  Cluster observations in the near-Earth magnetotail have shown that sometimes
the current sheet is bifurcated, i.e. it is divided in two layers. The
influence of magnetic turbulence on ion motion in this region is investigated
by numerical simulation, taking into account the presence of both protons and
oxygen ions. The magnetotail current sheet is modeled as a magnetic field
reversal with a normal magnetic field component $B_n$, plus a three-dimensional
spectrum of magnetic fluctuations $\delta {\bf B}$, which represents the
observed magnetic turbulence. The dawn-dusk electric field E$_y$ is also
included. A test particle simulation is performed using different values of
$\delta {\bf B}$, E$_y$ and injecting two different species of particles, O$^+$
ions and protons. O$^+$ ions can support the formation of a double current
layer both in the absence and for large values of magnetic fluctuations
($\delta B/B_0 = 0.0$ and $\delta B/B_0 \geq 0.4$, where B$_0$ is the constant
magnetic field in the magnetospheric lobes).
