Density distributions of impurities and related energy losses in tokamak plasmas

Abstract

Stationary density distributions of impurities such as carbon, oxygen and iron, in various states of ionization, and related energy losses in tokamak plasmas are calculated numerically, taking into account cross-field classical and anomalous diffusions and ionization-recombination processes. The numerical model provides results in good agreement with ST and TFR experiments. The computed results suggest that the diffusion of impurity ions is not classical, and related energy losses due to impurities cause strong cooling of the plasma near the boundary. The related energy losses will become more serious in a large tokamak of the next generation, since computation shows that they amount to 0.1 MWm⁻³ of power loss at a concentration of 5–10% carbon, 2–5% oxygen or 0.1–0.3% iron.