[P-EM17] Space Plasma Science

[PEM17-P07] Estimation of spurious electric field components produced by spacecraft charging based on the double probe measurements

*Tomoko Nakagawa¹, Tomoaki Hori², Yasumasa Kasaba³, Shoya Matsuda⁴, Yoshiya Kasahara⁴, Yoshizumi Miyoshi², Fuminori Tsuchiya³, Atsushi Kumamoto³, Atsuki Shinbori², Ayako Matsuoka⁵ (1.Tohoku Institute of Technology, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.Tohoku University, 4.Kanazawa University, 5.Kyoto University)

Keywords:Electric field measurement, double probe method, magnetosphere, photoelectrons, ARASE, spacecraft electric potential

Measurements of low-frequency electric field by double probe technique suffer from a spurious electric field component produced by the spacecraft charging and photoelectron cloud whose center is supposed to be shifted from the center of the orbit of the probes toward the sun. The waveforms of the spurious potential difference between the spacecraft and the probes are nearly sinusoidal, so it is not easy to separate them from the natural electric field. Furthermore, the higher harmonics of the waveform are contaminated by the modulation of the probe potential arising from the interaction of photoelectrons between the probe and the spacecraft when the external magnetic field connects them.
In this study, we analyze data from PWE/EFD onboard Arase, and remove the fast, spin-phase dependent variation of probe potential from the waveform, to obtain sinusoidal curve that is supposed to be the sum of the spurious electric field and natural electric field. On the assumption that the natural electric field is perpendicular to the eternal magnetic field and that the spurious electric field is parallel to the direction toward the sun, we can estimate the spurious component only when the eternal magnetic field is parallel to the orbital plane of the probes (the spin plane of the spacecraft). A possible relationship is examined between the spurious electric field component and the spacecraft electric potential, since the spacecraft potential is related with the spacecraft charging due to photoemission, and the photoelectron yield is determined by the solar irradiance and the surface material of the spacecraft, which do not change so abruptly. If we find the relationship, we can estimate the spurious electric field component and subtract it from observation.