Cryogenic cooling with cryocooler on a rotating system

Abstract

We developed a system that continuously maintains a cryocooler for long periods on a rotating table. A cryostat that holds the cryocooler is set on the table. A compressor is located on the ground and supplies high-purity (>99.999%) and high-pressure (1.7 MPa) helium gas and electricity to the cryocooler. The operation of the cryocooler and other instruments requires the development of interface components between the ground and rotating table. A combination of access holes at the center of the table and two rotary joints allows simultaneous circulation of electricity and helium gas. The developed system provides two innovative functions under the rotating condition, cooling from room temperature and the maintenance of a cold condition for long periods. We have confirmed these abilities as well as temperature stability under a condition of continuous rotation at 20 rpm. The developed system can be applied in various fields, e.g., in tests of Lorentz invariance, searches for axion, radio astronomy, and cosmology, and application of radar systems. In particular, there is a plan to use this system for a radio telescope observing cosmic microwave background radiation.

Status of the GroundBIRD Telescope

“…A stable long-term operation at 234 mK on the rotating table of 20 rpm is achieved and the detailed operation is described in Ref. [16]. The cryostat described above allows two mirrors in the Cross Dragone optics system to be at less than 4 K and the focal plane to be at 250 mK and a demonstration of such capability while the cryostat is under rotation of 20 rpm is shown in Fig.…”

“…The coldest head, labeled as He3U head reaches down to 234 mK when the cryostat is under rotation for long period. This is a clear demonstration of a stable operation of the cryostat under the 20 rpm rotation [16].…”

“…The two rotating structure [14] consists of two sets of tables and support structure. At the bottom of the tables, rotary joints for helium gas circulation and for electric power lines are mounted.…”

A compact rotating dilution refrigerator

“…This approach rules out using "dry" cryogen-free technology as this would involve a complex high pressure rotating seal in order to connect the rotating cryocooler to the bulky compressor in the laboratory frame (as used in Ref. 8). Also, our access to an in-house helium liquefier meant that a traditional "wet" system was the most effective and appropriate solution.…”

“…Furthermore, dynamic changes in rotation have also proven to be useful: turbulent vortex tangles can be created by impulsive spin-down 4,5 ; vortex waves 6 and vortex sheets 7 can occur when subject to an oscillatory component of rotation. The ability to rotate cryogenic apparatus can also be useful for some branches of astrophysics and particle physics 8 . Studies of superfluid 4 He under rotation now span over 60 years [9][10][11][12][13] .…”