A thermal energy storage and transfer assembly is disclosed for use in electron beam generating devices that generate residual energy. The residual energy comprises radiant thermal energy and kinetic energy of back scattered electrons. The thermal energy storage and transfer assembly absorbs and stores an amount of the residual energy to reduce the heat load on other components in the electron beam generating device. The thermal energy storage and transfer device comprises a body portion of a sufficient thermal capacity to permit the rate of transfer of the amount of the residual energy absorbed into the assembly to substantially exceed the rate of transfer of the amount of the residual energy out of the assembly. The assembly also comprises a heat exchange chamber filled with a circulating fluid that transfers the thermal energy out of the assembly. Additionally, in an x-ray generating device, an x-ray transmissive filter suitable for absorbing residual energy is positioned between the anode and an x-ray transmissive window. The filter reduces the exposure of the window to the residual energy. The filter may additionally comprise a coating layer that further reduces the exposure of the window to the residual energy.