Development of a Low-Temperature Helium Blower

A helium blower that can pre-cool superconducting magnets with helium gas at a temperature of 80K was developed. The blower incorporates self-acting gas journal bearings, Rayleigh step-type thrust bearings, a variable-speed induction-motor drive, and a backward impeller. The performance of the blower was measured in a vacuum chamber containing a tank of liquid nitrogen and two heat exchangers. Tests results show that pressure ratio is more than 1.2 and adiabatic efficiency is 61% at design point (mass flow rate of 0.005kg/s and rotational speed of 130, 000rpm). Moreover, for testing bearing reliability, the blower shaft could be successfully driven at up to 148, 300rpm and a start-stop test was done more than one hundred times, but there were no troubles with the shaft or bearings.