A system and method for collecting backscattered electrons within a substantially evacuated vessel containing both an electron-emitting cathode assembly and an electron-attracting anode assembly. The system and method comprises an electron collector assembly including a first plate, a second plate, an internal member, a fluid inlet, and a fluid outlet. The first plate is mounted within the vessel closest to the anode assembly. The second plate is mounted within the vessel closest to the cathode assembly. The internal member is positioned between the first plate and the second plate, and includes an internal conduit for conveying a heat absorbing cooling fluid therethrough.