[en] An energy characterization of the electron beam produced in a transient open-ended hollow cathode discharge is presented. The entire energy distribution function (EDF) of the beam ranging from 1 keV to tens of keV was measured for the first time using two methods: the bremsstrahlung emission from the interaction of the beam with a thick target and the magnetic deflection of the beam. It was experimentally proved that the EDF is composed of lower-energy electrons described by one or two exponential functions decreasing with energy and a quasi-Gaussian hump of high-energy electrons with a maximum at ∼0.5-0.7 of the energy corresponding to the breakdown voltage. The EDF is specific for each discharge configuration and depends on the breakdown voltage