APPLICABILITY OF THE RF-ONLY MODE IN A QUADRUPOLE MASS-SPECTROMETER FOR DIRECT ANALYSIS OF KEV IONS

This paper describes an applicability of a quadrupole mass spectrometer (QMS) for direct analysis of high energy ions up to 3 keV without decelerating fields. The QMS uses an rf-only mode in which only an rf voltage is applied to the quadrupole, although the conventional QMS applies the coincident de and rf voltages to the quadrupole. On the rf-only mode, the rf voltage is determined by a small triangular stability zone in the Mathieu stability diagram, where the point a = 0 and q = 7.547 in the a-q plane centers on the bottom of the triangle zone and the resolution of 104 is expected. The mass spectrum for air of 3 ke V ion beams was obtained on the rf-only mode, where the O-2 peak indicated the half-height resolution of 48. It was concluded that the rf-only mode is applicable for direct analysis of keV energy order ions, although further research to eliminate the conventional q < 0.9 related large peak is essential and the elimination will be realized using the pre-filter.