The invention relates to a pumped electron source (1) that includes an ionization chamber (4), an acceleration chamber (2) with an electrode (3) for extracting and accelerating primary ions and forming a secondary-electron beam, characterized in that the pumped electron source (1) includes a power supply (11) adapted for applying to the electrode (3) a positive voltage for urging a primary plasma (17) outside the acceleration chamber (2), and a negative voltage pulse for extracting and accelerating the primary ions and forming a secondary-electron beam.