Plasma source and atomic clock comprising the same

Abstract

A small plasma source capable of efficient discharge in ultra-high vacuum includes: a first magnet; a second magnet arranged such that a second pole opposite to a first pole of the first magnet is opposite to it; a third magnet arranged around the first magnet, with a second pole opposite to the first pole of the first magnet facing the same direction as the first pole of the first magnet; a fourth magnet arranged around the second magnet, with a first pole opposite to the second pole of the third magnet opposite to it; a first electrode disposed on one side of the first pole of the first magnet and the second pole of the third magnet; a second electrode disposed on one side of the second pole of the second magnet and the first pole of the fourth magnet, facing the first electrode; and a third electrode disposed between the first electrode and the second electrode. The shorter of the distances between the first and second magnets and between the third and fourth magnets, divided by the average thickness of the first to fourth magnets, is between 1 and 10.

Description

Technical Field

[0001] This invention relates to plasma sources and atomic clocks containing such plasma sources.

[0002] This application claims priority to Japanese Patent Application No. 2021-098407, filed on June 14, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Ultra-high vacuum sealed miniature batteries hold promise for applications in a variety of innovative devices. These ultra-high vacuum miniature batteries are first sealed in a medium vacuum (10⁻⁶ Ω·cm). －1 The vacuum level is lowered to 1 Pa, and then an ultra-high vacuum pump is used to evacuate the battery from the outside. Typically, ion pumps are widely used as ultra-high vacuum pumps, and a plasma source capable of efficient discharge can be used inside the ion pump.

[0004] As a small MEMS (Micro Electro Mechanical System) vacuum pump, there are known techniques for achieving a structure similar to an ion pump using MEMS processes (microfabrication and anode bonding). In this technique, the N pole of a first magnet and the S pole of a second magnet are positioned opposite each other. A first silicon cathode electrode is placed on one side of the first magnet, and a second silicon cathode electrode is placed on one side of the second magnet. The silicon anode is arranged such that a space is left between the first and second cathode electrodes. Such a small MEMS vacuum pump is difficult to achieve in approximately 10... －5 High-efficiency discharge under ultra-high vacuum conditions below Pa.

[0005] Additionally, a known technique involves placing the cathode in the center, the anode on a nearly identical surface surrounding the cathode, and placing magnets above the cathode and below the anode, with the different magnetic poles facing each other. This configuration confines electrons to generate a discharge, causing them to collide with residual gas for exhaust. Even with this technique, it is impossible to achieve an exhaust effect of approximately 10... －5 High-efficiency discharge is achieved under ultra-high vacuum conditions below Pa.

[0006] On the other hand, magnetron sputtering is a known method for forming films on a substrate. Its film-forming apparatus uses magnets arranged on the bottom side in the order of N-pole, S-pole, N-pole, and on the top side, magnets arranged in the order of S-pole, N-pole, S-pole, opposite to the bottom magnets. However, since the purpose of this technique is to form a thin film on the substrate, it cannot be directly applied to the problem of high-efficiency discharge under ultra-high vacuum conditions.

[0007] Existing technical documents

[0008] Patent documents

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-26559

[0010] [Patent Document 2] Japanese Patent Application Publication No. 63-303065

[0011] Non-patent literature

[0012] [Non-Patent Literature 1] T. Grzebyk et al., “MEMS Ion Adsorption High Vacuum Pumps”, Journal of Physics: Conference Series 773 (2016) 012047

[0013] [Non-Patent Literature 2] T. Grzebyk et al., “Magnetron-like Micro Ion Sources”, Vacuum 151(2018)167-174 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] Therefore, one aspect of the present invention is to provide a small plasma source capable of efficient discharge under ultra-high vacuum conditions.

[0016] The methods used to solve the problem

[0017] According to a first aspect of the invention, a plasma source comprises: (A) a first magnet; (B) a second magnet arranged such that a second magnetic pole of the second magnet, different from the first magnetic pole, is opposite to a first magnetic pole of the first magnet; (C) a third magnet arranged such that a second magnetic pole of the third magnet, different from the first magnetic pole, is opposite to the first magnetic pole in the same direction as the first magnetic pole of the first magnet, and the third magnet is arranged around the first magnet; (D) a fourth magnet arranged such that a first magnetic pole of the fourth magnet, different from the second magnetic pole, is opposite to a second magnetic pole of the third magnet, and the fourth magnet is arranged around the second magnet; and (E) a first electrode disposed on the first magnetic pole of the first magnet and the third magnet. (F) A second electrode, facing the first electrode, is disposed on the side where the second magnetic pole of the second magnet and the first magnetic pole of the fourth magnet are located; (G) A third electrode, disposed between the first and second electrodes, is configured such that its potential is higher than that of the first and second electrodes when a voltage is applied; wherein, in the first space between the first and second magnets and in the second space between the third and fourth magnets, the maximum magnetic field strength |By(max)| in the first direction from the second magnet to the first magnet and the minimum magnetic field strength |By(min)| in the aforementioned first direction satisfy |By(min)| / |By(max)|≧0.1. Furthermore, in the third space sandwiched between the first and second spaces, the maximum magnetic field strength |Bx(max)| in the second direction perpendicular to the first direction and the minimum magnetic field strength |Bx(min)| in the second direction satisfy |Bx(min)| / |Bx(max)|≤0.1.

[0018] According to a second aspect of the invention, a plasma source comprises: (A) a first magnet; (B) a second magnet arranged such that a second magnetic pole of the second magnet, different from the first magnetic pole, is opposite to a first magnetic pole of the first magnet; (C) a third magnet, such that a second magnetic pole of the third magnet, different from the first magnetic pole, is opposite to the first magnetic pole in the same direction as the first magnetic pole, and the third magnet is arranged around the first magnet; and (D) a fourth magnet, such that a first magnetic pole of the fourth magnet, different from the second magnetic pole, is opposite to the second magnetic pole of the third magnet, and the fourth magnet is arranged around the second magnet. (E) A first electrode, disposed on the side where the first magnetic pole of the first magnet and the second magnetic pole of the third magnet are located; (F) A second electrode, facing the first electrode, disposed on the side where the second magnetic pole of the second magnet and the first magnetic pole of the fourth magnet are located; (G) A third electrode, disposed between the first electrode and the second electrode, configured such that when a voltage is applied, its potential is higher than that of the first electrode and the second electrode; wherein the shorter of the distance between the first magnet and the second magnet and the distance between the third magnet and the fourth magnet is divided by the average thickness of the first to fourth magnets, and the value is more than 1 and less than 10. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating a plasma source according to the first embodiment;

[0020] Figure 2 This is a schematic diagram illustrating a plasma source according to the first embodiment;

[0021] Figure 3 This is a diagram illustrating the arrangement of magnets, etc., in the plasma source of the first embodiment;

[0022] Figure 4 (a) to Figure 4 (c) is an exemplary schematic diagram showing the distribution of magnetic field lines for each distance ratio between magnets;

[0023] Figure 5 (a) to Figure 5 (c) is an exemplary schematic diagram showing the distribution of magnetic field lines for the distance ratio between each magnet;

[0024] Figure 6 This is an exemplary schematic diagram showing the magnetic field strength distribution in the Y direction;

[0025] Figure 7 This is an exemplary schematic diagram showing the distribution of magnetic field strength in the X direction;

[0026] Figure 8 This is a diagram illustrating the effect of the plasma source in the first embodiment;

[0027] Figure 9 This is a schematic diagram showing the structure when a plasma source is used as an ion pump;

[0028] Figure 10 This is a schematic diagram showing the outline of a small cooled atomic clock;

[0029] Figure 11 This is a schematic diagram showing the outline of a small cooled atomic clock;

[0030] Figure 12 This is a schematic diagram illustrating an embodiment using a plasma source as a vacuum pump;

[0031] Figure 13 This is a schematic diagram illustrating the effect produced when a plasma source is used as a vacuum pump. Detailed Implementation

[0032] Example 1

[0033] Figure 1 This illustrates a structural example of the plasma source according to this embodiment. The plasma source according to this embodiment is... Figure 1 The magnetic yoke 1100 shown in (a) and Figure 1(b) shows the combination of the battery portion 1500. The magnetic yoke 1100 has an upper arm 1200 and a lower arm 1300, and a gap 1400 is provided between the upper arm 1200 and the lower arm 1300. The battery portion 1500 can be inserted into this gap 1400. That is, the length of the gap 1400 in the vertical direction is slightly longer than the thickness of the battery portion 1500.

[0034] The upper arm 1200 includes a cylindrical magnet 1220 and a cylindrical magnet 1210 surrounding the cylindrical magnet 1220. Specifically, the inner diameter of the cylindrical magnet 1210 is larger than the diameter of the cylindrical magnet 1220. Preferably, the center point of the cylindrical magnet 1220 when viewed from the top surface and the center point of the cylindrical magnet 1210 when viewed from the top surface are set to coincide. Furthermore, preferably, the thickness of the cylindrical magnet 1210 and the thickness of the cylindrical magnet 1220 are the same, and magnets with the same strength are used. Furthermore, preferably, the lower surfaces of the cylindrical magnet 1210 and the lower surfaces of the cylindrical magnet 1220 are set to coincide with the lower surface of the upper arm 1200.

[0035] The lower arm 1300 includes a cylindrical magnet 1320 and a cylindrical magnet 1210 surrounding the cylindrical magnet 1320. That is, the inner diameter of the cylindrical magnet 1310 is larger than the diameter of the cylindrical magnet 1320. Preferably, the center points of the cylindrical magnet 1320 and the cylindrical magnet 1310, when viewed from the top surface, are arranged to coincide. Furthermore, preferably, the thickness of the cylindrical magnet 1310 and the thickness of the cylindrical magnet 1320 are the same, and magnets with the same strength are used. Furthermore, preferably, the upper surfaces of the cylindrical magnet 1310 and the upper surfaces of the cylindrical magnet 1320 are arranged to coincide with the upper surface of the lower arm 1300. Note that... Figure 1 The cylindrical elements in (a) that are not marked with reference numerals are design connection parts that are not related to the following description, and therefore their description will be omitted.

[0036] Furthermore, more preferably, the cylindrical magnets 1210 and 1310, and the cylindrical magnets 1220 and 1320, have the same strength. For example, the magnets can be neodymium or samarium-cobalt magnets. Furthermore, preferably, the cylindrical magnets 1220 and 1320 have the same shape, and the cylindrical magnets 1210 and 1310 also have the same shape. Furthermore, preferably, the center points seen from the top surface of the cylindrical magnets 1220, 1210, 1320, and 1310 are arranged to coincide.

[0037] The battery section 1500 includes, for example, a plate-shaped upper electrode 1510 made of silicon, a plate-shaped lower electrode 1530 made of silicon, spacers 1541 to 1543 made of glass, and a plate-shaped electrode 1520 held between the upper electrode 1510 and the lower electrode 1530 by the spacers 1541 to 1543 and having a hole 1521. Furthermore, for ease of illustration, some spacers, such as spacers 1541 and the spacers below the electrode 1520, are not shown. Figure 1 A voltage with a higher potential than that of the upper electrode 1510 and the lower electrode 1530 is applied to electrode 1520. For example, the upper electrode 1510 and the lower electrode 1530 are grounded, and a positive voltage is applied to electrode 1520. Preferably, electrode 1520 is positioned between the upper electrode 1510 and the lower electrode 1530. Preferably, the hole 1521 is circular, and its diameter is equal to or greater than the inner diameter of the cylindrical magnets 1210 and 1310. More preferably, when viewed from the top surface, the center of the hole 1521 coincides with the center point of the cylindrical magnets 1220 and 1320. However, the shape of the hole 1521 is arbitrary. The hole 1521 is for forming Figure 3 The space 1700 shown is such that the upper electrode 1510 and the lower electrode 1530 are not completely shielded.

[0038] exist Figure 1 In (b), for ease of illustration, there are spaces on the left and right sides of the battery section 1500, but these spaces can also be made into enclosed spaces by adding spacers or changing the shape as appropriate.

[0039] Figure 2 The diagram schematically illustrates the combined state of the magnetic yoke 100 and the battery section 1500. The following description, in order to illustrate the detailed structure, shows a cross-section taken along the dashed line A-A' and viewed in the direction of the arrow.

[0040] Figure 3This is a schematic diagram illustrating the cross-section described above. In this embodiment, the S pole of cylindrical magnet 1220 faces the opposing cylindrical magnet 1320, and the N pole of cylindrical magnet 1320 faces the opposing cylindrical magnet 1220. The N pole of cylindrical magnet 1210 faces the opposing cylindrical magnet 1310, and the S pole of cylindrical magnet 1310 faces the opposing cylindrical magnet 1210. Furthermore, the positions of the S and N poles can be reversed. By arranging the magnets in this manner, magnetic field lines as shown are generated in the space 1700 sandwiched between the upper electrode 1510 and the lower electrode 1530 and further surrounded by spacers 1541 to 1543 and the electrode 1520. In this embodiment, a magnetron magnetic field Q and a parallel magnetic field P of a certain strength are generated through the magnetic circuit created by cylindrical magnets 1220 and 1320 and cylindrical magnets 1210 and 1310, in order to confine the plasma at a high density. Here, the direction from the lower arm 1300 to the upper arm 1200 opposite the lower arm 1300 is defined as the Y direction, and the direction orthogonal to the Y direction is defined as the X direction. When the magnetic field lines become denser (the magnetic field strength becomes stronger), electrons cannot advance and are bounced back. Due to the magnetron magnetic field Q, electrons cannot advance along the Y direction. Furthermore, since a zero magnetic field region appears between the upper and lower magnetron magnetic fields Q, electrons cannot pass through the magnetic field lines from the zero magnetic field region. In addition, they also cannot advance along the X direction due to the parallel magnetic field P. Therefore, the plasma is confined within region R, and a high-density plasma can be generated.

[0041] Note that in Figure 3 For ease of explanation, the thickness of the electrodes is emphasized. As an example, the diameters of cylindrical magnets 1220 and 1320 are 7 mm, and the outer diameters of cylindrical magnets 1210 and 1310 are 20 mm and the inner diameter is 10 mm. Furthermore, the distance between the upper electrode 1510 and the lower electrode 1530 is 4.4 mm. Note that in this embodiment, a small plasma source is assumed, and the maximum distance between the upper electrode 1510 and the lower electrode 1530 is assumed to be approximately 20 mm. To achieve this, the Debye length (plasma size) λD should be 1 / 10 or less of the aforementioned distance (1 mm or less, since two plasmas are generated above and below). More specifically, in 10... －4 At a vacuum level of Pa, the Debye length is 1 mm or less. When the Debye length (plasma size) exceeds 1 / 10 of the above distance, the number of charged particles that collide with the wall and disappear will be greater than the number of charged particles generated from the electrodes, making it impossible to maintain the plasma.

[0042] Only Figure 3The illustrated magnet arrangement cannot generate the aforementioned high-density plasma. In this embodiment, the magnet distance ratio is defined as the value obtained by dividing the shortest distance between the magnets in the upper arm 1200 and the magnets opposite to the magnets in the lower arm 1300 by the average thickness of the magnets used. Figure 3 In the example shown, the magnets all have the same thickness T, and the distances between the magnets in the upper arm 1200 and the magnets in the lower arm 1300 opposite to it are all the same L. In this case, L / T is the distance ratio between the magnets.

[0043] When the distance between magnets is smaller than L / T, such as 0.5, the magnets are too close to generate a sufficiently strong magnetron magnetic field. Figure 4 (a) The simulation results are shown schematically. Increasing the magnet spacing ratio L / T to, for example, 1.0 can generate a magnetron magnetic field and produce high-density plasma, such as... Figure 4 (b) The simulation results are illustrated schematically. When the magnet distance ratio L / T is further increased to, for example, 2.5, a sufficiently strong magnetron magnetic field and parallel magnetic field can be generated. Even when the magnet distance ratio L / T is further increased to, for example, 5.0, a sufficiently strong magnetron magnetic field and parallel magnetic field can still be generated, such as... Figure 5 (a) The simulation results are shown schematically. When the distance between magnets L / T is further increased to, for example, 10, as... Figure 5 (b) The schematic simulation results show that although the magnetron magnetic field becomes dominant, a certain degree of parallel magnetic field is also formed. When the distance between magnets L / T is further increased to, for example, 20, almost no parallel magnetic field is produced, and the magnetron magnetic field becomes dominant, as... Figure 5 (c) As illustrated in the simulation results, the plasma becomes unconfinable.

[0044] Based on the simulation results above, if the magnet distance ratio L / T is greater than or equal to 1 and less than or equal to 10, it can be used as a general plasma source. Furthermore, to achieve higher density plasma enclosure, a magnet distance ratio L / T of 2.5 or greater and less than or equal to 5 is preferred.

[0045] In addition, other parameters for generating sufficiently strong parallel and magnetron magnetic fields are also explained. Here, the direction from the magnet in the lower arm 1300 to the magnet in the upper arm 1200 is defined as the Y direction, and the direction perpendicular to it is defined as the X direction. The parallel magnetic field is the magnetic field in the Y direction, and the magnetron magnetic field is the magnetic field in the X direction. At this point, the strongest magnetic field strength |By(max)| is explored in the space between the magnet in the lower arm 1300 and the magnet in the upper arm opposite to it, which has the shortest distance (cylindrical magnets 1220 and 1320 or cylindrical magnets 1210 and 1310). Figure 6The illustration shows, for example, in Figure 3 The magnetic field strength along the Y direction is shown in the diagram with the magnets arranged as shown. The darker the black, the greater the absolute value of the magnetic field strength. In this example, the distance between cylindrical magnets 1220 and 1320 is the same as the distance between cylindrical magnets 1210 and 1310, but the focus here is on the pair of cylindrical magnets 1220 and 1320. Thus, the strongest magnetic field strength |By(max)| (thick white dashed line) can be obtained on the surface of cylindrical magnets 1220 and 1320. Furthermore, the weakest magnetic field strength |By(min)| is explored in the space between the pair of magnets that obtain the strongest magnetic field strength |By(max)| (i.e., cylindrical magnets 1220 and 1320). Figure 3 In the illustrated magnet arrangement, the weakest magnetic field strength |By(min)| can be obtained within the midpoint of the line segment passing through the surface (thick white dashed line) of the cylindrical magnets 1220 and 1320, which are perpendicular to |By(max)|, and within the surface (thick white dashed line in the middle) of that line segment. Then, using |By(min)| / |By(max)| as an index value, a preferred parallel magnetic field can be generated when |By(min)| / |By(max)| ≥ 0.1. This is the standard used to determine whether the preferred magnetic field emitted from the magnet is undisturbed and whether all magnetic flux is guided from the N pole to the S pole. Note that since the index value is 1 when |By(min)| = |By(max)|, therefore 1 > |By(min)| / |By(max)|.

[0046] On the other hand, the magnetron's magnetic field is a magnetic field in the X direction, and we are concerned with the magnetic field strength in the X direction. At this time, we explore the strongest magnetic field strength |Bx(max)| in the space W between the cylindrical magnets 1220 and 1320 and between the cylindrical magnets 1210 and 1310. Figure 7 The illustration shows, for example, in Figure 3 The magnetic field strength along the X direction is shown in the diagram with the magnets arranged as shown. Similarly, the darker the black, the greater the absolute value of the magnetic field strength. In this case, the strongest magnetic field strength |Bx(max)| can be obtained at the midpoint of the line segment connecting the ends of cylindrical magnet 1220 and cylindrical magnet 1210, and at the midpoint of the line segment connecting the ends of cylindrical magnet 1320 and cylindrical magnet 1310. Additionally, the weakest magnetic field strength |Bx(min)| is explored within the same space W. Figure 3The magnet arrangement shown achieves the weakest magnetic field strength, |Bx(min)|, at the midpoint of the line segment connecting the points where |Bx(max)| is obtained. Then, using |Bx(min)| / |Bx(max)| as an index value, an optimal magnetron magnetic field is generated when |Bx(min)| / |Bx(max)| ≤ 0.1. This means that the stronger the contrast between the zero-magnetic-field region and the high-intensity magnetic field formed by the magnetron magnetic field, the better. Note that since the index value is 0 when |Bx(min)| = 0, therefore 0 ≤ |Bx(min)| / |Bx(max)|.

[0047] More preferably, |By(min)| / |By(max)|≥0.3, |Bx(min)| / |Bx(max)|≤0.03.

[0048] As mentioned above, such as Figure 3 The basic magnet arrangement and use shown Figure 4 and Figure 5 Explain the detailed magnet arrangement, or use Figure 6 and Figure 7 The detailed explanation of the magnetron magnetic field and the parallel arrangement of the magnetic fields enables the confinement of high-density plasma.

[0049] Figure 8 It shows Figure 3 The diagram illustrates the relationship between vacuum level and ignition voltage when the magnets are arranged in a specific configuration and when only a parallel magnetic field can be generated. Furthermore, in the absence of magnets, the discharge occurs outside the electrodes, not in the space between them. Figure 8 In the diagram, circles indicate the generation of both a magnetron magnetic field and a parallel magnetic field, while squares indicate the generation of only a parallel magnetic field. The pressure is approximately 10. 2 Up to 10 －1 Even with a magnetic field generated by the magnetron, ignition can be achieved at approximately the same voltage as in the case of a parallel magnetic field only. However, from Figure 8 It can be seen that, obviously at 10 －1 In a high vacuum state below Pa, when the magnetron magnetic field is still generated, the ignition voltage is lower and discharge is more likely to occur. That is, it can be known that at 10 － 1 Plasma generation efficiency is improved under high vacuum conditions below Pa. It is expected that in 10... －6 Under ultra-high vacuum conditions below Pa, plasma generation efficiency will be improved.

[0050] Example 2

[0051] The plasma source shown in the first embodiment can be applied to an ion pump. When used as an ion pump, in Figure 3Based on the structure shown, a Ti film 1610 is formed on the surface of the upper electrode 1510 on the lower arm 1300 side, and a Ti film 1620 is formed on the surface of the lower electrode 1530 on the upper arm 1200 side, as shown. Figure 9 As shown.

[0052] In the ion pump, ions in the plasma collide with Ti atoms on the surfaces of the upper electrode 1510 and lower electrode 1530, which serve as cathodes. The Ti atoms are scattered in all directions, i.e., sputtered. The sputtered Ti atoms also form a Ti film on electrode 1520. Furthermore, the sputtered Ti atoms chemically adsorb reactive gases, increasing the vacuum level. Even inert gases are ionized through collisions with electrons and confined within the cathodes 1510 and 1530, as well as within the Ti films 1610 and 1620. Therefore, the vacuum level becomes even higher.

[0053] Example 3

[0054] The vacuum pump according to the second embodiment can be applied to a small cooling atomic clock. Figure 10 The diagram schematically illustrates the components related to the vacuum pump in a small cooled atomic clock, as well as the structure of the vacuum pump. The battery section 1500 and the atomic clock section 1800, sandwiched between the upper arm 1200 and the lower arm 1300 of the magnetic yoke 1100, are integrated and communicate with the internal space 1700 of the battery section 1500 and the cold atom generator 1810 in the atomic clock section 1800 via the space 1830 between the upper electrode 1510 and the electrode 1520 and the space 1840 between the electrode 1520 and the lower electrode 1530.

[0055] First, such as Figure 11 As shown, the battery section 1500 is inserted between the upper arm 1200 and the lower arm 1300 of the magnetic yoke 1100. A voltage is applied between the upper electrode 1510, the lower electrode 1530, and the electrode 1520 to generate plasma in the space 1700 of the battery section 1500. The space 1700 and the cold atom generator 1810 are then evacuated together. However, since the generation of cold atoms is adversely affected by the magnetic field, the battery section 1500 and the atomic clock section 1800 are separated from the magnetic yoke 1100, as shown... Figure 10 As shown. In this way, by configuring the magnetic yoke 1100 including the magnet, the battery section 1500 and the atomic clock section 1800 as detachable, it can be more suitable for use in small cooled atomic clocks.

[0056] Such miniature cooled atomic clocks are needed not only for high-precision positioning of moving objects such as automobiles, and for 5G and 6G mobile communication base stations, but also as a reference time in network communications such as mobile devices, cloud computing, and e-commerce, and as the basis for precision measurements in industrial and cutting-edge scientific and technological fields (Earth exploration and gravitational wave measurement). They are indispensable infrastructure for various activities in modern society. Furthermore, the plasma source according to this embodiment can be used as an ion generation source for ion beams, a light source, etc.

[0057] The embodiments of the present invention have been described above, but the present invention is not limited thereto. That is, values ​​other than those related to the magnet distance ratio L / T, |By(min)| / |By(max)|, and |Bx(min)| / |Bx(max)| can be changed to achieve values ​​related to these indices. Furthermore, the cylindrical magnets 1210 and 1310 can also be cylindrical formed by combining multiple magnets. Additionally, the cylindrical magnets 1220 and 1320, as well as the cylindrical magnets 1210 and 1310, can have shapes other than circular.

[0058] Furthermore, although many examples have been illustrated in which the distance between cylindrical magnets 1210 and 1310 is the same as the distance between cylindrical magnets 1220 and 1320, the distances can also be different. Furthermore, although Figure 3 Examples of axisymmetric plasma sources are shown, but they do not necessarily have to be axisymmetric.

[0059] Examples of small vacuum pumps

[0060] Figure 12 This is a diagram illustrating the experimental method. For example... Figure 12 As shown, the vacuum pump 2000 according to the second embodiment is placed in a volume of 280 cm³. 3 The glass tube is filled with a vacuum pump, and a voltage can be applied from outside the glass tube while it is sealed by a feed electrode. A turbomolecular pump (TMP) installed in the glass tube is used to evacuate the tube, and an ionization vacuum gauge is used to monitor the vacuum level inside the glass tube.

[0061] The glass tube was evacuated to 1 × 10⁻⁶ using a turbomolecular pump. －6 After Pa, the bellows valve was closed to seal the glass tube. Due to degassing adsorbed by the O-ring and the inner wall of the glass tube during valve sealing, the vacuum level immediately deteriorated after valve closure. The pressure rise was assessed and found to be 3 × 10⁻⁶. －3 Pa / min. When the valve is closed and the vacuum level deteriorates to 1×10⁻⁶ Pa / min. －2At a voltage of 1.2 kV, the cathode and anode of the vacuum pump 2000 were applied, and a discharge attempt was made for 6 minutes. Subsequently, discharge attempts were made by applying voltages of 1.5 kV and 1.8 kV for 6 minutes respectively.

[0062] As a result, Figure 13 As shown, the pressure before applying voltage is 1×10 －2 The pressure was 2.7 × 10 Pa, but when a voltage of 1.2 kV was applied to the vacuum pump 2000 and it was discharged for 6 minutes, the pressure was 2.7 × 10 Pa. －3 When a voltage of 1.5 kV is applied and discharged for 6 minutes, the pressure drops to 1.8 × 10 Pa. －3 After applying a voltage of 1.8 kV and discharging for 6 minutes, the pressure can be reduced to 1.7 × 10 Pa. －3 Pa. Therefore, it can be explained that vacuum degassing can be performed by using the plasma source according to the first embodiment.

[0063] This embodiment can be summarized as follows.

[0064] According to a first aspect of this embodiment, a plasma source includes: (A) a first magnet; (B) a second magnet arranged such that a second magnetic pole of the second magnet, different from the first magnetic pole, is opposite to a first magnetic pole of the first magnet; (C) a third magnet arranged such that a second magnetic pole of the third magnet, different from the first magnetic pole, is opposite to the first magnetic pole in the same direction as the first magnetic pole of the first magnet, and the third magnet is arranged around the first magnet; (D) a fourth magnet arranged such that a first magnetic pole of the fourth magnet, different from the second magnetic pole, is opposite to a second magnetic pole of the third magnet, and the fourth magnet is arranged around the second magnet; and (E) a first electrode disposed on the first magnetic pole of the first magnet and the third magnet. (F) A second electrode, facing the first electrode, is disposed on the side where the second magnetic pole of the second magnet and the first magnetic pole of the fourth magnet are located; (G) A third electrode, disposed between the first and second electrodes, is configured such that its potential is higher than that of the first and second electrodes when a voltage is applied; wherein, in the first space between the first and second magnets and in the second space between the third and fourth magnets, the maximum magnetic field strength |By(max)| in the first direction from the second magnet to the first magnet and the minimum magnetic field strength |By(min)| in the first direction satisfy |By(min)| / |By(max)|≧0.1. Furthermore, in the third space sandwiched between the first and second spaces, the maximum magnetic field strength |Bx(max)| in the second direction perpendicular to the first direction and the minimum magnetic field strength |Bx(min)| in the second direction satisfy |Bx(min)| / |Bx(max)|≤0.1.

[0065] By arranging the first to fourth magnets in such a magnetic field strength distribution, a small plasma source capable of efficient discharge under ultra-high vacuum conditions can be obtained. More preferably, |By(min)| / |By(max)|≥0.3, |Bx(min)| / |Bx(max)|≤0.03.

[0066] The plasma source of the second embodiment has the same structural elements (A) to (G) as the plasma source of the first embodiment. Then, the shorter of the distance between the first magnet and the second magnet and the distance between the third magnet and the fourth magnet is divided by the average thickness of the first to fourth magnets, and this value is 1 or more and 10 or less.

[0067] By adopting this magnet size and magnet arrangement, a small plasma source capable of efficient discharge under ultra-high vacuum conditions can be obtained.

[0068] Furthermore, the first and second magnets mentioned above can also be cylindrical, and the third and fourth magnets can also be cylindrical. From an efficiency point of view, axisymmetry is preferred.

[0069] Furthermore, in the plasma source according to the second aspect, it is more preferable to divide the shortest distance between the first magnet and the second magnet and the distance between the third magnet and the fourth magnet by a value of 2.5 or more and 5 or less of the average thickness of the first to fourth magnets, thereby achieving a higher density plasma confinement.

[0070] Furthermore, the first to fourth magnets can be detached from the battery including the first to third electrodes. In this way, after the plasma source is used as an ion pump, for example, if the magnetic force of the magnets has an adverse effect, the first to fourth magnets can be removed and the battery can be used.

[0071] The atomic clock according to this embodiment includes: a plasma source, wherein the first to fourth magnets are detachable from a battery including the first to third electrodes; and a cold atom generator connected to the aforementioned battery of the plasma source. Thus, by using an ion pump of the plasma source to vacuum-expel the cold atom generator, an ultra-high vacuum state can be obtained. Furthermore, the first to fourth magnets can be separated from the battery during cold atom generation.

Claims

1. A plasma source, characterized in that, include: First magnet; A second magnet is arranged opposite a first magnetic pole of the first magnet, with a second magnetic pole of the second magnet that is different from the first magnetic pole. A third magnet has a second magnetic pole that is different from the first magnetic pole facing it in the same direction as the first magnetic pole of the first magnet, and the third magnet is arranged around the first magnet. A fourth magnet, with respect to the second magnetic pole of the third magnet, has a first magnetic pole of the fourth magnet that is different from the second magnetic pole opposite to it, and the fourth magnet is arranged around the second magnet; The first electrode is disposed on the same side as the first magnetic pole of the first magnet and the second magnetic pole of the third magnet; The second electrode faces the first electrode and is disposed on the same side where the second magnetic pole of the second magnet and the first magnetic pole of the fourth magnet are located; A third electrode, disposed between the first and second electrodes, is configured such that its potential is higher than that of the first and second electrodes when a voltage is applied; wherein... In the first space between the first magnet and the second magnet, and in the second space between the third magnet and the fourth magnet, the maximum magnetic field strength |By(max)| in the first direction from the second magnet to the first magnet, and the minimum magnetic field strength |By(min)| in the first direction, satisfy |By(min)| / |By(max)|≥0.1, and In the third space sandwiched between the first space and the second space, the maximum magnetic field strength |Bx(max)| in the second direction perpendicular to the first direction and the minimum magnetic field strength |Bx(min)| in the second direction satisfy |Bx(min)| / |Bx(max)|≤0.

1.

2. A plasma source, characterized in that, include: First magnet; A second magnet is arranged opposite a first magnetic pole of the first magnet, with a second magnetic pole of the second magnet that is different from the first magnetic pole. A third magnet has a second magnetic pole that is different from the first magnetic pole facing it in the same direction as the first magnetic pole of the first magnet, and the third magnet is arranged around the first magnet. A fourth magnet, with respect to the second magnetic pole of the third magnet, has a first magnetic pole of the fourth magnet that is different from the second magnetic pole opposite to it, and the fourth magnet is arranged around the second magnet; The first electrode is disposed on the same side as the first magnetic pole of the first magnet and the second magnetic pole of the third magnet; The second electrode faces the first electrode and is disposed on the same side where the second magnetic pole of the second magnet and the first magnetic pole of the fourth magnet are located; A third electrode, disposed between the first and second electrodes, is configured such that its potential is higher than that of the first and second electrodes when a voltage is applied; wherein... The shorter of the distance between the first magnet and the second magnet and the distance between the third magnet and the fourth magnet, divided by the average thickness of the first magnet, the second magnet, the third magnet, and the fourth magnet, is between 1 and 10.

3. The plasma source according to claim 1 or 2, characterized in that: The first magnet and the second magnet are cylindrical; The third and fourth magnets are cylindrical.

4. The plasma source according to claim 1, characterized in that: The maximum magnetic field strength |By(max)| in the first direction from the second magnet to the first magnet and the minimum magnetic field strength |By(min)| in the first direction satisfy |By(min)| / |By(max)|≧0.3; The maximum magnetic field strength |Bx(max)| in the second direction perpendicular to the first direction and the minimum magnetic field strength |Bx(min)| in the second direction satisfy |Bx(min)| / |Bx(max)|≤0.

03.

5. The plasma source according to claim 2, characterized in that: The shorter of the distance between the first magnet and the second magnet and the distance between the third magnet and the fourth magnet, divided by the value of the average thickness of the first magnet, the second magnet, the third magnet and the fourth magnet, is between 2.5 and 5.

6. The plasma source according to any one of claims 1 to 5, characterized in that: The magnets, including the first magnet, the second magnet, the third magnet, and the fourth magnet, are removable for the battery, which includes the first electrode, the second electrode, and the third electrode.

7. An atomic clock, characterized in that, include: The plasma source as described in claim 6; A cold atom generator connected to a battery of the plasma source.

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