Development of 2K Cryostat

A Pool type Liquid Helium Cryostat for operating down to 2K was designed at CCDS. In this, the temperature of liquid helium, which has a normal boiling point of 4.2K is brought down further by pumping over the liquid. (Cryostat is a specially designed container to keep liquids of very low temperature, typically below –150° C).

This system operates under sub-atmospheric conditions. Apart from efficient thermal design to minimize heat in-leaks through different mechanisms, there are several technical issues which are required to be tackled in making a cryostat of this type.

This cryostat was fabricated by a local fabricator. It was first tested at normal liquid helium temperature (4.2K). Heat in-leak calculated from the boil-off was less than 70 mW. These values of heat in-leak, match closely with the values reached during the designed stage.

2K Temperature was reached in about 36 min after starting the evacuation pump at 4.2 K. We started with about 08 liters of liquid in the cryostat, and when we reached 2K it was still left with about 4.5 liters. After reaching 2K the helium boil-off was quite low for cooling from 2K to 1.7 K, as the self heat load of the cryostat to the 2K liquid chamber is about 70mW. In next hour only about 0.5 litres got boiled to maintain 1.7 K in the cryostat. This cryostat will be used among other to calibrate cryogenics temperature sensors in 4.2 to 1.8 K range.

2K Cryostat developed at CCDS

Pump for reducing the pressure was started at 13:25 hrs. After 37 min from start up 2K was reached. Lowest temperature 1.69 K was reached in 1 hr 35 min from starting the pump. (Data reproduced form experiment conducted on August 18, 2010).

More Links:
Reaching 2K using Liquid Helium