| Autor: |
Bergin M; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., Ward DJ; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., Lambrick SM; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., von Jeinsen NA; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., Holst B; Department of Physics and Technology, University of Bergen, Allegaten 55, 5007 Bergen, Norway., Ellis J; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., Jardine AP; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom., Allison W; The Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom. |
| Abstrakt: |
The design of a high-efficiency mass spectrometer is described, aimed at residual gas detection of low mass species using low-energy electron impact, with particular applications in helium atom microscopy and atomic or molecular scattering. The instrument consists of an extended ionization volume, where electrons emitted from a hot filament are confined using a solenoidal magnetic field to give a high ionization probability. Electron space charge is used to confine and extract the gas ions formed, which are then passed through a magnetic sector mass filter before reaching an ion counter. The design and implementation of each of the major components are described in turn, followed by the overall performance of the detector in terms of mass separation, detection efficiency, time response, and background count rates. The linearity of response with emission current and magnetic field is discussed. The detection efficiency for helium is very high, reaching as much as 0.5%, with a time constant of (198 ± 6) ms and a background signal equivalent to an incoming helium flux of (8.7 ± 0.2) × 10 6 s -1 . |
