Molecular beam detection using electron impact ionization
- 1 August 1974
- journal article
- Published by IOP Publishing in Journal of Physics E: Scientific Instruments
- Vol. 7 (8) , 627-634
- https://doi.org/10.1088/0022-3735/7/8/013
Abstract
Measurements of the ionization efficiency of an inverted cylindrical triode electron impact ionizer have been made on a fast atomic hydrogen beam (650-1250 eV), and are compared with a theory which postulates electron oscillations, which are treated on the assumption that the axial wire anode possesses calculable transmission factor. The electron space-charge configuration and its effect on the paths of the ions are treated quantitatively. The decrease of ionization efficiency with decreasing beam energy is explained as being primarily due to the ion-optical effect of the electron space-charge potential well. The ions formed in this well not only experience focusing, but in climbing out, suffer an energy defect. Energy analysis shows this to be proportional to ionizing current, 43 eV at 250 mA; the calculated value is 35 eV.Keywords
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