Simulation of Mercury-Driven Diffusion Pumps for Torus Exhaust Pumping

A new, continuous pumping train has been proposed for the European demonstration fusion power plant (DEMO). Mercury-driven linear diffusion pumps (LDPs) are suggested for use as high-vacuum pumps in this pumping train. In this work, we validate a 2-D simulation framework based on the direct simulation Monte Carlo (DSMC) method with experimental data of a two-stage mercury-driven LDP that was operated at the Lawrence Livermore National Laboratory (LLNL) in the 1950s. The simulation setup and assumed boundary conditions are described and their appropriateness discussed. Numerical results are compared to available experimental data for four different positions of the upper nozzle pipe. We find acceptable agreement between experimental and numerical results for the air pumping speed. This validation paves the way for using the simulation framework as a design and optimization tool in the further development process of the DEMO LDPs.