Prolate trochoidal mass spectrometer

A prolate trochoidal mass spectrometer is a chemical analysis instrument in which the ions of different mass-to-charge ratio are separated by means of mutually perpendicular electric and magnetic fields so that the ions follow a prolate trochoidal path. These devices are sometimes called cycloidal mass spectrometers, although the path is not a cycloid (the prolate trochoid path has loops, the cycloid has cusps).

Source: Wikipedia — Prolate trochoidal mass spectrometer (CC BY-SA 4.0)