Parker Solar Probe FIELDS Instrument Charging in the Near Sun Environment: Part 2: Comparison of In‐Flight Data and Modeling Results

• Published in: Journal of geophysical research. Space physics Vol. 126; no. 5
• Main Authors: Diaz‐Aguado, M. F., Bonnell, J. W., Bale, S. D., Wang, J., Gruntman, M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-05-2021
• Subjects: Antennas; Charged particles; Electric fields; Electric potential; Electrodes; Electromagnetic radiation; In situ measurement; Mathematical models; Numerical models; Perihelions; Plasma; plasma environment; Plasma sheaths; Solar probes; Solar wind; Solar wind flow; Space plasmas; Spacecraft; spacecraft charging; Spacecraft-environment interaction; Voltage
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2020JA028689

This research shows Part II of the Spacecraft Interaction Plasma Software (SPIS) used to model the parker solar probe (PSP) FIELDS instrument and its interactions with the Solar Wind. Flight data were used to run the PSP model and compared with models using past predicted parameters. The effect of voltage biasing between the antenna, its shield, and the spacecraft on the current balance of each surface was investigated at first perihelion (0.16AU). The model data were reduced to I–V curves to find current saturations (analysis results 52 µA vs. flight results 54–72 µA), and sheath resistances (analysis results of 307 kΩ vs. flight results of 51 kΩ). The recommended bias current to ensure optimal sensitivity of the FIELDS antenna was between −52 and −22 µA, which corresponded to a differential potential with respect to the spacecraft between −5 and 5 V. The analysis also shows that plasma sheath of the FIELDS antenna and the plasma sheath of the FIELDS shield interacted between each other with an impedance of ∼220 kΩ.
Plain Language Summary
Measuring the electric field in a space plasma is important for understanding how plasma flows are driven, charge particles are accelerated and heated, and how electromagnetic waves propagate. Measuring the voltage difference between two spatially separated electrodes immersed in a space plasma is one way to estimate the electric field that is present in the plasma. Interpretation of these voltage differences is complicated by the fact that the electrodes often float at a significant voltage relative to the nearby plasma so as to achieve current balance between the electrode and the charged particle environment around it. Different surfaces will float to different potentials depending upon their surface materials, their location relative to other surfaces, their orientation relative to the Sun's light and solar wind flows, and numerical modeling is required to accurately predict how all these factors influence what is observed. Comparison between such numerical models and in situ measurements of potentials and currents, allows one to better understand how the instrument works, and how to operate it better to produce the highest quality electric field estimates.
Key Points
We predict the floating potentials of the parker solar probe FIELDS antennas
We analyze the model antenna I–V curves to determine the optimal current and voltage biases for maximum sensor sensitivity
We compare the theoretical predictions with mission flight data and find qualitative agreement, but some quantitative differences