Spacecraft charging and ion wake formation in the near-Sun environment

TL;DR

This study uses 3-D simulations to analyze spacecraft charging near the Sun, revealing conditions for negative potential formation and the impact of ion wakes, which are crucial for upcoming solar missions.

Contribution

The paper introduces a self-consistent 3-D modeling approach to understand spacecraft charging and ion wake effects in high photoelectron environments near the Sun.

Findings

Spacecraft can develop negative potential despite strong photoelectron currents.

Electrostatic barriers can reflect photoelectrons, causing negative charging.

Ion wakes can amplify negative potential and affect electron escape.

Abstract

A three-dimensional (3-D), self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characteristic energy of the escaping photoelectrons. All of these conditions are present near the Sun. The numerical solutions also show that the spacecraft's negative potential can be amplified by an ion wake. The negative potential of the ion wake prevents secondary electrons from escaping the part of spacecraft in contact with the wake. These findings may be important for future spacecraft missions that go nearer to the Sun, such as Solar Orbiter and Solar Probe Plus.