Performance of Zr–Al getter pumps under transient load conditions

Abstract

Testing of the pump limiter concept in the Impurity Study Experiment (ISX‐B) tokamak will involve the use of Zr–Al nonevaporable getter pumps capable of handling intermittent pulses of hydrogen and/or deuterium in the presence of carbon and oxygen impurity concentrations of several percent. To study the pumping characteristics under these conditions we have installed a Zr–Al cartridge pump in a vacuum chamber equipped with a fast gas puff feed system, a quadrupole residual gas analyzer, and a high speed ion gauge for transient pressure measurements. In this paper we report on the performance of the pump over a wide range of gas loads up to that sufficient to provide tens of monolayers of coverage of the getter surface. With flow rates up to 13 Torr l/s, pumping speeds for hydrogen were measured to be 1200–1500 l/s at pressures up to 10 mTorr. The measurements were carried out with gas pulses ranging in length from 50 ms to over 1 s and under conditions that provided a constant pumping speed for impurity species.