Abstract:
Disclosed is an ion pump system capable of efficaciously utilizing electrical fields and magnetic fields in all portions of a getter face, and thus of substantially improving exhaust efficiency. In particular, the present disclosure is based on the discovery that disposing a plurality of disc-shaped electrodes upon an internal casing ( 12 ) and further disposing a plurality of disc-shaped electrodes also upon an external casing ( 11 ) eliminates saddle points, allowing efficacious utilization of electrical fields and magnetic fields in all portions of the getter face, and thus substantially improving exhaust efficiency.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an ion pump system having a plurality of disc-shaped electrodes. The present invention relates to an ion pump system capable of effectively using electric fields and magnetic fields in all portions of a getter surface, and thus of distinctly improving exhaust efficiency. 
       BACKGROUND ART 
       [0002]    WO 2009/101814 (Patent Literature 1 below) proposes an ion pump system having a plurality of electrode layers.  FIGS. 18 ,  20 , and  21  in WO 2009/101814 disclose an ion pump system having a magnet provided in an inner casing and a magnet provided in an outer casing. 
         [0003]    Patent Literature 1: WO 2009/101814 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    The ion pump system disclosed in WO 2009/101814 has high exhaust efficiency when compared with conventional ion pumps. Unfortunately, however, a saddle point as a portion where no effective magnetic field is present is inevitably present even if an electric field and a getter surface are present inside a casing. 
         [0005]    For example, no effective magnetic flux is present in a portion where an electrode is provided in a conventional ion pump system, creating a saddle point. 
         [0006]    Thus, an object of the present invention is to provide an ion pump system capable of effectively using electric fields and magnetic fields in all portions of a getter surface, and thus of distinctly improving exhaust efficiency. 
       Solution to Problem 
       [0007]    The present invention is based on the finding that saddle points can be eliminated and electric fields and magnetic fields in all portions of a getter surface can effectively be used by basically providing a plurality of disc-shaped electrodes from an inner casing and further a plurality of disc-shaped electrodes from an outer casing, and thus of distinctly improving exhaust efficiency. 
         [0008]    A first aspect of the present invention is relates to an ion pump system including an outer casing  11  and an inner casing  12  provided inside the outer casing  11 . The outer casing  11  includes a plurality of outer circumferential electrodes  21 . The plurality of outer circumferential electrodes  21  is disc-shaped electrodes mounted on the outer casing  11  toward the inner casing  12  at predetermined intervals. On the other hand, the inner casing  12  includes a plurality of inner circumferential electrodes  22 . The plurality of inner circumferential electrodes  22  is disc-shaped electrodes mounted on the inner casing  12  toward the outer casing  11  at predetermined intervals. The plurality of outer circumferential electrodes  21  and the plurality of inner circumferential electrodes  22  are parallel to each other. A portion  23  (inner circumferential portion of the outer circumferential electrode) closest to the inner casing  12  of the plurality of outer circumferential electrodes  21  is positioned closer to the inner casing  12  than to a portion  24  (outer circumferential portion of the inner circumferential electrode) closest to the outer casing  11  of the plurality of inner circumferential electrodes  22 . 
         [0009]    Because the configuration described above is provided, a magnetic flux is generated between the outer circumferential electrode  21  and the inner circumferential electrode  22 . Moreover, a magnetic flux is generated in all places of the outer casing  11  and the inner casing  12 . Therefore, according to the present invention, electric fields and magnetic fields can effectively be used in all portions of a getter surface, thereby distinctly improving exhaust efficiency. 
         [0010]    A preferred embodiment of the present invention further includes an inner magnet  31 . The inner magnet  31  is provided in a space  32  of the inner casing  12  on the side opposite to the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . 
         [0011]    An ion pump system with the inner magnet  31  can reduce leakage of the magnetic flux out of the system. 
         [0012]    A preferred embodiment of the present invention further includes an outer magnet  33 . The outer magnet  33  is provided in the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . 
         [0013]    A preferred embodiment of the present invention includes the inner casing  12  having a mesh portion, thereby enabling a gas present on the inner or outer of the inner casing  12  to move through the mesh portion. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0014]    According to the present invention, a plurality of disc-shaped electrodes is provided from an inner casing and further a plurality of disc-shaped electrodes is provided from an outer casing. Saddle points can thereby be eliminated so that electric fields and magnetic fields can effectively be used in all portions of a getter surface and exhaust efficiency can distinctly be improved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram illustrating an ion pump system according to the present invention. 
           [0016]      FIG. 2  is a diagram illustrating a state of electric fluxes and magnetic fluxes of the ion pump system in  FIG. 1 . 
           [0017]      FIG. 3  is a reference diagram illustrating a case when neither outer circumferential electrode nor inner circumferential electrode is present in  FIG. 1 . 
           [0018]      FIG. 4  is a schematic diagram illustrating the ion pump system having an inner magnet as a magnetic flux source. 
           [0019]      FIG. 5  is a schematic diagram illustrating the ion pump system having an outer magnet as a magnetic flux source. 
           [0020]      FIG. 6  is a schematic diagram illustrating the ion pump system in which an inner casing is configured by a mesh. 
           [0021]      FIG. 7  is a schematic diagram illustrating the ion pump system in which the outer magnet is present not only on the side face, but also on the bottom surface and the top surface. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]      FIG. 1  is a schematic diagram illustrating an ion pump system according to the present invention. As illustrated in  FIG. 1 , the ion pump system according to the present invention includes an outer casing  11  and an inner casing  12  provided inside the outer casing  11 . The outer casing  11  includes a plurality of outer circumferential electrodes  21 . The plurality of outer circumferential electrodes  21  is disc-shaped electrodes mounted on the outer casing  11  toward the inner casing  12  at predetermined intervals. On the other hand, the inner casing  12  includes a plurality of inner circumferential electrodes  22 . The plurality of inner circumferential electrodes  22  is disc-shaped electrodes mounted on the inner casing  12  toward the outer casing  11  at predetermined intervals. The plurality of outer circumferential electrodes  21  and the plurality of inner circumferential electrodes  22  are parallel to each other. A portion  23  (inner circumferential portion of the outer circumferential electrode) closest to the inner casing  12  of portions of the outer circumferential electrode  21  is positioned closer to the inner casing  12  than to a portion  24  (outer circumferential portion of the inner circumferential electrode) closest to the outer casing  11  of the plurality of inner circumferential electrodes  22 . The example illustrated in  FIG. 1  further includes an inner magnet  31 . The inner magnet  31  is provided in a space  32  of the inner casing  12  on the side opposite to the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . The example illustrated in  FIG. 1  further includes an outer magnet  33 . The outer magnet  33  is provided in the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . In  FIG. 1 , reference numeral  41  and reference numeral  42  mean flanges for connection. Each element will be described below. The known configuration of an ion pump system can be adopted when appropriate for the configuration of elements other than elements that will be described below. 
         [0023]    The outer casing  11  is a framework of an ion pump system. A cylindrical shape can be cited as the shape of the outer casing  11 . Various electrodes may be formed inside the framework. Wires to drive electrodes are provided and such a wire that can receive a drive signal from a drive signal source and propagate the drive signal to an inner electrode is preferable. Further, the outer casing  11  may function as an electrode. Incidentally, an element covering the outer casing  11  may be present outside the outer casing  11 . The outer magnet  33  is normally provided inside the outer casing  11 . However, as illustrated in  FIG. 1 , the outer magnet  33  may be provided on the outer of the outer casing  11 . Publicly known materials such as aluminum, titanium, and stainless can be cited as the material of the outer casing  11 . Among these materials, aluminum having titanium deposited on the surface thereof is preferable because the inner wall itself of the outer casing  11  can be used as an electrode. In this manner, the ion pump system can be made lighter and also the structure thereof can be made simpler and smaller. 
         [0024]    The inner casing  12  is a casing provided inside the outer casing  11 . An example of the inner casing is an inner casing disclosed in  FIGS. 16 and 20  of WO 2009/101814. The inner casing  12  preferably has a property to allow a magnetic flux to pass through to some extent. 
         [0025]    The outer circumferential electrodes  21  are disc-shaped electrodes mounted on the outer casing  11  toward the inner casing  12  at predetermined intervals. The interval at which the outer circumferential electrodes  21  are installed is preferably fixed. That is, the outer circumferential electrodes  21  are preferably provided at equal intervals on the outer casing  11 . The interval may appropriately be adjusted in accordance with the size of an ion pump and the voltage applied to an electrode. 
         [0026]    The outer circumferential electrode  21  is a disc-shaped electrode. The outer circumference of the outer circumferential electrode  21  is mounted on the outer casing  11 . On the other hand, the outer circumferential electrode  21  has a circular notch portion near the center thereof. Thus, the outer circumferential electrode  21  is not in contact with the inner casing  12 . The distance between the inner casing  12  and the outer casing  11  is set as d. Then, the length of the outer circumferential electrode  21  is set as l o . l o  is considered to be the distance from the outer casing  11  to the portion  23  (inner circumferential portion of the outer circumferential electrode) closest to the inner casing  12  of the outer circumferential electrode  21 . In this case, l o  can be cited as being 0.55 d or more and 0.95 d or less and may he 0.6 d or more and 0.9 d or less, 0.7 d or more and 0.9 d or less, or 0.7 d or more and 0.85 d or less. That is, if l o  is small, sufficient electric fluxes are not generated between the outer circumferential electrode  21  and the inner circumferential electrode  22 . On the other hand, if l o  is large, it becomes more difficult for a gas to move inside the casing, leading to lower exhaust efficiency. Any publicly known material having a conductive portion may be used as the material of the outer circumferential electrode. 
         [0027]    The inner circumferential electrodes  22  are disc-shaped electrodes mounted on the inner casing  12  toward the outer casing  11  at predetermined intervals. The interval at which the inner circumferential electrodes  22  are installed is preferably fixed. That is, the inner circumferential electrodes  22  are preferably provided at equal intervals on the inner casing  12 . The interval is preferably the same as the interval of the outer circumferential electrodes  21  and may appropriately be adjusted in accordance with the size of an ion pump and the voltage applied to an electrode. 
         [0028]    The inner circumferential electrode  22  is a disc-shaped electrode. The inner circumference of the inner circumferential electrode  22  is mounted on the inner casing  12 . The inner circumferential electrode  22  is not in contact with the outer casing  11 . Then, the length of the inner circumferential electrode  22  is set as l i . l i  is considered to be the distance from the inner casing  12  to the portion  24  (outer/inner circumferential portion of the inner circumferential electrode) closest to the outer casing  11  of the inner circumferential electrode  22 . In this case, l i  can be cited as being 0.55 d or more and 0.95 d or less and may be 0.6 d or more and 0.9 d or less, 0.7 d or more and 0.9 d or less, or 0.7 d or more and 0 85 d or less. That is, if l i  is small, sufficient electric fluxes are not generated between the inner circumferential electrode  22  and the inner circumferential electrode  22 . On the other hand, if l i  is large, it becomes more difficult for a gas to move inside the casing, leading to lower exhaust efficiency. Any publicly known material having a conductive portion may be used as the material of the outer circumferential electrode. 
         [0029]    One of the outer circumferential electrode  21  and the inner circumferential electrode  22  is a positive electrode and the other is a negative electrode. In the present invention, the polarity of the negative electrode and the positive electrode is preferably changeable. Such a change of the polarity can easily be achieved by changing the drive voltage of a drive unit. 
         [0030]    The outer circumferential electrode  21  and the inner circumferential electrode  22  have a disc-shaped shape. On the other hand, these electrodes may have a plurality of holes in a disc-shaped shape. Because of the plurality of holes of the disc, a gas flows effectively inside the casing. The size of each hole can be cited as being 0.01 d or more and 0.3 d or less and may be 0.05 d or more and 0.2 d or less. Holes are preferably provided symmetrically. The number of holes of each disc is preferably between 2 and 100. 
         [0031]    As illustrated in  FIG. 1 , the outer circumferential electrode  21  and the inner circumferential electrode  22  are preferably installed in parallel with each other. Moreover, as illustrated in  FIG. 1 , the outer circumferential electrode  21  and the inner circumferential electrode  22  are preferably present alternately at equal intervals. 
         [0032]    The example illustrated in  FIG. 1  further includes the inner magnet  31 . The inner magnet  31  is provided in the space  32  of the inner casing  12  on the side opposite to the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . A publicly known magnet used for an ion pump can appropriately be used. More specifically, the magnet may be a magnetic coil or a permanent magnet. The inner magnet  31  includes a plurality of cylindrical permanent magnets spaced in a direction parallel to the center axis of the inner casing (longitudinal direction of the center axis). That is, as illustrated in  FIG. 1 , the inner magnet  31  in this mode is formed by aligning a plurality of ring-shaped permanent magnets. An ion pump system in this mode has a plurality of divided cylindrical magnets installed with a predetermined space therebetween instead of using one cylindrical magnet and therefore, the ion pump system can be made lighter and also an efficient magnetic field can be generated. Moreover, by adopting such a configuration, the structure of arranging a magnetic field generated by an interference effect between a group of magnets of a pump portion on the inner and a group of magnets of the ion pump on the outer can be optimized to realize a more efficient exhaust operation. The example illustrated in  FIG. 1  has a magnetic field rectifier between the inner magnets  31 . 
         [0033]    The example illustrated in  FIG. 1  further includes the outer magnet  33 . The outer magnet  33  is provided in the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . A magnet like the inner. magnet  31  can be used as the outer magnet  33 . However, the outer magnet  33  preferably has a smaller magnetic force than the inner magnet  31 . A magnetic flux originating from the inner magnet  31  is normally not leaked out of the outer casing  11 . Thus, a relatively strong magnet can be adopted for the inner magnet  31 . On the other hand, if the magnetic force of the outer magnet  33  is strong, it becomes necessary to cover the outer magnet  33  with a magnetic shield so that a magnetic flux of the outer magnet  33  should not be leaked. Therefore, the outer magnet  33  preferably has a weaker magnetic force than the inner magnet  31 . The magnetic force of the outer magnet  33  can be cited as being, for example, 0.1 time or more and 1 time or less the magnetic force of the inner magnet  31  and may be 0.5 times or more and 0.9 times. Naturally, the outer magnet  33  and the inner magnet  31  have comparable magnetic forces. 
         [0034]      FIG. 2  is a diagram illustrating a state of electric fluxes and magnetic fluxes of the ion pump system in  FIG. 1 .  FIG. 3  is a reference diagram illustrating a case when neither outer circumferential electrode  21  nor inner circumferential electrode  22  is present in  FIG. 1 . 
         [0035]    If, as illustrated in  FIG. 3 , neither the outer circumferential electrode  21  nor the inner circumferential electrode  22  is present, a portion where an effective magnetic flux is not present arises. In this example, the outer casing  11  and the inner casing  12  function as electrodes. Then, in this example, an electric flux is generated between the outer casing  11  and the inner casing  12 . Because the outer casing  11  and the inner casing  12  are relatively far apart, the strength of the electric flux is relatively weak. As a result, the exhaust efficiency of the ion pump system illustrated in  FIG. 3  decreases. 
         [0036]    In the example illustrated in  FIG. 2 , on the other hand, a magnetic flux is generated also in a portion where no effective magnetic flux is present in  FIG. 3 . Accordingly, the effective area of electrodes involved in evacuation maintenance can be increased twofold to threefold. 
         [0037]    An ion pump system according to the present invention can be operated in the same manner as a publicly known ion pump. The principle of operation of an ion pump is publicly known. The principle of operation of an ion pump will briefly be described below. A voltage of a few kV is applied between the negative electrode and positive electrode of the ion pump. Then, primary electrons are emitted from the negative electrode. Primary electrons emitted from the negative electrode are affected by a magnetic field provided by a permanent magnet while being attracted to the positive electrode. Thus, primary electrons reach the positive electrode by whirling round in a long spiral motion. On the way to the positive electrode, primary electrons collide against neutral gas molecules to generate many positive ions and secondary electrons. Generated secondary electrons further make a spiral motion and collide against other gas molecules to generate positive ions and electrons. Each ion is adsorbed by the electrode. Thus, also in the present invention, primary electrons are emitted from the negative electrode when a potential difference is generated between the outer circumferential electrode  21  and the inner circumferential electrode  22  and a gas is adsorbed by the electrode according to the above principle. 
         [0038]    In addition to the above configuration, the ion pump system according to the present invention can adopt publicly known configurations used for an ion pump if appropriate. For example, a heating unit or cooling unit may be installed if appropriate. Collection efficiency of gas can be improved by cooling the system using the cooling unit. On the other hand, a gas captured by each electrode can be emitted by maintaining a vacuum through heating of the electrode by using the heating unit. 
         [0039]    Next, an ion pump system according to the present invention in a different embodiment from the above embodiment will be described.  FIG. 4  is a schematic diagram illustrating the ion pump system having an inner magnet as a magnetic flux source. This is a mode in which the inner magnet  31  is included in the casing as a magnetic flux source to provide a magnetic flux. The inner magnet  31  is provided in the space  32  of the inner casing  12  on the side opposite to the outer casing  11  to provide a magnetic field to the space between the outer casing  11  and the inner casing  12 . No outer magnet is present in the example illustrated in  FIG. 4 . Because no outer magnet is present in the ion pump system in this mode, circumstances in which a magnetic flux is leaked out of the ion pump system can be reduced. 
         [0040]    In the ion pump system in this mode, the length of the inner circumferential electrode  22  and the length l i  of the outer circumferential electrode  21  may be the same. On the other hand, an electric flux near the outer casing  11  may be weakened in the ion pump system in this mode. Thus, in the ion pump system in this mode, it is preferable to make the length l i . of the inner circumferential electrode  22  longer than the length l, of the outer circumferential electrode  21 . The length of the inner circumferential electrode  22  can be cited as being 1.05 times or more and 1.5 times or less the length l, of the outer circumferential electrode  21  and may be 1.1 times or more and 1.3 times or less. 
         [0041]    Next, an ion pump system according to the present invention in a different embodiment from the above embodiments will be described.  FIG. 5  is a schematic diagram illustrating the ion pump system having an outer magnet as a magnetic flux source. No inner magnet is present in the example illustrated in  FIG. 5 . Because no inner magnet is present in the ion pump system in this mode, the diameter of the inner casing  12  can be made smaller so that the electrode area can be increased. 
         [0042]    In the ion pump system in this mode, the length l i  of the inner circumferential electrode  22  and the length l o  of the outer circumferential electrode  21  may be the same. On the other hand, an electric flux near the inner casing  12  may be weakened in the ion pump system in this mode. Thus, in the ion pump system in this mode, it is preferable to make the length l o  of the outer circumferential electrode  21  longer than the length l i  of the inner circumferential electrode  22 . The length l o  of the outer circumferential electrode  21  can be cited as being 1.05 times or more and 1.5 times or less the length of the inner circumferential electrode  22  and may be 1.1 times or more and 1.3 times or less. In the mode illustrated in  FIG. 5 , the inner casing  12  may have a rod shape, instead of a cylindrical shape. 
         [0043]      FIG. 6  is a schematic diagram illustrating the ion pump system in which an inner casing is configured by a mesh. The ion pump system can adopt every element described above except that the inner casing  12  has a mesh portion. Because the inner casing  12  has a mesh portion in the ion pump system, a gas present on the inner or outer of the inner casing  12  can move through the mesh portion. An example of the mesh portion is the whole region where inner circumferential electrodes and outer circumferential electrodes are present. A mesh is a network structure having a plurality of regular holes. The size of a hole of the mesh may appropriately be adjusted. 
         [0044]      FIG. 7  is a schematic diagram illustrating the ion pump system in which the outer magnet is present not only on the side face, but also on the bottom surface and the top surface.  FIG. 1 , the outer magnet  33  is present on the side face of the outer casing in a cylindrical shape. An example of the outer magnet  33  is a magnet in a cylindrical shape surrounding the outer casing. In the example illustrated in  FIG. 7 , the outer magnet is present not only on the side face, but also on the bottom surface and the top surface An example of the outer magnets present on the bottom surface and the top surface is an outer magnet disposed concentrically with the inner casing  12  and the outer casing  11 . In the example illustrated in  FIG. 7 , the outer magnets present on the bottom surface and the top surface are each present in a double-circle shape. Thus, with the outer magnets also present on the bottom surface and the top surface, the magnetic force inside the outer casing can be made stronger. 
       INDUSTRIAL APPLICABILITY 
       [0045]    An ion pump system according to the present invention can suitably be utilized in a vacuum equipment industry and the field of material activation. An electromagnetic field generator according to the present invention can suitably be utilized in the field of material activation. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           11  Outer casing 
           12  Inner casing 
           21  Outer circumferential electrode 
           22  Inner circumferential electrode 
           23  Inner circumferential portion of the outer circumferential electrode 
           24  Outer/inner circumferential portion of the inner circumferential electrode 
           31  Inner magnet 
           32  Internal space of the inner casing 
           33  Outer magnet