Patent Publication Number: US-9847207-B2

Title: X-ray tube assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2014-253840, filed Dec. 16, 2014; No. 2015-003235, filed Jan. 9, 2015; and No. 2015-064432, filed Mar. 26, 2015, the entire contents of all of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an X-ray tube assembly. 
     BACKGROUND 
     A rotary-anode X-ray tube assembly is a device which urges electrons generated from a cathode electron emission source to collide with a rotating anode target to generate X-rays at an X-ray focus formed due to the collision of the electrons with the anode target. In general, the rotary-anode X-ray tube assembly is employed in an X-ray CT device or the like. 
     In a flying-focus (focal position shift) X-ray CT device, an X-ray focus is arranged at different positions during photography using X-rays by the rotary-anode X-ray tube assembly, and an angle of incidence of the X-rays incident on a detector through a subject is slightly varied. It is known that the resolution property of the X-ray photographic image is consequently improved. To thus arrange the X-ray focus at different positions by the rotary-anode X-ray tube assembly during the X-ray photography, the X-ray focus needs to be finely moved intermittently, continuously and periodically, in a short time of 1 msec or less. 
     Several systems for finely moving the X-ray focus in a short time are known. One of them is a magnetic electron beam change which deflects the electron beam by the deflecting magnetic field in which a magnetic pole is generated. In the magnetic electron beam deflection, a small-diameter portion is provided in a vacuum envelope located between the cathode and the anode target, and magnetic poles are arranged in the portion to generate the deflecting magnetic field. In a constitution of the magnetic electron beam deflection, a distance between the magnetic poles arranged in the small-diameter portion becomes short, a magnetic flux density can be increased at the electron beam position and an electron orbital can be certainly deflected. 
     Since the small-diameter portion is formed in the vacuum envelope, the cathode is arranged remote from the anode target, in the rotary-anode X-ray tube assembly. In addition, since the small-diameter portion is formed, a potential distribution is varied and the electron beam can hardly be converged. As a result, expansion, blur, and distortion of the X-ray focus, reduction in the electron emission quantity of the cathode, etc., may occur. 
     Thus, the object of the embodiments is to provide a rotary-anode X-ray tube assembly capable of certainly deflecting the electron orbital forwarding from the cathode to the anode target without forming the small-diameter portion in the vacuum envelope, and of suppressing occurrence of the expansion, blur, and distortion of the X-ray focus, reduction in the electron emission quantity of the cathode, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an example of an X-ray tube assembly of a first embodiment. 
         FIG. 2A  is a cross-sectional view showing a summary of the X-ray tube of the first embodiment. 
         FIG. 2B  is a cross-sectional view seen along line IIA-IIA in  FIG. 2A . 
         FIG. 2C  is a cross-sectional view seen along line IIB-IIB in  FIG. 2B . 
         FIG. 3  is a cross-sectional view showing a summary of an X-ray tube of a second embodiment. 
         FIG. 4A  is a cross-sectional view showing a summary of an X-ray tube of a third embodiment. 
         FIG. 4B  is a cross-sectional view seen along line IVA-IVA in  FIG. 4A . 
         FIG. 4C  is a cross-sectional view seen along line IVB-IVB in  FIG. 4B . 
         FIG. 5A  is a cross-sectional view showing a summary of the X-ray tube of a fourth embodiment. 
         FIG. 5B  is a cross-sectional view seen along line VA-VA in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an X-ray tube assembly, comprises: a cathode emitting an electron and comprising at least a surface portion formed of a first non-magnetic metal member having high electrical conductivity; an anode target comprising at least a surface portion formed of a second non-magnetic metal member having high electrical conductivity, being provided to be opposed to the cathode, and comprising a target surface from which X rays are generated by allowing the electron emitted from the cathode to collide with the target surface; a vacuum envelope containing the cathode and the anode target, having an interior sealed in vacuum airtight state, and having at least one depressed portion depressed from outside formed to sandwich the cathode from both sides; and a first magnetic deflector supplied with an AC current from a power supply, provided outside the vacuum envelope, comprising at least one first magnetic pole pair composed of two paired magnetic poles generating the alternating magnetic field, and generating an alternating magnetic field for deflecting an electron orbital of the electron emitted from the cathode toward the anode target, between the cathode and the anode target, by the first magnetic pole pair, the first magnetic pole pair being provided in close vicinity to a wall surface of the depressed portion so as to sandwich the cathode. 
     An X-ray tube assembly of embodiments will be described hereinafter with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a cross-sectional view showing an example of an X-ray tube assembly  10  of the first embodiment 
     As shown in  FIG. 1 , roughly, the X-ray tube assembly  10  comprises a stator coil  8 , a housing  20 , an X-ray tube  30 , a high-voltage insulating member  39 , a first magnetic deflector  60 , receptacles  301  and  302 , and X-ray shielding members  510 ,  520 ,  530  and  540 . For example, the X-ray tube assembly  10  is a rotary-anode X-ray tube assembly. The X-ray tube  30  is, for example, a rotary-anode X-ray tube. For example, the X-ray tube  30  is a neutral-grounding-type rotary-anode X-ray tube. Each of the X-ray shielding members  510 ,  520 ,  530 , and  540  is formed of lead. 
     In the X-ray tube assembly  10 , a space formed between an inside of the housing  20  and an outside of the X-ray tube  30  is filled with an insulating oil  9  serving as a coolant. For example, the X-ray tube assembly  10  is configured to circulate the insulating oil  9  by a circulation cooling system (cooler) (not shown) connected with the housing  20  by hoses (not shown) and cool the insulating oil  9 . In this case, the housing  20  comprises an intake port and a discharge port of the insulating oil  9 . The circulation cooling system comprises, for example, a cooler which radiates heat from the insulating oil  9  in the housing  20  and circulates the insulating oil  9 , conduits (hoses or the like) which communicates the cooler with the intake port and a discharge port of the housing  20  airtightly and liquid-tightly. The cooler comprises a circulating pump and a heat exchanger. The circulating pump discharges the insulating oil  9  heat exchanger taken in from the housing  20  side into the heat exchanger and produces a flow of the insulating oil  9  in the housing  20 . The heat exchanger is made to communicate with an interval between the housing  20  and the circulating pump and to discharge the heat of the insulating oil  9  to the outside. 
     A detailed configuration of the X-ray tube assembly  10  will be explained hereinafter with reference to the drawings. 
     The housing  20  comprises a cylindrically shaped housing body  20   e  and lid portions (side plates)  20   f ,  20   g  and  20   h . The housing body  20   e , and the lid portions  20   f ,  20   g  and  20   h  are formed of casting using aluminum. If they are formed of a resin material, a portion such as a screw portion, which needs to have much strength, a portion which is hard to form by injection molding using resin, a shielding layer (not shown) which prevents leakage of electromagnetic noise from the housing  20  to the outside, etc., may be formed in part of metal together with the resin material. A center axis passing through a cylindrical center of the housing body  20   e  is referred to as a tube axis TA. 
     An annular stepped portion is formed as an inner peripheral surface thinner than the housing body  20   e , at an opening portion of the housing  20   e . An annular groove portion is formed along the inner periphery of the stepped portion. The groove portion of the housing body  20   e  is formed by cutting the body from the step of the stepped portion to a position of a predetermined length in the outside direction along the tube axis TA. The predetermined length is, for example, substantially equal to the thickness of a lid portion  20   f . A C-type retaining ring  20   i  is fitted in the groove portion of the housing body  20   e . In other words, the opening portion of the housing body  20   e  is liquid-tightly closed by the lid portion  20   f , the C-type retaining ring  20   i , etc. 
     The lid portion  20   f  is formed in a disc shape. On the lid portion  20   f , a rubber member  2   a  is provided along the outer peripheral portion, which is fitted in the stepped portion formed at the opening portion of the housing body  20   e.    
     The rubber member  2   a  is formed in a shape of, for example, an O-ring. As explained above, the rubber member  2   a  is provided between the housing body  20   e  and the lid portion  20   f  to liquid-tightly seal an interval between the housing body  20   e  and the lid portion  20   f . A peripheral portion of the lid portion  20   f  is in contact with the stepped portion of the housing body  20   e , in a direction along the tube axis TA of the X-ray tube assembly  10 . 
     A C-type retaining ring  20   i  is a fixing member. The C-type retaining ring  20   i  is fitted in the groove portion of the housing body  20   e  and fixes the lid portion  20   f  as explained above, to restrict movement of the lid portion  20   f  in the direction along the tube axis TA. 
     The lid portions  20   g  and  20   h  are fitted in an opening portion opposite to the opening portion of the housing body  20   e  in which the lid portion  20   f  is provided. In other words, the lid portions  20   g  and  20   h  are provided to be parallel to the lid portion  20   f  and to be opposed to each other, at the end portion on the side opposite to the end portion of the housing body  20   e  at which the lid portion  20   f  is provided. The lid portion  20   g  is liquid-tightly fitted at a predetermined position inside the housing body  20   e . At the end portion of the housing body  20   e  at which the lid portion  20   h  is provided, an annular groove portion is formed on an inner peripheral portion on the outer side adjacent to the position at which the lid portion  20   h  is provided. A rubber member  2   b  is extensibly provided between the lid portions  20   g  and  20   h  to maintain the liquid-tight condition. The lid portion  20   h  is provided on an outer side than the lid portion  20   g , in the housing body  20   e . The C-type retaining ring  20   i  is fitted in the groove portion formed in close vicinity to the position at which the lid portion  20   h  is provided. In other words, the opening portion of the housing body  20   e  is liquid-tightly closed by the lid portions  20   g  and  20   h , the C-type retaining ring  20   i , the rubber member  2   b , etc. 
     The lid portion  20   g  is formed in a circular shape having substantially the same diameter as a diameter of the inner periphery of the housing body  20   e . The lid portion  20   g  includes an opening portion  20   k  for intake or discharge of the insulating oil  9 . 
     The lid portion  20   h  is formed in a circular shape having substantially the same diameter as the inner periphery of the housing body  20   e . A vent hole  20   m  through which air serving as an atmosphere comes in and goes out is formed in the lid portion  20   h.    
     The C-type retaining ring  20   j  is a fixing member which holds the state of the lid portion  20   h  clamped to a peripheral portion (sealing portion) of the rubber member  2   b.    
     The rubber member  2   b  is a rubber bellows (rubber film). The rubber member  2   b  is formed in a circular shape. The peripheral portion (sealing portion) of the rubber member  2   b  is formed in a shape of an O-ring. The rubber member  2   a  is provided between the housing body  20   e  and the lid portions  20   g  and  20   f  to liquid-tightly seal them. The rubber member  2   b  is provided on the inner periphery of the end portion of the housing body  20   e . In other words, the rubber member  2   b  is provided to divide a space of a certain part in the housing. In the present embodiment, the rubber member  2   a  is provided in a space surrounded by the lid portions  20   g  and  20   h  to liquid-tightly divide the space. The space on the lid portion  20   g  side is called a first space and the space on the lid portion  20   h  side is called a second space. The first space communicates with the space inside the housing  20   e  which is filled with the insulating oil  9  through the opening portion  20   k . For this reason, the first space is filled with the insulating oil  9 . The second space communicates with the outer space through the vent hole  20   m . For this reason, the second space is an air atmosphere. 
     An opening portion  20   o  is formed in the housing body  20   e . An X-ray radiation window  20   w  and an X-ray shielding portion  540  are provided at the opening portion  20   o . The opening portion  20   o  is liquid-tightly closed by the X-ray radiation window  20   w  and the X-ray shielding portion  540 . The X-ray shielding members  520  and  540  are provided to shield against the X-ray to the outside of the housing, at the opening portion  20   o , which will be explained in detail later. 
     The X-ray radiation window  20   w  is formed of a member which permits X-rays to easily pass therethrough. For example, the X-ray radiation window  20   w  is formed of a metal which is highly X-ray transmissive. 
     The X-ray shielding members  510 ,  520 ,  530  and  540  may be formed of a radio-opaque material containing at least lead or may be formed of a lead alloy or the like. 
     The X-ray shielding member  510  is provided on an inner surface of the lid portion  20   g . The X-ray shielding member  510  shields against X-rays radiated from the X-ray tube  30 . The X-ray shielding member  510  comprises a first shielding member  511  and a second shielding member  512 . The first shielding member  511  is provided on an inner surface of the lid portion  20   g . The first shielding member  511  is provided to cover the entire inner surface of the lid portion  20   g . The second shielding member  512  is provided such that one end portion of the second shielding member  512  is stacked on the inner surface of the first shielding member  511  while the other end portion of the second shielding member  512  is arranged inside the housing body  20   e  in the direction along the tube axis TA to be spaced apart from the opening portion  20   k . In other words, the second shielding member  512  is provided such that the insulating oil  9  comes in and goes out through the opening portion  20   k.    
     The X-ray shielding member  520  is formed in a substantially cylindrical shape. The X-ray shielding member  520  is provided at a part of the inner peripheral portion of the housing body  20   e . One of end portions of the X-ray shielding member  520  is in close vicinity to the first shielding member  511 . For this reason, the X-ray shielding members  510  and  520  can shield against X-ray leakage from the gap between the X-ray shielding members  510  and  520  to the outside of the housing. The X-ray shielding member  520  extends from the first shielding member  511  to a vicinity of the stator coil  8  along the tube axis. The X-ray shielding member  520  is fixed to the housing  20  as needed. 
     The X-ray shielding member  530  is formed in a cylindrical shape and fitted along the outer periphery of the receptacle  302  to be explained later, inside the housing  20 . The X-ray shielding member  530  is provided such that one of end portions of the cylinder is in contact with a wall surface of the housing body  20   e . At this time, a hole through which the end portion of the X-ray shielding member  530  passes is formed in the X-ray shielding member  520 . The X-ray shielding member  530  is fixed to the X-ray shielding member  520  as needed. 
     The X-ray shielding member  540  is formed in a frame shape and provided on a side edge of the opening portion  20   o  of the housing  20 . The X-ray shielding member  540  is provided along an inner wall of the opening portion  20   o . The end portion of the X-ray shielding member  540  inside the housing body  20   e  is in contact with the X-ray shielding member  520 . The X-ray shielding member  540  is fixed to the side edge of the opening portion  20   o  as needed. 
     The receptacle  301  for the anode and the receptacle  302  for the cathode are connected to the housing body  20   e . Each of the receptacles  301  and  302  is formed in a shape of a bottomed cylinder having an opening portion. In each of the receptacles  301  and  302 , the bottom portion is provided inside the housing  20  while the opening portion opens to the outside. For example, the receptacles  301  and  302  are provided to be spaced apart with a predetermined interval, inside the housing body  20   e , and their opening portions are provided to face in the same direction. 
     The receptacle  301  and a plug (not shown) to be inserted into the receptacle  301  are in a non-surface pressure type and formed to be detachable. A high voltage (for example, +70 to +80 kV) is supplied from the plug to a terminal  201  while the plug is coupled to the receptacle  301 . 
     The receptacle  301  is provided on the lid portion  20   f  side in the housing  20 , at a position inner than the lid portion  20   f . The receptacle  301  comprises a housing  321  serving as an electrically insulating member and the terminal  201  serving as a high-voltage supply terminal. 
     The housing  321  is formed of an insulating material, for example, resin. The housing  321  is formed in a shape of a bottomed cylinder having a plug-in outlet opening to the outside. The housing  321  comprises the terminal  201  on the bottom portion. An annular protrusion is formed on the outer surface of the housing  321 , at the end portion on the opening side. The protrusion of the housing  321  is formed to be fitted in a stepped portion  20   ea  which is a step formed at the end portion of the protrusion of the housing body  20   e . The terminal  201  is liquid-tightly attached to the bottom portion of the housing  321 , and penetrates the bottom portion. The terminal  201  is connected to a high-voltage supply terminal  44  to be explained later, via an insulated conductor. 
     In addition, a rubber member  2   f  is provided between the protrusion of the housing  321  and the housing body  20   e . The rubber member  2   f  is provided between the protrusion of the housing  321  and the step of the stepped portion  20   ea  to liquid-tightly seal the protrusion of the housing  321  and the housing body  20   e . In the present embodiment, the rubber member  2   f  is formed of an O-ring. The rubber member  2   f  prevents leakage of the insulating oil  9  to the outside of the housing  20 . The rubber member  2   f  is formed of, for example, sulfur-vulcanized rubber. 
     The housing  321  is fixed by a ring nut  311 . A screw groove is formed on an outer peripheral portion of the ring nut  311 . For example, the outer peripheral portion of the ring nut  311  is processed as a male screw while the inner peripheral portion of the stepped portion  20   ea  is processed as a female screw. The protrusion of the housing  321  is therefore pressed against the stepped portion  20   ea  via the rubber member  2   f  by screwing the ring nut  311 . As a result, the housing  321  is fixed to the housing body  20   e.    
     The receptacle  302  is provided on the lid portion  20   g  side in the housing  20 , at a position inner than the lid portion  20   g . The receptacle  302  is formed to be substantially similar to the receptacle  301 . The receptacle  302  comprises a housing  322  serving as an electrically insulating member and terminals  202  serving as high-voltage supply terminals. 
     The housing  322  is formed of an insulating material, for example, resin. The housing  322  is formed in a shape of a bottomed cylinder having a plug-in outlet opening to the outside. The housing  322  comprises the terminals  202  on the bottom portion. An annular protrusion is formed on the outer surface of the housing  322 , at the end portion on the opening side. The protrusion of the housing  322  is formed to be fitted in a stepped portion  20   eb  which is a step formed at the end portion of the protrusion of the housing body  20   e . The terminals  202  are liquid-tightly attached to the bottom portion of the housing  321 , and penetrate—the bottom portion. The terminals  202  are connected to the high-voltage supply terminals  54  to be explained later, via insulated conductors. 
     In addition, a rubber member  2   g  is provided between the protrusion of the housing  322  and the housing body  20   e . The rubber member  2   g  is provided between the protrusion of the housing  322  and the step of the stepped portion  20   eb  to liquid-tightly seal the protrusion of the housing  322  and the housing body  20   e . In the present embodiment, the rubber member  2   g  is formed of an O-ring. The rubber member  2   g  prevents leakage of the insulating oil  9  to the outside of the housing  20 . The rubber member  2   g  is formed of, for example, sulfur-vulcanized rubber. 
     The housing  322  is fixed by a ring nut  312 . A screw groove is formed on an outer peripheral portion of the ring nut  312 . For example, the outer peripheral portion of the ring nut  312  is processed as a male screw while the inner peripheral portion of the stepped portion  20   eb  is processed as a female screw. The protrusion of the housing  322  is therefore pressed against the stepped portion  20   eb  via the rubber member  2   g  by screwing the ring nut  312 . As a result, the housing  322  is fixed to the housing body  20   e.    
       FIG. 2A  is a cross-sectional view showing a summary of the X-ray tube  30 ,  FIG. 2B  is a cross-sectional view seen along line IIA-IIA in  FIG. 2A , and  FIG. 2C  is a cross-sectional view seen along line IIB-IIB in  FIG. 2B . In  FIG. 2C , a straight line orthogonal to the tube axis TA is referred to as straight line L 1  and a straight line orthogonal to the tube axis TA and straight line L 1  is referred to as straight line L 2 . 
     The X-ray tube  30  comprises a fixed shaft  11 , a rotary body  12 , bearings  13 , a rotor  14 , a vacuum envelope  31 , an anode target  35 , a cathode  36 , a high-voltage supply terminal  44 , high-voltage supply terminals  54 , and a KOV member  55 . 
     The fixed shaft  11  is formed in a columnar shape. The rotary body  12  is supported via the bearings  13  by the fixed shaft  11  so as to be rotatable. The fixed shaft  11  comprises a protrusion vacuum tightly attached to the vacuum envelope  31 , at one of end portions. The protrusion of the fixed shaft  11  is fixed to the high-voltage insulating member  39 . At this time, a distal portion of the protrusion of the fixed shaft  11  penetrates the high-voltage insulating member  39 . The high-voltage supply terminal  44  is electrically connected to the distal portion of the protrusion of the fixed shaft  11 . 
     The rotary body  12  is formed in a shape of a bottomed cylinder. The fixed shaft  11  is inserted into the rotary body  12 , and the rotary body  12  is provided coaxially with the fixed shaft  11 . The rotary body  12  is connected with an anode target  35  to be explained later, at the distal portion, on the bottom side, and provided to be rotatable together with the anode target  35 . 
     The bearings  13  are provided between an inner peripheral portion of the rotary body  12  and an outer peripheral portion of the fixed shaft  11 . 
     The rotor  14  is provided to be located inside the stator coil  8  formed in a cylindrical shape. 
     The high-voltage supply terminal  44  applies a relatively positive voltage to the anode target  35  via the fixed shaft  11 , the rotary body  12 , and the bearings  13 . The high-voltage supply terminal  44  is connected to the receptacle  301 , and is supplied with an electric current when a high-voltage supply source such as a plug (not shown) is connected to the receptacle  301 . The high-voltage supplying terminal  44  is a metal terminal. 
     The anode target  35  is formed in a disc shape. The anode target  35  is coaxially connected with the rotary body  12 , at the distal portion on the bottom side of the rotary body  12 . For example, the central axis of the rotary body  12  and the anode target  35  is provided along the tube axis TA. In other words, the axis of the rotary body  12  and the anode target  35  is parallel to the tube axis TA. In this case, the rotary body  12  and the anode target  35  are provided to be rotatable about the tube axis. 
     The anode target  35  comprises an umbrella-shaped target layer  35   a  provided on a part of an outer surface of the anode target. The target layer  35   a  emits X-rays when the electrons emitted from the cathode  36  collide on the target layer  35   a . An outer peripheral surface of the anode target  35  and a surface of the anode target  35  opposite to the target layer  35   a  are subjected to blackening treatment. The anode target  35  is formed of a non-magnetic member having high electrical conductivity. For example, the anode target  35  is formed of a non-magnetic member (second metal member) having high electrical conductivity such as copper, tungsten, molybdenum, niobium, tantalum or a non-magnetic stainless steel, titanium, chromium. The anode target  35  may have at least a surface portion formed of a non-magnetic metal member having high electrical conductivity. In addition, the anode target  35  may have the surface portion coated with a non-magnetic metal member having high electrical conductivity. As shown in  FIG. 2A , an angle of a portion inclined from the outer periphery of the anode target  35  formed on the umbrella-shaped portion toward a central flat portion is represented by θ. 
     The cathode  36  includes a filament (electron emission source) which emits the electrons (electron beams). The cathode  36  is provided at a position opposed to the target layer  35   a . The cathode  36  emits electrons toward the anode target  35 . For example, the cathode  36  is formed in a columnar shape and emits the electrons from the filament provided at the center of the circle of the column toward the surface of the anode target  35 . At this time, a straight line passing through the center of the cathode  36  is nearly parallel to the tube axis TA. A direction of the electrons emitted from the cathode  36  and an orbit of the electrons are often hereinafter explained as “an electron orbital”. A relatively negative voltage is applied to the cathode  36 . The cathode  36  is attached to a cathode support (cathode support or cathode supporting member)  37  to be explained later, and is connected with the high-voltage supply terminals  54  penetrating the inside of the cathode support  37 . The cathode  36  is often called an electron emission source. 
     The cathode  36  comprises a non-magnetic cover which covers an entire body of the outer periphery. The non-magnetic cover is provided in a cylindrical shape so as to surround the cathode  36 . The non-magnetic cover is formed of, for example, any one of copper, tungsten, molybdenum, niobium, tantalum and a non-magnetic stainless steel, titanium, chromium, or a non-magnetic metal member such as a metal material containing any one of them as a major component. Suitably, the non-magnetic cover is formed of a member (first metal member) having high electrical conductivity. In a case where the non-magnetic cover is arranged in an alternating magnetic field, the non-magnetic cover can generate distortion in the magnetic line of force, due to action of the alternating magnetic field in an opposite direction based on an eddy current, more strongly, when the electric conductance is high, than that when the electric conductance is low. By thus distorting the magnetic line of force, the magnetic line of force flows along the periphery of the cathode  36  and the magnetic field (alternating magnetic field) near the surface of the cathode  36  becomes strengthened. As a result, the cathode  36  can increase a force of deflecting the electrons of a first magnetic deflector  60  to be explained later. The cathode  36  may have at least the surface formed of a non-magnetic metal member having high electrical conductivity. Thus, for example, an entire body of the cathode  36  may be formed of a non-magnetic metal member having high electrical conductivity. 
     Furthermore, the cathode  36  comprises a non-magnetic cover surrounding the outer peripheral portion, but may be entirely formed of a non-magnetic metal or may be formed of a non-magnetic metal having high electrical conductivity, in an integrated structure. 
     The cathode support  37  fixes the cathode  36  at one of end portions and the KOV member  55  at the other end portion. The cathode support  37  includes the high-voltage supply terminals  54 . As shown in  FIG. 2A , the cathode support  37  is provided to extend from the KOV member  55  provided in the surrounding of the tube axis TA to the vicinity of the outer periphery of the anode target  35 . In addition, the cathode support  37  is provided nearly parallel to the anode target  35  and spaced apart from the anode target  35  with a predetermined interval. At this time, the cathode support  37  fixes the cathode  36  at the end portion on the outer peripheral side of the anode target  35 . The cathode support  37  may have the surrounding covered with a non-magnetic cover or may have at least the surface formed of a non-magnetic metal member having high electrical conductivity. 
     The KOV member  55  is formed of a low-thermal expansion alloy. The KOV member  55  has one of end portions fixed to the cathode support  37  and the other end portion fixed to the high-voltage insulating member  50 . The KOV member  55  covers the high-voltage supply terminals  54 , inside the vacuum envelope  31  to be explained later. 
     The high-voltage supply terminals  54  are bonded to the high-voltage insulating member  50  by brazing. The high-voltage supply terminals  54  penetrate the high-voltage insulating member  50  and is inserted into the vacuum envelope  31 . At this time, the insertion portions of the high-voltage supply terminals  54  are sealed in a vacuum tight state and are inserted into the vacuum envelope  31 . 
     The high-voltage supply terminals  54  pass through the inside of the cathode support  37  and are connected to the cathode  36 . The high-voltage supply terminals  54  apply a relatively negative voltage to the cathode  36 , and supply a filament current to a filament (electron emission source) (not shown) of the cathode  36 . The high-voltage supply terminals  54  are connected to the receptacle  302 , and are supplied with an electric current when a high-voltage supply source such as a plug (not shown) is connected to the receptacle  302 . The high-voltage supply terminals  54  are metal terminals. 
     The vacuum envelope  31  is sealed in a vacuum atmosphere (vacuum tight) state, and contains the X-ray tube  30  comprises the fixed shaft  11 , the rotary body  12 , the bearings  13 , the rotor  14 , the anode target  35 , the cathode  36 , the high-voltage supply terminal  54 , and the KOV member  55 . The vacuum vessel  32  as a component of the vacuum envelope  31 , encloses the cathode  36  and the anode target  35 . 
     The vacuum vessel  32  comprises an X-ray transmissive window  38  in a vacuum tight state. The X-ray transmissive window  38  is provided on a wall portion of the vacuum vessel  32  opposed to an area between the cathode  36  and the anode target  35 . The X-ray transmissive window  38  is formed of, for example, a metal such as beryllium, titanium, a stainless metal or aluminum, and provided at a portion opposed to the X-ray radiation window  20   w . For example, the vacuum vessel  32  is airtightly sealed by the X-ray transmissive window  38  formed of beryllium, which is a member permitting X-rays to be transmitted therethrough. Outside of the vacuum envelope  31 , the high-voltage insulating member  39  is arranged from the high-voltage supply terminal  44  side to the surrounding of the anode target  35 . The high-voltage insulating member  39  is formed of an electrically insulating resin. 
     The vacuum vessel  32  comprises depressed portions  32   a  and  32   b . The depressed portions  32   a  and  32   b  are formed on parts of the vacuum vessel  32 , which is provided at a position opposed to the cathode  36 . The parts of the vacuum vessel  32  include at least the surface of the vacuum vessel  32  which is opposed to the cathode  36  along the tube axis TA. The depressed portions  32   a  and  32   b  are depressions formed on parts of the vacuum vessel  32  to contain magnetic poles  68   a  and  68   b  of a first magnetic deflector  60  to be explained later, and are parts of the vacuum vessel  32  surrounding the depressions. For example, the depressed portions  32   a  and  32   b  are formed by depressing the vacuum vessel  32  from the outside so as to sandwich the cathode. In other words, wall surfaces of the depressed portions  32   a  and  32   b  are formed to protrude toward the cathode  36  as observed from the inside of the vacuum vessel  32 . The depressed portions  32   a  and  32   b  are formed not to be so much close to the surface of the anode target  35  and the surface of the cathode  36  to prevent discharge. For example, the depressed portion  32   a  is depressed up to a position farther from the surface of the anode target  35  than from the surface of the cathode  36  opposed to the surface of the anode target  35 , in the direction along the tube axis TA. Alternatively, the depressed portion  32   a  is depressed up to a position which is the same as the surface of the cathode  36  opposed to the surface of the anode target  35 , or a position slightly closer to the surface of the anode target  35  than to the surface of the cathode  36  opposed to the surface of the anode target  35 , in the direction along the tube axis TA. 
     In addition, in the depressed portions  32   a  and  32   b , corner portions protruding toward the anode target  35  side are formed to be inclined so as to be remote from the target surface of the anode target  35  and the surface of the cathode  36  for the purpose of preventing occurrence of discharge, etc. For example, a corner portion of the depressed portion  32   a  is formed at an angle of inclination corresponding to an angle of inclination of an end surface of the magnetic pole  68   a  to be explained later. Similarly, a corner portion of the depressed portion  32   b  is formed at an angle of inclination corresponding to an angle of inclination of an end surface of the magnetic pole  68   b  to be explained later. The corner portions of the depressed portions  32   a  and  32   b  may be smoothly curved. For example, each of the corner portions of the depressed portions  32   a  and  32   b  is formed to have a predetermined diameter. Each of the corner portions of the depressed portions  32   a  and  32   b  protruding toward the anode target  35  side may not be formed to have an inclination or a diameter. Alternatively, depressed portions may be formed as one body in the rotary direction, around the cathode  36 , or the number of depressed portions corresponding to the number of magnetic poles to be explained later may be formed. 
     The vacuum vessel  32  captures a recoil electron reflected from the anode target  35 . For this reason, vacuum vessel  32  is formed of a member whose temperature can not easily be raised due to impulse of the recoil electron, such as copper having a high thermal conductance. In the present embodiment, however, the vacuum vessel  32  should desirably be formed of a member which does not generate a diamagnetic field since the vacuum envelope  31  is influenced by the alternating magnetic field generated by the magnetic poles  68   a  and  68   b  to be explained later. For example, the vacuum vessel  32  is formed of a non-magnetic metal member. The non-magnetic metal member is, for example, copper, molybdenum, a non-magnetic stainless steel, Inconel, Inconel X, titanium, conductive ceramic, non-conductive ceramic having a surface coated with a metal thin film, etc. Suitably, the vacuum vessel  32  is formed of a non-magnetic, high-electric-resistance member to prevent an eddycurrent from being generated by the AC current. More suitably, in the vacuum vessel  32 , the depressed portions  32   a  and  32   b  are formed of a non-magnetic, high-electric-resistance member, and portions other than the depressed portions  32   a  and  32   b  are formed of a non-magnetic member such as copper having a high thermal conductance. 
     The high-voltage insulating member  39  is formed in an annular shape having one of ends shaped in a cone and the other end sealed. The high-voltage insulating member  39  is fixed to the housing  20  directly or indirectly via the stator coil  8  to be explained later. The high-voltage insulating member  39  produces electrical insulation between the fixed shaft  11 , and the housing  20  and the stator coil  8 . For this reason, the high-voltage insulating member  39  is provided between the stator coil  8  and the fixed shaft  11 . In other words, the high-voltage insulating member  39  is provided to contain the protrusion side of the fixed axis  11 . 
     In  FIG. 1 , the stator coil  8  is fixed to the housing  20  at a plurality of portions. The stator coil  8  is provided to surround an outer peripheral portion of the rotor  14  and the high-voltage insulating member  39 . The stator coil  8  rotates the rotor  14 , the rotary body  12  and the anode target  35 . Since a magnetic field to be applied to the rotor  14  is generated by supplying a predetermined current to the stator coil  8 , the anode target  35 , etc., are rotated at a predetermined speed. In other words, the rotor  14  is rotated, and the anode target  35  is rotated in accordance with the rotation of the rotor  14 , by supplying a current to the stator coil  8  serving as a rotation driver. 
     A space surrounded by the rubber bellows  2   b , the housing  20   e , the lid portion  20   f , and the receptacles  301  and  302 , inside the housing  20  is filled with the insulating oil  9 . The insulating oil  9  absorbs at least part of the heat generated by the X-ray tube  30 . 
     The first magnetic deflector  60  will be explained with reference to  FIG. 2A  to  FIG. 2C . 
     As shown in  FIG. 2B , the first magnetic deflector  60  comprises a coil  64 , a yoke  66 , and the magnetic poles  68   a  and  68   b . The first magnetic deflector  60  generates a magnetic field which intermittently or sequentially deflects the orbital of the electrons emitted from the filament contained in the cathode  36 . The first magnetic deflector  60  deflects the electrons (beams) emitted from the cathode  36 , in a direction along the diameter direction of the anode target  35 . The paired magnetic poles  68   a  and  68   b , which will be explained in detail later, are formed at the respective ends of the yoke  66 , respectively, in the first magnetic deflector  60 . The first magnetic deflector  60  may comprise a plurality of magnetic poles. The magnetic poles include at least a pair of magnetic poles that generate a magnetic field therebetween and are paired as a dipole. The magnetic poles that generate a magnetic field therebetween and are paired as a dipole are often hereinafter explained as a magnetic pole pair. 
     In addition, in the first magnetic deflector  60 , a current supplied from a deflection power supply (not shown) is controlled by a deflection power supply controller (not shown). The first magnetic deflector  60  can move a position of the focus, i.e., a point with which the electrons (beams) collide, intermittently or sequentially, on the surface of the anode target  35 , by allowing the supplied current to be controlled. In the present embodiment, the first magnetic deflector  60  is supplied with an AC current from a deflection power supply (not shown). In this case, the first magnetic deflector  60  generates an alternating magnetic field. As shown in  FIG. 2B , for example, the first magnetic deflector  60  generates alternating magnetic field MG 1 . 
     The coil  64  is supplied with the current from the deflection power supply (not shown) for the first magnetic deflector  60  and generates the magnetic field. The coil  64  is wound round a part of the yoke  66 . For example, the coil  64  is wound in lateral symmetry, from the center of the yoke  66 . 
     The yoke  66  is formed in a bracket shape. For example, the yoke  66  is provided such that a straight line along the tube axis TA passes through the center of the yoke  66 . In the present embodiment, two distal portions of the yoke  66  are provided in close vicinity to the depressed portions  32   a  and  32   b , respectively. At this time, the yoke  66  is provided to sandwich the cathode  36  between two distal portions. In addition, the coil  64  is wound round a part of the yoke  66 . 
     The yoke  66  is formed of a soft magnetic material and highly electric resistor in which an eddy current can hardly be generated by the alternating magnetic field. The yoke  66  is formed by, for example, a laminate in which thin plates formed of an Fe—Si alloy (silicon steel), an Fe—Al alloy, an electromagnetic stainless steel, an Fe—Ni high-magnetic-permeability alloy such as permalloy, a Ni—Cr alloy, an Fe—Ni—Cr alloy, an Fe—Ni—Co alloy, an Fe—Cr alloy, or the like, are sandwiched by an electrically insulating film and are layered, or an assembly formed by covering wire rods of above-explained materials with an electrically insulating film and bundling the wire rods, etc. The yoke  66  may be formed of an assembly formed by grinding above-explained materials to fine powder having a diameter of approximately 1 covering the powder surface with an electrically insulating film, and molding the powder by compression molding. Furthermore, the yoke  66  may be formed of soft ferrites, etc. 
     The magnetic poles  68   a  and  68   b  are provided at end portions of the yoke  66 , respectively. The magnetic poles  68   a  and  68   b  are provided so as to sandwich the cathode  36  between the magnetic poles. In other words, in the first magnetic deflector  60 , each of the magnetic poles  68   a  and  68   b  is provided on a straight line along a direction perpendicular to the emission direction of the electrons emitted from the filament included in the cathode  36 . 
     Suitably, to increase the magnetic flux density, each of the magnetic poles  68   a  and  68   b  is provided to be close to the emission direction (electron orbital) of the electrons emitted from the filament included in the cathode  36 . In other words, the magnetic pole  68   a  is provided in close vicinity to the corner portion of the depressed portion  32   a  while the magnetic pole  68   b  is provided near the corner portion of the depressed portion  32   b . For example, the surface of the end portion (end surface) of the magnetic pole  68   a  is formed in accordance with the inclination of the corner portion of the depressed portion  32   a  which protrudes toward the anode target  35  side. In this case, the magnetic pole  68   a  is provided such that the end surface of the magnetic pole  68   a  corresponds to the inclination of the corner portion of the depressed portion  32   a . Similarly, the end surface of the magnetic pole  68   b  is formed in accordance with the inclination of the corner portion of the depressed portion  32   b  which protrudes toward the anode target  35  side. In this case, the magnetic pole  68   b  is provided such that the end surface of the magnetic pole  68   b  corresponds to the inclination of the corner portion of the depressed portion  32   b.    
     The magnetic pole pair  68   a  and  68   b  (first magnetic pole pair) are formed in a substantially similar shape. The magnetic pole pair  68   a  and  68   b  (first magnetic pole pair) are paired as a dipole. The magnetic pole pair  68   a  and  68   b  are provided to face the surfaces (end surfaces) toward the electron emission direction of the cathode  36  to deflect the electrons emitted from the cathode  36  at positions which are not so close to the anode target  35 . In other words, the surface of the magnetic pole  68   a  is formed to be inclined toward the straight line along the electron emission direction. Similarly, the surface of the magnetic pole  68   b  is formed to be inclined toward the straight line along the electron emission direction. For example, the emission direction of the electron beam of the cathode  36  is the direction along the tube axis TA. At this time, the magnetic poles  68   a  and  68   b  are provided to be inclined at the same angle to the electron emission direction. As shown in  FIG. 2B , the angle from the electron emission direction along the tube axis TA to the surface of the magnetic pole  68   a  is represented by yl and the angle from the electron emission direction to the surface of the magnetic pole  68   b  is represented by γ 2 . Thus, γ 1  is equal to γ 2  if, for example, the magnetic poles  68   a  and  68   b  are provided to be inclined similarly. In addition, angles of inclination γ (γ 1  and γ 2 ) to the electron emission direction, of the magnetic poles  68   a  and  68   b , are set within a range of 0°&lt;γ&lt;90°. At this time, each of angles of inclination γ of the magnetic poles  68   a  and  68   b  is formed to fall within the range of 0°&lt;γ&lt;90°. For example, if angles of inclination γ 1  and γ 2  of the magnetic poles  68   a  and  68   b  are equal to each other, each of angles of inclination γ 1  and γ 2  of the magnetic poles  68   a  and  68   b  is formed within a range of 30°≦γ≦60°. Furthermore, each of angles of inclination γ 1  and γ 2  of the magnetic poles  68   a  and  68   b  may be formed to be 45° to the electron emission direction. It should be noted that a plurality of magnetic pole pairs may be provided in the first magnetic deflector  60 . 
     In the present embodiment, the electrons are emitted from the filament in the cathode  36  toward the focus of the electrons of the anode target  35  when the X-ray tube assembly  1  is driven. The direction of emission of the electrons is assumed to be along a straight line which passes through the center of the cathode  36 . In addition, angles of inclination γ 1  and γ 2  of the magnetic poles  68   a  and  68   b  of the first magnetic deflector  60  shown in  FIG. 2B  are equal to each other. The first magnetic deflector  60  is supplied with an AC current from a deflection power supply (not shown). When the first magnetic deflector  60  is supplied with an AC current, the first magnetic deflector  60  generates a magnetic field between the magnetic pole pair  68   a  and  68   b  which are paired as a dipole. In the present embodiment, the magnetic pole pair  68   a  and  68   b  are provided to generate the magnetic fields between the cathode  36  and the anode target  35 . In other words, the first magnetic deflector  60  generates a magnetic field between the cathode  36  and the anode target  35 . The electrons emitted from the cathode  36  collide with the anode target  35  so as to cross the magnetic field generated between the cathode  36  and the anode target  35 , along the tube axis TA. 
     The first magnetic deflector  60  can move the electron beams passing through the magnetic field, intermittently or sequentially, by allowing the AC current supplied from the deflection power supply (not shown) to be controlled. The first magnetic deflector  60  deflects the electrons (beams) emitted from the cathode  36 , in the direction along the diameter direction of the anode target  35 , by controlling the current supplied from the deflection power supply controller (not shown). In other words, the first magnetic deflector  60  can move the position of the focus, i.e., the point with which the electrons collide on the surface of the anode target  35 , by controlling the current supplied by the deflection power supply controller (not shown). In the present embodiment, the first magnetic deflector  60  can move the electron beams in the direction perpendicular to the magnetic field. For example, the first magnetic deflector  60  moves the electron beams in two directions perpendicular to the alternating magnetic field MG 1 , similarly to direction D 1  shown in  FIG. 2C . 
     When the first magnetic deflector  60  generates the alternating magnetic field MG 1 , the non-magnetic cover of the cathode  36  allows the magnetic field to be generated in the direction opposite to the alternating magnetic field MG 1 , based on the eddy current, since the non-magnetic cover is formed of a non-magnetic material having high electrical conductivity. Similarly, the anode target  35  allows the magnetic field to be generated in the direction opposite to the alternating magnetic field MG 1 , based on the eddy current, since the anode target  35  is formed of a non-magnetic material having high electrical conductivity. The alternating magnetic field MG 1  is distorted by actions of the magnetic fields in the opposite direction as generated from the non-magnetic cover and the anode target  35 . By thus distorting the alternating magnetic field MG 1 , the alternating magnetic field MG 1  flows in the direction substantially perpendicular to the electron emission direction, at a position between the surface of the anode target  35  and the surface of the cathode  36  as shown in  FIG. 2B . In addition, by thus distorting the alternating magnetic field MG 1 , the strength (magnetic flux density) of the alternating magnetic field MG 1  in the area close to the position between the surface of the anode target  35  and the surface of the cathode  36  is increased. As a result, the deflecting force to the electrons (beams) is increased by increasing the magnetic flux density, and the first magnetic deflector  60  can efficiently deflect the electrons (beams). 
     In the present embodiment, the X-ray tube assembly  1  comprises the X-ray tube  30  comprising the depressed portions  32   a  and  32   b , and the first magnetic deflector  60  which deflects the electrons emitted from the X-ray tube  30 . The first magnetic deflector  60  allows a magnetic field to be generated between the cathode  36  and the anode target  35  by the magnetic poles  68   a  and  68   b . Each of the magnetic pole pair  68   a  and  68   b  is provided to face the surface toward the electron emission direction, with the predetermined inclination, to deflect the electrons emitted from the cathode  36  at the position between the anode target  35  and the cathode  36 . The cathode  36  comprises a non-magnetic cover formed of a non-magnetic metal member having high electrical conductivity, at a peripheral portion thereof, inside the vacuum envelope  31  of the X-ray tube  30 . In addition, the anode target  35  is also formed of a non-magnetic metal member having high electrical conductivity. Thus, when the first magnetic deflector  60  is provided with the AC current, a part of the alternating magnetic field MG 1  generated by the first magnetic deflector  60  is strengthened. As a result, the first magnetic deflector  60  can certainly deflect the electrons emitted from the cathode  36 . 
     In addition, in the X-ray tube assembly  1 , the distance between the anode target  35  and the cathode  36  can be reduced since a small-diameter portion is not provided between the anode target  35  and the cathode  36 . As a result, occurrence of expansion, blur, and distortion of the X-ray focus, reduction in the electron emission quantity of the cathode  36 , etc., can be reduced in the X-ray tube assembly  1  of the present embodiment. 
     Next, an X-ray tube assembly of another embodiment will be explained. In another embodiment, portions like or similar to those of the above-explained first embodiment are denoted by the same reference numbers or symbols and detailed descriptions are omitted. 
     Second Embodiment 
     An X-ray tube assembly  1  of the second embodiment is different from the X-ray tube assembly  1  of the first embodiment with respect to the depressed portions  32   a  and  32   b  and the first magnetic deflector  60 . 
       FIG. 3  is a cross-sectional view showing a summary of an X-ray tube  30  of the second embodiment. In  FIG. 3 , a straight line orthogonal to tube axis TA is referred to as straight line L 1 , a straight line orthogonal to the tube axis TA and straight line L 1  is referred to as straight line L 2 , and a straight line which is orthogonal to a straight line along an electron emission direction and straight line L 1  and which is parallel to straight line L 2  is referred to as straight line L 3 . In addition, a straight line drawn to be inclined at angle αO to straight line L 3 , around the straight line along the electron emission direction is referred to as straight line L 4 . The straight line along the electron emission direction is assumed to pass through the center of the cathode  36 . 
     As shown in  FIG. 3 , each of depressed portions  32   a  and  32   b  comprises a wall portion bent to surround the cathode  36 , in the X-ray tube  30  of the second embodiment. The wall portions of the depressed portions  32   a  and  32   b  opposes to each other on a straight line orthogonal to the straight line along the electron emission direction. The wall portions of the depressed portions  32   a  and  32   b  may not be bent to surround the cathode  36 . 
     For example, as shown in  FIG. 3 , the depressed portion  32   a  comprises the wall portion which perpendicularly intersects straight line L 4  and which is opposed to the cathode  36 . Similarly, the depressed portion  32   b  comprises the wall portion which perpendicularly intersects straight line L 4  and which is opposed to the cathode  36 . The wall portions of the depressed portions  32   a  and  32   b  are provided on straight line L 4  to be opposed to each other. 
     The first magnetic deflector  60  is provided to rotate at a predetermined angle around the straight line along the direction of emission of the electron beam. For example, as shown in  FIG. 3 , the first magnetic deflector  60  is provided to be inclined parallel to straight line L 4 . In this case, the magnetic poles  68   a  and  68   b  of the first magnetic deflector  60  are provided to sandwich the cathode  36  on straight line L 4 . 
     In the present embodiment, the first magnetic deflector  60  can deflect the electron beam, simultaneously, in a diameter direction and a direction of rotation of the anode target  35 , by alternating magnetic field MG 1  generated by the paired magnetic poles  68   a  and  68   b . In other words, the first magnetic deflector  60  can move a focus of the electron beam at a rate tan αO of the distance of movement in the direction of rotation to the distance of movement in the diameter direction, of the anode target. Generally the shape of the focus, viewed through the X-ray transmissive window  38  along the straight line orthogonal to the tube axis TA and intersecting with the center of the focus, is referred to as the effective focus. If the focus moves in the diameter direction by x, then the effective focus moves in the tube axis direction by x tan θ. On the other hand, if the focus moves in the direction of rotation by y(=x tan αO), then the effective focus moves in the direction of rotation by the same extent, y(=x tan αO). 
     For example, to move the effective focus in an equal distance in the tube axis direction (that is the direction along the length of the effective focus) and the direction of rotation (that is the direction along the width of the effective focus), the first magnetic deflector  60  is arranged such that angle αO which is made by straight line L 4  to straight line L 3  is equal to angle of inclination θ of the anode target  35 . 
     In the present embodiment, the first magnetic deflector  60  is provided to rotate at a predetermined angle around the straight line along the direction of emission of the electron beam. As a result, the first magnetic deflector  60  can deflect the electron beam emitted from the cathode  36  in a direction different from that of the first embodiment. 
     Third Embodiment 
     An X-ray tube assembly  1  of the third embodiment is different from the X-ray tube assembly  1  of the above-explained embodiment with respect to a feature of further comprising a second magnetic deflector  70 . 
     The X-ray tube assembly  1  of the third embodiment is configured substantially equally to the X-ray tube assembly  1  of the second embodiment. In the third embodiment, portions like or similar to those of the above-explained second embodiment are denoted by the same reference numbers or symbols and detailed descriptions are omitted. 
       FIG. 4A  is a cross-sectional view showing a summary of an X-ray tube  30  of the third embodiment,  FIG. 4B  is a cross-sectional view seen along line IVA-IVA in  FIG. 4A , and  FIG. 4C  is a cross-sectional view seen along line IVB-IVB in  FIG. 4B . In  FIG. 4B , a straight line orthogonal to tube axis TA is referred to as straight line L 1 , a straight line orthogonal to the tube axis TA and straight line L 1  is referred to as straight line L 2 , and a straight line which is orthogonal to a straight line along an electron emission direction and straight line L 1  and which is parallel to straight line L 2  is referred to as straight line L 3 . In addition, a straight line drawn to be inclined at angle α 1  to straight line L 3 , around the straight line along the electron emission direction is referred to as straight line L 5 , and a straight line drawn to be inclined at angle α 2  to straight line L 3 , around the straight line along the electron emission direction is referred to as straight line L 6 . The straight line along the electron emission direction is assumed to pass through the center of the cathode  36 . Angles of inclination α 1  and α 2  of the respective straight line L 5  and straight line L 6  are hereinafter set to be equal angles for convenience of explanation. Angles of inclination α 1  and α 2  may be different from each other. 
     Besides the configuration of the X-ray tube assembly  1  of the second embodiment, the X-ray tube assembly  1  of the third embodiment further comprises a second magnetic deflector  70 . The second magnetic deflector  70  is configured substantially equally to the first magnetic deflector  60 . As shown in  FIG. 4B , a depressed portion  32   a  is formed to accept a magnetic pole  68   a  and a magnetic pole  78   a  to be explained later while a depressed portion  32   b  is formed to accept a magnetic pole  68   b  and a magnetic pole  78   b  to be explained later. 
     The second magnetic deflector  70  is configured substantially equally to the first magnetic deflector  60 , and its detailed explanations are omitted. 
     As shown in  FIG. 4C , the second magnetic deflector  70  comprises a coil  74 , a yoke  76 , and the magnetic poles  78   a  and  78   b . In addition, as shown in  FIG. 4C , the second magnetic deflector  70  forms alternating magnetic field MG 2  which intermittently or sequentially deflects the orbital of the electrons emitted from a filament contained in the cathode  36 . The second magnetic deflector  70  deflects the electrons (beams) emitted from the cathode  36 , in a direction along the diameter direction of an anode target  35 . The second magnetic deflector  70  is constituted by the paired magnetic poles  78   a  and  78   b  at both ends of the yoke  76 . 
     The second magnetic deflector  70  is provided in close vicinity to the depressed portions  32   a  and  32   b  of the X-ray tube  30 , outside the X-ray tube  30 . As shown in  FIG. 4A , the second magnetic deflector  70  is provided coaxially with the first magnetic deflector  60 , on the straight line parallel to the tube axis TA passing through the center of the cathode  36 , in the present embodiment. In addition, the second magnetic deflector  70  is provided to rotate at a predetermined angle around the straight line along the electron emission direction. For example, as shown in  FIG. 4B , the first magnetic deflector  60  is provided to be inclined along straight line L 5  while the second magnetic deflector  70  is provided to be inclined along straight line L 6 . 
     In the second magnetic deflector  70 , a current supplied from a deflection power supply (not shown) is controlled by a deflection power supply controller (not shown). The second magnetic deflector  70  can move a position of the focus, intermittently or sequentially, on the surface of the anode target  35 , by allowing the supplied current to be controlled. In the present embodiment, the second magnetic deflector  70  is supplied with an AC current from a deflection power supply (not shown). In this case, the second magnetic deflector  70  generates an alternating magnetic field. It should be noted that the deflection power supply and the deflection power supply controller may be the same as or different from those of the first magnetic deflector  60 . 
     The magnetic poles  78   a  and  78   b  (second magnetic pole pair) are provided at end portions of the yoke  76 , respectively. The magnetic poles  78   a  and  78   b  are provided such that the cathode  36  opposed to the anode target  35  is provided between the magnetic poles  78   a  and  78   b . In other words, in the second magnetic deflector  70 , the pair of magnetic poles  78   a  and  78   b  are provided on a straight line along a direction perpendicular to the emission direction of the electrons emitted from the filament included in the cathode  36  or, for example, straight line L 6 . 
     The magnetic pole pair  78   a  and  78   b  are formed in a substantially similar shape. The magnetic pole pair  78   a  and  78   b  are paired as a dipole. Similarly to the magnetic pole pair  68   a  and  68   b , the magnetic pole pair  78   a  and  78   b  are provided to face toward the electron emission direction of the cathode  36  to deflect the electrons emitted from the cathode  36  at positions which are not so close to the anode target  35 . For example, the emission direction of the electron beam of the cathode  36  is the direction along the tube axis TA. At this time, the magnetic poles  78   a  and  78   b  are provided to be inclined at the same angle to the electron emission direction. As shown in  FIG. 4C , the angle from the electron emission direction along the tube axis TA to the surface of the magnetic pole  78   a  is represented by γ 3  and the angle from the electron emission direction to the surface of the magnetic pole  78   b  is represented by γ 4 . Thus, γ 3  is equal to γ 4  if, for example, the magnetic poles  78   a  and  78   b  are provided to be inclined similarly. In addition, angles of inclination γ (γ 1 , γ 2 , γ 3  and γ 4 ) to the electron emission direction, of the magnetic poles  78   a  and  78   b , are set within a range of 0°&lt;γ&lt;90°. At this time, each of angles of inclination γ of the magnetic poles  78   a  and  78   b  is formed to fall within the range of 0°&lt;γ&lt;90°. For example, if angles of inclination γ 3  and γ 4  of the magnetic poles  78   a  and  78   b  are equal to each other, each of angles of inclination γ 3  and γ 4  of the magnetic poles  78   a  and  78   b  is formed within a range of 30°≦γ≦60°. Furthermore, each of angles of inclination γ 3  and γ 4  of the magnetic poles  78   a  and  78   b  may be formed to be 45° to the electron emission direction. It should be noted that a plurality of magnetic pole pairs may be provided in the second magnetic deflector  70 . 
     In the present embodiment, the electrons are emitted from the filament in the cathode  36  toward the focus of the electrons of the anode target  35  when the X-ray tube assembly  1  is driven. The direction of emission of the electrons is assumed to be along a straight line which passes through the center of the cathode  36 . The first magnetic deflector  60  and the second magnetic deflector  70  are provided at positions at which two sets of dipoles, i.e., the magnetic pole pair  68   a  and  68   b  and the magnetic pole pair  78   a  and  78   b , are rotated at predetermined angles α (α 1  and α 2 ) toward opposite sides to straight line L 3 , around the center axis of the cathode  36 . Each of the magnetic pole pair  68   a  and  68   b  of the first magnetic deflector  60  is provided on straight line L 5  that is rotated at angle α 1  to straight line L 3 . Each of the magnetic pole pair  78   a  and  78   b  of the second magnetic deflector  70  is provided on straight line L 5  that is rotated at angle α 2  to straight line L 3 . 
     In addition, angles of inclination γ 1  and γ 2  of the magnetic poles  68   a  and  68   b  of the first magnetic deflector  60  are equal to angles of inclination γ 3  and γ 4  of the magnetic poles  78   a  and  78   b  of the second magnetic deflector  70 . Each of the first magnetic deflector  60  and the second magnetic deflector  70  is supplied with an AC current from a deflection power supply (not shown). When the first magnetic deflector  60  is supplied with the AC current from the deflection power supply, the first magnetic deflector  60  generates alternating magnetic field MG 1  between the magnetic pole pair  68   a  and  68   b  serving as a dipole. Similarly, the second magnetic deflector  70  generates alternating magnetic field MG 2  between the magnetic pole pair  78   a  and  78   b  serving as a dipole. In the present embodiment, the magnetic pole pair  68   a  and  68   b , and the magnetic pole pair  78   a  and  78   b  are provided to generate the magnetic fields between the cathode  36  and the anode target  35 . The electrons emitted from the cathode  36  collide with the anode target  35  so as to cross the alternating magnetic field MG 1  and/or alternating magnetic field MG 2  generated between the cathode  36  and the anode target  35 , along the tube axis TA. 
     Each of the first magnetic deflector  60  and the second magnetic deflector  70  can move the electron beam passing through the magnetic field, intermittently or sequentially, by allowing the AC current supplied from the deflection power supply (not shown) to be controlled. 
     The X-ray tube assembly  1  of the present embodiment can move the focus with which the electrons collide, on the anode target  35 , simultaneously, in the diameter direction and the direction of rotation, by deflecting magnetic fields generated by two sets of the paired magnetic poles  68   a  and  68   b  and the paired magnetic poles  78   a  and  78   b.    
     The first magnetic deflector  60  can deflect the electron beam, simultaneously, in the diameter direction and the direction of rotation of the anode target  35 , by alternating magnetic field MG 1  generated by the paired magnetic poles  68   a  and  68   b . In addition, the second magnetic deflector  70  can deflect the electron beam, simultaneously, in the diameter direction and the direction of rotation of the anode target  35 , by alternating magnetic field MG 2  generated by the paired magnetic poles  78   a  and  78   b . In other words, the first magnetic deflector  60  and the second magnetic deflector  70  can move the focus of the electron beam, at a predetermined rate of the distance of movement in the direction of rotation to the distance of movement in the diameter direction, of the anode target  35 . The predetermined rate can be selected within the range between 0 and tan α, by adjusting the ratio of the magnetic field strength of MG 1  and the magnetic field strength of MG 2 . 
     In the present embodiment, the X-ray tube assembly  1  comprises the first magnetic deflector  60  and the second magnetic deflector  70 . As a result, the first magnetic deflector  60  and the second magnetic deflector  70  can freely move the focus of the electron beam on the anode target  35 , by adjusting the rate of their respective magnetic field strengths. 
     Fourth Embodiment 
     An X-ray tube assembly  1  of the fourth embodiment is different from the X-ray tube assembly  1  of the above-explained embodiment with respect to structures of a first magnetic deflector  60  and a second magnetic deflector  70 . 
     The X-ray tube assembly  1  of the fourth embodiment is configured substantially equally to the X-ray tube assembly  1  of the third embodiment. Thus, in the fourth embodiment, portions like or similar to those of the above-explained third embodiment are denoted by the same reference numbers or symbols and detailed descriptions are omitted. 
       FIG. 5A  is a cross-sectional view showing a summary of an X-ray tube  30  of the fourth embodiment and  FIG. 5B  is a cross-sectional view seen along line VA-VA of  FIG. 5A . In  FIG. 5B , a straight line orthogonal to tube axis TA is referred to as straight line L 1 , a straight line orthogonal to the tube axis TA and straight line L 1  is referred to as straight line L 2 , and a straight line which is orthogonal to a straight line along an electron emission direction and straight line L 1  and which is parallel to straight line L 2  is referred to as straight line L 3 . In addition, a straight line drawn to be inclined at angle β 1  to straight line L 3 , around the straight line along the electron emission direction is referred to as straight line L 7 , and a straight line drawn to be inclined at angle β 2  to straight line L 3 , around the straight line along the electron emission direction is referred tows straight line L 8 . The straight line along the electron emission direction is assumed to pass through the center of the cathode  36 . Angles of inclination β 1  and β 2  of the respective straight line L 7  and straight line L 8  are hereinafter set to be equal angles, for convenience of explanation. Angles of inclination β 1  and β 2  may be different from each other. 
     In the X-ray tube assembly  1  of the fourth embodiment, the first magnetic deflector  60  is provided to be rotated at 90 degrees to the installation of the first magnetic deflector  60  of the first embodiment. For example, as shown in  FIG. 5A , the first magnetic deflector  60  is provided such that both end portions (magnetic poles  68   a  and  68   b ) of a yoke  66  are contained in a depressed portion  32   a . Similarly, the second magnetic deflector  70  is provided such that both end portions (magnetic poles  78   a  and  78   b ) of a yoke  76  are contained in a depressed portion  32   b.    
     For example, as shown in  FIG. 5B , the magnetic poles  68   a  and  68   b  are arranged parallel to straight line L 1  and provided in the depressed portion  32   a  while the magnetic poles  78   a  and  78   b  are arranged parallel to straight line L 1  and provided in the depressed portion  32   b . At this time, the magnetic poles  68   a  and  78   a  are provided to sandwich the cathode  36  on straight line L 7  while the magnetic poles  68   b  and  78   b  are provided to sandwich the cathode  36  on straight line L 8 . 
     In the present embodiment, the electrons are emitted from the filament in the cathode  36  toward the focus of the electrons of the anode target  35  when the X-ray tube assembly  1  is driven. The direction of emission of the electrons is assumed to be along a straight line which passes through the center of the cathode  36 . The magnetic poles  68   a  and  68   b  are contained in the depressed portion  32   a . Similarly, the magnetic poles  78   a  and  78   b  are provided to be contained in the depressed portion  32   b.    
     Each of the first magnetic deflector  60  and the second magnetic deflector  70  is supplied with an AC current from a deflection power supply (not shown). When the first magnetic deflector  60  is supplied with the AC current from the deflection power supply, the first magnetic deflector  60  generates alternating magnetic field MG 1  between the magnetic pole pair  68   a  and  68   b  serving as a dipole. Similarly, the second magnetic deflector  70  generates alternating magnetic field MG 2  between the magnetic pole pair  78   a  and  78   b  serving as a dipole. At this time, the magnetic poles  68   a  and  68   b  generate alternating magnetic field MG 3  in a diameter direction of the anode target  35 . The magnetic poles  78   a  and  78   b  generate alternating magnetic field MG 4  in a diameter direction of the anode target  35 , on a side opposite to the magnetic poles  68   a  and  68   b  with the cathode  36  interposed therebetween. In the present embodiment, the magnetic pole pair  68   a  and  68   b , and the magnetic pole pair  78   a  and  78   b  are provided to generate the magnetic fields between the cathode  36  and the anode target  35 . 
     Each of the first magnetic deflector  60  and the second magnetic deflector  70  can move the electron beam passing through the magnetic field, intermittently or sequentially, by allowing the AC current supplied from the deflection power supply (not shown) to be controlled. Each of the first magnetic deflector  60  and the second magnetic deflector  70  deflects the electrons (beam) emitted from the cathode  36 , in the direction along the direction of rotation of the anode target  35 , by controlling the current supplied from the deflection power supply controller (not shown). In other words, the first magnetic deflector  60  and the second magnetic deflector  70  can move the focus of the electron beam on the anode target  35 , in the direction along the direction of rotation of the anode target  35 . 
     According to the present embodiment, the first magnetic deflector  60  is provided such that the magnetic poles  68   a  and  68   b  are contained in the depressed portion  32   a . Similarly, the second magnetic deflector  70  is provided such that the magnetic poles  78   a  and  78   b  of the yoke  76  are contained in the depressed portion  32   b . As a result, the first magnetic deflector  60  and the second magnetic deflector  70  can deflect the electrons (beam) emitted from the cathode  36 , in the direction along the direction of rotation of the anode target  35 . 
     According to the above-explained embodiment, the X-ray tube assembly comprises the X-ray tube comprising the depressed portions, and the magnetic deflectors which deflect the electrons emitted from the X-ray tube. Each of the magnetic deflectors comprises a plurality of magnetic poles. The magnetic poles include at least a magnetic pole pair serving as a dipole. The magnetic pole pair allow the magnetic field to be generated between the cathode and the anode target. Each of the magnetic poles included in the magnetic pole pair has the surface face to the electron emission direction, to deflect the electrons emitted from the cathode at the position between the anode target and the cathode. The cathode comprises, for example, a non-magnetic cover formed of a non-magnetic metal member having high electrical conductivity, at a peripheral portion thereof, inside the vacuum envelope of the X-ray tube. In addition, the anode target is also formed of, for example, a non-magnetic metal member having high electrical conductivity. Thus, when each magnetic deflector is provided with the AC current, a part of the magnetic field generated by the magnetic deflector is strengthened. As a result, the magnetic deflector can certainly deflect the electrons emitted from the cathode. 
     In addition, in the X-ray tube assembly, the distance between the anode target and the cathode can be reduced since a small-diameter portion is not provided between the anode target and the cathode. As a result, occurrence of expansion, blur, and distortion of the X-ray focus, reduction in the electron emission quantity of the cathode, etc., can be reduced in the X-ray tube assembly  1  of the present embodiment. 
     In the above-explained embodiments, the X-ray tube assembly  1  is a rotary-anode X-ray tube assembly, but may be a stationary-anode X-ray tube assembly. 
     In the above-explained embodiments, the X-ray tube assembly  1  is a neutral-grounding-type X-ray tube assembly, but may be an anode-grounding or cathode-grounding X-ray tube assembly. 
     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.