Thanks to space-borne experiments of cosmic-ray ( CR ) detection , such as the AMS and PAMELA missions in low-Earth orbit , or the Voyager-1 spacecraft in the interstellar space , a large collection of multi-channel and time-resolved CR data has become available .
Recently , the AMS experiment has released new precision data , on the proton and helium fluxes in CRs , measured on monthly basis during its first six years of mission .
The AMS data reveal a remarkable long-term behavior in the temporal evolution of the proton-to-helium ratio at rigidity \R \equiv { p / Z } \lesssim 3 GV .
As we have argued in a recent work , such a behavior may reflect the transport properties of low-rigidity CRs in the inteplanetary space .
In particular , it can be caused by mass/charge dependence of the CR diffusion coefficient .
In this paper , we present our developments in the numerical modeling of CR transport in the Milky Way and in the heliosphere .
Within our model , and with the help of approximated analytical solutions , we describe in details the relations between the properties of CR diffusion and the time-dependent evolution of the proton-to-helium ratio .