A desktop cyclotron main magnet structure

Abstract

This invention discloses a main magnet structure for a desktop cyclotron accelerator. This main magnet structure employs a combination of a small magnetic gap and a shallow valley region, a non-linear magnetic pole structure, an angle-variable chamfered padding structure, and a locally thickened main magnet cover plate to suppress magnetic leakage. The combination of the small magnetic gap and the shallow valley region improves the average magnetic field. The non-linear magnetic pole structure compensates for the magnetic field reduction caused by the high-frequency through-hole by increasing the angular width of the magnetic poles, ensuring the magnetic field meets the isochronous acceleration requirements. The angle-variable chamfered padding structure improves the linear relationship between the padding amount and the change in magnetic field, facilitating accurate estimation of magnetic field padding. The locally thickened cover plate structure minimizes the increase in the main magnet's weight while ensuring compliance with leakage magnetic field standards. This invention solves the problems of magnetic field leakage and magnetic field reduction caused by the center plane being too close to the upper cover plate, and also addresses the issue of the increased magnetic pole angle encroaching on the high-frequency cavity installation space.

Description

Technical Field

[0001] This invention belongs to the technical field of small cyclotrons, and particularly relates to a main magnet structure for a desktop cyclotron. Background Technology

[0002] Compared to conventional cyclotrons of the same energy, desktop cyclotrons have a diameter reduced to three-fifths and a height reduced to nearly half. Simultaneously, the average magnetic field of a desktop cyclotron is significantly higher. This higher average magnetic field is because, with the same beam magnetic stiffness, a smaller cyclotron radius requires a higher magnetic flux density. The 20-30% smaller radius of a desktop cyclotron means a higher average magnetic field. This smaller size and significantly higher average magnetic field present challenges in designing the main magnet.

[0003] One of the challenges in designing the main magnet for a desktop cyclotron is that the high-frequency holes on the main magnet cover plate are too close to the center plane, leading to a significant decrease in the average magnetic field. Due to the installation requirements of the accelerator cavity and vacuum system, four circular holes need to be made in the cover plate. Because the magnet is removed from these holes, the magnetic field at these locations is weaker than in other areas, resulting in a substantial decrease in the magnetic field and creating a magnetic field defect. Excessive localized decrease in the average magnetic field can cause a severe deviation from isochronism, excessive beam slippage, and beam loss, further contributing to the decline in the average magnetic field. Figure 2 As shown.

[0004] The second challenge in designing the main magnet for a desktop cyclotron is the increased average magnetic field, which necessitates a larger pole angle. Traditional magnetic field padding methods are no longer suitable for this increased angle. These methods involve machining the two sides of a strip to create uneven, curved surfaces. Since these raised areas occupy additional space on both sides of the poles, using this traditional padding method with an increased pole angle severely restricts the installation space for the high-frequency cavity, potentially even encroaching on it entirely.

[0005] The third challenge in designing the main magnet for a desktop cyclotron is that, due to their lightweight nature and high average magnetic field, they typically generate a large leakage magnetic field. Excessive magnetic flux density in the accelerator cover can cause severe leakage. This leakage magnetic field can affect the operation of peripheral components, such as the vacuum pump and vacuum gauge. Measurements show that without targeted local thickening of the cover, the leakage magnetic flux density at 200mm from the cover is close to 80 Gs. Generally, the leakage magnetic field at 200mm from the accelerator should be less than 50 Gs. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a main magnet structure for a desktop cyclotron. The first objective is to solve the problem that the high-frequency holes in the main magnet cover plate of the desktop cyclotron are too close to the center plane, resulting in a severe decrease in the average magnetic field. The second objective is to solve the problem that traditional magnetic field padding methods cannot meet the low-cost and high-efficiency acceleration requirements of desktop cyclotrons. The third objective is to solve the problem that desktop cyclotrons are lightweight and have a high average magnetic field, but often generate a large leakage magnetic field.

[0007] To solve its technical problem, the present invention adopts the following technical solution:

[0008] A desktop cyclotron main magnet structure is characterized by the following features: The main magnet structure employs a combination of a small magnetic gap and a shallow valley region, a non-linear magnetic pole structure, an angle-variable chamfered padding structure, and a locally thickened main magnet cover plate to suppress magnetic leakage. The combination of the small magnetic gap and shallow valley region is used to meet the requirement of increasing the average magnetic field in a miniaturized desktop cyclotron. The non-linear magnetic pole structure compensates for the magnetic field reduction caused by the high-frequency through-hole by increasing the angular width of the magnetic poles, ensuring isochronous acceleration and reducing the amount of padding required. The angle-variable chamfered padding structure improves the linear relationship between the padding amount and the change in magnetic field, facilitating accurate estimation of magnetic field padding. The locally thickened cover plate structure minimizes the increase in the weight of the main magnet while ensuring compliance with magnetic leakage standards.

[0009] Furthermore, the small magnetic gap refers to the distance between the magnetic poles and the center plane of the accelerator being less than 15mm; the shallow valley region refers to the distance between the cover plate and the center plane of the accelerator being less than 50mm; the requirement to improve the average magnetic field to realize a miniaturized desktop cyclotron accelerator means that the average magnetic field of the desktop small cyclotron reaches more than 1.3T.

[0010] Furthermore, the main magnet adopts a non-linear magnetic pole structure, that is, the magnetic pole angle width is locally increased to a certain extent at the high-frequency through hole position. By increasing the magnetic pole angle width, the magnetic field reduction caused by the high-frequency through hole is compensated, so that the magnetic field can meet the isochronous acceleration requirements with a small amount of padding.

[0011] Furthermore, the magnetic pole angle width of the main magnet at the high-frequency through-hole position is locally increased to a certain extent, and this increased magnetic pole angle width is just enough to compensate for the reduction in magnetic field caused by the high-frequency through-hole.

[0012] Furthermore, the chamfering padding structure with varying angles is characterized by using a fixed cutting height and length while varying the cutting angle, with the cutting volume of the chamfering padding being linearly related to the padding amount.

[0013] Furthermore, the locally thickened leakage magnetic field suppression structure of the main magnet cover plate is a targeted local thickening of the area where the inner contour of the main magnet cover plate is circular and the outer contour is octagonal.

[0014] Furthermore, the targeted local thickening means that after thickening by 20mm, the leakage magnetic field flux density at a distance of 200mm from the cover plate is less than 50Gs.

[0015] Advantages and effects of the present invention

[0016] 1. This invention addresses the problem of high magnetic field saturation in desktop cyclotron accelerators, which typically results in significant magnetic field leakage externally, affecting the operation of peripheral components, by employing a non-linear magnetic pole structure, specifically a locally increased magnetic pole angle width at the high-frequency through-hole location, and a leakage magnetic suppression structure with locally thickened main magnet cover plate (i.e., targeted local thickening of the area where the inner contour of the main magnet cover plate is circular and the outer contour is octagonal). Furthermore, it solves the internal problem of a significantly weakened magnetic field at the opening of the cover plate compared to other areas, leading to magnetic field defects and beam loss.

[0017] 2. This invention solves the problem of insufficient or even occupied installation space for the high-frequency cavity caused by the increased main magnetic pole angle of the desktop cyclotron accelerator. This is achieved by using a chamfered padding structure with varying angles, namely, a fixed cutting height, varying the cutting angle, varying the cutting angle and width above the insert, and making the side of the insert adjacent to the high-frequency cavity a vertical plane. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the non-linear magnetic pole structure of the present invention;

[0019] Figure 2 A schematic diagram illustrating how the structure of the shallow valley region causes a significant reduction in the magnetic field.

[0020] Figure 3a This is a schematic diagram of the chamfered padding structure with varying angles according to the present invention. Figure 1 ;

[0021] Figure 3bThis is a schematic diagram of the chamfered padding structure with varying angles according to the present invention. Figure 2 ;

[0022] Figure 4 Before the local thickening of the cover plate of the desktop accelerator, the magnetic flux density, which is octagonal in shape and circular in shape, reached 2T and was close to saturation.

[0023] Figure 5a This is a front view of the partial thickening of the main magnet cover plate of the present invention;

[0024] Figure 5b This is a top view of the partial thickening of the main magnet cover plate of the present invention;

[0025] Figure 5c A perspective view showing a partial thickening of the main magnet cover plate of the present invention;

[0026] Figure 6a This is a schematic diagram showing that the leakage magnetic flux density at a distance of 200mm from the cover plate is close to 80G when no targeted local thickening of the cover plate is applied.

[0027] Figure 6b A schematic diagram showing that after the cover plate is locally thickened by 20mm, the leakage magnetic flux density at a distance of 200mm from the cover plate is less than 50Gs.

[0028] Figure 7a The diagram illustrates the principle of existing technology that uses a fixed 45-degree angle for chamfering and padding, so that the cut volume and the padding amount are in a square relationship.

[0029] Figure 7b The present invention employs a method of fixed height and length, while varying chamfer width for padding, so that the cut volume and padding amount have a linear relationship.

[0030] Figure 7c This is a graph showing the relationship between the amount of magnetic field padding and the magnetic field strength. Detailed Implementation

[0031] Design principle of this invention:

[0032] 1. The design of the main magnetic field of the desktop cyclotron accelerator revolves around resolving two contradictions: First, while the average magnetic field is significantly higher, the accelerator height is also considerably shorter. ① Internally, the increased height results in the main magnetic field at the center plane being very close to the upper and lower cover plates, causing a significant local drop in magnetic field due to the openings in these plates. This drop is caused by the eight mounting holes in the cover plates, resulting in fewer magnets in certain areas. ② Externally, the increased height leads to higher magnetic saturation of the main magnets, making magnetic leakage at the cover plates more likely. Measurements show that without targeted thickening of the cover plates, the magnetic flux density at 200mm from the cover plates is close to 80Gs, while the general requirement is for magnetic leakage at 200mm from the accelerator to be less than 50Gs. The second contradiction is that while the average magnetic field is significantly higher, the installation space for the high-frequency cavity is also much more limited. To increase the average magnetic field, it's not only necessary to reduce the gap in the central plane and bring the magnetic poles closer together, but more importantly, to increase the pole angle. Increasing the pole angle increases the area of ​​the magnetic poles, thereby improving the average magnetic field. However, this further complicates the installation space for the high-frequency cavity because increasing the pole angle requires adding pole padding strips on both sides. Traditional pole padding involves adding uneven curved surfaces on both sides of the strip; the protruding areas represent areas with a stronger magnetic field, and the concave areas represent areas with a weaker magnetic field, thus achieving magnetic field compensation. This traditional method, by padding on both sides of the strips, occupies a significant amount of space on both sides of the pole. If the pole angle is further increased, it will inevitably encroach on the installation space for the high-frequency cavity. In short, a significantly higher average magnetic field necessitates a larger pole angle, which in turn significantly compresses the space available for installing the high-frequency cavity—this is the second contradiction.

[0033] 2. Solution of this invention: ① Employing a small magnetic gap to achieve an average magnetic field of over 1.3T. To improve the average magnetic field, a small magnetic gap is used in the magnetic pole peak region, meaning the distance between the magnetic pole and the accelerator center plane is less than 15mm. Simultaneously, a shallow valley structure is employed, meaning the distance between the cover plate and the accelerator center plane is less than 50mm. Under the combined effect of these two factors, the desktop cyclotron accelerator can achieve an average magnetic field of over 1.3T with a relatively small excitation current while also saving energy. ② Design of a non-linear magnetic pole structure: Due to the installation requirements of the accelerator cavity and vacuum system, four circular holes need to be made in the cover plate. Because of the shallow valley structure, the cover plate is too close to the center plane (less than 50mm). At these four openings, the magnetic field decreases significantly due to the reduced number of magnets, creating magnetic field defects and resulting in a severe drop in the average magnetic field. Figure 2As shown. Excessive decrease in the local average magnetic field can lead to a serious deviation from isochronism in the magnetic field, excessive beam slippage, and beam loss. If a traditional deep valley accelerator is used, the magnetic field at the center plane is less affected by the weakening of the magnetic field at the opening of the cover plate because the cover plate is 300mm away from the center plane. However, in a desktop cyclotron accelerator, the magnetic field at the center plane is significantly weakened because the opening of the cover plate is too close to the center plane. To compensate for this defect, a non-linear magnetic pole structure is adopted for the main magnet, that is, the magnetic pole angle width is locally increased to a certain extent at the high-frequency through-hole position. By increasing the angle width of the magnetic pole, the magnetic field reduction caused by the high-frequency through-hole is compensated, so that the magnetic field meets the isochronism acceleration requirements. ③ Angle-changing chamfered padding structure design: In order not to occupy the installation space of the high-frequency cavity, this invention adopts a fixed cutting height and length, and a variable cutting angle. The fixed cutting height is as follows: Figure 3a , 3b As shown, the lower half of the side of the insert away from the magnetic pole is a vertical plane. A chamfer is made at the top of this vertical plane, tilting inwards, with varying cutting angles and widths. This changes the surface of the insert not on the side, but diagonally upwards from the top, effectively rotating the uneven surface from the side to the top. Because this method ensures that the closest point between the insert and the high-frequency cavity is two parallel surfaces, rather than a surface after padding, it resolves the contradiction of a significantly higher average magnetic field and limited space for the high-frequency cavity. It also clearly defines the boundary between the magnetic pole and the high-frequency cavity, preventing installation problems due to space constraints. The difference between this invention's "angle-variable chamfer padding" and existing technologies: Existing technologies also use a fixed 45-degree chamfer padding. However, the volume cut by the existing 45-degree chamfer padding is quadratically related to the padding amount, resulting in a non-linear relationship between the padding magnetic field and the padding amount. The cutting volume of the chamfering padding in this invention, which uses a "fixed cutting height and varied cutting angle," is linearly related to the padding amount. Therefore, when the padding amount is large, the padding amount in this solution has a better linear relationship with the change in magnetic field, which is beneficial for the accurate estimation of magnetic field padding. ④ Design for locally thickening the main magnet cover to suppress magnetic leakage: Desktop cyclotrons, due to their light weight and high average magnetic field, usually generate a large magnetic leakage field. When the magnetic flux density of the accelerator cover is too high, it will cause serious magnetic leakage. The magnetic leakage field will affect the operation of peripheral components of the accelerator, such as vacuum pumps and vacuum gauges. Generally, it is required that the magnetic leakage at a distance of 200mm from the accelerator be less than 50Gs. After calculation, the magnetic flux density of the accelerator cover reaches a maximum of 2T, which is close to saturation. The traditional approach is to use a thicker cover, but this solution will seriously increase the total weight of the main magnet and cannot meet the requirements of lightweighting. This invention makes targeted local thickening of the cover at the high magnetic flux density location, such as... Figure 5a , 5bAs shown in Figure 5c, a boss with an octagonal outer contour and a circular inner contour is designed separately on the upper surface of the original upper cover plate and the lower surface of the lower cover plate. The area covered by the boss is the area with more serious magnetic leakage. Since the area of ​​the boss is less than half of the area of ​​the entire upper or lower cover plate, the weight of the main magnet is reduced as much as possible while ensuring that the magnetic leakage meets the standard.

[0034] 3. Proof that the cutting volume V and the padding amount X of this invention have a linear relationship:

[0035] like Figure 7a The image shows a triangular prism cut from a strip using existing technology. Since the 45-degree triangle is an isosceles triangle with two equal sides (X), the volume of the cut triangular prism is V = X. 2 *L, where X 2 Let X be the change in magnetic field padding. 2 The relationship between V and the cutting volume V is non-linear: V∝x 2 Therefore, as Figure 7c As shown, there is a certain nonlinear relationship between the padding magnetic field and the padding amount.

[0036] like Figure 7b As shown, the dashed line represents the irregular triangular prism cut from the insert using the method of this invention. During the cutting process, the length L and height H of the irregular triangular prism remain constant, while the cutting width X changes. Therefore, the cutting volume of the irregular triangular prism V = X * L * H. Since... Figure 7b The change in magnetic field compensation X is linearly related to the cutting volume V, therefore, as Figure 7c As shown, there is also a linear relationship between the padding magnetic field and the padding amount. The varying cutting width X is also the varying cutting angle.

[0037] Based on the above-mentioned inventive principles, this invention designs a desktop cyclotron main magnet structure.

[0038] A desktop cyclotron main magnet structure, such as Figure 1 , Figure 3a , Figure 3b , Figure 5a , Figure 5b , Figure 5c , Figure 6bAs shown, its features are as follows: the main magnet structure adopts a combination of a small magnetic gap and a shallow valley region, a non-linear magnetic pole structure, an angle-varying chamfered padding structure, and a locally thickened leakage magnetic field suppression structure for the main magnet cover plate; the structure combining the small magnetic gap and the shallow valley region is used to meet the requirement of increasing the average magnetic field for miniaturized desktop cyclotrons; the non-linear magnetic pole structure is used to compensate for the magnetic field reduction caused by the high-frequency through-hole by increasing the angular width of the magnetic poles, so that the magnetic field meets the isochronous acceleration requirements; the angle-varying chamfered padding structure is used to make the padding amount and the magnetic field change amount have a better linear relationship, which is beneficial to the accurate estimation of magnetic field padding; the locally thickened leakage magnetic field suppression structure for the cover plate is used to minimize the increase in the weight of the main magnet while ensuring that the leakage magnetic field meets the standard.

[0039] Furthermore, the small magnetic gap means that the distance between the magnetic pole and the center plane of the accelerator is less than 15mm; the shallow valley region means that the distance between the cover plate and the center plane of the accelerator is less than 50mm; the requirement to improve the average magnetic field to realize the miniaturized desktop cyclotron accelerator means that the average magnetic field of the desktop small cyclotron reaches more than 1.3T.

[0040] Furthermore, the main magnet adopts a non-linear magnetic pole structure, that is, the magnetic pole angle width is locally increased to a certain extent at the high-frequency through hole position. By increasing the magnetic pole angle width, the magnetic field reduction caused by the high-frequency through hole is compensated, so that the magnetic field meets the isochronous acceleration requirements.

[0041] Furthermore, the magnetic pole angle width of the main magnet at the high-frequency through-hole position is locally increased to a certain extent, and this increased magnetic pole angle width is just enough to compensate for the reduction in magnetic field caused by the high-frequency through-hole.

[0042] Furthermore, the chamfering padding structure with varying angles is achieved by using a fixed cutting height and length while varying the cutting angle.

[0043] Furthermore, the locally thickened leakage magnetic field suppression structure of the main magnet cover plate is a targeted local thickening of the area where the inner contour of the main magnet cover plate is circular and the outer contour is octagonal.

[0044] Furthermore, the targeted local thickening means that after thickening by 20mm, the leakage magnetic field flux density at a distance of 200mm from the cover plate is less than 50Gs.

[0045] 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 desktop cyclotron main magnet structure, characterized in that: The main magnet structure employs a combination of a small magnetic gap and a shallow valley region, a non-linear magnetic pole structure, an angle-variable chamfered padding structure, and a locally thickened main magnet cover plate to suppress magnetic leakage. The combination of the small magnetic gap and shallow valley region is used to meet the requirement of increasing the average magnetic field in a miniaturized desktop cyclotron accelerator. The non-linear magnetic pole structure compensates for the magnetic field reduction caused by the high-frequency through-hole by increasing the angular width of the magnetic poles, ensuring the magnetic field meets the isochronous acceleration requirements. The angle-variable chamfered padding structure improves the linear relationship between the padding amount and the change in magnetic field, facilitating accurate estimation of magnetic field padding. The locally thickened cover plate to suppress magnetic leakage minimizes the increase in the main magnet's weight while ensuring compliance with leakage standards. The main magnet adopts a non-linear magnetic pole structure, that is, the magnetic pole angle width is locally increased to a certain extent at the high-frequency through hole position. By increasing the magnetic pole angle width, the magnetic field reduction caused by the high-frequency through hole is compensated, so that the magnetic field meets the isochronous acceleration requirements.

2. The main magnet structure of a desktop cyclotron accelerator according to claim 1, characterized in that: The small magnetic gap refers to the distance between the magnetic poles and the center plane of the accelerator being less than 15mm; the shallow valley region refers to the distance between the cover plate and the center plane of the accelerator being less than 50mm; the requirement to improve the average magnetic field to realize a miniaturized desktop cyclotron accelerator means that the average magnetic field of the desktop mini cyclotron accelerator reaches more than 1.3T.

3. The main magnet structure of a desktop cyclotron accelerator according to claim 1, characterized in that: The magnetic pole angle width of the main magnet at the high-frequency through hole position is locally increased to a certain extent. This increased magnetic pole angle width is just enough to compensate for the reduction in magnetic field caused by the high-frequency through hole.

4. The main magnet structure of a desktop cyclotron accelerator according to claim 1, characterized in that: The chamfering padding structure with varying angles is characterized by using a fixed cutting height and length while varying the cutting angle, with the cutting volume of the chamfering padding being linearly related to the padding amount.

5. The main magnet structure of a desktop cyclotron accelerator according to claim 1, characterized in that: The aforementioned localized thickening of the main magnet cover plate to suppress magnetic leakage is a targeted localized thickening of the area on the main magnet cover plate where the inner contour is circular and the outer contour is octagonal.

6. The main magnet structure of a desktop cyclotron accelerator according to claim 5, characterized in that: The targeted local thickening means that after thickening by 20mm, the leakage magnetic flux density at a distance of 200mm from the cover plate is less than 50Gs.

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