Development of a movable quadrupole mass spectrometer for measuring gas density

Abstract

A quadrupole mass spectrometer (QMS) with a specially designed analyzing head which was movable in a dynamic vacuum system was fabricated and the performance was tested. The head comprises a collimator and an airtight casing containing a rf tuning and its detection circuit. The rf circuit is tuned by supplying variable frequency of the rf voltage since the resonance frequency depends weakly on environmental temperature. This QMS can be obtain a normal mass spectrum for a mass range 1–50 amu even when the vessel is baked to 150 °C. The measured pressure rise of Ar is 1.08×10−5 Pa at a distance of 125 mm from the effusing nozzle of argon gas with a flow rate of 1.9×10−5 Pa m3 s−1, which is two times as large as the calculated value.