The focusing of an ion beam from a quadrupole mass filter using an electrostatic octopole lens

A new very simple method of focusing an ion beam from a quadrupole mass filter has been devised. Using an electrostatic octopole lens it is possible to obtain narrow, high-intensity, low-energy ion beams suitable for use in beam studies of ion-molecule reactions. Only two voltages are necessary to focus the beam unless operating near the space charge limit. It was found that beam intensities and angles are limited only by space charge effects. The system is very much easier to operate than a magnetic sector mass spectrometer and retarding lens, and its performance is equal to an in some respects better than that of the magnetic sector. (author)