The effect of compressibility on magnetic island dynamics

Magnetic islands are commonly generated in fusion plasmas with toroidal geometry. Their study is important because they affect the global dynamics of the plasma but there are several aspects that are still poorly understood, in particular the role of compressibility. The present work develops the analytical and numerical solution of the nonlinear tearing mode for magnetic islands with a width less than the sonic Larmor radius, w « ρ_s, taking into account the compressibility of the plasma. A cold ion fluid model is used in the semi-collisional regime for the slab geometry approximation. The differences in plasma profiles between the incompressible and compressible cases are shown, as well as the corresponding effect on the natural velocity of the islands through the plasma. The effect that plasma compressibility has on the evolution of the width of the magnetic islands and, consequently, on the stability of the tearing mode is studied.