Recent developments in ion mass spectrometers in the energy range below 100 keV

The recognition that heavy ions often have similar or higher abundance than protons in space plasmas and the fact that ions with masses and/or charges larger than unity are ideally suited to test theories on origin, transport, acceleration, and loss of these plasmas led to the development of new and more sophisticated mass spectrometers during the last decade. The characteristics of several state-of-the-art instruments which have been flown or selected for missions will be discussed and aims for future developments will be given.