Simulations of xenon beam ions emitted from electric thrusters in Earth’s magnetosphere

Abstract

This study sought to characterize the behavior of exhausted electric thruster xenon ions in the near-Earth magnetospheric environment as functions of various trajectory and particle attributes, neglecting effects of electric fields, plasma waves and particle collisions. This was done via simulation using the AeroTracer program, a software tool which computes ion trajectories within the magnetosphere by applying an adaptive step-size Runge-Kutta technique to the fully relativistic Lorentz equation. Over 3,800 independent simulations were performed, with variables including release position, release energy and direction, ion charge, and orbital phase. Initial release altitude was a major driver in determining whether the ion eventually fell to Earth (“Below Minimum Altitude” or BMA), remained trapped by the simulation’s end (“Maximum Number of Steps” or MNS), or traveled beyond the magnetosphere (“Lost to Space” or LTS). Ions expelled at the highest altitudes investigated - 60,000 km and above - almost invariably were lost to space. Like altitude, increasing inclination and energy were important factors that reduced trapping, affecting the outcome probabilities. Higher charge state produced strong improvement of trapping capability. Effects of orbital phase, day of year and solar cycle phase were also apparent. A transition region was found in the 20,000 km to 60,000 km altitude range, within which the sensitivity of outcomes to parameter variation increased. The ordered sequence MNS> BMA> LTS was found to be consistent with decreasing confinement capability, and it was manifested consistently as parameters were varied.