Abstract
Using the plasma data measured in-situ in the inner heliosphere (Helios 1 and 2), we focus on the proton beam development with an increasing radial distance from the Sun as well as on the connection between the proton beam parameters and the α core properties. We found that the relative content of α core is correlated with the relative proton beam abundance, and this effect is more pronounced in the fast solar wind streams during solar maximum.
Since the fast wind is expected to come from distinct source regions, coronal holes, the connection between the α core and proton beam could indicate that the coronal holes are able to produce different types of the fast solar wind streams. On the other hand, in the collisionally old slow solar wind, merging of the proton beam with core is observed.
In the parameter space of the α-proton core relative drift and the relative proton beam abundance, we distinguished two regimes and observed transition between them for the intermediate streams. We proposed two different scenarios of how the proton beam could be reduced.
First, the protons in the intermediate streams could be heated via the alpha/proton magnetosonic instability and initiate the proton core and beam merging. Second, the proton beam could be reduced in order to balance the total ion momentum in the solar wind frame.