Study of the Proton Beam Parameters near the Sun

One of the commonly observed features of the solar wind is the simultaneous streaming of two different proton populations, one of which is the dominant denser core, and the other is the less dense and faster-propagating, minor population called the beam. The proton beam relative abundance is typically 10-20%, and the proton beam moves relative to the core along the interplanetary magnetic field at about 1.2 local Alfven speed. The origin and evolution of the proton beam is not yet fully understood.  A previous study based on data from the Helios mission suggests that the seed of the proton beam forms close to the Sun, leading to the observed correlation between the relative abundance of the proton beam and alpha particles. The Parker Solar Probe (PSP) mission, which has already achieved its closest approach to the Sun, gives us an opportunity to study the proton beam parameters near the solar wind source regions. We focus on the non-thermal features of the ion velocity distribution functions (VDFs) observed near the Sun by PSP. We investigate the mechanisms that change the proton beam parameters both in the initial phase of the solar wind expansion and on its way towards the Earth.