Stabilization of pressure-driven magnetohydrodynamic modes by separatrix in dipole plasma confinement

The eigenvalue problem is solved for the short-wavelength pressure-driven magnetohydrodynamic modes in configuration with closed magnetic field lines in the poloidal direction. Here we show that the magnetic separatrix (which determines the boundary of the confinement region) provides a substantial stabilizing effect by which the total volume inside the separatrix becomes stable even for very high beta values. The plasma inertia and compressibility are properly formulated to give the correct growth rate of the mode.