Langmuir Probe Measurements in the Ionosphere

Electric probes have been the primary instruments for the in situ investigation of plasma parameters in the Earth’s ionosphere. This dissertation is a compendium of three papers, each dealing with a separate spacecraft that carried one or more instruments based on the electric probe technique. The first paper presents data from the Sudden Atom Layer sounding rocket that carried an RF Impedance Probe, a DC fixed-bias Langmuir Probe (DCP), and an Electric Field Probe. The combined dataset indicates a case of payload surface charging, the causes of which are investigated within the paper. A generic circuit model is developed to analyze payload charging and behavior of Langmuir-type instruments. Our analysis indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth’s mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environments. The second paper presents data from the Floating Potential Measurement Unit (FPMU) that is deployed on the International Space Station. The FPMU instrument suite consists of three different Langmuir-type probes and a Plasma Impedance Probe (PIP). We first give a brief overview of the instrumentation, and then describe the algorithm used to reduce Langmuir probe I-V curves to plasma parameters. It is shown that the derived temperatures agree well with International Reference Ionosphere (IRI) model, while the derived density matches better with the USU-Global Assimilation of Ionospheric Measurement model. The third paper presents the dataset from the EQUIS II sounding rocket campaign. The rocket payloads carried a PIP, a DCP, and an internally heated Sweeping Langmuir Probe. The ratio of the payload surface area to the cumulative area of the instrument and its guard was about 250. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not very accurate. We further show that the ion saturation region analysis of the I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the PIP, and the derived temperatures agree reasonably well with the IRI model