Simulation of erosion of the tungsten wall by impurities in the divertor plasma

Abstract

Divertor is a component that directly contacts the plasma in tokamak. To ensure the lifetime of the device, it is necessary to reduce the erosion of the divertor wall by plasma. In this work, a particle-in-cell model is used to study the influences of plasma temperature and impurity concentration on the erosion of tungsten divertor wall by carbon and beryllium ions. The steady-state sheath, particle and energy fluxes to the wall, and the energies and angle of the incident ions can be obtained. Then, these data can be used as the input parameters for the plasma-surface interaction model, to evaluate the erosion rate of the plate based on the empirical formulas for physical sputtering. It is found that the erosion by heating plays a negligible role under the plasma condition of this work. Due to the low physical sputtering threshold energy of tungsten by impurities and the impurity ions accelerated by sheath, the physical sputtering of the tungsten by the impurities plays an dominant role in the total erosion. In addition, the erosion rate increases with the increase of plasma temperature and impurity concentration.

Estimation of tungsten production from the upper divertor in EAST during edge localized modes*

“…Moreover, we assume that the impurity density is much lower than the main ion and thus the impurity does not disturb the plasma sheath. [18] At the sheath edge, the one-dimensional electron distribution function is assumed as…”

“…Figure 1(b) plots the angular dependence of the W physical sputtering caused by some ions with bombardment energy E i = 1000 eV. However, in the current EAST discharges, the magnetic field strength is not very strong (B ∼ 2 T), and it is shown from the particle-in-cell simulation that the incident angle of W physical sputtering yield by impurity bombardment in the absence of the magnetic field can be approximately expressed as [18] cos…”

Dust charging and levitating in a sheath of plasma containing energetic particles

“…Moreover, we assume that the impurity density is much lower than that of background ions and thus the impurity does not disturb the plasma. [14,24,25] The dust particle is assumed to be isolated and then cannot modify the sheath. For the thermal background and energetic ions, the continuity and momentum equations are…”