A novel pinnig ion source of a new extraction orifice shape

Abstract

A novel Penning ion source with a new extraction orifice shape comprises an extraction orifice, the extraction orifice comprises a rectangular region and a special-shaped region connected with the rectangular region, the special-shaped region gradually decreases in width from one end connected with the rectangular region to the other end, and the symmetry axes of the rectangular region and the special-shaped region coincide; the length-width ratio of the extraction orifice is 1-3.5:1.The novel Penning ion source with the new extraction orifice shape adopts a new special-shaped extraction orifice structure, the longitudinal size of the slit is reduced, the transverse size is increased, the longitudinal emission width of the extracted beam is reduced, the area of the beam emission surface is expanded, and the extracted beam intensity is increased.

Description

Technical Field

[0001] This invention belongs to the field of nuclear technology and relates to an ion source, specifically a novel Penning ion source with a novel extraction aperture shape. Background Technology

[0002] Low-energy cyclotron accelerators have wide applications in fields such as biology, medicine, and basic physics research. In the medical field, cyclotron accelerators can be used to produce various radionuclides, allowing these radionuclides to participate in human metabolism using isotope labeling, and enabling targeted radiodiagnosis and treatment. In recent years, the rapid development of positron emission tomography (PET) technology has led to the widespread application and development of small medical cyclotron accelerators with energies of 10–20 MeV. ¹¹C, ¹³N, and ¹⁵O are all components of life. The radioactive isotope drug FDG synthesized from ¹⁸F has glucose properties, making it more likely to accumulate in tumor cells after injection into the human body. Its radioactivity can be captured and visualized by X-ray tomography scanners, revealing images of cancerous areas.

[0003] Cyclotrons typically operate under high vacuum (less than 1 E⁻³ Pa). In operation, charged particles (and negative hydrogen ions) are first drawn from an initial ion source, accelerated, and confined to a circular path by a magnetic field. A rapidly alternating high-voltage radio frequency source alters the electric field within the cyclotron chamber, causing the ion source to cyclone and gain kinetic energy. After acquiring sufficient energy, the ions are guided to a target material to produce different radionuclides as needed.

[0004] In medical cyclotrons, the negative hydrogen ion source is an indispensable and crucial component. The intensity and quality of the generated negative hydrogen ion beam directly affect the accelerator's beam parameters and production efficiency. However, the extracted beam suffers severe axial loss in the central region of the cyclotron, leading to a significant reduction in the final target beam intensity. The design of the ion source extraction system is a critical factor influencing this axial loss in the accelerator's central region. Ion source extraction apertures are mostly narrow slits, which to some extent increase the beam's axial width, resulting in severe axial loss in the central region. The ion source extraction system refers to the device that extracts ions from the plasma generated by the ion source. A plasma emission surface is formed at the extraction aperture of the extraction system. Ions generated by the ion source exit from this emission surface, and the ion beam is accelerated and extracted using a subsequent extraction voltage. The plasma emission surface affects the beam's emissivity; the greater the emissivity, the more severe the beam loss. The shape of the plasma emitting surface is typically located at an equipotential surface determined by the space charge and the extracted electric field. The main factors determining the emitting surface are the conductivity and the electrode geometry, which plays a crucial role in the formation of the extracted electric field near the emitting surface. Therefore, the design of the aperture geometry of the ion source extraction hole is critical and important.

[0005] Penning ion sources are mainly divided into axial extraction and radial extraction. In radial extraction of Penning ion sources, in order to ensure that there is a large gas resistance inside the ion source and increase the extracted beam current, the extraction hole is usually designed as a long and narrow rectangular slit. The slit is 2-10mm long, 0.1-1.0mm wide, and usually 0.05-0.5mm thick. Figure 7 and Figure 8 Designed using existing technology. The main disadvantage of this slit-type ion source is:

[0006] 1. The extracted beam has a large longitudinal distance and a certain divergence after being extracted from the emitting surface. The magnetic and electric fields in the central region of the accelerator make it difficult to axially focus this beam, resulting in severe longitudinal loss of the acceleration gap in the central region of the accelerator, small beam emission area of ​​the extraction aperture, and limited beam intensity.

[0007] 2. The shape of the straight-hole electrode cannot effectively allow the extracted electric field to penetrate into the emitter hole, resulting in low extraction capability. In addition, the "edge effect" of the inner wall (due to the weakening of the electric field near the wall, the emitting surface is close to the edge of the wall) exacerbates aberrations and increases emissivity.

[0008] 3. Within the emitting surface of this rectangular slit, some emitting positions experience higher beam loss rates in the central region due to differences in the electric field generated by the leads, while emitting positions theoretically experiencing lower loss rates in the central region are not located within the emitting surface of this rectangular slit. The narrow rectangular slit cannot fully utilize the accelerator's beam receiving capability, resulting in low beam trapping efficiency. Summary of the Invention

[0009] To overcome the technical defects of the existing technology, this invention discloses a novel Penning ion source with a novel extraction hole shape.

[0010] The Penning ion source with a novel extraction hole shape according to the present invention includes an extraction hole, characterized in that the extraction hole includes a rectangular region and an irregularly shaped region connected to the rectangular region, the width of the irregularly shaped region gradually decreases from one end connected to the rectangular region to the other end, and the axes of symmetry of the rectangular region and the irregularly shaped region coincide.

[0011] The length-to-width ratio of the outlet hole is 1-3.5:1, where the length is the length of the rectangular area and the width is the sum of the maximum widths of the rectangular area and the irregular area.

[0012] Preferably, the cross-section at the boundary of the outlet hole is wedge-shaped, and the wedge angle is greater than 10 degrees and less than 90 degrees.

[0013] Preferably, the irregular region is an isosceles triangle.

[0014] Preferably, the irregular region includes an isosceles trapezoidal region connected to the rectangular region and an isosceles triangle connected to the isosceles trapezoidal region.

[0015] Preferably, the isosceles trapezoidal region and the isosceles triangle have the same height.

[0016] Preferably, the inflection points in the irregularly shaped area are rounded corners.

[0017] The Penning ion source with the novel extraction aperture shape described in this invention employs a new irregularly shaped extraction aperture structure. The longitudinal dimension of the slit is reduced, while the transverse dimension is increased, thereby reducing the longitudinal emission width of the extracted beam and expanding the area of ​​the beam emission surface, thus increasing the intensity of the extracted beam. The electric field formed from the emission surface to the extraction electrode within the extraction aperture structure region of this invention is beneficial for improving the beam capture efficiency in the central region, significantly enhancing the beam receiving capability of the accelerator, reducing the beam loss rate in the central region, and effectively improving the target current intensity of the accelerator. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a specific embodiment of the novel lead-out hole described in this invention;

[0019] Figure 2 for Figure 1 Schematic diagram of cross section along the AA direction;

[0020] Figure 3 for Figure 1 Enlarged view of point C2;

[0021] Figure 4 for Figure 2 Enlarged view of point B2;

[0022] Figure 5 This is a schematic diagram of another shape of the novel lead-out hole described in this invention;

[0023] Figure 6 This is a schematic diagram of another shape of the novel lead-out hole described in this invention;

[0024] Figure 7 This is a schematic diagram of the lead-out hole in the prior art;

[0025] Figure 8 for Figure 7 Schematic diagram of the cross section along the A1-A1 direction;

[0026] Figure 9 This is a contour plot of the beam loss rate according to a specific embodiment of the present invention;

[0027] Figure 10 This is a schematic diagram comparing the electric field line distribution near the boundary of the lead-out hole with that of the prior art and the present application.

[0028] Figure 11 This is a schematic diagram comparing the beam boundary near the outlet boundary of existing technology and the present application. Detailed Implementation

[0029] The following is in conjunction with the appendix Figures 1 to 8 The specific embodiments of the present invention will be further described in detail below.

[0030] The novel Penning ion source with a novel extraction hole shape according to the present invention includes an extraction hole, wherein the extraction hole includes a rectangular region and an irregularly shaped region connected to the rectangular region, the width of the irregularly shaped region gradually decreases from one end connected to the rectangular region to the other end, and the axes of symmetry of the rectangular region and the irregularly shaped region coincide.

[0031] The length-to-width ratio of the outlet hole is 1-3.5:1, where the length is the length of the rectangular area and the width is the sum of the maximum widths of the rectangular area and the irregular area.

[0032] Compared to existing technologies, this invention reduces the longitudinal dimension of the extraction aperture while increasing its transverse dimension, thereby decreasing the longitudinal emission width of the extracted beam. The irregular surface expands the area of ​​the beam emission surface, significantly increasing the intensity of the extracted beam. Based on beam studies in the central region of cyclotron accelerators, the electric field formed between the emission surface and the extraction electrode within this irregular structure region is beneficial for improving beam capture efficiency in the central region, significantly enhancing the accelerator's beam receiving capability, reducing beam loss rate in the central region, and effectively increasing the target beam intensity on the accelerator.

[0033] Figure 9 The following is a contour plot obtained by calculating the beam loss rate in the central region of the accelerator using the particle tracking module of COMSOL (a multiphysics simulation software), which is performed on a small-scale scan of the extraction surface. Figure 9 In the diagram, the x and y axes represent the coordinate positions of the lead-out plane, and the color depth represents the loss rate in the central region. It can be seen from the contour map that the loss rate of the irregular slit in the central region is less than 40%, while the loss rate of the lead-out slit in the central region of the prior art is about 54%. It can be seen that the lead-out hole described in this invention can effectively reduce the loss rate of the beam in the central region.

[0034] Meanwhile, this invention improves the shape of the external cut electrode near the lead-out hole, and incorporates existing technologies such as... Figure 8 The straight hole electrode shown is designed in a wedge shape and concave inward, such as... Figure 4 As shown, the angle α of the wedge-shaped notch is 10°-90°; this structure allows the lead-in field to penetrate into the emitter aperture more effectively, effectively avoiding aberrations caused by excessive curvature of the equipotential surface at the aperture edge, resulting in a more uniform equipotential surface curvature near the emitter surface and reducing beam emissivity. Figure 10 and Figure 11 A comparative schematic diagram is provided showing the electric field line distribution and beam boundary of the existing technology and the present application with the wedge-shaped cross-section of the extraction hole boundary. Figure 10 and Figure 11The right side of the image shows the flat-shaped cross-section of the prior art, while the left side shows the wedge-shaped cross-section used in this application. It can be seen that the distribution of electric field lines near the flat-shaped cross-section of the prior art is significantly different on the left and right, and the beam boundary tilt angle is large. However, after using the wedge-shaped cross-section electrode, the distribution of electric field lines is more uniform, and the beam boundary is smoother.

[0035] like Figure 3 In one specific embodiment shown, the outlet hole is approximately equal to a rectangle and an isosceles triangle. The two sides of the isosceles triangle can be designed as two straight sides, and more preferably, they can be designed to be concave inward. That is, the irregular area includes an isosceles trapezoidal area connected to the rectangular area and an isosceles triangle connected to the isosceles trapezoidal area, such as... Figure 5 As shown; the recessed position can be near the midpoint of the side, for example, within ±0.5mm of the midpoint. Ideally, the recessed position and the vertex of the isosceles triangle should be designed as an arc, such as... Figure 6 As shown.

[0036] Outer notch design at the edge of the lead-in hole: the notch angle α is 10°-90°, refer to the specific shape. Figure 2 .

[0037] The Penning ion source with the novel extraction aperture shape described in this invention employs a new irregularly shaped extraction aperture structure. The longitudinal dimension of the slit is reduced, while the transverse dimension is increased, thereby reducing the longitudinal emission width of the extracted beam and expanding the area of ​​the beam emission surface, thus increasing the intensity of the extracted beam. The electric field formed from the emission surface to the extraction electrode within the extraction aperture structure region of this invention is beneficial for improving the beam capture efficiency in the central region, significantly enhancing the beam receiving capability of the accelerator, reducing the beam loss rate in the central region, and effectively improving the target current intensity of the accelerator.

[0038] The foregoing descriptions are preferred embodiments of the present invention. Unless there is a clear contradiction between the preferred embodiments or a prerequisite for a particular preferred embodiment, the preferred embodiments can be arbitrarily combined and used. The embodiments and specific parameters described are only for clearly illustrating the inventor's invention verification process and are not intended to limit the scope of patent protection of the present invention. The scope of patent protection of the present invention shall still be determined by its claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A novel Penning ion source with an extraction aperture shape, comprising an extraction aperture, characterized in that, The outlet hole includes a rectangular area and an irregularly shaped area connected to the rectangular area. The width of the irregularly shaped area gradually decreases from one end connected to the rectangular area to the other end. The axes of symmetry of the rectangular area and the irregularly shaped area coincide. The length-to-width ratio of the outlet hole is 1-3.5:1, where the length is the length of the rectangular area and the width is the sum of the maximum widths of the rectangular area and the irregular area; The irregular region includes an isosceles trapezoidal region connected to the rectangular region and an isosceles triangle connected to the isosceles trapezoidal region, thereby reducing the longitudinal emission width of the extracted beam, increasing the area of ​​the beam emission surface, and increasing the intensity of the extracted beam.

2. The Penning ion source as described in claim 1, characterized in that, The cross-section at the boundary of the outlet hole is wedge-shaped, and the wedge angle is greater than 10 degrees and less than 90 degrees.

3. The Penning ion source as described in claim 1, characterized in that, The isosceles trapezoidal region and the isosceles triangle have the same height.

4. The Penning ion source as described in any one of claims 1 or 3, characterized in that, The inflection points in the irregular region are rounded.

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