A system for expressing an ion path in a time-of-flight (TOF) mass spectrometer. The present invention uses two successive curved sectors, with the second one reversed, to form S-shaped configuration such that an output ion beam is parallel to an input ion beam, such that the ions makes two identical but opposed turns, and such that the geometry of the entire system folds into a very compact volume. Geometry of a TOF mass spectrometer system in accordance with embodiments of the present invention further includes straight drift regions positioned before and after the S-shaped configuration and, optionally, a short straight region positioned between the two curved sectors with total length equal to about the length of the central arc of both curved sectors.