A Time of Flight mass analyzer is disclosed comprising an annular ion guide having a longitudinal axis and comprising a first annular ion guide section and a second annular ion guide section. Ions are introduced into the first annular ion guide section so that the ions form substantially stable circular orbits within the first annular ion guide section about the longitudinal axis. An ion detector is disposed within the annular ion guide. Ions are orthogonally accelerated in a first axial direction from the first annular ion guide section into the second annular ion guide section. An axial DC potential is maintained along at least a portion of the second annular ion guide section so that the ions are reflected in a second axial direction which is substantially opposed to the first axial direction. The ions undergo multiple axial passes through the second annular ion guide section before being detected by the ion detector.