First in Situ Estimates of the Sheath Resistance for the PSP/FIELD Antenna: Employing an Electron Shot Noise Model
(2026) The Astrophysical Journal — Vol. 997, n° 2, p. 137 (2026)
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- Authors
Zheng, Xianming 
Martinović, Mihailo M. Klein, Kristopher G. Pierrard, Viviane Xue, Xianghui
- Abstract
- Quasi-thermal noise is an important diagnostic tool for measuring electron density and temperature in space plasmas, with its low-frequency range being dominated by electron shot noise. However, previous missions have shown that conventional shot noise models often yield poor fits in the low frequency ( f < fp), limiting the accurate characterization of electron parameters. To address this issue, we introduce an effective sheath resistance into the previous model, thereby establishing a calibrated shot noise model that improves measurements of electron parameters in the inner heliosphere. Methodologically, we applied the steep-descent and Levenberg– Marquardt method algorithm to determine the electron density and temperature above the plasma frequency; we then isolate the pure shot noise by subtracting other noise sources; and finally, we derive the antenna impedance using measurements below the plasma frequency ( fp). Based on Parker Solar Probe (PSP) observations during PSP Encounter 4 ∼ 8 (with unbiased antennas operating in the dipole regime), we obtain an effective antenna capacitance of 8.30 ± 0.21pF and an effective resistance in the range of 0.5 ∼ 4MΩ, with their radial of the capacitances and resistances of r 0.072 ± 0.001 and r2.57 ± 0.02, respectively.
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Citations
Zheng, X., Martinović, M. M., Klein, K. G., Pierrard, V., Liu, M., Wang, Y., Wu, T., Ember, W., Li, J., Maruyama, N., Chi, Y., Yao, Y., Yu, B., & Xue, X. (2026). First in Situ Estimates of the Sheath Resistance for the PSP/FIELD Antenna: Employing an Electron Shot Noise Model. The Astrophysical Journal, 997(2), 137. https://doi.org/10.3847/1538-4357/ae25e6 (Original work published 2026)