Spacecraft Observations and Theoretical Understanding of Slow Electron Holes.

We present Magnetospheric Multiscale observations showing large numbers of slow electron holes with speeds clustered near the local minimum of double-humped velocity distribution functions of background ions. Theoretical computations show that slow electron holes can avoid the acceleration that otherwise prevents their remaining slow only under these same circumstances. Although the origin of the slow electron holes is still elusive, the agreement between observation and theory about the conditions for their existence is remarkable.

Kinetic solution to the Mach probe problem in transversely flowing strongly magnetized plasmas.

The kinetic equation governing a strongly magnetized transverse plasma flow past a convex ion-collecting object is solved numerically for arbitrary ion to electron temperature ratio tau . The approximation of isothermal ions adopted in a recent fluid treatment of the same plasma model [I. H. Hutchinson, Phys. Rev. Lett. 101, 035004 (2008)] is shown to have no more than a small quantitative effect on the solution. In particular, the ion flux density to an elementary portion of the object still only depends on the local surface orientation. We rigorously show that the solution can be condensed in a single "calibration factor" M c, function of tau only, enabling Mach probe measurements of parallel and perpendicular flows by probing flux ratios at two different angles in the plane of flow and magnetic field.

Fully self-consistent ion-drag-force calculations for dust in collisional plasmas with an external electric field.

The ion drag force on a spherical dust particle immersed in a flowing plasma with an external electric field is self-consistently calculated using the particle-in-cell code SCEPTIC in the entire range of charge-exchange collisionality. Our results, not based on questionable approximations, extend prior analytic calculations valid only in a few limiting regimes. Particular attention is given to the force direction, shown never to be directed opposite to the flow except in the continuum limit, where other forces are of a much stronger magnitude.