Alfvén waves in the solar corona: resonance velocity, damping length, and charged particles acceleration by kinetic Alfvén waves

Abstract

Abstract Recent advances in heliospheric exploration spurred by NASA’s Parker Solar Probe (PSP) mission require a deeper understanding of the intricate dynamics of the solar corona and wind. This study provides a detailed examination of kinetic Alfvén waves (KAWs) within the $$0 - 10$$ 0 - 10 RSun range, a region only briefly explored in future PSP passages. Employing the framework of kinetic plasma theory and incorporating a non-thermal Cairns velocity distribution, we investigate the impact of the non-thermal index parameter $$\Lambda$$ Λ on the resultant resonance velocity $$\mathrm {v_{res}}$$ v res . The results reveal a notable change in the distance (RSun) over which the particles transport energy and the magnitude of resonance velocity for $$\Lambda >0$$ Λ > 0 . We also derive the perpendicular resonance velocity $$\mathrm {v_{res\perp }}$$ v res ⊥ and the group velocity $$\mathrm {v_g}$$ v g expressions of particles and KAWs, respectively. We find that $$\mathrm {v_{res\perp }}$$ v res ⊥ and the normalized group velocity $$\mathrm {v_g}/\mathrm {v_A}$$ v g / v A are significantly influenced by $$\Lambda$$ Λ . In contrast to the resonance speed and group velocity, the damping length $$\mathrm {L_D}$$ L D of KAWs is evaluated for different parameters. We find that KAWs experience accelerated damping and exhibit an increased damping length for $$\Lambda >0$$ Λ > 0 . We evaluate KAWs by the influence of the magnetic field, variation in height relative to the solar radius RSun, and the electron-to-ion temperature ratio $$\mathrm {T_e}/\mathrm {T_i}$$ T e / T i . Collectively, these findings illustrate that KAWs not only are important for heating processes but also accelerate charged particles across considerable distances within the solar corona and solar wind regions. The analytical insights gleaned from this study find practical application in understanding wave phenomena in the solar and heliospheric regimes, particularly exploring the role of non-thermal particles in observed heating processes.