An important medium for ion energization and non-thermal ions' energy release in the near-Sun solar wind: ion-scale waves

Ion-scale waves are typically characterized by frequencies near the proton cyclotron frequency, quasi-monochromaticity, propagating quasi-parallel or antiparallel to the background magnetic field, and left-handed or right-handed circular polarization in the spacecraft frame. In collisionless solar wind, one of the major mechanisms determining ion energization and non-thermal ions' energy release is wave–particle interactions of ion-scale waves. Recently, PSP's observations within 0.3 au suggest that there are plenty of ion-scale waves, which are closely related to non-thermal ions. Meanwhile, ion-scale waves (especially for Alfven/ion cyclotron waves) can be the energy source for energizing ions through wave-particle interactions. Therefore, ion-scale waves could be very important medium for ion energization and non-thermal ions' energy release in the mear-Sun solar wind.