X-ray tubes are vacuum diodes that operate at high voltages.
An X-ray tube consists of two electrodes, an anode and a cathode, which are used for the target to be bombarded with electrons and the filament to emit electrons, respectively. Both poles are sealed in high vacuum glass or ceramic housings.
The power supply section of the X-ray tube contains at least a low voltage power supply for heating the filament and a high voltage generator for applying a high voltage to the two poles. When a tungsten wire passes enough current to create an electron cloud, and enough voltage (on the order of kilovolts) is applied between the anode and cathode, the electron cloud is pulled toward the anode. At this time, the electrons hit the tungsten target in a high-energy and high-speed state. The high-speed electrons reach the target surface, and their movement is suddenly blocked. A small part of their kinetic energy is converted into radiation energy and released in the form of X-rays. The radiation generated in this form is called for bremsstrahlung.
Changing the filament current can change the temperature of the filament and the amount of electrons emitted, thereby changing the tube current and the intensity of X-rays. Changing the excitation potential of the X-ray tube or choosing a different target can change the energy of the incident X-ray or the intensity at different energies. Due to the bombardment of high-energy electrons, the X-ray tube operates at a high temperature, which requires forced cooling of the anode target.
Although the energy efficiency of X-ray tubes to generate X-rays is very low, at present, X-ray tubes are still the most practical X-ray generating devices and have been widely used in X-ray instruments. At present, medical applications are mainly divided into diagnostic X-ray tubes and therapeutic X-ray tubes.