Adiabatic specific heat measurement at very low temperatures using GM refrigerator

Abstract

We have developed an adiabatic specific heat measurementt using a 4 K GM refrigerator system that can measure down to 1.3 K with exactly the same accuracy as liquid helium environmen. The cryogenic environment can be obtained by liquefying about 20 L of helium gas at room temperature into a 1 K pot by a cascade method and evacuating it with a rotary pump. The 1 K pot temperature reaches 1.2 K. The specific heat measurement probe is mounted on the 1 K pot and is covered with three radiation shields, and the helium liquefied in the 1 K pot is maintained for about 70 minutes after the refrigerator is stopped, and the 1 K pot temperature maintains below 1.5 K. In this state, the specific heat from 1.3 K to 10 K can be measured. By tightly fixing the adenda to the support (base), temperature fluctuations due to mechanical vibration of the refrigerator can be greatly suppressed, and above 2.5 K, specific heat measurement with almost the same accuracy as when the refrigerator is stopped can be performed. By combining these two types of measurements, we can measure the specific heat with exactly the same accuracy as in a liquid helium environment.