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.