HIVAC, A Computer Code for the Monte Carlo Calculation of Molecular Flow in a High Vacuum System.

摘要

The HIVAC code calculates the gas conductance of cylindrical vacuum systems in the molecular flow regime. It is assumed that the mean free path is large compared to the dimensions of the vacuum system so the gas molecules interact with the vacuum conductor and not with each other. The algorithm is based on Monte Carlo methods, and transmission probabilities are first obtained by tracking a large number of molecules through the conductor as they collide with the walls. The collisional model assumes that the molecules first stick, then are re-emitted in a random direction weighted according to a cosine distribution. The conductance is obtained from the transmission probability by multiplying by the aperture conductance. Conductance values relate the gas throughput to the pressure drop across the vacuum conductor. They can therefore be used in other codes that simulate both transient and steady-state behavior of complete vacuum systems. The allowable geometries are described by a set of linked and nested cones and cylinders, an approach patterned after a similar code CHUBBY (Chubb 1966). This approach provides an easy way to model a wide variety of configurations having cylindrical symmetry. The following section describes the method and mathematical models. Next the implementation as a computer code is discussed, followed by instructions on the use of the code. The final section documents the verification and validation of the code. 5 refs., 7 figs. (ERA citation 14:023369)