Abstract: A focal plane detector assembly of a mass spectrometer includes an ion detector configured to detect ions crossing a focal plane of the spectrometer and an electrically conductive mesh lying in a plane parallel to the focal plane, positioned such that ions exiting a magnet of the mass spectrometer pass through the mesh before contacting the ion detector. The mesh is maintained at a low voltage potential, relative to a circuit ground, which shields ions passing through the magnet from high voltage charges from other devices, such as microchannel plate electron multipliers. The mesh may be mounted directly to the magnet or positioned some distance away. The detector array may include any suitable device, including a faraday cup detector array, a strip charge detector array, or a CCD detector array.

Abstract: A mass spectrometer suitable to measure both positive and negative particles, such as ions for example in a vacuum chamber. This spectrometer is provided with a turnable permanent magnet segment, which provides the gap of a yoke with adequate magnetic flux having the appropriate direction to separate the positive or the negative particles. Changing the polarity adjusts the flight path of the ions. Thus, negatively charged ions and positively charged ions will follow similar flight paths under opposite polarities, permitting the use of a single array of detectors. One or more coils may be used in place of or in addition to the turnable permanent magnet segment in order to provide the appropriate magnetic flux to the gap, and/or facilitate the turning process of the turnable magnet segment. The turnable magnet and/or the coils may be inside or outside the vacuum chamber.