ON THE TRANSMISSION FUNCTION OF AN ION-ENERGY AND MASS-SPECTROMETER

The operation of a mass spectrometer system with an electrostatic ener gy analyser, designed for measurements of mass-resolved ion-energy dis tributions, is discussed. We show how the electric fields in the diffe rent electrostatic lenses present in the system can be optimized. Thes e lenses direct the ions entering the system into the energy filter an d the quadrupole mass filter. These lenses can exhibit chromatic aberr ation. The conditions without chromatic aberration have been found by simulating the ion trajectories in the part of the system up to the en ergy filter. Also, an experimental method is presented to find these s ettings. We show that the energy-dependent transmission of ions throug h the system is mainly determined by its acceptance angle. Ion-energy spectra from an argon plasma have been measured and corrected for the transmission of the ions through the system. Published by Elsevier Sci ence B.V.