Brunetti, D.Graves, J. P.Ham, C. J.Saarelma, S.2024-02-202024-02-202024-02-202024-01-0110.1088/1361-6587/ad0b35https://infoscience.epfl.ch/handle/20.500.14299/204430WOS:001108064200001A plasma resistivity-β driving mechanism aimed at explaining the appearance of long wavelength global instabilities in free boundary high-β tokamak plasmas with a divertor is presented. These perturbations resemble very closely the resistive wall mode phenomenon. Performing a proper toroidal analysis, we show that the magnetohydrodynamic stability is worsened by the interplay of plasma β and resistivity. By modelling the effect of a magnetic separatrix through a careful positioning of the resonant surfaces, we find that in an ideal plasma wall effects are effectively screened, so that the ideal β limit becomes independent of the wall position/physics. A lower wall dependent critical β is found if plasma resistivity is allowed. We find that global stability can be improved with a toroidal flow, small enough not to induce equilibrium modification. The rotation stabilisation effectiveness depends upon the proximity of the plasma equilibrium parameters to the resistive marginal boundary.Physical SciencesMagnetohydrodynamicsTokamakStabilityRwmtext::journal::journal article::research article