How do electrons close to Earth reach almost the speed of light?

In the Van Allen radiation belts, electrons can reach almost the speed of light. Researchers have revealed conditions for such strong accelerations. They had demonstrated in 2020: during solar storm plasma waves play a crucial role. However, it remained unclear why ultra-relativistic electron energies are not achieved in all solar storms. They now show: extreme depletions of the background plasma density are crucial.

from Top Technology News -- ScienceDaily https://ift.tt/39Iw1aM