The mass spectrometer includes a mass analyzer having a pair of planar electrode structures. The electrode structures are disposed opposite one another, parallel to one another, and axially offset from one another, and are structured to generate, in response to a common pattern of voltages applied to them, a cylindrically-symmetric, annular electric field surrounding a cylindrical central region. The electric field includes an annular axially focusing lens region surrounding the central region, and an annular mirror region surrounding the lens region. Ions injected tangentially in the central region towards the electric field reach an ion detector after executing a number of ellipse-like orbits, which enables a long flight path to be accommodated within a small evacuated space.