第七届青年地学论坛

The Proton beam is an important population for solar wind kinetic physics but remains unclear for its roles in wave activity. Especially, the full vector of the proton beam bulk velocity and its influence on wave growth/dissipation has not been addressed before. We aim to explore the origin of kinetic wave events prevailing in the solar wind by analyzing the measurements from Solar Orbiter and comparing with the theoretical prediction of plasma wave theory. The observed ion-scale cyclotron wave event is identified to be outward-propagating unstable left-handed waves. Remarkably, the drift velocity vector between core and beam is not field-aligned as traditionally expected. Furthermore, it is found that the non-field-aligned fluctuating bulk velocity of the beam is responsible for the damping of unstable waves, while field-core interaction plays the opposite role in boosting the growth. At periods from 8 s to 100 s, the normalized residual energies (σ_r) of both components are larger than 0.5. The normalized cross-helicity (σ_c) is statistically positive for core while negative for beam. We unprecedentedly elucidate that the non-field-aligned beams exist and may stem from the dierences between the velocity fluctuations of the core and the beam. The core and the beam components have opposite eects on the wave growth: bolstering vs. restraining. Our perspective may shed new light on the energy conversion of coherent waves or turbulence by emphasizing the concerns of core and beam separately.