Patent Publication Number: US-2023148363-A1

Title: Electron beam generation source, electron beam emission device, and x-ray emission device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electron beam generation source, an electron beam emission device, and an X-ray emission device. 
     BACKGROUND ART 
     A fluorescent display tube that discharges electrons from an electron discharge part toward a phosphor to emit light from the phosphor is described in Patent Literature 1. In an electron beam generation source of this fluorescent display tube, tension of the electron discharge part is held by applying a pressing force of a tension holding part (a spring) to the electron discharge part having a linear shape. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Unexamined Patent Publication No. H8-264138 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the above fluorescent display tube, the electron discharge part having a linear shape and the tension holding part are disposed parallel to each other, and ends of both are connected by a connecting part, and thus the pressing force of the tension holding part is applied to the electron discharge part. In such a configuration, it is difficult to apply the pressing force of the tension holding part to the electron discharge part along an axis of the electron discharge part, and axial deviation of the electron discharge part may occur due to action of a moment. 
     Therefore, an object of the present disclosure is to provide an electron beam generation source, an electron beam emission device, and an X-ray emission device in which a pressing force or a tensile force of a tension holding part can be appropriately applied to an electron discharge part to curb axial deviation of the electron discharge part. 
     Solution to Problem 
     According to an aspect of the present disclosure, there is provided an electron beam generation source including: an electron discharge part extending on a desired axis and configured to discharge electrons; a movable part connected to one end of the electron discharge part; a support part configured to support the movable part to be movable along the axis; and a tension holding part configured to hold tension of the electron discharge part by applying a pressing force or a tensile force to the movable part, wherein the movable part and the tension holding part are disposed on the axis. 
     In this electron beam generation source, the electron discharge part, the movable part, and the tension holding part are provided on the same axis. Therefore, the electron beam generation source can easily apply the pressing force or the tensile force of the tension holding part to the electron discharge part in an axial direction via the movable part. As a result, even in a case where the pressing force or the tensile force of the tension holding part is applied, axial deviation of the electron discharge part is curbed. In this way, the electron beam generation source can appropriately apply the pressing force or the tensile force of the tension holding part to the electron discharge part to curb the axial deviation of the electron discharge part. 
     The tension holding part may apply the pressing force or the tensile force to the movable part such that the movable part moves along the axis. In this case, the electron beam generation source can further curb the axial deviation of the electron discharge part in a case where the pressing force or the tensile force of the tension holding part is applied. 
     The movable part may be disposed such that a position of a center of gravity of the movable part is positioned on the axis. In this case, even in a case where the pressing force or the tensile force of the tension holding part is applied, the movable part swinging due to action of a moment is curbed. As a result, the electron beam generation source can further curb the axial deviation of the electron discharge part. 
     The electron discharge part and the tension holding part may be made of different members. In this case, the electron beam generation source can curb the conduction of heat from the electron discharge part to the tension holding part and can curb the heating of the tension holding part. 
     The support part may include a housing part having an internal space for accommodating the tension holding part inside. In this case, the electron beam generation source can curb the influence of the radiant heat from the electron discharge part on the tension holding part by the housing part provided in the support part. As a result, the electron beam generation source can curb fluctuations in the pressing force or the tensile force of the tension holding part due to the influence of heat and deterioration due to heat and can stably hold the tension of the electron discharge part. 
     The housing part may cover the tension holding part such that the tension holding part cannot be directly seen from the electron discharge part. In this case, the electron beam generation source can prevent the electrons discharged from the electron discharge part from directly hitting the tension holding part and can curb heating deterioration and damage caused by the collision of the electrons. 
     The housing part may include a movable part holding part that extends along the axis and holds the movable part to be movable along the axis. In this case, the housing part can stably hold the movable part to be movable by the movable part holding part. 
     The movable part holding part may be a through hole extending along the axis and having a circular column shape. In this case, the movable part can rotate in the through hole. For example, when the tension holding part expands and contracts, the tension holding part is twisted, and thus a force in a rotational direction may be applied to the movable part. Even in this case, the rotation of the movable part in the through hole curbs the concentration of a force of the twisting on a part of the movable part, and the tension of the electron discharge part is maintained. As a result, the electron beam generation source can curb the influence of the twisting even in a case where the tension holding part is twisted. 
     The electron discharge part may have a straight linear shape. In this case, the electron beam generation source can uniformly emit electrons at each position in an axial direction. 
     The electron discharge part may have a coiled part having a coiled shape. In this case, the electron beam generation source can have a function of holding tension with respect to the electron discharge part. 
     The electron beam generation source may further include a frame configured to support the other end of the electron discharge part and the tension holding part. In this case, the electron beam generation source can be easily handled by making the electron beam generation source into one body using the frame. 
     There may be provided an electron beam emission device including: such an electron beam generation source; a main body configured to accommodate the electron beam generation source; and an electron extraction part configured to extract electrons from the electron beam generation source to the outside of the main body. Further, there may be provided an X-ray emission device including: such an electron beam generation source; a main body configured to accommodate the electron beam generation source; an X-ray generation part configured to generate X-rays when electrons are incident from the electron beam generation source; and an X-ray extraction part configured to extract the X-rays to the outside of the main body. In this case, it is possible to obtain an electron beam emission device and an X-ray emission device capable of curbing the axial deviation of the electron discharge part. 
     Advantageous Effects of Invention 
     According to the present disclosure, a pressing force or a tensile force of a tension holding part can be appropriately applied to an electron discharge part to curb axial deviation of the electron discharge part. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of an electron beam emission device according to an embodiment. 
         FIG.  2    is a partial cross-sectional view showing an internal structure of the electron beam emission device of  FIG.  1   . 
         FIG.  3    is a cross-sectional view along line III-III of  FIG.  1   . 
         FIG.  4    is a perspective view of a filament unit. 
         FIG.  5    is a cross-sectional view of the filament unit. 
         FIG.  6    is a cross-sectional perspective view of a tension holding unit. 
         FIG.  7    is a cross-sectional view of the tension holding unit. 
         FIG.  8    is a cross-sectional perspective view of a tension holding unit of a first modification example. 
         FIG.  9    is a cross-sectional perspective view of a tension holding unit of a second modification example. 
         FIG.  10    is a cross-sectional perspective view of a tension holding unit of a third modification example. 
         FIG.  11    is a cross-sectional perspective view of a tension holding unit of a fourth modification example. 
         FIG.  12    is a cross-sectional perspective view of a tension holding unit of a fifth modification example. 
         FIG.  13    is a cross-sectional perspective view of a tension holding unit of a sixth modification example. 
         FIG.  14    is a cross-sectional perspective view of a tension holding unit of a seventh modification example. 
         FIG.  15    is a cross-sectional view showing an example of an attachment structure of a filament to a movable body. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding elements will be denoted by the same reference signs and redundant description will be omitted. 
     An electron beam emission device  1  shown in  FIG.  1    is used for, for example, ink curing, sterilizing, or surface reforming on an irradiation target by irradiating the irradiation target with electron beams EB. Hereinafter, an electron beam emitting side (a side of a window  9 ) which is a side from which the electron beams EB are emitted by the electron beam emission device  1  will be described as a “front side.” 
     As shown in  FIGS.  1  to  3   , the electron beam emission device  1  includes a filament unit (an electron beam generation source)  2 , a vacuum container (a main body)  3 , a cathode holding member  4 , a cathode holding member  5 , a rail  6 , a high voltage introduction insulation member  7 , an insulation support member  8 , and a window (an electron extraction part)  9 . The filament unit  2  is an electron beam generation unit that generates the electron beams EB. Further, the filament unit  2  is a long unit. 
     The vacuum container  3  is formed of a conductive material such as a metal. The vacuum container  3  has a substantially cylindrical shape. The vacuum container  3  forms a vacuum space R having a substantially circular column shape inside. The filament unit  2  is disposed inside the vacuum container  3  in an axial direction (a major axis direction) of the vacuum space R having a substantially circular column shape. An opening  3   a  through which the vacuum space R and an external space communicate with each other is provided at a position on the front side in the vacuum container  3  with respect to the filament unit  2 . The window  9  is fixed to the opening  3   a  to be vacuum-sealed. 
     The window  9  includes a window material  9   a  and a support  9   b . The window material  9   a  is formed in a thin film shape. As a material of the window material  9   a , a material having excellent transparency for the electron beams EB (for example, beryllium, titanium, aluminum, or the like) is used. The support  9   b  is disposed on a side of the vacuum space R of the window material  9   a  and supports the window material  9   a . The support  9   b  is a mesh-like member and has a plurality of holes through which the electron beams EB pass. 
     An exhaust port  3   b  for exhausting air in the vacuum container  3  is provided at a position on a rear side in the vacuum container  3  with respect to the filament unit  2 . A vacuum pump (not shown) is connected to the exhaust port  3   b , and the air in the vacuum container  3  is discharged by the vacuum pump. As a result, the inside of the vacuum container  3  becomes the vacuum space R. In both ends of the vacuum container  3  having a substantially cylindrical shape, an opening  3   c  on the other side and an opening  3   d  on one side are closed by a flange  7   a  of the high voltage introduction insulation member  7  and a lid  3   e , respectively. 
     A pair of cathode holding members  4  and  5  that have a cathode potential are disposed in the vacuum container  3 . The rail  6  which has a cathode potential and also serves as a surrounding electrode that surrounds the filament unit  2  is provided between the cathode holding member  4  on the other side and the cathode holding member  5  on one side. The rail  6  is a conductive and long member having a substantially C-shaped cross section. The rail  6  is disposed such that an opening having a substantially C-shaped cross section faces the front side (a side of the window  9 ). The rail  6  holds the filament unit  2  in an inside portion (an inside space). For example, the filament unit  2  is held in the rail  6  by being inserted into the inside of the rail  6  through insertion holes provided in the cathode holding member  5  and the insulation support member  8  in a state where the lid  3   e  of the vacuum container  3  is removed. 
     The high voltage introduction insulation member  7  is provided at an end of the vacuum container  3  on a side of the opening  3   c  on the other side. The other end of the high voltage introduction insulation member  7  projects to the outside of the vacuum container  3  through the opening  3   c . The high voltage introduction insulation member  7  has the flange  7   a  protruding outward in a radial direction thereof and seals the opening  3   c  of the vacuum container  3 . The high voltage introduction insulation member  7  is formed of an insulation material (for example, an insulation resin such as an epoxy resin, ceramic, or the like). The cathode holding member  4  holds one end of the high voltage introduction insulation member  7  in a state where the cathode holding member  4  is electrically insulated from the vacuum container  3  which has a ground potential. 
     Further, the high voltage introduction insulation member  7  is a high withstand voltage type connector for receiving supply of a high voltage from a power source device outside the electron beam emission device  1 . A plug (not shown) for supplying a high voltage from the power source device is inserted into the high voltage introduction insulation member  7 . An internal wiring for supplying a high voltage supplied from the outside to the filament unit  2  and the like is provided inside the high voltage introduction insulation member  7 . This internal wiring is covered with an insulation material constituting the high voltage introduction insulation member  7 , and insulation with respect to the vacuum container  3  is ensured. 
     The insulation support member  8  is provided at an end of the vacuum container  3  on a side of the opening  3   d  on the one side (an end on a side of the lid  3   e ). The insulation support member  8  is formed of an insulation material (for example, an insulation resin such as an epoxy resin, ceramic, or the like). The cathode holding member  5  holds the other end of the insulation support member  8  in a state where the cathode holding member  5  is electrically insulated from the vacuum container  3 . 
     As shown in  FIGS.  3  to  5   , the filament unit  2  is configured as one unit to be attachable to and detachable from the rail  6 . The filament unit  2  includes a filament (an electron discharge part)  10 , a main frame (a frame)  11 , a grid electrode  12 , a sub frame  13 , a power supply line  14 , a guide member  15 , a terminal holding member  16 , a filament fixing member  17 , and a tension holding unit  20 . 
     The main frame  11  is a long member having a substantially U-shaped (C-shaped) cross section. The main frame  11  is disposed such that an opening having a substantially U-shaped cross section faces the front side (a side of the window  9 ). The filament fixing member  17  is provided at the other end of the main frame  11  in the inside (an inside space) of the main frame  11 . Further, the tension holding unit  20  is provided at one end of the main frame  11  in the inside (the inside space) of the main frame  11 . 
     The filament  10  is an electron discharge part that discharges electrons that become the electron beams EB when heated by energization. The filament  10  is a linear member and extends on a desired axis L extending from one side to the other side. The filament  10  is formed of a metal material having a high melting point, for example, a material containing tungsten as a main component. One end of the filament  10  is connected to the tension holding unit  20 . The other end of the filament  10  is connected to the filament fixing member  17 . As described above, the main frame  11  supports the tension holding unit  20  connected to the one end of the filament  10  and the filament fixing member  17  connected to the other end of the filament  10 . 
     The terminal holding member  16  is attached to the other end of the main frame  11 . The terminal holding member  16  holds a filament terminal T1 for supplying a current for the filament  10  to discharge electrons, a high voltage terminal T2 for supplying a cathode potential to the filament unit  2 , and a grid electrode terminal T3 for supplying an applied voltage to the grid electrode  12  in a state where the terminals T1, T2, and T3 are electrically insulated from each other. The filament terminal T1 is connected to the other end of the power supply line  14 . The high voltage terminal T2 is electrically connected to the filament fixing member  17 . 
     The sub frame  13  is a long member having a substantially U-shaped cross section. The sub frame  13  is disposed parallel to the main frame  11 . The power supply line  14  is connected to the tension holding unit  20  from a connection position with the filament terminal T1 through the inside (an inside space) of the sub frame  13 . The sub frame  13  has a protective function for the power supply line  14 . The main frame  11  and the sub frame  13  are connected to each other by a plurality of guide members  15 . An outer surface of the guide member  15  is slidably in contact with an inner surface of the rail  6 . 
     The grid electrode  12  is disposed on the front side with respect to the filament  10  and is supported by the guide member  15  via an insulation member  18 . A plurality of holes are formed in the grid electrode  12  (see  FIG.  4    and the like). The grid electrode  12  is electrically connected to the grid electrode terminal T3 via a wiring (not shown). 
     The tension holding unit  20  holds tension of the filament  10 . Here, the tension holding unit  20  can hold the tension of the filament  10  by pressing or pulling a movable body connected to the one end of the filament  10  by a spring. In the present embodiment, the tension holding unit  20  holds the tension of the filament  10  by pulling the movable body by the spring. The tension holding unit  20  is attached to the main frame  11  in a state where the tension holding unit  20  is electrically insulated from the main frame  11  via an insulation member or the like. One end of the power supply line  14  is connected to the tension holding unit  20 . The tension holding unit  20  can supply the electric power supplied via the power supply line  14  to the filament  10  while holding the tension of the filament  10 . 
     The filament unit  2  is inserted into the inside (the inside space) of the rail  6  through the insertion holes provided in the cathode holding member  5  and the insulation support member  8  with the other end provided with the filament terminal T1 or the like as a head and is fixed thereto. At a position where the filament unit  2  has been inserted, tip ends of the filament terminal T1, the high voltage terminal T2, and the grid electrode terminal T3 are in contact with tip ends of three connection terminals provided in the high voltage introduction insulation member  7 . As a result, the filament terminal T1 and the like are electrically connected to the connection terminals provided in the high voltage introduction insulation member  7 . 
     The filament  10  discharges electrons when a high negative voltage such as minus several tens of kV to minus several hundreds of kV is applied in a state where the filament  10  is heated by energization. A predetermined voltage is applied to the grid electrode  12 . For example, a voltage on a positive side of about 100 V to 150 V with respect to the negative voltage applied to the filament  10  may be applied to the grid electrode  12 . The grid electrode  12  forms an electric field for drawing out electrons and curbing diffusion of the electrons. As a result, the electrons discharged from the filament  10  are emitted to the front side as the electron beams EB from the holes provided in the grid electrode  12 . 
     Next, the details of the tension holding unit  20  for holding the tension of the filament  10  will be described with reference to  FIGS.  6  and  7   . In the following description, for convenience of explanation, a side (the other side) on which the filament  10  is provided with respect to the tension holding unit  20  is referred to as a “left side,” and a side (one side) on which the tension holding unit  20  is provided with respect to the filament  10  is referred to as a “right side.” That is, a left-right direction is a direction along the axis L extending from the one side to the other side. 
     As shown in  FIGS.  6  and  7   , the tension holding unit  20  includes a movable body (a movable part)  21 , a housing (a support part, a housing part)  22 , a spring (a tension holding part)  23 , and a foil material (a power supply path part)  24 . The movable body  21  is connected to the one end of the filament  10 . The movable body  21  has a circular column  21   a  and a connection part  21   b . The circular column  21   a  has a circular column shape extending in the left-right direction. The one end of the filament  10  is fixed to an end of the circular column  21   a  on the left side. As a method for fixing the circular column  21   a  and the filament  10  to each other, various methods can be adopted. The connection part  21   b  is connected to an end of the circular column  21   a  on the right side. The other end of the spring  23  and the other end of the foil material  24  are connected to the connection part  21   b . The movable body  21  is formed of a conductive material. The movable body  21  is formed of, for example, a material such as stainless steel, copper, or a copper alloy. 
     The movable body  21  is provided on the axis L. A state in which the movable body  21  is provided on the axis L is a disposition state in which the axis L is positioned inside an outer edge of the movable body  21  when viewed from the direction along the axis L. The same intention applies to a state in which other members are provided on the axis L. Further, the movable body  21  may be disposed such that a position of a center of gravity of the movable body  21  is positioned on the axis L. 
     The housing  22  is a box body having an accommodation space (an internal space) S inside. The spring  23 , the foil material  24 , and the end of the movable body  21  on the right side are accommodated in the accommodation space S of the housing  22 . The housing  22  may be constituted by a box part  22   a  having an open surface such that the spring  23  and the like can be accommodated in the accommodation space S and a lid  22   b  covering an opening of the box part  22   a . A guide hole (a movable part holding part)  22   d  is provided in a filament side wall  22   c  (a wall on the left side which constitutes the housing  22 ) which is a wall of the housing  22  on a side of the filament  10  (the other side). The guide hole  22   d  extends along the axis L. Further, the guide hole  22   d  is a through hole having a circular column shape extending along the axis L. A diameter of the guide hole  22   d  is larger than a diameter of the circular column  21   a  of the movable body  21  by a desired value. The guide hole  22   d  guides the circular column  21   a  of the movable body  21  to be movable along the axis L. That is, the housing  22  holds the movable body  21  to be movable along the axis L by the guide hole  22   d.    
     A power supply line connection part  22   f  to which the one end of the power supply line  14  is connected is provided in a power supply side wall  22   e  (a wall on the right side constituting the housing  22 ) which is a wall on a side (the one side) opposite to a side of the filament  10  in the housing  22 . For example, the end of the power supply line  14  is electrically connected to the housing  22  by a bolt at the power supply line connection part  22   f . As a result, the housing  22  is electrically connected to a power source device (a power supply device) that supplies power to the filament  10  via the power supply line  14  and the like. The housing  22  is formed of a conductive material. The housing  22  is formed of, for example, a material such as stainless steel, copper, or a copper alloy. 
     The spring  23  is accommodated in the accommodation space S of the housing  22 . The spring  23  is provided on the axis L. The other end of the spring  23  is connected to an end of the connection part  21   b  on the right side. A connection position between the spring  23  and the connection part  21   b  is positioned on the axis L. One end of the spring  23  is connected to the power supply side wall  22   e  of the housing  22 . The housing  22  covers the spring  23  such that the spring  23  cannot be seen directly from the filament  10 . A connection position (a connection portion) between the spring  23  and the movable body  21  is positioned in the accommodation space S. 
     The spring  23  is a tension spring. The spring  23  applies a tensile force to the movable body  21  such that the movable body  21  moves along the axis L. That is, the spring  23  pulls the movable body  21  in one side direction along the axis L from the connection position to the movable body  21 . The movable body  21  connects the one end of the filament  10  and the other end of the spring  23  to each other. As a result, the spring  23  pulls the filament  10  via the movable body  21  by applying a tensile force to the movable body  21  and holds the tension of the filament  10 . The spring  23  is formed of, for example, a material such as stainless steel or Inconel. The spring  23  may be formed of a material which is different from the filament  10 . A load of the spring  23  needs to be in a desired range during an operation (when the filament  10  is energized), and if the load deviates from that range, problems such as loosening, plastic deformation, and disconnection of the filament  10  may occur. Therefore, when the load of the spring  23  is Fa, an allowable tensile load of the filament  10  is Fx, and the sum of a weight and a frictional force of the movable body  21  is Fy, a relationship of Fx+Fy&gt;Fa needs to be established. Further, it should be noted that the heating of the filament  10  by energization causes a relationship of the allowable tensile load of the filament  10 , that is, the allowable tensile load Fx1 at a room temperature &gt;the allowable tensile load Fx2 at the time of heating. Therefore, the load of the spring  23  is preferably in the range of 0.01 N to 1000 N, more preferably 0.01 N to 100 N, and even more preferably 0.1 N to 10 N. 
     The foil material  24  is accommodated in the accommodation space S of the housing  22 . The foil material  24  serves as a power supply path for supplying the electric power supplied to the housing  22  via the power supply line  14  to the movable body  21 . One end of the foil material  24  is connected to the power supply side wall  22   e  of the housing  22 , and the other end of the foil material  24  is connected to the connection part  21   b  of the movable body  21 . A connection portion between the foil material  24  and the movable body  21  is positioned in the accommodation space S. As a result, the foil material  24  is electrically connected to the filament  10  via the movable body  21 . The foil material  24  is formed of a material having a better electrical conductivity than the spring  23 . That is, an electric resistance value of the spring  23  is larger than an electric resistance value of the foil material  24 . The foil material  24  is formed of, for example, copper or the like as a material having a good electrical conductivity and a good flexibility. For example, in a case where the spring  23  is formed of stainless steel, the electric resistance is about 6Ω. For example, copper is used as the material of the foil material  24 , and a length thereof is, for example, 50 mm. An electrical resistivity of copper is 1.7×10 −8  Ω·m. Therefore, if a cross-sectional area of the foil material  24  is 1.4×10 −2  mm 2  or more, the electric resistance value of the foil material  24  can be sufficiently lowered to 1/100 or less of the electric resistance value of the spring  23  formed of stainless steel. 
     The foil material  24  is a thin film shaped member formed of a metal (a metal thin film part). A thickness of the foil material  24  is thinner than a width of the foil material  24 , and the width of the foil material  24  is smaller than a length of the foil material  24 . The foil material  24  extends from the power supply side wall  22   e  toward the movable body  21  and is fixed to the connection part  21   b  in a state where a tip end is folded back in a U shape. As described above, the foil material  24  has a folded-back part  24   a  which is folded back in a U shape and includes regions which are overlapped each other (doubled) in a positional relationship along the axis L at an end on the left side thereof, and the regions are separated from each other in a direction perpendicular to the axis L. Therefore, the length of the foil material  24  is longer than that of the spring  23  and longer than a length (a length of a straight line) from a connection position A between the foil material  24  and the power supply side wall  22   e  to a connection position B between the foil material  24  and the movable body  21 . As a result, even in a case where the movable body  21  moves along the axis L, the position of the folded-back part  24   a  moves in the foil material  24  (the doubled regions become larger or smaller), and thus the foil material  24  can maintain a state in which the power supply side wall  22   e  and the movable body  21  are connected to each other while allowing the movable body  21  to move. 
     As shown in  FIG.  7   , the housing  22  may further include a partitioning part  22   g  in which one end is fixed to the power supply side wall  22   e  and the other end extends toward the movable body  21 . The partitioning part  22   g  extends from the end of the spring  23  on the left side to the end of the spring  23  on the left side to place the foil material  24  in a state where the partitioning part  22   g  is separated from the spring  23  and partitions the spring  23  and the foil material  24  from each other. As a result, the foil material  24  is prevented from coining into contact with the spring  23 . 
     In this way, the tension holding unit  20  can maintain the tension of the filament  10  with the tensile force of the spring  23 . Further, a length (a free length) of the spring  23  is such that a tensile force can be applied to the movable body  21  even in a case where a length of the filament  10  becomes longer due to thermal expansion. For example, in a case where the material forming the filament  10  is tungsten, when the filament  10  having a total length of 500 mm is heated to 2000° C., the filament  10  becomes longer by about 5 mm due to thermal expansion with a coefficient of linear expansion of tungsten of 5.2×10 −6  [1/K] (2000° C.). Therefore, in order to absorb the thermal expansion length of the filament  10 , the movable body  21  needs to be able to move by at least about 5 mm In addition, it is more preferable to secure a moving range in consideration of thermal expansion of peripheral members (for example, the main frame  11 ). As a result, the tension holding unit  20  can maintain the tension of the filament  10  with the tensile force of the spring  23  even in a case where the length of the filament  10  changes due to thermal expansion. In this way, a state where the filament  10  is stretched in a straight linear shape by the tension holding unit  20  is maintained. 
     Further, in the tension holding unit  20 , the power supply side wall  22   e  to which the power supply line  14  is connected and the movable body  21  to which the filament  10  is connected are connected to each other by the spring  23  and the foil material  24 . Here, the foil material  24  is formed of a material having a better electrical conductivity than the spring  23 . As a result, the electric power is supplied from the power supply side wall  22   e  to the movable body  21  mainly through the foil material  24  rather than the spring  23 . As a result, heat generation of the spring  23  due to energization is curbed, and thus fluctuations in the tensile force, deterioration, or the like of the spring  23  due to the influence of heat is curbed. In this way, the tension holding unit  20  can hold the tension of the filament  10  by the spring  23  while supplying the electric power to the filament  10  through the foil material  24  via the movable body  21 . More specifically, since the electric power supply to the filament  10  is performed via the movable body  21 , the movable body  21  is in charge of rubbing or the like due to the mechanical sliding operation caused by the expansion and contraction of the spring  23 , and thus it is possible to curb the influence on the holding of the tension of the filament  10  by the spring  23  and the electric power supply to the filament  10  by the foil material  24  while curbing the mechanical damage to the filament  10 . 
     As described above, in the electron beam emission device  1  (the filament unit  2 ), the filament  10 , the movable body  21 , and the spring  23  are provided on the same axis L. Therefore, the electron beam emission device  1  can easily apply the tensile force of the spring  23  to the filament  10  via the movable body  21  in the direction of the axis L. As a result, even in a case where the tensile force of the spring  23  is applied, axial deviation (deviation from the axis L) of the filament  10  is curbed. In this way, the electron beam emission device  1  can appropriately apply the tensile force of the spring  23  to the filament  10  to curb the axial deviation of the filament  10 . As a result, it is possible to obtain more uniform electron discharge distribution. 
     The spring  23  applies a tensile force to the movable body  21  such that the movable body  21  moves along the axis L. In this case, the electron beam emission device  1  can further curb the axial deviation of the filament  10  in a case where the tensile force of the spring  23  is applied. 
     In a case where the position of a center of gravity of the movable body  21  is disposed to be positioned on the axis L, even in a case where the tensile force of the spring  23  is applied, the movable body  21  swinging due to action of a moment is curbed. As a result, the electron beam emission device  1  can further curb the axial deviation of the filament  10 . 
     Since the filament  10  and the spring  23  are formed of different members, the electron beam emission device  1  can curb the conduction of heat from the filament  10  to the spring  23  and can curb the heating of the spring  23 . 
     The spring  23  is accommodated in the accommodation space S of the housing  22 . In this case, the electron beam emission device  1  can curb the influence of the radiant heat from the filament  10  on the spring  23 . As a result, the electron beam emission device  1  can curb fluctuations in the tensile force of the spring  23  due to the influence of heat and deterioration due to heat and can stably hold the tension of the filament  10 . 
     The housing  22  covers the spring  23  such that the spring  23  cannot be seen directly from the filament  10 . In this case, the electron beam emission device  1  can prevent the electrons discharged from the filament  10  from directly hitting the spring  23  and can curb heating deterioration and damage caused by the collision of the electrons. 
     The housing  22  is provided with the guide hole  22   d  extending along the axis L and holding the movable body  21  to be movable along the axis L. In this case, the housing  22  can stably hold the movable body  21  to be movable by the guide hole  22   d.    
     The guide hole  22   d  is a through hole having a circular column shape extending along the axis L. In this case, the movable body  21  can rotate in the guide hole  22   d . As a result, in the tension holding unit  20 , for example, even if the spring  23  is twisted at the time of expansion and contraction of the spring  23  and a force in a rotational direction is applied to the movable body  21 , it is possible to hold the tension of the filament  10  while curbing the concentration of a force of the twisting on a part of the movable body  21  by the rotation of the movable body  21  in the guide hole  22   d . As a result, the electron beam emission device  1  can curb the influence of the twisting even in a case where the spring  23  is twisted. 
     The filament  10  has a straight linear shape due to the tension being held by the tension holding unit  20 . In this case, the electron beam emission device  1  can uniformly emit electrons at each position in the direction of the axis L. 
     The filament unit  2  includes the main frame  11  that holds the tension holding unit  20  to which the one end of the filament  10  is connected and the filament fixing member  17  to which the other end of the filament  10  is connected. In this case, the filament unit  2  can be easily handled by making the filament unit  2  into one body using the main frame  11 . Further, since the filament unit  2  can be attached to and detached from the rail  6  of the electron beam emission device  1 , and the filament  10  and the tension holding unit  20  are attached to and detached from the rail  6  of the electron beam emission device  1  together with the filament unit  2 . 
     Next, various modification examples of the tension holding unit provided in the electron beam emission device  1  will be described. Hereinafter, a difference from the tension holding unit  20  in the above embodiment and a difference between tension holding units in the modification examples will be mainly described. 
     First Modification Example 
     As shown in  FIG.  8   , a tension holding unit  20 A in a first modification example includes a movable body  21 A, a housing  22 A, a spring  23 , and an annular elastic body (a power supply path part)  25 . The movable body  21 A has a circular column shape extending in the left-right direction. The one end of the filament  10  is fixed to an end of the movable body  21 A on the left side. The other end of the spring  23  is connected to an end of the movable body  21 A on the right side. The movable body  21 A is provided on the axis L. Further, the movable body  21 A is disposed such that a position of a center of gravity of the movable body  21 A is positioned on the axis L. The movable body  21 A is formed of a conductive material. The movable body  21 A is formed of, for example, a copper alloy, stainless steel, or the like as a material having a good electrical conductivity. 
     The housing  22 A is a box body having an accommodation space S inside. The spring  23  is accommodated in the accommodation space S of the housing  22 A. The housing  22 A may be constituted by a box part  22   a  having an open surface such that the spring  23  can be accommodated in the accommodation space S. A guide hole  22   d  is provided in a filament side wall  22   c  of the housing  22 A. A diameter of the guide hole  22   d  is larger than a diameter of the movable body  21 A by a desired value. A length of the guide hole  22   d  in the direction of the axis L is longer than a length of the movable body  21 A. The guide hole  22   d  guides the movable body  21 A to be movable along the axis L. That is, the housing  22 A holds the movable body  21 A to be movable along the axis L by the guide hole  22   d . The housing  22 A is formed of a conductive material. The housing  22 A is formed of, for example, a copper alloy, stainless steel, or the like as a material having a good electrical conductivity. 
     The spring  23  is provided on the axis L. The other end of the spring  23  is connected to an end of the movable body  21 A on the right side. A connection position between the spring  23  and the movable body  21 A is positioned on the axis L. One end of the spring  23  is connected to a power supply side wall  22   e  of the housing  22 A. The housing  22 A covers the spring  23  such that the spring  23  cannot be seen directly from the filament  10 . 
     The spring  23  applies a tensile force to the movable body  21 A such that the movable body  21 A moves along the axis L. That is, the spring  23  pulls the movable body  21 A in one side direction along the axis L from the connection position to the movable body  21 A. As a result, the spring  23  pulls the filament  10  via the movable body  21 A by applying a tensile force to the movable body  21 A and holds the tension of the filament  10 . 
     The annular elastic body  25  is accommodated in the guide hole  22   d  of the housing  22 A. The annular elastic body  25  serves as a power supply path for supplying the electric power supplied to the housing  22 A via the power supply line  14  to the movable body  21 A. The annular elastic body  25  is formed of an elastic member having an annular shape and conductivity. The annular elastic body  25  is fitted into a recess  21   c  extending over the entire region in a circumferential direction in an outer peripheral surface of the movable body  21 A in a cross section in the direction perpendicular to the axis L. 
     A portion of an outer peripheral edge (one end) of the annular elastic body  25  in a radial direction (a direction perpendicular to the axis L) is in contact with an inner peripheral surface of the guide hole  22   d  of the housing  22 A and is electrically connected thereto. A portion of an inner peripheral edge (the other end) of the annular elastic body  25  in the radial direction is in contact with an outer peripheral surface (an inner wall surface of the recess  21   c ) of the movable body  21 A and is electrically connected thereto. That is, in the state where the annular elastic body  25  is fitted into the recess  21   c , a diameter of an outer periphery of the annular elastic body  25  is larger than a diameter of an outer periphery of the movable body  21 A, and a diameter of an inner periphery of the annular elastic body  25  is smaller than at least a diameter of an outer periphery of the movable body  21 A. As a result, the annular elastic body  25  is electrically connected to the housing  22 A and is also electrically connected to the filament  10  via the movable body  21 A. The annular elastic body  25  is formed of a material having a better electrical conductivity than the spring  23 . That is, an electric resistance value of the spring  23  is larger than an electric resistance value of the annular elastic body  25 . The annular elastic body  25  is formed of, for example, a copper alloy or the like as a material having a good electrical conductivity. 
     In this way, the tension holding unit  20 A can maintain the tension of the filament  10  with the tensile force of the spring  23  as in the tension holding unit  20  in the embodiment. Further, in the tension holding unit  20 A, the housing  22 A and the movable body  21 A are connected to each other by the spring  23  and the annular elastic body  25 . Further, the annular elastic body  25  is formed of a material having a better electrical conductivity than the spring  23 . As a result, the electric power is supplied from the housing  22 A to the movable body  21 A mainly through the annular elastic body  25  rather than the spring  23 . As a result, heat generation of the spring  23  due to energization is curbed, and thus fluctuations in the tensile force, deterioration, or the like of the spring  23  due to the influence of heat is curbed. In this way, the tension holding unit  20 A can hold the tension of the filament  10  by the spring  23  while supplying the electric power to the filament  10  through the annular elastic body  25  via the movable body  21 A. 
     As described above, also in a case where the electron beam emission device  1  is provided with the tension holding unit  20 A, it is possible to exhibit the same operation and effect as in the case where the electron beam emission device  1  is provided with the tension holding unit  20  in the embodiment. 
     Second Modification Example 
     As shown in  FIG.  9   , a tension holding unit  20 B in a second modification example includes a movable body  21 B, a housing  22 B, a spring (a tension holding part)  26 , and a foil material (a power supply path part)  27 . The movable body  21 B is connected to the one end of the filament  10 . The movable body  21 B has a circular column  21   a  and a small-diameter circular column  21   d . The small-diameter circular column  21   d  includes a main body  21   d   1  having a diameter smaller than that of the circular column  21   a  and a tip end  21   d   2  having a diameter smaller than that of the main body  21   d   1 . The main body  21   d   1  is connected to an end of the circular column  21   a  on the left side, and the tip end  21   d   2  is connected to an end of the main body  21   d   1  on the left side. The one end of the filament  10  is fixed to an end of the tip end  21   d   2  of the small-diameter circular column  21   d  on the left side. The movable body  21 B is provided on the axis L. Further, the movable body  21 B is disposed such that a position of a center of gravity of the movable body  21 B is positioned on the axis L. The movable body  21 B is formed of a conductive material. The movable body  21 B is formed of, for example, a material such as stainless steel, copper, or a copper alloy. 
     The housing  22 B further includes a housing side spring receiving part (a housing side tension receiving part)  22   h  with respect to the housing  22 A (see  FIG.  8   ) in the first modification example. The housing side spring receiving part  22   h  is provided on a surface of the filament side wall  22   c  on a side of the filament  10  (the other side). The housing side spring receiving part  22   h  is provided with a small-diameter hole  22   j  through which the tip end  21   d   2  of the small-diameter circular column  21   d  of the movable body  21 B can be inserted. A diameter of the small-diameter hole  22   j  is smaller than a diameter of a guide hole  22   d  and larger than a diameter of the tip end  21   d   2 . The housing  22 B is formed of a conductive material. The housing  22 B is formed of, for example, a material such as stainless steel, copper, or a copper alloy. 
     The spring  26  is accommodated in the guide hole  22   d  of the housing  22 B. The spring  26  is provided on the axis L. The main body  21   d   1  of the small-diameter circular column  21   d  of the movable body  21 B passes through the inside of the spring  26 . That is, an outer diameter of the spring  26  is smaller than an inner diameter of the guide hole  22   d , and an inner diameter of the spring  26  is larger than an outer diameter of the main body  21   d   1  of the small-diameter circular column  21   d . One end of the spring  26  is in contact with an end face of the circular column  21   a  of the movable body  21 B on the left side. The other end of the spring  26  is in contact with a surface of the housing side spring receiving part  22   h  on the right side. That is, the end surface of the circular column  21   a  of the movable body  21 B on the left side becomes a movable body side spring receiving part (a movable body side tension receiving part)  21   e  with which the spring  26  is in contact. The housing side spring receiving part  22   h  is positioned on a side of the filament  10  from the movable body side spring receiving part  21   e . The spring  26  is disposed between the movable body side spring receiving part  21   e  and the housing side spring receiving part  22   h . The housing side spring receiving part  22   h  covers the spring  26  such that the spring  26  cannot be seen directly from the filament  10  (partitions the filament  10  the spring  26  from each other). 
     The spring  26  is a compression spring. The spring  26  applies a pressing force to the movable body  21 B such that the movable body  21 B moves along the axis L. That is, the spring  26  presses the movable body  21 B in one side direction along the axis L from a contact position with the movable body  21 B. The movable body  21 B is connected to the one end of the filament  10 . As a result, the spring  26  pulls the filament  10  in a right direction via the movable body  21 B by applying a pressing force to the movable body  21 B and holds the tension of the filament  10 . The spring  26  is formed of, for example, a material such as stainless steel or Inconel. The spring  26  may be formed of a material which is different from the filament  10 . 
     The foil material  27  is accommodated in the accommodation space S of the housing  22 B. The foil material  27  serves as a power supply path for supplying the electric power supplied to the housing  22 B via the power supply line  14  to the movable body  21 B. One end of the foil material  27  is connected to the power supply side wall  22   e  of the housing  22 B, and the other end of the foil material  27  is connected to the circular column  21   a  of the movable body  21 B. As a result, the foil material  27  is electrically connected to the filament  10  via the movable body  21 B. The foil material  27  is formed of a material having a better electrical conductivity than the spring  26 . That is, an electric resistance value of the spring  26  is larger than an electric resistance value of the foil material  27 . The foil material  27  is formed of, for example, copper or the like as a material having a good electrical conductivity and a good flexibility. 
     The foil material  27  is a thin film shaped member formed of a metal (a metal thin film part). A thickness of the foil material  27  is thinner than a width of the foil material  27 , and the width of the foil material  27  is smaller than a length of the foil material  27 . The length of the foil material  27  is longer than a length (a length of a straight line along the axis L) from a connection position A between the foil material  27  and the power supply side wall  22   e  to a connection position B between the foil material  27  and the movable body  21 B. As a result, even in a case where the movable body  21 B moves along the axis L, the foil material  24  can maintain a state in which the power supply side wall  22   e  and the movable body  21 B are connected to each other while allowing the movable body  21 B to move. 
     In this way, the tension holding unit  20 B can maintain the tension of the filament  10  with the pressing force of the spring  26 . Further, a length (a free length) of the spring  26  is such that a pressing force can be applied to the movable body  21 B even in a case where a length of the filament  10  becomes longer due to thermal expansion. As a result, the tension holding unit  20 B can maintain the tension of the filament  10  with the pressing force of the spring  26  even in a case where the length of the filament  10  changes due to thermal expansion. In this way, a state where the filament  10  is stretched in a straight linear shape by the tension holding unit  20 B is maintained. 
     Further, in the tension holding unit  20 B, the housing  22 B and the movable body  21 B are connected to each other by the spring  26  and the foil material  27 . Here, the foil material  27  is formed of a material having a better electrical conductivity than the spring  26 . As a result, the electric power is supplied from the power supply side wall  22   e  to the movable body  21 B mainly through the foil material  27  rather than the spring  26 . As a result, heat generation of the spring  26  due to energization is curbed, and thus fluctuations in the pressing force or the like of the spring  26  due to the influence of heat is curbed. In this way, the tension holding unit  20 B can hold the tension of the filament  10  by the spring  26  while supplying the electric power to the filament  10  through the foil material  27  via the movable body  21 B. 
     As described above, also in a case where the electron beam emission device  1  is provided with the tension holding unit  20 B, it is possible to exhibit the same operation and effect as in the case where the electron beam emission device  1  is provided with the tension holding unit  20  in the embodiment. 
     As described above, in the electron beam emission device  1  (the filament unit  2 ) provided with the tension holding unit  20 B, the filament  10 , the movable body  21 B, and the spring  26  are provided on the same axis L. Therefore, the electron beam emission device  1  can easily apply the pressing force of the spring  26  to the filament  10  via the movable body  21 B in the direction of the axis L. As a result, even in a case where the pressing force of the spring  26  is applied, axial deviation (deviation from the axis L) of the filament  10  is curbed. In this way, the electron beam emission device  1  provided with the tension holding unit  20 B can appropriately apply the pressing force of the spring  26  to the filament  10  to curb the axial deviation of the filament  10 . As a result, it is possible to obtain more uniform electron discharge distribution. 
     The spring  26  applies a pressing force to the movable body  21 B such that the movable body  21 B moves along the axis L. In this case, the electron beam emission device  1  provided with the tension holding unit  20 B can further curb the axial deviation of the filament  10  in a case where the pressing force of the spring  26  is applied. 
     The movable body  21 B is disposed such that a position of a center of gravity of the movable body  21 B is positioned on the axis L. In this case, even in a case where the pressing force of the spring  26  is applied, the movable body  21 B swinging due to action of a moment is curbed. As a result, the electron beam emission device  1  provided with the tension holding unit  20 B can further curb the axial deviation of the filament  10 . 
     The filament  10  and the spring  26  are formed of different members. In this case, the electron beam emission device  1  provided with the tension holding unit  20 B can curb the conduction of heat from the filament  10  to the spring  26  and can curb the heating of the spring  26 . 
     The spring  26  is accommodated in the guide hole  22   d  of the housing  22 B. In this case, the electron beam emission device  1  provided with the tension holding unit  20 B can curb the influence of the radiant heat from the filament  10  on the spring  26 . As a result, the electron beam emission device  1  provided with the tension holding unit  20 B can curb fluctuations in the pressing force of the spring  26  due to the influence of heat and deterioration due to heat and can stably hold the tension of the filament  10 . 
     The small-diameter hole  22   j  provided in the housing side spring receiving part  22   h  has a smaller diameter than the guide hole  22   d  and has a diameter sufficient for the small-diameter circular column  21   d  to pass therethrough. Further, the housing side spring receiving part  22   h  covers the spring  26  such that the spring  26  cannot be seen directly from the filament  10 . In this case, the electron beam emission device  1  provided with the tension holding unit  20 B can prevent the electrons discharged from the filament  10  from directly hitting the spring  26  and can curb heating deterioration and damage caused by the collision of the electrons. 
     Third Modification Example 
     As shown in  FIG.  10   , a tension holding unit  20 C in a third modification example is configured to include the annular elastic body  25  of the tension holding unit  20 A (see  FIG.  8   ) in the first modification example instead of the foil material  27  in the configuration of the tension holding unit  20 B (see  FIG.  9   ) in the second modification example. Specifically, the tension holding unit  20 C includes a movable body  21 C, a housing  22 B, an annular elastic body (a power supply path part)  25 , and a spring  26 . A recess  21   c  is provided in an outer peripheral surface of a circular column  21   a  of the movable body  21 C. The annular elastic body  25  is fitted into the recess  21   c  of the circular column  21   a.    
     The tension holding unit  20 C can maintain the tension of the filament  10  with the pressing force of the spring  26  as in the tension holding unit  20 B in the second modification example. Further, in the tension holding unit  20 C, the housing  22 B and the movable body  21 C are connected to each other by the annular elastic body  25  and spring  26 . Here, the annular elastic body  25  is formed of a material having a better electrical conductivity than the spring  26 . As a result, the electric power is supplied from the housing  22 B to the movable body  21 C mainly through the annular elastic body  25  rather than the spring  26 . As a result, heat generation of the spring  26  due to energization is curbed, and thus fluctuations in the pressing force or the like of the spring  26  due to the influence of heat is curbed. In this way, the tension holding unit  20 C can hold the tension of the filament  10  by the spring  26  while supplying the electric power to the filament  10  through the annular elastic body  25  via the movable body  21 C. 
     As described above, also in a case where the electron beam emission device  1  is provided with the tension holding unit  20 C, it is possible to exhibit the same operation and effect as in the case where the electron beam emission device  1  is provided with the tension holding unit  20 B in the second modification example. 
     Fourth Modification Example 
     As shown in  FIG.  11   , a tension holding unit  20 D in a fourth modification example further includes an insulation ring (an insulation member)  28  and an insulation ring (and insulation member)  29  with respect to the configuration of the tension holding unit  20 B (see  FIG.  9   ) in the second modification example. That is, the tension holding unit  20 D includes a movable body  21 B, a housing  22 B, a spring  26 , a foil material  27 , an insulation ring  28 , and an insulation ring  29 . 
     The insulation ring  28  is disposed between the spring  26  and a housing side spring receiving part  22   h . The insulation ring  28  electrically insulates the housing  22 B and the spring  26  from each other. The insulation ring  28  is formed of a material having a less conductivity than the spring  26 . An outer edge of the insulation ring  28  projects toward the spring  26  in a direction along the axis L to surround an outer peripheral portion of the spring  26 . As a result, the insulation ring  28  can prevent the outer peripheral portion of the spring  26  from coining into contact with the inner peripheral surface of the guide hole  22   d . Further, the spring  26  is also positioned in the direction perpendicular to the axis L by an inner peripheral portion of the insulation ring  28 , and thus the contact between the spring  26  and the small-diameter circular column  21   d  of the movable body  21 B is also curbed. 
     Similarly, the insulation ring  29  is disposed between the movable body side spring receiving part  21   e  of the circular column  21   a  of the movable body  21 B and the spring  26 . The insulation ring  29  electrically insulates the movable body  21 B and the spring  26  from each other. The insulation ring  29  is formed of a material having a less conductivity than the spring  26 . An outer edge of the insulation ring  29  projects toward the spring  26  in a direction along the axis L to surround an outer peripheral portion of the spring  26 . As a result, the insulation ring  29  can prevent the outer peripheral portion of the spring  26  from coining into contact with the inner peripheral surface of the guide hole  22   d . Further, the spring  26  is also positioned in the direction perpendicular to the axis L by an inner peripheral portion of the insulation ring  29 , and thus the contact between the spring  26  and the small-diameter circular column  21   d  of the movable body  21 B is also curbed. 
     The tension holding unit  20 D may be configured to include only any one of the insulation ring  28  and the insulation ring  29 . 
     As described above, the tension holding unit  20 D in the fourth modification example can further curb the flow of electricity to the spring  26  by providing the insulation rings  28  and  29 . As a result, the tension holding unit  20 D can further curb heat generation of the spring  26  due to energization. 
     Fifth Modification Example 
     As shown in  FIG.  12   , a tension holding unit  20 E in a fifth modification example further includes an insulation ring (an insulation member)  28  and an insulation ring (and insulation member)  29  with respect to the configuration of the tension holding unit  20 C (see  FIG.  10   ) in the third modification example. That is, the tension holding unit  20 E includes a movable body  21 C, a housing  22 B, an annular elastic body  25 , a spring  26 , an insulation ring  28 , and an insulation ring  29 . The insulation rings  28  and  29  have the same configuration as the insulation rings  28  and  29  in the fourth modification example. 
     As described above, the tension holding unit  20 E in the fifth modification example can further curb the flow of electricity to the spring  26  by providing the insulation rings  28  and  29 . As a result, the tension holding unit  20 E can further curb heat generation of the spring  26  due to energization. 
     Here, for example, even in the tension holding unit  20  in the embodiment described with reference to  FIGS.  6  and  7   , it is possible to further curb the flow of electricity to the spring  23 . Specifically, in the connection part  21   b  of the tension holding unit  20  shown in  FIGS.  6  and  7   , a portion to which the spring  23  is connected (a portion to be hooked) may be made of an insulation material (for example, ceramic or the like). Alternatively, the portion of the connection part  21   b  to which the spring  23  is connected may be subjected to insulation coating. Further, the spring  23  of the tension holding unit  20  may be subjected to insulation coating. Similarly, for example, in the movable body  21 A of the tension holding unit  20 A of the first modification example described with reference to  FIG.  8   , a portion to which the spring  23  is connected (a portion to be hooked) may be made of an insulation material (for example, ceramic or the like). Alternatively, the portion of the movable body  21 A to which the spring  23  is connected may be subjected to insulation coating. Further, the spring  23  of the tension holding unit  20 A may be subjected to insulation coating. Even in these cases, the tension holding units  20  and  20 A can further curb the flow of electricity to the spring  23  and can further curb heat generation of the spring  23  due to energization. 
     Sixth Modification Example 
     As shown in  FIG.  13   , in a tension holding unit  20 F in a sixth modification example, the housing  22  of the tension holding unit  20  in the embodiment is divided into two. Specifically, the tension holding unit  20 F includes a movable body  21 , a housing  22 F, a spring  23 , and a foil material  24 . The housing  22 F includes a first housing  22   k  and a second housing  22   m.    
     The first housing  22   k  is provided with the guide hole  22   d  through which the circular column  21   a  of the movable body  21  passes. The second housing  22   m  has the accommodation space S for accommodating the spring  23  and a portion of the foil material  24  on a side of the power supply side wall  22   e . The first housing  22   k  and the second housing  22   m  are attached to the main frame  11  of the filament unit  2  via an insulation material. That is, the first housing  22   k  and the second housing  22   m  are electrically insulated from each other. 
     As described above, also in a case where the electron beam emission device  1  is provided with the tension holding unit  20 F, it is possible to exhibit the same operation and effect as in the case where the electron beam emission device  1  is provided with the tension holding unit  20  in the embodiment. Further, the tension holding unit  20 F can supply the electric power to the movable body  21  from the power supply side wall  22   e  via the foil material  24  without directly supplying the electric power to the movable body  21  from the inner peripheral surface of the guide hole  22   d  provided in the first housing  22   k . In this way, the tension holding unit  20 F is not configured to supply the electric power via the members sliding on each other, and thus it is possible to supply the electric power to the movable body  21  more reliably. 
     Seventh Modification Example 
     As shown in  FIG.  14   , in a tension holding unit  20 G in a seventh modification example, the housing  22 A of the tension holding unit  20 A in the first modification example is divided into two. Specifically, the tension holding unit  20 G includes a movable body  21 A, a housing  22 G, a spring  23 , and an annular elastic body  25 . The housing  22 G includes a first housing  22   n  and a second housing  22   p.    
     The first housing  22   n  is provided with the guide hole  22   d  through which the movable body  21 A passes. The one end of the spring  23  is connected to an end of the movable body  21 A on the right side. The other end of the spring  23  is connected to the second housing  22   p . The first housing  22   n  and the second housing  22   p  are attached to the main frame  11  of the filament unit  2  via an insulation material. That is, the first housing  22   n  and the second housing  22   p  are electrically insulated from each other. 
     The end of the power supply line  14  is connected to the first housing  22   n . In the tension holding unit  20 G, the electric power is supplied from the first housing  22   n  to the filament  10  via the annular elastic body  25  and the movable body  21 A. As a result, heat generation of the spring  23  due to energization is curbed, and thus fluctuations in the tensile force or the like of the spring  23  due to the influence of heat is curbed. In this way, the tension holding unit  20 G can hold the tension of the filament  10  by the spring  23  while supplying the electric power to the filament  10  through the annular elastic body  25  via the movable body  21 A. 
     Example of Filament Fixing Method 
     Next, an example of a method of fixing the filament  10  to the tip end of the movable body  21  of the tension holding unit  20  in the embodiment will be described. The method of fixing the filament  10 , which will be described below, is also applicable to the various modification examples of the tension holding unit described above. As shown in  FIG.  15   , a bolt hole  21   f  extending along the axis L is provided in the tip end surface (the other end surface) of the circular column  21   a  of the movable body  21 . A filament fixing member  40  is attached to the tip end (the one end side) of the filament  10 . The filament fixing member  40  includes a tubular part  41  and a flange  42 . The tip end of the filament  10  is inserted into the tubular part  41  and fixed thereto. Here, the tubular part  41  may be attached to the filament  10  by the tip end of the filament  10  being placed on an inner peripheral surface thereof by caulking. The flange  42  protrudes outward from the outer peripheral surface of the end of the tubular part  41  on a side of the movable body  21 . 
     The filament fixing member  40  is fixed to the tip end of the movable body  21  by a perforated bolt  50 . The perforated bolt  50  is provided with a through hole  50   a  extending in an axial direction of the perforated bolt  50 . The tubular part  41  of the filament fixing member  40  and a part of the filament  10  are inserted into the through hole  50   a  such that the flange  42  comes into contact with the tip end of the perforated bolt  50 . The perforated bolt  50  is attached to the bolt hole  21   f  of the circular column  21   a  in a state where the tubular part  41  or the like is inserted into the through hole  50   a . The filament fixing member  40  attached to the tip end of the filament  10  is fixed to the tip end of the circular column  21   a  when the flange  42  is sandwiched between the tip end of the perforated bolt  50  and a bottom portion of the bolt hole  21   f  of the circular column  21   a.    
     In this way, in the configuration shown in  FIG.  15   , the filament  10  can be easily attached to and detached from the movable body  21  using the perforated bolt  50 . As a result, in this configuration, it is easy to replace the filament  10 . Further, according to this configuration, the movable body  21  can easily pull the filament  10  in the direction of the axis L while curbing the axial deviation. 
     Although the embodiment and various modification examples of the present disclosure have been described above, the present disclosure is not limited to the above embodiment and various modification examples. The configurations which will be described below are applicable to all the embodiment and various modification examples as much as possible. In the tension holding unit  20  of the embodiment, if the spring  23  may not be a configuration in which the spring  23  pulls the movable body  21  in a direction along the axis L as long as a configuration in which, for example, the moving direction of the movable body  21  is guided the guide hole  22   d  is provided. For example, even if the spring  23  is configured to pull the movable body  21  in a direction slightly deviated from the axis L, the moving direction of the movable body  21  only has to be guided in a direction of the axis L by the guide hole  22   d . In the tension holding unit  20  of the embodiment, the movable body  21  is not limited to that the position of a center of gravity of the movable body  21  is positioned on the axis L. 
     In the tension holding unit  20  of the embodiment, the spring  23  is not limited to being accommodated in the accommodation space S of the housing  22 . For example, in a case where the housing  22  does not have the accommodation space S, the spring  23  may be configured not to be accommodated in the accommodation space S. In the tension holding unit  20  of the embodiment, the spring  23  is not limited to the configuration in which the spring  23  is disposed not to be directly seen from the filament  10 . In the tension holding unit  20  of the embodiment, the movable body  21  may not be guided by the guide hole  22   d  of the housing  22 . In a case where the movable body  21  is guided by the guide hole  22   d  of the housing  22 , the shape of the movable body  21  and the guide hole  22   d  is not limited to the circular column shape extending along the axis L. The movable body  21  and the guide hole  22   d  may have a shape other than the circular column shape, for example, a polygonal shape. 
     The filament  10  is not limited to the straight linear member in all parts. For example, the filament  10  may have a coiled part having a coiled shape. In this case, the filament  10  can hold the tension of the filament  10  even by its own coiled part. In this way, the electron beam emission device can have a function of holding tension with respect to the filament  10 . 
     Further, the filament unit  2  may be used as an electron beam generation source provided in an X-ray emission device that emits X-rays. In a case where the filament unit  2  is used as an electron beam generation source of an X-ray emission device, the X-ray emission device further includes a main body that accommodates the filament unit  2 , an X-ray target (for example, tungsten, molybdenum, or the like) as an X-ray generation part that generates X-rays when electrons are incident from the filament unit  2 , and an X-ray extraction part for extracting X-rays to the outside of the main body. In this case, as an example of the X-ray extraction part, the window  9  shown in  FIG.  1    may be changed to a window for X-ray emission constituted by a window material having a high X-ray permeability (for example, beryllium, diamond, or the like) and the X-ray target provided on a surface of the window material on a side of the vacuum space R. As a result, the electron beams EB emitted from the filament unit  2  can be incident on the X-ray target, and the X-rays can be emitted from the X-ray target. 
     At least a part of the above-described embodiment and various modification examples may be arbitrarily combined. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Electron beam emission device 
               2  Filament unit (electron beam generation source) 
               10  Filament (electron discharge part) 
               11  Main frame (frame) 
               20 ,  20 A to  20 G Tension holding unit 
               21 ,  21 A to  21 C Movable body 
               22 ,  22 A,  22 B,  22 F,  22 G housing (support part, housing part) 
               22   d  Guide hole (movable part holding part) 
               23 ,  26  Spring (tension holding part) 
             L Axis 
             S Accommodation space (internal space)