The role of magnetic flux rope in ion acceleration: MHD simulations and test particle tracing

Magnetic flux ropes (MFRs), playing a crucial role in particle energization andenergy transport in the solar-terrestrial space, are helical structures produced by magneticreconnection. It has been both theoretically predicted and observationally confirmed thatmagnetic flux ropes and associated pro cesses are inherently three-dimensional in space.How such complicated magnetic flux ropes modulate particle energization and transportin the Earth magnetosphere system has not been fully explored. In this study, an MHDmodel is used to examine the evolution of large-scale magnetic flux ropes in themagnetotail and a test particle model is further employed to study the associated ionenergization. Results show that magnetic reconnections take place at multiple X-lines inthe magnetotail current sheet, generating a twisted magnetic flux rope with a length ofabout 10 Re in azimuth. It propagates earthward following the tail reconnection but itseast and west wings are significantly distorted azimuthally. Test particle tracing revealsthat ions can be trapped within the rope while being effectively accelerated. The ropetherefore brings in energetic plasma sources into the inner magnetosphere as it transportsearthward. These results demonstrate that the magnetic flux rope is an important sourcecarrier for the ring current energization.