Plasma surface currents in the presence of a resistive wall and their connection to Halo currents during disruptions in tokamaks

The dependence of plasma surface currents on equilibrium plasma parameters in the presence of a resistive wall is analysed analytically within a linear cylindrical model for pressureless ideal plasma with flat and parabolic current profiles. The wall is treated without any restrictions on its magnetic thickness. This can mimic possible conditions in tokamak plasmas during the current quench phase of a major disruption. Earlier studies [1, 2] predict that plasma surface currents have to be taken into account for explanation of the Halo currents intensity and distribution. Our results show that in the presence of conducting structures this is true only in a very narrow window of edge safety factor a q and that in a wide region of a q the wall eddy currents are comparable or much larger than the plasma skin currents. The study reveals ranges of plasma and wall parameters for which the surface and eddy currents could play a role in Halo dynamics. The comparison of the results with previous works [1, 2] on this topic is also presented. [1] L. E. Zakharov, Phys. Plasmas 15, 062507 (2008). [2] L. E. Zakharov, Phys. Plasmas 18, 062503 (2011).