Numerical modeling of the solar modulation of Helium isotopes in the inner heliosphere

The observation of cosmic ray Helium isotopes at the Earth had been done precisely with the PAMELA and AMS02 space detectors and reported from July 2006 to December 2007 and from May 2011 to April 2017, respectively. These available observations span time frames that include the solar magnetic field reversal epoch. In this work, a comprehensive, threedimensional numerical modulation model for the transport of cosmic rays in the heliosphere is utilized to compute the modulation of galactic Helium isotopes from minimum activity in the previous A < 0 cycle, through solar maximum, and toward minimum activity in the current A > 0 cycle. A particular objective is to reproduce the main features of the He-3(2) to He-4(2) ratio observed at rigidities between 2.15 GV and 15.3 GV. We find that the numerical model can reproduce the apparent single rigidity power law dependence and time dependence of this ratio above 4 GV in good agreement with observations.