Abstract:
An X-ray tube includes a cathode including an emitter emitting an electron beam, an anode at which a target material is disposed, the target material emitting an X-ray by colliding with the electron beam, and an insulating spacer isolating the anode, wherein the cathode or the anode is disposed between the emitter and the insulating spacer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Korean Patent Application Numbers 10-2015-0054595 filed on Apr. 17, 2015 and 10-2016-0012962 filed on Feb. 2, 2016, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    An aspect of the present disclosure relates to a structure of an X-ray tube. 
         [0004]    2. Description of the Related Art 
         [0005]      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. 
         [0006]    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 V ref  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 V ref . 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 V g , a focusing voltage V f , and an anode voltage V a  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. 
       SUMMARY 
       [0007]    Embodiments provide a structure of an X-ray tube, which can stably driven under high-voltage conditions and constantly maintain focusing characteristics of an electron beam under current limit conditions. 
         [0008]    According to an aspect of the present disclosure, there is provided an X-ray tube including: a cathode including an emitter emitting an electron beam; an anode at which a target material is disposed, the target material emitting an X-ray by colliding with the electron beam; and an insulating spacer isolating the anode, wherein the cathode or the anode is disposed between the emitter and the insulating spacer. 
         [0009]    The X-ray tube may further include an outer cover surrounding the cathode and the anode, the outer cover blocking the cathode and the anode from external air. The insulating spacer may electrically isolate the anode and the outer cover from each other. The anode may be disposed between the emitter and the insulating spacer. The influence of the electron beam on the insulating spacer may be blocked by the anode. 
         [0010]    The outer cover may include a conductor, and may be grounded. 
         [0011]    The insulating spacer may electrically isolate the anode and the cathode from each other. The cathode may be disposed between the emitter and the insulating spacer. The influence on the electron beam on the insulating spacer may be blocked by the cathode. 
         [0012]    At least one of the cathode and the anode may include a conductor. 
         [0013]    The X-ray tube may further include a focusing electrode. The focusing electrode may be connected to the cathode, and the same level voltage may be supplied to the focusing electrode and the cathode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the example embodiments to those skilled in the art. 
           [0015]    In the drawing figures, dimensions may be exaggerated for clarity of illustration. It will be understood that when an element is referred to as being “between” two elements, it can be the only element between the two elements, or one or more intervening elements may also be present. Like reference numerals refer to like elements throughout. 
           [0016]      FIG. 1  is a view illustrating a general structure of an X-ray tube requiring a high acceleration voltage. 
           [0017]      FIG. 2  is a view illustrating a structure of an X-ray tube according to an embodiment of the present disclosure. 
           [0018]      FIG. 3  is a view illustrating a structure of an X-ray tube according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Like reference numerals indicate like elements throughout the specification and drawings. In the following description, detailed explanation of known related functions and constitutions may be omitted to avoid unnecessarily obscuring the subject manner of the present disclosure. Names of elements used in the following description are selected in consideration of facility of specification preparation. Thus, the names of the elements may be different from names of elements used in a real product. 
         [0020]    In the entire specification, when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the another element or be indirectly connected or coupled to the another element with one or more intervening elements interposed therebetween. In addition, when an element is referred to as “including” a component, this indicates that the element may further include another component instead of excluding another component unless there is different disclosure. 
         [0021]      FIG. 2  is a view illustrating a structure of an X-ray tube according to an embodiment of the present disclosure. The X-ray tube  200  according to the embodiment of the present disclosure includes a cathode  110 , a gate  120 , a focusing electrode  130 , an anode  140 , an insulating spacer  150 , an active current control unit  60 , and an outer cover  160 . 
         [0022]    Basic functions of the cathode  110 , the gate  120 , the focusing electrode  130 , and the anode  140  are identical to those of the cathode  10 , the gate  20 , the focusing electrode  30 , and the anode  40 , respectively, and therefore, their detailed descriptions may be omitted. A high-level positive voltage may be supplied to the anode  140 . 
         [0023]    The focusing electrode  130  includes a conductor and is connected to the cathode  110  such that the same level voltage can be supplied thereto. Unlike  FIG. 1 , the focusing electrode  130  is not provided with a power source for independent potential control. As shown in  FIG. 2 , the focusing electrode  130  is the same electrode as the cathode  110 . In this case, when the active current control unit  60  operates in a current limit mode, the voltage of the cathode  110  my be changeable such that the same field emission current is extracted depending on a change in characteristics of an emitter  111 . In this state, the potential of the focusing electrode  130  is also changed together with that of the cathode  110 . That is, when a small field emission current is extracted as the characteristics of the emitter  111  are deteriorated, the voltage level of the cathode  110  is decreased to a reference voltage V′ ref , and therefore, the difference between the voltage level of the cathode  110  with a voltage level V′ g  of the gate  120  is increased. At this time, an emitted electron beam may be further diffused due to the increased voltage difference between the gate  120  and the cathode  110 . In this case, since the voltage level of the focusing electrode  130  is also decreased along the voltage level of the cathode  110 , the focusing electrode  130  has the same focusing characteristics by focusing a larger quantity of electron beams. However, structural forms of the focusing electrode  130 , i.e., a distance between gate electrodes, an opening size of the focusing electrode  130 , and the like are to be determined by considering the gate voltage V′ g  supplied to the gate  120  when the potential of the cathode  110  is the reference voltage V′ ref , an anode voltage V′ a  supplied to the anode  140 , and the like. 
         [0024]    While the insulating spacer  50  shown in  FIG. 1  electrically isolates between the cathode  10  and the anode  40 , the insulating spacer  150  shown in  FIG. 2  electrically isolates between the outer cover  160  and the anode  140 . 
         [0025]    The outer cover  160  includes a conductive layer, and may be grounded (0V) to a ground electrode (not shown). In this case, an electron beam has no influence on the outer cover  160  that includes the conductive layer and is grounded. 
         [0026]    In  FIG. 1 , since no conductor exists between electrons (e − ) emitted in the form of an electron beam from the emitter  11  in the cathode  10  and the insulating spacer  50 , the electrons (e − ) may have influence on the insulating spacer  50 . On the other hand, in  FIG. 2 , the anode  140  is disposed between the emitter  111  and the insulating spacer  150 . Also, the anode  140  exists between electrons (e − ) emitted in the form of an electron beam from the emitter  111  in the cathode  110  and the insulating spacer  150 , and the outer cover  160  including the conductive layer is grounded. When the anode  140  includes a conductor, the influence of the electrons (e − ) on the insulating spacer  150  is blocked by the anode  140  disposed between the electrons (e − ) and the insulating spacer  150 . In addition, the electron beam has no influence on the outer cover  160  that includes the conductive layer and is grounded. Thus, it is possible to prevent the accumulation of electric charges and the generation of arcs. 
         [0027]      FIG. 3  is a view illustrating a structure of an X-ray tube according to another embodiment of the present disclosure. The X-ray tube  300  according to the embodiment of the present disclosure includes a cathode  210 , a gate  220 , a focusing electrode  230 , an anode  240 , an insulating spacer  250 , and an active current control unit  60 . 
         [0028]    Basic functions of the cathode  210 , the gate  220 , the focusing electrode  230 , the anode  240 , and the insulating spacer  250  are identical to those of the cathode  10 , the gate  20 , the focusing electrode  30 , the anode  40 , and the insulating spacer  50 , respectively, and therefore, their detailed descriptions may be omitted. 
         [0029]    A basic operation of the X-ray tube  300  shown in  FIG. 3  is similar to that of the X-ray tube  200  shown in  FIG. 2 . However, the X-ray tube  300  may be a negative acceleration drive X-ray tube in which the anode  240  is grounded (0V), and a high-level negative voltage is supplied to the cathode  210 . 
         [0030]    In  FIG. 1 , since no conductor exists between electrons (e − ) emitted in the form of an electron beam from the emitter  11  in the cathode  10  and the insulating spacer  50 , the electrons (e − ) may have influence on the insulating spacer  50 . On the other hand, in  FIG. 3 , the cathode  210  is disposed between an emitter  211  and the insulating spacer  250 . Also, the cathode  210  exists between electrons (e − ) emitted in the form of an electron beam from the emitter  211  in the cathode  210  and the insulating spacer  250 , and the anode  240  is grounded. When the cathode  210  includes a conductor, the influence of the electrons (e − ) on the insulating spacer  250  is blocked by the cathode  210  disposed between the electrons (e − ) and the insulating spacer  250 . In addition, the insulating spacer  250  is disposed in a direction opposite to that in which the electrons (e − ) advance based on the emitter  211 , and an electron beam has no influence on the anode  240  that includes a conductive layer and is grounded. Thus, it is possible to prevent the accumulation of electric charges and the generation of arcs. 
         [0031]    According to the present disclosure, it is possible to provide a structure of an X-ray tube, which is stable under high-voltage conditions. Also, it is possible to provide a structure of an X-ray tube, in which focusing characteristics of an electron beam are not changed when current is controlled. 
         [0032]    Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure as set forth in the following claims.