English: The main components are labelled. The transport of β-electrons and magnetic adiabatic collimation of their momenta p are illustrated. a–f, View into the tritium source depicts three systematic effects: molecular excitations during β-decay (a), scattering of electrons off the gas molecules (b) and spatial distribution of the electric potential in the source Usrc(r, z) (c). The view into the spectrometer illustrates the main background processes arising from radon decays inside the volume of the spectrometer (d), highly excited Rydberg atoms sputtered off from the structural material via α-decays of 210Po (e) and positive ions created in a Penning trap between the two spectrometers (f). Low-energy electrons, created in the volume as a consequence of radon decays or Rydberg-atom ionizations, can be accelerated by qUana towards the focal-plane detector, making them indistinguishable from signal electrons.