A mass spectrometer comprising: a chamber; an injection device adapted to inject charged particles into the chamber; field generating apparatus adapted to establish: at least one field acting on the charged particles, the at least one field having: an angular trapping component configured to form at least one channel between a rotation axis and the periphery of the chamber, the at least one channel being defined by energy minima of the angular trapping component, the field generating apparatus being further adapted to rotate the angular trapping component about the rotation axis, whereby in use charged particles are angularly constrained along the at least one channel by the angular trapping component to rotate therewith, a centrifugal force thereby acting on the charged particles; and a radial balancing component having a magnitude increasing monotonically with increasing radius from the rotation axis, at least in the vicinity of the at least one channel, whereby in use charged particles move along the at least one channel under the combined influence of the centrifugal force and the radial balancing component to form one or more particle orbits according to the charge to mass ratios of the particles; and a detector configured to detect at least one of the particle orbits. a chamber; an injection device adapted to inject charged particles into the chamber; field generating apparatus adapted to establish: at least one field acting on the charged particles, the at least one field having: an angular trapping component configured to form at least one channel between a rotation axis and the periphery of the chamber, the at least one channel being defined by energy minima of the angular trapping component, the field generating apparatus being further adapted to rotate the angular trapping component about the rotation axis, whereby in use charged particles are angularly constrained along the at least one channel by the angular trapping component to rotate therewith, a centrifugal force thereby acting on the charged particles; and a radial balancing component having a magnitude increasing monotonically with increasing radius from the rotation axis, at least in the vicinity of the at least one channel, whereby in use charged particles move along the at least one channel under the combined influence of the centrifugal force and the radial balancing component to form one or more particle orbits according to the charge to mass ratios of the particles; and a detector configured to detect at least one of the particle orbits. at least one field acting on the charged particles, the at least one field having: an angular trapping component configured to form at least one channel between a rotation axis and the periphery of the chamber, the at least one channel being defined by energy minima of the angular trapping component, the field generating apparatus being further adapted to rotate the angular trapping component about the rotation axis, whereby in use charged particles are angularly constrained along the at least one channel by the angular trapping component to rotate therewith, a centrifugal force thereby acting on the charged particles; and a radial balancing component having a magnitude increasing monotonically with increasing radius from the rotation axis, at least in the vicinity of the at least one channel, whereby in use charged particles move along the at least one channel under the combined influence of the centrifugal force and the radial balancing component to form one or more particle orbits according to the charge to mass ratios of the particles; and a detector configured to detect at least one of the particle orbits. an angular trapping component configured to form at least one channel between a rotation axis and the periphery of the chamber, the at least one channel being defined by energy minima of the angular trapping component, the field generating apparatus being further adapted to rotate the angular trapping component about the rotation axis, whereby in use charged particles are angularly constrained along the at least one channel by the angular trapping component to rotate therewith, a centrifugal force thereby acting on the charged particles; and a radial balancing component having a magnitude increasing monotonically with increasing radius from the rotation axis, at least in the vicinity of the at least one channel, whereby in use charged particles move along the at least one channel under the combined influence of the centrifugal force and the radial balancing component to form one or more particle orbits according to the charge to mass ratios of the particles; and a detector configured to detect at least one of the particle orbits.