  Rich observational phenomenology associated with Pulsar B in PSR
J0737$-$3039A/B system resembles in many respects phenomena observed in the
Earth and Jupiter magnetospheres, originating due to the wind-magnetosphere
interaction. We consider particle dynamics in the fast corotating magnetosphere
of Pulsar B, when the spin period is shorter than the third adiabatic period.
We demonstrate that trapped particles occasionally experience large radial
variations of the L-parameter (effective radial distance) due to the parametric
interaction of the gyration motion with the large scale electric fields induced
by the deformations of the magnetosphere, in what could be called a
betatron-induced diffusion. The dynamics of particles from the wind of Pulsar A
trapped inside Pulsar B magnetosphere is governed by Mathieu's equation, so
that the parametrically unstable orbits are occasionally activated; particle
dynamics is not diffusive per se. The model explains the high plasma density on
the closed field lines of Pulsar B, and the fact that the observed eclipsing
region is several times smaller than predicted by the hydrodynamic models.
