Transformation of a Double Focusing B-E Mass Spectrometer for Multiple-Cell Knudsen Effusion – Part I: Scientific Concepts

Abstract

Knudsen Effusion Mass Spectrometry (KEMS) is a powerful method in the field of experimental thermodynamics at high temperatures. Since 2005, the long term project of transforming and upgrading a double-focusing VG Micromass 54-38K mass spectrometer for multiple-cell effusion has started at the IM2NP in Marseille/France. The scientific concepts underlying the transformation are presented in this first paper. The molecular beam effusing from the Knudsen cells must be sampled under restricted collimation conditions. The resulting geometric constraints are taken into account in the design of the large main vacuum chamber necessary to house a multiple-cell effusion furnace. Decrease of the molecular transmission between the cell and the ionization source needs to be counterbalanced by an increase in the sensitivity of the ionization source. Other modifications of the instrument are reviewed. The first tests and results will be the subject of a second paper to be published.