Mass spectrometer beam system for applications in the stratosphere

Abstract

Mass spectrometer investigations in the stratosphere require a special gas inlet system in order to reduce the high ambient pressures to ion source operating pressures. This paper describes a system where pressure reduction is achieved by differential pumping using high-speed liquid helium pumps and small orifices. Ambient gas particles are formed into a molecular beam, with a flag mechanism allowing the separation of beam and background particles. Laboratory tests have shown that the system has the capability of identifying gases with abundances below 10−8. Many problems encountered in the gas analysis of trace constituents are reduced, such as adsorption and desorption processes of walls and memory effects of pumps.