ADSORPTION OF HELIUM AT 4,2-K BY SOME ADSORBENTS USED FOR HE-3 PUMPING IN LOW-TEMPERATURE CRYOSTATS

A stand is developed to study the pumping characteristics of cryopumps for internal He-3 pumping in low-temperature cryostats. Isotherms of He-4 adsorption at 4.2 K were measured for three carbon adsorbents (co mmercial carbon SKT-4B, activated fibrous carbon AFC <<Dnepr>>, metall ized carbon BKTM). For three identical adsorption pumps with different adsorbents the speed of He-4 pumping is measured as a function of pre ssure and degree of the pump filling. The operation of these three pum ps is investigated under conditions close to those of their use in low -temperature cryostats for He-3 pumping.