Numerical Study of Langmuir Probes: Improving Accuracy Using PIC Simulations

Abstract

Did you know that in the vacuum of space, there is no vacuum? In fact, most of space is filled with charged particles in a plasma state. Close to Earth, Geomagnetic phenomena, space weather, and radio interference such as GPS scintillation are all explained with plasma dynamics. Space is also the largest laboratory we have for plasma physics. It is, therefore, no surprise that accurate measurements of the surrounding plasma of a spacecraft are a part of the foundation for understanding our own ionosphere. A common approach to probing a plasma is with Langmuir probes, which are conducting objects that collect an electrical current, from which we can infer plasma parameters, usually using orbital-motion-limited (OML) theory. It is known that OML will be erroneous under certain conditions. However, due to the complexity and scales of the problem, several sources of error have not been adequately studied and are therefore not well understood or accounted for. In this dissertation, we use Particle-in-Cell simulations to further our understanding by uncovering limits to the idealized OML theory and building models to correct several such error sources. The thesis focuses on charged-neutral collisional effects, the effects of imperfect geometries, and probes in magnetized plasmas.