Ion source extraction electrode system for eliminating image bending

Abstract

The invention discloses an ion source extraction electrode system for eliminating image bending, which comprises a plasma electrode, an extraction electrode surrounded by the plasma electrode and a beam control electrode surrounded by the extraction electrode, and the electrodes are arranged in a mutually separated manner; an ion extraction part of the plasma electrode is provided with a first strip-shaped slit with a first arc-shaped opening; the extraction electrode is provided with a second strip-shaped slit with a second arc-shaped opening; the beam control electrode is provided with a third strip-shaped slit with a third arc-shaped opening; the first strip-shaped slit, the second strip-shaped slit and the third strip-shaped slit are oppositely arranged; the invention aims to solve a plurality of technical problems existing in an extraction electrode system and a collector in an existing isotope electromagnetic separator, including but not limited to the problems of bending, frequent sparking phenomenon, heat effect caused by dark current, vulnerability of a collector panel, lack of universality and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ion source extraction electrode systems, and particularly relates to an ion source extraction electrode system for eliminating image bending. Background Art

[0002] The electromagnetic isotope separation method separates isotopes by taking advantage of the fact that ions with the same energy but different masses have different deflection radii in a transverse magnetic field. An electromagnetic isotope separator is a device that uses the electromagnetic separation method to obtain the target isotope, and it mainly consists of an ion source, a collector, a separation magnet, a vacuum system, and corresponding auxiliary equipment. The working principle of the electromagnetic separation method determines that it can separate the vast majority of isotopes on the periodic table of elements, and at the same time has extremely high separation efficiency, and can obtain isotopes with extremely high purity. Especially for many heavy metal isotopes required in the field of radioactive diagnostic and therapeutic drugs, currently, the electromagnetic isotope separator is the only viable technical means.

[0003] The ion source extraction electrode system is one of the important components of an electromagnetic isotope separator. One end of it is connected to the ion source discharge plasma chamber, and the other end is connected to the separation magnet system. Its function is to extract an ion beam with a certain energy from the ion source plasma and effectively transmit it to the downstream separation magnet system. The extraction electrode system directly determines the parameters of the extracted beam current, such as beam energy, energy spread, beam current intensity, emittance, divergence angle, etc., and these parameters will affect the aberration, dispersion, production capacity, purity, etc. of the electromagnetic separator, and thus directly affect the separation effect of the target isotope.

[0004] The extraction electrode system of the existing electromagnetic separator ion source generally has a three-electrode structure, including an extraction slit electrode, a focusing electrode, and a grounding electrode. The slit of the extraction slit electrode generally adopts a regular rectangular or racetrack design. In addition, there are no measures for temperature control arranged on the electrode structure. These designs will bring the following problems, which greatly limit the development of high-current electromagnetic separators.

[0005] (1) At present, isotope electromagnetic separators all adopt the design of regular rectangular or racetrack-shaped extraction slits. Especially for high-intensity electromagnetic separators, it is required to increase the length of the slit in the vertical direction to increase the extraction area and thus obtain the extraction of high-intensity beams. However, according to the ion optics adopted by the electromagnetic separator, in this design, images with varying degrees of curvature will be formed on the beam focal plane. Moreover, the longer the slit length, the greater the degree of image curvature. This problem will bring difficulties to the design of the collector of the electromagnetic separator. On the one hand, the curved image requires a curved receiving port that conforms to its shape to be opened on the collector panel, which limits the available space for the design of the receiving port. On the other hand, the design of the curved receiving port will increase the manufacturing difficulty and complexity. At the same time, during actual operation, the collector will be ablated, deformed, and sputtered due to long-term bombardment by high-intensity focused ion beams. The receiving port panel is a vulnerable component and needs to be replaced frequently. The processing of the curved receiving port panel will inevitably greatly increase the operation and maintenance costs.

[0006] In addition, if an isotope electromagnetic separator is used to separate multiple isotopes, the dispersion of isotopes with different mass numbers is different, and the degree of image curvature is also different. For the separation and reception of isotopes of each different element, a panel with a specific receiving port needs to be processed, which results in the lack of generality of the receiver, thus affecting the flexibility of the overall production of the electromagnetic separator and greatly increasing the production cost.

[0007] (2) The phenomenon of frequent arcing in the existing extraction electrode system restricts the normal operation of the isotope electromagnetic separator on the one hand; on the other hand, it is easy to cause damage to the electrodes. The slit of the extraction electrode will overheat and melt and deform, which will affect the quality of the extracted beam, such as the beam divergence angle, emittance, energy spread, etc., and further reduce the isotope separation effect.

[0008] There is a large dark current in the focusing electrode, resulting in Ohmic heating. There is no temperature control measure in the existing technology, causing the electrode port to overheat and deform, affecting the focusing effect and reducing the beam quality. Some technologies use high-purity graphite materials with high melting points to make the focusing electrodes. Although they have good heat resistance and are not easy to deform, their material cost is high, and they are fragile, increasing the processing and maintenance difficulties. In addition, if the electrode temperature is too low, metal atoms will cool and deposit at the slit, changing the slit size and also affecting the beam quality.

[0009] (3) Although the patent (ZL201610905788.X) adopts the design of the lead-out seam and the concave and hollow structures of the support plate, there is still a dark current of 10 mA, and it is still difficult to solve the influence of the thermal effect on the lead-out electrode. Although the patent (ZL202311675212.5) adopts the design of a replaceable receiver panel, it is still necessary to design and process panels with different slit shapes for different received isotopes, as well as to obtain the image width and dispersion of the isotopes. Moreover, there is also the problem of frequent disassembly and replacement. Since this component is often subjected to high-temperature thermal deposition, there is a deformation problem, which will affect the assembly error and the position accuracy of the receiver, resulting in a decrease in the abundance of separated isotopes and bringing pollution. Summary of the Invention

[0010] The object of the present invention is to provide an ion source lead-out electrode system for eliminating image bending to solve the influence caused by image bending in the prior art.

[0011] To solve the above technical problems, the present invention provides an ion source lead-out electrode system for eliminating image bending, including a plasma electrode, a lead-out electrode surrounded by the plasma electrode, and a beam control electrode surrounded by the lead-out electrode; a first strip-shaped slit is provided at the ion lead-out part of the plasma electrode, and a first arc-shaped opening is provided on the surface of the first strip-shaped slit facing the lead-out electrode; a first insulating column is connected between the lead-out electrode and the plasma electrode to separate the lead-out electrode from the plasma electrode; the lead-out electrode is provided with a second strip-shaped slit, the second strip-shaped slit is arranged opposite to the first strip-shaped slit, and a second arc-shaped opening is provided on the surface of the second strip-shaped slit facing away from the first strip-shaped slit; a second insulating column is connected between the beam control electrode and the lead-out electrode to separate the beam control electrode from the lead-out electrode; the beam control electrode is provided with a third strip-shaped slit, the third strip-shaped slit is arranged opposite to the second strip-shaped slit, and a third arc-shaped opening is provided on the surface of the third strip-shaped slit facing away from the second strip-shaped slit.

[0012] In one embodiment, the heights of the first strip-shaped slit, the second strip-shaped slit, and the third strip-shaped slit are 10 - 100 mm, the widths are 0.5 - 5 mm, and the thicknesses are 0.5 - 5 mm; the opening angle of the first strip-shaped slit is 67.5° - 70°.

[0013] In one embodiment, the curvature radii R0 of the first arc-shaped opening, the second arc-shaped opening, and the third arc-shaped opening are R0 = -R i ·G h / G v 2 , where the R i is the image curvature radius, and the Gh is the magnification factor in the horizontal direction, and the G v is the magnification factor in the vertical direction.

[0014] In one embodiment, in the plasma electrode and the extraction electrode, at least the interior of the plasma electrode is provided with a cooling channel, and the cooling channel is connected to an external cooling circuit system.

[0015] In one embodiment, in the plasma electrode and the extraction electrode, at least the surface of the plasma electrode is provided with a resistance wire and a thermocouple, and the resistance wire and the thermocouple are used to cooperate for temperature regulation.

[0016] In one embodiment, the surface roughness of the plasma electrode, the extraction electrode, and the beam control electrode is less than or equal to 0.8.

[0017] In one embodiment, the surfaces of the plasma electrode, the extraction electrode, and the beam control electrode are all covered with a coating having a low secondary electron emission coefficient.

[0018] In one embodiment, both the first insulating column and the second insulating column are of a corrugated structure.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. After setting the first arc-shaped opening, the second arc-shaped opening, and the third arc-shaped opening, the beam transmission efficiency can be improved, image bending can be effectively eliminated, and an ideal straight beam spot can be obtained at the focal plane, so that the receiving port of the collector panel adopts a fixed shape, simplifying the design and manufacturing process and reducing costs.

[0021] 2. The plasma electrode and the extraction electrode of the present invention can be made of materials with high temperature resistance and low resistivity to reduce problems such as ohmic heating effect and ablation deformation; at the same time, processing means such as precision machining, 3D printing, surface polishing, surface coating or film plating can be used to improve the accuracy of the first strip-shaped slit, the second strip-shaped slit, and the third strip-shaped slit, reduce the surface roughness and secondary electron emission coefficient of the electrode, and find the optimal geometric parameters through simulation to reduce the arcing frequency and improve the beam quality.

[0022] 3. The active cooling adopted by the present invention can cooperate with the cooling channel inside the electrode and the external cooling circuit system to achieve heat management of the electrode system, reduce ohmic heating caused by dark current, avoid electrode damage caused by overheating, and improve the stability of beam extraction and transmission.

[0023] 4. The extraction electrode system and its design method proposed by the present invention are applicable to various ion source types on isotope electromagnetic separators, including Calutron ion sources, ECR ion sources, arc discharge ion sources, surface ionization ion sources, etc. It has strong versatility and is convenient for use and promotion.

[0024] From the above beneficial effects, it can be seen that the present invention aims to solve multiple technical problems existing in the extraction electrode system and the collector in existing isotope electromagnetic separators, including but not limited to problems such as bending, frequent arcing, thermal effects caused by dark current, easy damage of the collector panel, and lack of versatility. These problems seriously affect the stability and working efficiency of the equipment and limit its application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 is the structural schematic diagram provided by the embodiment of the present invention;

[0027] Figure 2 is Figure 1 the cross-sectional structural schematic diagram of

[0028] Figure 3 is Figure 2 the structural schematic diagram of the first strip-shaped slit of

[0029] Figure 4 is Figure 3 the cross-sectional structural schematic diagram of

[0030] The reference numerals are as follows:

[0031] 10. Plasma electrode; 11. Discharge chamber; 12. First strip-shaped slit; 13. First arc-shaped opening; 14. Cooling channel;

[0032] 20. Extraction electrode; 21. Second strip-shaped slit;

[0033] 30. Beam control electrode; 31. Third strip-shaped slit;

[0034] 41. First insulating column; 42. Second insulating column. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0036] The present invention provides an ion source extraction electrode 20 system for eliminating image bending, and an embodiment thereof is as follows Figure 1 and Figure 2 shown, including a plasma electrode 10, an extraction electrode 20 surrounded by the plasma electrode 10, and a beam control electrode 30 surrounded by the extraction electrode 20.

[0037] Regarding the plasma electrode 10, as Figures 1 to 4 shown, the outer shapes of the plasma electrode 10, the extraction electrode 20, and the beam control electrode 30 are all approximately similar to a cap-like structure with a flanged outer edge. Therefore, in the direction from the outside to the inside, the plasma electrode 10 can be sleeved outside the extraction electrode 20, and the extraction electrode 20 can be sleeved outside the beam control electrode 30.

[0038] Among them, a discharge cavity 11 is provided inside the part of the plasma electrode 10 similar to the cap top. The discharge cavity 11 is provided with an opening on the surface facing the extraction electrode 20 to realize the extraction of ions. Specifically, at this time, a first strip-shaped slit 12 is provided at the ion extraction part of the plasma electrode 10, and a first arc-shaped opening 13 is provided on the surface of the first strip-shaped slit 12 facing the extraction electrode 20. When in application, a positive high voltage of 20 - 100 kV can be fed into the plasma electrode 10, and its electrode surface is parallel to the electrode surface of the extraction electrode 20, so as to form an electric field for ion extraction and acceleration between the two, so that the first strip-shaped slit 12 can extract ions from the discharge cavity 11 and form an ion beam.

[0039] In addition, a cooling channel 14 is provided in the plasma electrode 10 in this embodiment. The cross-section of the cooling channel 14 is in a fishbone shape to ensure a wider coverage range. By connecting the cooling channel 14 to an external cooling circuit system, it can be used to adjust the electrode temperature, avoid deformation due to excessive temperature, or damage to the first strip-shaped slit 12 caused by local ablation.

[0040] Furthermore, a resistance wire and a thermocouple are provided on the surface of the plasma electrode 10 in this embodiment. The thermocouple can realize the temperature monitoring of the plasma electrode 10, and the resistance wire can realize the heating of the plasma electrode 10. Therefore, through the mutual cooperation of the two, the temperature control of the plasma electrode 10 can be realized to ensure that the temperature of the plasma electrode 10 can always be maintained within a reasonable range.

[0041] Even further, at this time, the surface roughness of the plasma electrode 10 is 0.8, its surface is covered with a low secondary electron emission coefficient coating, and the height of the first strip-shaped slit 12 is 100 mm, the width is 5 mm, the thickness is 5 mm, and the opening angle is 70°.

[0042] Regarding the extraction electrode 20, as Figure 1 and Figure 2As shown, a first insulating column 41 is connected between the extraction electrode 20 and the plasma electrode 10. A plurality of first insulating columns 41 are circumferentially arranged on the flanging of the extraction electrode 20, so that the extraction electrode 20 and the plasma electrode 10 are separated from each other.

[0043] Among them, the extraction electrode 20 is provided with a second strip-shaped slit 21. The second strip-shaped slit 21 is arranged opposite to the first strip-shaped slit 12, and the second strip-shaped slit 21 is provided with a second arc-shaped opening on the surface facing away from the first strip-shaped slit 12. When in application, a negative high voltage of 1-10 kV can be fed into the extraction electrode 20. Its electrode surface is parallel to the electrode surface of the plasma electrode 10 and also parallel to the electrode surface of the beam control electrode 30 at the same time. Thus, a deceleration electric field is formed between the extraction electrode 20 and the beam control electrode 30, which can effectively suppress secondary electrons in the beam. And at this time, the second strip-shaped slit 21 can be used for focusing and accelerating the beam.

[0044] In addition, a cooling channel is provided in the extraction electrode 20 in this embodiment. The cross-section of the cooling channel is fishbone-shaped to ensure a wider coverage range. By connecting the cooling channel to an external cooling circuit system, it can be used to adjust the electrode temperature, avoid deformation due to excessive temperature, or damage to the second strip-shaped slit 21 caused by local ablation.

[0045] Furthermore, in this embodiment, a resistance wire and a thermocouple are provided on the surface of the extraction electrode 20. The thermocouple can monitor the temperature of the extraction electrode 20, and the resistance wire can heat the extraction electrode 20. Therefore, through the mutual cooperation of the two, the temperature control of the extraction electrode 20 can be realized to ensure that the temperature of the extraction electrode 20 can always be maintained within a reasonable range.

[0046] Even further, the surface roughness of the extraction electrode 20 is 0.8 at this time. Its surface is covered with a low secondary electron emission coefficient coating, and the height of the second strip-shaped slit 21 is 100 mm, the width is 5 mm, and the thickness is 5 mm.

[0047] Regarding the beam control electrode 30, as Figure 1 and Figure 2 shown, a second insulating column 42 is connected between the beam control electrode 30 and the extraction electrode 20. A plurality of second insulating columns 42 are circumferentially arranged on the flanging of the beam control electrode 30, so that the beam control electrode 30 and the extraction electrode 20 are separated from each other.

[0048] Among them, the beam control electrode 30 is provided with a third strip-shaped slit 31. The third strip-shaped slit 31 is arranged opposite to the second strip-shaped slit 21, and the third strip-shaped slit 31 is provided with a third arc-shaped opening on the surface facing away from the second strip-shaped slit 21.

[0049] Further, at this time, the surface roughness of the beam control electrode 30 is 0.8, and its surface is covered with a coating with a low secondary electron emission coefficient. The height of the third strip-shaped slit 31 is 100 mm, the width is 5 mm, and the thickness is 5 mm.

[0050] For the above embodiments, the following points need to be pointed out:

[0051] First, the first strip-shaped slit 12, the second strip-shaped slit 21, and the third strip-shaped slit 31 have preferred setting parameters. To ensure better results, it is recommended to set the height of the first strip-shaped slit 12, the second strip-shaped slit 21, and the third strip-shaped slit 31 to be 10 - 100 mm, the width to be 0.5 - 5 mm, and the thickness to be 0.5 - 5 mm; the opening angle of the first strip-shaped slit 12 is 67.5° - 70°.

[0052] Second, the radius of curvature of the first arc-shaped opening 13, the second arc-shaped opening, and the third arc-shaped opening has an important impact on the actual application effect. To ensure better results, it is recommended to set the radius of curvature R0 of the first arc-shaped opening 13, the second arc-shaped opening, and the third arc-shaped opening to be R i ·G h / G v 2 where R i is the image radius of curvature, G h is the magnification in the horizontal direction, and G v is the magnification in the vertical direction.

[0053] Among them, G h and G v can be given by simulation calculation first, and then corrected using experimental measurement data. Typical values are: R i = 1.5 m, G h = -1.393, G v = -0.835, R0 = 3 m.

[0054] Third, cooling channels 14 are provided in both the plasma electrode 10 and the extraction electrode 20 in the above embodiments, but this is not the only feasible solution. During design, cooling channels 14 can be provided in at least the plasma electrode 10 inside the plasma electrode 10 and the extraction electrode 20, and it is only necessary to ensure that the cooling channels 14 are connected to the external cooling circuit system.

[0055] Among them, the shape of the cooling channel 14 is not particularly limited. It can be the fishbone shape mentioned above, or the comb tooth shape, or a design form with a wide coverage range can also be considered.

[0056] Fourth, in the above embodiments, heating wires and thermocouples are provided in both the plasma electrode 10 and the extraction electrode 20, but this is not the only feasible solution. During design, heating wires and thermocouples can be provided in the plasma electrode 10 and the extraction electrode 20, and at least on the surface of the plasma electrode 10, so as to enable the heating wires and thermocouples to cooperate for temperature control.

[0057] Fifth, as can be seen from the above embodiments, in this embodiment, the surfaces of the plasma electrode 10, the extraction electrode 20, and the beam current control electrode 30 are all covered with a coating having a low secondary electron emission coefficient, and preferred setting parameters are provided for the surface roughness of the plasma electrode 10, the extraction electrode 20, and the beam current control electrode 30. Therefore, to ensure better effects, it is recommended that the surface roughness of the plasma electrode 10, the extraction electrode 20, and the beam current control electrode 30 be less than or equal to 0.8.

[0058] Specifically, the plasma electrode 10, the extraction electrode 20, and the beam current control electrode 30 can be made of high-melting-point non-metals, metals, or their alloys, such as graphite, tungsten, molybdenum, tungsten-copper alloys, etc. Processing can be carried out using conventional precision machining or 3D printing technology, which can effectively ensure the machining accuracy of the slit. After the electrodes are processed, their surfaces can be precisely polished to make the surface roughness lower than 0.8, and further coating or film plating treatment with a low secondary electron emission coefficient can be carried out.

[0059] Sixth, in addition to playing a role in mechanically fixing and supporting each electrode, the above-mentioned first insulating column 41 and second insulating column 42 also serve an effective electrical insulation purpose; and after setting the first insulating column 41 and the second insulating column 42 to be corrugated structures in this embodiment, the insulating creepage length can be effectively increased at the same space height, thereby improving the high-voltage withstand capacity.

[0060] Among them, the first insulating column 41 and the second insulating column 42 can both be made of pure aluminum oxide or doped aluminum oxide materials, and a chromium oxide coating can be added to the surface to further increase the voltage withstand strength.

[0061] Seventh, the external cooling circuit system can be connected to the cooling channels 14 in the plasma electrode 10 and the extraction electrode 20 through insulating pipelines, can withstand a DC high voltage of up to 100 kV, the coolant uses commercial electronic fluorinated liquid, and the cooling pump uses a standard commercial liquid cooling unit, which can provide a flow rate of not less than 10 L / min and a cooling temperature control with a maximum accuracy of ±0.1 °C (5 - 35 °C).

[0062] Eighth, for the heating wires and thermocouples, both the heating and temperature measurement systems are powered by a floating power supply, the temperature measurement range is 0 - 1600 °C, and the accuracy is within ±0.5 °C or ±1%.

[0063] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An ion source extraction electrode system for eliminating image bending, characterized in that it includes a plasma electrode, an extraction electrode surrounded by the plasma electrode, and a beam control electrode surrounded by the extraction electrode; a first strip-shaped slit is provided at the ion extraction part of the plasma electrode, and a first arc-shaped opening is provided on the surface of the first strip-shaped slit facing the extraction electrode; a first insulating column is connected between the extraction electrode and the plasma electrode to separate the extraction electrode from the plasma electrode; the extraction electrode is provided with a second strip-shaped slit, the second strip-shaped slit is arranged opposite to the first strip-shaped slit, and a second arc-shaped opening is provided on the surface of the second strip-shaped slit facing away from the first strip-shaped slit; a second insulating column is connected between the beam control electrode and the extraction electrode to separate the beam control electrode from the extraction electrode; the beam control electrode is provided with a third strip-shaped slit, the third strip-shaped slit is arranged opposite to the second strip-shaped slit, and a third arc-shaped opening is provided on the surface of the third strip-shaped slit facing away from the second strip-shaped slit.

2. The ion source extraction electrode system according to claim 1, characterized in that the heights of the first strip-shaped slit, the second strip-shaped slit, and the third strip-shaped slit are 10 - 100 mm, the widths are 0.5 - 5 mm, and the thicknesses are 0.5 - 5 mm; the opening angle of the first strip-shaped slit is 67.5° - 70°.

3. The ion source extraction electrode system according to claim 1, characterized in that The radius of curvature R0 of the first arcuate opening, the second arcuate opening, and the third arcuate opening is R0 = -R i ·G h / G v 2 , where the R i is the image radius of curvature, and the G h is the magnification in the horizontal direction, and the G v is the magnification in the vertical direction.

4. The ion source extraction electrode system according to claim 1, characterized in that in the plasma electrode and the extraction electrode, at least the plasma electrode is internally provided with a cooling channel, and the cooling channel is connected to an external cooling circuit system.

5. The ion source extraction electrode system according to claim 1, characterized in that in the plasma electrode and the extraction electrode, at least the surface of the plasma electrode is provided with a resistance wire and a thermocouple, and the resistance wire and the thermocouple are used to cooperate for temperature regulation.

6. The ion source extraction electrode system according to claim 1, characterized in that the surface roughnesses of the plasma electrode, the extraction electrode, and the beam control electrode are all less than or equal to 0.

8.

7. The ion source extraction electrode system according to claim 1, characterized in that the surfaces of the plasma electrode, the extraction electrode, and the beam control electrode are all covered with a low secondary electron emission coefficient coating.

8. The ion source extraction electrode system according to claim 1, characterized in that both the first insulating column and the second insulating column are of a corrugated structure.

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