Methods of speeding up the cool-down of superconducting magnets that are cooled using Small coolers at temperatures below 30 K

Abstract

The two primary ways of cooling superconducting magnets with small coolers are by conduction from the magnet to one or more the coolers cold heads through high thermal conductivity straps or by fluid flow through a thermal siphon cooling loop. Both methods have been used for cooling down magnets. The thermal siphon cooling loop can also be used to produce liquid helium or liquid hydrogen within the cooling loop. Over 85 percent of the cooldown time is used to cool a magnet coil from 300 K to 80 K. This is also true when a helium refrigerator is used to cool down a magnet. The primary reason for this is the magnet material enthalpy at 80 K is between 4 and 6 percent of the material enthalpy at 300 K. The cooler refrigeration increases with the cold head temperature, but the magnet material enthalpy increases more. If one wants to speed up the cool-down rate, one must remove the heat faster in the temperature range between 80 K and 300 K. Two primary methods for speeding up the cooldown of magnet that is kept cold using coolers will be presented.