Helios alphafit plasma dataset v2.1

A data set which contains estimates of number density, velocity, and temperatures of the alpha particle population in the solar wind, along with proton beam fraciton estimates, created from systematic fitting of all the original Helios 3D distribution functions during the first perihelion pass of the Helios 1 spacecraft.

See the user guide at https://zenodo.org/record/2358793 for information on the variables.