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Bremsstrahlung from high-power electron-beam diodes increases and becomes spatially more uniform when the tantalum anode is first pulse-heated to remove gas from the surface and interior, and then pulse-heated again to white hot just prior to and during the high-power pulse. Heating the tantalum eliminates protons, retards beam pinching, and increases the far-field X-ray dose relative to unheated tantalum. The radiation pattern becomes symmetric and hollow, producing a more uniform near-field dose distribution than for unheated tantalum. With a white-hot anode, the diode current is single-species Child-Langmuir until the voltage exceeds 1 MV, at which point it reaches critical current. These phenomena demonstrate reduced effects from ions in the diode. The increase in dose is a result of both reduced ion current and enhanced electron reflexing through the subrange tantalum foil. The heating technique is compatible with high-power generators such as Decade, whose x-radiation output would increase by as much as 30%.