Linde Kryotechnik (LKT) is developing helium refrigeration systems capable of handling an increasingly wide range of heat loads at various temperatures. Cold turbomachinery is often used to either establish the system pressure (e.g. in a sub-atmospheric cryostat) or to generate helium circulation in isolated cooling loops subjected to strong transient loads. Specifically, cold compressors, cold turbo blowers and cold circulators are key components that enable these demands to be met in a thermally and cost-efficient matter. 
Cold compressors are used for plants with sub-atmospheric loads below the lambda point. A cold compressor string, typically consisting of three to four cold compressors arranged in series, performs a pre-compression of very low pressure (15–35 mbar.a) return flows, enabling them to be effectively processed in heat exchangers of a Claude/Brayton process. On the one hand, this allows effective cooling of high?pressure supply flows and improves the overall plant efficiency. On the other hand, the higher return?flow density reduces the required capacity of vacuum pumps or warm compressors. 
Cold turbo blowers typically operate with a pressure ratio of 1.1-1.3, significantly lower than the pressure ratio of 3-4 achieved by the cold compressors. However, they can be used to slightly compress the cold return flow and set the cryostat pressure independently of the warm compressor, providing more flexibility to the cryostat operations. Additionally, they enable larger pressure drops in the return lines, permitting the use of smaller vacuum?insulated transfer?line diameters and thereby reducing cost and space requirements. 
Fusion reactors require cryogenic infrastructure that can provide multiple cooling capacities and respond efficiently to both transient heat loads and fluctuating return temperatures. To address these challenges, cooling loops independent of the primary cycle are implemented. Cold Circulators ensure the required flow rates within these loops. 
In this presentation, the applications of these machines will be illustrated and discussed through three representative LKT projects.

Keywords
Cold Compressor|Cold Turbo Blower|Cold Circulator|Large Helium Refrigerator