“…In more recent times, magnetic fields are increasingly being used to simply guide charged particles, like electrons, muons, ions, or other, efficiently from a source to a detector. Such setups are found in magnetic photoelectron imaging [6,7,8], invented in the early 1980ies, molecular reaction microscopes [9,10] (early nineties), retardation spectrometers [11,12,13] (early nineties), time projection chambers [14] (mid-seventies), and in muon [15], neutron [16,17], or nuclear decay [18] spectrometers, to name just a few experiments and surveys. In these applications charged particles are emitted over a wide range of emission angles (0 < θ /2), and the number of orbits of gyration may vary widely (0 < n < ).…”