High-Voltage Plasma Sheaths Around Long Conductive Structures in Flowing Plasmas: Simulations and Experiments

Summary form only given. Long conductive structures immersed in flowing space plasmas have several potential science and engineering applications. Among them are propellantless in-orbit spacecraft tether propulsion and high-energy charge precipitation from the Earth's radiation belts, also known as remediation of radiation belts. In addition, the use of Langmuir probes as in-space plasma diagnostic tool is well known. However, existing models commonly used as design tools for these applications are limited in terms of cross-sectional geometry and the range of voltage bias or plasma flow speed. To address this need, a steady-state kinetic computational model called kinetic plasma solver (KiPS-1D and KiPS-2D) was developed allowing for self-consistent simulations of collisionless, unmagnetized flowing plasmas in a vast region surrounding any two-dimensional conductive object. Using the KiPS simulations it was possible to assess interference effects between two parallel cylinders. It was also possible to predict for negatively biased probes substantial sheath asymmetries causing compression on the ram side and long tails on the wake side and to predict this behavior as a function of plasma flow characteristics and high bias potentials. We were able to test basic predictions over certain ranges of plasma flow and bias using Michigan's Large Vacuum Tank Facility (LVTF) and an expanding plasma source. From these experiments we were able to establish good agreement with simulation predictions. Finally, we were able to validate the basic prediction that much larger overall sheath structures could be generated by multi-wire structures (arranged to make a larger, but porous cylinder) but requiring less power than would otherwise be needed for the same number of isolated wires