Comparison of properties of the solar wind helium component close to the Sun and at 1 AU

The relative helium abundance (AHe) and alpha-proton relative drift often serve as one of the solar wind source identifiers. However, observations at 1 AU suggest that these relative properties may be affected by the interaction of different solar wind streams. Since the influence of stream interaction is reduced near the Sun, a comparison of observations at 1 AU and close to the Sun could help to reveal the processes which lead to AHe variations. In-situ measurements near the Sun are provided by the SWEAP instrument onboard Parker Solar Probe. It consists of electrostatic analyzers (SPANs) and the Faraday cup (SPC). SPAN-Ai measures the 3-D ion distribution from the shadowed region behind the spacecraft thermal shield and is equipped with a mass-to-charge detection. SPC is directed to the Sun and provides fast measurements of the ion reduced distribution function (RDF) as a function of energy/charge. We develop a new data analysis technique for computations of the proton and helium parameters from the RDFs measured by SPC and compare it with SPAN observations. Then, we combine the PSP measurements with observations at 1 AU and focus on variations of the helium properties. Finally, we discuss the connection between AHe variations and changes of the solar wind source region.