A re-evaluation of the characteristics of the intermediate flow regime with simultaneous thermal accommodation has shown the full potential of the Cryogenic Diffusion Pump for Fusion Reactor applications. A device with a characteristic diameter of 1m will have a pumping speed of 150m3s−1 for Deuterium at an inlet pressure of 2 × 10−2 Pa (Reactor Burn phase) and 400m3s−1 at an inlet pressure of 0.1 Pa (Reactor Dwell phase). Simultaneously, it separates impurities, Hydrogen isotopes and Helium and compresses the Helium. The Helium compression ratio (already proven to be ≥25 for 3% Helium in D2) can be further enhanced by additional D2 or He driven Diffusion Pump and Ejector stages. The latter feature will also simplify pumping requirements for the Helium Glow Discharge scenario: recirculation of Helium at 0.1 Pa (driven by D2 or He Ejector) and simultaneous removal of DT and impurities by cryocondensation requires no mechanical pump at all or only small turbomolecular-drag pump combinations for He jet drive. The design offers superior tritium compatibility: all metal, fully bakeable, it avoids use of absorbers and argon for helium pumping, thereby reducing overall tritium inventory both in the pump itself and by replacing major fuel clean-up facilities. The advantages of using the Cryogenic Diffusion Pump in a Fusion Reactor Vacuum System are discussed in detail.
