Magnetic field stochasticity in the presence of current sheets

The stochasticity of field lines around a current sheet induced by static magnetic perturbations is investigated. By means of Hamiltonian analysis, it is pointed out that the system exhibits two different chaotic regimes, depending 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 wavelengths of the perturbation, stochasticity is mainly due to the breaking of adiabatic invariants.