Design and performance assessment of cold compressor for a typical cold box of large tokamak machines

Abstract

The Cold Compressor (CC) is used to lower the saturation temperature of liquid helium (LHe) under varying heat load conditions from the application side, i.e. superconducting magnets and cryopumps for large Tokamak machines. The CC is a key component of a typical cold box, attached to the LHe bath, which compresses and transfers the vapor generated during the heat exchange via heat exchangers as well as the flash generated downstream from the Joule-Thomson (JT) valve connected to the cryoplant. The emphasis of the present paper is a conceptual design and performance assessment of the CC. The CC is designed to pump 0.33 kg/sec of 4.2 K saturated helium vapor at a pressure ratio of 1.39; with an off-design range of 0.2–0.5 kg/sec. Operating speeds are between 10 and 25 krpm, with a speed of 17 krpm at the design point. Due to different heat loads from superconducting magnets and cryopumps, different process pressure and flow rates of the CC for large tokamak machines are expected. Hence, as an important component of the CC, the impeller design with blade profile generation has been carried for the higher thermodynamic efficiency of the CC. Characteristics curves of the CC have been obtained at different speed values. Analysis has been carried out using computational fluid dynamics (CFD) tool to analyze various situations during real operation.