Ambipolar electrostatic field in negatively charged dusty plasma

<p>It is well known that in the magnetosphere of the outer planets (eg. Saturn, Jupiter, Neptune), even in the absence of an electric current, a polarization electric field develops as a consequence of charge separation in a plasma, providing a restoring force to maintain charge neutrality. It is also well established that certain regions of these planetary systems (ionosphere, icy moons, rings) are populated by significant amount of charged dust that play an important role in the physical and chemical processes in the surrounding plasma environment.<br>In the present work, we study the effect of the charged dust grains on the polarization electric field using Saturn’s F-ring region as a case study. We derive a general expression for E parallel to the magnetic field (E_para) and then using the Cassini RPWS/LP measurements we estimate for the first time in situ E_para close to Janus/Epimetheus ring during the F ring grazing orbits. We further demonstrate that the presence of charged dust,  as small as nanometers in size, can significantly influence the plasma transport processes, in particular the ambipolar diffusion along the magnetic field lines. We show that, close to the ring plane (Z <0.1 Rs), the dusty plasma amplifies E_para by at least one order of magnitude and reverses its direction. Such a reversal implies a confinement of the electrons above the equatorial plane. Furthermore, we show a clear correlation between the amplification of the ambipolar eletrostatic field and the ions and electrons number densities, that could be used in other dusty environments where in-situ measurements are not available yet (in our solar system or the interstellar medium).</p>