Classical modeling of positronium cooling in silicon nanochannel plates

Silicon nanochannel plates (NCPs) are employed in a variety of experiments as sources of cold positronium (Ps) via positron to Ps conversion. Despite the widespread use of NCPs, no comprehensive model of the dynamics of the cooling process of Ps within the nanochannels has been provided yet. In this work, we present a classical Monte Carlo model of Ps cooling produced in NCPs and validate it against experimental values present in the literature. Our model allows us to estimate crucial characteristics such as the cooling time in NCPs, the angular distribution of emitted Ps, and the fraction of Ps annihilating into three gamma quanta. The simulated energy spectra of emitted Ps closely match experimental results for NCPs held at room temperature. At cryogenic temperature the classical thermalization model does not accurately reproduce the measured spectra, which we attribute to a transition in the cooling process towards a regime where quantum effects play a significant role.