Modeling Long Probes in Flowing Plasmas using KiPS-2D, a Novel Steady-State Vlasov Solver

A Consistent steady-state kinetic 2D plasma model and the corresponding computational solver were developed and used for the modeling of long conductive electron-collecting probes in o wing mesosonic plasmas. Sheath asymmetries, not accounted for in previous treatments of ion-collecting probes in o wing plasmas, are modeled here and shown to consititute an important mechanism for the departure from OML theory for electron current collection in the mesosonic regime. The eects of collisions are addressed by dividing the space surrounding the probe into a collisionless computational space and a collisional background plasma. The implementation of the solver consists of successive linearizations of the nonlinear Poisson-Vlasov operator, within a Tikhonov-regularized Newton iterative process. The Finite Element Method is used for the Poisson solver, while the inside-out trajectory tracking procedure is used for the Vlasov solver. The parallel solver allows for the arbitrary velocity distributions of both species within the computational domain, provides an adaptive, unstructured meshing strategy, and allows simulation of very large computational domains. Results show indication of a small enhancement, with respect to OML theory, of the collected current to an electron-attracting probe in a o wing plasma. This enhancement is attributed to the elongation of the pre-sheath into the collisional zone of the plasma, which causes an enhanced density of incoming electrons upstream from the probe, and is seen to dominate the opposing decrease in electron collection due to additional potential barriers created by a wake-side depression of the electric potential. The primary issue is the accumulation of noise in the solution that subsides in spite of the employed Tikhonov regularization, limiting the progress of the iterative scheme. Improvements in the Vlasov solver to reduce the amount of quadrature noise it generates are planned to improve the consistency of solutions.