Ion and neutral beam tracking with a microchannel plate array detector

Abstract

Microchannel plate array detectors (MPADs) are very useful in determining ion beam profiles, although complications can easily arise when voltage gradients which emanate from the device defocus approaching ions. High-energy neutral particles activate the MPAD with a sensitivity similar to ions, yet are unaffected by the voltage gradients. The auto-neutralization reaction ▪ provides a convenient and intense source of high-energy neutral particles useful for determining beam profiles. This unimolecular reaction occurs during a time span that allows for acceleration and focusing of the ion beam prior to auto-neutralization. The neutrals are produced with sufficient intensity to allow the neutral image to be viewed on an MPAD phosphor screen for an 8 cm drift region up to 2 m from the source at 7 kV. The neutrals give definitive beam profiles since they are unaffected by electric/magnetic fields and they are readily adapted to tracing ion beam images at various positions along the beam path. The application of neutral species as an aid in optimizing focusing in a sector mass spectrometer is discussed.