ABSTRACT
The price of liquid helium has risen over the past few years due to several factors including the reserves at the Bureau of Land Management in the US becoming depleted. Any given refrigerator design includes a cost benefit analysis over the lifetime of the equipment. In recent years reliable 4 K coolers have become available and this has led to the situation where the use of closed-cycle refrigerators (or “cryocoolers”) is more likely to be considered.
