Jarrod Santo Bianco, The University of Texas at Austin

"Simulating Alfvén Wave Collapse and Wave-Particle Interactions in the Solar Wind"

Abstract: Field aligned proton beams drifting with respect to the core proton population at the local Alfvén speed have been commonly observed in the Alfvénic solar wind at distances from the sun, R>0.3 AU. Interestingly, observations by Parker Solar Probe have shown that proton beams are far more common than previously thought. Closer to the sun, beams can also achieve drift speeds exceeding the Alfvén speed, possibly triggering kinetic instabilities. Understanding the origin, evolution and stability of proton beams in the solar wind, and how they interact with waves and fields, is fundamental in understanding solar wind dynamics and heating. In this work, wave-particle interactions mediated by the collapse of an Alfvén wave are investigated with a hybrid Particle-in-Cell (PIC) code that mimics dynamical effects introduced by the solar wind radial expansion. Starting with an amplitude-modulated Alfvén wave, I will show that the Alfvén wave undergoes a local collapse leading to the formation of a field-aligned beam drifting at the Alfvén speed. I will discuss the initial wave collapse and how the radial expansion of the wind affects wave-particle interactions over long time scales. We finally discuss remaining open questions and future work.