A new kinetic model for neoclassical impurity particle transport simulation has been developed. Our model is able to simulate the following two effects, which have been theoretically predicted, but neglected in most of the existing kinetic impurity transport simulations in the SOL (scrape-off layer)/Divertor plasmas of tokamak; (1) the neoclassical inward pinch (NC IWP) due to the density gradient of background plasmas and (2) the neoclassical temperature screening effect (NC TSE, outward transport) caused by the plasma temperature gradient. The IWP and TSE, both proportional to the impurity charge number Z, become especially important for higher-Z impurities such as tungsten. In this paper we focus on the case where background plasmas are in the Pfirsch–Schlüter regime. The velocity distribution of background plasma ions is modelled by a distorted Maxwellian distribution, which includes the Pfirsch–Schlüter flow velocity and the Pfirsch–Schlüter heat flux density, in order to reproduce the NC IWP and NC TSE. A series of test simulations have been performed for a toroidal magnetic field geometry. Characteristics of the neoclassical transport, such as dependencies on the safety factor and on the impurity charge number, have been confirmed.

In order to obtain a better understanding of tungsten (W) transport processes, we are developing the Monte-Carlo W transport code IMPGYRO. The code has the following characteristics which are important for calculating W transport: (1) the exact Larmor motion of W ions is computed so that the effects of drifts are automatically taken into account; (2) Coulomb collisions between W impurities and background plasma ions are modelled using the Binary Collision Model which provides more precise kinetic calculations of the friction and thermal forces. By using the IMPGYRO code, the W production/transport in the ITER geometry has been calculated under two different divertor operation modes (Case A: partially detached state and Case B: high recycling state) obtained from the SOLPS-ITER code suite calculation without the effect of drifts. The results of the W-density in the upstream SOL (scrape-off layer) strongly depend on the divertor operation mode. From the comparison of the W impurity transport between Case A and Case B, obtaining a partially detached state is shown to be effective to reduce W-impurities in the upstream SOL. The limitations of the employed model and the validity of the above results are discussed and future problems are summarized for further applications of IMPGYRO code to ITER plasmas.

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Temperature Screening Effect (TSE) on the impurity transport in fusion plasmas has been studied by a kinetic Monte Carlo simulation model [Y. Homma and A. Hatayama, J. Comput. Phys. 250, 206 (2013)]. The TSE drift is induced by the background-plasma tempetature gradient across the magnetic field, and is dependent on various parameters of the impurity species as well as on the background-plasma condition. A series of test simulations has been performed in wide range of parameter space. It has been confirmed that the parametric dependences of the TSE drift are correctly reproduced by our kinetic model.

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