A compact design for velocity-map imaging energetic electrons and ions

We present a compact design for a velocity-map imaging spectrometer for energetic electrons and ions. The standard geometry by Eppink and Parker [A. T. J. B. Eppink and D. H. Parker, Rev. Sci. Instrum. 68, 3477 (1997)] is augmented by just two extended electrodes so as to realize an additional einzel lens. In this way, for a maximum electrode voltage of 7 kV we experimentally demonstrate imaging of electrons with energies up to 65 eV. Simulations show that energy acceptances of <270 and <1,200 eV with an energy resolution of dE / E <5% are achievable for electrode voltages of <20 kV when using diameters of the position-sensitive detector of 42 and 78 mm, respectively.