Patent Publication Number: US-9887061-B2

Title: X-ray tube device and method for using X-ray tube device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of PCT/JP2012/073340 filed Sep. 12, 2012. The subject matter of each is incorporated herein by reference in entirety. 
     TECHNICAL FIELD 
     The present invention relates to an X-ray tube device and a method for using an X-ray tube device, and more particularly, it relates to an X-ray tube device and a method for using an X-ray tube device each including an emitter having a flat plate-like electron emission portion. 
     BACKGROUND ART 
     In general, an X-ray tube device including an emitter having a flat plate-like electron emission portion is known. Such an X-ray tube device is disclosed in National Patent Publication Gazette No. 2010-534396, for example. 
     An X-ray tube device disclosed in the aforementioned National Patent Publication Gazette No. 2010-534396 includes an emitter including a flat plate-like electron emission portion and a pair of (two) terminal portions connecting the electron emission portion and an electrode to each other. An anisotropic polycrystalline material (tungsten) having a long crystal structure is employed for the electron emission portion. The terminal portions support the lower surface (a surface opposite to an electron emission surface) of the flat plate-like electron emission portion in the vicinity of both ends and have a function of applying an electric current to the electron emission portion. The electron emission portion is applied with an electric current through the terminal portions to be heated to at least about 2000° C., whereby the electron emission portion emits an electron. Therefore, the electron emission portion is creep-deformed by a high temperature associated with the use of the emitter and external force acting on the electron emission portion. In the aforementioned National Patent Publication Gazette No. 2010-534396, the electron emission portion is configured such that the longitudinal direction of crystal grains is oriented in a prescribed direction, and the mechanical strength of the electron emission portion in the direction (a direction parallel to the electron emission surface) of action of principal stress loading in normal use is improved. Thus, a deterioration of the electron emission characteristics of the emitter and a reduction in the lifetime of the emitter resulting from the creep deformation are suppressed. 
     PRIOR ART 
     Patent Document 
     Patent Document 1: National Patent Publication Gazette No. 2010-534396 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Although the X-ray tube device according to the aforementioned National Patent Publication Gazette No. 2010-534396 is configured such that the orientation of the crystal grains of the electron emission portion is aligned in the prescribed direction in terms of a material in order to improve the mechanical strength in the direction parallel to the electron emission surface, there is such a problem that it is difficult to sufficiently suppress the phenomenon (sagging phenomenon) where the electron emission portion is sunk by the creep deformation associated with prolonged use to be deformed in the structure in which the vicinities of both ends of the flat plate-like electron emission portion are supported by the pair of terminal portions. When the electron emission portion is sunk by the sagging phenomenon, the convergence of electrons emitted from the emitter is reduced, and hence the focal point diameter of an X-ray emitted from the X-ray tube device cannot fall within a desired range. Thus, in order to maintain a desired X-ray focal point diameter over a longer period of time and further increase the lifetime of the emitter, it is desirable to sufficiently suppress sinking of the electron emission portion. 
     The present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide an X-ray tube device and a method for using an X-ray tube device each capable of sufficiently suppressing sinking of an electron emission portion resulting from creep deformation associated with use. 
     Means for Solving the Problems 
     In order to attain the aforementioned object, an X-ray tube device according to a first aspect of the present invention includes an anode and a cathode including an emitter emitting an electron to the anode, and the emitter includes an electron emission portion in a flat plate shape, a pair of terminal portions extending from the electron emission portion, connected to an electrode, and a supporting portion provided separately from the terminal portions, insulated from the electrode, supporting the electron emission portion. 
     In the X-ray tube device according to the first aspect of the present invention, as hereinabove described, the emitter is provided with the supporting portion provided separately from the terminal portions, insulated from the electrode, supporting the electron emission portion, whereby the electron emission portion in the flat plate shape can be structurally supported by not only the terminal portions but also the supporting portion provided separately from the terminal portions. Thus, sinking (sagging phenomenon) of the electron emission portion structurally inevitably generated in the electron emission portion in the flat plate shape, resulting from creep deformation associated with use can be sufficiently suppressed by the supporting portion, which is not material but structural means. Furthermore, the dedicated supporting portion insulated from the electrode is provided, whereby the supporting portion can easily support the electron emission portion without obstructing a current pathway flowing from the electrode to the electron emission portion through the terminal portions. 
     In the aforementioned X-ray tube device according to the first aspect, the supporting portion is preferably arranged to support the vicinity of a deformed portion of the electron emission portion where the degree of variation of flatness of the electron emission portion resulting from creep deformation associated with the use of the emitter is relatively large. According to this structure, the sinking (sagging phenomenon) of the electron emission portion can be effectively suppressed by supporting the vicinity of the deformed portion where the variation of flatness is large. 
     In this description, the “flatness” denotes the amount of deviation of the electron emission portion from each of upper and lower reference surfaces in a projection view in a lateral direction parallel to the electron emission portion, setting the upper and lower surfaces of the ideal electron emission portion in an undeformed state as the reference surfaces. The upper surface of the electron emission portion is set as an electron emission surface, and the lower surface thereof is set as a surface opposite to the electron emission surface. The “deformed portion” is a portion of the electron emission portion where the degree of variation of flatness is relatively large in the case where a state of providing no supporting portion is assumed. The position of the deformed portion in the electron emission portion is determined according to the shape of the electron emission portion and can be derived by a simulation, for example. According to the present invention, the “vicinity of the deformed portion” includes the deformed portion and a region in the vicinity of the deformed portion. 
     In the aforementioned structure in which the supporting portion supports the vicinity of the deformed portion, the electron emission portion is preferably formed in the flat plate shape by a current path which is winding, and the supporting portion is preferably arranged to support the current path on the outer peripheral side of the electron emission portion including the deformed portion. In the case where the electron emission portion is formed in the flat plate shape by the current path which is winding, as described above, the deformed portion whose flatness is easily varied structurally exists in the current path of the electron emission portion on the outer peripheral side (the current path on the outer peripheral side is easily creep-deformed). Thus, the supporting portion is arranged to structurally support the current path on the outer peripheral side as in the present invention, whereby the sinking (sagging phenomenon) of the electron emission portion can be more effectively suppressed. 
     In the aforementioned structure in which the supporting portion supports the current path on the outer peripheral side of the electron emission portion, the current path preferably includes at least a first portion on the outer peripheral side extending from one of the terminal portions toward the other of the terminal portions and a second portion extending from the other of the terminal portions toward one of the terminal portions on an inner peripheral side with respect to the first portion continuously from the first portion, and the supporting portion is preferably arranged to support the vicinity of a connection portion between the first portion and the second portion. In the case where the current path is windingly formed to include the first portion on the outer peripheral side and the second portion on the inner peripheral side, as described above, the vicinity of the connection portion between the first portion and the second portion becomes a portion whose flatness is particularly easily varied. Thus, the supporting portion is arranged to support the vicinity of the connection portion between the first portion and the second portion as in the present invention, whereby the vicinity of a part of the deformed portion whose flatness is particularly easily varied can be structurally supported, and hence the sinking (sagging phenomenon) of the electron emission portion can be reliably and more effectively suppressed. 
     In the aforementioned X-ray tube device according to the first aspect, the supporting portion is preferably formed to extend to the same side as that of the terminal portions in a direction intersecting with the electron emission portion, and one end thereof is preferably fixed while the other end thereof is coupled to the electron emission portion or is arranged at a position in contact with the electron emission portion. According to this structure, it is only required to add the supporting portion on the side of the emitter closer to the terminal portions, and hence the supporting portion can be structurally easily provided. The supporting portion is only required to support the electron emission portion, and hence the supporting portion may only come into contact with the electron emission portion from the same side as that of the terminal portions to support the same without being coupled and fixed to the electron emission portion. 
     In the aforementioned X-ray tube device according to the first aspect, the supporting portion is preferably formed in the flat plate shape integrally with the electron emission portion by pulling out from an outer peripheral portion of the electron emission portion in the flat plate shape and bending to the same side as that of the terminal portions. According to this structure, the supporting portion and the electron emission portion can be integrally formed of a common flat plate material, and hence the supporting portion can be easily formed. Furthermore, the supporting portion can be provided without an increase in the number of components, unlike the case where the supporting portion and the electron emission portion are provided separately from each other. 
     The aforementioned X-ray tube device according to the first aspect preferably further includes a tubular enclosure housing the emitter and a target as the anode, rotating about a central axis, and a pair of supporting portions are preferably provided at positions opposed to each other through the central axis. According to this structure, in the so-called enclosure rotation type X-ray tube device in which the emitter rotates together with the enclosure, a mechanical balance about the rotation central axis can be maintained even in the case where the supporting portions are provided in the emitter, and hence the deformation can be suppressed while the rotation of the emitter in use (during rotation) is stabilized. 
     In the aforementioned X-ray tube device according to the first aspect, the electron emission portion preferably has a protrusion portion protruding in a direction opposite to the deformation direction of a deformed portion in a region including the deformed portion where the degree of variation of flatness of the electron emission portion resulting from creep deformation associated with the use of the emitter. According to this structure, the protrusion portion protruding in the direction opposite to the deformation direction can cancel out the variation of flatness even when the creep deformation is generated in the electron emission portion. Thus, while the supporting portion suppresses deformation, the protrusion portion can cancel out additional deformation even when the deformation is further generated, and hence sinking of the electron emission portion can be more sufficiently suppressed. 
     In this case, the protrusion portion preferably protrudes in a direction opposite to a direction of action of gravity in use. According to this structure, the protrusion portion can cancel out the creep deformation of the electron emission portion resulting from gravity constantly acting on the emitter. 
     In the aforementioned structure in which the electron emission portion has the protrusion portion, the electron emission portion is preferably formed in the flat plate shape by a current path which is winding, and the protrusion portion is preferably arranged in the current path on the outer peripheral side of the electron emission portion including the deformed portion. According to this structure, the deformed portion whose flatness is easily varied structurally exists in the current path of the electron emission portion on the outer peripheral side, and hence the sinking (sagging phenomenon) of the portion whose flatness is easily varied in the electron emission portion can be effectively canceled out. 
     In this case, the current path preferably includes at least a first portion on the outer peripheral side extending from one of the terminal portions toward the other of the terminal portions and a second portion extending from the other of the terminal portions toward one of the terminal portions on an inner peripheral side with respect to the first portion continuously from the first portion, and the protrusion portion is preferably formed by inclining the first portion such that the vicinity of a connection portion between the first portion and the second portion protrudes. According to this structure, the vicinity of the connection portion between the first portion and the second portion structurally becomes the portion whose flatness is particularly easily varied, and hence the sinking (sagging phenomenon) of the vicinity of the part of the deformed portion whose flatness is particularly easily varied in the electron emission portion can be reliably and more effectively canceled out. 
     In the aforementioned X-ray tube device according to the first aspect, the electron emission portion is preferably formed in the flat plate shape by a current path which is winding and has a wide portion whose path width is larger than those of other portions of the current path, and the wide portion is preferably arranged in a region including a deformed portion where the degree of variation of flatness of the electron emission portion resulting from creep deformation associated with the use of the emitter is relatively large. According to this structure, the mechanical strength of the current path (wide portion) in the region including the deformed portion can be relatively improved as compared with that of other portions. Thus, while the supporting portion suppresses deformation, the wide portion can further suppress deformation, and hence the sinking of the electron emission portion can be more sufficiently suppressed. 
     In this case, the wide portion is preferably arranged in the current path on the outer peripheral side of the electron emission portion including the deformed portion. According to this structure, the deformed portion whose flatness is easily varied structurally exists in the current path of the electron emission portion on the outer peripheral side, and hence the sinking (sagging phenomenon) of the portion whose flatness is easily varied in the electron emission portion can be effectively suppressed. 
     In the aforementioned structure in which the wide portion is arranged in the current path on the outer peripheral side, the electron emission portion preferably includes at least a first portion on the outer peripheral side extending from one of the terminal portions toward the other of the terminal portions and a second portion extending from the other of the terminal portions toward one of the terminal portions on an inner peripheral side with respect to the first portion continuously from the first portion, and the wide portion is preferably formed in the first portion including the vicinity of a connection portion between the first portion and the second portion. According to this structure, the vicinity of the connection portion between the first portion and the second portion structurally becomes the deformed portion whose flatness is particularly easily varied, and hence the sinking (sagging phenomenon) of the vicinity of the part of the deformed portion whose flatness is particularly easily varied in the electron emission portion can be reliably and more effectively suppressed. 
     A method for using an X-ray tube device according to a second aspect of the present invention is a method for using an X-ray tube device including an anode and a cathode including an emitter emitting an electron to the anode, in which the emitter includes an electron emission portion in a flat plate shape, a pair of terminal portions extending from the electron emission portion, connected to an electrode, and a supporting portion provided separately from the terminal portions, insulated from the electrode, supporting the electron emission portion, and includes steps of emitting the electron in a state where the emitter is oriented in a first direction along a gravity direction to be opposed to the anode and generating an X-ray and applying an electric current to at least the emitter to heat the emitter in a state where the emitter is oriented in a second direction along the gravity direction, opposite to the first direction to be opposed to the anode. 
     In the method for using an X-ray tube device according to the second aspect of the present invention, as hereinabove described, the X-ray tube device including the emitter including the supporting portion provided separately from the terminal portions, insulated from the electrode, supporting the electron emission portion is used, whereby the electron emission portion in the flat plate shape can be structurally supported by not only the terminal portions but also the supporting portion provided separately from the terminal portions, and hence sinking of the electron emission portion resulting from creep deformation associated with use can be sufficiently suppressed. Furthermore, according to the present invention, at least the emitter is applied with an electric current to be heated in the state where the emitter is oriented in the second direction along the gravity direction, opposite to the first direction to be opposed to the anode, whereby the sinking of the electron emission portion resulting from the creep deformation (deformation generated by applying an electric current to the emitter to heat the same in the first direction) generated in the step of generating an X-ray in normal use can be canceled out by deformation in the opposite direction generated by applying an electric current to the emitter to heat the same in the opposite second direction. Thus, the sinking of the electron emission portion resulting from the creep deformation associated with use can be more sufficiently suppressed. 
     A method for using an X-ray tube device according to a third aspect of the present invention is a method for using an X-ray tube device including an anode and an emitter having an electron emission portion in a flat plate shape emitting an electron to the anode, and includes steps of emitting the electron in a state where the emitter is oriented in a first direction along a gravity direction to be opposed to the anode and generating an X-ray and applying an electric current to at least the emitter to heat the emitter in a state where the emitter is oriented in a second direction along the gravity direction, opposite to the first direction to be opposed to the anode. 
     In the method for using an X-ray tube device according to the third aspect of the present invention, as hereinabove described, at least the emitter is applied with an electric current to be heated in the state where the emitter is oriented in the second direction along the gravity direction, opposite to the first direction to be opposed to the anode, whereby sinking of the electron emission portion resulting from creep deformation (deformation generated by applying an electric current to the emitter to heat the same in the first direction) generated in the step of generating an X-ray in normal use can be canceled out by deformation in the opposite direction generated by applying an electric current to the emitter to heat the same in the opposite second direction. Thus, the creep deformation of the electron emission portion in use can be canceled out, and hence the sinking of the electron emission portion resulting from the creep deformation associated with use can be sufficiently suppressed. 
     In the aforementioned method for using an X-ray tube device according to the third aspect, the step of applying an electric current to at least the emitter to heat the emitter in the state where the emitter is oriented in the second direction is preferably carried out under the same condition as that of application of an electric current to the emitter to heat the emitter in the step of generating an X-ray for a time substantially equal to a time to apply an electric current to the emitter to heat the emitter in the step of generating an X-ray. According to this structure, the amount of deformation substantially equal to the amount of deformation of the electron emission portion generated in normal use can be generated in the opposite direction by the step of applying an electric to the emitter to heat the same in the second direction. Thus, the sinking of the electron emission portion can be effectively suppressed, and excessive deformation in the opposite direction can be prevented by the step of applying an electric current to the emitter to heat the same in the second direction. 
     An X-ray tube device according to a fourth aspect of the present invention includes an anode and a cathode including an emitter emitting an electron to the anode, the emitter includes an electron emission portion in a flat plate shape, and a pair of terminal portions extending from both ends of the electron emission portion, connected to an electrode, and the electron emission portion has a protrusion portion protruding in a direction opposite to the deformation direction of a deformed portion in a region including the deformed portion where the degree of variation of flatness of the electron emission portion resulting from creep deformation associated with the use of the emitter is relatively large. 
     In the X-ray tube device according to the fourth aspect of the present invention, as hereinabove described, the electron emission portion is provided with the protrusion portion protruding in the direction opposite to the deformation direction of the deformed portion in the region including the deformed portion where the degree of variation of flatness of the electron emission portion resulting from the creep deformation associated with the use of the emitter is relatively large, whereby the protruding portion protruding in the direction opposite to the deformation direction can cancel out the variation of flatness even when the creep deformation is generated in the electron emission portion. Thus, the variation of flatness in the region including the deformed portion can be canceled out, and hence sinking of the electron emission portion resulting from the creep deformation associated with use can be sufficiently suppressed. 
     An X-ray tube device according to a fifth aspect of the present invention includes an anode and a cathode including an emitter emitting an electron to the anode, the emitter includes an electron emission portion formed in a flat plate shape by a current path which is winding, having a wide portion whose path width is larger than those of other portions of the current path, and a pair of terminal portions extending from both ends of the electron emission portion, connected to an electrode, and the wide portion is arranged in a region including a deformed portion where the degree of variation of flatness of the electron emission portion resulting from creep deformation associated with the use of the emitter is relatively large. 
     In the X-ray tube device according to the fifth aspect of the present invention, as hereinabove described, the wide portion is arranged in the region including the deformed portion where the degree of variation of flatness of the electron emission portion resulting from the creep deformation associated with the use of the emitter is relatively large, whereby the mechanical strength of the current path (wide portion) in the region including the deformed portion can be relatively improved as compared with that of other portions. Thus, generation of the deformation in the region (wide portion) including the deformed portion can be suppressed, and hence sinking of the electron emission portion resulting from the creep deformation associated with use can be sufficiently suppressed. 
     Effect of the Invention 
     As hereinabove described, according to the present invention, the X-ray tube device and the method for using an X-ray tube device each capable of sufficiently suppressing the sinking of the electron emission portion resulting from the creep deformation associated with use can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A schematic longitudinal sectional view showing the overall structure of an X-ray tube device according to a first embodiment of the present invention. 
         FIG. 2  A schematic perspective view showing an emitter of the X-ray tube device according to the first embodiment of the present invention. 
         FIG. 3  A top plan view (plan view) showing an electron emission portion of the emitter shown in  FIG. 2 . 
         FIG. 4  A side elevational view (front elevational view) of the emitter shown in  FIG. 2 . 
         FIG. 5  A side elevational view of the emitter shown in  FIG. 2  as viewed from the side of a terminal portion. 
         FIG. 6  A schematic view showing simulation results of variation of flatness in an emitter according to Comparative Example. 
         FIG. 7  A schematic view showing simulation results of variation of flatness in an emitter according to Example of the present invention. 
         FIG. 8  A schematic view for illustrating an emitter according to a modification of the first embodiment of the present invention. 
         FIG. 9  A schematic view for illustrating an emitter of an X-ray tube device according to a second embodiment of the present invention. 
         FIG. 10  A schematic view for illustrating another emitter of the X-ray tube device according to the second embodiment of the present invention. 
         FIG. 11  A schematic view for illustrating an emitter according to a modification of the second embodiment of the present invention. 
         FIG. 12  A perspective view schematically showing an emitter of an X-ray tube device according to a third embodiment of the present invention. 
         FIG. 13  A top plan view (plan view) showing an electron emission portion of the emitter shown in  FIG. 12 . 
         FIG. 14  A schematic view for illustrating an emitter of an X-ray tube device according to a fourth embodiment of the present invention. 
         FIG. 15  A schematic view for illustrating another emitter of the X-ray tube device according to the fourth embodiment of the present invention. 
         FIG. 16  A perspective view schematically showing an emitter of an X-ray tube device according to a fifth embodiment of the present invention. 
         FIG. 17  A top plan view (plan view) showing an electron emission portion of the emitter shown in  FIG. 16 . 
         FIG. 18  A schematic view showing an apparatus configuration for illustrating a method for using an X-ray tube device according to a sixth embodiment of the present invention. 
         FIG. 19  A schematic view for illustrating the method for using the X-ray tube device according to the sixth embodiment of the present invention. 
         FIG. 20  A schematic view for illustrating a method for using an X-ray tube device according to a seventh embodiment of the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments are hereinafter described on the basis of the drawings. 
     First Embodiment 
     The structure of an X-ray tube device  100  according to a first embodiment is now described with reference to  FIGS. 1 to 3 . 
     The X-ray tube device  100  includes an electron source  1  generating an electron beam, a target  2 , an enclosure  3  internally housing the electron source  1  and the target  2 , and a magnetic field generator  4  provided outside the enclosure  3 , as shown in  FIG. 1 . According to the first embodiment, the X-ray tube device  100  is a rotating anode X-ray tube device in which the target  2  rotates, and more specifically an enclosure rotation type X-ray tube device in which the enclosure  3  rotates integrally with the target  2  the enclosure  3 . The electron source  1  and the target  2  are examples of the “cathode” and the “anode” in the present invention, respectively. 
     The electron source  1  is fixedly mounted on one end of the enclosure  3  in an axial direction (direction  A ) through an insulating member  5 . The electron source  1  is arranged on the rotation axis  3   a  of the enclosure  3  and is configured to rotate integrally with the enclosure  3  about the rotation axis  3   a . The electron source  1  includes an emitter  10  and a pair of electrodes  1   a  for applying an electric current to the emitter  10  to heat the same, as shown in  FIG. 2 . The structure of the emitter  10  is described later. 
     As shown in  FIG. 1 , the target  2  is integrally (fixedly) mounted on the other end of the enclosure  3  in the axial direction (direction  A ) to be opposed to the electron source  1 . The target  2  has a disc shape inclined such that the edge  2   a  is thinned outward. The center of the target  2  coincides with the rotation axis  3   a  of the enclosure  3 , and the target  2  is configured to rotate integrally with the enclosure  3  about the rotation axis  3   a.    
     The target  2  and the electron source  1  are connected to a positive terminal and a negative terminal of an unshown power source portion, respectively. A positive high voltage is applied to the target  2 , and a negative high voltage is applied to the electron source  1 , whereby the electron beam is generated from the electron source  1  toward the target  2  along the rotation axis  3   a  (axial direction  A ). 
     The enclosure  3  has a tubular shape extending in the axial direction  A  about the rotation axis (central axis)  3   a . The enclosure  3  is supported by shafts  7  and bearings  7   a  provided on both ends to be rotatable about the rotation axis  3   a . The enclosure  3  is drivingly rotated by a motor  6  coupled to the shaft  7 . One end of the enclosure  3  is sealed by the disc-shaped insulating member  5 , and the other end of the enclosure  3  is sealed by the target  2 . The inside of the enclosure  3  is evacuated. The enclosure  3  is made of a non-magnetic metal material such as stainless steel (SUS), and the insulating member  5  is made of an insulating material such as ceramic. 
     The magnetic field generator  4  includes a plurality of magnetic poles arranged on an annular core and coils wound around the magnetic poles. The magnetic field generator  4  has a function of generating a magnetic field for focusing and deflecting the electron beam from the electron source  1  toward the target  2 . As shown in  FIG. 1 , the electron beam toward the target  2  along the axial direction  A  is focused and deflected by the action of the magnetic field generated from the magnetic field generator  4  and hits the inclined edge  2   a  of the target  2 . Consequently, an X-ray is generated from the edge  2   a  of the target  2  and is externally emitted through an unshown window portion of the enclosure  3 . 
     The structure of the emitter  10  of the electron source  1  is now described in detail. As shown in  FIGS. 2 to 5 , the emitter  10  is made of pure tungsten or a tungsten alloy and integrally has a flat plate-like electron emission portion  11 , a pair of terminal portions  12 , and a pair of supporting portions  13 . According to the first embodiment, the electron emission portion  11 , the pair of terminal portions  12 , and the pair of supporting portions  13  are cut from a single flat plate material and are integrally formed by bending. 
     The emitter  10  is a so-called thermionic emitter and is configured to be applied with an electric current from the electrodes  1   a  through the pair of terminal portions  12  to be heated. Thus, the flat plate-like electron emission portion  11  is applied with a prescribed electric current to be heated to a prescribed temperature (about 2400 K to about 2500 K), whereby the electron emission portion  11  emits an electron. 
     As shown in  FIGS. 2 and 3 , the electron emission portion  11  is formed in a flat plate shape by a winding (meandering) current path  20  and is formed in a circular shape in a plan view. A central portion  24  of the electron emission portion  11  coincides with the rotation axis  3   a  of the enclosure  3 , and the emitter  10  rotates about the central portion  24  (rotation axis  3   a ) following the rotation of the enclosure  3 . 
     The current path  20  is formed with a substantially constant path width W 1  and is connected to the terminal portions  12  on both ends of the current path  20 . The current path  20  includes first portions  21 , second portions  22 , third portions  23 , and the central portion  24 . A pair of first portions  21  are outer peripheral portions provided to extend in an arcuate shape from one (the other) terminal portion  12  toward the other (one) terminal portion  12 . The second portions  22  are provided to extend in an arcuate shape toward the opposite terminal portions  12  on the inner peripheral side with respect to the first portions  21  continuously from the first portions  21 . The third portions  23  are provided to further extend in an arcuate shape toward the opposite sides continuously from the second portions  22  and to be connected to the central portion  24 . 
     As shown in  FIGS. 2, 4, and 5 , the pair of terminal portions  12  extend from ends of the current path  20  (electron emission portion  11 ) and are formed by bending in a direction Z 1 , and ends of the terminal portions  12  are fixed to the electrodes  1   a  of the electron source  1 . The terminal portions  12  serve as connection terminals with the electrodes  1   a  for applying an electric current to the electron emission portion  11  to heat the same and have a function of supporting the electron emission portion  11  by being fixed to the electrodes  1   a . The terminal portions  12  each have a flat plate shape with a width equal to the path width (W 1 ) of the current path  20 . 
     As shown in  FIGS. 2 to 5 , the pair of supporting portions  13  are provided separately from the terminal portions  12 , are insulated from the electrodes  1   a , and are formed to support the electron emission portion  11 . The pair of supporting portions  13  are arranged to be opposed to each other through the rotation axis (central axis)  3   a  of the enclosure  3  in a plan view. These supporting portions  13  extend from prescribed portions of the current path  20  (electron emission portion  11 ) and are formed in a flat plate shape by bending in the same direction Z 1  as that of the terminal portions  12 . Ends of the supporting portions  13  are fixed by fixing members  1   b  provided on a base portion (not shown) of the electron source  1 . The fixing members  1   b  are insulated from the electrodes  1   a . The ends of the supporting portions  13  may be directly fixed to the base portion (not shown) of the electron source  1 . Illustration of the electrodes  1   a  and the fixing members  1   b  is omitted in  FIGS. 3 and 4 . 
     The supporting portions  13  each have a width W 2  smaller than the path width W 1  of each of the terminal portions  12  and the current path  20 , and according to the first embodiment, the width W 2  is about a half of the width W 1 . The width W 2  of each of the supporting portions  13  is only required to be equal to or larger than that required to obtain strength capable of supporting the electron emission portion  11 . In order to be capable of suppressing escape of the heat of the electron emission portion  11 , which has been applied with an electric current to be heated, to the supporting portions  13 , the width W 2  of each of the supporting portions  13  is preferably smaller. 
     According to the first embodiment, the supporting portions  13  are arranged to support the vicinities of deformed portions Df of the electron emission portion  11  (current path  20 ) where the degree of variation of the flatness of the electron emission portion  11  resulting from creep deformation (sagging phenomenon) associated with the use of the emitter  10  is relatively large. 
     The deformed portions Df of the electron emission portion  11  are determined by the shape of the electron emission portion and can be derived by a computational method such as a simulation, for example.  FIG. 6  shows simulation results (Comparative Example) for evaluating the creep deformation of the emitter in the case where no supporting portion  13  is provided. The creep deformation of the electron emission portion is generated mainly by a high temperature at the time of applying an electric current to the emitter to heat the same and external force (gravity, inertial force related to centrifugal force, or the like) acting on the electron emission portion. However, strictly speaking, slip or the like of metal crystal grains constituting the emitter is generated, and hence it is difficult to accurately reproduce the creep deformation by the simulation. Therefore, the magnitude of gravity was adjusted to obtain deformation equivalent to experimentally confirmed creep deformation after ten thousand exposures (X-ray irradiation), taking into consideration only the creep deformation generated by gravity, whereby the creep deformation was reproduced. 
     In  FIG. 6 , the degree of the creep deformation (sagging phenomenon) is evaluated by flatness. The flatness is the amount of deviation of the electron emission portion  11  from each of an upper (the side of an electron emission surface) reference surface Rt and a lower (a side opposite to the electron emission surface) reference surface Rb in a projection view (see  FIG. 4 ) as viewed from a side parallel to the electron emission portion  11 . Therefore, in an undeformed state, the upper surface (electron emission surface)  11   a  of the electron emission portion  11  coincides with the upper reference surface Rt and the flatness is +0 while the lower surface  11   b  of the electron emission portion  11  coincides with the lower reference surface Rb and the flatness is −0. It is assumed that the flatness is +X if the upper surface  11   a  of the electron emission portion  11  is deviated by X in a direction Z 2  (upper surface side) due to the sagging phenomenon, and the flatness is −Y if the lower surface  11   b  is deviated by Y in the direction Z 1  (lower surface side). In the simulation, a gravity direction (vertically downward) G 2  coincides with the direction Z 1  (flatness minus direction) from the upper surface  11   a  toward the lower surface  11   b.    
     In the case where no supporting portion  13  is provided, as shown in  FIG. 6 , the flatness of the electron emission portion  11  is significantly varied in the current path  20  of the electron emission portion  11  on the outer peripheral side (see dark hatched regions in  FIG. 6 ). Specifically, regions around connection portions P 1  of the current path  20  between the first portions  21  and the second portions  22  (about halve of the first portions  21  and about halve of the second portions  22  with respect to the connection portions P 1 ) become the deformed portions Df where the variation of flatness is relatively large. Although the same hatching is denoted, the variation of flatness is maximized (−52 μm) in the connection portions P 1  of the deformed portions Df. This result is easily understood also from that the electron emission portion  11  has a structure of supporting the weights of the second portions  22 , the third portions  23 , and the central portion  24  on the inner peripheral side by ends (the connection portions P 1  with the second portions  22 ) of the first portions  21  supported by the pair of terminal portions  12 . 
     On the basis of the aforementioned simulation results (Comparative Example), according to the first embodiment, the supporting portions  13  are the current path  20  on the outer peripheral side of the electron emission portion  11  and are arranged to support the vicinities of the connection portions P 1  (deformed portions Df) between the first portions  21  and the second portions  22 . 
     According to the first embodiment, as hereinabove described, the supporting portions  13  provided separately from the terminal portions  12 , insulated from the electrodes  1   a , supporting the electron emission portion  11  is provided, whereby the flat plate-like electron emission portion  11  can be structurally supported by not only the terminal portions  12  but also the supporting portions  13  provided separately from the terminal portions  12 . Thus, sinking (sagging phenomenon) of the electron emission portion  11  resulting from the creep deformation associated with use can be sufficiently suppressed by the supporting portions  13 , which are not material but structural means. Furthermore, it is only required to provide the dedicated supporting portions  13  insulated from the electrodes  1   a , and hence the supporting portions  13  can easily support the electron emission portion  11  without obstructing current pathways flowing from the electrodes  1   a  to the electron emission portion  11  through the terminal portions  12 . 
     According to the first embodiment, as hereinabove described, the supporting portions  13  are arranged to support the vicinities of the deformed portions Df of the electron emission portion  11  where the degree of variation of the flatness of the electron emission portion  11  resulting from the creep deformation associated with the use of the emitter  10  is relatively large. Thus, the sinking (sagging phenomenon) of the electron emission portion  11  can be effectively suppressed by supporting the vicinities of the deformed portions Df where the variation of flatness is large. 
     According to the first embodiment, as hereinabove described, the supporting portions  13  are arranged to support the vicinities of the connection portions P 1  between the first portions  21  and the second portions  22  on the outer peripheral side. Thus, the vicinities of the connection portions P 1  whose flatness is the most easily varied can be structurally supported, and hence the sinking (sagging phenomenon) of the electron emission portion  11  can be reliably and more effectively suppressed. 
     According to the first embodiment, as hereinabove described, the supporting portions  13  are formed in the flat plate shape integrally with the electron emission portion  11  by pulling out from the outer peripheral portion of the flat plate-like electron emission portion  11  and bending to the same side as that of the terminal portions  12 . Thus, the supporting portions  13  and the electron emission portion  11  can be integrally formed of the common flat plate material, and hence the supporting portions  13  can be easily formed. Furthermore, the supporting portions  13  can be provided without an increase in the number of components, unlike the case where the supporting portions  13  and the electron emission portion  11  are provided separately from each other. 
     According to the first embodiment, as hereinabove described, the pair of supporting portions  13  are provided at positions opposed to each other through the rotation axis (central axis)  3   a . Thus, in the enclosure rotation type X-ray tube device  100  in which the emitter  10  rotates together with the enclosure  3 , a mechanical balance about the rotation axis (central axis)  3   a  can be maintained even in the case where the supporting portions  13  are provided in the emitter  10 , and hence the deformation can be suppressed while the rotation of the emitter  10  in use (during rotation) is stabilized. 
     EXAMPLE 
     Results of a simulation (Example) conducted in order to confirm effects of the X-ray tube device  100  according to the first embodiment are now described with reference to  FIG. 7 . 
     The results of the simulation (Example) in  FIG. 7  denote results of a simulation conducted on the emitter  10  according to the aforementioned first embodiment, in which the supporting portions  13  are provided, under the same conditions as those of the simulation results shown in  FIG. 6  (Comparative Example in which no supporting portion  13  is provided). 
     As shown in  FIG. 7 , in Example, the amount of variation of flatness in the connection portions P 1  of the deformed portions Df where the amount of variation of flatness was maximized in  FIG. 6  was 0 μm (no variation of flatness). In Example, the variation of flatness in the connection portions P 1  was suppressed, and hence the variation of flatness was maximized in the connection portions P 2  between the second portions  22  and the third portions  23  on the inner peripheral side, in which the amount of variation was −13 μm. Thus, it has been confirmed that the maximum amount of variation of flatness resulting from the sagging phenomenon is reduced from −52 μm (Comparative Example) in the connection portions P 1  having no supporting portion to −13 μm (Example) in the connection portions P 2 . 
     The flatness of the connection portions P 2  was −36 in Comparative Example shown in  FIG. 6 . Therefore, when the variation of flatness was viewed with respect to each portion, the amount of variation of flatness in the connection portions P 1  was reduced from −52 μm (Comparative Example) to 0 μm (Example), and the amount of variation of flatness in the connection portions P 2  was reduced from −36 μm (Comparative Example) to −13 μm (Example). It has been confirmed from these results that the variation of flatness resulting from the creep deformation is sufficiently suppressed over the entire electron emission portion  11  including the deformed portions Df by providing the supporting portions  13 . 
     Modification of First Embodiment 
     In the aforementioned first embodiment, the example of forming the supporting portions  13  integrally with the current path  20  (electron emission portion  11 ) has been shown, but in a modification of the first embodiment, supporting portions are provided separately from a current path  20  (electron emission portion  11 ). 
     In an emitter  110  according to the modification of the first embodiment, supporting portions  113  are formed to extend to the side of a lower surface  11   b  (in a direction Z 1 ), which is the same as that of terminal portions  12 , in a direction intersecting with (orthogonal to) the electron emission portion  11 , as shown in view (a) and view (c) of  FIG. 8 . One ends of the supporting portions  113  are fixed by fixing members  1   b  provided on a base portion (not shown) of an electron source  1 , and the other ends  113   a  (see view (b) of  FIG. 8 ) of the supporting portions  113  are fixedly coupled to the electron emission portion  11  or are arranged at positions in contact with the lower surface  11   b  of the electron emission portion  11 . In other words, the supporting portions  113  are only required to support the electron emission portion  11  in order to be capable of suppressing the creep deformation of the electron emission portion  11 , and it is not necessary to fix the supporting portions  113  to the electron emission portion  11 .  FIG. 8  shows an example of bringing the other ends  113   a  of the supporting portions  113  into contact with the lower surface  11   b  of the electron emission portion  11 . 
     According to this modification of the first embodiment, the supporting portions  113  are formed separately from the electron emission portion  11 , and hence the supporting portions  113  may be made of a material (a material other than tungsten and a tungsten alloy) different from that for the electron emission portion  11 . The supporting portions  113  may be made of a metal material having a high melting point other than tungsten, such as molybdenum, a ceramic material such as alumina (Al 2 O 3 ) or silicon nitride (Si 3 N 4 ), or the like, for example. Furthermore, the supporting portions  113  may be formed in a shape other than a flat plate shape, such as a columnar shape. 
     According to this modification of the first embodiment, it is only required to add the supporting portions  13  on the side of the emitter  110  closer to the terminal portions  12 , and hence the supporting portions  113  can be structurally easily provided. 
     Second Embodiment 
     An emitter  210  or  230  of an X-ray tube device  200  (see  FIG. 1 ) according to a second embodiment of the present invention is now described with reference to  FIGS. 1, 9, and 10 . In the second embodiment, an example of configuring deformed portions Df of an electron emission portion  11  to protrude in a direction opposite to the deformation direction (gravity direction) of creep deformation, in addition to the structure of the aforementioned first embodiment in which the supporting portions  13  are provided in the electron emission portion  11 , is described. According to the second embodiment, the structure other than the emitter is similar to that according to the aforementioned first embodiment, and hence the description is omitted. Portions of the emitter similar to those according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIG. 9 , the emitter  210  of the X-ray tube device  200  according to the second embodiment is provided such that a direction Z 1  (flatness minus direction) from an upper surface  11   a  toward a lower surface  11   b  coincides with a gravity direction (vertically downward) G 2  in use. An electron emission portion  211  of the emitter  210  is formed with protrusion portions  212  protruding in the direction (direction Z 2 ) opposite to the deformation direction (gravity direction) of the deformed portions Df in regions containing the deformed portions Df where the degree of variation of the flatness of the electron emission portion  211  resulting from creep deformation associated with the use of the emitter  210  is relatively large. 
     The protrusion portions  212  are arranged in a current path  20  (first portions  21 ) of the electron emission portion  211  on the outer peripheral side of the electronic emission portion  211  containing the deformed portions Df. The protrusion portions  212  are formed by inclining the first portions  21  such that the vicinities of connection portions P 1  between the first portions  21  and second portions  22  protrude. 
     Specifically, according to the second embodiment, as to a first portion  21  on the side of one terminal portion  12  (referred to as the terminal portion  12   a ), the first portion  21  from a position  A  on the side of the terminal portion  12   a  to a position B on the side of a connection portion P 1  is inclined in the direction Z 2 . Thus, the first portion  21  on the side of the terminal portion  12   a  protrudes in the direction Z 2  such that the flatness is +α at the position B (protrudes by α with respect to an upper reference surface Rt). 
     Similarly, as to a first portion  21  on the side of the other terminal portion  12  (hereinafter referred to as the terminal portion  12   b ), the first portion  21  from a position C on the side of the terminal portion  12   b  to a position D on the side of a connection portion P 1  is inclined in the direction Z 2 . Thus, the first portion  21  on the side of the terminal portion  12   b  also protrudes in the direction Z 2  such that the flatness is +α at the position D (protrudes by α with respect to the upper reference surface Rt). 
     The first portions  21  are inclined to form the protrusion portions  212 , whereby the second portions  22 , third portions  23 , and a central portion  24  of the electron emission portion  211  also protrude slightly in the direction Z 2 , and the upper surface  11   a  of the electron emission portion  211  as a whole is substantially parallel to the upper reference surface Rt. 
     Due to the aforementioned structure, in the emitter  210 , the protrusion portions  212  previously protruding in the direction Z 2  such that the flatness is +α can cancel out the variation of flatness in the direction Z 1  coinciding with the gravity direction G 2 . In other words, according to the second embodiment, in the case where the flatness is varied by about −α in the direction Z 1  by a sagging phenomenon, the flatness is 0. Thus, sinking in the direction Z 1  resulting from the sagging phenomenon is reduced by the amount of protrusion α of the protrusion portions  212 , and the lifetime of the emitter  210  until when a desired X-ray focal point diameter fails to be obtained can be increased. The amount of protrusion α of the protrusion portions  212  is preferably larger as long as the desired X-ray focal point diameter can be obtained. 
     The orientation of the emitter with respect to the gravity direction is varied according to the orientation of the X-ray tube device  200  in use (during exposure) in an apparatus mounted with the X-ray tube device  200 . Therefore, as to the use of the X-ray tube device  200 , the X-ray tube device  200  including the aforementioned emitter  210  may be employed in the case where the deformation direction (gravity direction G 2 ) coincides with the direction Z 1  (flatness minus direction) from the upper surface  11   a  toward the lower surface  11   b , and the X-ray tube device  200  including the emitter  230  shown in  FIG. 10  may be employed in the case where the deformation direction (gravity direction G 2 ) coincides with the direction Z 2  (flatness plus direction) from the lower surface  11   b  toward the upper surface  11   a.    
     As shown in  FIG. 10 , the emitter  230  is provided such that the direction Z 2  (flatness plus direction) from the lower surface  11   b  toward the upper surface  11   a  coincides with the gravity direction G 2  in use, inversely to the emitter  210 . An electron emission portion  231  of the emitter  230  is formed with protrusion portions  232  protruding in the direction Z 1 . 
     Specifically, as to a first portion  21  on the side of one terminal portion  12   a , the first portion  21  from a position  A  on the side of the terminal portion  12   a  to a position B on the side of a connection portion P 1  is inclined in the direction Z 1  and protrudes in the direction Z 1  such that the flatness is −α (protrudes by α with respect to a lower reference surface Rb). Similarly, as to a first portion  21  on the side of the other terminal portion  12   b , the first portion  21  from a position C on the side of the terminal portion  12   b  to a position D on the side of a connection portion P 1  is inclined in the direction Z 1  and protrudes in the direction Z 1  such that the flatness is −α. Thus, the protrusion portions  232  of the emitter  230  are formed by inclining the first portions  21  in the direction Z 1  such that the vicinities of the connection portions P 1  of the electron emission portion  231  protrude. 
     According to the second embodiment, as hereinabove described, the electron emission portion  211  ( 231 ) is provided with the protrusion portions  212  ( 232 ) protruding in the direction opposite to the deformation direction of the deformed portions Df in the regions containing the deformed portions Df. Thus, the protrusion portions  212  ( 232 ) protruding in the direction opposite to the deformation direction can cancel out the variation of flatness even when the creep deformation is generated in the electron emission portion  211  ( 231 ). In other words, in the emitter  210  shown in  FIG. 9 , the protrusion portions  212  previously protruding in the opposite direction Z 2  can cancel out the variation of flatness in the direction Z 1  coinciding with the gravity direction G 2 . In the emitter  230  shown in  FIG. 10 , the protrusion portions  232  previously protruding in the opposite direction Z 1  can cancel out the variation of flatness in the direction Z 2  coinciding with the gravity direction G 2 . Thus, while supporting portions  13  suppress deformation, the protrusion portions ( 212 )  232  can cancel out additional deformation even when the deformation is further generated, and hence sinking of the electron emission portion  211  ( 231 ) can be more sufficiently suppressed. 
     According to the second embodiment, as hereinabove described, the protrusion portions  212  ( 232 ) are configured to protrude in the direction opposite to the gravity direction G 2  in use. Thus, the protrusion portions  212  ( 232 ) can cancel out the creep deformation of the electron emission portion  211  ( 231 ) resulting from gravity constantly acting on the emitter  210  ( 230 ). 
     According to the second embodiment, as hereinabove described, the protrusion portions  212  ( 232 ) are formed by inclining the first portions  21  such that the vicinities of the connection portions P 1  between the first portions  21  and the second portions  22  protrude. Thus, the sinking (sagging phenomenon) of the electron emission portion  211  ( 231 ) in the vicinity of the connection portions P 1  whose flatness is the most easily varied can be reliably and more effectively canceled out. 
     The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment. 
     Modification of Second Embodiment 
     In the aforementioned second embodiment, the protrusion portions  212  ( 232 ) are configured to protrude in the direction opposite to the gravity direction G 2  in use, but in a modification of the second embodiment, protrusion portions are configured to protrude in a direction different from a gravity direction G 2 . 
     Sinking (sagging phenomenon) of an electron emission portion resulting from creep deformation associated with use is generated by a high temperature at the time of applying an electric current to an emitter to heat the same and external force (gravity, inertial force related to centrifugal force, or the like), as described above. Therefore, even in the case where the emitter is oriented in a transverse direction orthogonal to the gravity direction, for example, the flatness of the electron emission portion may be varied by centrifugal force acting on the emitter following rotation of an enclosure  3  or the flatness of the electron emission portion may be varied by inertial force when an entire X-ray tube device is moved by a movement mechanism. 
     Thus, according to the modification of the second embodiment, protrusion portions  212   a  ( 232   a ) are provided in an electron emission portion  211   a  ( 231   a ) to protrude in a direction opposite to a deformation direction based on the sagging phenomenon even in the case where the gravity direction G 2  and the deformation direction are different from each other, as in an emitter  210   a  shown in view (a) of  FIG. 11  or an emitter  230   a  shown in view (b) of  FIG. 11 . 
     In the emitter  210   a  shown in view (a) of  FIG. 10 , the protrusion portions  212   a  are formed to protrude in a direction Z 2  (flatness plus direction) opposite to the deformation direction in the case where the deformation direction of deformed portions Df is a direction Z 1  (flatness minus direction) from an upper surface  11   a  toward a lower surface  11   b.    
     In the emitter  230   a  shown in view (b) of  FIG. 10 , the protrusion portions  232   a  are formed to protrude in the direction Z 1  (flatness minus direction) opposite to the deformation direction in the case where the deformation direction of deformed portions Df is the direction Z 2  (flatness plus direction) from the lower surface  11   b  toward the upper surface  11   a.    
     Even in the case where the orientation (vertical direction) of the emitter  210   a  ( 230   a ) is different from the gravity direction G 2 , as in this modification of the second embodiment, the protrusion portions  212   a  ( 232   a ) protruding in the direction opposite to the creep-deformation direction are provided in the electron emission portion  211   a  ( 231   a ), whereby sinking (sagging phenomenon) of the electron emission portion  211   a  ( 231   a ) can be canceled out. 
     Third Embodiment 
     An emitter  310  of an X-ray tube device  300  according to a third embodiment of the present invention is now described with reference to  FIGS. 1, 12, and 13 . In the third embodiment, an example of increasing the path width of a current path including deformed portions of an electron emission portion in addition to the structure of the aforementioned first embodiment in which the supporting portions  13  are provided in the electron emission portion  11  is described. According to the third embodiment, the structure other than the emitter is similar to that according to the aforementioned first embodiment, and hence the description is omitted. Portions similar to those according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIGS. 12 and 13 , an electron emission portion  311  of the emitter  310  of the X-ray tube device  300  (see  FIG. 1 ) according to the third embodiment has wide portions  312  whose path widths are larger than those of other portions in a current path  320 . Specifically, the current path  320  is formed such that the path widths of portions other than the wide portions  312  are W 3  and the path widths of the wide portions  312  are W 4  larger than W 3 . 
     The wide portions  312  are regions including deformed portions Df and are arranged in the current path  320  of the electron emission portion  311  on the outer peripheral side. More specifically, the wide portions  312  are formed over entire first portions  21  including the vicinities (deformed portions Df) of connection portions P 1  between the first portions  21  and second portions  22  of the current path  320 . In other words, according to the third embodiment, the entire first portions  21  in the current path  320  are the wide portions  312  each having a path width W 4 , and the second portions  22  and third portions  23  each have a path width W 3 . Consequently, in the electron emission portion  311 , the mechanical strength of the first portions  21  (wide portions  312 ) on the outer peripheral side, the path widths of which are relatively large, is larger than that of the second portions  22  and the third portions  23  on the inner peripheral side. 
       FIGS. 12 and 13  show an example of making the path widths W 4  of the first portions  21  (wide portions  312 ) larger than the path width W 1  (see  FIG. 3 ) of the emitter  10  according to the aforementioned first embodiment and making the path widths W 3  of the second portions  22  and the third portions  23  other than the wide portions  312  equal to the path width W 1 . According to the third embodiment, the path widths of the wide portions  312  are only required to be relatively larger than the path widths of other portions. Therefore, the path widths of the wide portions  312  may be made relatively larger by making the path widths of the portions (the second portions  22  and the third portions  23 ) other than the wide portions  312  smaller than W 1 . 
     According to the third embodiment, as hereinabove described, the wide portions  312  whose path widths are larger than those of other portions of the current path  320  are provided in the electron emission portion  311 . Furthermore, the wide portions  312  are arranged in the regions including the deformed portions Df where the degree of variation of the flatness of the electron emission portion  311  resulting from creep deformation associated with the use of the emitter  310  is relatively large. Thus, the mechanical strength of the current path  320  (wide portions  312 ) in the region including the deformed portions Df can be relatively improved as compared with that of other portions. Thus, while supporting portions  13  suppress deformation, the wide portions  312  can further suppress deformation, and hence sinking of the electron emission portion  311  can be more sufficiently suppressed. 
     According to the third embodiment, as hereinabove described, the wide portions  312  are formed in the first portions  21  including the vicinities of the connection portions P 1  (deformed portions Df) between the first portions  21  and the second portions  22 , on the outer peripheral side of the electron emission portion  311 . Thus, the sinking (sagging phenomenon) of the electron emission portion  311  in the vicinity of the connection portions P 1  (deformed portions Df) whose flatness is the most easily varied can be reliably and more effectively suppressed. 
     Fourth Embodiment 
     An emitter  410  ( 430 ) of an X-ray tube device  400  according to a fourth embodiment of the present invention is now described with reference to  FIGS. 1, 14, and 15 . In the aforementioned second embodiment, the example of providing both the supporting portions  13  and the protrusion portions  212  ( 232 ) in the electron emission portion  11  has been shown, but in this fourth embodiment, an example of providing only protrusion portions in an electron emission portion is described. According to the fourth embodiment, the structure other than the emitter is similar to that according to the aforementioned second embodiment, and hence the description is omitted. Portions similar to those according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIGS. 14 and 15 , in the emitter  410  ( 430 ) of the X-ray tube device  400  (see  FIG. 1 ) according to the fourth embodiment, no supporting portion  13  is provided, but only protrusion portions  212  ( 232 ) are formed, unlike in the emitter  210  ( 230 ) (see  FIGS. 9 and 10 ) according to the aforementioned second embodiment. The structure of the protrusion portions  212  ( 232 ) is similar to that according to the aforementioned second embodiment. 
     The emitter  410  shown in  FIG. 14  is an example in which the deformation direction of deformed portions Df in an electron emission portion  411  is a direction Z 1  (flatness minus direction) and coincides with a gravity direction G 2  in use. 
     The emitter  430  shown in  FIG. 15  is an example in which the deformation direction of deformed portions Df in an electron emission portion  431  is a direction Z 2  (flatness plus direction) and coincides with the gravity direction G 2  in use. 
     Similarly to the aforementioned second embodiment, also according to the fourth embodiment, as to the use of the X-ray tube device  400 , the X-ray tube device  400  including the emitter  410  shown in  FIG. 14  may be employed in the case where the direction Z 1  (flatness minus direction) coincides with the deformation direction (gravity direction), and the X-ray tube device  400  including the emitter  430  shown in  FIG. 15  may be employed in the case where the direction Z 2  (flatness plus direction) coincides with the deformation direction (gravity direction). 
     According to the fourth embodiment, as hereinabove described, the protrusion portions  212  ( 232 ) protruding in a direction opposite to the deformation direction of the deformed portions Df are previously provided in regions including the deformed portions Df of the electron emission portion  411  ( 431 ), whereby the protrusion portions  212  ( 232 ) protruding in the direction opposite to the deformation direction can cancel out the variation of flatness even when creep deformation is generated in the electron emission portion  411  ( 431 ). Thus, the variation of flatness in the regions including the deformed portions Df can be canceled out, and hence sinking of the electron emission portion  411  ( 431 ) resulting from the creep deformation associated with use can be sufficiently suppressed. 
     Thus, according to the fourth embodiment, no supporting portion  13  is provided, but only the protrusion portions  212  ( 232 ) are provided, whereby the sinking of the electron emission portion  411  ( 431 ) can be suppressed. 
     Also in the case where the gravity direction G 2  does not coincide with the deformation direction of the deformed portions Df, as in the modification of the second embodiment shown in  FIG. 11 , protrusion portions  212   a  ( 232   a ) protruding in the direction opposite to the deformation direction of the deformed portions Df are formed, whereby the sinking of the electron emission portion  411  ( 431 ) can be suppressed. 
     Fifth Embodiment 
     An emitter  510  of an X-ray tube device  500  according to a fifth embodiment of the present invention is now described with reference to  FIGS. 1, 16, and 17 . In the aforementioned third embodiment, the example of providing both the supporting portions  13  and the wide portions  312  in the electron emission portion  11  has been shown, but in the fifth embodiment, an example of providing only wide portions in an electron emission portion is described. According to the fifth embodiment, the structure other than the emitter is similar to that according to the aforementioned third embodiment, and hence the description is omitted. Portions similar to those according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIGS. 16 and 17 , in an electron emission portion  511  of the emitter  510  of the X-ray tube device  500  (see  FIG. 1 ) according to the fifth embodiment, no supporting portion  13  is provided, but only wide portions  312  are formed in a current path  520 , unlike in the emitter  310  according to the aforementioned third embodiment. The structure of the wide portions  312  is similar to that according to the aforementioned third embodiment. 
     Also in this fifth embodiment, the path widths of the wide portions  312  may be made relatively larger by making the path widths of portions (second portions  22  and third portions  23 ) other than the wide portions  312  smaller. 
     According to the fifth embodiment, as hereinabove described, the wide portions  312  whose path widths are larger than those of other portions of the current path  520  are provided in the electron emission portion  511 . Furthermore, the wide portions  312  are arranged in regions including deformed portions Df. Thus, the mechanical strength of the current path  520  (wide portions  312 ) in the regions including the deformed portions Df can be relatively improved. Consequently, generation of creep deformation in the regions (wide portions  312 ) including the deformed portions Df can be suppressed, and hence sinking of the electron emission portion  511  resulting from the creep deformation associated with the use of the emitter  510  can be suppressed. 
     Thus, according to the fifth embodiment, no supporting portion  13  is provided, but only the wide portions  312  are provided, whereby the sinking of the electron emission portion  511  can be sufficiently suppressed. 
     Sixth Embodiment 
     A method for using an X-ray tube device according to a sixth embodiment of the present invention is now described with reference to  FIGS. 1, 2, 18, and 19 . In this sixth embodiment, an example of using any of the X-ray tube devices according to the aforementioned first to fifth embodiments (or the first and second modifications), arranging an emitter in a direction opposite to that in the use of the X-ray tube device (during exposure), and applying an electric current to the emitter to heat the same is described. In the sixth embodiment, an example of using the X-ray tube device  100  (see  FIG. 1 ) according to the aforementioned first embodiment is shown as an example of the structures shown in the aforementioned first to fifth embodiments (or the first and second modifications). 
     An example of an apparatus configuration for using the X-ray tube device  100  is now described. The X-ray tube device  100  is a medical X-ray tube, for example, and is mounted on an X-ray imaging apparatus such as an X-ray apparatus or a tomographic X-ray apparatus. 
     As shown in  FIG. 18 , an X-ray imaging apparatus  601  includes an irradiating portion  602  incorporating the X-ray tube device  100  and a supporting mechanism  603  movably supporting the irradiating portion  602 . The irradiating portion  602  is supported to be rotatable about a shaft by a rotation shaft  603   a  of the supporting mechanism  603  and is configured to be movable vertically and horizontally together with the rotation shaft  603   a . An imaging portion  604  including an X-ray detector is arranged to be opposed to the irradiating portion  602  in a direction of X-ray irradiation by the irradiating portion  602  (X-ray tube device  100 ). This imaging portion  604  is also supported by a supporting mechanism  605  to be capable of moving up and down. 
     In the use of the X-ray imaging apparatus  601 , an X-ray is irradiated from the X-ray tube device  100  in a state where a subject (patient) is arranged at a prescribed imaging position  606  between the irradiating portion  602  and the imaging portion  604 . The imaging portion  604  detects the X-ray irradiated from the irradiating portion  602  (X-ray tube device  100 ) to carry out X-ray imaging. 
     In the use (during exposure), the emitter  10  emits an electron in a state where the same is oriented in a direction G 1  (vertically upward) along a gravity direction (vertically downward) G 2  to be opposed to a target  2  in order to generate an X-ray. In other words, as shown in view (a) of  FIG. 19 , the upper surface  11   a  of the electron emission portion  11  is the electron emission surface, and hence the emitter  10  is applied with an electric current to be heated in a state where the direction Z 2  of the emitter  10  from the lower surface  11   b  toward the upper surface  11   a  is oriented in the direction G 1 , whereby the X-ray is generated. 
     Consequently, when the creep deformation (sagging phenomenon) associated with use (exposure) is generated, the electron emission portion  11  is deformed in a direction Z 1  coinciding with the gravity direction G 2 , and the flatness is varied in a minus direction. 
     According to the sixth embodiment, in the non-use of the X-ray tube device  100  (when no exposure is carried out), the irradiation portion  602  (X-ray tube device  100 ) is rotated about the rotation shaft  603   a , and the emitter  10  is applied with an electric current to be heated in an upside-down state. 
     Specifically, as shown in view (b) of  FIG. 19 , the irradiation portion  602  (X-ray tube device  100 ) is rotated to invert the emitter  10  such that the direction Z 2  of the emitter  10  is oriented in the direction G 2  opposite to that in use. Then, the emitter  10  is applied with an electric current to be heated in a state where the emitter  10  (electron emission portion  11 ) is opposed to the target  2  such that the direction Z 2  of the emitter  10  is oriented in the direction G 2  opposite to the direction G 1 . 
     Consequently, when the creep deformation (sagging phenomenon) associated with application of an electric current and heating is generated, the electron emission portion  11  is deformed in the direction Z 2  coinciding with the gravity direction G 2 , and the flatness is varied in a plus direction. Therefore, due to the inversion and heating in non-use shown in view (b) of  FIG. 19 , the variation of flatness in the minus direction in use shown in view (a) of  FIG. 19  is canceled out by the variation of flatness in the plus direction. 
     Thereafter, in subsequent use (during subsequent exposure), the emitter  10  is returned to a state where the same is oriented in the direction G 1  to be opposed to the target  2  again, as shown in view (c) of  FIG. 19 , and an X-ray is generated. The above is repeated, whereby the variation of the flatness of the electron emission portion  11  generated in the use of the X-ray tube device  100  can be canceled out in non-use. 
     According to the sixth embodiment, the inversion and heating in non-use shown in view (b) of  FIG. 19  is carried out under the same conditions (heating temperature (current value)) as those of application of an electric current to the emitter  10  to heat the same in use for a time substantially equal to the total time to apply an electric current to the emitter  10  to heat the same in use. During this inversion and heating in non-use, it is only required to apply an electric current to the emitter  10  and heat the same, and hence it is not required to generate an X-ray. The inversion and heating in non-use may be carried out during night-time hours when the X-ray imaging apparatus  601  is not used, on holidays for a facility using the X-ray imaging apparatus  601 , or the like, for example. 
     According to the sixth embodiment, as hereinabove described, the emitter  10  is applied with an electric current to be heated in the state where the same is orientated in the direction G 2  along the gravity direction, opposite to the direction G 1  in use (during exposure) to be opposed to the target  2 . Thus, the variation of the flatness of the electron emission portion  11  in the direction Z 1  resulting from the creep deformation generated in normal use (during exposure) can be canceled out by the variation of flatness in the opposite direction (direction Z 2 ) generated by applying an electric current to the emitter  10  and heating the same in the state where the same is oriented in the direction G 2 . Thus, sinking (sagging phenomenon) of the electron emission portion  11  resulting from the creep deformation associated with the use of the emitter  10  can be effectively suppressed. 
     According to the sixth embodiment, as hereinabove described, the X-ray tube device  100  including the emitter  10  having the supporting portions  13  (see  FIG. 2 ) provided separately from the terminal portions  12 , insulated from the electrodes  1   a , supporting the electron emission portion  11  is used, whereby the flat plate-like electron emission portion  11  can be supported by the supporting portions  13 , and hence the sinking (sagging phenomenon) of the electron emission portion  11  resulting from the creep deformation associated with use can be suppressed. 
     In this sixth embodiment, the example of using the X-ray tube device  100  according to the aforementioned first embodiment has been shown, but the present invention is not restricted to this. In the sixth embodiment, any of the X-ray tube devices according to the aforementioned second to fifth embodiments (or the modifications of the first and second embodiments) other than the first embodiment may be used. Also in these cases, the sinking (sagging phenomenon) of the electron emission portion  11  can be suppressed similarly. 
     Seventh Embodiment 
     A method for using an X-ray tube device according to a seventh embodiment of the present invention is now described with reference to  FIGS. 1, 6, and 20 . In this seventh embodiment, an example of arranging an emitter in a direction opposite to that in the use of an X-ray tube device (during exposure) and applying an electric current to the emitter to heat the same in the structure of the X-ray tube device other than the X-ray tube devices according to the aforementioned first to fifth embodiments (or the modifications of the first and second embodiments) is described. 
     An emitter  710  of an X-ray tube device  700  (see  FIG. 1 ) used in the seventh embodiment is provided with no supporting portion  13 , unlike the emitter  10  according to the aforementioned first embodiment. The emitter  710  is provided with no protrusion portion  212  ( 232 ) shown in the aforementioned second embodiment or wide portion  312  shown in the aforementioned third embodiment and has a structure similar to that of the emitter according to Comparative Example shown in  FIG. 6 . The remaining structure of the emitter  710  is similar to that according to the aforementioned first embodiment, and hence the description is omitted. 
     According to the seventh embodiment, as shown in view (a) to view (c) of  FIG. 20 , the X-ray tube device  700  having the emitter  710  is employed to generate an X-ray in use (during exposure) in a state where the emitter  710  is oriented in a direction G 1  (vertically upward) along a gravity direction and apply an electric current to the emitter  710  to heat the same (invert the emitter  710  to heat the same) in non-use in a state where the emitter  710  is oriented in a direction G 2  (a direction of action of gravity, vertically downward) opposite to that in use. The structure of an X-ray imaging apparatus using the X-ray tube device  700 , the specific operation of the X-ray tube device  700  in use (during exposure), and the specific operation of the X-ray tube device  700  in non-use (during inversion and heating) are similar to those according to the aforementioned sixth embodiment. 
     Consequently, the variation of the flatness of an electron emission portion  711  in a minus direction (direction Z 1 ) in use shown in view (a) is canceled out by the variation of the flatness of the electron emission portion  711  in a plus direction (direction Z 2 ) during inversion and heating in non-use shown in view (b) of  FIG. 20 . 
     According to the seventh embodiment, as hereinabove described, the emitter  710  is applied with an electric current to be heated in a state where the same is orientated in the direction G 2  along the gravity direction, opposite to the direction G 1  in use (during exposure) to be opposed to a target  2 . Thus, the variation of the flatness of the electron emission portion  711  in the direction Z 1  resulting from creep deformation generated in normal use (during exposure to X-ray) can be canceled out by the variation of flatness in the opposite direction (direction Z 1 ) generated by applying an electric current to the emitter  710  and heating the same in the state where the same is oriented in the direction G 2 . Thus, sinking (sagging phenomenon) of the electron emission portion  711  resulting from the creep deformation associated with the use of the emitter  710  can be sufficiently suppressed. 
     Thus, according to the seventh embodiment, no supporting portion  13  is provided, but the emitter  710  is only inverted and heated, whereby the sinking of the electron emission portion  711  can be sufficiently suppressed. 
     The embodiments and Example disclosed this time must be considered as illustrative in all points and not restrictive. The range of the present invention is shown not by the above description of the embodiments and Example but by the scope of claims for patent, and all modifications within the meaning and range equivalent to the scope of claims for patent are further included. 
     For example, while the example of applying the present invention to the enclosure rotation type X-ray tube device has been shown in each of the aforementioned first to seventh embodiments, the present invention is not restricted to this. The present invention may be applied to an X-ray tube device other than the enclosure rotation type X-ray tube device, such as an anode rotation type X-ray tube device in which only an enclosure is fixed or an anode fixed X-ray tube device, for example. 
     While the example of providing the circular electron emission portion in the plan view has been shown in each of the aforementioned first to seventh embodiments, the present invention is not restricted to this. According to the present invention, the plan view of the electron emission portion may be rectangular or polygonal so far as the electron emission portion is in a flat plate shape. When the electron emission portion is employed in the enclosure rotation type X-ray tube device in which the emitter (electron emission portion) rotates, the plan view of the electron emission portion is preferably circular or roughly circularly polygonal in view of stability of rotation. 
     While the example of forming the flat plate-like electron emission portion by the current path having the first to third portions and the central portion has been shown in each of the aforementioned first to seventh embodiments, the present invention is not restricted to this. According to the present invention, the flat plate-like electron emission portion may be formed by a current path in a shape different from the shape shown in each of the aforementioned embodiments. In this case, the positions of the deformed portions where the variation of flatness is large are varied according to the shape of the current path constituting the electron emission portion, and hence the arrangement of the supporting portions may be determined according to the shape of the electron emission portion (current path). 
     While the example of forming the supporting portions to extend to the same side as that of the terminal portions of the emitter has been shown in each of the aforementioned first to third and sixth embodiments, the present invention is not restricted to this. According to the present invention, the supporting portions may be formed to extend to a side different from that of the terminal portions and may be provided to extend to the lateral side (in a direction parallel to the flat plate-like electron emission portion) of the emitter, for example. 
     While the example of providing the pair of (two) supporting portions in the emitter has been shown in each of the aforementioned first to third and sixth embodiments, the present invention is not restricted to this. One or three or more supporting portions may be provided. In the case where there are many supporting portions, however, heat of the electron emission portion during application of an electric current and heating may be released to the supporting portions, and the temperature distribution of the electron emission portion may be varied. Thus, so far as the number of supporting portions is sufficient to support the electron emission portion, it is preferable to provide as small a number of supporting portions as possible. 
     While the example of mounting the X-ray tube device on the X-ray imaging apparatus  601  such as the X-ray apparatus has been shown as an example of use in each of the aforementioned sixth and seventh embodiments, the present invention is not restricted to this. The present invention may be applied to an X-ray tube device used in an industrial apparatus such as an X-ray inspection apparatus (non-destructive inspection apparatus), for example, in addition to the medical X-ray imaging apparatus. 
     REFERENCE NUMERALS 
     
         
           1 : electron source (cathode) 
           1   a : electrode 
           2 : target (anode) 
           3 : enclosure 
           10 ,  110 ,  210 ,  210   a ,  230 ,  230   a ,  310 ,  410 ,  430 ,  510 ,  710 : emitter 
           11 ,  211 ,  211   a ,  231 ,  231   a ,  311 ,  411 ,  431 ,  511 ,  711 : electron emission portion 
           12  ( 12   a ,  12   b ): terminal portion 
           13 ,  113 : supporting portion 
           20 ,  320 ,  520 : current path 
           21 : first portion 
           22 : second portion 
           212 ,  212   a ,  232 ,  232   a : protrusion portion 
           312 : wide portion 
         Df: deformed portion 
         P 1 : connection portion 
           100 ,  200 ,  300 ,  400 ,  500 ,  700 : X-ray tube device