The stability of charged-particle motion in sheared magnetic reversals
M. TSALAS a1, S. C. CHAPMAN a1andG. ROWLANDS a1 a1 Department of Physics, University of Warwick, Coventry CV4 7AL, UK
We consider the motion of charged particles in a static magnetic reversal
with a shear component, which has application for the stability of current sheets,
such as in the Earth's geotail and in solar flares. We examine how the topology of
the phase space changes as a function of the shear component by.
At zero by, the
phase space may be characterized by regions of stochastic and regular orbits (KAM
surfaces). Numerically, we find that as we vary by, the position of the periodic orbit
at the centre of the KAM surfaces changes. We use multiple-timescale perturbation
theory to predict this variation analytically. We also find that for some values of
by, all the KAM surfaces are destroyed owing to a resonance effect between two
timescales, making the phase space globally chaotic. By investigating the stability
of the solutions in the vicinity of the fixed point, we are able to predict for what
values of by this happens and when the KAM surfaces reappear.