Patent Publication Number: US-10763069-B2

Title: X-ray tube and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-003524, filed Jan. 12, 2017, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an X-ray tube and a method of manufacturing the same. 
     BACKGROUND 
     An X-ray tube comprises a cathode which emits electrons and an anode target which irradiates X-rays by collision of the emitted electrons, in a vacuum envelope in a vacuum atmosphere. The cathode comprises an electron emission source and a cathode cup which accommodates the electron emission source. The electron emission source is composed of a filament which emits electrons and a support terminal which supports the filament. The filament is provided to be electrically insulated from the cathode cup. The filament is joined to the support terminal by welding or the like. 
     The filament is heated by heat generated by a flowing current and emits electrons (thermoelectrons) to the anode target. The filament is repeatedly heated in accordance with emission of the electrons and strength of the joint between the filament and the support terminal is thereby reduced. The filament may be therefore displaced from the joint of the support terminal. A focal position of the electrons on the anode target may be displaced by displacement of the filament. In addition, the filament may be brought into contact with the cathode cup (filament touch). If the filament is brought into contact with the cathode cup, a current may not flow to the filament. 
     The embodiments have been accomplished in consideration of this point and aim to provide an X-ray tube and an X-ray tube manufacturing method that can prevent displacement of the filament of the cathode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration showing an example of an X-ray tube according to First Embodiment. 
         FIG. 2  is a front view showing an example of a cathode. 
         FIG. 3  is a partially sectional view showing a part of a structure of the cathode. 
         FIG. 4A  is an expanded sectional view showing an example of an electron emission source. 
         FIG. 4B  is an expanded sectional view showing an example of a distal portion of a leg portion. 
         FIG. 5A  is a cross-sectional view showing an example of a support terminal in which each of sections of a first terminal portion and a second terminal portion is formed in a rectangular shape. 
         FIG. 5B  is a cross-sectional view showing an example of a support terminal in which each of parts of the sections of the first terminal portion and the second terminal portion is formed along a shape of a leg portion. 
         FIG. 6  is a cross-sectional view showing an example of a jig in which the filament and the support terminal are installed. 
         FIG. 7A  is a cross-sectional view showing the filament and the support terminal installed in the jig. 
         FIG. 7B  is an expanded sectional view showing a distal portion of the leg portion. 
         FIG. 8A  is a cross-sectional view schematically showing the filament and the support terminal installed in the jig. 
         FIG. 8B  is an expanded sectional view showing a distal portion of the leg portion. 
         FIG. 9  is a flowchart showing an example of a method of manufacturing an electron emission source of an X-ray tube  1  according to First Embodiment. 
         FIG. 10A  is an expanded sectional view showing an example of the electron emission source of the X-ray tube according to Modified Example 1. 
         FIG. 10B  is an expanded sectional view showing an example of a distal portion of the leg portion. 
         FIG. 11A  is an expanded sectional view showing an example of the electron emission source of the X-ray tube according to Modified Example 1. 
         FIG. 11B  is an expanded sectional view showing an example of the distal portion of the leg portion. 
         FIG. 12A  is an expanded sectional view showing an example of the electron emission source of the X-ray tube according to Modified Example 2. 
         FIG. 12B  is an expanded sectional view showing an example of the distal portion of the leg portion. 
         FIG. 13A  is an expanded sectional view showing an example of the electron emission source of the X-ray tube according to Modified Example 3. 
         FIG. 13B  is an expanded sectional view showing an example of the distal portion of the leg portion. 
         FIG. 14  is an expanded sectional view showing an example of a structure of the electron emission source of the X-ray tube according to Modified Example 4. 
         FIG. 15A  is a cross-sectional view showing an example of a support terminal in which each of sections of a first terminal portion and a second terminal portion is formed in a rectangular shape. 
         FIG. 15B  is a cross-sectional view showing an example of a support terminal in which each of parts of the sections of the first terminal portion and the second terminal portion is formed along a shape of a leg portion. 
         FIG. 16A  is an expanded sectional view showing an example of the electron emission source of the X-ray tube according to Modified Example 5. 
         FIG. 16B  is an expanded sectional view showing an example of the distal portion of the leg portion. 
         FIG. 17  is a cross-sectional view showing an example of a jig in which the filament and the support terminal are installed. 
         FIG. 18A  is a cross-sectional view showing the filament and the support terminal installed in the jig. 
         FIG. 18B  is an expanded sectional view showing a distal portion of the leg portion. 
         FIG. 19A  is a cross-sectional view schematically showing the filament and the support terminal installed in the jig. 
         FIG. 19B  is an expanded sectional view showing a distal portion of the leg portion. 
         FIG. 20  is an expanded sectional view showing an example of a partial structure of the support terminal of the X-ray tube according to Modified Example 6. 
         FIG. 21A  is an expanded sectional view showing an example of an electron emission source. 
         FIG. 21B  is an expanded sectional view showing an example of the distal portion of the leg portion. 
         FIG. 22A  is a cross-sectional view showing the filament and the support terminal installed in the jig. 
         FIG. 22B  is an expanded sectional view showing a support portion of the leg portion. 
         FIG. 23A  is a cross-sectional view schematically showing the filament and the support terminal installed in the jig. 
         FIG. 23B  is an expanded sectional view showing a support portion of the leg portion. 
         FIG. 24  is a flowchart showing an example of a method of manufacturing an electron emission source of an X-ray tube  1  according to the Second Embodiment. 
         FIG. 25A  is an expanded sectional view showing an example of an electron emission source according to a comparative example. 
         FIG. 25B  is an expanded sectional view showing an example of the fixed portion of the leg portion according to the comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an X-ray tube, comprises: a cathode comprising: a filament comprising a coil emitting electrons, and a leg portion extending from the coil to a distal portion and including a corner portion at the distal portion; a support terminal including a gap, and comprising an opening portion in which the gap is opened and a bottom portion located an end portion of the gap on a side opposite to the opening portion; and a cathode cup accommodating the filament and the support terminal and being connected to the support terminal, the distal portion being located in the gap, the support terminal comprising a protruding portion protruding in the gap, being located more closely to the bottom portion side than the distal portion, and being joined to the corner portion of the leg portion. 
     According to another embodiment, a method of manufacturing an X-ray tube comprising a cathode, the cathode comprising: a filament comprising a coil emitting electrons, and a leg portion extending from the coil to a distal portion and including a corner portion at the distal portion; a support terminal including a gap, and comprising an opening portion in which the gap is opened and a bottom portion located an end portion of the gap on a side opposite to the opening portion; and a cathode cup accommodating the filament and the support terminal and being connected to the support terminal, the method comprising: inserting the distal portion of the leg portion into the gap of the support terminal; supplying a current while applying a pressure to a first surface of the support terminal on an outer side and a second surface of the support terminal located outside on an opposite side with the corner portion of the leg portion sandwiched between the first surface and the second surface, by a pair of electrodes; urging a third surface of the support terminal and a fourth surface opposed to the third surface to abut on the corner portion in the gap; and joining the third surface and the fourth surface to the corner portion. 
     The embodiments will be described hereinafter with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is an illustration showing an example of an X-ray tube  1  according to the First Embodiment. A first direction X, a second direction Y, and a third direction Z are orthogonal to each other. 
     An X-ray tube  1  comprises a vacuum envelope  10 , an anode body structure  20 , and a cathode body structure  30 . The vacuum envelope  10  is formed of, for example, a glass valve formed of glass. The vacuum envelope  10  includes the anode body structure  20  and the cathode body structure  30  in the inside which is maintained in a vacuum atmosphere. 
     The anode body structure  20  comprises an approximately umbrella-shaped anode target (target disc)  21  and a rotation mechanism  23 . The anode target  21  is formed in an umbrella-like and approximately disc shape. Electrons (electron beams) collide with an umbrella-shaped surface of the anode target  21  and the anode target  21  thereby emits X-rays. The anode target  21  is supported by the rotation mechanism  23 . The anode target  21  rotates in accordance with the rotation of the rotation mechanism  23 . The anode target  21  is composed of a target layer which emits X-rays and a target base which supports the target layer. The target layer is formed of, for example, tungsten. The target base is formed of, for example, molybdenum alloy (TZM). In addition, a stator coil (not shown) is provided outside the vacuum envelope  10 . The stator coil generates a magnetic field by being supplied with a current from a power supply (not shown) and urges the rotation mechanism  23  to be rotated by the generated magnetic field. 
     The cathode body structure  30  comprises a cathode  31  and a cathode supporter  33 . The cathode  31  faces the anode target  21  inside the vacuum envelope  10 . A high voltage is applied to the cathode  31  and the cathode  31  thereby emits electrons (electron beams) to the anode target  21 . 
       FIG. 2  is a front view showing an example of cathode  31 .  FIG. 2  shows the cathode  31  on the X-Y plane seen from the third direction Z. 
     The cathode  31  comprises a cathode cup (converging electrode)  310  and at least one electron emission source, for example, two electron emission sources  321 R and  321 L. 
     The cathode cup  310  controls electrons emitted from the electron emission source. For example, the cathode cup  310  is supplied with a current and thereby urges the electrons emitted from the electron emission sources  321 R and  321 L to be converged at a focus on the anode target  21 . In the example illustrated in  FIG. 2 , two groove portions  331 R and  331 L to accommodate the electron emission sources are formed on the cathode cup  310 . The electron emission sources  321 R and  321 L are provided in accommodation grooves on bottom portions of the groove portions  331 R and  331 L, respectively. Each of the electron emission sources  321 R and  321 L emits electrons toward the anode target  21 . 
       FIG. 3  is a partially sectional view showing a part of the structure of the cathode  31 .  FIG. 3  is a partially sectional view showing the cathode  31  when seeing the Y-Z plane from the first direction X. The electron emission source  321 R and a partial section of the cathode cup  310  cut along line in  FIG. 2  are schematically shown in  FIG. 3 .  FIG. 3  shows the electron emission source  321 R alone for convenience of explanations but the electron emission source  321 L may also be configured similarly. The electron emission source  321 R will be explained below but the electron emission source  321 L can also be explained similarly to the electron emission source  321 R. 
     Holes HL 11  and HL 12  are formed in the groove portion  331 R of the cathode cup  310 . As shown in  FIG. 3 , the holes HL 11  and HL 12  are separated from each other. Each of the holes HL 11  and HL 12  extends in the third direction Z. Tubular portions TB 11  and TB 12  are provided in the holes HL 11  and HL 12 , respectively, by a method such as caulking or brazing. The tubular portions TB 11  and TB 12  are formed of an insulating material in a cylindrical shape. Sleeves SL 11  and SL 12  are provided in the tubular portions TB 11  and TB 12 , respectively, by a method such as caulking or brazing. The sleeves SL 11  and SL 12  are formed in a cylindrical shape. 
     The electron emission source  321 R comprises a filament FL 1  and a pair of support terminals (terminals or anchor portions)  401 F and  401 B. The filament FL 1  comprises a coil portion C 1  and a pair of leg portions LG 11  and LG 12  extending from the coil portion C 1 . The filament FL 1  is formed of, for example, tungsten or an alloy containing tungsten as its main component. The coil portion C 1  is supplied with a current and thereby heated, and emits electrons (thermoelectrons). The coil portion C 1  is separated from an inner surface of the groove portion  331 R of the cathode cup  310 . In the example illustrated in  FIG. 3 , the coil portion C 1  is provided parallel to a bottom surface of the groove portion  331 R and extends in the second direction Y. The leg portion LG 11  extends from an end portion of the coil portion C 1  in a direction, for example, toward the inside of the hole HL 11  in the third direction Z. The leg portion LG 12  extends from the other end portion of the coil portion C 1  which is located on the side opposite to the leg portion LG 11 , in a direction, for example, toward the inside of the hole HL 12  in the third direction Z. The leg portions LG 11  and LG 12  are formed in a rod shape, for example, a columnar shape. The leg portions LG 11  and LG 12  are supported by support terminals  401 F and  401 B, respectively. Each of the support terminals  401 F and  401 B passes a current supplied from a power source (not shown) to the coil portion C 1  of the filament FL 1 . The support terminals  401 F and  401 B are formed of, for example, iron, an alloy containing iron as its main component, niobium, or an alloy containing niobium as its main component. The support terminals  401 F and  401 B are fixed to sleeves SL 11  and SL 12 , respectively. The support terminals  401 F and  401 B are electrically insulated from the cathode cup  310  via the sleeves SL 11  and SL 12  by tubular portions TB 11  and TB 12 , respectively. In other words, the electron emission source  321 R is electrically insulated from the cathode cup  310 . 
       FIG. 4A  and  FIG. 4B  are cross-sectional views showing an example of a structure of the electron emission source  321 R cut along IV-IV shown in  FIG. 3 .  FIG. 4A  and  FIG. 4B  show an example of a section of the electron emission source  321 R when seeing the X-Z plane from the second direction Y. The structure of the cathode  31  other than the electron emission source  321 R is not shown in  FIG. 4A  and  FIG. 4B . For convenience of explanations, the only structure of the support terminal  401 F and the leg portion LG 11  of the filament FL 1  is shown but the same structure can also be applied to the leg portion LG 12  and the support terminal  401 B. Therefore, the leg portion LG 11  and the support terminal  401 F will be explained below, but the leg portion LG 12  and the support terminal  401 B can be explained similarly to the leg portion LG 11  and the support terminal  401 F.  FIG. 4A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 4B  is an expanded sectional view showing an example of a distal portion TP 11  of the leg portion LG 11 . 
     A gap (slit) CL 11  is formed in the support terminal  401 F. In the example illustrated in  FIG. 4A , the gap CL 11  in the support terminal  401 F is formed horizontally in the Y-Z plane. In other words, the gap CL 11  is formed horizontally to the plane horizontal to the filament FL 1 , in the support terminal  401 F. The gap CL 11  includes an opening portion AP 1  which opens to one direction. In the following explanations, one of portions of the support terminal  401 F based on the gap CL 11  is called a first terminal portion  41 Fa and the other portion is called a second terminal portion  41 Fb. The direction of the opening portion AP 1  is called an opening portion side, in the support terminal  401 F. A part of the support terminal  401 F located at the end portion of the gap CL 11  which is opposed to the opening portion side is called a bottom portion. The direction of the bottom portion is called a bottom portion side, in the support terminal  401 F. In addition, in the first direction X, the direction toward the gap CL 11  is called an inner side and the direction opposed to the inner side is called an outer side. An inner surface of the first terminal portion  41 Fa is called an inner surface IN 1  and an outer surface of the first terminal portion  41 Fa is called an outer surface OU 1 . An inner surface of the second terminal portion  41 Fb is called an inner surface IN 2  and an outer surface of the second terminal portion  41 Fb is called an outer surface OU 2 . The gap CL 11  in the support terminal  401 F may not be formed horizontally to the plane horizontal to the filament FL 1 , for example, the Y-Z plane. For example, the gap CL 11  in the support terminal  401 F may be formed obliquely to the plane horizontal to the filament FL 1 , for example, the Y-Z plane. The outer surface OU 2  is located on the side opposite to the outer surface OU 1  with the gap CL 11  sandwiched between the outer surfaces. In addition, the support terminal  401 F may be provided obliquely with the filament FL 1 . 
     The support terminal  401 F comprises a pair of depressions on the outer surfaces. In the example illustrated in  FIG. 4A , the support terminal  401 F comprises a pair of depressions  412  and  414 . The depressions  412  and  414  are formed on the outer surfaces OU 1  and OU 2  of the support terminal  401 F, respectively. The depression  412  is opposed to the depression  414  with the gap CL 11  sandwiched between the depressions. The leg portion LG 11  extends from the coil portion C 1  to the end portion (hereinafter called a distal portion) TP 11  on the side opposite to the coil portion C 1 . In the example illustrated in  FIG. 4A , the distal portion TP 11  of the leg portion LG 11  is located between the depressions  412  and  414 , in the gap CL 11 . 
     The support terminal  401 F comprises a protruding portion which protrudes inside the gap CL 11 . In the example illustrated in  FIG. 4B , the support terminal  401 F includes two protruding portions PR 1  and PR 2  which are opposite to each other inside the gap CL 11 . The protruding portion PR 1  is formed such that inner surface IN 1  of the first terminal portion  41 Fa of the support terminal  401 F protrudes inwardly. The protruding portion PR 2  is formed such that the inner surface IN 2  of the second terminal portion  41 Fb of the support terminal  401 F protrudes inwardly, similarly to the protruding portion PR 1 . In the example illustrated in  FIG. 4B , the protruding portions PR 1  and PR 2  are separated in a distance smaller than a width INT of the gap CL 11  in the first direction X. For example, the protruding portions PR 1  and PR 2  are separated in a distance smaller than a diameter (or a width in the first direction X) LD 1  of the leg portion LG 11 . In addition, the protruding portions PR 1  and PR 2  are separated on the side of the opening portion from a bottom portion BT 1 , in the third direction Z. The protruding portions PR 1  and PR 2  are separated but may be contacted (welded by pressure or crimped) or joined (welded). In addition, the protruding portions PR 1  and PR 2  may be in a different shape. For example, the protruding portion PR 1  may protrude more inwardly than the protruding portion PR 2 . For example, at least one of the protruding portions PR 1  and PR 2  may be spaced apart but may be contacted (welded by pressure or crimped) or joined (welded). 
     The leg portion LG 11  includes a corner portion at the distal portion TP 11 . The corner portion of the distal portion TP 11  of the leg portion LG 11  is fixed to the protruding portions PR 1  and PR 2  and the inner surfaces IN 1  and IN 2 . The corner portion is a portion at which two or more planes and lines intersect at a certain angle. A point of intersection at which two or more planes and lines intersect at a certain angle at the corner portion is often called a corner. For example, the corner portion is a portion extending from the bottom surface of the distal portion TP 11  of the leg portion LG 11  along a side surface. For convenience of explanations, the inner surface IN 1  side of the corner portion of the leg portion LG 11  is hereinafter called corner portion CP 1 , and the inner surface IN 2  side is called a corner portion CP 2 . In the example illustrated in  FIG. 4B , the corner portion CP 1  of the leg portion LG 11  is fixed to the protruding portion PR 1  and the inner surface IN 1  of the first terminal portion  41 Fa via a joint portion CN 1 . The corner portion CP 2  is fixed to the protruding portion PR 2  and the inner surface IN 2  of the second terminal portion  41 Fb via a joint portion CN 2 , similarly to the corner portion CP 1 . At this time, for example, the protruding portion PR 1  is located more closely to the bottom portion side than the distal portion TP 11  and joined to the bottom surface side of the corner portion CP 1 . The protruding portion PR 2  is located more closely to the bottom portion side than the distal portion TP 11  and joined to the bottom surface side of the corner portion CP 2 , similarly to the protruding portion PR 1 . The inner surface IN 1  is joined to the side surface side of the corner portion CP 1 . The inner surface IN 2  is joined to the side surface side of the corner portion CP 2 . The corner portion CP 1  of the leg portion LG 11  may be fixed to at least one of the protruding portion PR 1  and the inner surface IN 1  of the first terminal portion  41 Fa via the joint portion CN 1 . The corner portion CP 2  of the leg portion LG 11  may be fixed to at least one of the protruding portion PR 2  and the inner surface IN 2  of the second terminal portion  41 Fb via the joint portion CN 2 . 
     Each of the joint portions CN 1  and CN 2  is formed of a conductive metallic member. For example, the joint portion CN 1  is formed by melting at least one of the corner portion CP 1  of the leg portion LG 11  and the inner surface IN 1  (and the protruding portion PR 1 ) of the support terminal  401 F. The joint portion CN 2  is formed by melting at least one of the corner portion CP 2  of the leg portion LG 11  and the inner surface IN 2  (and the protruding portion PR 2 ) of the support terminal  401 F. In the example illustrated in  FIG. 4B , the joint portions CN 1  and CN 2  are separated from each other. The joint portion CN 1  may be formed integrally with at least one of the corner portion CP 1  of the leg portion LG 11  and the inner surface IN 1  (and the protruding portion PR 1 ) of the support terminal  401 F. The joint portion CN 2  may be formed integrally with at least one of the corner portion CP 2  of the leg portion LG 11  and the inner surface IN 2  (and the protruding portion PR 2 ) of the support terminal  401 F. 
       FIG. 25A  and  FIG. 25B  are cross-sectional views showing an example of a structure of the electron emission source  321 R according to a comparative example.  FIG. 25A  and  FIG. 25B  show an example of a section of the electron emission source  321 R when seeing the X-Z plane from the second direction Y, similarly to  FIG. 4A  and  FIG. 4B . The electron emission source  321 R according to the comparative example shown in  FIG. 25A  and  FIG. 25B  has substantially the same structure as the electron emission source  321 R according to the present embodiment shown in  FIG. 4 , portions like or similar to those of the electron emission source  321 R of the present embodiment are denoted by the same reference numbers and their detailed descriptions are omitted.  FIG. 25A  is an expanded sectional view showing an example of the electron emission source  321 R according to the comparative example.  FIG. 25B  is an expanded sectional view showing an example of a fixed portion AA 11  of the leg portion LG 11  according to the comparative example. 
     In the example illustrated in  FIG. 25A , the fixed portion AA 11  of the leg portion LG 11  is located between the depressions  412  and  414 . The fixed portion AA 11  is a part of the leg portion LG 11  located more closely to the coil portion C 1  side than the distal portion TP 11 . For this reason, the distal portion TP 11  of the leg portion LG 11  is located more closely to the bottom portion side than the range sandwiched between the depressions  412  and  414 , in the gap CL 11 . 
     In the example illustrated in  FIG. 25B , the fixed portion AA 11  of the leg portion LG 11  is fixed to the inner surface IN 1  via a joint portion AD 1  and fixed to the inner surface IN 2  via a joint portion AD 2 . The joint portion AD 1  is formed by melting at least one of the fixed portion AA 11  of the leg portion LG 11  and the inner surface IN 1  of the support terminal  401 F. The joint portion AD 2  is formed by melting at least one of the fixed portion AA 11  of the leg portion LG 11  and the inner surface IN 2  of the support terminal  401 F. Each of the joint portions AD 1  and AD 2  is formed of a conductive metallic member. The joint portion AD 1  may be formed integrally with at least one of the fixed portion AA 11  of the leg portion LG 11  and the inner surface IN 1  of the support terminal  401 F. The joint portion AD 2  may be formed integrally with at least one of the fixed portion AA 11  of the leg portion LG 11  and the inner surface IN 2  of the support terminal  401 F. 
     In the comparative example, the support terminal  401 F is welded by pressure (or crimped) on the leg portion LG 11  by welding, for example, resistance welding (spot welding) at the manufacturing time. Resistance welding is a manner of welding of superposing a plurality of members to be welded, holding a part to be welded in the superposed members between a pair of electrodes, supplying a current while applying a pressure to the part to be welded by the electrodes, and welding and joining the part with Joule heat which is generated at a contact resistance of the part by supplying the current. If the support terminal  401 F is joined to the leg portion LG 11  by resistance welding, a part of the support terminal  401 F which corresponds to the position of the fixed portion AA 11  is sandwiched between the electrodes from the outside, a force is exerted on this part and a current is supplied to the part. The inner surfaces IN 1  and IN 2  of the support terminal  401 F protrude to the fixed portion AA 11  of the leg portion LG 11  by the force exerted by the electrodes and are made to abut on the fixed portion AA 11  of the leg portion LG 11 . At this time, for example, each of the inner surfaces IN 1  and IN 2  of the support terminal  401 F is brought into line contact with the fixed portion AA 11  of the leg portion LG 11 . In this case, the force exerted on the support terminal  401 F by the electrodes is dispersed at the part at which each of the inner surfaces IN 1  and IN 2  of the support terminal  401 F is brought into line contact with the fixed portion AA 11  of the leg portion LG 11 . In other words, a stress generated at the part in line contact becomes smaller. For this reason, each of the inner surfaces IN 1  and IN 2  of the support terminal  401 F is not sufficiently crimped on the fixed portion AA 11  of the leg portion LG 11 . The current supplied by the electrodes is therefore dispersed at the part at which the inner surfaces IN 1  and IN 2  of the support terminal  401 F are brought into line contact with the fixed portion AA 11  of the leg portion LG 11 . In other words, a current density at the part in line contact becomes smaller. For this reason, the inner surfaces IN 1  and IN 2  of the support terminal  401 F may not be joined to the fixed portion AA 11  of the leg portion LG 11  with a sufficient strength. 
     In contrast, in the present embodiment, the support terminal  401 F is joined (welded) on the leg portion LG 11  by welding, for example, resistance welding at the manufacturing time. If the support terminal  401 F is joined to the leg portion LG 11  by resistance welding, a part of the support terminal  401 F which corresponds to the position of the distal portion TP 11  of the leg portion LG 11  is sandwiched between the electrodes from the outside, a force is exerted on this part and a current is supplied to the part. The inner surfaces IN 1  and IN 2  of the support terminal  401 F protrude to the distal portion TP 11  of the leg portion LG 11  by the force exerted by the electrodes and are made to abut on the corner portions CP 1  and CP 2 . At this time, for example, the inner surface IN 1  is made to abut on a corner of the corner portion CP 1  and plastically deformed to cover the corner portion CP 1 . The inner surface IN 2  is made to abut on a corner of the corner portion CP 2  and plastically deformed to cover the corner portion CP 2 , similarly to the inner surface IN 1 . At this time, the inner surface IN 1  is plastically deformed and the protruding portion PR 1  is thereby formed on the bottom portion side. The inner surface IN 2  is plastically deformed and the protruding portion PR 2  is thereby formed. At this time, the force exerted on the support terminal  401 F by the electrodes is concentrated on the part at which the inner surfaces IN 1  and IN 2  of the support terminal  401 F are brought into contact with the corners of the corner portions CP 1  and CP 2  of the distal portion TP 11 , respectively. In other words, a stress generated at the part in contact becomes larger. For this reason, the inner surfaces IN 1  and IN 2  of the support terminal  401 F are sufficiently crimped on the corner portions CP 1  and CP 2  of the leg portion LG 11 . In other words, the inner surfaces IN 1  and IN 2  of the support terminal  401 F are sufficiently crimped on the corner portions CP 1  and CP 2  of the leg portion LG 11  in narrower range as compared with a case in which the inner surfaces are brought into contact. For this reason, the current supplied by the elements mainly flows at the part at which the inner surfaces IN 1  and IN 2  of the support terminal  401 F are brought into contact with the corner portions CP 1  and CP 2  of the distal portion TP 11 . In other words, a current density at the part in contact becomes larger. The inner surfaces IN 1  and IN 2  (and the protruding portions PR 1  and PR 2 ) of the support terminal  401 F can be therefore joined to the corner portions CP 1  and CP 2  of the leg portion LG 11  with a sufficient strength. 
       FIG. 5A  and  FIG. 5B  are cross-sectional views showing several examples of the partial structure of the support terminal  401 F cut along V-V shown in  FIG. 4 .  FIG. 5A  and  FIG. 5B  show several examples of a section of the support terminal  401 F when seeing the X-Y plane from the third direction Z.  FIG. 5A  is a cross-sectional view showing an example of the support terminal  401 F in which each of sections of a first terminal portion  41 Fa and a second terminal portion  41 Fb is formed in a semicircular shape.  FIG. 5B  is a cross-sectional view showing an example of the support terminal  401 F in which each of sections of the first terminal portion  41 Fa and the second terminal portion  41 Fb is formed in a fan shape. 
     In the example illustrated in  FIG. 5A , each of the sections of the first terminal portion  41 Fa and the second terminal portion  41 Fb of the support terminal  401 F is formed in a semicircular shape. The first terminal portion  41 Fa and the second terminal portion  41 Fb of the support terminal  401 F are opposed with the leg portion LG 11  sandwiched between the terminal portions. In the example illustrated in  FIG. 5A , the support terminal  401 F can prevent displacement of the leg portion LG 11  to a direction vertical with the plane horizontal to the filament FL 1 , for example, the first direction X of the leg portion LG 11 . In the example illustrated in  FIG. 5B , each of the sections of the first terminal portion  41 Fa and the second terminal portion  41 Fb of the support terminal  401 F is formed in a fan shape. Each of a part of the inner surface IN 1  of the first terminal portion  41 Fa and a part of the inner surface IN 2  of the second terminal portion  41 Fb, of the support terminal  401 F, is formed in an arch shape along the outer peripheral shape of the leg portion LG 11 . In the support terminal  401 F, a part of the inner surface IN 1  and a part of the inner surface IN 2  which are not formed in an arch shape are opposed parallel. In addition, the part of the inner surface IN 1  and the part of the inner surface IN 2  which are not formed in an arch shape are separated in a distance smaller than the diameter LD 1  of the leg portion LG 11 . The first terminal portion  41 Fa and the second terminal portion  41 Fb of the support terminal  401 F are opposed with the leg portion LG 11  sandwiched between the terminal portions. The leg portion LG 11  is located between the part of the inner surface IN 1  and the part of the inner surface IN 2  of the second terminal portion  41 Fb which are formed in an arch shape. In the example illustrated in  FIG. 5B , the support terminal  401 F can prevent displacement of the leg portion LG 11  to a direction vertical with the plane horizontal to the filament FL 1 , for example, the first direction X. In addition, the support terminal  401 F can also prevent displacement of the leg portion LG 11  to a direction horizontal to the plane horizontal to the filament FL 1 , for example, the second direction Y. The sectional shape of the support terminal  401 F shown in  FIG. 5A  and  FIG. 5B  is a mere example and may be a sectional shape other than this. For example, the section of the support terminal  401 F may be formed in a rectangular shape. In addition, the gap CL 11  may be formed obliquely in the section of the support terminal  401 F. 
     An example of a method of manufacturing the electron emission source  321 R according to the present embodiment will be hereinafter explained with reference to  FIG. 6  to  FIG. 8B . For convenience of explanations, the manufacturing method will be explained below with the leg portion LG 11  and the support terminal  401 F but the same manufacturing method as that using the leg portion LG 11  and the support terminal  401 F can be applied to the leg portion LG 12  and the support terminal  401 B. In addition, the only manufacturing method of the electron emission source  321 R will be explained but the same manufacturing method as that of the electron emission source  321 L can be applied to the electron emission source  321 L. 
       FIG. 6  is a cross-sectional view showing an example of a jig JG in which the filament FL 1  and the support terminal  401 F are installed. The jig JG comprises a base PED, an electrode EL, and a support plate SB. A base PED side is called a lower side while a support plate SB side is called an upper side in the following explanations. An object is placed on a surface SF 1  of the base PED. The electrode EL is provided at a position separated from the surface SF 1  of the base PED in a specific distance to the upper direction. The electrode EL includes at least a pair of electrodes, for example, a pair of electrodes EL 1  and EL 2 . The electrodes EL 1  and EL 2  are opposed to each other. The electrodes EL 1  and EL 2  are movable to a direction parallel to the surface SF 1  of the base PED. In addition, the electrodes EL 1  and EL 2  are connected to a positive power source and a negative power source (not shown), respectively. For this reason, the voltage is applied from the power sources and the electrodes EL 1  and EL 2  are thereby supplied with currents. The support plate SB is formed in a flat plate shape. A through hole SH is formed in the support plate SB. The support plate SB is installed at a position separated from the surface SF 1  of the base PED in an arbitrary distance to the upper direction. For example, the support plate SB is installed such that the distal portion TP 11  of the leg portion LG 11  of the filament FL 1  is located between the electrodes EL 1  and EL 2 . The electrodes EL 1  and EL 2  may be configured to be movable longitudinally to the base PED. In addition, the base PED may be configured to be movable longitudinally, in the jig JG. 
     As shown in  FIG. 6 , the support terminal  401 F is installed on the surface SF 1  of the base PED. The filament FL 1  is installed on the support plate SB. When the filament FL 1  is installed on the support plate SB, the coil portion C 1  is supported on a surface SF 2  of the support plate SB. The leg portion LG 11  is inserted into the through hole SH of the support plate SB. At this time, the distal portion TP 11  of the leg portion LG 11  is located between the electrodes EL 1  and EL 2 . For example, the corner portions CP 1  and CP 2  of the leg portion LG 11  are located between the electrodes EL 1  and EL 2 . For example, the distal portion TP 11  of the leg portion LG 11  is separated from the bottom portion BT 1  of the support terminal  401 F to the opening portion side. In this case, the distal portion TP 11  is separated from the bottom portion BT 1  of the bottom portion BT 1 , and the support terminal  401 F and the leg portion LG 11  can be therefore crimped efficiently by the electrodes EL 1  and EL 2 . 
       FIG. 7A  and  FIG. 7B  are cross-sectional views showing an example of the support terminal  401 F on which the force is exerted by the electrode EL.  FIG. 7A  is a cross-sectional view showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 7B  is an expanded sectional view showing the distal portion TP 11  of the leg portion LG 11 . 
     As shown in  FIG. 7A , the electrodes EL 1  and EL 2  sandwich the support terminal  401 F from both sides to exert force on the outer surfaces OU 1  and OU 2  of the support terminal  401 F. The depressions  412  and  414  are formed on the outer surfaces OU 1  and OU 2  of the support terminal  401 F by the electrodes EL 1  and EL 2 , respectively. 
     As shown in  FIG. 7B , the inner surfaces IN 1  and IN 2  of the support terminal  401 F protrude to the distal portion TP 11  of the leg portion LG 11  and are made to abut on the corners of the corner portions CP 1  and CP 2 , by the force exerted by the electrodes EL 1  and EL 2 . For this reason, a stress is concentrated on the corner of the corner portion CP 1  of the leg portion LG 11 , and the inner surface IN 1  of the support terminal  401 F is thereby plastically deformed to cover the corner portion CP 1 . A stress is concentrated on the corner of the corner portion CP 2  of the leg portion LG 11 , and the inner surface IN 2  of the support terminal  401 F is thereby plastically deformed to cover the corner portion CP 2 . The inner surfaces IN 1  and IN 2  of the support terminal  401 F are plastically deformed, and the protruding portions PR 1  and PR 2  are thereby formed more closely to the bottom portion side than the distal portion TP 11  of the leg portion LG 11 . For this reason, the protruding portions PR 1  and PR 2  can prevent displacement of the leg portion LG 11 , for example, displacement to the bottom portion side in the gap CL 11 , and the like. 
       FIG. 8A  and  FIG. 8B  are cross-sectional views showing the support terminal  401 F joined to the distal portion TP 11  of the leg portion LG 11 .  FIG. 8A  is a cross-sectional view schematically showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 8B  is an expanded sectional view showing the distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 8A , the electrodes EL 1  and EL 2  supply a current while exerting force on the outer surfaces OU 1  and OU 2  of the support terminal  401 F. At this time, a current having a sufficient current density flows between the inner surfaces IN 1  and IN 2  and the protruding portions PR 1  and PR 2  of the support terminal  401 F and the corner portions CP 1  and CP 2  of the leg portion LG 11 . For this reason, Joule heat sufficient for welding is generated between the corner portion CP 1  of the leg portion LG 11  and the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F. Joule heat sufficient for welding is generated between the corner portion CP 2  of the leg portion LG 11  and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F. For this reason, the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F are molten and joined to the corner portion CP 1  to cover the corner portion CP 1  of the leg portion LG 11 . In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are molten and joined to the corner portion CP 2  to cover the corner portion CP 2  of the leg portion LG 11 . For example, as shown in  FIG. 8B , the joint portion CN 1  is formed between the corner portion CP 1  of the leg portion LG 11  and the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F to cover the corner portion CP 1  of the leg portion LG 11 . The joint portion CN 2  is formed between the corner portion CP 2  of the leg portion LG 11  and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F to cover the corner portion CP 2  of the leg portion LG 11 . The joint portion CN 1  is formed by meting at least one of the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F and the corner portion CP 1  of the leg portion LG 11 . The joint portion CN 2  is formed by meting at least one of the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F and the corner portion CP 2  of the leg portion LG 11 . The inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F are thus joined with a sufficient strength since the inner surface IN 1  and the protruding portion PR 1  cover the corner portion CP 1 . The inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are thus joined with a sufficient strength since the inner surface IN 2  and the protruding portion PR 2  cover the corner portion CP 2 . For this reason, the support terminal  401 F can prevent displacement of the leg portion LG 11 , for example, displacement to the opening portion side in the gap CL 11 , and the like. 
       FIG. 9  is a flowchart showing an example of a method of manufacturing the electron emission source  321 R of the X-ray tube  1  according to the present embodiment. 
     First, the support terminal  401 F is installed in the jig JG (S 901 ). The leg portion LG 11  of the filament FL 1  is inserted into the gap CL 11  of the support terminal  401 F (S 902 ). At this time, the distal portion TP 11  of the leg portion LG 11  is located at a position at which the distal portion can be welded by the electrodes EL 1  and EL 2 . 
     The support terminal  401 F is welded by pressure (crimped) on the distal portion TP 11  of the leg portion LG 11  by the electrodes EL 1  and EL 2  (S 903 ). At this time, the inner surface IN 1  is made to abut on the corner of the corner portion CP 1  of the leg portion LG 11  and plastically deformed to cover the corner portion CP 1 , by the force exerted on the electrodes EL 1  and EL 2 . In addition, the inner surface IN 2  is made to abut on a corner of the corner portion CP 2  of the leg portion LG 11  and plastically deformed to cover the corner portion CP 2 . At this time, the inner surface IN 1  of the support terminal  401 F at the protruding portion PR 1  protrudes to the inner side of the gap CL 11  by the force exerted on the electrodes EL 1  and EL 2  and is formed more closely to the bottom portion side than the distal portion of the leg portion LG 11 . The inner surface IN 2  of the support terminal  401 F at the protruding portion PR 2  protrudes to the inner side of the gap CL 11  and is formed more closely to the bottom portion side than the distal portion of the leg portion LG 11 . 
     In this state, the support terminal  401 F is welded on the distal portion TP 11  of the leg portion LG 11  by the electrodes EL 1  and EL 2  (S 904 ). At this time, the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F are molten and joined to the corner portion CP 1  of the leg portion LG 11 , by the heat generated by the current supplied from the electrodes EL 1  and EL 2 . The inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are molten and joined to the corner portion CP 2  of the leg portion LG 11 , by the heat generated by the current supplied from the electrodes EL 1  and EL 2 . The corner portion CP 1  of the leg portion LG 11  is fixed to the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F. The corner portion CP 2  of the leg portion LG 11  is fixed to the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F. The corner of the leg portion LG 12  is fixed to the inner surface of the support terminal  401 B, similarly to the support terminal  401 F and the leg portion LG 11 . After that, the steps of manufacturing the electron emission source  321 R are ended. 
     In the X-ray tube  1 , according to the present embodiment, the corner portions CP 1  and CP 2  of the leg portion LG 11  of the filament FL 1  are fixed to the inner surface IN 1  and the protruding portion PR 1 , and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F via the joint portions CN 1  and CN 2 , respectively, in the cathode  31 . Since the force exerted on the support terminal  401 F by the electrodes EL 1  and EL 2  is concentrated on the corners of the corner portions CP 1  and CP 2  of the leg portion LG 11 , at the manufacturing time, the inner surfaces IN 1  and IN 2  of the support terminal  401 F are plastically deformed at the corners of the corner portions CP 1  and CP 2  and deformed to cover the corner portions CP 1  and CP 2 . At this time, the inner surfaces IN 1  and IN 2  are plastically deformed, and the protruding portions PR 1  and PR 2  are thereby formed. The inner surface IN 1  and the protruding portion PR 1 , and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are joined to the corner portions CP 1  and CP 2  with a sufficient strength. For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . As a result, the X-ray tube  1  can prevent contact of the filament FL 1  on the cathode cup  310 , and the like. 
     Next, the X-ray tube and the X-ray tube manufacturing method according to modified examples and the other embodiment will be explained. In the modified examples and the other embodiment to be explained below, portions like or similar to those of the above-explained First Embodiment are denoted by the same reference numerals and their detailed explanations are omitted or simplified, and portions different from the First Embodiment will be particularly explained in detail. 
     Modified Example 1 
     The X-ray tube  1  according to Modified Example 1 of the First Embodiment is different from the X-ray tube  1  according to the First Embodiment with respect to a feature that in the electron emission source, for example, the electron emission source  321 R, the corner portions CP 1  and CP 2  of the leg portion LG 11  are located outside the range sandwiched between the depressions  412  and  414  in the gap CL 11 . 
       FIG. 10A  and  FIG. 10B  are cross-sectional views showing an example of a structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 1 of the First Embodiment. In  FIG. 10A  and  FIG. 10B , a boundary position on the opening portion side is called position UP while a boundary position on the bottom portion side is called position BP, in the range sandwiched between the depressions  412  and  414 .  FIG. 10A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 10B  is an expanded sectional view showing an example of the distal portion TP 11  of the leg portion LG 11 . 
     The distal portion TP 11  of the leg portion LG 11  is located more closely to the opening portion side than the range sandwiched between the electrodes (i.e., the range sandwiched between the depressions  412  and  414 ), in the support terminal  401 F. In the example illustrated in  FIG. 10A , the distal portion TP 11  of the leg portion LG 11  is located near the position UP, in the gap CL 11 . 
     In the example illustrated in  FIG. 10B , the corner portions CP 1  and CP 2  of the leg portion LG 11  are located more closely to the opening portion side than the range sandwiched between the depressions  412  and  414 . For example, the corner portions CP 1  and CP 2  of the leg portion LG 11  are located more closely to the opening portion side than the position UP. The protruding portions PR 1  and PR 2  are formed to be longer than the protruding portions PR 1  and PR 2  shown in  FIG. 4 , respectively. In this case, too, a current is supplied with a sufficient current density, and the inner surface IN and the protruding portion PR of the support terminal  401 F are thereby joined to the corner portion CP 1  of the leg portion LG 11  with a sufficient strength. In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are also joined to the corner portion CP 2  of the leg portion LG 12  with a sufficient strength. 
       FIG. 11A  and  FIG. 11B  are cross-sectional views showing an example of the structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 1 of the First Embodiment. In  FIG. 11A  and  FIG. 11B , a boundary position on the opening portion side is called position UP while a boundary position on the bottom portion side is called position BP, in the range sandwiched between the depressions  412  and  414 .  FIG. 11A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 11B  is an expanded sectional view showing an example of the distal portion TP 11  of the leg portion LG 11 . 
     The distal portion TP 11  of the leg portion LG 11  is located more closely to the bottom portion side than the range sandwiched between the depressions  412  and  414 . In the example illustrated in  FIG. 11A , the distal portion TP 11  of the leg portion LG 11  is located near the position BP, in the gap CL 11 . 
     In the example illustrated in  FIG. 11B , the corner portions CP 1  and CP 2  of the leg portion LG 11  are partially located more closely to the bottom portion side than the range sandwiched between the depressions  412  and  414 . For example, the corner portions CP 1  and CP 2  of the leg portion LG 11  are partially located more closely to the bottom portion side than the position BP. The protruding portions PR 1  and PR 2  are formed to be shorter than the protruding portions PR 1  and PR 2  shown in  FIG. 4 , respectively. In this case, too, a current is supplied with a sufficient current density, and the inner surface IN and the protruding portion PR of the support terminal  401 F are thereby joined to the corner portion CP 1  of the leg portion LG 11  with a sufficient strength. In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are also joined to the corner portion CP 2  of the leg portion LG 12  with a sufficient strength. 
     In the X-ray tube  1  according to Modified Example 1, the corner portions CP 1  and CP 2  of the leg portion LG 11  of the filament FL 1  of the electron emission source, for example, the electron emission source  321 R, are located outside the range sandwiched between the depressions  412  and  414 , in the gap CL 11 . In this case, too, a current is supplied with a sufficient current density, and the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F are thereby joined to the corner portion CP 1  of the leg portion LG 11  with a sufficient strength. In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are also joined to the corner portion CP 2  of the leg portion LG 12  with a sufficient strength. For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . 
     Modified Example 2 
     The X-ray tube  1  according to Modified Example 2 of the First Embodiment is different from the above-explained X-ray tube  1  with respect to a feature that in the electron emission source, for example, the electron emission source  321 R, the protruding portions PR 1  and PR 2  of the support terminal  401 F are joined to each other. 
       FIG. 12A  and  FIG. 12B  are cross-sectional views showing an example of the structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 2 of the First Embodiment.  FIG. 12A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 12B  is an expanded sectional view showing an example of the distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 12A , the distal portion TP 11  of the leg portion LG 11  is located between the depressions  412  and  414 , in the gap CL 11 . In the example illustrated in  FIG. 12B , the protruding portions PR 1  and PR 2  of the support terminal  401 F are joined to each other. In addition, the protruding portions PR 1  and PR 2  are joined at a position between the bottom surface of the leg portion LG 11  and the protruding portions PR 1  and PR 2 . The leg portion LG 11  is larger than the leg portion LG 11  of the above-explained embodiment with respect to the range in which the protruding portions PR 1  and PR 2  are joined. The leg portion LG 11 , and the inner surfaces IN 1  and IN 2  and the protruding portions PR 1  and PR 2  are joined via the joint portions CN 1  and CN 2 , with a sufficient strength. 
     In the X-ray tube  1  according to Modified Example 2, the protruding portions PR 1  and PR 2  of the support terminal  401 F are joined to each other. The corner portion CP 1  of the leg portion LG 11  is joined to the protruding portion PR 1  and the inner surface IN 1  via the joint portion CN 1 . The corner portion CP 2  of the leg portion LG 11  is joined to the protruding portion PR 1  and the inner surface IN 2  via the joint portion CN 2 . The joint portions CN 1  and CN 2  are joined at a position between the bottom surface of the leg portion LG 11  and the protruding portions PR 1  and PR 2 . For this reason, the leg portion LG 11 , and the inner surfaces IN 1  and IN 2  and the protruding portions PR 1  and PR 2  are joined via the joint portions CN 1  and CN 2 , with a sufficient strength. For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . 
     Modified Example 3 
     The X-ray tube  1  according to Modified Example 3 of the First Embodiment is different from the above-explained X-ray tube  1  with respect to a feature that in the electron emission source, for example, the electron emission source  321 R, the outer surfaces OU 1  and OU 2  of the support terminal  401 F are formed in a planar shape. 
       FIG. 13A  and  FIG. 13B  are cross-sectional views showing an example of the structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 3 of the First Embodiment.  FIG. 13A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 13B  is an expanded sectional view showing an example of the distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 13A , the outer surfaces OU 1  and OU 2  of the support terminal  401 F are formed in a planar shape. In the example illustrated in  FIG. 13B , the corner portion CP 1  of the leg portion LG 11  is fixed to the protruding portion PR 1  and the inner surface IN 1  of the support terminal  401 F via the joint portion CN 1 . In addition, the corner portion CP 2  of the leg portion LG 11  is fixed to the protruding portion PR 2  and the inner surface IN 2  of the support terminal  401 F via the joint portion CN 2 . 
     In the X-ray tube  1  according to Modified Example 3, the outer surface of the support terminal  401 F is formed in a planar shape. In this case, too, a current is supplied with a sufficient current density, and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are thereby joined to the corner portion CP 1  of the leg portion LG 11  with a sufficient strength. In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are also joined to the corner portion CP 2  of the leg portion LG 12  with a sufficient strength. For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . 
     Modified Example 4 
     The X-ray tube  1  according to Modified Example 4 of the First Embodiment is different from the above-explained X-ray tube  1  with respect to an orientation of the support terminal  401 F in the electron emission source, for example, the electron emission source  321 R. 
       FIG. 14  is a cross-sectional view showing an example of a structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 4 of the First Embodiment.  FIG. 14  shows an example of a section of the electron emission source  321 R when seeing the X-Z plane from the second direction Y. In the example illustrated in  FIG. 14 , the gap CL 11  of the support terminal  401 F is provided horizontally in the X-Z plane. In other words, the gap CL 11  is provided vertically to a plane horizontal to the filament FL 1 , of the support terminal  401 F. For example, the support terminal  401 F shown in  FIG. 14  is provided by rotating the support terminal  401 F shown in  FIG. 4  around an axis extending in the third direction Z at ninety degrees. The support terminal  401 F shown in  FIG. 14  may be provided by rotating the support terminal  401 F shown in  FIG. 4  around an axis extending in the second direction Y at an angle other than ninety degrees. 
       FIG. 15A  and  FIG. 15B  are cross-sectional views showing several examples of the partial structure of the support terminal  401 F cut along XV-XV shown in  FIG. 14 .  FIG. 15A  and  FIG. 15B  show several examples of a section of the support terminal  401 F when seeing the X-Y plane from the third direction Z.  FIG. 15A  is a cross-sectional view showing an example of the support terminal  401 F in which each of sections of the first terminal portion  41 Fa and the second terminal portion  41 Fb is formed in a semicircular shape.  FIG. 15B  is a cross-sectional view showing an example of the support terminal  401 F in which each of sections of the first terminal portion  41 Fa and the second terminal portion  41 Fb is formed in a fan shape. 
     The section of the support terminal  401 F shown in  FIG. 15A  indicates the structure obtained by rotating the section of the support terminal  401 F shown in  FIG. 5A  around an axis extending in the third direction Z at ninety degrees. The section of the support terminal  401 F shown in  FIG. 15B  indicates the structure obtained by rotating the section of the support terminal  401 F shown in  FIG. 5B  around an axis extending in the second direction Y at ninety degrees. The sectional shape of the support terminal  401 F shown in  FIG. 15A  and  FIG. 15B  is a mere example and may be a sectional shape other than this. For example, the section of the support terminal  401 F may be formed in a rectangular shape. 
     In the X-ray tube  1  according to Modified Example 4, the gap CL 11  is formed vertically to the plane horizontal to the filament FL 1 , in the support terminal  401 F. For this reason, the support terminal  401 F can prevent displacement of the leg portion LG 11  to a direction horizontal to the plane horizontal to the filament FL 1 , for example, the second direction Y. 
     Modified Example 5 
     The X-ray tube  1  according to Modified Example 5 of the First Embodiment is different from the above-explained X-ray tube  1  with respect to a feature of comprising a middle member IM between the leg portion LG 11  of the filament FL 1  and the inner surface of the support terminal  401 F, in the electron emission source, for example, the electron emission source  321 R. 
       FIG. 16A  and  FIG. 16B  are cross-sectional views showing an example of a structure of the electron emission source  321 R of the X-ray tube  1  according to Modified Example 5 of the First Embodiment.  FIG. 16A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 16B  is an expanded sectional view showing an example of the distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 16A , the electron emission source  321 R comprises the middle member IM between the leg portion LG 11  of the filament FL 1  and the inner surface of the support terminal  401 F. The support terminal  401 F is formed of, for example, molybdenum or an alloy containing molybdenum as a main component. The middle member IM is formed of, for example, platinum or an alloy containing platinum as a main component. The middle member IM is formed of, for example, foil or plating. 
     In the example illustrated in  FIG. 16B , the corner portion CP 1  of the leg portion LG 11  is fixed to the protruding portion PR 1  and the inner surface IN 1  via the joint portion CN 1 . The corner portion CP 2  of the leg portion LG 11  is joined to the protruding portion PR 2  and the inner surface IN 2  via the joint portion CN 2 . For example, the joint portion CN 1  is formed by melting at least one of the corner portion CP 1  of the leg portion LG 11 , the inner surface IN 1  (and the protruding portion PR 1 ) of the support terminal  401 F, and the middle member IM. The joint portion CN 2  is formed by melting at least one of the corner portion CP 2  of the leg portion LG 11 , the inner surface IN 2  (and the protruding portion PR 2 ) of the support terminal  401 F, and the middle member IM. In the example illustrated in  FIG. 16B , the middle member IM is provided more closely to the opening portion side than the joint portions CN 1  and CN 2 , in the gap CL 11  between the inner surface of the support terminal  401 F and the leg portion LG 11 . The middle member IM may be included in the joint portions CN 1  and CN 2 . For this reason, as shown in  FIG. 16B , for example, the middle member IM may not be provided more closely to the opening portion side than the joint portions CN 1  and CN 2 , in the gap CL 11  between the inner surface of the support terminal  401 F and the leg portion LG 11 . 
     An example of a method of manufacturing the electron emission source  321 R according to Modified Example 5 will be hereinafter explained with reference to  FIG. 17  to  FIG. 19B . 
       FIG. 17  is a cross-sectional view showing an example of the jig JG in which the filament FL 1  and the support terminal  401 F are installed. 
     As shown in  FIG. 17 , the support terminal  401 F is installed on the surface SF 1  of the base PED. At this time, the leg portion LG 11  comprises at least the middle member IM at the distal portion TP 11 . The distal portion TP 11  of the leg portion LG 11  is located between the electrodes EL 1  and EL 2 . 
       FIG. 18A  and  FIG. 18B  are cross-sectional views showing an example of the support terminal  401 F on which the force is exerted by the electrode EL.  FIG. 18A  is a cross-sectional view showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 18B  is an expanded sectional view showing the distal portion TP 11  of the leg portion LG 11 . 
     As shown in  FIG. 18A , the electrodes EL 1  and EL 2  sandwich the support terminal  401 F from both sides to exert force on the outer surfaces OU 1  and OU 2  of the support terminal  401 F. The depressions  412  and  414  are formed on the outer surfaces OU 1  and OU 2  of the support terminal  401 F by the electrodes EL 1  and EL 2 , respectively. 
     As shown in  FIG. 18B , the inner surfaces IN 1  and IN 2  of the support terminal  401 F protrude to the distal portion TP 11  of the leg portion LG 11  and are made to abut on the corners of the corner portions CP 1  and CP 2 , by the force exerted by the electrodes EL 1  and EL 2 . For this reason, a stress is concentrated on the corner of the corner portion CP 1  of the leg portion LG 11 , and the inner surface IN 1  of the support terminal  401 F is thereby plastically deformed to cover the corner portion CP 1 . A stress is concentrated on the corner of the corner portion CP 2  of the leg portion LG 11 , and the inner surface IN 2  of the support terminal  401 F is thereby plastically deformed to cover the corner portion CP 2 . 
       FIG. 19A  and  FIG. 19B  are cross-sectional views showing the support terminal  401 F joined to the leg portion LG 11  of the filament FL 1 .  FIG. 19A  is a cross-sectional view schematically showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 19B  is an expanded sectional view showing the distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 19A , the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F are molten and joined to the corner portion CP 1  to cover the corner portion CP 1  of the leg portion LG 11  via the middle member IM. In addition, the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F are molten and joined to the corner portion CP 2  to cover the corner portion CP 2  of the leg portion LG 11  via the middle member IM. For example, as shown in  FIG. 19B , the joint portion CN 1  is formed between the corner portion CP 1  of the leg portion LG 11  and the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F to cover the corner portion CP 1  of the leg portion LG 11 . The joint portion CN 2  is formed between the corner portion CP 2  of the leg portion LG 11  and the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F to cover the corner portion CP 2  of the leg portion LG 11 . The joint portion CN 1  is formed by meting at least one of the inner surface IN 1  and the protruding portion PR 1  of the support terminal  401 F, the corner portion CP 1  of the leg portion LG 11 , and the middle member IM. The joint portion CN 2  is formed by meting at least one of the inner surface IN 2  and the protruding portion PR 2  of the support terminal  401 F, the corner portion CP 2  of the leg portion LG 11 , and the middle member IM. Thus, performance of welding between the leg portion LG 11  of the filament FL 1  and the support terminal  401 F is improved by providing the middle member IM between the leg portion LG 11  and the inner surface of the support terminal  401 F. 
     According to Modified Example 5, the X-ray tube  1  comprises the middle member IM between the leg portion LG 11  and the inner surface of the support terminal  401 F, in the electron emission source, for example, the electron emission source  321 R. For this reason, performance of welding between the leg portion LG 11  and the inner surface of the support terminal  401 F, in the X-ray tube  1 , is improved at the manufacturing time. 
     Modified Example 6 
     The X-ray tube  1  according to Modified Example 6 of the First Embodiment is different from the above-explained X-ray tube  1  with respect to a sectional shape of the support terminal  401 F in the electron emission source, for example, the electron emission source  321 R. 
       FIG. 20  is an expanded sectional view showing an example of a partial structure of the support terminal  401 F of the X-ray tube  1  according to Modified Example 6 of the First Embodiment.  FIG. 20  shows an example of the section of the support terminal  401 F when seeing the X-Y plane from the third direction Z. A center CNT 1  of the center of width in the first direction X of the section of the support terminal  401 F is shown in  FIG. 20 . In  FIG. 20 , one of portions of the support terminal  401 F based on the center CNT 1  is called a first terminal portion  41 Fa and the other portion is called a second terminal portion  41 Fb. In the example illustrated in  FIG. 20 , a circular gap CL 11  is formed in the section of the support terminal  401 F. In the section of the support terminal  401 F shown in  FIG. 20 , the gap CL 11  does not extend up to the outside. The section of the support terminal  401 F shown in  FIG. 20  is a mere example and may be a section other than this. 
     In the X-ray tube  1  according to Modified Example 6, the circular gap CL 11  is formed in the section of the support terminal  401 F. For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . 
     Second Embodiment 
     An X-ray tube  1  according to Second Embodiment is different from the above-explained X-ray tube  1  with respect to a feature that a leg portion LG 11  of a filament FL 1  is joined to a support terminal  401 F at a plurality of parts in an electron emission source, for example, an electron emission source  321 R. 
       FIG. 21A  and  FIG. 21B  are cross-sectional views showing an example of a structure of the electron emission source  321 R according to the Second Embodiment.  FIG. 21A  is an expanded sectional view showing an example of the electron emission source  321 R.  FIG. 21B  is an expanded sectional view showing an example of a distal portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 21A , the support terminal  401 F comprises a pair of depressions  412  and  414  and a pair of depressions  416  and  418 . The depressions  416  and  418  are formed on outer surfaces OU 1  and OU 2  of the support terminal  401 F, respectively. The depression  416  is formed more closely to the outer surface OU 1  on the opening portion side than the depression  412 . The depression  418  is formed more closely to the outer surface OU 2  on the opening portion side than the depression  414 . The depression  416  is opposed to the depression  418  with the gap CL 11  sandwiched between the depressions. In the example illustrated in  FIG. 21A , a support portion SP 11  of the leg portion LG 11  is located between the depressions  416  and  418 , in the gap CL 11 . In the leg portion LG 11 , the support portion SP 11  is located more closely to the coil portion C 1  side than the distal portion TP 11 . 
     In the example illustrated in  FIG. 21B , the support portion SP 11  of the leg portion LG 11  is fixed to the inner surface IN 1  via a joint portion WE 1  and fixed to the inner surface IN 2  via a joint portion WE 2 . The joint portion WE 1  is formed by melting at least one of the support portion SP 11  of the leg portion LG 11  and the inner surface IN 1  of the support terminal  401 F. The joint portion WE 2  is formed by melting at least one of the support portion SP 11  of the leg portion LG 11  and the inner surface IN 2  of the support terminal  401 F. Each of the joint portions WE 1  and WE 2  is formed of a conductive metallic member. The joint portion WE 1  may be formed integrally with at least one of the support portion SP 11  of the leg portion LG 11  and the inner surface IN 1  of the support terminal  401 F. The joint portion WE 2  may be formed integrally with at least one of the support portion SP 11  of the leg portion LG 11  and the inner surface IN 2  of the support terminal  401 F. 
     An example of a method of manufacturing the electron emission source  321 R according to the present embodiment will be hereinafter explained with reference to  FIG. 22A ,  FIG. 22B ,  FIG. 23A , and  FIG. 23B . 
     First, the support terminal  401 F is installed on the surface SF 1  of the base PED. The distal portion TP 11  of the leg portion LG 11  of the filament FL 1  is located between the electrodes EL 1  and EL 2 . The steps of joining the distal portion TP 11  of the leg portion LG 11  and the support terminal  401 F are the same as the steps explained with reference to  FIG. 6  to  FIG. 8B , and their explanations are omitted. 
       FIG. 22A  and  FIG. 22B  are cross-sectional views showing an example of the support terminal  401 F on which the force is exerted by the electrode EL.  FIG. 22A  is a cross-sectional view showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 22B  is an expanded sectional view showing the support portion TP 11  of the leg portion LG 11 . 
     As shown in  FIG. 22A , the electrodes EL 1  and EL 2  sandwich the support terminal  401 F from both sides to exert force on the outer surfaces OU 1  and OU 2  of the support terminal  401 F. The depressions  416  and  418  are formed on the outer surfaces OU 1  and OU 2  of the support terminal  401 F by the electrodes EL 1  and EL 2 , respectively. 
     As shown in  FIG. 22B , the inner surfaces IN 1  and IN 2  of the support terminal  401 F protrude to the support portion SP 11  of the leg portion LG 11  and are made to abut on the support portion SP 11 , by the force exerted by the electrodes EL 1  and EL 2 . At this time, each of the inner surfaces IN 1  and IN 2  of the support terminal  401 F is brought into line contact with the support portion SP 11  of the leg portion LG 11 . 
       FIG. 23A  and  FIG. 23B  are cross-sectional views showing the support terminal  401 F joined to the support portion SP 11  of the leg portion LG 11 .  FIG. 23A  is a cross-sectional view schematically showing the filament FL 1  and the support terminal  401 F installed in the jig JG.  FIG. 23B  is an expanded sectional view showing the support portion TP 11  of the leg portion LG 11 . 
     In the example illustrated in  FIG. 23A , the electrodes EL 1  and EL 2  supply a current while exerting force on the outer surfaces OU 1  and OU 2  of the support terminal  401 F. At this time, each of the inner surfaces IN 1  and IN 2  of the support terminal  401 F is molten and joined to the support portion SP 11  of the leg portion LG 11 . As shown in  FIG. 23B , for example, the joint portion WE 1  is formed between the support portion SP 11  of the leg portion LG 11  and the inner surface IN 1  of the support terminal  401 F. The joint portion WE 2  is formed between the support portion SP 11  of the leg portion LG 11  and the inner surface IN 2  of the support terminal  401 F. The joint portion WE 1  is formed by meting at least one of the inner surface IN 1  of the support terminal  401 F and the support portion SP 11  of the leg portion LG 11 . The joint portion WE 2  is formed by meting at least one of the inner surface IN 2  of the support terminal  401 F and the support portion SP 11  of the leg portion LG 11 . 
       FIG. 24  is a flowchart showing an example of a method of manufacturing the electron emission source  321 R of the X-ray tube  1  according to the present embodiment. The same processing in the flowchart in  FIG. 24  as that in the flowchart in  FIG. 9  is denoted by the same reference numeral, and the detailed explanations are simplified or omitted. 
     First, the support terminal  401 F is installed in the jig JG (S 901 ), and the leg portion LG 11  of the filament FL 1  is inserted into the gap CL 11  of the support terminal  401 F (S 902 ). The support terminal  401 F is welded by pressure (crimped) on the distal portion TP 11  of the leg portion LG 11  by the electrodes EL 1  and EL 2  (S 903 ). 
     In this state, the support terminal  401 F is welded on the distal portion TP 11  of the leg portion LG 11  by the electrodes EL 1  and EL 2  (S 904 ). 
     Furthermore, the support terminal  401 F is welded by pressure (crimped) on an upper side (coil portion C 1  side) than the distal portion TP 11  of the leg portion LG 11  by the electrodes EL 1  and EL 2  (S 2501 ). At this time, the inner surfaces IN 1  and IN 2  are welded to the support portion SWP 11  by the current supplied by the electrodes EL 1  and EL 2  while being made to abut on the support portion SP 11  by the electrodes EL 1  and EL 2  with the force exerted on the electrodes EL 1  and EL 2 , respectively (S 2502 ). In the flowchart shown in  FIG. 24 , the processing of bringing the support terminal  401 F into contact with the distal portion TP 11  of the leg portion LG 11  by pressure is performed prior to the processing of bringing the support terminal  401 F into contact with the upper side of the distal portion TP 11  of the leg portion LG 11  by pressure, but may be performed after this processing. In addition, the welding step in S 2502  may be omitted after the crimping step in S 2501 , in the flowchart shown in  FIG. 24 . 
     The X-ray tube  1 , according to the Second Embodiment, is joined to the support terminal  401 F by the support portion SP 11  and the distal portion TP 11  of the leg portion LG 11  of the filament FL 1 . For this reason, the X-ray tube  1  can prevent displacement of the leg portions of the filament FL 1 , for example, the leg portion LG 11 . As a result, the X-ray tube  1  can prevent contact of the filament FL 1  on the cathode cup  310 , and the like. 
     In the Second Embodiment, the leg portion LG 11  of the filament FL 1  is fixed to the support terminal  401 F at two portions but may be fixed at two or more portions. In addition, the support portion SP 11  of the leg portion LG 11  may not be fixed to the inner surfaces IN 1  and IN 2  of the support terminal  401 F via the joint portions WE 1  and WE 2 . For example, the support portion SP 11  of the leg portion LG 11  may be supported (welded by pressure or crimped) while sandwiched between the protruding inner surfaces IN 1  and IN 2 . This corresponds to the case of omitting the welding step in S 2502  after the crimping step in S 2501 , in the flowchart shown in  FIG. 24 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.