Effect of Field-Line Curvature on the Ionospheric Accessibility of Relativistic Electron Beam Experiments

• Main Authors: Jake M. Willard, Jay R. Johnson, Jesse M. Snelling, Andrew T. Powis, Igor D. Kaganovich, Ennio R. Sanchez
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2019-08-01
• Series: Frontiers in Astronomy and Space Sciences
• Subjects: beam injection from space; field-line mapping; accessibility; loss cone; field-line curvature; energy-variable accelerator
• Online Access: https://www.frontiersin.org/article/10.3389/fspas.2019.00056/full

Magnetosphere-ionosphere coupling is a particularly important process that regulates and controls magnetospheric dynamics such as storms and substorms. However, in order to understand magnetosphere-ionosphere coupling it is necessary to understand how regions of the magnetosphere are connected to the ionosphere. It has been proposed that this connection may be established by firing electron beams from satellites that can reach an ionospheric footpoint creating detectable emissions. This type of experiment would greatly aid in identifying the relationship between convection processes in the magnetotail and the ionosphere and how the plasma sheet current layer evolves during the growth phase preceding substorms. For practical purposes, the use of relativistic electron beams with kinetic energy on the order of 1 MeV would be ideal for detectability. However, Porazik et al. (2014) has shown that, for relativistic particles, higher order terms of the magnetic moment are necessary for consideration of the ionospheric accessibility of the beams. These higher order terms are related to gradients and curvature in the magnetic field and are typically unimportant unless the beam is injected along the magnetic field direction, such that the zero order magnetic moment is small. In this article, we address two important consequences related to these higher order terms. First, we investigate the consequences for satellites positioned in regions subject to magnetotail stretching and demonstrate systematically how curvature affects accessibility. We find that curvature can reduce accessibility for beams injected from the current sheet, but can increase accessibility for beams injected just above the current sheet. Second, we investigate how detectability of ionospheric precipitation of variable energy field-aligned electron beams could be used as a constraint on field-line curvature, which would be valuable for field-line reconstruction and/or stability analysis.