Laboratory investigation into electric field sensor instabilities: Calibration and testing

The observation and interpretation of electric fields have been crucial to the understanding of space physics, particularly on the kinetic scale. The basic principle for electric field measurements can be considered straightforward. However, it has proven difficult to measure electric fields from current state-of-the-art voltage probes without perturbing the space plasma itself. There are numerous documented observations from electric field instruments that have no geophysical explanation for their behavior, implying that they can only be induced by the interaction between probe and plasma. The cause of these anomalies requires a full understanding of the factors that contribute to the measurements of voltage probes. We developed a procedure to isolate the sources of impedance between various components of a physical voltage probe model and a controlled plasma population via the space physics simulation chamber at the Naval Research Laboratory. This paper describes the laboratory setup, procedure, and results from the first round of tests performed on this voltage probe model and discusses improvements to future campaigns. Initial results show that some changes to the model design and the measurement of plasma parameters are required, but interactions with the plasma are observed, and the calibration method used successfully returns impedance values similar to values from direct measurements.