A strong current negative hydrogen multi-peak field radio frequency ion source extraction structure

Abstract

The application discloses a strong current negative hydrogen multi-peak field radio frequency ion source extraction structure, which is provided with a plasma electrode, a sucking electrode, a sucking electrode magnet, a sucking electrode baffle, a plasma electrode fixing piece, a sucking electrode fixing piece and a ground electrode which are sequentially arranged on the bottom of an ion source cavity along an axial direction; an opening of the plasma electrode is provided with an opening angle inclined surface, and a boron-doped diamond film is plated on the upper surface of the opening angle inclined surface for surface production of negative hydrogen ions; the sucking electrode is used for improving the envelope shape of the negative hydrogen ion extraction, so that the envelope shape is neither divergent nor contracted; the sucking electrode magnet is used for guiding the track of the negative hydrogen ion extraction to be a straight line track; the application increases the yield by adding the inclined surface on the plasma electrode of the extraction structure; and the yield is improved by designing the thickness of the sucking electrode and the axial distance between the sucking electrode and the plasma electrode, so that the highest points of the filtering magnetic field on the upper surface of the plasma electrode and the sucking electrode magnet are superposed under the condition of avoiding breakdown.

Description

Technical Field

[0001] This invention belongs to the field of cyclotron technology, and particularly relates to a high-current negative hydrogen multi-peak field radio frequency ion source extraction structure. Background Technology

[0002] In cyclotrons, ion source technology is a key technology. An ion source is a device that ionizes neutral atoms or molecules and extracts an ion beam from them. The ion source is the source of the beam, determines the beam quality, and directly affects the performance of the cyclotron.

[0003] High-current negative hydrogen radio frequency ion sources are a type of high-yield, high-current ion source that has been widely in demand in recent years, with extraction current exceeding 100 mA. Compared with existing low-yield, low-current ion sources, the difficulty in achieving high-yield, high-current ion sources lies in:

[0004] One of the difficulties is the contradiction between high-yield extraction and the limited space for generating negative hydrogen ions. Existing technologies, such as patent number: 201020700147.9, patent name: Magnet structure for generating virtual filtering magnetic field, can only generate negative hydrogen ions within the cavity (1) and have no other generation method, such as its attached Figure 1 As shown, the plasma electrode (located at the end of the cavity, immediately adjacent to the cavity) has no angle at its inlet, and its inlet and outlet are vertically aligned. Therefore, it only produces negative hydrogen ions from the volume, not from the surface. To increase production, the feed power must be increased, which in turn increases material and manufacturing costs. Without increasing costs, the ion source's production can only be limited to its current output and cannot be further increased.

[0005] The second challenge lies in the contradiction between high yield and the space charge effect. High yield means generating a large amount of plasma in the ion source extraction region. Extracting a large amount of plasma leads to a significant space charge effect, resulting in greater beam emittance and divergence. The plasma sheath influences and determines the shape of the plasma emission surface, placing higher demands on the extraction structure. If the spacing, angle, extraction end thickness, extraction electrode shape, and the thickness and shape of the ground electrode are not properly designed, the plasma sheath will affect the emission surface shape: it will be either divergent or over-focused. In a divergent shape, the divergent beam will hit the receiving beam pipe at the application end; in an over-focused shape, the beam will continue to diverge in its subsequent path, which is also undesirable. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by proposing a high-current negative hydrogen multi-peak field radio frequency ion source extraction structure. The aim is to resolve the contradiction between high-yield extraction and the limited space for negative hydrogen ion generation, as well as the contradiction between high yield and space charge effect in the prior art.

[0007] The present invention proposes the following technical solutions to solve its technical problems.

[0008] A multi-peak high-current negative hydrogen radio frequency ion source extraction structure is characterized by the following: the extraction structure includes a plasma electrode 4-1, an absorber 4-2, an absorber magnet 4-3, an absorber baffle 4-4, a plasma electrode fixing component 4-5, an absorber fixing component 4-6, and a ground electrode 4-7 arranged sequentially 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 central opening, and the entrance side of the opening is provided with an angled inclined surface, the upper surface of which is coated with a boron-doped diamond film, and this angled inclined surface is used for the surface generation of negative hydrogen ions; the absorber 4-2 is used to improve the extraction of negative hydrogen ions. The envelope shape is designed to be neither divergent nor contracted. The suction stage 4-2 has a pointed protrusion that extends towards the lower surface of the plasma electrode. The suction magnet 4-3 is used to guide the negative hydrogen ions to a straight track and deflect electrons in the negative hydrogen beam to the suction stage baffle 4-4. The suction magnet 4-3 is arranged in two layers in the middle of the suction stage 4-2, each layer consisting of a pair of mutually inclined permanent magnets. The ground electrode 4-7 is used to form a voltage field for the negative hydrogen ion extraction with the plasma electrode 4-1. The electrodes are separated by an insulator, and an adjustable suction stage voltage is applied between the suction stage and the plasma electrode to adjust the beam distribution.

[0009] Furthermore, the attracting magnet 4-3 is arranged in two layers in the middle of the attracting electrode 4-2. Each layer consists of a pair of permanent magnets that are inclined to each other. Specifically, the pair of permanent magnets in the upper layer are in a figure-eight shape and each is inclined at a 45-degree angle to the plane of the plasma electrode 4-1. The pair of permanent magnets in the lower layer are in an inverted figure-eight shape and each is inclined at a 45-degree angle to the plane of the plasma electrode 4-1. The magnetic field direction of the pair of permanent magnets in the lower layer is opposite to that of the pair of permanent magnets in the upper layer. The pair of permanent magnets in the lower layer with opposite magnetic field directions are used to correct the extraction direction of negative hydrogen ions.

[0010] Furthermore, the opening angle of the plasma electrode 4-1 in the middle is 45°, the thickness is 4mm, the aperture is 16mm, and there is a 1mm*1mm groove, with a voltage to ground of 60kV.

[0011] Furthermore, the axial distance between the absorber 4-2 and the plasma electrode is 3.5 mm, and the thickness is 15 mm (3*5 mm). Two pairs of 3*5*25 mm permanent magnets are embedded in the middle. The first aperture is 12 mm, the sharp corner is 1 mm away from the plasma electrode, and the aperture at the protruding part of the sharp corner is 17 mm. The second aperture is 15 mm. The third aperture is 16 mm with rounded corners. Its voltage to ground is 47-50 kV, that is, the voltage between the plasma electrode and the absorber is 10-13 kV.

[0012] Furthermore, the thickness of the ground electrode 4-7 is 5mm, and the axial distance between it and the absorber 2 is 13.5mm.

[0013] Advantages and effects of the present invention

[0014] 1. This invention addresses the technical requirements of high-voltage and high-current extraction from a high-current negative hydrogen multi-peak field radio frequency ion source. By adding an inclined surface to the plasma electrode of the extraction structure, the generation of negative hydrogen ions changes from bulk generation to bulk generation plus surface generation, thereby increasing the yield and solving the problem of extracting negative hydrogen currents exceeding 100mA under 60kV high voltage.

[0015] 2. This invention designs the thickness of the absorber electrode and the axial distance between the absorber electrode and the plasma electrode to be minimized under the conditions of cooling and avoiding breakdown, so that the magnetic field of the absorber electrode can be superimposed on the highest point of the filtering magnetic field on the upper surface of the plasma electrode, thereby improving the yield. The current intensity index has reached the leading level in China.

[0016] 3. By designing the absorber tip angle, the present invention makes the distance between the absorber tip angle and the plasma electrode 1mm, which effectively improves the beam emission surface divergence caused by the space charge effect, making the beam emission surface closer to a straight line. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the negative hydrogen ion source device of the present invention;

[0018] Figure 2 This is a schematic diagram of the built-in radio frequency antenna of the ion source of the present invention;

[0019] Figure 2a This is a schematic diagram showing that when the thickness, dielectric constant, and resistivity of the built-in antenna coating of the present invention meet certain conditions, the plasma sheath approaches zero potential.

[0020] Figure 2b This is a schematic diagram illustrating the realization of a plasma sheath without potential in this invention;

[0021] Figure 3a A cross-sectional view of a multi-peak field magnet within a conventional multi-peak field negative hydrogen ion source;

[0022] Figure 3bThis is a top view of a multi-peak field magnet in a conventional multi-peak field negative hydrogen ion source; where a is a radial magnet array and b is a tangential magnet array.

[0023] Figure 3c This is a cross-sectional view of the filter magnet array within the multi-peak field negative hydrogen ion source of the present invention;

[0024] Figure 3d This is a top view of the filter magnet array inside the multi-peak field negative hydrogen ion source of the present invention;

[0025] Figure 4a This is a cross-sectional view of the ion source extraction structure of the present invention;

[0026] Figure 4b This is a dimensional diagram of the ion source extraction structure of the present invention;

[0027] Figure 4c This is a schematic diagram of the superimposed magnetic field of the filter field of the multi-peak field negative hydrogen ion source composite structure of the present invention;

[0028] Figure 4d This is a schematic diagram of the simulated 120mA ion beam envelope extracted by the ion source extraction structure of the present invention.

[0029] Figure 4d This is a schematic diagram of the simulated 120mA ion beam envelope extracted by the ion source extraction structure of the present invention.

[0030] Figure 4e This is a schematic diagram of the reverse magnetic field of the lower layer of the ion source extraction structure of the present invention to correct the negative hydrogen ion extraction trajectory.

[0031] In the diagram: 1: Negative hydrogen ion source; 1-1: Top cover of the ion source's built-in radio frequency antenna; 1-2: Inner cavity of the ion source; 1-3: Outer cavity of the ion source; 2: Built-in radio frequency antenna of the ion source; 3: Multi-peak field magnet; 4: Ion source extraction structure; 3-1: Filter magnet array; 4: Ion source extraction structure; 4-1: Plasma electrode; 4-2: Adsorber; 4-3: Adsorber magnet; 4-4: Adsorber baffle; 4-5: Plasma electrode fixing component; 4-6: Adsorber fixing component; 4-7: Ground electrode. Detailed Implementation

[0032] Design principle of the invention

[0033] Design principle of high-yield, high-current negative hydrogen ion source extraction structure:

[0034] ① The generation of negative hydrogen ions on the inclined surface increases the yield. This invention adds a 45-degree inclined surface at the inlet of plasma electrode 4-1, allowing negative hydrogen ions to be generated not only within the ion source cavity above plasma electrode 4-1 but also on the current 45-degree inclined surface. The principle of generating negative hydrogen ions on the surface is as follows: when residual electrons in the air collide with excited hydrogen atoms, in addition to producing fast electrons, slow electrons, and even negative hydrogen ions, a considerable number of positive hydrogen atoms are also generated. When these positive hydrogen atoms hit the inclined surface coated with a specific layer, negative hydrogen ions are generated. Existing technology does not have an inclined surface on the plasma electrode; its plasma electrode inlet lacks a "surface," and without a "surface," it cannot receive positive hydrogen atoms. Therefore, negative hydrogen ions can only be generated within the cavity, resulting in low yield. ② The design principle of the absorption field: When a large amount of plasma is generated within the ion source cavity, a 60kV high voltage draws the plasma out. The drawn plasma forms a plasma sheath on the plasma electrode, thus determining the shape of the plasma emission surface and consequently changing the shape of the extracted beam. This invention utilizes an adsorption field that can influence the shape of the plasma sheath without altering the extraction energy, thereby improving the beam extraction state. ③ Design principle of plasma electrode 4-1 thickness: If the plasma electrode is too thick, and the adsorption voltage between the upper surface of plasma electrode 4-1 and adsorption stage 4-2 is too weak, the adsorption field cannot penetrate well into the emission aperture, reducing the extraction capability. Therefore, in this design, the thickness of plasma electrode 4-1 should be minimized without affecting structural strength, and a suitable adsorption voltage should be selected. ④ Design principle of the sharp corner of adsorption electrode 4-2: The adsorption stage has a sharp protrusion, which can enhance the adsorption field penetrating into the emission aperture. At the same time, due to the space charge effect, the increase in the thickness of adsorption electrode 4-2 and its axial distance from plasma electrode 4-1 both increase the divergence angle. Therefore, in this design, the thickness of adsorption stage and its axial distance from plasma electrode should be minimized under the conditions of cooling and avoiding breakdown. ⑤ Design principle of magnet 4-2: Research shows that when negative hydrogen ions are extracted, a beam of electrons (slower) 100 times stronger is also extracted. Therefore, in this design, while meeting the dimensions of magnet 4-2, a suitable magnet needs to be embedded in the magnet to deflect the electrons to the magnet baffle. ⑤ Design principle of magnet 4-7: The aperture size has little impact on the performance of the extracted beam, but it determines the final beam radius injected into the accelerator.

[0035] Based on the above principles, this invention designs a high-current negative hydrogen multi-peak field radio frequency ion source extraction structure.

[0036] A multi-peak field high current negative hydrogen radio frequency ion source extraction structure as follows Figure 4aAs shown, its features are: the extraction structure is provided with a plasma electrode 4-1, an absorber 4-2, an absorber magnet 4-3, an absorber baffle 4-4, a plasma electrode fixing component 4-5, an absorber fixing component 4-6, and a ground electrode 4-7 arranged sequentially 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 central opening, and the entrance side of the opening is provided with an angled inclined surface, the upper surface of which is coated with a boron-doped diamond film, and this angled inclined surface is used for the surface generation of negative hydrogen ions; the absorber 4-2 is used to improve the envelope shape of the extracted negative hydrogen ions, so that the... The envelope shape is neither divergent nor contracted. The suction stage 4-2 has a pointed protrusion that extends towards the lower surface of the plasma electrode. The suction magnet 4-3 is used to guide the negative hydrogen ions to a straight track and deflect the electrons in the negative hydrogen beam to the suction stage baffle 4-4. The suction magnet 4-3 is arranged in two layers in the middle of the suction stage 4-2, each layer being a pair of permanent magnets tilted towards each other. The ground electrode 4-7 is used to form a voltage field for the negative hydrogen ion extraction with the plasma electrode 4-1. The electrodes are separated by an insulator, and an adjustable suction stage voltage is applied between the suction stage and the plasma electrode to adjust the beam distribution.

[0037] Supplementary Note 1:

[0038] Existing plasma electrodes have a trapezoidal inlet with the shorter side on top and the longer side on the bottom, lacking a 45-degree incline. This invention places the longer side of the trapezoid on top and the shorter side on the bottom, forming an inlet inclined surface. This inclined surface enables a second generation of negative hydrogen ions. The first generation occurs within the ion source cavity, while the second generation occurs on the surface. The surface generation occurs when positive hydrogen atoms react with a boron-doped diamond film on the surface to produce negative hydrogen ions. The first generation within the cavity involves slow electrons and excited hydrogen atoms producing negative hydrogen ions. Positive hydrogen atoms are generated by collisions between participating electrons in the air and introduced hydrogen atoms, producing fast electrons, slow electrons, and even negative hydrogen ions and positive hydrogen atoms. Positive hydrogen atoms constitute a significant proportion. Therefore, utilizing positive hydrogen atoms to generate negative hydrogen ions a second time is crucial for increasing yield.

[0039] Furthermore, such as Figure 4a , 4e As shown, the attracting magnet 4-3 is arranged in two layers in the middle of the attracting electrode 4-2. Each layer consists of a pair of permanent magnets that are inclined to each other. Specifically, the pair of permanent magnets in the upper layer are in a figure-eight shape and each is inclined at a 45-degree angle to the plane of the plasma electrode 4-1. The pair of permanent magnets in the lower layer are in an inverted figure-eight shape and each is inclined at a 45-degree angle to the plane of the plasma electrode 4-1. The magnetic field direction of the pair of permanent magnets in the lower layer is opposite to that of the pair of permanent magnets in the upper layer. The pair of permanent magnets in the lower layer with opposite magnetic field directions are used to correct the extraction direction of negative hydrogen ions.

[0040] Supplementary Note 2:

[0041] like Figure 4e As shown, the two magnets in the upper layer are aligned with the direction of the filter field, while the two magnets in the lower layer are aligned with the direction of the filter field. The negative hydrogen ions in the extraction structure will be deflected in one direction under the action of the magnets in the upper layer. Since the magnets in the lower layer are aligned with the magnets in the upper layer, the trajectory of the deflected negative hydrogen ion beam will be deflected in the opposite direction, thus achieving a linear beam trajectory.

[0042] Furthermore, such as Figure 4a , 4e As shown, the opening angle in the middle of the plasma electrode 4-1 is 45°, the thickness is 4mm, the aperture is 16mm, and there is a 1mm*1mm groove. Its voltage to ground is 60kV.

[0043] Furthermore, such as Figure 4e As shown, the axial distance between the absorber 4-2 and the plasma electrode is 3.5 mm, and the thickness is 15 mm (3*5 mm). Two pairs of 3*5*25 mm permanent magnets are embedded in the middle. The first aperture is 12 mm, the sharp corner is 1 mm away from the plasma electrode, and the aperture at the protruding part of the sharp corner is 17 mm. The second aperture is 15 mm. The third aperture is 16 mm with rounded corners. Its voltage to ground is 47-50 kV, that is, the voltage between the plasma electrode and the absorber is 10-13 kV.

[0044] Supplementary Note 3:

[0045] like Figure 4a As shown, the two sharp corners of the absorber 4-2 extend toward the plasma electrode 4-1 and are 1 mm apart from the plasma electrode. Under a constant voltage (the voltage of the plasma electrode 4-1 is 6 kV and the voltage of the absorber is 4.7 kV), the closer the two electrodes are, the more obvious the voltage difference will be. The more obvious the voltage difference is, the easier it is to adjust the shape of the beam envelope to be a straight line. Figure 4d As shown, when the sharp corner of the absorber extends toward the plasma electrode, under the repulsive force of the electric field at the sharp corner, the shape of the beam envelope in the upper left corner changes from being close to the plasma electrode to being far away from the plasma electrode, which improves the shape of the envelope at the sharp corner, making it easier for the envelope at the sharp corner to form a single unit with the subsequent straight envelope.

[0046] Furthermore, such as Figure 4e As shown, the thickness of the ground electrode 4-7 is 5mm, and the axial distance between it and the absorber 2 is 13.5mm.

[0047] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A multi-peak high-current negative hydrogen radio frequency ion source extraction structure, characterized in that: The extraction structure is provided with, in sequence along the axial direction, a plasma electrode (4-1), an anode (4-2), an anode magnet (4-3), an anode baffle (4-4), a plasma electrode fixing member (4-5), an anode fixing member (4-6), and a ground electrode (4-7) arranged at the bottom of the ion source cavity; the plasma electrode (4-1) is used for receiving particles to be extracted and allowing the particles to pass through the middle opening, and the entrance side of the opening is provided with a dihedral angle inclined surface, the upper surface of the dihedral angle inclined surface is plated with a boron-doped diamond thin film, and the dihedral angle inclined surface is used for the surface generation of negative hydrogen ions; the anode (4-2) is used for improving the envelope shape of the extraction of negative hydrogen ions, so that the envelope shape is neither divergent nor contracted, and the anode (4-2) has a sharp corner extending to the lower surface of the plasma electrode; the anode magnet (4-3) is used for guiding the trajectory of the extraction of negative hydrogen ions to be a straight line, and deflecting the electrons in the negative hydrogen beam to the anode baffle (4-4); the anode magnet (4-3) is arranged in the middle of the anode (4-2) in two layers, and each layer is a pair of mutually inclined permanent magnets; the ground electrode (4-7) is used for forming 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 anode voltage is added between the anode and the plasma electrode to adjust the beam distribution; The anode magnet (4-3) is arranged in the middle of the anode (4-2) in two layers, and each layer is a pair of mutually inclined permanent magnets, specifically: the pair of permanent magnets in the upper layer is in a figure-eight shape, each forms a 45-degree inclination with the plane of the plasma electrode (4-1), the pair of permanent magnets in the lower layer is in an inverted figure-eight shape, and each forms a 45-degree inclination with the plane of the plasma electrode (4-1), the magnetic field direction of the pair of permanent magnets in the lower layer is opposite to that of the pair of permanent magnets in the upper layer, and the pair of permanent magnets in the lower layer with opposite magnetic field directions is used for correcting the extraction direction of negative hydrogen ions; The dihedral angle of the opening in the middle of the plasma electrode (4-1) is 45°, the thickness is 4mm, the aperture is 16mm, and there is a 1mm*1mm groove, and the voltage to ground is 60kV; The axial distance between the anode (4-2) and the plasma electrode (4-1) is 3.5mm, the thickness is 15mm, and two pairs of 3*5*25mm permanent magnets are embedded in the middle; the first aperture is 12mm, the axial distance of the sharp corner to the plasma electrode is 1mm, the aperture at the sharp corner extension is 17mm; the second aperture is 15mm; the third aperture is 16mm, which is a round corner, and the voltage to ground is 47-50kV, that is, the anode voltage between the plasma electrode and the anode is 10-13kV; The thickness of the ground electrode (4-7) is 5mm, and the axial distance to the anode (2) is 13.5mm.

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