Quiescent H-Mode 3D MHD Free-Boundary Equilibrium

Free boundary magnetohydrodynamic equilibrium states with spontaneous three dimensional deformations of the plasma-vacuum interface are computed with the 3D VMEC solver [Hirshman {\em et al.}, Comput.~Phys.~Commun.~\textbf{43} (1986) 143]. The structures we have obtained have the appearance of saturated ideal external kink/peeling modes. Large edge pressure gradients yield toroidal mode number $n=1$ corrugations when the edge bootstrap current is large and $n=4$ distortions when this current is small. The deformations of the plasma boundary region induces a nonaxisymmetric Pfirsch-Schl\"uter current that drives a field-aligned current ribbon which is consistent with experimental observations reported. We claim that the equilibrium states we compute model the Edge Harmonic Oscillation [K.H.~Burrell {\em et al.}, Phys.~Plasmas {\bf 22} (2005) 021805. W.M.~Solomon {\em et al.}, Phys.~Rev.~Lett.~{\bf 113} (2014) 135001] observed on DIII-D and the Outer Mode [E.R.~Solano {\em et al.}, Phys.~Rev.~Lett.~{\bf 104} (2014) 135001] found in JET during Quiescent H-mode operation.