Impact Ionization Double Peaks Analyzed in High Temporal Resolution on Solar Orbiter

Abstract. Solar Orbiter is equipped with electrical antennas performing fast measurements of the surrounding electric field. The antennas register high velocity dust impacts through the electrical signatures of impact ionization. Although the basic principle of the detection has been known for decades, the understanding of the underlying process is not complete, due to unique mechanical and electrical design of each spacecraft and the variability of the process. 

We present a study of electrical signatures of dust impacts on Solar Orbiter's body, as measured with Radio and Plasma Waves electrical suite. A large proportion of the signatures present a double-peak electrical waveforms in addition to the fast pre-spike due to electron motion, which are systematically observed for the first time. We believe this is due to Solar Orbiter's unique antenna design and a high temporal resolution of the measurements. The double peaks are explained as due to two distinct processes. Qualitative and quantitative features of both peaks are described. The process for producing the primary peak is known for a long time and the process for producing the secondary peak was proposed before (Pantellini et al., 2012a) for Solar Terrestrial Relations Observatory (STEREO), although the corresponding delay of 100 μs – 300 μs against the primary peak was not observed until now.

The primary peak's amplitude is believed to be the better measure of the impact-produced charge and suggests that the typical amount is around 8 pC. The observed asymmetry between the primary peaks measured with individual antennas is quantitatively explained as electrostatic induction. A relationship between the primary and the secondary peaks' amplitudes is found to be non-linear and the relation is partially explained with a model for electrical interaction through the antennas' photoelectron sheath.