LTS magnets are typically used and kept at 4K, but when being build or retrofitted they will be at ambient temperature. Cool-down at the factory or installation site can be done using LN2 and LHe, but this is an inefficient process involving a number of operational steps. This paper described how cool-down can be achieved simpler and more efficiently using a closed loop helium gas flow. In this concept no nitrogen gas is introduced in the LHe cryostat, while a temperature of less than 20K will be reached, which will limit the amount of LHe required. The helium gas is cooled by a cryocooler and circulated through the magnet using a high efficiency cryogenic fan. The temperature of this loop will gradually drop from ambient to final temperature. This will give maximum cooling capacity and efficiency of the cryocooler as it is kept at relatively high temperatures as long as possible. The challenge in the design of such a closed loop is the allowed cryostat pressure and connection sizes of each individual magnet design. These tend to be low and small, resulting in high volume flows and large flow losses. In this paper we describe the flow and heat exchange models we have designed to determine the most effective cooling loop for a certain set of parameters for an individual magnet design.
|Submitters Country||The Netherlands|