Development of a mass spectrometer using two rotating electric fields

The authors propose a new principle for a mass analyzer involving a pair of rotating electric fields (REFs). Its design is reviewed from the perspectives of electronics, ion optics, and operating principle. The use of REFs to separate ions by mass was demonstrated by introducing a Ga focused-ion-beam column directly into the REFs optical system. By optimizing the system phase contrast, the 69Ga+ ions were made to converge to the central axis while the 71Ga+ formed an annular pattern. Asymmetries in annular patterns are caused by nonuniformity in the alternating current voltage of each REF electrode. By varying the frequency, the locations of the 69Ga+ and 71Ga+ projections can be exchanged between the center and exterior.