Small helium bath cryopump for electron optical devices Original Research Article

A small helium bath cryopump for electron optical devices has been designed and manufactured. The filling volumes of LHe and LN2 are 2.5 and 3.6 l, respectively. Special electron beam welding methods were utilised for the pump structure. The heat loads of the cryogens were minimised using numerical methods. An LHe refill interval of 30 days was reached, whereas that of LN2 is 6 days. Good agreement between the calculated and measured values has been found. An ultimate pressure of 3×10−7 Pa and a pumping speed better than that of a comparable ion pump were reached during a preliminary testing of pumping properties.