Complex scrape-off layer analysis of KT-1 edge plasmas

For the first time, the overall profiles of the KT-1 tokamak edge plasma parameters, including transport coefficients, are measured using single and triple electric probes, and the results are analyzed using simple fluid approximations. The cross-particle diffusion coefficient (D) in the boundary plasma is calculated from the measured density scrape-off length (λn). The particle density and the electron temperature fall exponetially in the radial direction with an e-folding length of λn =0.17 cm and a temperature scrape-off of λe= 0.45 cm. Based upon a simple scrape-off layer (SOL) model. the experimental values of the scrape-off length (λn,e)are used to calculate the cross-field diffusion coefficient ( D = 1.0 x 103 cm2/s); roughly corresponding to one third of the Bohm value An SOL model, including the contribution from recombination, is constructed to evaluate Bohm diffusion in the KT-1 edge plasmas. From these deduced values, the cross-field heat conductivity in the SOL is calculated to be ∼ 3.0D