Patent Publication Number: US-2017372865-A1

Title: X-ray tube device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of PCT Application No. PCT/JP2016/052138, filed Jan. 26, 2016 and based upon and claiming the benefit of priority from Japanese Patent Application No. 2015-037842, filed Feb. 27, 2015, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an X-ray tube device. 
     BACKGROUND 
     A rotating anode X-ray tube device is a device which causes electrons generated from the electron generation source of a cathode to collide with a rotating anode target and generates X-rays from the X-ray focal spot formed by the collision of the electrons of the anode target. In general, the rotating anode X-ray tube device is used for an X-ray computed tomography (CT) device, etc. 
     In general, the rotating anode X-ray tube device forms the focal spot of electron beams in different sizes on the anode target based on the purpose. Thus, the rotating anode X-ray tube device comprises a filament corresponding to the shape of the focal spot to be formed, and a focusing groove provided in a cathode cup for accommodating the filament. As a technology which continuously changes the size of the focal spot in a broader range, for example, a structure of changing a circular electron beam to a linear focal spot with a quadrupole magnetic field is known. 
     The reference related to the above technology is shown below, and the entire contents of which are incorporated herein by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an example of an X-ray tube device according to a first embodiment. 
         FIG. 2A  is a cross-sectional view showing the general outline of an X-ray tube according to the first embodiment. 
         FIG. 2B  is a cross-sectional view taken along line IIA-IIA of  FIG. 2A . 
         FIG. 2C  is a cross-sectional view taken along line IIB-IIB of  FIG. 2B . 
         FIG. 3  is a cross-sectional view showing the principle of a quadrupole magnetic field generation unit according to the first embodiment. 
         FIG. 4  is a cross-sectional view showing the general outline of an X-ray tube according to a second embodiment. 
         FIG. 5A  shows the principle of a dipole magnetic field according to the second embodiment. 
         FIG. 5B  shows the principle of a quadrupole magnetic field generation unit according to the second embodiment. 
         FIG. 6A  shows the general outline of the X-ray tube according to modification example 1 of the second embodiment. 
         FIG. 6B  is a cross-sectional view taken along line VIA-VIA of  FIG. 6A . 
         FIG. 7A  is a cross-sectional view showing the principle of a quadrupole magnetic field according to modification example 1 of the second embodiment. 
         FIG. 7B  is a cross-sectional view showing the principle of a dipole magnetic field according to modification example 1 of the second embodiment. 
         FIG. 7C  is a cross-sectional view showing the principle of the quadrupole magnetic field generation unit according to modification example 1 of the second embodiment. 
         FIG. 8  is a cross-sectional view showing the general outline of the X-ray tube according to modification example 2 of the second embodiment. 
         FIG. 9  is a cross-sectional view taken along line VIII-VIII of  FIG. 8 . 
         FIG. 10  is a cross-sectional view showing an example of an X-ray tube device according to a third embodiment. 
         FIG. 11A  is a cross-sectional view showing the general outline of an X-ray tube according to the third embodiment. 
         FIG. 11B  is a cross-sectional view taken along line XIA-XIA of  FIG. 11A . 
         FIG. 11C  is a cross-sectional view taken along line XIB 1 -XIB 1  of  FIG. 11B . 
         FIG. 11D  is a cross-sectional view taken along line XIB 2 -XIB 2  of  FIG. 11B . 
         FIG. 11E  is a cross-sectional view taken along line XID-XID of  FIG. 11D . 
         FIG. 12A  is a cross-sectional view showing the principle of a quadrupole magnetic field according to the third embodiment. 
         FIG. 12B  is a cross-sectional view showing the principle of dipoles according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an X-ray tube device comprises: a cathode which emits an electron in a direction of an electron path; an anode target which faces the cathode and comprises a target surface generating an X-ray when the electron emitted from the cathode collides with the target surface; a vacuum envelope which accommodates the cathode and the anode target and is sealed in a vacuum-tight manner; and a quadrupole magnetic field generation unit which forms a magnetic field when direct current is supplied from an electric source, is eccentrically provided with respect to a straight line accordance with the electron path outside the vacuum envelope, and comprises a quadrupole surrounding a circumference of a part of the electron path. 
     Various embodiments of an X-ray tube device are explained in detail below with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a cross-sectional view showing an example of an X-ray tube device  10  according to a first embodiment. 
     As shown in  FIG. 1 , the X-ray tube device  10  of the first embodiment roughly comprises a stator coil  8 , a housing  20 , an X-ray tube  30 , a high-voltage insulating member  39 , a quadrupole magnetic field generation unit  60 , receptacles  301  and  302 , and X-ray shielding units  510 ,  520 ,  530  and  540 . For example, the X-ray tube device  10  is a rotating anode-side X-ray tube device. The X-ray tube  30  is, for example, a rotating anode X-ray tube. For example, the X-ray tube  30  is a neutral grounded rotating anode X-ray tube. X-ray shielding units  510 ,  520 ,  530  and  540  are formed of lead. 
     In the X-ray tube device  10 , an insulating oil  9  which is a coolant fills a space defined between the inner side of housing  20  and the external side of the X-ray tube  30 . For example, the X-ray tube device  10  is configured to circulate the insulating oil  9  by a cyclic cooling system (cooler; not shown) connected to housing  20  by hose (not shown) for refrigeration. In this case, housing  20  comprises an inlet and an outlet for the insulating oil  9 . The cyclic cooling system comprises, for example, a cooler which causes the insulating oil  9  in housing  20  to release heat and circulate, and a duct (hose, etc.,) connecting the cooler to the inlet and outlet of housing  20  in a liquid-tight and air-tight manner. The cooler comprises a circulation pump and a heat exchanger. The circulation pump discharges the insulating oil  9  taken in from the housing  20  side to the heat exchanger, and produces the flow of the insulating oil  9  inside housing  20 . The heat exchanger is connected between housing  20  and the circulation pump, and releases the heat of the insulating oil  9  to outside. 
     Now, this specification explains the detailed structure of the X-ray tube device  10  with reference to the accompanying drawings. 
     Housing  20  comprises a tubular housing main unit  20   e , and cover units (side plates)  20   f ,  20   g  and  20   h . The housing main unit  20   e  and cover units  20   f ,  20   g  and  20   h  are formed by casting with aluminum. When a resinous material is used, metal may be also partially used for, for example, a portion which should be strong, such as a screw portion, a portion which is hardly manufactured by injection molding with resin, or a shielding layer (not shown) which prevents electromagnetic noise from leaking out to the outside of housing  20 . The central axis passing through the center of the circle of the cylinder of the housing main unit  20   e  is defined as a tube axis TA. 
     The housing main unit  20   e  comprises an aperture portion comprising an annular step portion formed as an inner circumferential surface having a wall thickness less than the wall thickness of the housing main unit  20   e . An annular groove portion is formed along the inner circumference of the step portion. The groove portion of the housing main unit  20   e  is manufactured by cutting at the position of a predetermined length from the step of the step portion to the external side along the tube axis TA. The predetermined length is, for example, a length substantially equal to the thickness of cover unit  20   f . A C-shaped snap ring  20   i  fits in the groove portion of the housing main unit  20   e . The aperture portion of the housing main unit  20   e  is sealed in a liquid-tight manner by cover unit  20   f  and C-shaped snap ring  20   i , etc. 
     Cover unit  20   f  is shaped like a disk. A rubber member  2   a  is provided along the outer circumferential portion of cover unit  20   f . Cover unit  20   f  fits in the step portion formed in the aperture portion of the housing main unit  20   e.    
     Rubber member  2   a  has, for example, an O-ring shape. As stated above, rubber member  2   a  is provided between the housing main unit  20   e  and cover unit  20   f , and seals the space between the housing main unit  20   e  and cover unit  20   f  in a liquid-tight manner. The peripheral portion of cover unit  20   f  is in contact with the step portion of the housing main unit  20   e  in a direction parallel to the tube axis TA of the X-ray tube device  10 . 
     C-shaped snap ring  20   i  is a fixing member. C-shaped snap ring  20   i  fits in the groove portion of the housing main unit  20   e  as described above and fixes cover unit  20   f  to prevent cover unit  20   f  from moving in a direction parallel to the tube axis TA. 
     In an aperture portion on a side opposite to the aperture portion of the housing main unit  20   e  in which cover unit  20   f  is provided, cover units  20   g  and  20   h  fit. Cover units  20   g  and  20   h  are provided parallel to cover unit  20   f  so as to face each other at an end portion on a side opposite to the end portion of the housing main unit  20   e  in which cover unit  20   f  is provided. Cover unit  20   g  fits in a predetermined portion inside the housing main unit  20   e , and is provided in a liquid-tight manner. At the end portion of the housing main unit  20   e  at which cover unit  20   h  is provided, an annular groove portion is formed in the inner circumferential portion of the external side adjacent to the installation position of cover unit  20   h . A rubber member  2   b  is provided between cover units  20   g  and  20   h  so as to retain the liquid-tight state such that rubber member  2   b  is expandable and shrinkable. Cover unit  20   h  is provided on the external side in the housing main unit  20   e  in comparison with cover unit  20   g . In this groove portion, a C-shaped snap ring  20   j  fits. Thus, the aperture portion of the housing main unit  20   e  is sealed by cover units  20   g  and  20   h , C-shaped snap ring  20   j , rubber member  2   b , etc., in a liquid-tight manner. 
     Cover unit  20   g  has a circular shape having a diameter substantially equal to that of the inner circumference of the housing main unit  20   e . Cover unit  20   g  comprises an aperture portion  20   k  for injecting and discharging the insulating oil  9 . 
     Cover unit  20   h  has a circular shape having a diameter substantially equal to that of the inner circumference of the housing main unit  20   e . A ventilation hole  20   m  through which air as atmosphere passes is formed in cover unit  20   h.    
     C-shaped snap ring  20   j  is a fixing member which retains the state in which cover unit  20   h  is pressed onto the peripheral portion (sealing portion) of rubber member  2   b.    
     Rubber member  2   b  is a rubber bellows (rubber film). Rubber member  2   b  is circular. The peripheral portion (sealing portion) of rubber member  2   b  has an O-ring shape. Rubber member  2   b  is provided between the housing main unit  20   e  and cover units  20   g  and  20   h , and seals the space between them in a liquid-tight manner. Rubber member  2   b  is provided along the inner circumference of the end portion of the housing main unit  20   e . Rubber member  2   b  is provided so as to separate a partial space inside the housing. In the present embodiment, rubber member  2   b  is provided in the space surrounded by cover units  20   g  and  20   h , and separates this space into two in a liquid-tight manner. The space on the cover unit  20   g  side is referred to as a first space. The space on the cover unit  20   h  side is referred to as a second space. The first space communicates with the internal space of the housing main unit  20   e  filled with the insulating oil  9  via aperture portion  20   k . Thus, the first space is filled with the insulating oil  9 . The second space communicates with the external space via the ventilation hole  20   m . Thus, the second space is air atmosphere. 
     An aperture portion  20   o  penetrates a part of the housing main unit  20   e . An X-ray irradiation window  20   w  and X-ray shielding unit  540  are provided in aperture portion  20   o . Aperture portion  20   o  is sealed by the X-ray irradiation window  20   w  and X-ray shielding unit  540  in a liquid-tight manner. As explained in detail later, X-ray shielding units  520  and  540  are provided to prevent X-ray irradiation to the outside of housing  20  in aperture portion  20   o.    
     The X-ray irradiation window  20   w  is formed of a material which transmits X-rays. For example, the X-ray irradiation window  20   w  is formed of metal which transmits X-rays. 
     X-ray shielding units  510 ,  520 ,  530  and  540  should be formed of a material which does not transmit X-rays and contains at least lead. X-ray shielding units  510 ,  520 ,  530  and  540  may be formed of lead alloy, etc. 
     X-ray shielding unit  510  is provided on the inner surface of cover unit  20   g . X-ray shielding unit  510  blocks the X-rays emitted from the X-ray tube  30 . X-ray shielding unit  510  comprises a first shielding unit  511  and a second shielding unit  512 . The first shielding unit  511  is attached to the inner surface of cover unit  20   g . The first shielding unit  511  is provided so as to cover the entire inner surface of cover unit  20   g . An end portion of the second shielding unit  512  is stacked on the inner surface of the first shielding unit  511 . The other end portion of the second shielding unit  512  is provided inside the housing main unit  20   e  to be spaced apart from aperture portion  20   k  along the tube axis TA. The second shielding unit  512  is provided such that the insulating oil  9  passes through aperture portion  20   k.    
     X-ray shielding unit  520  is substantially cylindrical. X-ray shielding unit  520  is provided in a part of the inner circumferential portion of the housing main unit  20   e . An end portion of X-ray shielding unit  520  is close to the first shielding unit  511 . Thus, it is possible to block X-rays which may be emitted from the space between X-ray shielding unit  510  and X-ray shielding unit  520 . X-ray shielding unit  520  is cylindrical, and extends from the first shielding unit  511  to the vicinity of the stator coil  8  along the tube axis. In the present embodiment, X-ray shielding unit  520  extends from the first shielding unit  511  to a position just before the stator coil  8 . X-ray shielding unit  520  is fixed to housing  20  depending on the need. 
     X-ray shielding unit  530  is cylindrical, and fits in the outer circumference of receptacle  302  described later inside housing  20 . X-ray shielding unit  530  is provided such that an end portion of the cylinder is in contact with the wall surface of the housing main unit  20   e . At this time, a hole for the passage of an end portion of X-ray shielding unit  530  is formed in X-ray shielding unit  520 . X-ray shielding unit  530  is fixed to the outer circumference of receptacle  302  described later depending on the need. 
     X-ray shielding unit  540  is shaped like a frame, and is provided in a side edge of aperture portion  20   o  of housing  20 . X-ray shielding unit  540  is provided along the internal wall of aperture portion  20   o . An end portion of X-ray shielding unit  540  inside the housing main unit  20   e  is in contact with X-ray shielding unit  520 . X-ray shielding unit  540  is fixed to the side edge of aperture portion  20   o  depending on the need. 
     Receptacle  301  for an anode and receptacle  302  for a cathode are connected to the housing main unit  20   e . Each of receptacles  301  and  302  is shaped like a tube comprising a bottom and an aperture portion. The bottom portion of each of receptacles  301  and  302  is provided inside housing  20 . Further, their aperture portions open to outside. For example, receptacles  301  and  302  are provided across an intervening gap in the housing main unit  20   e . Further, their aperture portions face in the same direction. 
     A plug (not shown) inserted into receptacle  301  and receptacle  302  is of a non-surface-pressure type, and is detachably formed. In a state where the plug is connected to receptacle  301 , high voltage (for example, +70 to +80 kV) is applied from the plug to a terminal  201 . 
     Receptacle  301  is provided on the cover unit  20   f  side in housing  20 . Further, receptacle  301  is provided on the internal side in comparison with cover unit  20   f . Receptacle  301  comprises a housing  321  as an electric insulating member, and terminal  201  as a high-voltage supply terminal. 
     Housing  321  is formed of, for example, resin, as an insulating material. Housing  321  is shaped like a cylinder comprising a bottom in which a plug insertion hole opens to outside. Housing  321  comprises terminal  201  in the bottom portion. Housing  321  comprises an annular projection portion on the outer surface in the end portion on the aperture portion side. The projection portion of housing  321  is formed so as to fit in a step portion  20   ea  which is a step formed in an end portion of the projection portion of the housing main unit  20   e . Terminal  201  is attached to the bottom portion of housing  321  in a liquid-tight manner, and penetrates the bottom portion. Terminal  201  is connected to a high-voltage supply terminal  44  as described later via an insulating covering line. 
     A rubber member  2   f  is provided between the projection portion of housing  321  and the housing main unit  20   e . Rubber member  2   f  is provided between the projection portion of housing  321  and the step of step portion  20   ea , and seals the space between the projection portion of housing  321  and the housing main unit  20   e  in a liquid-tight manner. In the present embodiment, rubber member  2   f  has an O-ring shape. Rubber member  2   f  prevents the insulting oil  9  from leaking out to the outside of housing  20 . Rubber member  2   f  is rubber formed of, for example, sulfur vulcanization. 
     Housing  321  is fixed with a ring nut  311 . A screw groove is formed in the outer circumferential portion of ring nut  311 . For example, the outer circumferential portion of ring nut  311  is processed into a male screw. The inner circumferential portion of step portion  20   ea  is processed into a female screw. Thus, when ring nut  311  is mounted, the projection portion of housing  321  is pressed onto step portion  20   ea  via rubber member  2   f . As a result, housing  321  is fixed to the housing main unit  20   e.    
     Receptacle  302  is provided on the cover unit  20   g  side in housing  20 . Further, receptacle  302  is provided on the internal side in comparison with cover unit  20   g . Receptacle  302  is formed in the substantially same manner as receptacle  301 . 
     Receptacle  302  comprises a housing  322  as an electric insulating member, and a terminal  202  as a high-voltage supply terminal. 
     Housing  322  is formed of, for example, resin, as an insulating material. Housing  322  is shaped like a cylinder comprising a bottom in which a plug insertion hole opens to outside. Housing  322  comprises terminal  202  in the bottom portion. Housing  322  comprises an annular projection portion on the outer surface in the end portion on the aperture portion side. The projection portion of housing  322  is formed so as to fit in a step portion  20   eb  which is a step formed in an end portion of the projection portion of the housing main unit  20   e . Terminal  202  is attached to the bottom portion of housing  321  in a liquid-tight manner, and penetrates the bottom portion. Terminal  202  is connected to a high-voltage supply terminal  54  as described later via an insulating covering line. 
     A rubber member  2   g  is provided between the projection portion of housing  322  and the housing main unit  20   e . Rubber member  2   g  is provided between the projection portion of housing  322  and the step of step portion  20   eb , and seals the space between the projection portion of housing  321  and the housing main unit  20   e  in a liquid-tight manner. In the present embodiment, rubber member  2   g  has an O-ring shape. Rubber member  2   g  prevents the insulting oil  9  from leaking out to the outside of housing  20 . Rubber member  2   g  is rubber formed of, for example, sulfur vulcanization. 
     Housing  322  is fixed with a ring nut  312 . A screw groove is formed in the outer circumferential portion of ring nut  312 . For example, the outer circumferential portion of ring nut  312  is processed into a male screw. The inner circumferential portion of step portion  20   eb  is processed into a female screw. Thus, when ring nut  312  is mounted, the projection portion of housing  322  is pressed onto step portion  20   eb  via rubber member  2   g . As a result, housing  322  is fixed to the housing main unit  20   e.    
       FIG. 2A  is a cross-sectional view showing the general outline of the X-ray tube  30  according to the first embodiment.  FIG. 2B  is a cross-sectional view taken along line of  FIG. 2A .  FIG. 2C  is a cross-sectional view taken along line IIB-IIB of  FIG. 2B . In  FIG. 2C , a straight line perpendicular to the tube axis TA is defined as straight line L 1 , and a straight line perpendicular to the tube axis TA and straight line L 1  is defined as straight line L 2 . 
     The X-ray tube  30  comprises a fixed axis  11 , a rotator  12 , a bearing  13 , a rotor  14 , a vacuum envelope  31 , a vacuum container  32 , an anode target  35 , a cathode  36 , high-voltage supply terminal  44  and high-voltage supply terminal  54 . 
     In  FIG. 2C , a straight line which is perpendicular to a straight line parallel to the center of the cathode  36  or the emission direction of an electron beam and is parallel to straight line L 2  is defined as straight line L 3 . 
     The fixed axis  11  is cylindrical. The fixed axis  11  rotatably supports the rotator  12  via the bearing  13 . The fixed axis  11  comprises a projection portion attached to the vacuum envelope  31  in an air-tight manner at an end portion. The projection portion of the fixed axis  11  is fixed to a high-voltage insulating member  39 . At this time, the end portion of the projection portion of the fixed axis  11  penetrates the high-voltage insulating member  39 . High-voltage supply terminal  44  is electrically connected to the end portion of the projection portion of the fixed axis  11 . 
     The rotator  12  is shaped like a tube comprising a bottom. The fixed axis  11  is inserted into the rotator  12 . The rotator  12  is provided concentrically with the fixed axis  11 . The rotator  12  is connected to the anode target  35  described later at the end portion on the bottom portion side, and is rotatably provided together with the anode target  35 . 
     The bearing  13  is provided between the inner circumferential portion of the rotator and the outer circumferential portion of the fixed axis  11 . 
     The rotor  14  is provided on the internal side of the cylindrical stator coil  8 . 
     High-voltage supply terminal  44  applies relatively positive voltage to the anode target  35  via the fixed axis  11 , the bearing  13  and the rotator  12 . High-voltage supply terminal  44  is connected to receptacle  301 . When a high-voltage supply source such as a plug (not shown) is connected to receptacle  301 , current is supplied to receptacle  301 . High-voltage supply terminal  44  is a metal terminal. 
     The anode target  35  is shaped like a disk. The anode target  35  is connected to the end portion of the rotator  12  on the bottom portion side concentrically with the rotator  12 . For example, the central axis of the rotator  12  and the anode target  35  is provided along the tube axis TA. The axis of the rotator  12  and the anode target  35  is parallel to the tube axis TA. In this case, the rotator  12  and the anode target  35  are provided so as to be rotatable around the tube axis TA. 
     The anode target  35  comprises an umbrella target layer  35   a  provided in a part of the outer surface of the anode target. The target layer  35   a  emits X-rays in connection with the collision of the electrons emitted from the cathode  36 . Blackening treatment is applied to the outer surface of the anode target  35  and the surface of the anode target  35  on a side opposite to the target layer  35   a . The anode target  35  is formed of a nonmagnetic material having a high electric conductivity. For example, the anode target  35  is formed of copper, tungsten, molybdenum, niobium, tantalum or nonmagnetic stainless steel. The anode target  35  may have a structure in which at least the surface portion is formed of a nonmagnetic metal material having a high electric conductivity. Alternatively, the anode target  35  may have a structure in which the surface portion is covered with a covering member formed of a nonmagnetic metal material having a high electric conductivity. 
     Nonmagnetic materials having a high electric conductivity can more strongly twist magnetic lines generated by an AC magnetic field having an opposite direction based on eddy current than nonmagnetic materials having a low electric conductivity when they are provided in the AC magnetic field. Since the magnetic lines are twisted in this way, even when the quadrupole magnetic field generation unit  60  described later is close to the anode target  35  and generates an AC magnetic field, the magnetic lines flow along the surface of the anode target  35 , and thus, the magnetic field (AC magnetic field) near the surface of the anode target  35  is strengthened. 
     The cathode  36  includes a filament (electron generation source) which emits electrons (electron beams). The cathode  36  is provided at a position facing the target layer  35   a . The cathode  36  is a predetermined distance distant from the surface of the anode target  35 . The cathode  36  emits electrons to the anode target  35 . For example, the cathode  36  is cylindrical and emits electrons to the surface of the anode target  35  from the filament provided in the center of the circle. At this time, the straight line passing through the center of the cathode  36  is parallel to the tube axis TA. In the following description, the direction of the electrons emitted from the cathode  36  and their path may be referred to as an electron path. Relatively negative voltage is applied to the cathode  36 . The cathode  36  is attached to a cathode supporting unit (cathode supporter or a cathode supporting member)  37  as described later, and is connected to high-voltage supply terminal  54  passing through the cathode supporting unit  37 . It should be noted that the cathode  36  may be referred to as an electron generation source. In the cathode  36 , the position for emitting electron beams coincides with the center. The center of the cathode  36  may include the straight line passing through the center in the following description. 
     The cathode supporting unit  37  comprises the cathode  36  in an end portion. The other end portion of the cathode supporting unit  37  is connected to the internal wall of the vacuum envelop  31  (vacuum container  32 ). The cathode supporting unit  37  internally comprises high-voltage supply terminal  54 . As shown in  FIG. 2A , the cathode supporting unit  37  extends from the internal wall of the vacuum envelop  31  (vacuum container  32 ) so as to reach the surface of the cathode  36  toward the anode target  35 . For example, the cathode supporting unit  37  is cylindrical, and is provided concentrically with the cathode  36 . At this time, an end surface of the cathode supporting unit  37  is connected to the surface of the vacuum envelop  31  (vacuum container  32 ). The other end surface of the cathode supporting unit  37  is connected to the surface of the cathode  36 . 
     The cathode  36  comprises a nonmagnetic cover covering the entire outer circumference. The nonmagnetic cover is cylindrical so as to surround the circumference of the cathode  36 . The nonmagnetic cover is formed of, for example, one of copper, tungsten, molybdenum, niobium, tantalum and nonmagnetic stainless steel, or is a nonmagnetic metal member formed of a metal material containing one of these elements as the main component. The nonmagnetic cover is preferably formed of a material having a high electric conductivity. Nonmagnetic covers having a high electric conductivity can more strongly twist magnetic lines generated by an AC magnetic field having an opposite direction based on eddy current than nonmagnetic covers having a low electric conductivity when they are provided in the AC magnetic field. Since the magnetic lines are twisted in this way, even when the quadrupole magnetic field generation unit  60  described later is close to the cathode  36  and generates an AC magnetic field, the magnetic lines flow along the circumference of the cathode  36 , and thus, the magnetic field (AC magnetic field) near the surface of the cathode  36  is strengthened. The cathode  36  may be structured such that at least the surface portion is formed of a nonmagnetic metal material having a high electric conductivity. 
     An end portion of high-voltage supply terminal  54  is connected to the cathode  36  by passing through the cathode supporting unit  37 . The other end portion of high-voltage supply terminal  54  is connected to receptacle  302 . When a high-voltage supply source such as a plug (not shown) is connected to receptacle  302 , high-voltage supply terminal  54  supplies current to the cathode  36 . High-voltage supply terminal  54  is a metal terminal. High-voltage supply terminal  54  applies relatively negative voltage to the cathode  36  and supplies filament current to the filament (electron emission source; not shown) of the cathode  36 . 
     The vacuum envelope  31  is sealed in vacuum atmosphere (in a vacuum-tight manner) and internally accommodates the fixed axis  11 , the rotator  12 , the bearing  13 , the rotor  14 , the vacuum container  32 , the anode target  35 , the cathode  36  and high-voltage supply terminal  54 . 
     The vacuum container  32  comprises an X-ray transmissive window  38  in a vacuum-tight manner. The X-ray transmissive window  38  is provided in the wall portion of the vacuum envelope  31  (vacuum container  32 ) so as to face the target surface of the anode target  35  between the cathode  36  and the anode target  35 . The X-ray transmissive window  38  is formed of, for example, metal, such as beryllium, titanium, stainless steel or aluminum, and is provided in a portion facing the X-ray irradiation window  20   w . For example, the vacuum container  32  is sealed by the X-ray transmissive window  38  formed of beryllium as a member which transmits X-rays in an air-tight manner. 
     In the vacuum envelope  31 , the high-voltage insulating member  39  is provided from the high-voltage supply terminal  44  side to the circumference of the anode target  35 . The high-voltage insulating member  39  is formed of electric insulating resin. 
     The vacuum envelope  31  (vacuum container  32 ) comprises an accommodation unit  31   a  for installing the cathode  36 . The accommodation unit  31   a  comprises a small radial portion  31   b  having a less radius in a portion between the anode target  35  and the cathode  36 . For example, the accommodation unit  31   a  is cylindrical. The accommodation unit  31   a  is a part of the vacuum envelope  31 , and extends from the vicinity of the X-ray transmissive window  38  toward the outside of the X-ray tube  30  along a straight line parallel to the tube axis TA. The accommodation unit  31   a  is provided so as to face the surface of the anode target  35 . For example, as shown in  FIG. 2A , the accommodation unit  31   a  faces the surface of the end portion of the anode target  35  in the radial direction, and extends from the vicinity of the X-ray transmissive window  38  along a straight line parallel to the tube axis TA. 
     The small radial portion  31   b  is provided to strengthen the effect of the magnetic field for the electron beams emitted from the cathode  36  when the quadrupole magnetic field generation unit  60  described later is installed. The small radial portion  31   b  is formed so as to have a radius less than that of the accommodation unit  31   a  around the small radial portion  31   b . As shown in  FIG. 2A  and  FIG. 2B , the small radial portion  31   b  is formed so as to have a radius less than that of the accommodation unit  31   a  around the small radial portion  31   b  between the anode target  35  and the cathode  36 . 
     The vacuum envelope  31  collects the recoil electrons reflected on the anode target  35 . Thus, the temperature of the vacuum envelope  31  is easily increased by the effect of the collision of recoil electrons. Normally, the vacuum envelope  31  is formed of a material having a high thermal conductivity such as copper. When the vacuum envelope  31  is influenced by an AC magnetic field, the vacuum envelope  31  is preferably formed of a material which does not generate a diamagnetic field. For example, the vacuum envelope  31  is formed of a nonmagnetic metal material. The vacuum envelope  31  is preferably formed of a nonmagnetic material having a high electric resistance such that overcurrent is not generated by alternating current. The nonmagnetic material having a high electric resistance is, for example, nonmagnetic stainless steel, Inconel, Inconel X, titanium, conductive ceramics or nonconductive ceramics coated with a metal thin film. 
     The high-voltage insulating member  39  has an annular shape such that an end is conical and the other end is closed. The high-voltage insulating member  39  is directly fixed to housing  20  or indirectly fixed to housing  20  via the stator coil  8  described later, etc. 
     The high-voltage insulating member  39  electrically disconnects the fixed axis  11  from either housing  20  or the stator coil  8 . Thus, the high-voltage insulating member  39  is provided between the stator coil  8  and the fixed axis  11 . The high-voltage insulating member  39  is provided so as to internally accommodate the X-ray tube  30  (vacuum container  32 ) on the projection portion side of the fixed axis  11  of the X-ray tube  30 . 
     Returning to  FIG. 1 , the stator coil  8  is fixed to housing  20  at a plurality of positions. The stator coil  8  is provided around the outer circumferential portions of the rotor  14  and the high-voltage insulating member  39 . The stator coil  8  rotates the rotor  14 , the rotator  12  and the anode target  35 . When a predetermined current is supplied to the stator coil  8 , the magnetic field applied to the rotor  14  is generated. Thus, the anode target  35 , etc., is rotated at a predetermined speed. When current is supplied to the stator coil  8  which is a rotation device, the rotor  14  rotates. In line with the rotation of the rotor  14 , the anode target  35  rotates. 
     Inside housing  20 , the insulating oil  9  fills the space surrounded by rubber bellows  2   b , the housing main unit  20   e , cover unit  20   f  and receptacles  301  and  302 . The insulating oil  9  absorbs at least part of the heat generated by the X-ray tube  30 . 
     Returning to  FIG. 2A  to  FIG. 2C , the quadrupole magnetic field generation unit  60  is explained. 
     As shown in  FIG. 2B  and  FIG. 2C , the quadrupole magnetic field generation unit  60  comprises coils  64  ( 64   a ,  64   b ,  64   c  and  64   d ), a yoke  66  and magnetic poles  68  ( 68   a ,  68   b ,  68   c  and  68   d ). 
     The quadrupole magnetic field generation unit  60  generates a magnetic field when an electric source supplies current to the quadrupole magnetic field generation unit  60 . The quadrupole magnetic field generation unit  60  is capable of changing, for example, the strength (the density of magnetic flux) or direction of the magnetic field to be generated based on the strength or direction of the supply current. 
     The quadrupole magnetic field generation unit  60  comprises a quadrupole in which four magnetic poles are arranged close to each other such that adjacent magnetic poles have opposite polarities. When two adjacent magnetic poles are regarded as a dipole, and the other two magnetic poles are regarded as the other dipole, the directions of the magnetic fields generated by the two dipoles are opposite to each other. Thus, the quadrupole magnetic field generation unit  60  has an influence on the shape of the electron beams, such as the width or height, depending on the magnetic field to be generated. Neither the width nor the height of electron beams relates to the spatial arrangement of the X-ray tube  30 . Each of the width and the height is a length in a direction perpendicular to a straight line accordance with the emission direction of electron beams. The width and the height are lengths in directions perpendicular to each other. In the quadrupole magnetic field generation unit  60  of the present embodiment, four magnetic poles  68  are provided in the form of a square. As described in detail later, in the quadrupole magnetic field generation unit  60 , magnetic poles  68   a ,  68   b ,  68   c  and  68   d  face each other inside the yoke  66 . For example, as shown in  FIG. 2C , in the quadrupole magnetic field generation unit  60 , magnetic pole  68   a  faces magnetic pole  68   d , and magnetic pole  68   b  faces magnetic pole  68   c.    
     The quadrupole magnetic field generation unit  60  is provided around the small radial portion  31   b  in the inner circumferential portion of the yoke  66  described later. The quadrupole magnetic field generation unit  60  is eccentrically provided such that its center does not overlap the central axis of the cathode  36 . In other words, the quadrupole magnetic field generation unit  60  is provided such that the central position is off (in other words, eccentric with respect to) the central axis of the cathode  36 . At this time, the center of the quadrupole magnetic field generation unit  60  substantially coincides with the center of the yoke  66  having a hollow circular or polygonal shape as described later. For example, as shown in  FIG. 2C , the quadrupole magnetic field generation unit  60  is provided at a position moved from the central position of the cathode  36  in the radial direction (or along straight line L 1 ) toward the central position of the anode target  35 . Alternatively, the quadrupole magnetic field generation unit  60  may be provided so as to be off (in other words, eccentric) in a direction perpendicular to the path of electron beams (electron path) in a manner different from that of the above description. 
     When an electric source (not shown) for the quadrupole magnetic field generation unit  60  supplies current to coils  64 , coils  64  generate a magnetic field. For example, each coil  64  is an electromagnetic coil. In the present embodiment, direct current is supplied from an electric source (not shown) to coils  64 . Coils  64  include a plurality of coils  64   a ,  64   b ,  64   c  and  64   d . Coils  64   a  to  64   d  are wound onto a part of magnetic poles  68   a ,  68   b ,  68   c  and  68   d  described later, respectively. 
     The yoke  66  has a hollow polygonal shape or a hollow cylindrical shape. The yoke  66  is formed of a soft magnetic material which has a high electric resistance and is difficult to generate eddy current by an AC magnetic field. For example, the yoke  66  is formed as a stacked element in which a thin plate formed of Fe—Si alloy (silicon steel), Fe—Al alloy, electromagnetic stainless steel, Fe—Ni high-permeability alloy such as permalloy, Ni—Cr alloy, Fe—Ni—Cr alloy, Fe—Ni—Co alloy or Fe—Cr alloy is interposed between electric insulating films, or as aggregate prepared by covering line members formed of the above materials with electric insulating films, bundling the line members and solidifying the bundle. Alternatively, the yoke  66  may be formed as a compact prepared by grinding the above materials into fine particles of approximately 1 μm, covering the surfaces with an electric insulating film and compressing them. Alternatively, the yoke  66  may be formed of soft ferrite, etc. 
     Magnetic poles  68  include a plurality of magnetic poles  68   a ,  68   b ,  68   c  and  68   d . Magnetic poles  68   a ,  68   b    68   c  and  68   d  are provided in the inner circumferential wall of the yoke  66 . Magnetic poles  68   a  to  68   d  are provided so as to surround the electron path of electron beams around the small radial portion  31   b . In the quadrupole magnetic field generation unit  60 , magnetic poles  68   a  to  68   d  are evenly provided in the rotational direction of the anode target  35  at positions in a direction perpendicular to the emission direction of electrons emitted from the filament included in the cathode  36 . For example, as shown in  FIG. 2C , magnetic poles  68   a  to  68   d  are provided at the positions of the vertexes of the square. Magnetic poles  68   a  to  68   d  are preferably provided so as to be close to the emission direction (electron path) of electrons emitted from the filament included in the cathode  36  to increase the density of magnetic flux. 
     Magnetic poles  68   a  to  68   d  have substantially the same shape. Magnetic poles  68   a  to  68   d  include two dipoles each corresponding to a pair of magnetic poles. For example, magnetic pole  68   a  and magnetic pole  68   b  are a dipole (a pair of magnetic poles  68   a  and  68   b ). Magnetic pole  68   c  and magnetic pole  68   d  are a dipole (a pair of magnetic poles  68   c  and  68   d ). When direct current is supplied to magnetic poles  68  via respective coils  64  ( 64   a ,  64   b ,  64   c  and  64   d ), a pair of magnetic poles  68   a  and  68   b  forms a DC magnetic field having a direction opposite to that of a pair of magnetic poles  68   c  and  68   d . Magnetic poles  68   a  to  68   d  are provided such that the surface (end surface) faces the electron path of the electron beams emitted from the cathode  36  to change the shape of the electron beams emitted from the cathode  36  to increase the density of magnetic flux. 
     The principle of the quadrupole magnetic field generation unit  60  of the present embodiment is explained below with reference to the accompanying drawings.  FIG. 3  shows the principle of the quadrupole magnetic field generation unit of the present embodiment. In  FIG. 3 , an X-direction and a Y-direction are directions perpendicular to the direction in which electron beams are emitted, and are perpendicular to each other. The X-direction is a direction from the magnetic pole  68   b  (magnetic pole  68   a ) side to the magnetic pole  68   d  (magnetic pole  68   c ) side. The Y-direction is a direction from the magnetic pole  68   d  (magnetic pole  68   b ) side to the magnetic pole  68   c  (magnetic pole  68   a ) side. 
     In  FIG. 3 , it is assumed that an electron beam BM 1  travels from the front side to the far side of the figure. It is assumed that the electron beam BM 1  is roundly emitted. In  FIG. 3 , magnetic pole  68   a  generates a north-pole magnetic field. Magnetic pole  68   b  generates a south-pole magnetic field. Magnetic pole  68   c  generates a south-pole magnetic field. Magnetic pole  68   d  generates a north-pole magnetic field. In this case, a magnetic field from magnetic pole  68   c  to magnetic poles  68   a  and  68   d  and a magnetic field from magnetic pole  68   b  to magnetic poles  68   a  and  68   d  are formed. When the electron beam BM 1  passes through substantially the center of the space surrounded by magnetic poles  68   a  to  68   d , the shape of the electron beam BM 1  is changed in directions facing each other in the X-direction by the Lorentz force of the generated magnetic field, and is changed to directions moving away from each other in the Y-direction. In the present embodiment, the quadrupole magnetic field generation unit  60  is provided such that the center is eccentric with respect to the central position of the cathode  36  in the radial direction of the anode target  35  (or the Y-direction). Thus, the electron beam BM 1  is strongly influenced by the Lorentz force in the directions facing each other in the X-direction and the Lorentz force going in one of the directions in the Y-direction. For example, as shown in  FIG. 3 , the electron beam BM 1  is strongly influenced by the Lorentz force in the directions facing each other in the X-direction and the Lorentz force going in a direction opposite to the direction going to the center of the anode target  35  in the Y-direction (the radial direction of the anode target  35 ). In the quadrupole magnetic field generation unit  60 , when the position for the electron beam emitted from the cathode  36  is changed, the strength of the effect of the magnetic field having an influence on the electron beam is changed. As a result, as shown in  FIG. 3 , in the electron beam BM 1 , the width in the X-direction is reduced. However, the length in the Y-direction does not substantially change, and deviates to a direction opposite to the direction going to the center of the anode target  35  in the Y-direction (or the radial direction of the anode target  35 ). 
     In the present embodiment, when the X-ray tube device  1  is driven, electrons are emitted from the filament included in the cathode  36  to the focal spot on the anode target  35  with which the electrons collide. Here, the direction in which electrons are emitted (electron path) is assumed to be parallel to the straight line passing through the center of the cathode  36 . In the quadrupole magnetic field generation unit  60 , an electric source (not shown) supplies direct current to each coil  64  (coils  64   a  to  64   d ). When direct current is supplied from the electric source, the quadrupole magnetic field generation unit  60  generates a magnetic field between magnetic poles  68   a  to  68   d  as a quadruple. The electron beam emitted from the cathode  36  collides with the anode target  35  so as to cross the magnetic field generated between the cathode  36  and the anode target  35 . At this time, the shape of the electron beam is formed (focused) by the magnetic field generated by the quadrupole magnetic field generation unit  60 . In the present embodiment, the quadrupole magnetic field generation unit  60  is provided such that the central position deviates (is eccentric) in the radial direction of the anode target  35 . Thus, the quadrupole magnetic field generation unit  60  is capable of reducing the width of the beam and deflecting the electron beam to the radial direction of the anode target  35  in a manner different from a case where the quadrupole magnetic field generation unit  60  is provided concentrically with the central axis of the cathode  36 . For example, as shown in  FIG. 3 , the quadrupole magnetic field generation unit  60  is capable of changing the shape of the electron beam roundly emitted to an elliptical shape (in other words, focusing the electron beam into an elliptical shape) by shrinking the electron beam in the X-direction. Further, the quadrupole magnetic field generation unit  60  is capable of deflecting the electron beam in a direction opposite to the direction going to the center of the anode target  35  in the Y-direction (the radial direction of the anode target  35 ). In this case, the quadrupole magnetic field generation unit  60  is capable of reducing the size of the apparent focal spot of the electron beam and increasing the size of the actual focal spot of collision on the anode target  35  surface. As a result, thermal load for the anode target  35  is reduced. 
     In the present embodiment, the X-ray tube device  1  comprises the X-ray tube  30 , and the quadrupole magnetic field generation unit  60  which generates a magnetic field forming an electron beam. The quadrupole magnetic field generation unit  60  generates a magnetic field between magnetic poles  68   a  to  68   d  when direct current is supplied from an electric source to each coil  64 . The quadrupole magnetic field generation unit  60  is capable of changing the shape of and deflecting the electron beam emitted from the cathode  36  by the magnetic field generated by magnetic poles  68   a  to  68   d . At this time, the quadrupole magnetic field generation unit  60  is provided such that the central position is moved from the position of the path of an electron beam in accordance with the desired shape of the beam and the desired direction of deflection. In this way, the X-ray tube device  1  of the present embodiment is capable of magnetically changing the shape of an electron beam to an optimal shape based on the intended purpose. 
     Now, this specification explains an X-ray tube device according to another embodiment. In the embodiment, the same structural elements as those of the first embodiment are denoted by like reference numbers, detailed description thereof being omitted. 
     Second Embodiment 
     According to a second embodiment, an X-ray tube device  1  comprises coils for deflecting an electron beam in addition to the structures of the first embodiment. 
       FIG. 4  shows the general outline of the X-ray tube device according to the second embodiment. 
     As shown in  FIG. 4 , in the second embodiment, a quadrupole magnetic field generation unit  60  further comprises deflection coil units  69   a  and  69   b.    
     The quadrupole magnetic field generation unit  60  generates dipole DC magnetic fields by superimposition such that the magnetic fields generated from two pairs of magnetic poles have the same direction. The quadrupole magnetic field generation unit  60  comprises a pair of magnetic poles  68   a  and  68   c , and a pair of magnetic poles  68   b  and  68   d . A pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form a magnetic field as a dipole. The quadrupole magnetic field generation unit  60  forms a magnetic field by superimposing a DC magnetic field on the DC magnetic field generated between a pair of magnetic poles  68   a  and  89   c  and a pair of magnetic poles  68   b  and  68   d  when current is supplied to each of deflection coils  69   a  and  69   b  described later. 
     In the quadrupole magnetic field generation unit  60 , the direct current supplied from an electric source (not shown) to deflection coil units  69   a  and  69   b  described later is controlled by a deflection electric source controller (not shown). The quadrupole magnetic field generation unit  60  is capable of changing the shape of and deflecting an electron beam having the desired direction when the quadrupole magnetic field generation unit  60  is provided such that the center is eccentric in a direction perpendicular to the electron path. For example, as shown in  FIG. 4 , the quadrupole magnetic field generation unit  60  is capable of reducing the width of the electron beam emitted from a cathode  36  and correcting the movement in the radial direction caused by the change in the width by deflection. The quadrupole magnetic field generation unit  60  is capable of adjusting the position of the focal spot on the surface of an anode target  35  with which the electron beam collides and reducing the thermal load on the focal spot. 
     Deflection coil units  69   a  and  69   b  (a first deflection coil unit and a second deflection coil unit) are electromagnetic coils which generate a magnetic field based on the current supplied from an electric source (not shown). In the present embodiment, when direct current is supplied from an electric source (not shown) to each of deflection coil units  69   a  and  69   b , deflection coil units  69   a  and  69   b  generate a DC magnetic field. Defection coil units  69   a  and  69   b  are capable of deflecting the path of an electron beam to a predetermined direction by changing the ratio of the current to be supplied. Each of deflection coil units  69   a  and  69   b  is wound onto a portion between adjacent ones of magnetic poles  68   a  to  68   d  connected to a yoke  66 . As shown in  FIG. 4 , deflection coil unit  69   a  is wound onto the main unit of the yoke  66  between magnetic poles  68   a  and  68   c . Deflection coil unit  69   b  is wound onto the main unit of the yoke  66  between magnetic poles  68   b  and  68   d . In this case, a pair of magnetic poles  68   a  and  68   c  generates a DC magnetic field between them. A pair of magnetic poles  68   b  and  68   d  generates a DC magnetic field between them. 
     This specification explains the principle of the quadrupole magnetic field generation unit  60  of the present embodiment with reference to the accompanying drawings.  FIG. 5A  shows the principle of a dipole magnetic field according to the second embodiment.  FIG. 5B  shows the principle of the quadrupole magnetic field generation unit  60  according to the second embodiment. In  FIG. 5A  and  FIG. 5B , an X-direction and a Y-direction are directions perpendicular to the direction in which an electron beam is emitted, and are perpendicular to each other. The X-direction is a direction from the magnetic pole  68   a  (magnetic pole  68   b ) side to the magnetic pole  68   c  (magnetic pole  68   d ) side. The Y-direction is a direction from the magnetic pole  68   d  (magnetic pole  68   b ) side to the magnetic pole  68   c  (magnetic pole  68   a ) side. 
     In  FIG. 5A  and  FIG. 5B , it is assumed that an electron beam BM 1  travels from the front side to the far side of the figure. In  FIG. 5A  and  FIG. 5B , a pair of magnetic poles  68   a  and  68   c  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   b  and  68   d  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   a  and  68   c  generates a DC magnetic field going in a direction accordance with the X-direction. A pair of magnetic poles  68   b  and  68   d  generates a DC magnetic field accordance with the X-direction. When the quadrupole magnetic field generation unit  60  is not influenced by deflection coil unit  69   a  or  69   b , the quadrupole magnetic field generation unit  60  generates the magnetic field shown in  FIG. 3  of the first embodiment. 
     As shown in  FIG. 5A , it is assumed that deflection coil unit  69   a  generates a north-pole magnetic field in magnetic pole  68   a  and generates a south-pole magnetic field in magnetic pole  68   c . Similarly, deflection coil unit  69   b  generates a north-pole magnetic field in magnetic pole  68   b  and generates a south-pole magnetic field in magnetic pole  68   d . Thus, a magnetic field from magnetic pole  68   a  to magnetic pole  68   c  and a magnetic field from magnetic pole  68   b  to magnetic pole  68   d  are formed by deflection coils  69   a  and  69   b , respectively. 
     In the quadrupole magnetic field generation unit  60 , because of the effect of the magnetic fields of deflection coil units  69   a  and  69   b  shown in  FIG. 5A , the magnetic field generated in deflection coil unit  69   a  is superimposed on the magnetic field from magnetic pole  68   a  to magnetic pole  68   c . Further, the magnetic field generated in deflection coil unit  69   b  is superimposed on the magnetic field from magnetic pole  68   d  to magnetic pole  68   b . Thus, as shown in  FIG. 5B , the quadrupole magnetic field generation unit  60  generates a superimposed magnetic field from magnetic pole  68   c  to magnetic pole  68   a  in addition to the magnetic field of the quadrupole. Here, the magnetic fields between magnetic pole  68   b  and magnetic pole  68   d  are cancelled by each other. 
     In the present embodiment, when the X-ray tube device  1  is driven, electrons are emitted from the filament included in the cathode  36  to the focal spot of the electrons on the anode target  35 . The direction in which the electrons are emitted is assumed to be parallel to the straight line passing through the center of the cathode  36 . In the quadrupole magnetic field generation unit  60 , direct current is supplied from an electric source (not shown) to deflection coil units  69   a  and  69   b . For example, when direct current is supplied from the electric source, the quadrupole magnetic field generation unit  60  forms a magnetic field by superimposing the magnetic fields generated in deflection coil units  69   a  and  69   b  on the magnetic fields of the quadrupole between a pair of magnetic poles  68   a  and  68   c  as a dipole and a pair of magnetic poles  68   b  and  68   d  as a dipole. In this way, for example, as shown in  FIG. 5B , when the quadrupole magnetic field generation unit  60  deviates from (is eccentric with respect to) the electron path in a perpendicular direction, the quadrupole magnetic field generation unit  60  is capable of performing correction by deflecting the movement (deflection or eccentricity) in the length direction (Y-direction) caused when the electron beam is changed in the width direction (X-direction) by the magnetic fields of the quadrupole to the opposite direction. 
     In the present embodiment, the X-ray tube device  1  comprises the quadrupole magnetic field generation unit  60  comprising deflection coil units  69   a  and  69   b . The quadrupole magnetic field generation unit  60  is capable of generating a superimposed deflection magnetic field when direct current is supplied from an electric source to deflection coil units  69   a  and  69   b . In the first embodiment, the quadrupole magnetic field generation unit  60  deviates (is eccentric) in a direction perpendicular to the path of the electron beam, and thus, the electron beam is deflected in a single direction. However, in the present embodiment, the quadrupole magnetic field generation unit  60  is capable of performing correction by deflecting the movement (deflection or eccentricity) in the length direction (Y-direction) caused when the shape of the electron beam is changed in the width direction (X-direction) to the opposite direction. Thus, the X-ray tube device  1  of the present embodiment is capable of magnetically changing the shape of an electron beam to an optimal shape in accordance with the intended use. 
     In the present embodiment, in the quadrupole magnetic field generation unit  60 , direct current is supplied from an electric source to deflection coil units  69   a  and  69   b . However, alternating current may be supplied. 
     In this case, the quadrupole magnetic field generation unit  60  generates dipole AC magnetic fields such that the magnetic fields generated from two pairs of magnetic poles have the same direction. For example, the quadrupole magnetic field generation unit  60  comprises a pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d . A pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form a magnetic field as a dipole. A pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form an AC magnetic field between them. 
     The quadrupole magnetic field generation unit  60  is capable of intermittently or continuously deflecting the path of electrons by the AC magnetic field generated between dipoles when alternating current is supplied. In the quadrupole magnetic generation unit  60 , the alternating current supplied from an electric source (not shown) to deflection coil units  69   a  and  69   b  described later is controlled by a deflection electric source controller (not shown) such that the focal spot of collision with the electron beam emitted from the cathode  36  is intermittently or continuously moved. The quadrupole magnetic field generation unit  60  is capable of deflecting the electron beam emitted from the cathode  36  to a direction parallel to the radial direction of the anode target  35 . The quadrupole magnetic field generation unit  60  is capable of moving the position of the focal spot on the surface of the anode target  35  with which an electron beam collides. 
     Now, this specification explains some modification examples of the present embodiment below with reference to the accompanying drawings. Each X-ray tube device  1  of the modification examples has structures similar to those of the X-ray tube device  1  of the second embodiment. The same structural elements as those of the X-ray tube device  1  of the second embodiment are denoted by like reference numbers, detailed description thereof being omitted. 
     Modification Example 1 
     In the X-ray tube device  1  of modification example 1 of the second embodiment, each deflection coil is provided at a position rotated by 90° around the cathode  36  in comparison with deflection coils  69   a  and  69   b  of the second embodiment. 
       FIG. 6A  is a cross-sectional view showing the general outline of an X-ray tube  30  according to modification example 1 of the second embodiment.  FIG. 6B  is a cross-sectional view taken along line VIA-VIA of  FIG. 6A . 
     As shown in  FIG. 6A  and  FIG. 6B , the quadrupole magnetic field generation unit  60  of modification example 1 of the present embodiment further comprises deflection coil units  69   c  and  69   d . As shown in  FIG. 6B , for example, the quadrupole magnetic field generation unit  60  of modification example 1 is eccentrically provided with respect to the central axis of the cathode  36  in accordance with the direction of straight line L 3 . 
     When an electric source (not shown) supplies current to deflection coil units  69   c  and  69   d  (a third deflection coil unit and a fourth deflection coil unit), deflection coil units  69   c  and  69   d  generate a magnetic field. In the present embodiment, when direct current is supplied from an electric source (not shown) to each of deflection coil units  69   c  and  69   d , deflection coil units  69   c  and  68   d  generate a DC magnetic field. Deflection coil units  69   c  and  69   d  are capable of deflecting the path of an electron beam to a predetermined direction based on the supplied current. Each of deflection coil units  69   c  and  69   d  is wound onto a portion between adjacent ones of magnetic poles  68   a  to  68   d  connected to the yoke  66 . As shown in  FIG. 6B , deflection coil unit  69   c  is wound onto the main unit of the yoke  66  between magnetic poles  68   a  and  68   b . Deflection coil unit  69   d  is wound onto the main unit of the yoke  66  between magnetic pole units  68   c  and  68   d . In this case, for example, a pair of magnetic poles  68   a  and  68   b  generates a DC magnetic field between them. A pair of magnetic poles  68   c  and  68   d  generates a DC magnetic field between them. 
     Now, this specification explains the principle of the quadrupole magnetic field generation unit  60  of the present embodiment with reference to the accompanying drawings.  FIG. 7A  is a cross-sectional view showing the principle of a quadrupole magnetic field according to modification example 1 of the second embodiment.  FIG. 7B  is a cross-sectional view showing the principle of a dipole magnetic field according to modification example 1 of the second embodiment.  FIG. 7C  is a cross-sectional view showing the principle of the quadrupole magnetic field generation unit according to modification example 1 of the second embodiment. In  FIG. 7A  to  FIG. 7C , the X-direction and the Y-direction are directions perpendicular to the direction in which an electron beam is emitted, and are perpendicular to each other. The X-direction is a direction from the magnetic pole  68   b  (magnetic pole  68   a ) side to the magnetic pole  68   d  (magnetic pole  68   c ) side. The Y-direction is a direction from the magnetic pole  68   b  (magnetic pole  68   d ) side to the magnetic pole  68   a  (magnetic pole  68   c ) side. 
     In  FIG. 7A  to  FIG. 7C , it is assumed that the electron beam BM 1  travels from the front side to the far side of the drawings. In  FIG. 7A  to  FIG. 7C , a pair of magnetic poles  68   a  and  68   b  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   c  and  68   d  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   a  and  68   b  generates a DC magnetic field going in a direction accordance with the Y-direction. A pair of magnetic poles  68   c  and  68   d  generates a DC magnetic field accordance with the Y-direction. 
     As shown in  FIG. 7A , in modification example 1, when the quadrupole magnetic field generation unit  60  is not influenced by deflection coil unit  69   c  or  69   d , the quadrupole magnetic field generation unit  60  generates the magnetic field shown in  FIG. 3  of the first embodiment. 
     As shown in  FIG. 7B , deflection coil unit  69   c  generates a south-pole magnetic field in magnetic pole  68   a  and generates a north-pole magnetic field in magnetic pole  68   b . Similarly, deflection coil unit  69   d  generates a south-pole magnetic field in magnetic pole  68   c  and generates a north-pole magnetic field in magnetic pole  68   d . Thus, a magnetic field from magnetic pole  68   b  to magnetic pole  68   a  and a magnetic field from magnetic pole  68   d  to magnetic pole  68   c  are formed by deflection coil units  69   c  and  69   d , respectively. 
     In the quadrupole magnetic field generation unit  60 , because of the effect of the magnetic fields of deflection coil units  69   c  and  69   d  shown in  FIG. 7B , the magnetic field generated in deflection coil unit  69   c  is superimposed on the magnetic field having a direction from magnetic pole  68   b  to magnetic pole  68   a . Further, the magnetic field generated in deflection coil unit  69   d  is superimposed on the magnetic field having a direction from magnetic pole  68   c  to magnetic pole  68   d . As shown in  FIG. 5B , the quadrupole magnetic field generation unit  60  generates a superimposed magnetic field from magnetic pole  68   a  to magnetic pole  68   b  in addition to the magnetic fields of the quadrupole shown in  FIG. 7A . Here, the magnetic fields between magnetic pole  68   c  and magnetic pole  68   d  are cancelled by each other. 
     In the present embodiment, when the X-ray tube device  1  is driven, electrons are emitted from the filament included in the cathode  36  to the focal spot of the electrons on the anode target  35 . It is assumed that the direction in which electrons are emitted is parallel to the straight line passing through the center of the cathode  36 . In the quadrupole magnetic field generation unit  60 , direct current is supplied from an electric source (not shown) to deflection coil units  69   c  and  69   d . For example, when direct current is supplied from the electric source, the quadrupole magnetic field generation unit  60  forms a magnetic field by superimposing the magnetic fields generated in deflection coil units  69   c  and  69   d  on the magnetic fields of the quadrupole between a pair of magnetic poles  68   a  and  68   b  as a dipole and a pair of magnetic poles  68   c  and  68   d  as a dipole. Thus, for example, as shown in  FIG. 7C , when the quadrupole magnetic field generation unit  60  deviates from (is eccentric with respect to) the electron path in a perpendicular direction, the quadrupole magnetic field generation unit  60  is capable of performing correction by deflecting the movement (deflection or eccentricity) in the width direction (Y-direction) caused when the shape of the electron beam is changed in the length direction (Y-direction) by the magnetic fields of the quadrupole to the opposite direction. 
     In the present embodiment, the X-ray tube device  1  comprises the quadrupole magnetic field generation unit  60  comprising deflection coil units  69   c  and  69   d . The quadrupole magnetic field generation unit  60  is capable of generating a superimposed magnetic field when direct current is supplied from an electric source to deflection coil units  69   c  and  69   d . In the first embodiment, the quadrupole magnetic field generation unit  60  deviates from (is eccentric with respect to) the path of an electron beam in a perpendicular direction, and thus, the electron beam is deflected in a single direction. However, in the present embodiment, the quadrupole magnetic field generation unit  60  is capable of performing correction by deflecting the movement (deflection or eccentricity) in the width direction (Y-direction) caused when the shape of the electron beam is changed in the length direction (Y-direction) to the opposite direction. Thus, the X-ray tube device  1  of the present embodiment is capable of magnetically changing the shape of an electron beam to an optimal shape in accordance with the intended purpose. 
     In modification example 1 of the present embodiment, direct current is supplied from an electric source to deflection coil units  69   c  and  69   d  of the quadrupole magnetic field generation unit  60 . However, alternating current may be supplied. 
     In this case, the quadrupole magnetic field generation unit  60  generates dipole AC magnetic fields such that the magnetic fields generated from two pairs of magnetic poles have the same direction. For example, the quadrupole magnetic field generation unit  60  comprises a pair of magnetic poles  68   a  and  68   b , and a pair of magnetic poles  68   c  and  68   d . A pair of magnetic poles  68   a  and  68   b  and a pair of magnetic poles  68   c  and  68   d  each form a magnetic field as a dipole. A pair of magnetic poles  68   a  and  68   b  and a pair of magnetic poles  68   c  and  68   d  each form an AC magnetic field between them. 
     The quadrupole magnetic field generation unit  60  is capable of intermittently or continuously deflecting the path of electrons by the AC magnetic fields generated between dipoles when alternating current is supplied. In the quadrupole magnetic generation unit  60 , the alternating current supplied from an electric source (not shown) to deflection coil units  69   c  and  69   d  described later is controlled by a deflection electric source controller (not shown) such that the focal spot of collision with the electron beam emitted from the cathode  36  is intermittently or continuously moved. The quadrupole magnetic field generation unit  60  is capable of deflecting the electron beam emitted from the cathode  36  to a direction parallel to the radial direction of the anode target  35 . The quadrupole magnetic field generation unit  60  is capable of moving the position of the focal spot on the surface of the anode target  35  with which an electron beam collides. 
     Modification Example 2 
     The X-ray tube device  1  of modification example 2 of the second embodiment comprises the quadrupole magnetic field generation unit  60  comprising the above deflection coil units  69   a  and  69   b , and a quadrupole magnetic field generation unit comprising deflection coil units  69   c  and  69   d.    
       FIG. 8  is a cross-sectional view showing the general outline of the X-ray tube  30  according to modification example 2 of the second embodiment.  FIG. 9  is a cross-sectional view taken along line VIII-VIII of  FIG. 8 . 
     As shown in  FIG. 8 , the X-ray tube  30  of modification example 2 of the present embodiment comprises two quadrupole magnetic field generation units  601  and  602 . Quadrupole magnetic field generation units  601  and  602  are provided in a small radial portion  31   b . Quadrupole magnetic field generation units  601  and  602  are arranged in the small radial portion  31   b . Quadrupole magnetic field generation unit  601  is provided on the anode target  35  side in the small radial portion  31   b . Quadrupole magnetic field generation unit  602  is provided on the cathode  36  side in the small radial portion  31   b  in comparison with quadrupole magnetic field generation unit  601 . 
     Quadrupole magnetic field generation units  601  and  602  deviate from (are eccentric with respect to) the electron path of the electron beam emitted from the cathode  36  in a perpendicular direction. For example, as shown in  FIG. 9 , quadrupole magnetic field generation unit  601  is provided so as to deviate (be eccentric) in a direction parallel to straight line L 3  in a manner similar to that of modification example 1 of the second embodiment. Quadrupole magnetic field generation unit  602  is eccentrically provided in a direction parallel to straight line L 1  (the radial direction of the anode target  35 ) in a manner similar to that of the second embodiment. 
     Quadrupole magnetic field generation unit  601  has a structure similar to that of quadrupole magnetic field generation unit  60  of modification example 1 of the second embodiment. Thus, detailed description of the same structural elements is omitted. Quadrupole magnetic field generation unit  601  comprises coils  64  ( 64   a   1 ,  64   b   1 ,  64   c   1  and  64   d   1 ), a yoke  66   ya  and magnetic poles  68  ( 68   a   1 ,  68   b   1 ,  68   c   1  and  68   d   1 ). 
     Coils  64  ( 64   a   1 ,  64   b   1 ,  64   c   1  and  64   d   1 ) are similar to coils  64  ( 61   a ,  64   b ,  64   c  and  64   d ) of modification example 1 of the second embodiment, respectively. 
     Yoke  66   ya  is similar to yoke  66  of modification example 1 of the second embodiment. 
     Magnetic poles  68  ( 68   a   1 ,  68   b   1 ,  68   c   1  and  68   d   1 ) are similar to magnetic poles  68  ( 68   a ,  68   b ,  68   c  and  68   d ) of modification example 1 of the second embodiment, respectively. 
     Quadrupole magnetic field generation unit  602  has a structure similar to that of quadrupole magnetic field generation unit  60  of the second embodiment. Quadrupole magnetic field generation unit  602  comprises coils  64  ( 64   a   2 ,  64   b   2 ,  64   c   2  and  64   d   2 ), a yoke  66   yb , and magnetic poles  68  ( 68   a   2 ,  68   b   2 ,  68   c   2  and  68   d   2 ). 
     Coils  64  ( 64   a   2 ,  64   b   2 ,  64   c   2  and  64   d   2 ) are similar to coils  64  ( 64   a ,  64   b ,  64   c  and  64   d ) of the second embodiment, respectively. 
     Yoke  66   yb  is similar to yoke  66  of the second embodiment. 
     Magnetic poles  68  ( 68   a   2 ,  68   b   2 ,  68   c   2  and  68   d   2 ) are similar to magnetic poles  68  ( 68   a ,  68   b ,  68   c  and  68   d ) of the second embodiment, respectively. 
     In the present embodiment, the X-ray tube device  1  comprises quadrupole magnetic field generation unit  601  comprising deflection coil units  69   a  and  69   d , and quadrupole magnetic field generation unit  602  comprising deflection coil units  69   c  and  69   d . Quadrupole magnetic field generation units  601  and  602  are each capable of generating a superimposed magnetic field when direct current is supplied from an electric source to deflection coil units  69   a  and  69   d  and deflection coil units  69   c  and  69   d . Thus, the X-ray tube device  1  of the present embodiment is capable of magnetically changing the shape of an electron beam into an optimal shape in accordance with the intended purpose. 
     Now, this specification explains an X-ray tube device according to a third embodiment. In the third embodiment, the same structural elements as those of the above embodiments are denoted by like reference numbers, detailed description thereof being omitted. 
     Third Embodiment 
     According to the third embodiment, an X-ray tube device  10  does not comprise an accommodation unit  31   a . Thus, an anode target  35  is close to a cathode  36 . In this respect, the third embodiment is different from the above embodiments. The X-ray tube device  10  of the third embodiment is different from those of the above embodiments in terms of the structures of a vacuum envelope  31  (vacuum container  32 ), a quadrupole magnetic field generation unit, etc. 
       FIG. 10  is a cross-sectional view showing an example of the X-ray tube device according to the third embodiment. 
       FIG. 11A  is a cross-sectional view showing the general outline of an X-ray tube  30  according to the third embodiment.  FIG. 11B  is a cross-sectional view taken along line XIA-XIA of  FIG. 11A .  FIG. 11C  is a cross-sectional view taken along line XIB 1 -XIB 1  of  FIG. 11B .  FIG. 11D  is a cross-sectional view taken along line XIB 2 -XIB 2  of  FIG. 11B .  FIG. 113  is a cross-sectional view taken along line XID-XID of  FIG. 11D . 
     In  FIG. 11B  and  FIG. 11E , a straight line perpendicular to a tube axis TA is defined as straight line L 1 . A straight line perpendicular to the tube axis TA and straight line L 1  is defined as straight line L 2 . In  FIG. 11B  and  FIG. 11E , a straight line which is perpendicular to a straight line parallel to the center of the cathode  36  or the emission direction of an electron beam and is parallel to straight line L 2  is defined as straight line L 3 . 
     In addition to the structures of the above embodiments, the X-ray tube  30  comprises a KOV member  55 . 
     The anode target  35  is formed of a nonmagnetic material having a high electric conductivity. For example, the anode target  35  is formed of copper, tungsten, molybdenum, niobium, tantalum, nonmagnetic stainless steel, etc. The anode target  35  may be structured such that at least the surface portion is formed of a nonmagnetic metal material having a high electric conductivity. Alternatively, the anode target  35  may be structured such that the surface portion is covered with a covering member formed of a nonmagnetic metal material having a high conductivity. 
     The cathode  36  is attached to a cathode supporting unit (a cathode supporter or a cathode supporting member)  37  as described later, and is connected to a high-voltage supply terminal  54  passing through the cathode supporting unit  37 . The cathode  36  may be referred to as an electron generation source. In the cathode  36 , the emission position of an electron beam coincides with the center. The center of the cathode  36  may include the straight line passing through the center in the following description. 
     The cathode supporting unit  37  comprises the cathode  36  in an end portion, and comprises the KOV member  55  in the other end portion. The cathode supporting unit  37  internally comprises high-voltage supply terminal  54 . As shown in  FIG. 11A , the cathode supporting unit  37  is provided so as to extend from the KOV member  55  provided around the tube axis TA to the vicinity of the outer circumference of the anode target  35 . The cathode supporting unit  37  is provided substantially parallel to the anode target  35  across an intervening predetermined gap. At this time, the cathode supporting unit  37  comprises the cathode  36  in the end portion on the outer circumferential side of the anode target  35 . 
     The KOV member  55  is formed of low-expansion alloy. An end portion of the KOV member  55  is attached to the cathode supporting unit  37  by brazing. The other end portion of the KOV member  55  is attached to a high-voltage insulating member  50  by brazing. The KOV member  55  covers high-voltage supply terminal  54  inside the vacuum envelope  31  described later. 
     High-voltage supply terminal  54  is attached to high-voltage insulating member  50  by brazing. High-voltage supply terminal  54  and the KOV member  55  penetrate the vacuum container  32  described later and are inserted into the vacuum envelope  31 . At this time, the insertion portion of high-voltage supply terminal  54  is sealed in a vacuum-tight manner and is inserted into the vacuum envelope  31 . 
     High-voltage supply terminal  54  passes through the cathode supporting unit  37  and is connected to the cathode  36 . High-voltage supply terminal  54  applies relatively negative voltage to the cathode  36  and supplies filament current to the filament (electron emission source; not shown) of the cathode  36 . High-voltage supply terminal  54  is connected to a receptacle  302 . When a high-voltage supply source (not shown) such as a plug is connected to the receptacle  302 , current is supplied to high-voltage supply terminal  54 . High-voltage supply terminal  54  is a metal terminal. 
     The vacuum envelope  31  is sealed in vacuum atmosphere (in a vacuum-tight manner), and internally accommodates a fixed axis  11 , a rotator  12 , a bearing  13 , a rotor  14 , the vacuum container  32 , the anode target  35 , the cathode  36 , high-voltage supply terminal  54  and the KOV member  55 . 
     The vacuum container  32  comprises an X-ray transmissive window  38  in a vacuum-tight manner. The X-ray transmissive window  38  is provided in the wall portion of the vacuum envelope  31  (vacuum container  32 ) facing the area between the cathode  36  and the anode target  35 . The X-ray transmissive window  38  is formed of, for example, metal such as beryllium, titanium, stainless steel or aluminum, and is provided in a portion of the vacuum container  32  facing the X-ray emission window  20   w . For example, the vacuum container  32  is sealed in an air-tight manner by the X-ray transmissive window  38  formed of beryllium as a member which transmits X-rays. In the vacuum envelope  31 , a high-voltage insulating member  39  is provide from the high-voltage supply terminal  44  side to the vicinity of the anode target  35 . High-voltage insulating member  39  is formed of electric-insulating resin. 
     The vacuum envelope  31  (vacuum container  32 ) comprises concave portions for accommodating the end portion of a quadrupole magnetic generation unit  60  as described later. As shown in  FIG. 11B , in the present embodiment, the vacuum envelope  31  (vacuum container  32 ) comprises a plurality of concave portions  32   a ,  32   b ,  32   c  and  32   d . Each of concave portions and  32   d  is formed in a part of the vacuum envelope  31  (vacuum container  32 ). Each of concave portions  32   a ,  32   b ,  32   c  and  32   d  is a part of the vacuum envelope  31  (vacuum container  32 ) surrounding the concave portion. For example, concave portions  32   a  to  32   d  are formed by hollowing the vacuum envelope  31  (vacuum container  32 ) from outside so as to surround the cathode  36  in a direction perpendicular to the direction in which an electron beam is emitted. When observed from the internal side of the vacuum envelope  31  (vacuum container  32 ), concave portions  32   a  to  32   d  are formed so as to project parallelly to the emission direction of the electron beam of the cathode  36 . 
     Concave portions  32   a  to  32   d  are evenly arranged around the central axis from a predetermined central position (the center of the concave portions). For example, concave portions  32   a  to  32   d  are arranged at equal angle intervals based on a position (the center of the concave portions) deviating in a perpendicular direction from the electron path around the cathode  36 . In this case, concave portion  32   b  is formed at a position by 90° in a rotational direction (in a counterclockwise direction) with respect to concave portion  32   a  around the center of the concave portions. Similarly, concave portion  32   d  is formed at a position by 90° in the rotational direction with respect to concave portion  32   b  around the center of the cathode  36 . Concave portion  32   c  is formed at a position by 90° in the rotational direction with respect to concave portion  32   d  around the center of the cathode  36 . 
     For example, as shown in  FIG. 115 , concave portion  32   a  is provided at the position of 45° from straight line L 1  in the rotational direction around the center of the concave portions. Concave portion  32   b  is set at the position rotated by 90° from concave portion  32   a  the rotational direction around the center of the cathode  36 . Concave portion  32   d  is provided at the position rotated by 90° from concave portion  32   b  in the rotational direction around the center of the cathode  36 . Concave portion  32   c  is provided at the position rotated by 90° from concave portion  32   d  in the rotational direction around the center of the cathode  36 . Thus, concave portions  32   a  to  32   d  are provided at the positions of the vertexes of a square. 
     Concave portions  32   a  to  32   d  are formed such that they are not extremely close to the surface of the anode target  35  or the surface of the cathode  36  to prevent discharge, etc. For example, concave portion  32   a  is hollowed to a position more distant from the surface of the anode target  35  than the surface of the cathode  36  facing the surface of the anode target  35  in a direction parallel to the tube axis TA. Alternatively, concave portion  32   a  may be hollowed to the same position as the surface of the cathode  36  or a position slightly closer to the surface of the anode target  35  than the surface of the cathode  36  in a direction parallel to the tube axis TA. In concave portions  32   a  to  32   d , to separate them from the target surface of the anode target  35  and the surface of the cathode  36  for the prevention of discharge, etc., the corner portions projecting to the anode target  35  side are curved or inclined. For example, as shown in  FIG. 11C , the corner portions of concave portions  32   a  to  32   d  are curved. The corner portions of concave portions  32   a  to  32   d  may be formed at inclined angles along the inclined angles of magnetic poles  68  ( 68   a ,  68   b ,  68   c  and  68   d ) described later, respectively. In concave portions  32   a  to  32   d , the corner portions projecting to the anode target  35  side may not have an inclination or diameter. 
     The number of concave portions may not be four as long as they are provided so as to surround a part of the axis (electron path) parallel to the emission direction of the electron beam of the cathode  36 . For example, concave portions  32   a  to  32   d  may be integrally formed. Alternatively, concave portions  32   a  and  32   b  may be integrally formed, and concave portions  32   c  and  32   d  may be integrally formed. 
     The vacuum envelope  31  collects the recoil electrons reflected on the anode target  35 . Thus, the temperature of the vacuum envelope  31  is easily increased by the effect of the collision with the recoil electrons. Normally, the vacuum envelope  31  is formed of a material having a high thermal conductivity such as copper. When the vacuum envelope  31  is influenced by an AC magnetic field, the vacuum envelope  31  is preferably formed of a material which does not generate a diamagnetic field. For example, the vacuum envelope  31  is formed of a nonmagnetic metal material. The vacuum envelope  31  is preferably formed of a nonmagnetic material having a high electric resistance to prevent overcurrent by alternating current. The nonmagnetic material having a high electric resistance is, for example, nonmagnetic stainless steel, Inconel, Inconel X, titanium, conductive ceramics, nonconductive ceramics coated with a metal thin film. More preferably, in the vacuum envelope  31 , concave portions  32   a  to  32   d  are formed of a nonmagnetic material having a high electric resistance, and the portions other than concave portions  32   a  to  32   d  are formed of a nonmagnetic material having a high thermal conductivity such as copper. 
     This specification explains the details of the quadrupole magnetic field generation unit  60  below with reference to  FIG. 11B  to  FIG. 11E . 
     As shown in  FIG. 11B  and  FIG. 11E , the quadrupole magnetic field generation unit  60  comprises coils  64  ( 64   a ,  64   b ,  64   c  and  64   d ), a yoke  66  ( 66   a ,  66   b ,  66   c  and  66   d ), magnetic poles  68  ( 68   a ,  68   b ,  68   c  and  68   d ), and deflection coil units  69   a  and  69   b.    
     In the present embodiment, the quadrupole magnetic field generation unit  60  is provided such that the center is eccentric with respect to the electron path emitted from the cathode  36  in a perpendicular direction. For example, as shown in  FIG. 11E , the four magnetic poles  68  of the quadrupole magnetic field generation unit  60  are provided in a square form. As described in detail later, the quadrupole magnetic field generation unit  60  comprises magnetic poles  68   a ,  68   b ,  68   c  and  68   d  at the ends of projection portions  66   a ,  66   b ,  66   c  and  66   d  projecting from the main unit of the yoke  66 . 
     As schematically shown in  FIG. 11C  and  FIG. 11D , a pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form a magnetic field between them. In the quadrupole magnetic field generation unit  60 , the direct current supplied from an electric source (not shown) to deflection coil units  69   a  and  69   b  described later is controlled by a deflection electric source controller (not shown). The quadrupole magnetic field generation unit  60  is capable of changing the shape of and deflecting the electron beam having a predetermined direction when the quadrupole magnetic field generation unit  60  is provided such that the center is eccentric with respect to the electron path in a perpendicular direction. For example, as shown in  FIG. 4 , the quadrupole magnetic field generation unit  60  is capable of reducing the width of the electron beam emitted from the cathode  36  and correcting the movement of the focal spot on the anode target  35  in the radial direction caused by the change in the width by deflection. The quadrupole magnetic field generation unit  60  is capable of adjusting the position of the focal spot on the surface of the anode target  35  with which an electron beam collides and reducing the thermal load on the focal spot. 
     When an electric source (not shown) for the quadrupole magnetic field generation unit  60  supplies current to coils  64 , coils  64  generate a magnetic field. In the present embodiment, direct current is supplied from an electric source (not shown) to coils  64 . Coils  64  include a plurality of coils  64   a ,  64   b ,  64   c  and  64   d . Coils  64   a  to  64   d  are wound onto a part of projection portions  66   a ,  66   b ,  66   c  and  66   d  of the yoke  66  described later, respectively. 
     The yoke  66  comprises projection portions  66   a ,  66   b ,  66   c  and  66   d  projecting from the main unit. Projection portions  66   a  to  66   d  project in a direction parallel to the emission direction (electron path) of an electron beam. Projection portions  66   a  to  66   d  project in the same direction, and are parallel to each other. Projection portions  66   a  to  66   d  have the same length and shape. The main unit of the yoke  66  has a hollow polygonal shape or a hollow cylindrical shape. In the present embodiment, the yoke  66  is provided such that four projection portions  66   a  to  66   d  are accommodated in concave portions  32   a  to  32   d , respectively. At this time, the yoke  66  is provided such that the cathode  36  is surrounded by four projection portions  66   a  to  66   d . Coils  64  are wound onto a part of the respective four projection portions. 
     Specifically, coil  64   a  is wound onto a part of projection portion  66   a  of the yoke  66 . The portion around which coil  64   a  does not wind is accommodated in concave portion  32   a . Similarly, coils  64   b ,  64   c  and  64   d  are wound onto a part of respective projection portions  66   b ,  66   c  and  66   d . The portions around which coil  64   b ,  64   c  or  64   d  does not wind are accommodated in concave portions  32   b ,  32   c  and  32   d , respectively. 
     Magnetic poles  68  include a plurality of magnetic poles  68   a ,  68   b ,  68   c  and  68   d . Magnetic poles  68   a ,  68   b ,  68   c  and  68   d  are provided in the end portions of projection portions  66   a ,  66   b ,  66   c  and  66   d  of the yoke  66 , respectively. Magnetic poles  68   a  to  68   d  are provided so as to surround the cathode  36 . In the quadrupole magnetic field generation unit  60 , magnetic poles  68   a  to  68   d  are evenly provided around the center (the center of the magnetic poles) at the respective positions in a direction perpendicular to the emission direction of the electrons emitted from the filament included in the cathode  36 . At this time, the position of the center of the arrangement of magnetic poles  68   a  to  68   d  (the center of the magnetic poles) is an intersection of the straight lines passing through the centers of magnetic poles  68   a  to  68   d.    
     For example, in a manner similar to that of the above concave portions  32   a  to  32   d , as shown in  FIG. 11B , magnetic pole  68   a  is provided at the position of 45° from straight light L 1  around the magnetic pole center C 1  in the rotational direction (in a counterclockwise direction). Magnetic pole  68   b  is set at a position rotated by 90° from magnetic pole  68   a  around the magnetic pole center C 1  in the rotational direction. Magnetic pole  68   d  is provided at a position rotated by 90° from magnetic pole  68   b  around the magnetic pole center C 1  in the rotational direction. Magnetic pole  68   c  is provided at a position rotated by 90° from magnetic pole  68   d  around the magnetic pole center C 1  in the rotational direction. Thus, magnetic poles  68   a  to  68   d  are provided at the positions of the vertexes of a square. 
     Magnetic poles  68   a  to  68   d  are preferably provided so as to be moderately close to the emission direction (electron path) of the electrons emitted from the filament included in the cathode  36  to increase the density of magnetic flux. Magnetic pole  68   a  is provided near the curved wall surface of concave portion  32   a  on the cathode  36  side. Similarly, magnetic poles  68   b  to  68   d  are provided near the curved wall surfaces of concave portions  32   b  to  32   d  on the cathode  36  side. Concave portions  32   a  to  32   d  are provided such that they are not excessively close to the cathode  36  to prevent discharge, etc. 
     Magnetic poles  68   a  to  68   d  have substantially the same shape. Magnetic poles  68   a  to  68   d  include two dipoles each including a pair of magnetic poles. For example, magnetic poles  68   a  and  68   b  are a dipole (a pair of magnetic poles  68   a  and  68   b ). Magnetic poles  68   c  and  68   d  are a dipole (a pair of magnetic poles  68   c  and  68   d ). When direct current is supplied to magnetic poles  68  via coils  64 , a pair of magnetic poles  68   a  and  68   b  forms a DC magnetic field having a direction opposite to that of a pair of magnetic poles  68   c  and  68   d . The surfaces (end surfaces) of magnetic poles  68   a  to  68   d  face the center of the magnetic poles to change the shape of the electron beam emitted from the cathode  36  in a state where the density of magnetic flux is increased as much as possible without being excessively close to the anode target  35 . Magnetic poles  68   a  to  68   d  are formed such that their surfaces face each other. 
     For example, magnetic poles  68   a  to  68   d  have inclined surfaces at the same angle with respect to the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA. The inclined angle from the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA to the surface of magnetic pole  68   a  is defined as γ 1 . The inclined angle from the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA to the surface of magnetic pole  68   d  is defined as γ 4 . The inclined angle from the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA to the surface of magnetic pole  68   b  is defined as γ 2 . The inclined angle from the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA to the surface of magnetic pole  68   c  is defined as γ 3 . Thus, for example, when magnetic poles  68   a  to  68   d  are provided at the same inclination, γ 1 =γ 2 =γ 3 =γ 4 . At this time, the inclination angles γ (γ 1 , γ 2 , γ 3  and γ 4 ) of magnetic poles  68   a  to  68   d  are set in the range of 0′&lt;γ&lt;90°. At this time, the inclined angles γ of magnetic poles  68   a  to  68   d  are set in the range of 0°&lt;γ&lt;90°. For example, when the inclined angles of magnetic poles  68   a  to  68   d  are the same as each other (γ 1 =γ 2 =γ 3 =γ 4 ), inclinations γ 1 , γ 2 , γ 3  and γ 4  of pairs of magnetic poles  68   a  to  68   d  are formed in the range of 30°≦γ≦60°. Further, inclinations γ 1 , γ 2 , γ 3  and γ 4  of magnetic poles  68   a  to  68   d  may be formed so as to be 45° with respect to the straight line passing through the magnetic pole center C 1  and parallel to the tube axis TA. 
     Deflection coil units  69   a  and  69   b  (a first deflection coil unit and a second deflection coil unit) are electromagnetic coils which generate a magnetic field when an electric source (not shown) supplies current to deflection coil units  69   a  and  69   b . In the present embodiment, each of deflection coil units  69   a  and  69   b  generates a DC magnetic field when direct current is supplied from an electric source (not shown). Each of deflection coil units  69   a  and  69   b  is wound onto a portion between adjacent ones of projection portions  66   a  to  66   d  of the main unit of the yoke  66 . As shown in  FIG. 11C  and  FIG. 11D , deflection coil unit  69   a  is wound onto the main unit of the yoke  66  between projection portions  66   a  and  66   c . Deflection coil unit  69   b  is wound onto the main unit of the yoke  66  between projection portions  66   b  and  66   d . In this case, a pair of magnetic poles  68   a  and  68   c  generates a DC magnetic field between them. A pair of magnetic poles  68   b  and  68   d  generates a DC magnetic field between them. 
     Deflection coil units  69   a  and  69   b  generate a dipole magnetic field formed in a direction which is perpendicular to the radial direction of the anode target  35  and is parallel to the width direction of the filament included in the cathode  36 . Deflection coil units  69   a  and  69   b  are capable of deflecting the path of an electron beam to a predetermined direction by the flowing current. 
     This specification explains the principle of the quadrupole magnetic field generation unit  60  of the present embodiment below with reference to the accompanying drawings.  FIG. 12A  shows the principle of a quadrupole magnetic field according to the third embodiment.  FIG. 12B  shows the principle of the dipoles according to the second embodiment. In  FIG. 12A  and  FIG. 12B , an X-direction and a Y-direction are directions perpendicular to the direction in which an electron beam is emitted, and are perpendicular to each other. The X-direction is a direction from the magnetic pole  68   b  (magnetic pole  68   a ) side to the magnetic pole  68   d  (magnetic pole  68   c ) side. The Y-direction is a direction from the magnetic pole  68   a  (magnetic pole  68   c ) side to the magnetic pole  68   b  (magnetic pole  68   d ) side. 
     In  FIG. 12A  and  FIG. 12B , in a manner different from that of  FIG. 3 ,  FIG. 5  and  FIG. 7 , it is assumed that an electron beam BM 1  travels from the far side to the front side of the drawings. In  FIG. 12A  and  FIG. 12B , a pair of magnetic poles  68   a  and  68   c  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   b  and  68   d  is a dipole (a pair of magnetic poles). A pair of magnetic poles  68   a  and  68   c  generates a DC magnetic field going in a direction accordance with the X-diction. A pair of magnetic poles  68   b  and  68   d  generates a DC magnetic field accordance with the X-direction. 
     As shown in  FIG. 12A , when the quadrupole magnetic generation unit  60  is not influenced by deflection coil unit  69   a  or  69   b , it is assumed that the quadrupole magnetic generation unit  60  generates a north-pole magnetic field in magnetic pole  68   a , generates a south-pole magnetic field in magnetic pole  68   b , generates a south-pole magnetic field in magnetic pole  68   c  and generates a north-pole magnetic field in magnetic pole  68   d.    
     As shown in  FIG. 12B , it is assumed that deflection coil unit  69   a  generates a north-pole magnetic field in magnetic pole  68   a  and generates a south-pole magnetic field in magnetic pole  68   c . Similarly, deflection coil unit  69   b  generates a north-pole magnetic field in magnetic pole  68   b  and generates a south-pole magnetic field in magnetic pole  68   d . Thus, a magnetic field from magnetic pole  68   a  to magnetic pole  68   c  and a magnetic field from magnetic pole  68   b  to magnetic pole  68   d  are formed by deflection coil units  69   a  and  69   b , respectively. 
     In the quadrupole magnetic field generation unit  60 , because of the effect of the magnetic fields of deflection coil units  69   a  and  69   b  shown in  FIG. 12B , the magnetic field generated in deflection coil unit  69   a  is superimposed on the magnetic field having a direction from magnetic pole  68   a  to magnetic pole  68   c . Further, the magnetic field generated in deflection coil unit  69   b  is superimposed on the magnetic field having a direction from magnetic pole  68   d  to magnetic pole  68   b . Thus, the quadrupole magnetic field generation unit  60  generates a superimposed magnetic field from magnetic pole  68   a  to magnetic pole  68   c  in addition to the magnetic fields of the quadrupole. Here, the magnetic fields between magnetic poles  68   b  and  68   d  are cancelled by each other. 
     In the present embodiment, when the X-ray tube device  1  is driven, electrons are emitted from the filament included in the cathode  36  to the focal spot of the electrons on the anode target  35 . Here, the direction in which electrons are emitted is assumed to be parallel to the straight line passing through the center of the cathode  36 . Inclinations γ 1  to γ 4  of magnetic poles  68   a  to  68   d  of the quadrupole magnetic field generation unit  60  shown in  FIG. 11B  are the same as each other. In the quadrupole magnetic field generation unit  60 , an electric source (not shown) supplies direct current to coils  64 . When direct current is supplied from the electric source, the quadrupole magnetic field generation unit  60  generates a magnetic field between magnetic poles  68   a  to  68   d  as a quadruple. The electron beam emitted from the cathode  36  collides with the anode target  35  so as to cross the magnetic field generated between either the cathode  36  or the cathode supporting unit  37  and the anode target  35  along the tube axis TA. At this time, the shape of the electron beam is formed (focused) by the magnetic field generated by the quadrupole magnetic field generation unit  60 . In the present embodiment, for example, as shown in  FIG. 3 , the quadrupole magnetic field generation unit  60  changes the shape of the electron beam roundly emitted to an elliptical shape which is slender in the Y-direction (in other words, the quadrupole magnetic field generation unit  60  focuses the electron beam into an elliptical shape which is slender in the Y-direction). In this case, the quadrupole magnetic field generation unit  60  is capable of reducing the size of the apparent focal spot of the electron beam and increasing the size of the actual focal spot of collision on the anode target  35  surface. As a result, thermal load for the anode target  35  is reduced. 
     In the present embodiment, the X-ray tube device  1  comprises the X-ray tube  30  comprising concave portions  32   a  to  32   d , and the quadrupole magnetic field generation unit  60  comprising deflection coil units  69   a  and  69   b . The quadrupole magnetic field generation unit  60  is capable of generating a superimposed magnetic field when an electric source supplies direct current to deflection coil units  69   a  and  69   b . In the first embodiment, an electron beam is deflected in a single direction by providing the quadrupole magnetic field generation unit  60  eccentrically with respect to the path of an electron beam in a perpendicular direction. However, in the present embodiment, the quadrupole magnetic field generation unit  60  is capable of performing correction by deflecting the movement (deflection or eccentricity) in the length direction (Y-direction) caused when the shape of an electron beam is changed in the width direction (X-direction). In this way, the X-ray tube device  1  of the present embodiment is capable of magnetically changing the shape of an electron beam to an optimal shape in accordance with the intended use. 
     In the X-ray tube device  1  of the present embodiment, the distance between the anode target  35  and the cathode  36  is less than that of the above embodiments. Thus, the X-ray tube device  1  of the present embodiment is capable of reducing the expansion, blurring or distortion of an X-ray focal spot and preventing the reduction in the amount of emission of electrons in the cathode  36 . 
     The X-ray tube device  1  of the present embodiment may further comprise deflection coil units  69   c  and  69   d . When an electric source (not shown) supplies current to deflection coil units  69   c  and  69   d  (a third deflection coil unit and a fourth deflection coil unit), deflection coil units  69   c  and  69   d  generate a magnetic field. In the present embodiment, when an electric source (not shown) supplies direct current to deflection coil units  69   c  and  69   d , deflection coil units  69   c  and  69   d  generate a DC magnetic field. Each of deflection coil units  69   c  and  69   d  is wound onto the portion between adjacent ones of projection portions  66   a  to  66   d  of the main unit of the yoke  66 . For example, deflection coil unit  69   c  is wound onto the main unit of the yoke  66  between projection portions  66   a  and  66   b . Deflection coil unit  69   d  is wound onto the main unit of the yoke  66  between projection portions  66   c  and  66   d . In this case, a pair of magnetic poles  68   a  and  68   b  generates a DC magnetic field between them. A pair of magnetic poles  68   c  and  68   d  generates a DC magnetic field between them. 
     Deflection coil units  69   c  and  69   d  generate a dipole magnetic field formed in the radial direction of the anode target  35 , in other words, a direction parallel to the length direction perpendicular to the width direction of the filament included in the cathode  36 . Deflection coil units  69   c  and  69   d  are capable of deflecting the path of an electron beam to a predetermined direction by flowing current. 
     In the present embodiment, the quadrupole magnetic field generation unit  60  may comprise deflection coil units  69   a ,  69   b ,  69   c  and  69   d . At this time, alternating current may be supplied from an electric source to deflection coil units  69   a  to  69   d . In this case, the quadrupole magnetic field generation unit  60  generates dipole AC magnetic fields such that the magnetic fields generated from two pairs of magnetic poles have the same direction. 
     When alternating current is supplied to deflection coil units  69   a  and  69   b , for example, the quadrupole magnetic field generation unit  60  comprises a pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d . A pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form a magnetic field as a dipole. A pair of magnetic poles  68   a  and  68   c  and a pair of magnetic poles  68   b  and  68   d  each form an AC magnetic field between them. 
     When alternating current is supplied to deflection coil units  69   c  and  69   d , for example, the quadrupole magnetic field generation unit  60  comprises a pair of magnetic poles  68   a  and  68   b  and a pair of magnetic poles  68   c  and  68   d . A pair of magnetic poles  68   a  and  68   b  and a pair of magnetic poles  68   c  and  68   d  each form a magnetic field as a dipole. A pair of magnetic poles  68   a  and  68   b  and a pair of magnetic poles  68   c  and  68   d  each form an AC magnetic field between them. 
     The quadrupole magnetic field generation unit  60  is capable of intermittently or continuously deflecting the path of electrons by the AC magnetic fields generated between the dipoles when alternating current is supplied. In the quadrupole magnetic field generation unit  60 , the alternating current supplied from an electric source (not shown) to each of deflection coil units  69   a  to  69   d  described later is controlled by a deflection electric source controller (not shown) such that the focal spot of collision with the electron beam emitted from the cathode  36  is intermittently or continuously moved. The quadrupole magnetic field generation unit  60  is capable of deflecting the electron beam emitted from the cathode  36  to a direction parallel to the radial direction of the anode target  35 . Thus, the quadrupole magnetic field generation unit  60  is capable of moving the position of the focal spot on the surface of the anode target  35  with which an electron beam collides. 
     Further, the X-ray tube device  1  of the present embodiment may comprise a first quadrupole magnetic field generation unit comprising deflection coil units  69   a  and  69   b , and a second quadrupole magnetic field generation unit comprising deflection coil units  69   c  and  69   d . In this case, the quadrupole magnetic field generation unit  60  may deflect the electron beam emitted from the cathode  36  to an arbitrary direction of the anode target  35 . 
     According to the above embodiments, each X-ray tube device  1  comprises an X-ray tube comprising a plurality of concave portions, and a quadrupole magnetic field generation unit which forms the electron beam to be emitted in the X-ray tube. The quadrupole magnetic field generation unit generates magnetic fields between a plurality of magnetic poles when direct current is supplied from an electric source to coils. The quadrupole magnetic field generation unit is capable of changing the shape of the electron beam emitted from a cathode by the magnetic fields generated by the plurality of magnetic poles. As a result, each X-ray tube device  1  of the embodiments is allowed to reduce the expansion, blurring or distortion of an X-ray focal spot and prevent the reduction in the amount of emission of electrons of the cathode. 
     In the above embodiments, each X-ray tube device  1  is a rotating anode X-ray tube. However, each X-ray tube device  1  may be a fixed anode X-ray tube. 
     In the above embodiments, each X-ray tube device  1  is a neutral grounded X-ray tube device. However, each X-ray tube device  1  may be an anode grounded or cathode grounded X-ray tube device. 
     In the above embodiments, the cathode  36  comprises a nonmagnetic cover surrounding the outer circumferential portion. However, they may be entirely formed of a nonmagnetic material or a nonmagnetic metal material having a high electric conductivity as an integral structure. 
     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.