Geant4 simulation for the responses to X-rays and charged particles through the eXTP focusing mirrors

A geometrical and physical model of Wolter-I type mirrors has been implemented in Geant4 for the design of the enhanced X-ray Timing and Polarimetry observatory (eXTP). It can simultaneously simulate the mirror responses to X-rays and charged particles. A new geometry class G4Hyperboloid is created and verified, which allows an exact surface profile description of Wolter-I optics. A physics model for the interaction of X-rays and matter is implemented to effectively estimate the focusing performances with reasonable accuracy, including the effective area and the point spread function. Scattering models of charged particles at grazing incidence are discussed. The multiple scattering model provided by the latest Geant4 release can be used instead of the single scattering model with reasonable accuracy and CPU cost when the step size is properly constrained.