Characteristics of transient plasma layers produced by irradiation of graphite targets by high power quasi-stationary plasma streams under the disruption simulation conditions

Simulation experiments to model the situation occurring at the divertor plates during disruptions and ELMy H-modes of tokamak were carried out with plasma streams generated at the Kharkov QSPA. The facility ultimate plasma parameters were as follows: plasma energy density - above 2 kJ/cm2, proton energy - 0.9 keV, plasma density - 1016 cm-3, pulse duration - 0.1-0.15 ms. Graphite targets of different sizes utilized in these experiments. It was shown that high density target plasma layer, with densities up to 6.1017 cm-3, were formed above the target surface, when incident plasma interacted with target, and sustained during the whole pulse. Density and thickness (usually within 3 to 5 cm) increased with increasing incident plasma power and target surface. The main part of incident plasma energy (∼90%) is absorbed by the transient layer on the first 2-3 cm of its thickness. The average erosion coefficient of the graphite under the influence of incident plasma was of the order of 1 μm/kJ. (orig.)