A long-life multi-filament high-current negative hydrogen multi-peak field ion source

Abstract

The invention discloses a long-life multi-filament high-current negative hydrogen multi-peak field ion source, comprising: an ion source filament, an ion source upper cover plate, an ion source filament rod, an ion source inner cavity, an ion source outer cavity, a permanent magnet array located between the ion source inner cavity and the ion source outer cavity, an ion source extraction structure, and an ion source composite structure filter field located at the second layer and the bottom layer of the permanent magnet array and the ion source extraction structure; the ion source composite structure filter field is an ion source composite structure filter field with a thickened magnetic field design, the composite structure filter field with a thickened magnetic field design superimposes a magnetic field at the highest point of the filter field and filters fast electrons; the ion source filament is a spiral four-filament structure; the ion source extraction structure is an ion source extraction structure that extracts a negative hydrogen current intensity higher than 30 mA under a high voltage of 40 kV; the invention solves the problem in the prior art that the filter magnetic field is too thin or too small, resulting in low yield, by enhancing the magnetic field strength and increasing the magnetic field thickness.

Description

Technical Field

[0001] The invention belongs to the technical field of filament ion sources, and in particular relates to a long-life multi-filament high-current negative hydrogen multi-peak field ion source. Background Art

[0002] Ion source technology is a key component of cyclotron accelerators. An ion source is a device that ionizes neutral atoms or molecules and extracts an ion beam from them. As the source of the beam, the ion source determines beam quality and directly impacts cyclotron performance.

[0003] Filament ion sources and built-in antenna ion sources have different applications. The former operates in continuous mode, while the latter operates in pulsed mode. The high-current negative hydrogen filament ion source in continuous mode has been widely used in recent years as a high-yield, high-current, and long-life ion source. Its extraction current is above 30 mA, and its service life is required to be greater than half a year. Compared with the low-yield, low-current, and short-life filament ion sources in the existing technology, the difficulties in achieving a high-yield, high-current, and long-life ion source are:

[0004] 1. Compared with low yield, high yield produces too many electrons. The more electrons there are, the more fast electrons are generated by the collision between electrons and hydrogen. The too many fast electrons make the original magnetic field unable to filter out so many fast electrons. After the fast electrons enter the extraction area, they collide with the negative hydrogen ions that have been generated, and the negative hydrogen ions disappear, resulting in a decrease in yield.

[0005] 2. The reason why "there are too many fast electrons in the existing technology, resulting in the original magnetic field being unable to filter out so many fast electrons" is because the magnetic field of the multi-peak field virtual filtering field in the existing technology is relatively thin (the so-called filtering field is the magnetic field that changes direction from vertical to horizontal, thereby intercepting the fast electrons moving vertically downward). The thin magnetic field of the filtering field is because the filtering magnetic field is arranged near the extraction outlet, that is, there is only a short distance from the N pole to the S pole near the extraction outlet. Ideally, the fast electrons will turn 180 degrees and be completely bounced back when encountering the filtering field. The principle of the fast electron changing direction is that the magnetic field causes the fast electrons to change direction. When the filtering field is thin, the fast electrons have only one chance to change direction. In one chance, there will always be a part that cannot reach a 180-degree deflection, for example, only a 150-degree deflection. When the distance from the N pole to the S region is relatively long, even if the turning angle is not large enough, it will not enter the extraction structure and will remain inside the cavity. However, when the magnetic field of the filtering field is thin, if it cannot be fully reflected back 180 degrees, some fast electrons will directly enter the extraction area, thereby causing the fast electrons to collide with the negative hydrogen ions in the extraction area, causing the negative hydrogen ions to disappear and return to their initial state, thereby reducing the yield of negative hydrogen ions.

[0006] 3. The reason why existing technologies "exceed the number of fast electrons, preventing the original magnetic field from filtering them out" is that the existing multi-peak virtual filter field is too small. Increasing the output requires increasing the filament area, which increases the filament current and arc power. This results in higher energy high-energy electrons. Higher energy high-energy electrons require higher magnetic field strength, but the existing virtual filter field of the ion source is too small.

[0007] 1) One of the reasons why the virtual filtering field in the existing technology is too small is that the highest peak of the filtering field is not in the cavity. For example, Patent No.: 201020700147.9, Patent Name: Magnet Structure for Generating Virtual Filtering Magnetic Field, its virtual filtering magnetic field is located inside the cavity, but the highest point of its magnetic field strength is located on the lower surface of the plasma electrode in the extraction area outside the cavity. Since filtering out electrons depends on the magnetic field strength of the area, when the highest point of the magnetic field strength is not in the cavity, the block electrons filtered out are not sufficient, and some fast electrons enter the extraction area due to inadequate filtering. Since the negative hydrogen ions in the extraction area are doped with fast electrons, the fast electrons will destroy some of the negative hydrogen ions, causing the negative hydrogen ions in the extraction area to return to their initial state, resulting in a reduction in the yield of negative hydrogen ions in the extraction area;

[0008] 2) The second reason why the existing technology's virtual filtering field magnetic field is too small is: the latest theoretical research shows that the H- yield produced by the interaction between the high-temperature excited state H2* and the 0.5eV slow electrons is higher, rather than the previously believed 1eV. This requires further increasing the magnetic field strength to filter out the 1eV electrons. The existing virtual filtering field magnetic field is designed based on filtering out 1eV electrons. Compared with 0.5eV electrons and 1eV electrons, 1eV electrons can still destroy the negative hydrogen ions in the extraction area. Therefore, the existing technology's virtual filtering field magnetic field based on filtering 1eV appears to be too small. Summary of the Invention

[0009] In order to solve the problems existing in the prior art, the present invention proposes a long-life multi-filament high-current negative hydrogen multi-peak field ion source, the purpose of which is to solve the problem that the filtering magnetic field is too thin and too small during the realization of a high-yield, high-current, long-life ion source, making it difficult to achieve high yield.

[0010] In order to solve the technical problems, the present invention proposes the following technical solutions:

[0011] A long-life multi-filament high-current multi-peak field negative hydrogen ion source 1, which comprises, from top to bottom and from outside to inside: an ion source filament 2, an ion source upper cover plate 1-1, an ion source filament holder 1-2, an ion source inner cavity 1-3, an ion source outer cavity 1-4, a permanent magnet array 3 located between the ion source inner cavity 1-3 and the ion source outer cavity 1-4, an ion source extraction structure 4, and an ion source composite structure filter field located at the second layer and the bottom layer of the permanent magnet array and the ion source extraction structure;

[0012] The ion source filament 2 is used to generate a DC electric field, which is externally connected to a steady current source. A large current is connected through the ion source filament 2 located on the ion source filament holder 1-2, so that the ion source filament 2 is heated and emits electrons; the electrons emitted by the ion source filament 2 when heated collide with the hydrogen gas introduced into the ion source under the action of the arc voltage applied to the ion source upper cover 1-1 to generate negative hydrogen ions;

[0013] The permanent magnet array 3 is used to provide a confining magnetic field in the ion source cavity 1-3; the permanent magnet array 3 includes a radial magnet array and a tangential magnet array arranged at intervals along the circumferential direction from the top layer to the bottom layer, and a last layer of filtering magnet array 3-1.

[0014] The ion source composite structure filter field is used to form a composite transverse magnetic field to filter out fast electrons. The ion source composite structure filter field is composed of a filter magnet array 3-1 and an extraction structure attracting magnet 4-3.

[0015] Its characteristics are: the ion source composite structure filter field is an ion source composite structure filter field with a thickened magnetic field design, the composite structure filter field with a thickened magnetic field design superimposes a magnetic field at the highest point of the filter field and filters fast electrons; the ion source filament is a spiral four-filament structure; the ion source extraction structure 4 is an ion source extraction structure that extracts a negative hydrogen current intensity higher than 30mA under a high voltage of 40kV.

[0016] Furthermore, the filtering magnet array 3-1 is used to adjust the position of the highest point of the filtering magnetic field before the plasma electrode, so that the fast electrons are fully filtered out before reaching the extraction structure, and the filtering magnet array 3-1 is also used to thicken the axial distribution of the filtering magnetic field.

[0017] Furthermore, the filtering magnet array 3-1 adjusts the position of the highest point of the filtering magnetic field in front of the plasma electrode, which means that the radial magnet in the middle of the bottom layer of the filtering magnet array 3-1 and the tangential magnets on both sides thereof are of the same polarity and raised, so that the magnetic field formed by the magnets in the lead-out area and the magnetic fields formed by the magnets in the middle of the bottom layer and on both sides of the filtering magnet array 3-1 with the same polarity and raised are superimposed, thereby forming a filtering magnetic field at the highest point of the superimposed magnetic field.

[0018] Furthermore, the filtering magnet array 3-1 thickens the axial distribution of the filtering magnetic field, which means that tangential magnets b4 and b5 of opposite polarity are added to the second layer of the permanent magnet array 3 from top to bottom, that is, at the filament position, to thicken the filtering field. The thickness of the axial distribution of the filtering magnetic field is about 100 mm, and the remaining radial magnets and tangential magnets of the permanent magnet array 3 are used to form a multi-peak field that confines the plasma.

[0019] Furthermore, the radial magnet in the middle of the bottom layer of the filtering magnet array 3-1 and the tangential magnets on both sides of the radial magnet have the same polarity and are raised. Specifically, the filtering magnet array 3-1 is provided with the two opposite radial magnets at the bottom layer of the permanent magnet array 3 replaced by radial magnets b2 with reversed polarity, and tangential magnets b1 and tangential magnets b3 of the same polarity are added on both sides of the radial magnets b2 after the polarity is reversed, and the distance between the radial magnets b2, tangential magnets b1, and tangential magnets b3 and the bottom surface is raised so that the raised distance of the three magnets is 18 mm.

[0020] Furthermore, the ion source extraction structure 4 is provided with a plasma electrode 4-1, an attracting electrode 4-2, an attracting electrode magnet 4-3, an attracting level baffle 4-4, a plasma electrode fixing part 4-5, an attracting electrode fixing part 4-6, and a grounding level 4-7, which are arranged in sequence along the axial direction at the bottom of the ion source cavity; the plasma electrode 4-1 is used to receive the particles to be extracted and allow the particles to pass through the opening in the middle; the attracting level 4-2 is used to improve the envelope shape of the negative hydrogen ion extraction, so that the envelope shape is neither divergent nor contracted, and the attracting level 4-2 has a sharp-angle extension. The pole magnet 4-3 is used to guide the negative hydrogen ion extraction trajectory into a straight trajectory, and deflects the electrons in the negative hydrogen beam to the suction level baffle; the pole magnet 4-3 is divided into two layers, upper and lower, arranged in the middle of the pole 4-2, and each layer is a pair of permanent magnets inclined to each other; the ground level is used to form a voltage field for the extraction of negative hydrogen ions with the plasma electrode; wherein the electrodes are separated by an insulator, and an adjustable suction level voltage is applied between the pole 4-2 and the plasma electrode 4-1 to adjust the beam distribution.

[0021] Furthermore, a pair of oppositely arranged figure-eight 45-degree inclination pole magnets 4-3 on the upper layer have a magnetic field component in one direction that is consistent with the filtering magnetic field direction of the filtering magnet array 3-1, and the two magnetic fields are superimposed together, thereby forming a superimposed magnetic field for filtering fast electrons; a pair of oppositely arranged figure-eight 45-degree inclination pole magnets 4-3 on the upper layer have a magnetic field component in another direction that is used to deflect slow electrons in the negative hydrogen beam to the suction baffle, thereby realizing the separation of electrons and negative hydrogen ions.

[0022] Furthermore, the axial distance between the suction electrode 4-2 and the plasma electrode 4-1 is 4 mm, the thickness of the suction electrode is 15 mm (3*5 mm), and two pairs of 3*5*25 mm permanent magnets are embedded in the middle.

[0023] Furthermore, the opening angle of the hole in the middle of the plasma electrode 4-1 is about 62.5°, the thickness is 3mm, the aperture is 14mm, and its voltage to ground is 40kV; the axial distance between the suction electrode 4-2 and the plasma electrode 4-1 is 4mm, the thickness is 15mm (3*5mm), and two pairs of 3*5*25mm permanent magnets are embedded in the middle; its first aperture is 10mm, the axial distance between the sharp corner and the upper surface of the plasma electrode is 2.5mm, and the aperture at the protruding point of the sharp corner is 22mm; the second aperture is 18mm; the third aperture is 14mm, which is a rounded corner, and its voltage to ground is 30-34kV, that is, the suction voltage between the plasma electrode and the suction level is 6-10kV; the thickness of the ground electrode is 5mm, and the axial distance from the suction electrode is 14mm.

[0024] Furthermore, the ion source filament is a tantalum wire with a diameter of 3 mm and a length of about 15-20 cm. It adopts a four-filament structure and is wound into a spiral shape with 10-12 turns and a spiral diameter of 8-10 mm. During operation, a filament current greater than 600 A will be passed through.

[0025] Advantages and effects of the present invention

[0026] 1. The present invention solves the problem of the prior art that the filter magnetic field is too thin and too small to intercept too many fast electrons, resulting in a low yield, by increasing the magnetic field strength and thickness. That is, by raising the position of the filter field so that its highest point is just before the lead-out structure and then thickening the filter field on this basis.

[0027] 2. The present invention enhances the filtration field through the superposition magnetic field of the composite structure, further solving the problem of the prior art that the filtration magnetic field is too thin and too small, which prevents too many fast electrons from being intercepted, resulting in an inability to improve the yield: by aligning the magnetic field direction of the pair of upper magnetic field magnets 4-3 with the magnetic field direction of the filter magnet array 3-1 in the cavity, one of the conditions for magnetic field superposition is met; by superimposing the two magnetic fields to achieve the best superposition state, the second condition for magnetic field superposition is met, that is, the thickness of the plasma electrode 4-1 and the axial distance from the magnetic field magnet 4-2 to the plasma electrode 4-1. This axial distance is a compromise distance: on the one hand, it is better to take into account the electric field, on the other hand, it is also better to take into account the fact that sparks will not occur due to being too close. Therefore, the distance between the magnetic field magnet 4-2 and the plasma electrode is selected to be 4mm. The above design further achieves the goal of a high-yield, high-current, and long-life ion source. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the negative hydrogen ion source device of the present invention;

[0029] Figure 2 Schematic diagram of the ion source filament of the present invention;

[0030] Figure 3a This is a cross-sectional view of a multi-peak field magnet in a multi-peak field negative hydrogen ion source in the prior art;

[0031] Figure 3b This is a top view of the multi-peak field magnet in the prior art multi-peak field negative hydrogen ion source; a is the radial magnet array, b is the tangential magnet array;

[0032] Figure 3c A cross-sectional view of the filtering magnet array within the multi-peak field negative hydrogen ion source of the present invention;

[0033] Figure 3d A top view of the filter magnet array within the multi-peak field negative hydrogen ion source of the present invention;

[0034] Figure 4a It is a cross-sectional view of the extraction structure of the ion source of the present invention;

[0035] Figure 4b The figure shows the structure and dimensions of the ion source of the present invention;

[0036] Figure 4c Schematic diagram of the superimposed magnetic field of the multi-peak field negative hydrogen ion source composite structure filtering field of the present invention;

[0037] Figure 4d This is a schematic diagram of the 30mA ion simulation beam envelope drawn out by the ion source extraction structure of the present invention.

[0038] Figure 4e Schematic diagram of the negative hydrogen ion extraction trajectory corrected by the reverse magnetic field of the lower polar magnet of the ion source extraction structure of the present invention;

[0039] In the figure: 1: negative hydrogen ion source; 1-1: filament ion source upper cover; 1-2: ion source filament holder; 1-3: ion source inner cavity; 1-4: ion source outer cavity; 2: ion source filament; 3: permanent magnet array; 4: ion source extraction structure; 3-1: filter magnet array; 4: ion source extraction structure; 4-1: plasma electrode; 4-2: suction electrode; 4-3: suction electrode magnet; 4-4: suction level baffle; 4-5: plasma electrode fixing part; 4-6: suction electrode fixing part; 4-7: ground electrode. DETAILED DESCRIPTION

[0040] Design principle of the present invention

[0041] 1. Design to solve the problem of thin filtering magnetic field in the prior art_The design principle of the thickened filtering magnetic field of the high-yield, high-current negative ion source of the present invention: The thickening of the filtering magnetic field must meet two conditions at the same time to truly achieve the effect of thickening. The purpose of thickening is to intercept too many fast electrons in the ion source cavity so that the fast electrons will not enter the extraction area. The interception of too many fast electrons in the ion source cavity depends on the strength and thickness of the filtering magnetic field. The purpose of increasing the thickness of the magnetic field is to change the turning of the fast electrons from one turn to multiple turns, and multiple turns can form the final 180-degree turn. However, if the strength of the magnetic field is not enough, the angle of each turn is small, or the number of fast electrons turned is small, then when reaching the end of the extraction outlet, there will still be a part of the fast electrons that cannot be completely intercepted and will enter the extraction structure. Therefore, the strength and thickness of the filtering magnetic field complement each other.

[0042] The method of enhancing the magnetic field strength of the filter field of the present invention is to raise the position of the filter field so that its highest point is just before the lead-out structure, and then thicken the filter field. ① Formation of the filter field: The filter field of the present invention is as follows Figure 3c 、 3d As shown, in Figure 3c In the , the filtering field direction is perpendicular to the computer screen, that is, the direction of penetrating into the paper. Figure 3c Rotate 90 degrees clockwise and look down. Figure 3d direction, Figure 3d The filter field shown is a horizontal filter field. The filter field is formed by using the three magnets at the bottom layer to be magnets of the same polarity and arranged 180 degrees relative to each other, that is, the other end of the 180-degree polarity S is the three magnets of polarity N; Figure 3d In the transverse filtering field, the N pole is on the right and the S pole is on the left, thus forming a transverse magnetic field pointing to the left. Since the transverse magnetic field is perpendicular to the vertical magnetic field perpendicular to it, it changes the direction of the magnetic field and can intercept fast electrons and change their direction. ② Raise the filtering field so that its highest point is in front of the extraction structure: In order to prevent fast electrons from entering the extraction structure and destroying the negative hydrogen ions, it is necessary to Figure 3c The filtration field is raised, and the filtration field is raised as Figure 3c The middle b1, b2, and b3 poles are raised as shown. After calculation, the present invention raises the three magnets 18mm above the bottom layer. At this time, the highest point of the filter field is just before the extraction structure. ③ Thickening the filter field: Since the electron path of the filament ion source is longer, a thicker filter field can better filter electrons. Therefore, it is necessary to Figure 3d The filter field thickens, and the filter field thickens as Figure 3c The middle poles 5 and 6 are elevated as shown. After calculation, the present invention elevates two magnets in the opposite direction of magnets 1, 2, and 3 above the second layer of the multi-peak field magnet (where the filament is located) to make the filter field thickness 100 mm.

[0043] 2. Design to solve the problem of small filtering magnetic field in existing technology _ Design of the high-yield, high-current negative ion source composite structure filtering field of the present invention:

[0044] ① Forming a multi-peak field for confining plasma: The multi-peak field magnet of the present invention includes both radial magnets and tangential magnets (the radial magnets have polarities pointing in the radial direction, and the tangential magnets have polarities pointing in the tangential direction of the circumference), forming a confinement field for confining plasma. Compared with the prior art, the last layer of the multi-peak field magnet of the present invention has both radial magnets and tangential magnets. The bottom layer of the multi-peak field magnet is as follows: Figure 3c shown.

[0045] ② Forming a filtering field to filter high-energy electrons: For a multi-peak negative hydrogen ion source, the ion source plasma chamber is divided from top to bottom into two parts: a high-temperature discharge chamber and a low-temperature ion extraction zone. In the high-temperature discharge chamber, electrons remaining in the vacuum are accelerated by the DC electric field generated by the filament, where they collide with hydrogen molecules or atoms to produce high-energy excited H₂*. The excited H₂* interacts with slow electrons in the discharge chamber to produce negative hydrogen ions (H₁). This reaction is called dissociative adsorption. However, negative hydrogen ions (H₁) are destroyed by fast electrons. Therefore, the high-temperature discharge chamber and the low-temperature ion extraction zone are divided by the filtering magnetic field. The filtering field ensures that slow electrons in the discharge chamber enter the extraction zone to generate negative hydrogen ions, while preventing fast electrons from entering the extraction zone and destroying existing negative hydrogen ions. It is a critical component of the multi-peak negative hydrogen ion source, and its structure directly affects the yield of negative hydrogen ions.

[0046] ③ The present invention elevates the filtration field so that its highest point is just before the lead-out structure and thickens the filtration field. After the three magnetic poles at the bottom layer are raised, the filtration magnetic field is just before the lead-out structure. Figure 4a As shown, it falls on the upper surface of the plasma electrode 4-1 or in the area near the upper surface. Because the prior art does not raise the distance between the three magnetic poles and the bottom surface, and because the field strength of the attracting magnet is greater than the field strength of the three magnets on the bottom layer, the highest point of the superimposed filtered magnetic field falls on the lower surface of the plasma electrode. As a result, the filtered magnetic field within the cavity is not at its highest point. Furthermore, the prior art uses a thinning design for the filtered magnetic field, resulting in a weak filtered magnetic field.

[0047] ④ Design principle of superimposed magnetic fields: The composite structure's superimposed magnetic fields enhance the filtration field and further improve yield: The attracting magnets 4-3 are arranged in two layers, upper and lower, between the attracting electrode 4-2. Each layer consists of a pair of mutually inclined permanent magnets. When the magnetic field direction of the upper pair of attracting magnets 4-3 aligns with the magnetic field direction of the filtering magnet array 3-1 within the cavity, one of the conditions for magnetic field superposition is met. The second condition for magnetic field superposition is to achieve the optimal superposition of the two magnetic fields. This optimal superposition depends on the thickness of the plasma electrode 4-1 and the axial distance between the attracting electrode 4-2 and the plasma electrode 4-1. The thicker the plasma electrode or the greater the axial distance between the attracting electrode 4-2 and the plasma electrode 4-1, the weaker the superposition of the two magnetic fields. At the same time, under the condition of a certain potential difference (the plasma electrode potential to ground is 40 kV, and the attracting electrode potential to ground is 34 kV), the greater the distance between the two electrodes, the less the electric field affects the shape of the plasma sheath. However, if the distance is too close, it is more likely to cause breakdown. Therefore, the present invention selects a compromise number: on the one hand, it is better to take into account the electric field, on the other hand, it is better to take into account the magnetic field, and it is also necessary to take into account that there will be no sparks due to the distance being too close. Therefore, the distance between the suction electrode 4-2 and the plasma electrode is selected to be 4mm.

[0048] 3. Design of the extraction structure of high-yield, high-current negative hydrogen ion source: ① Design principle of the suction field: When a large amount of plasma is generated in the ion source cavity, the 40kV high voltage will extract the plasma. The extracted plasma will form a plasma sheath on the plasma electrode, thereby determining the shape of the plasma emission surface and changing the shape of the extracted beam. The present invention adopts the suction field to affect the shape of the plasma sheath without changing the extraction energy, thereby improving the beam extraction state. ② Design principle of the thickness of the plasma electrode 4-1: If the plasma electrode is too thick, and the suction voltage between the upper surface of the plasma electrode 4-1 and the suction level 4-2 is too weak, the suction field cannot penetrate into the emission hole well, and the extraction ability is reduced. Therefore, in this design, without affecting the structural strength, the thickness of the plasma electrode 4-1 should be reduced as much as possible, and a suitable suction voltage should be selected. ③ Design principle of the sharp corner of the attractor 4-2: The attractor has a sharp corner that can enhance the attractor field penetrating into the emission hole. At the same time, due to the space charge effect, the increase in the thickness of the attractor 4-2 and its axial distance from the plasma electrode 4-1 will increase the divergence angle. Therefore, in this design, the thickness of the attractor and its axial distance from the plasma electrode should be minimized under the conditions of cooling and avoiding breakdown. ④ Design principle of the magnet of the attractor 4-2: According to research, when negative hydrogen ions are extracted, a 100-fold electron beam (slow) will be extracted. Therefore, in this design, it is necessary to embed a suitable magnet in the attractor while meeting the size of the attractor 4-2 to deflect the electrons to the attractor baffle. ⑤ Design principle of the geoelectric stage 4-7: The aperture size has little effect on the performance of the extracted beam, but its aperture determines the beam radius that is ultimately injected into the accelerator.

[0049] 4. High-yield, high-current negative hydrogen ion source filament structure design: ① Multi-filament design: The filament used in the present invention is tantalum filament. The electron emission characteristics of tantalum filament and tungsten filament in a vacuum are basically the same, but in practice it is found that the negative hydrogen ion beam generated by tantalum filament is brighter and has a higher current intensity, but it degrades faster than tungsten filament under higher arc current. The increase in the number of filaments means an increase in the number of emitted electrons, a higher degree of plasma ionization, and a stronger outgoing current. ② Design of spirally thickened filament: The spiral-shaped, thickened filament is adopted because the overall length of the thickened filament is longer after spiral winding in a limited space, and the material loss is smaller when running with a large current, that is, the service life is greatly increased. In addition, the electron emission area of ​​the spirally wound filament is larger, which increases the number of electrons emitted.

[0050] Based on the above invention principle, the present invention designs a long-life multi-filament high-current multi-peak field negative hydrogen ion source 1

[0051] A long-life multi-filament high-current multi-peak field negative hydrogen ion source 1 Figure 1 、 Figure 2, which includes, from top to bottom and from outside to inside: an ion source filament 2, a filament ion source upper cover 1-1, an ion source filament holder 1-2, an ion source inner cavity 1-3, an ion source outer cavity 1-4, a permanent magnet array 3 located between the ion source inner cavity 1-3 and the ion source outer cavity 1-4, an ion source extraction structure 4, an ion source composite structure filter field located at the second layer and the bottom layer of the permanent magnet array and the ion source extraction structure;

[0052] The ion source filament 2 is used to generate a direct current electric field. It is externally connected to a steady current source. A large current is connected through the ion source filament 2 located on the ion source filament holder 1-2, so that the ion source filament 2 is heated and emits electrons. The electrons emitted by the ion source filament 2 when heated collide with the hydrogen gas introduced into the ion source under the action of the arc voltage applied to the filament ion source upper cover 1-1 to generate negative hydrogen ions.

[0053] The permanent magnet array 3 is used to provide a confining magnetic field in the ion source cavity 1-3; the permanent magnet array 3 includes a radial magnet array and a tangential magnet array arranged at intervals along the circumferential direction from the top layer to the bottom layer, and a last layer of filtering magnet array 3-1.

[0054] The ion source composite structure filter field is used to form a composite transverse magnetic field to filter out fast electrons. The ion source composite structure filter field is composed of a filter magnet array 3-1 and an extraction structure attracting magnet 4-3.

[0055] Its characteristics are: the ion source composite structure filter field is an ion source composite structure filter field with a thickened magnetic field design, the composite structure filter field with a thickened magnetic field design superimposes a magnetic field at the highest point of the filter field and filters fast electrons; the ion source filament is a spiral four-filament structure; the ion source extraction structure 4 is an ion source extraction structure that extracts a negative hydrogen current intensity higher than 30mA under a high voltage of 40kV.

[0056] Furthermore, if Figure 3c 、 Figure 4c As shown, the filtering magnet array 3-1 is used to adjust the position of the highest point of the filtering magnetic field before the plasma electrode, so that the fast electrons are fully filtered out before reaching the extraction structure, and the filtering magnet array 3-1 is also used to thicken the axial distribution of the filtering magnetic field.

[0057] Furthermore, if Figure 3c 、 Figure 4c As shown, the filtering magnet array 3-1 adjusts the position of the highest point of the filtering magnetic field in front of the plasma electrode, which means that the radial magnet in the middle of the bottom layer of the filtering magnet array 3-1 and the tangential magnets on both sides thereof are of the same polarity and raised, so that the magnetic field formed by the magnets in the lead-out area and the magnetic fields formed by the magnets in the middle of the bottom layer and on both sides of the filtering magnet array 3-1 with the same polarity and raised are superimposed, thereby forming a filtering magnetic field at the highest point of the superimposed magnetic field.

[0058] Furthermore, if Figure 3c As shown, the filtering magnet array 3-1 thickens the axial distribution of the filtering magnetic field, which means that tangential magnets b4 and b5 of opposite polarity are added to the second layer of the permanent magnet array 3 from top to bottom, that is, at the filament position, to thicken the filtering field. The thickness of the axial distribution of the filtering magnetic field is about 100 mm. The remaining radial magnets and tangential magnets of the permanent magnet array 3 are used to form a multi-peak field that confines the plasma.

[0059] Furthermore, if Figure 3c As shown, the radial magnet in the middle of the bottom layer of the filtering magnet array 3-1 and the tangential magnets on both sides of the radial magnet have the same polarity and are raised. Specifically, the filtering magnet array 3-1 is provided with two opposite radial magnets at the bottom layer of the permanent magnet array 3 replaced with radial magnets b2 with reversed polarity, and tangential magnets b1 and tangential magnets b3 of the same polarity are added on both sides of the radial magnets b2 after the reversed polarity, and the distance between the radial magnets b2, tangential magnets b1, and tangential magnets b3 and the bottom surface is raised so that the raised distance of the three magnets is 18 mm.

[0060] Furthermore, if Figure 4a 、 4b As shown, the ion source extraction structure 4 is provided with a plasma electrode 4-1, an attracting electrode 4-2, an attracting electrode magnet 4-3, an attracting level baffle 4-4, a plasma electrode fixing part 4-5, an attracting electrode fixing part 4-6, and a grounding level 4-7, which are arranged in sequence along the axial direction at the bottom of the ion source cavity; the plasma electrode 4-1 is used to receive the particles to be extracted and allow the particles to pass through the opening in the middle; the attracting level 4-2 is used to improve the envelope shape of the negative hydrogen ion extraction, so that the envelope shape is neither divergent nor contracted, and the attracting level 4-2 has a sharp corner extending out. , with its pointed corner extending toward the lower surface of the plasma electrode; the pole magnet 4-3 is used to guide the negative hydrogen ion extraction trajectory into a straight trajectory, and to deflect the electrons in the negative hydrogen beam to the suction level baffle; the pole magnet 4-3 is divided into two layers, upper and lower, arranged in the middle of the pole 4-2, and each layer is a pair of permanent magnets inclined to each other; the ground level is used to form a voltage field for the extraction of negative hydrogen ions with the plasma electrode; wherein, the electrodes are separated by an insulator, and an adjustable suction level voltage is applied between the pole 4-2 and the plasma electrode 4-1 to adjust the beam distribution.

[0061] Furthermore, if Figure 4a 、 4bAs shown, the upper layer has a pair of oppositely arranged figure-eight 45-degree tilted pole magnets 4-3, and the direction of their respective magnetic field components in one direction is consistent with the direction of the filtering magnetic field of the filtering magnet array 3-1, and the two magnetic fields are superimposed together, thereby forming a superimposed magnetic field for filtering fast electrons; the upper layer has a pair of oppositely arranged figure-eight 45-degree tilted pole magnets 4-3, and the magnetic field components in the other direction are used to deflect the slow electrons in the negative hydrogen beam to the suction baffle, thereby realizing the separation of electrons and negative hydrogen ions.

[0062] Furthermore, if Figure 4a 、 4b As shown, the axial distance between the suction electrode 4-2 and the plasma electrode 4-1 is 4 mm, the suction electrode thickness is 15 mm (3*5 mm), and two pairs of 3*5*25 mm permanent magnets are embedded in the middle.

[0063] Furthermore, the opening angle of the hole in the middle of the plasma electrode 4-1 is about 62.5°, the thickness is 3mm, the aperture is 14mm, and its voltage to ground is 40kV; the axial distance between the suction electrode 4-2 and the plasma electrode 4-1 is 4mm, the thickness is 15mm (3*5mm), and two pairs of 3*5*25mm permanent magnets are embedded in the middle; its first aperture is 10mm, the axial distance between the sharp corner and the upper surface of the plasma electrode is 2.5mm, and the aperture at the protruding point of the sharp corner is 22mm; the second aperture is 18mm; the third aperture is 14mm, which is a rounded corner, and its voltage to ground is 30-34kV, that is, the suction voltage between the plasma electrode and the suction level is 6-10kV; the thickness of the ground electrode is 5mm, and the axial distance from the suction electrode is 14mm.

[0064] Furthermore, the ion source filament is a tantalum wire with a diameter of 3 mm and a length of about 15-20 cm. It adopts a four-filament structure and is wound into a spiral shape with 10-12 turns and a spiral diameter of 8-10 mm. During operation, a filament current greater than 600 A will be passed through.

[0065] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the above embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A long-life multi-filament high-current negative hydrogen multi-peak field ion source (1), which comprises, from top to bottom and from outside to inside: An ion source filament (2), a filament ion source upper cover (1-1), an ion source filament holder (1-2), an ion source inner cavity (1-3), an ion source outer cavity (1-4), a permanent magnet array (3) located between the ion source inner cavity (1-3) and the ion source outer cavity (1-4), an ion source extraction structure (4), and an ion source composite structure filter field located at the second layer and the bottom layer of the permanent magnet array (3) and the ion source extraction structure (4); The ion source filament (2) is used to generate a direct current electric field, and is externally connected to a steady current source. A large current is connected via the ion source filament (2) located on the ion source filament holder (1-2), so that the ion source filament (2) is heated and emits electrons; the electrons emitted by the ion source filament (2) when heated collide with hydrogen gas introduced into the ion source under the action of an arc voltage applied to the filament ion source upper cover plate (1-1) to generate negative hydrogen ions; The permanent magnet array (3) is used to provide a confining magnetic field in the inner cavity (1-3) of the ion source; the permanent magnet array (3) includes a radial magnet array and a tangential magnet array arranged at intervals along the circumferential direction from the top layer to the bottom layer, and a last layer of filtering magnet array (3-1); The ion source composite structure filter field is used to form a composite transverse magnetic field to filter out fast electrons, and the ion source composite structure filter field is composed of a filter magnet array (3-1) and an extraction structure attracting magnet (4-3); The invention is characterized in that: the ion source composite structure filter field is an ion source composite structure filter field with a thickened magnetic field design, the composite structure filter field with a thickened magnetic field design superimposes a magnetic field at the highest point of the filter field and filters fast electrons; the ion source filament (2) is a spiral four-filament structure; the ion source extraction structure (4) is an ion source extraction structure that extracts a negative hydrogen current intensity higher than 30mA under a high voltage of 40kV; The filtering magnet array (3-1) thickens the axial distribution of the filtering magnetic field, which means that tangential magnets b4 and b5 of opposite polarities are added to the second layer from the top to the bottom of the permanent magnet array (3), that is, at the position of the filament, to thicken the filtering field. The thickness of the axial distribution of the filtering magnetic field is 100 mm. The filtering magnet array (3-1) is used to adjust the position of the highest point of the filtering magnetic field before the plasma electrode, so that fast electrons are fully filtered out before reaching the extraction structure, and the filtering magnet array (3-1) is also used to thicken the distribution of the filtering magnetic field in the axial direction; Specifically, the radial magnet in the middle of the bottom layer of the filtering magnet array (3-1) and the tangential magnets on both sides thereof are of the same polarity and raised, so that the magnetic field formed by the lead-out area magnetic pole magnet (4-3) and the magnetic field formed by the magnets in the middle of the bottom layer of the filtering magnet array (3-1) and on both sides thereof which are of the same polarity and raised are superimposed, thereby forming a filtering magnetic field at the highest point of the superimposed magnetic field; The pole magnets (4-3) are arranged in two layers, upper and lower, in the middle of the pole magnet (4-2). Each layer is a pair of permanent magnets tilted towards each other. When the magnetic field direction of the pair of pole magnets (4-3) in the upper layer is consistent with the magnetic field direction of the filter magnet array (3-1) in the cavity, one of the conditions for magnetic field superposition is met. The second condition for magnetic field superposition is to achieve the best superposition state of the two magnetic fields. The determination of whether the superposition of the two magnetic fields reaches the best superposition state depends on the thickness of the plasma electrode (4-1) and the axial distance between the pole magnet (4-2) and the plasma electrode (4-1). The thickness of the plasma electrode (4-1) is 3 mm, and the axial distance between the pole magnet (4-2) and the plasma electrode (4-1) is 4 mm.

2. A long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 1, characterized in that: The method comprises the following steps: the radial magnet in the middle of the bottom layer of the filtering magnet array (3-1) and the tangential magnets on both sides of the radial magnet have the same polarity and are raised. Specifically, the filtering magnet array (3-1) is provided with two opposite radial magnets at the bottom layer of the permanent magnet array (3) replaced with radial magnets (b2) with reversed polarity, and tangential magnets (b1) and tangential magnets (b3) of the same polarity are added to both sides of the radial magnets (b2) after the reversed polarity. The distance between the radial magnets (b2), the tangential magnets (b1) and the tangential magnets (b3) and the bottom surface is raised so that the raised distance of the three magnets is 18 mm.

3. The long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 1, characterized in that: The ion source extraction structure (4) is provided with a plasma electrode (4-1), an attracting electrode (4-2), an attracting electrode magnet (4-3), an attracting electrode baffle (4-4), a plasma electrode fixing part (4-5), an attracting electrode fixing part (4-6), and a grounding electrode (4-7) which are sequentially arranged along the axial direction at the bottom of the ion source cavity; the plasma electrode (4-1) is used to receive particles to be extracted and allow the particles to pass through the opening in the middle; the attracting electrode (4-2) is used to improve the envelope shape of the negative hydrogen ion extraction so that the envelope shape is neither divergent nor contracted, and the attracting electrode (4-2) has a sharp corner extending outward. , with its pointed corner extending toward the lower surface of the plasma electrode; the said attracting pole magnet (4-3) is used to guide the orbit of the negative hydrogen ion extraction into a straight orbit, and to deflect the electrons in the negative hydrogen beam to the attracting pole baffle; the attracting pole magnet (4-3) is divided into two layers, upper and lower, arranged in the middle of the attracting pole (4-2), and each layer is a pair of permanent magnets inclined to each other; the said ground electrode (4-7) is used to form a voltage field for the extraction of negative hydrogen ions with the plasma electrode (4-1); wherein, the electrodes are separated by an insulator, and an adjustable attracting pole voltage is applied between the attracting pole (4-2) and the plasma electrode (4-1) to adjust the beam distribution.

4. A long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 3, characterized in that: A pair of oppositely arranged 45-degree inclination magnets (4-3) in the upper layer have a magnetic field component in one direction that is consistent with the filtering magnetic field direction of the filtering magnet array (3-1), and the two magnetic fields are superimposed together, thereby forming a superimposed magnetic field for filtering fast electrons; a pair of oppositely arranged 45-degree inclination magnets (4-3) in the upper layer have a magnetic field component in another direction that is used to deflect slow electrons in the negative hydrogen beam to the magnetic field baffle, thereby achieving separation of electrons and negative hydrogen ions.

5. The long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 3, characterized in that: The axial distance between the suction pole (4-2) and the plasma electrode (4-1) is 4 mm, the thickness of the suction pole (4-2) is 15 mm, and two pairs of 3*5*25 mm permanent magnets are embedded in the middle.

6. The long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 1, characterized in that: The opening angle of the plasma electrode (4-1) is 62.5°, the thickness is 3mm, the aperture is 14mm, and the voltage to ground is 40kV; the axial distance between the suction electrode (4-2) and the plasma electrode (4-1) is 4mm, the thickness is 15mm, and two pairs of 3*5*25mm permanent magnets are embedded in the middle; the first aperture is 10mm, the axial distance between the sharp corner and the upper surface of the plasma electrode is 2.5mm, and the aperture at the point where the sharp corner protrudes is 22mm; the second aperture is 18mm; the third aperture is 14mm, which is a rounded corner, and the voltage to ground is 30-34kV, that is, the voltage of the suction electrode (4-2) between the plasma electrode and the suction electrode (4-2) is 6-10kV; the ground electrode (4-7) is 5mm thick and the axial distance from the suction electrode (4-2) is 14mm.

7. The long-life multi-filament high-current negative hydrogen multi-peak field ion source (1) according to claim 1, characterized in that: The ion source filament (2) is a tantalum filament with a diameter of 3 mm and a length of 15-20 cm. It adopts a four-filament structure and is wound into a spiral shape. The number of spirals is 10-12 and the spiral diameter is 8-10 mm. During operation, a filament current greater than 600 A is passed through.

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