An Efficient Damper of Thermal Oscillations for Two-Stage Pulse Tube Cryocoolers

We have developed a passive system to efficiently reduce the amplitude of temperature oscillations in low-frequency Pulse Tube (PT) cryocoolers. It consists of a small, well-insulated tank of liquid 4He, placed between the cold head of the PT and the user. As a result, we have been able to reduce the amplitude of thermal oscillations by a factor of 192, from 173 mK to 0.9 mK. The same damping efficiency can be obtained even if a thermal power of up to 100 mW is dissipated over it: the temperature oscillations remain consistently small as long as the Helium remains in its liquid phase. Even after its transition to the gas phase, the thermal oscillations continue to be stable, and despite increasing in amplitude by one order of magnitude, reaching 9 mK, they remain 19 times lower than those at the cold head of the PT. The advantage of this tool resides in the fact that it is a small, very compact sealed Helium reservoir, free of moving parts and external links.