A structure for collecting scattered electrons within a substantially evacuated vessel containing both an electron-emitting cathode and an electron-attracting anode is disclosed herein. The electron-collecting structure includes a two-sided first plate, a two-sided second plate, a fluid inlet, and a fluid outlet. The first plate is both electrically conductive and thermally emissive and is mountable within the vessel so that its first side at least partially faces the anode. The second plate is also thermally emissive and has a first side that is substantially conterminous with the second side of the first plate. Furthermore, the second plate additionally has an internal conduit for conveying a heat-absorbing fluid within. Both the fluid inlet and the fluid outlet are in fluid communication with the conduit in the second plate. During operation, the structure is able to attract scattered electrons and transfer thermal energy attributable to the electrons away from the structure.