Proton basic data needed for electrohydrodynamic helium plasma modeling at sub-relativistic energies: Comparison with electron data

We present a complete dataset of collision cross sections for proton–helium interactions across the sub-relativistic energy range, from very-low energies (10−4 eV) up to at least 500 keV. The dataset includes elastic scattering (using quantal methods), charge transfer (quantum-mechanical molecular orbital close-coupling method), single ionization (Improved Empirical Formula for K-shell ionization model), and 23 electronic excitations (SE2PEAK model) up to principal quantum number n = 5. While momentum-transfer cross sections given in the literature vary between 0.1 and 104 eV, the present work extends the energy range down to 10−3 eV up to 500 keV and, crucially, integrates these elastic data within a unified framework that includes major inelastic channels—especially state-resolved excitation to triplet states (n = 2–4), which are absent in prior datasets. This full set of elastic and inelastic cross sections is then used as input for optimized Monte Carlo simulations to calculate transport and reaction coefficients for protons in helium over a wide range of reduced electric fields (E/N) from 0.1 to 104 Td. The resulting proton transport data are compared with electron transport data in helium calculated from a multi-term solution of the Boltzmann equation over the same E/N range. The comparison highlights the expected significant differences in the behavior of protons and electrons, primarily due to their mass disparity and distinct collision cross sections. The calculated transport coefficients (drift velocity or mobility, and transversal and longitudinal diffusion coefficients) and macroscopic collision frequencies for protons are presented vs E/N, revealing the dominant role of elastic collisions and charge transfer at low E/N and the onset of inelastic processes at higher values. These transport and reaction coefficients, given for the first time in the literature for such E/N range, provide a robust foundation for advanced electrodynamic modeling of electron–proton plasmas in helium, relevant for applications, such as fusion edge plasmas or electric plasma propulsion.