The connection of refrigeration to a superconducting magnet with a minimum amount of cryogen

Abstract

The shortage of helium, particularly liquid helium, has made the use of cryogen free magnets attractive. The attractiveness of cryogen free magnets depends on the operating temperature of the magnet, the distance from the cold head to the magnet being cooled, the thermal conductivity of the connection and the size of the magnet being cooled down. Connecting a cold source to something being cooled can be like connecting a vacuum pump to a magnet through a pipe. This paper discusses cooling down and cooling a magnet that operates over a temperature range from 4 K to 80 K using coolers. Two approaches are discussed. The first is by conduction through high thermal conductivity metal straps. The second is by using a natural convection thermal-siphon cooling loop. The thermal siphon cooling loop can operate like a cryogen free magnet where all the fluid is stored in the cooling loop.