A vacuum tube that produces X-rays. The tube includes an emitter, either a filament or cathode, which emits electrons and an anode to collect the electrons, thus establishing a flow of electrical current, known as the beam, through the tube. A high-voltage power source (e.g., 60 kV to 150 kV) is connected across cathode and anode to accelerate the electrons. When the electrons strike the anode (X-ray target) they generate X-rays through the bremsstrahlung process. The resulting X-ray spectrum depends on the anode material and the accelerating voltage. Device that generates the X-ray beam. See also kV source.