Double Focusing Mass Spectrometer
The double focusing mass spectrometer is a state of the art high resolution mass spectrometer (resolution m/Dm greater than 3000 at 1% peak height) with a high dynamic range and a good sensitivity. It is based on well proven design concepts which were optimized for mass resolution and dynamic range using modern methods for calculating ion optical properties.
The DFMS has two basic operation modes: a gas mode for analyzing cometary gases and an ion mode for measuring cometary ions. Switching between the gas and ion modes requires changing only a few potentials in the ion source and suppression of the electron emission that is used to ionize the gas. All other operations are identical for the two modes.
Figure 1 gives an overview of the DFMS. The three main parts are the ion source, the analyzer and the detectors. The instrument is housed in a vacuum-tight enclosure and will be thoroughly degassed by baking and launched under vacuum. The ion source region will be opened during the cruise phase to the comet by removing the protective cap. At the same time the analyzer section vent, pointing at free space, away from the comet and the ion source will also be opened.