Properties of Alpha Particles in Magnetic Switchbacks

Magnetic switchbacks, or sudden reversals in the radial direction of the magnetic field, are one of the more striking observations of Parker Solar Probe thus far in its mission, but their precise production mechanisms are still unknown. In this work the properties of alpha particles are studied inside and outside individual switchbacks. We find that there are no compositional differences in the alpha particle abundance ratio, Na/Np, inside vs outside. This supports recent theoretical work by Mallet et al which postulates that magnetic switchbacks are generated in-situ as a natural consequence of the non-linear evolution of Alfvénic fluctuations in an expanding Solar wind. In addition, we observe alpha velocity enhancements in switchbacks, albeit smaller than the corresponding ones seen in the protons. This is understood as being due to the interplay between the alpha-proton differential speed Vap and the Alfvén wave phase speed associated with the switchback Vw, with the Alfvenic motion of the alpha particles vanishing as the difference |Vw - Vap| decreases. Finally, the spherical motion of both the alphas and the protons about fixed points in velocity space singles out a wave frame. We examine how well experimentally the two species wave-frames agree, and their relationship to the de Hoffman-Teller frame.