Speaker
Description
The flux of Galactic Cosmic Rays (GCR) reaching the solar atmosphere is a key ingredient for studies of heliospheric modulation and secondary-particle production. The transport of charged particles in the interplanetary medium is commonly described by Parker’s transport equation (Parker, 1965), which provides the theoretical framework for diffusion, convection by the solar wind, gradient-curvature drifts, and adiabatic energy losses under the influence of the Interplanetary Magnetic Field (IMF). In this context, Seckel, Stanev, and Gaisser (1991) developed a seminal model for secondary-particle production by GCR interactions with the solar atmosphere, emphasizing the crucial role of magnetic-field effects in the transport of GCR toward the solar surface. Later, the model developed by Bobik et al. (2012) provided a refined treatment of GCR transport by solving Parker’s equation with rigidity-dependent diffusion coefficients and heliospheric conditions, allowing for a more accurate description of modulation across different energy regimes. In this work, we present an implementation of IMF diffusion processes using the Geant4 Monte Carlo simulation toolkit, aiming to model the transport of GCR with energies in the 1 GeV to 10 TeV range from Earth’s orbit to the solar surface. We use a Geant4 application developed by Tuneu et al. (2021) to implement the transport of charged particles in the presence of magnetic fields, based on the guiding-center approach, and extend it to include the effects of magnetic mirroring and gradient-curvature drifts, solar-wind modulation, stochastic magnetic turbulence through pitch-angle scattering, and adiabatic energy losses. The results of our simulations show that the inclusion of these transport effects suppresses the low-energy GCR flux compared to the purely ballistic case, while the heliospheric transparency increases progressively at higher energies. The resulting energy-dependent GCR flux at the solar atmosphere will be used as input for modeling gamma-ray emission from the quiescent Sun produced by GCR interactions.