JINR Dubna, KIREE and PGPI RAS Moskow
IAP RAS N. Novgorod,KPNPI RAS Gatchina
An Ultrahigh-Vacuum Nitrogen-Free Helium Cryostat for cooling of scanning tunneling microscopes
1 - Joint Institute for Nuclear Research;
2 -Institute of Radio Engineering and Electronics, Russian Academy of Sciences;
3 - Prokhorov General Physics Institute, Russian Academy of Sciences.
The designs of the cooling systems for ultrahigh- vacuum scanning tunneling microscopes (STMs) can be divided into four groups:
(1) flow-type cryostats [1,2]
(2) cooling systems based on closed-cycle refrigerators 
(3) coolant-filled cryostats with nitrogen jackets [4–5]
(4) coolant-filled nitrogen-free cryostats .A comparatively large amount of consumed cryogenic liquid—with the consumption of liquid helium reaching 1 l/h—is one of the disadvantages of flow-type systems. Cooling systems based on closed-cycle refrigerators show more promise, but their use causes a serious problem of a significant level of vibrations produced by a compressor (with a typical power of 5– 10 kW) and the cooling system itself. Cryostats filled with liquid coolants are quite compatible with ultrahigh- vacuum equipment. A drawback of conventional cryostats with nitrogen jackets is the vibration caused by boiling liquid nitrogen. This problem is absent in coolant-filled nitrogen-free cryostats, which, in our opinion, show promise for cooling STMs. The compact nitrogen-free helium cryostat described in  has a helium vessel volume of 2.9 l and can continuously operate for 48 h. The design of a compact ultrahigh-vacuum nitrogen-free helium cryostat is described. The volume of its helium vessel is 2.7 l, and the continuous operational life exceeds 65 h. This cryostat is intended for performing scanning tunneling spectroscopy at low temperatures under ultrahigh-vacuum conditions.
Production of cryostats for research and applied sciences.