Magnetic shielding structure for detector in neutral particle analyzer of Tokamak device
By using a combination of a common magnetic shield, an independent magnetic shield, and a grid-shaped grid in the neutral particle analyzer of a tokamak device, the problem of signal distortion of the PMT detector under strong magnetic field conditions was solved, achieving effective magnetic field shielding and signal transmission, and ensuring the normal operation of the detector.
Patent Information
- Application Number
- CN202511146153.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-15
- Publication Date
- 2025-11-21
AI Technical Summary
In tokamak devices, the photomultiplier array of the neutral particle analyzer is susceptible to interference from stray magnetic fields, which leads to a decrease in signal gain. Existing magnetic shielding structures cannot simultaneously guarantee signal transmittance and magnetic field shielding effectiveness in strong magnetic field environments.
The system combines a common magnetic shield and an independent magnetic shield, and adds a grid-shaped grille to the front-end signal input window to divide it into independent magnetic compensation areas. Low-carbon steel or permalloy materials are used to achieve precise magnetic field control of the PMT detector.
While maintaining a 60% window open rate, the magnetic field is attenuated to below 25 Gs, which is the normal operating range for the PMT detector, to ensure signal integrity and detector geometric fit.
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Figure CN120998549A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of high-temperature plasma diagnosis, and in particular to a magnetic shielding structure of a detector in a neutral particle analyzer (NPA) for a tokamak device. BACKGROUND
[0002] In the field of magnetic confinement nuclear fusion research, a tokamak device realizes controllable fusion reaction by confining high-temperature plasma through a strong magnetic field. As a core diagnostic device, a neutral particle analyzer (NPA) undertakes the monitoring and measurement tasks of key parameters such as plasma fuel isotope ratio (deuterium-tritium ratio D / T) and high-energy particle distribution function. The particle energy detection technology of NPA will rely on a photomultiplier tube array (PMT), and the kinetic energy signal of the incident particles will be converted into a fluorescence signal through a scintillator technology, and then the output signal will be amplified by the PMT. However, the photoelectron multiplication process inside the PMT is extremely susceptible to external magnetic field interference, and the working threshold requirement is ≤25Gs. When the magnetic field is greater than 25Gs, the secondary electron emission is significantly inhibited, and the signal gain decreases. However, the inherent stray magnetic field of the tokamak and the stray magnetic field of the magnetic signal analysis unit of the neutral particle analyzer diagnosis itself will interfere with the PMT signal, resulting in a decrease in the performance of the neutral particle analyzer diagnosis.
[0003] The largest nuclear fusion experimental device in the world (ITER) currently uses an open double-layer magnetic shielding cover, which uses a common magnetic shielding cover and an independent magnetic shielding cover (low carbon steel) to wrap the PMT array, but the detector window remains open to ensure signal transmission rate. The stray magnetic field of ITER and the magnetic field of the analysis magnet can meet the requirements of the PMT detector through the double-layer detector magnetic shielding. However, the neutral particle analyzer installed on the EAST device is faced with a stray magnetic field as high as 130Gs, and the double-layer magnetic shielding structure cannot reduce the magnetic field to the working threshold requirement of the PMT for the magnetic field. For the full-closed shielding cover commonly used for magnetic shielding, although the magnetic field can be reduced to a minimum, the front-end signal input window of the detector must be open to receive ions passing through the electromagnetic analysis unit of the neutral particle analyzer, so this method is completely infeasible for the shielding of the detector. For the method of increasing the thickness of the shielding layer, the effect is not significant, and the neutral particle analyzer detector cannot accommodate an ultra-thick shielding body due to size and other limiting factors. Therefore, a new type of magnetic shielding structure is needed that can solve the above problems at the same time. SUMMARY
[0004] The application provides a magnetic shielding structure for a detector in a neutral particle analyzer of a tokamak device, and aims at solving the problem of insufficient magnetic shielding of a PMT detector in the neutral particle analyzer in the EAST environment in the prior art.
[0005] To achieve the above object, the application adopts the following technical scheme:
[0006] The magnetic shielding structure for the detector in the neutral particle analyzer of the tokamak device comprises a common magnetic shielding cover and independent magnetic shielding covers; the common magnetic shielding cover is closed on five sides and open at the front end, and the signal input window surface thereof is extended beyond the surface of the detector to optimize signal reception and preliminarily isolate the magnetic field; the independent magnetic shielding covers provide completely closed side protection and a detector mounting end surface; the common magnetic shielding cover and the independent magnetic shielding covers are both made of high magnetic permeability material to ensure efficient magnetic flux shunting; the front end (signal input) window of the common magnetic shielding cover is integrated with a cross-shaped grid; the cross-shaped grid is composed of two groups of orthogonal parallel ribs, divides the open area into nine independent magnetic field compensation units, and realizes fine magnetic field regulation of the working environment of the detector.
[0007] Further, the material of the cross-shaped grid is low-carbon steel or permalloy.
[0008] Further, the thickness of the cross-shaped grid is 1-2 mm, the width is 4-6 mm, and the relative magnetic permeability is 4000-5000.
[0009] Further, the cross-shaped grid is integrally cut and shaped, and the cross-shaped grid is integrally welded on the front end signal input window surface.
[0010] Further, the detector drives 9 detection effective areas, which are located at the vacancies of the cross-shaped grid.
[0011] Further, it works in a magnetic field environment less than 25Gs.
[0012] Further, the material of the common magnetic shielding cover is low-carbon steel or permalloy.
[0013] Further, the independent magnetic shielding cover comprises two functional cavities.
[0014] Further, the cross-shaped grid comprises nine square open areas, and the open areas are accurately aligned with the nine light anodes of the PMT.
[0015] Further, the material of the independent magnetic shielding cover is low-carbon steel or permalloy.
[0016] Compared with the prior art, the beneficial effects of the present application are:
[0017] The present application realizes that the magnetic field is attenuated to below 25Gs under the premise that the window opening rate is about 60% (0% for the traditional closed type), solves the technical contradiction that the signal integrity and magnetic shielding of the PMT detector cannot be compatible in a strong magnetic field environment, and realizes the geometric adaptability of the multi-anode detector under the premise that the magnetic shielding reaches the effect. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 is a schematic view of a magnetic shielding structure of a detector in a neutral particle analyzer for a tokamak device provided by the present application.
[0019] Figure 2 is a front view size of the detector and a display of the effective area of the detector, and it should be understood that the detector structure shown in the figure is only schematic, and the actual H14220 type or equivalent device known in the art can be used.
[0020] Figure 3 is a schematic view of a comparison of different thicknesses of the common magnetic shielding cover.
[0021] Fig. 4 (a) and Fig. 4 (b) are respectively a comparison of different thicknesses of the independent magnetic shielding cover and a comparison of different sizes of the functional cavities in the independent magnetic shielding shell with the common magnetic shielding cover.
[0022] Fig. 5 (a) and Fig. 5 (b) are respectively a comparison of increasing different width grids on the basis of the common and independent magnetic shielding, and a comparison of the grid thickness on the basis of the 4mm width grid.
[0023] Figure 6 is a schematic view of the influence of the forward envelope margin value of the common magnetic shielding on the shielding effect.
[0024] Figure 7 is a schematic view of the magnetic field size of the detector area after not shielding, using ITER double-layer shielding and the present application.
[0025] Wherein, the reference signs are: public magnetic shield cover 1, independent magnetic shield cover 2, well-shaped grid 3, functional cavity 4. DETAILED DESCRIPTION
[0026] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.
[0027] As Figure 1 shown, the present application provides a magnetic shielding structure for a detector in a neutral particle analyzer of a tokamak device, which includes a public magnetic shield cover 1, a plurality of independent magnetic shield covers 2 (according to the number of detectors), and a well-shaped grid 3 on the front-end signal input window of the independent magnetic shield cover. The plurality of independent magnetic shield covers 2 are arranged in parallel and placed in the public magnetic shield cover 1. The part of the public magnetic shield cover 1 that is more than the front-end signal input window of the independent magnetic shield cover 2 is called the public magnetic shielding forward envelope margin value by the present application.
[0028] The independent magnetic shield cover 1 includes two upper and lower functional cavities 4, and there are two horizontal and vertical grid ribs on the front-end signal input window, forming a well-shaped grid 3. The horizontal and vertical rib widths and thicknesses are the same, with a width of about 4-6 mm and a thickness of about 1-3 mm. The particles from the electromagnetic analysis unit of the neutral particle analyzer enter the detector from the signal input window, and the particles will enter the detector from the square open surface left by the well-shaped grid 3.
[0029] The public magnetic shield cover 1, the independent magnetic shield cover 2, and the well-shaped grid 3 are all made of materials with high relative magnetic permeability, such as low-carbon steel and permalloy.
[0030] The public magnetic shield cover wraps the entire detector array system, and the material used is soft magnetic steel (low-carbon steel belongs to a kind of soft magnetic steel), which functions to reduce the external magnetic field of the detector by more than half.
[0031] Further, the public magnetic shield cover 1 has an open surface for front-end signal input, and the coverage needs to exceed the front-end signal input window.
[0032] Each PMT module is equipped with an independent magnetic shield cover 2, which is also made of soft magnetic steel and serves as the main magnetic shield. The structure only leaves the front-end signal input window open, including the upper and lower functional cavities 4 and the detector placement area.
[0033] Further, the upper and lower functional cavities function to dissipate heat (to prevent the core components from overheating), route wires (high-voltage cable / signal line paths), mount support interfaces, and maintain (module maintenance access).
[0034] The cross-shaped grid 3 is welded to the front-end signal input window of the independent magnetic shielding cover 2, and the material is also soft magnetic steel. The cross-shaped grid 3 is composed of two horizontal and two vertical ribs, which divides the entire window into three rows and three columns, including nine square open areas, which are precisely aligned with the nine light anodes of the PMT. It has a magnetic guiding effect rather than just a physical barrier, which can protect the PMT detector from magnetic field interference and also prevent particles from hitting the PMT detector.
[0035] Further, the ribs of the cross-shaped grid 3 are 4-6 mm wide to ensure that the magnetic field shielding achieves the desired effect.
[0036] As shown in Figure 2 The detector used is a H14220 series PMT detector produced by Hamamatsu, and the front of the detector contains nine effective detection areas (blue areas). Due to the fact that some areas are not used for detection, a high magnetic permeability grid can be used to block the magnetic field without affecting the entry of particles into the detector.
[0037] As shown in Figure 3 With only the common magnetic shielding cover 1, the magnetic field comparison after shielding with different thicknesses of the common magnetic shielding cover 1 is shown in Figure 3 It can be seen that there is little difference in shielding effect before and after the cover thickness is thinned and thickened, so the thickness of the common magnetic shielding cover is manufactured according to the requirements. Figure 3 In the simulation modeling, Y is the Y-axis direction, and B is the magnetic field size.
[0038] As shown in Figures 4(a) and 4(b), the comparison of the thickness of the independent magnetic shielding cover and the size of the functional cavity in the independent magnetic shielding cover is shown. As can be seen from Figures 4(a) and 4(b), the thickness of the independent magnetic shielding cover and the size of the functional cavity have little effect on the magnetic shielding, so it can be selected according to the actual situation and requirements.
[0039] Figures 5(a) and 5(b) show a comparison of adding grids of different widths to common and independent magnetic shielding, and a comparison of grid thickness based on a 4mm wide grid. As can be seen from Figures 5(a) and 5(b), grid widths of 2-6mm can reduce the magnetic field to less than 25Gs; the wider the grid, the better the magnetic field shielding effect. With a 4mm width, a thicker grid provides better magnetic field shielding. The sawtooth shape of the curves in the figures is because the magnetic field is stronger in the particle impact area where there is no grid magnetic conduction; the magnetic field is weaker in the area behind the grid due to the grid's magnetic conduction, hence the sawtooth shape.
[0040] like Figure 6 As shown, the larger the forward envelope margin value of the common magnetic shielding, the better the shielding effect.
[0041] like Figure 7 As shown, the magnetic field in the unshielded and ITER-shielded configurations is higher than the required PMT detection level of less than 25 Gs, making it impossible to function properly in the EAST environment. After implementing this invention, the stray magnetic field in the detector area is reduced to less than 25 Gs, allowing the PMT detector to operate normally.
[0042] While specific implementation methods of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples. Various changes or modifications can be made to these implementation methods without departing from the principles and implementation of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.
Claims
1. A magnetic shielding structure for a detector in a neutral particle analyzer of a tokamak device, characterized in that, It includes a common magnetic shield and independent magnetic shields; the common magnetic shield is closed on five sides and open at the front, with its signal input window extending beyond the detector surface to optimize signal reception and initially isolate the magnetic field; the independent magnetic shield provides fully enclosed side protection and a detector mounting end face; both the common and independent magnetic shields are made of high permeability materials to ensure efficient magnetic flux shunting; the front signal input window of the independent magnetic shield integrates a grid-shaped grille; the grid-shaped grille consists of two sets of orthogonal parallel ribs, dividing the open area into nine independent magnetic field compensation units, enabling precise magnetic field control of the detector's working environment.
2. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The grid-shaped grille is made of low-carbon steel or permalloy.
3. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 2, characterized in that, The thickness of the grid is 1-2mm, the width is 4-6mm, and the relative permeability is 4000-5000.
4. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 2, characterized in that, The grid-shaped grille is cut and formed in one piece, and the grid-shaped grille is welded as a whole to the front signal input window surface.
5. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The detector has nine effective detection areas, located in the gaps of the grid.
6. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, It operates in a magnetic field environment of less than 25 Gs.
7. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The material of the public magnetic shield is low-carbon steel or permalloy.
8. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The independent magnetic shielding cover contains two functional cavities, upper and lower.
9. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The grid-shaped grille consists of nine square open areas, which are precisely aligned with the nine photoanodes of the PMT.
10. The magnetic shielding structure for the detector in a neutral particle analyzer for a tokamak device according to claim 1, characterized in that, The material of the independent magnetic shield is low-carbon steel or permalloy.