Investigation of Ionospheric Plasma Flow Effects on Current Collection to Parallel Wires Using Self-Consistent Steady-State Kinetic Simulations

Multi-wire structures are needed for practical implementations of bare electrodynamic tether systems in space propulsion and radiation belt remediation applications. Using KiPS-2D, a self-consistent, steady-state kinetic solver developed at the University of Michigan, we study the sheath structure and ion current collection properties of a set of two ion-attracting cylinders immersed in a flowing plasma. The effect of plasma flow, center-tocenter spacing and orientation of the set of wires with respect to plasma flow is analyzed. Results indicate that a strong coupling exists between the cylinders’ sheath structures even when their sheaths are separated spatially, whether in a stationary or flowing plasma and for both the parallel-to-flow and perpendicular-to-flow orientations. This coupling reflects strongly in the ion current collection levels observed, through unpopulated bounded ion trajectories connecting both cylinders (reducing current collection) and ion beam focusing of one cylinder onto the other (enhancing current collection). Results at wide spacings show that, when oriented parallel to plasma flow, the set of cylinders collects significantly less (by about 20%) ion current than in a stationary plasma. Conversely, at wide spacings a set of cylinders oriented perpendicular to plasma flow collects significantly more (about 30% more) current than in a stationary plasma. The latter enhancement is primarily attributed to the focusing of ions by each cylinder onto the other cylinder’s wake-side surface.