A Refrigerator for Deep Cooling of Subterahertz Detectors for Radio Astronomy Research

A dilution cryostat is described, which is designed to carry out observations at dusk in the millimeter range on an optical telescope with a mirror with a diameter of 6 m, when observation in the optical range is still impossible. The cryostat, which cools the detector down to 0.1 K, is built according to the scheme of dissolving ³He in ⁴He with ³He circulation due to its condensation on a cold wall cooled by sorption pumping of pure liquid ³He from a separate volume. The working conditions are provided by the contact with the stabilizing unit, which accumulates 0.6 L of liquid ⁴He during active operation of a Gifford–McMahon refrigerator within the time between measurement cycles. During measurements, the refrigerator turns off, which completely eliminates vibrations that interfere with measurements.