A Study On Trajectories Of Charged Particles With Arbitrary Pitch Angles In The Earth’s Magnetosphere

Plasma particle injection during geomagnetic storms and substorms has a great influence on space environment. This process leads to the ring current enhancement or decay, causes proton aurora, and influences the physical and chemical process of the upper atmosphere. More seriously, the enhancement of ring current will generates a induced potential on the ground surface and a geomagnetically induced current (GIC) in power transmission system. The DC current will lead to a "half-wave saturation" of transformer, and the transformer will be tremendously damaged and even burned by the heat produced by "half-wave saturation". Magnetic storm induced by the enhancement of ring current could cause huge damage of Power systems and economic losses, so the study of enhancement and decay of the ring current is significant.The conversion between open and closed orbits of charged particles and the acceleration of ring current charged particles are two important mechanisms of ring current enhancement. In this study, we will investigate trajectories of the ring current particles for different energy and pitch angle, and summarize the characteristics of the ring current particles trajectories. The UBK method is adopted to calculate the drift orbits of protons and electrons at different energies or pitch angles for the midnight (MLT= 0). The source region of the particles and the characteristics of the drift orbits are discussed on the basis of the numerical results. For pitch angle a= 90° and the trajectory passing L= 7, the protons drift around the Earth in the counterclockwise direction below ～2keV, in the clockwise direction above ～4keV, in the closed orbits above ～15keV. For pitch angle a = 90° and the trajectory passing L = 7, the electrons always in the clockwise direction, and in the closed orbit above 5keV. For pitch angle a = 90° and the trajectory passing L = 4, the orbits of protons are closed except for ～10 keV, indicating that protons originating from the plasma sheet at～10 keV stay closer to the Earth. For pitch angle a = 90。and the trajectory passing L = 4, all the orbits of electrons are closed. Protons with smaller pitch angles tend to move towards the dawnside. The higher the proton energy is, the smaller the influence of the pitch angle on the orbit is. Moreover, the pitch angle has little effects on orbits of electrons. For large Kp index, the variation of the trajectories of charged particles with energy is not obvious. The trajectories of charged particles with higher energy can be closed, and the trajectories through the same position in Kp= 1 condition are closer to the earth.