Studies of edge plasma phenomena in T-10

A scoop limiter equipped with Langmuir and heat flux probes in its scoop channels has been operated in T-10. Results concerning the properties of the scoop plasma and the neutral gas pressure in the pump duct are reported together with a Monte Carlo simulation of the neutral component which fairly well agrees with the observations. A 3-D model of the scrape-off layer (SOL) in tokamaks has been developed and evaluated with respect to plasma density, taking into account the multiplicity of connection lengths due to the complex interplay of the q-dependent magnetic topology and the particular limiter geometry (rail limiter in T-10). It turns out that such a SOL is highly non-uniform in accordance with experimental data from direct Langmuir probing, limiter thermography and a post mortem investigation of limiter damage. Results of a 2-D Monte Carlo calculation (geometry of T-10) of the distribution of neutrals originating from the limiter by recycling, considering the effect of backscattering, show good agreement with corresponding measurements and, furthermore, can explain the discrepancy between the neoclassical and the observed magnitude of ion heat transport: it is the neutrals that are the carriers of the additional efflux of ion energy in question. (author)