The xenon pumping speed testing system of the large-diameter external cryopump was designed to meet the plume test requirements for prototype electric propulsion. The flowmeter method was utilized to measure the xenon pumping speed. The test results show that the averaged effective pumping speed of double-cryopumps is 52200L/s

and that of single-cryopump is 27100L/s. The pumping speed ratio of two configurations is 1.93. It can be concluded that the pumping speed has in linear relationship with the number of cryopump

and the coefficient is irrelevant with the gas type. The averaged effective pumping speed of xenon is less than its nominal pumping speed

and the averaged pumping efficiency is 0.83. Under the identical inflow conditions

the averaged effective pumping speed ratio of nitrogen is 0.53

slightly less than the theoretical pumping speed ratio of 0.55. Consequently

it can be concluded that results assessment of large-diameter external cryopump design index can guide the engineering application

showing certain reference significance.