Recently, the Astrophysical Journal published the latest numerical work on the particle acceleration. Dr. LI Yan from Yunnan Observatories of the Chinese Academy of Sciences and his cooperators investigate the acceleration process of charged particles in the turbulent magnetic reconnection current sheet, and give some new results of particle acceleration.

Solar flare is the most violent energy release process in the solar atmosphere. Observations show that high-energy non-thermal particles account for 10% - 50% of the released energy. The induced electric field generated by magnetic reconnecting current sheet is an effective mechanism to accelerate high-energy particles. However, long current sheet is usually unstable and highly turbulent, which will produce various plasma instabilities, most notably the formation and merger of magnetic islands. The motion of charged particles in this electromagnetic field structure is very complex, and the details of acceleration are still unclear.

Researchers performed 2.5-dimensional magnetohydrodynamic (MHD) simulations of magnetic reconnection taking place in the coronal current sheet, and obtain the self-consistent electromagnetic field at different times, with high spatial resolution and time cadence. Then, researchers looked into the motion of electrons and protons and studied in detail the dynamics of both particles via the test-particle approach.

Their results show that the energy spectra of protons and electrons that possess a single power-law shape were deduced for various phases of the magnetic reconnection process. The evolution of the spectrum shows a soft-hard-soft pattern that has been observed in flares.

For the motion of the magnetic island, it yields the occurrence of the opposite electric field at both endpoints of the island; hence, tracking the accelerated particles around magnetic islands suggests that the parallel acceleration does not apparently impact the energy gain of particles, but the perpendicular acceleration does.

On the other, the impact of the guide field on the motion pattern of both protons and electrons is not apparent, unless those particles could be accelerated to fairly high energy.

This research helps us to better understand the charged particles acceleration in turbulent magnetic reconnecting current sheet.

Contact:
LI Yan
Yunnan Observatories, CAS
Email: liyan821@ynao.ac.cn