Assessing prediction robustness in atmospheric helium plasma models under rate coefficient uncertainties

Uncertainties among published rate coefficients for key plasma chemical particle production and destruction reactions often affect the predictive reliability of helium plasma models at atmospheric pressure. In this study, we assess the reliability of model predictions for a helium microdischarge given the existing uncertainty in the literature. A one-dimensional, current driven fluid model is applied to a 1 mm plane parallel discharge operated from 10 to 100 mA. The baseline helium chemistry set is systematically altered by replacing individual reactions with alternative literature rate coefficients in a one factor at a time sensitivity framework. The analysis tracks both basic plasma parameters such as discharge current–voltage characteristics, electron density and temperature, gas heating, and helium species quantities such as helium excited metastable, excimer, and atomic and molecular ions. The results show a clear asymmetry in robustness. The partitioning among excited and ionic helium species is often highly sensitive to the selected rate coefficients, however, the macroscopic discharge characteristics remain comparatively stable across most of the investigated cases. The strongest non-interchangeable reactions are those governing direct and stepwise ionization, electron assisted recombination, ion conversion, and excimer formation. By contrast, several radiative and superelastic channels are effectively negligible within the present operating range. A further comparison of simple, full, and extended helium mechanisms shows that chemistry completeness affects not only quantitative predictions but also qualitative trends in metastable, excimer, and ion populations. Within the present mechanism-level comparison, the extended mechanism gives a more internally consistent high-current balance, although this behavior reflects the combined effect of several added reaction groups rather than mechanism completeness alone. These results identify robust and data-limited predictions of the pure-helium kernel and reaction classes requiring refinement. For impurity-containing plasmas, the rankings offer indirect guidance, since quenching, Penning ionization, charge transfer, and molecular-ion chemistry may alter sensitivities.