The Evolution of Beam Spot in the Geomagnetic Field During Long-Range Propagation of Relativistic Electron Beam

Research on the location and shape of a beam spot at a target altitude can lay the foundation for understanding and diagnosing the long-range propagation of relativistic electron beams. Only a few studies have focused on this approach. In this study, a terrestrial atmosphere with a 3-D geomagnetic field was constructed in accordance with the International Geomagnetic Reference Field model and a relevant atmosphere model. Monte Carlo simulations were applied to the long-range propagation of relativistic (1-10 MeV) electron beams in the altitude range of 200-300 km. The results showed that when beams with various parameters were emitted in one location, the centers of the beam spots were distributed in concentric circles with different radii. The direction of the geomagnetic field determined the locations of the circle centers, whereas the beam energy and pitch angle determined the radii. When the initial gyrophase changed, the center of the beam spot rotated through the same angle. The beam spot was distributed as a partial ring with a width mainly related to the initial beam radius when the energy spread was relatively small. If the energy spread exceeded the limit, the beam spot was ring-shaped; the ring width was determined by both the initial beam radius and the energy spread.