Abstract: Multistage charged-particle accelerator for operating with accelerating voltages higher than 150 kV, consists essentially of a high-voltage insulator, a source for producing charged particles, a Wehnelt cylinder, an anode and a post-accelerating tube containing stack-wise positioned post-accelerating electrodes. A high vacuum is used for insulating the parts carrying the high voltages, at least one cylindrical screen, surrounding these parts, being interposed between them and the vacuum vessel, which can itself also function as a cylindrical screen.