Heating and acceleration of charged particles during magnetic dipolarizations

Аннотация

In this paper, we analyzed the thermal and energy characteristics of the plasma components observed during the magnetic dipolarizations in the near tail by the Cluster satellites. It was previously found that the first dipolarization the ratio of proton and electron temperatures (T_p/T_e) was ~6–7. At the time of the observation of the first dipolarization front T_p/T_e decreases by up to ~3–4. The minimum value T_p/T_e (~2.0) is observed behind the front during the turbulent dipolarization phase. Decreases in T_p/T_e observed at this time are associated with an increase in T_e, whereas the proton temperature either decreases or remains unchanged. Decreases of the value T_p/T_e during the magnetic dipolarizations coincide with increase in wave activity in the wide frequency band up to electron gyrofrequency f_ce. High-frequency modes can resonantly interact with electrons causing their heating. The acceleration of ions with different masses up to energies of several hundred kiloelectron-volts is also observed during dipolarizations. In this case, the index of the energy spectrum decreases (a fraction of energetic ions increases) during the enhancement of low-frequency electromagnetic fluctuations at frequencies that correspond to the gyrofrequency of this ion component. Thus, we can conclude that the processes of the interaction between waves and particles play an important role in increasing the energy of plasma particles during magnetic dipolarizations.