Molecular beam facility for studying mass spectrometer performance

An apparatus is described which produces neutral gas beams in the velocity range from thermal to 6 km/s. This facility makes possible studies simulating the motion of instruments through tenuous atmospheres. The use of the apparatus in studying the response of an open-source mass spectrometer similar to those carried on high-speed spacecraft, such as earth satellites or planetary probes for investigating ambient atmospheric composition, is examined. Experiments performed included ones of response of an open source mass spectrometer when: (a) the instrument was in a normal mode of operation; (b) the instrument’s ion source potentials were adjusted so as to reject gas particles which struck instrument surfaces; (c) the gas beam was restricted so that selected portions of the ion source were struck; and (d) the gas beam struck the ion source at angles other than normal incidence.