Numerical study of plasma-wall transition using an Eulerian Vlasov code

Abstract.

A one-dimensional Eulerian Vlasov code is used to study the self-consistent solution of a plasma facing a floating collector, in the absence of an external magnetic field. Both electrons and ions are treated with a kinetic equation. A Bhatnagar-Gross-Krook (BGK) collision term is used to describe the collisions. Acceleration of the ion flow at the Debye sheath entrance is observed together with the formation of a stable steep negative electric field in front of the floating collector. This negative electric field acts to accelerate the positive ions towards the plate, pushing back the negative electrons, such that at steady state the total current collected at the plate is zero. The codes are run for a sufficiently long time on the ions time scale to ensure the ions (argon) distribution function is reaching a steady state. For the different parameters used, the solution shows the existence of persistent regular oscillations of constant amplitude when the electron collisions are very small or negligible. These oscillations will be studied. The increase in the electron collisions damps these oscillations and helps the system reach an equilibrium.