The first part of this project was dedicated to designing and constructing a new mass spectrometer with the ability to measure the elemental and isotope composition of a vapor in chemical and isotope equilibrium with a condensed phase contained in a Knudsen cell. It was decided that the new mass spectrometer would be fitted to a currently existing double focusing instrument equipped with a multicollection system, the Neptune Plus produced by THERMO Fisher Instruments. A key issue was to ensure that the sensitivity and stability of the instrument would be sufficient for precise isotope measurements. For this purpose, we have modeled the molecular beam transmission, the electron beam emitted by filaments facing each other and the ion beam extracted into the mass spectrometer with the aim of optimizing the molecular beam transmission, improving the electron focusing onto the molecular beam and enhancing the ion extraction and focusing. An optimization of these parameters was achieved in order to provide better performances compared with existing instruments. Our design resulted in an enhancement in the ion production and transmission by a factor of approximately 100. This means that it should be possible to obtain precise measurements of isotope ratios, given that the maximum gas pressure in the Knudsen cell is 10-4 bar. Several additional improvements were also made in the design of the instrument including in the cooling system, in the oven regulation and the pumping system. In parallel, a new mechanical design of the source housing and electronics has been initiated together with a specific software for controlling the instrument.
