NONLINEAR GROWTH AND MOTION OF MAGNETIC ISLANDS IN REGIMES WITH A HIGH FRACTION OF BOOTSTRAP CURRENT-DENSITY

The nonlinear evolution of magnetic islands is investigated in regimes with a high fraction of bootstrap current density, which are of great interest for advanced tokamak scenarios. For a sufficiently large fra ction of the equilibrium bootstrap current density (measured against t he local magnetic shear and the poloidal magnetic fields), the nonline ar island growth and the saturated magnetic island width are found to depend neither on the original local equilibrium magnetic shear nor on the fraction of the bootstrap current density. In addition, in the po sitive magnetic shear region the magnetic islands together with its ra tional surface move inwards. The results of corresponding numerical si mulations agree well with analytical predictions.