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The understanding of the halo current properties during disruptions is key todesign and operate large scale tokamaks in view of the large thermal andelectromagnetic loads that they entail. For the first time, we present a fullyself-consistent model for halo current simulations including neutral particlesand sheath boundary conditions. The model is used to simulate VerticalDisplacement Events (VDEs) occurring in the COMPASS tokamak. Recent COMPASSexperiments have shown that the parallel halo current density at theplasma-wall interface is limited by the ion saturation current duringVDE-induced disruptions. We show that usual MHD boundary conditions can lead tothe violation of this physical limit and we implement this current densitylimitation through a boundary condition for the electrostatic potential. Sheathboundary conditions for the density, the heat flux, the parallel velocity and arealistic parameter choice (e.g. Spitzer $\eta$ and Spitzer-H\"arm$\chi_\parallel$ values) extend present VDE simulations beyond the state of theart. Experimental measurements of the current density, temperature and heatflux profiles at the COMPASS divertor are compared with the results obtainedfrom axisymmetric simulations. Since the ion saturation current density($J_{sat}$) is shown to be essential to determine the halo current profile,parametric scans are performed to study its dependence on different quantitiessuch as the plasma resistivity and the particle and heat diffusioncoefficients. In this respect, the plasma resistivity in the halo regionbroadens significantly the $J_{sat}$ profile, increasing the halo width at asimilar total halo current.

Simulations of COMPASS Vertical Displacement Events with a self-consistent model for halo currents including neutrals and sheath boundary conditions