Disclosed herein are a high-voltage generator (120) for an x-ray source, an x-ray gun, an electron beam apparatus, a rotary vacuum seal, a target assembly for an x-ray source, a rotary x-ray emission target (500), and an x-ray source. These various aspects may separately and/or together enable the construction of an x-ray source which can operate at energies of up to 500 kV and beyond, which is suitable for use in commercial and research x-ray applications such as computerised tomography. In particular, the high-voltage generator includes a shield electrode (123a, 123b) electrically connected intermediate of a first voltage multiplier (122a, 122b) and a second voltage multiplier (122b, 122c). The electron beam apparatus includes control photodetectors (202a, 202b - not shown) and photo emitters (201a, 202a) having a transparent conductive shield (203a and 203b, 203c - not shown) arranged therebetween. The rotary vacuum seal includes a pumpable chamber (302) at a position intermediate between high-pressure and low- pressure ends of a bore (301) for a rotating shaft (401). The rotary target assembly is configured such that when a torque between a bearing housing (403) and a vacuum housing exceeds a predetermined torque, the bearing housing rotates relative to the vacuum housing. The rotary x-ray emission target (500) has a plurality of target plates (560) supported on a hub, the plates being arranged on the hub to provide an annular target region about an axis rotation of the hub. The x- ray gun is provided with a shield electrode (123a) maintained at a potential difference relative to the x-ray target different to the electron beam emission cathode.