Neutral Mass Spectrometer (NMS)

Description

The objective of this investigation is to determine the chemical and isotopic composition and physical state of the Jovian atmosphere, including vertical variations from 0.1 to 10 bars or greater. Mixing ratios are determined for He to 1% accuracy and for H2O, CH4, and NH3 to 5% accuracy. The isotopic ratio of Ne20 to Ne22 is measured to an accuracy of 2%. All species with mass numbers 1 to 52, plus selected species at higher mass numbers (including krypton and xenon) are measured. The instrument is a quadrupole mass spectrometer with an electron impact ion source having redundant electron beam guns of variable kinetic energy and a secondary electron multiplier ion detector. The dual-channel sample inlet system includes an enrichment system for trace-gas and isotope determination, a tandem getter, and a sputter ion pump. The mass range is 1 - 52, 84, and 131 u. The dynamic range is 1.E+8. Other species with masses greater than 52 u can be sought at the sacrifice of integration time below 52 u. The scan period is 3 to 60 s. The instrument is mounted on the Probe with the sample inlet port near the stagnation point and the sample outlet port near the minimum pressure point. The total mass is 7.1 kg and the total power is 15 W.