HELIUM CRYOPUMP FOR ELECTRON OPTICAL DEVICES DESIGN AND PRELIMINARY CRYOGENIC TESTING

摘要

A helium cryopump for electron optical devices was designed and preliminary cryogenic parameters of the first pump sample were tested. Low LHe consumption should enable economical operation of the pump without recycling the evaporated He. The pumping cryopanel is cooled by normal LHe down to 4.2 K. A LN2 bath is utilized for the LHe bath thermal shielding. Two additional heat radiation shields cooled by the vapours of the consumed cryoliquids are installed to decrease the LHe and LN2 losses. Three chevron screens placed between the input orifice and the cryopanel are used to protect the internal parts against direct heat radiation from the parts at ambient temperature. The chevron systems were replaced by low emissivity screens in the preliminary tests. Predicted low evaporation rates of LHe and LN2 were achieved.