Behavior of lithium ions in the turbulent near-wall tokamak plasma under heating of ions and electrons of the main plasma

Abstract

Turbulent dynamics of the near-wall tokamak plasma is simulated by numerically solving the nonlinear reduced Braginskii magnetohydrodynamic equations with allowance for a lithium ion admixture. The effects of turbulence and radiation of the admixture are analyzed in the framework of a self-consistent approach. The radial distributions of the radiative loss power and the density of Li⁰ atoms and Li⁺¹ ions are obtained as functions of the electron and ion temperatures of the main plasma in the near-wall layer. The results of numerical simulations show that supply of lithium ions into the low-temperature near-wall plasma substantially depends on whether the additional power is deposited into the electron or ion component of the main plasma. If the electron temperature in the layer increases (ECR heating), then the ion density drops. At the same time, an increase in the temperature of the main ions (ICR heating) leads to an increase in the density of Li⁺¹ ions. The results of numerical simulations are explained by the different influence of the electron and ion temperatures on the atomic processes governing the accumulation and loss of particles in the balance equations for neutral Li⁰ atoms and Li⁺¹ ions in the admixture. The radial profile of the electron temperature and the corresponding distribution of the radiative loss power for different densities of neutral Li⁰ atoms on the wall are obtained. The calculations show that the presence of Li⁺¹ ions affects turbulent transport of the main ions. In this case, the electron heat flux increases by 20–30% with increasing Li⁺¹ density, whereas the flux of the main ions drops by nearly the same amount. The radial profile of the turbulent flux of lithium ions is obtained. It is demonstrated that the appearance of the pinch effect is related to the positive density gradient of lithium ions across the calculation layer. For the parameters of the T-10 tokamak, the effect of radiative cooling of the near-wall plasma layer becomes appreciable when the near-wall density of neutral lithium atoms exceeds 7 × 10¹¹ cm⁻³. In this case, the density of radiative loss power in the center of the layer is estimated to be about 500–600 kW/m³.