Reverse flow and parameter profiles in a dense tokamak divertor plasma

The analytical theory devised to describe parameter distribution and flow patterns of a dense plasma in the scrape-off-layer (SOL) of a tokamak agrees reasonably well with 2D modelling results as well as experimental data and can be used for quantitative assessments of the parameters of interest. It is shown that a reverse flow (away from the divertor plates) occurs in a SOL plasma with high recycling, and that the characteristic width of the layer with reverse plasma flow Δ T is narrower than the characteristic widths of the radial profiles of plasma temperature and density Δ T , which are approximately equal to each other. The characteristic value of the reverse flow Γ m exceeds the particle flow from the main plasma volume to the edge layer Γ s . The rather complex convective structures which occur in the SOL as a result of this may lead to localization of impurities in the region of the X-point, preventing them from reaching the bulk tokamak plasma. These effects might be the cause of the high radiation energy losses from the divertor region in the JT-60 tokamak in the improved divertor confinement regime