Ion transmission studies of mulitple-sector isotope-ratio mass spectrometers

Theoretical and experimental studies were conducted to determine the ion transmission efficiency of multiple-sector isotope-ratio mass spectrometers with tandem magnets of normal geometry. The computer program GIOS (General Ion Optical Systems) was used to perform theoretical calculations of focusing properties and ion transmission efficiency. Actual transmission through multiple-sector instruments was determined from measurements of the ion beam vertical profile at the focus of each sector. Transmission was found to be strongly dependent on source filament geometry. The studies also determined a way to significantly increase ion transmission without changing the basic geometry of existing instruments. A cylindrical einzel lens located near the focus between the magnets provides vertical focusing of the ion beam without perturbing focal properties in the plane of mass dispersion. With a single V-filament ion source, a transmission increase from ∼75% to ∼100% was achieved. 19 refs., 17 figs., 2 tabs