Stability and refrigeration of magnet cryosystems near 1.8 K using the thermomechanical effect

Superconducting magnets may exhibit a significantly increased critical surface when the operating temperature is lowered. It is also known that the stability associated with superconductor-coolant interaction is enhanced in superfluid Helium-4 (He II), provided the coolant ducts have been optimized. The use of He II has been promoted in several large systems. The authors have investigated magnet cryosystem options which utilize the thermomechanical effect (fountain effect) of He II and its inverse, the mechano-caloric effect, for refrigeration (called vortex refrigeration). Examples are presented for simplified thermodynamic state changes of cycle operation. Topics covered include heat leak utilization for the He II range and the quantification of vortex refrigeration.