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 2-D 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 DELTA(T) is narrower than the characteristic widths of the radial profiles of plasma temperature and density DELTA(T), which are approximately equal to each other. The characteristic value of the reverse flow GAMMA(m) exceeds the particle flow from the main plasma volume to the edge layer GAMMA(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.