1. Field
An aspect of the present disclosure relates to a structure of an X-ray tube.
2. Description of the Related Art
FIG. 1 illustrates a general structure of an X-ray tube requiring a high acceleration voltage may be configured to include a cathode 10 for emitting an electron beam, an emitter 11, a gate 20, a focusing electrode 30, and an anode 40. The electrodes may be electrically isolated from each other by an insulating spacer 50. The insulating spacer 50 may have a tubular shape. When the emitter 11 is a thermoelectron source, the gate 20, the focusing electrode 30, and the like may be omitted. When the emitter 11 is a field emission electron, the focusing electrode 30 may be integrated with the gate 20 to have the same potential. Electrons (e−) emitted in the form of an electron beam from the emitter 11 are accelerated by a voltage difference between the anode 40 and the cathode 10 and then attracted toward the anode 40. Although not shown in this figure, when the electrons collide with a target material (not shown) disposed at the anode 40, an X-ray is emitted. The anode 40 may be an inclined anode or a transmissive anode. Since the insulating spacer 50 is positioned around the path along which the electrons accelerated with a high voltage are attracted toward the anode 40, electric charges are accumulated in the insulating spacer 50, and therefore, an abnormal operation may be caused. The electric charges accumulated in the insulating spacer 50 may be transferred to another electrode under a high-voltage atmosphere. In this case, the X-ray tube may be damaged due to flow of the electric charges in an arc form.
When the field emission electron source is used, the quantity of emitted electrons may be controlled using an active current control unit 60 configured by connecting a high-voltage field effect transistor, etc. in series to the cathode 10 as shown in FIG. 1. In this case, a reference voltage Vref of the active current control unit 60 may be a ground voltage (0V). Current limit conditions may be determined according to characteristics of a field emission emitter, gate voltages, and gate-source voltages applied to the field effect transistor. Here, the voltage of the cathode 10 may be increased as compared with the reference voltage Vref. The voltage of the cathode 10 may be fluctuated depending on a change in characteristics of the emitter 11 by the active current control unit 60 that controls a field emission current to be constant under the current limit conditions. If a gate voltage Vg, a focusing voltage Vf, and an anode voltage Va are maintained constant, focusing characteristics of an electron beam may be changed as the voltage of the cathode 10 is changed under the current limit conditions.