Abstract
Tracing magnetic field-lines of the Earth's magnetosphere using beams of relativistic electrons will open up new insights into space weather and magnetospheric physics. Analytic models and a single-particle-motion code were used to explore the dynamics of an electron beam emitted from an orbiting satellite and propagating until impact with the Earth. The impact location of the beam on the upper atmosphere is strongly influenced by magnetospheric conditions, shifting up to several-degrees in latitude between different phases of a simulated storm. The beam density cross-section evolves due to cyclotron motion of the beam centroid and oscillations of the beam envelope. The impact density profile is ring shaped, with major radius $\sim 22$ meters, given by the final cyclotron radius of the beam centroid, and ring thickness $\sim 2$ meters given by the final beam envelope. Motion of the satellite may also act to spread the beam, however it will remain sufficiently focused for detection by ground-based optical and radio detectors. An array of such ground stations will be able to detect shifts in impact location of the beam, and thereby infer information regarding magnetospheric conditions.
Highlights
The injection of artificial electron beams into the Earth’s magnetosphere has proven to be a powerful diagnostic tool for studying the physics of the magnetosphere, ionosphere and upper atmosphere (Winckler, 1980)
The section begins by studying the motion of a single electron with energy E0 injected onto a dipole field line until it impacts with the Earth
A single electron beam pulse consists of 100 minipulses and total pulse time of Tp = 0.5 s. At these time scales it becomes important to consider the motion of the electron gun platform. If this platform were to remain stationary during firing, the impact density distribution would appear similar to that of a single mini-pulse; since the accelerator is attached to a moving satellite, the beam impact location will be smeared out, as each mini-pulse is injected onto a slightly different field line
Summary
The injection of artificial electron beams into the Earth’s magnetosphere has proven to be a powerful diagnostic tool for studying the physics of the magnetosphere, ionosphere and upper atmosphere (Winckler, 1980). It has been proposed that relativistic electron beams could be an ideal diagnostic for field-line tracing within the magnetosphere, assisting in the validation and development of advanced magnetospheric models. Such a diagnostic may provide additional insights via the active modification of the space-plasma environment (National Research Council, 2013). Attached to an orbiting satellite, such a compact linear accelerator could launch relativistic electrons onto various field lines of the magnetosphere over a range of magnetospheric conditions. Electrons launched from the satellite will trace the field-lines of the magnetosphere until precipitation in the upper atmosphere.
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