Analysis of cooldown performance for ISABELLE helium refrigerator

The ISABELLE refrigerator was designed to provide cooling for 1000 superconducting magnets. It has the dual duty of providing cooling at steady-state operating conditions and to cooldowm massive magnets from ambient temperature. During the cooldown, tremendous quantities of heat must be removed from the magnets and 75,000 liters of cold helium must be supplied to fill the system. In the planning for ISABELLE, this procedure has been estimated to require approximately two weeks. Because of this long cooldown time and the fact that during cooldown the refrigerator will be operated quite differently from its steady-state design configuration, it is important to maximize the cooling capacity and identify the cooldown procedure.