower divertor. Divertor Langmuir probe data at the targets and upstream data from reciprocating Langmuir probes and interferometry/reflectometry is used to create a simulated background plasma with the OSM and EIRENE codes. W-I spectroscopic data from WEST at the lower divertor and baffle is used to estimate the sputtered W flux as an input to the impurity transport code DIVIMP. A potential mechanism for far-SOL impurities from the baffle to transport into the near-SOL is proposed and discussed in terms of the model’s force balances. Analysis of simulated impurity transport showed similar impurity density at the separatrix for the mid and high-power cases despite the high-power case having 10% more sputtered W. This is explained by the combination of differing trends in the sourcing and screening with scaling power.

Highlights • Heat exhaust issues are studied by SOLPS simulation for CFETR phase II with argon seeding. • Low core impurity density can be achieved for high electron density due to both the decrease in the required impurity concentration for fixed radiation power and the improvement of the impurity screening of divertor plasma. • The simulation results are fitted by the Matthew law, which can provide the relationship between the n e , Z eff , and P rad. Abstract For the future fusion reactor, where no intrinsic radiative impurity, like carbon, is allowed to exist, impurity seeding is an indispensable way to exhaust the power across the separatrix. Meanwhile, the impurity concentration has to be limited in order to avoid significant dilution of the fuel in core plasma. For CFETR phase II with a fusion power ∼1 GW, the radiative divertor with argon seeding is studied by SOLPS simulation. Under a high radiative power fraction ∼80% of the power across the separatrix, a density scan is performed for different deuterium ion density at the core-edge boundary. The divertor plasma is fully detached and impurity radiation is concentrated in the divertor region. The relationship between the electron density n e , effective charge Z eff and radiated power P rad are well fitted to the Matthew law, which is considered helpful to find a consistent operation scenario by further core-edge integrated modeling for CFETR phase II. [ABSTRACT FROM AUTHOR]

Since tungsten is considered as the optional divertor target material for the future fusion devices, e.g., China Fusion Engineering Test Reactor (CFETR), it is crucial to have a good screening of the tungsten impurity to keep a low core tungsten concentration. In this paper, based on the two-point model, possible divertor plasma parameters are predicted in high recycling regime for CFETR. Further analysis of tungsten ionization lengths shows that when target temperature is low enough (less than 15 eV), the increase of upstream density may cause an increase of ionization length, and thus a degradation of divertor tungsten screening effect may happen. The 2-D simulations of tungsten transport are then performed by using Osm-Eirene-Divimp edGE [onion skin model (OSM)-EIRENE-DIVvertor IMPurities (DIVIMP)] code package. The target plasma parameters, in the region of those predicted by the two-point model, are set as input in OSM-EIRNEN to generate the background plasma. DIVIMP code is used to further simulate the tungsten impurity transport process. The results reveal that although the decrease of target plasma temperature may reduce the tungsten impurity prompt redeposition rate, the benefit of a lower erosion rate can make compensation. Therefore, to control the core tungsten concentration, lower target plasma temperature is preferred in high recycling regime. [ABSTRACT FROM AUTHOR]