Solar Orbiter Observations of Proton and Alpha Particle Kinetic Signatures Related to the Presence of Switchbacks in the Inner Heliosphere: A Case Study

Abstract We investigate how ions, namely protons and alpha particles, kinetically react to the presence of strong deflections in the magnetic field, the so-called switchbacks, in the first stream of slow Alfvénic wind observed by Solar Orbiter at the heliocentric distance of 0.64 au. We focus on an isolated, large-scale switchback, and we study in detail ion kinetic properties. Beyond the expected correlation between the magnetic deflection and ion velocity related to the Alfvénic nature of the switchbacks, we find that, within the switchback, proton and alpha particle densities increase, suggesting ongoing wave activity. Very interestingly, we observe a clear correlation between the magnetic deflection and alpha particle temperature, while no correlation has been found with proton temperature. This is an indication of a possible role played by switchbacks in preferentially heating heavy ions. Our results suggest that the presence of switchbacks can induce a deformation of the proton velocity distribution function, while the preferential heating of alpha particles could be due to a denser secondary beam and a smaller relative drift speed between the beam and core.