Impact of E×B drifts on impurity distribution in the scrape-off layer of a tokamak

1089-7674

AIP Digital Archive

Physics

As shown in recent years, a strong electrostatic field exists in the tokamak Scrape-Off-Layer (SOL) and divertor zone. In the present paper it is demonstrated that the E×B drifts resulting from it, compete with the impurity velocities caused by friction with the main ions, as well as with thermal forces. This effect can redistribute impurity flows significantly. Particularly, it may lead to impurity flow reversal. Fluid equations for the test impurities are derived using the two most representative ionization states model. As shown to first approximation, impurity motion does not depend on the ionization state. For a favorable magnetic-field direction, when the ion ∇B drift is directed towards the X-point, in the private region the impurities flow from the outer to the inner divertor plate. On the contrary, in the SOL the impurity flow is directed from the inner to the outer plate. Significant impurity velocity shear exists near the separatrix, and creates the effect of flow reversal. Diffusion across the flux surfaces transports impurities flowing away from the divertor plates to regions with the opposite flow direction. A reduced visual model is presented. © 2000 American Institute of Physics.

Electronic Resource