AVS 71 Session VT-TuA: Novel Vacuum Methods and Application

In the simulation of molecular flow through complex vacuum geometries, the transmission probability is a key parameter, particularly when modeling systems with surface adsorption or desorption effects, such as NEG-coated pipes or cryogenic beamlines. Traditionally, calculating the impact of varying sticking coefficients on transmission requires separate Test Particle Monte Carlo (TPMC) simulation runs for each coefficient, posing a significant computational burden often exceeding many hours of computation time in simulation frameworks like Molflow+.

We present a novel approach that enables the extraction of transmission probabilities for arbitrary sticking coefficients using only a single TPMC simulation conducted with zero sticking (s = 0). This method leverages the statistical distribution of particle bounces before exiting the system. By recording the number of wall interactions for each particle in a single simulation and applying a bounce-weighted exponential scaling factor of the form (1 - s)^N, we can reconstruct transmission probabilities for any s with high accuracy.

This methodology was validated using Molflow+ in an elbow-shaped vacuum geometry. The resulting predictions for various s-values closely matched full simulation results, confirming the reliability and computational efficiency of this approach. This technique enables rapid conductance analyses significantly reducing the total computation time to few minutes and supports more efficient vacuum system design across a wide range of applications.

Helium-3, implanted into lunar regolith by the solar wind, represents a resource with transformative potential: a $17 trillion annual market spanning future nuclear fusion and quantum computing applications. Unlike terrestrial mining, any attempt to recover helium-3 and other volatiles must operate entirely within the hard vacuum of the lunar surface. There is no atmosphere for heat transfer, no fluid dynamics to aid separation, and abrasive dust complicates all surface interactions. These realities mean that lunar resource recovery is not simply a mining challenge, but fundamentally a vacuum science and engineering problem. Approaches to heating, capturing, and storing gases must be compatible with an environment where vacuum is not a laboratory condition but the baseline operating medium. This presentation will frame helium-3 extraction as a problem domain where vacuum expertise is essential. The goal is to highlight the scale of the opportunity, the centrality of vacuum in making it possible, and the need for collaboration between the space resource and vacuum science communities to advance solutions.