Gasdynamic enhancement of hydrogen exhaust in Holweck stages via nitrogen entrainment

The efficient exhaust of light gases, particularly hydrogen isotopes, constitutes a critical bottleneck for Holweck molecular drag stages in applications ranging from fusion reactors to extreme ultraviolet lithography. The high thermal velocity of hydrogen drives severe back-diffusion that often overwhelms the weak rotor traction. To overcome the physical limits of conventional geometric optimization, this study proposes a gasdynamic entrainment strategy utilizing a heavy carrier gas (nitrogen) and investigates the underlying kinetic mechanisms using the Direct Simulation Monte Carlo method. A comprehensive parametric study reveals a non-monotonic dependence of hydrogen pumping performance on nitrogen concentration, identifying three distinct flow regimes: entrainment onset, sustained entrainment, and dilution dominance. Notably, the introduction of nitrogen significantly enhances hydrogen transport, reversing the net flux from a backflow state to a forward-pumping regime, with the mass flow rate increasing by orders of magnitude within the optimal window (30%–70% nitrogen molar fraction). Microscopic analysis of velocity distribution functions demonstrates that this enhancement is driven by vigorous cross-species momentum transfer, where heavy nitrogen molecules act as a kinetic moving boundary to drag light hydrogen molecules against the adverse pressure gradient. Furthermore, geometric optimization indicates that a spiral angle of 30°–35° maximizes this entrainment benefit by balancing Couette flow and leakage. These findings provide a physics-based pathway for designing robust hybrid vacuum systems for high-load light gas environments.