Apparatuses and method are provided. For example, in one embodiment, a ring electrode includes a plurality of sub-rings adapted to provide an electric field inside a spectrometer. The sub-rings have an internal sub-ring radius. There is a ring insulator between adjacent sub-rings. Each said ring insulator has substantially the same internal radius as the sub-rings. In another embodiment, a method is provided for insertion of the ring electrode inside the spectrometer.