3D effects of nitrogen seeding positions on toroidal asymmetry of SOL plasma transport and deposition on CFETR X-divertor

The poloidally and toroidally localized nitrogen-14 (¹⁴N) injection on CFETR X-divertor configuration has been studied using the three-dimensional (3D) Monte Carlo transport code EMC3-EIRENE. It provides a good route to elucidate the impact of several ¹⁴N seeding positions (i.e., two upstream SOL regions and two downstream divertor regions) on the toroidal asymmetry of scrape-off layer (SOL) plasma transport and deposition behaviors. The strong asymmetry of electron density and temperature distribution is observed when ¹⁴N impurities are injected at upstream SOL regions. It results from the toroidally connected spiral-like structures of strong power dissipation caused by peak ¹⁴N impurities density, following from the source positions down to the divertor region. The ¹⁴N seeding at downstream divertor regions gives rise to the occurrence of symmetric electron density and temperature profiles in the toroidal direction. The deposition pattern of ¹⁴N ions on divertor plates has been calculated to evaluate the 3D cooling effect on the divertor plasma by scanning various ¹⁴N injection positions. The ¹⁴N injected at upstream SOL regions induces several stripe-like structures of peak ¹⁴N ion deposition on divertor targets. It turns out to be the strong 3D radiative cooling effect on divertor plasmas. The island-like structures of peak ¹⁴N ion deposition on divertor targets show a weak cooling effect localized around the injection positions.