Application of a high critical temperature superconductor bearing for high vacuum measurement

Abstract

A novel and ultrahigh vacuum compatible, high critical temperature superconductor suspension is described in its application to a rotating disc vacuum gauge. The noncontacting and robust suspension comprises a permanent magnet (and attached disc) suspended freely in a vacuum and below a liquid nitrogen cooled YBa2Cu3O7 pellet which is held outside the vacuum chamber. This configuration supersedes a fiber suspension. Molecular torque developed from a high speed disc accelerates the suspended disc and facilitates a measurement of total pressure. The offset of the superconductor suspension (analogous to that of the spinning rotor gauge) is about 5×10−6 mbar, nitrogen equivalent. After 50 h the offset reduced by up to 21% of its initial value. In the range 1.6×10−3–3.6×10−6 mbar, the pressure measured using this device was within ±20% of that measured by a spinning rotor gauge; at lower pressures the agreement with an ionization gauge degraded to ±80%. Improvements in pellet structure reduce internal losses in the bearing and in the offset term, by a factor of 10, and should enable measurements in ultrahigh vacuum.