Magnetic field stochasticity in the presence of current sheets

The stochasticity of field lines around a current sheet induced by static m agnetic perturbations is investigated. By means of Hamiltonian analysis, it is pointed out that the system exhibits two different chaotic regimes, dep ending on the wavelength of the perturbation: At short wavelengths (shorter than the length of the separatrix), resonant processes determine the onset of stochasticity and can be modeled by a simple mapping; at long wavelengt hs of the perturbation, stochasticity is mainly due to the breaking of adia batic invariants. (C) 1999 American Institute of Physics. [S1070-664X(99)02 208-9].