A magnet structure with a background magnetic field

Abstract

The application relates to the technical field of superconducting magnet fault arc test, and discloses a magnet structure with a background magnetic field, wherein the magnet structure comprises a fireproof part, a first fixing part, and a first magnet coil and a second magnet coil which are connected with each other in series; wherein the first magnet coil and the second magnet coil are coaxially arranged, and a combustion space inside the two forms a magnetic field; a test gap is arranged between the first magnet coil and the second magnet coil; the fireproof part is arranged in the combustion space, and a heat insulation space is formed between the fireproof part and the inner side wall of the first magnet coil and the inner side wall of the second magnet coil; the fireproof part is further provided with a sample insertion channel which is aligned with the test gap; the first fixing part comprises a plurality of clamps for fixing test samples which pass through the test gap and the sample insertion channel in sequence; the magnet structure can provide a stable background magnetic field for test of the spatial propagation characteristics of a fault arc in a simulated fusion device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of superconducting magnet fault arc test, in particular to a magnet structure with background magnetic field. BACKGROUND

[0002] In the operation process of the fusion device, the arc fault as a sudden high energy release phenomenon, is extremely easy to cause serious damage to the superconducting magnet system. Each detail change of the spatial propagation path, energy deposition mode, etc. of the arc will affect the final arc fault.

[0003] However, the existing arc test platform only focuses on simulating the arc phenomenon to obtain the conclusions of "current / voltage drive, thermal balance, shape stability", etc. However, such test platform cannot test the propagation behaviors of the arc deflection, contraction, rotation and extinction in the magnetic field, which is not conducive to supporting the experimental research on the arc behaviors of the nuclear fusion device. SUMMARY

[0004] The present application provides a magnet structure with background magnetic field, which solves the problem that the existing arc test platform cannot test the spatial propagation characteristics of the fault arc in the background field.

[0005] To solve the above technical problems, the present application provides a magnet structure with background magnetic field, which comprises a fireproof part, a first fixing part, and a first magnet coil and a second magnet coil connected in series; wherein,

[0006] The first magnet coil and the second magnet coil are coaxially arranged, and a magnetic field is formed in the combustion space inside them; a test gap is arranged between the first magnet coil and the second magnet coil;

[0007] The fireproof part is arranged in the combustion space, and a heat insulation space is formed between the fireproof part and the inner side wall of the first magnet coil and the inner side wall of the second magnet coil, and the fireproof part is further provided with a sample insertion channel aligned with the test gap;

[0008] The first fixing part comprises a plurality of clamps for fixing the test sample sequentially passing through the test gap and the sample insertion channel.

[0009] As one of the preferred schemes, the magnetic induction intensity of the magnetic field is at least 2000 Gauss; the spatial range of the magnetic field is 500mm in radial direction and 600mm in axial direction.

[0010] As one of the preferred schemes, the test gap is greater than 100mm; the thickness of the heat insulation space is 10cm.

[0011] As one of the preferred solutions, the fireproof device is further provided with a front observation window corresponding to the test gap and the combustion space.

[0012] As one of the preferred solutions, the magnet structure is further provided with a top observation window corresponding to the top of the combustion space.

[0013] As one of the preferred solutions, the magnet structure is further provided with a high-speed camera arranged outside the front observation window and an infrared thermal imager arranged outside the top observation window.

[0014] As one of the preferred solutions, the magnet structure is further provided with a second fixing member for fixing the first magnet coil and the second magnet coil; two ends of the second fixing member are connected with the outer wall of the first magnet coil and the outer wall of the second magnet coil respectively, so that the first magnet coil and the second magnet coil are coaxially aligned.

[0015] As one of the preferred solutions, the magnet structure is further provided with a series busbar; two ends of the series busbar are connected with the same-named end of the first magnet coil and the same-named end of the second magnet coil respectively, so that the first magnet coil and the second magnet coil form a series loop.

[0016] As one of the preferred solutions, the magnet structure is further provided with an electrode busbar; one end of the electrode busbar is connected with the non-same-named end of the first magnet coil or the non-same-named end of the second magnet coil, and the other end of the electrode busbar is connected with an external magnet power supply.

[0017] As one of the preferred solutions, the magnet structure is further provided with an electrode connecting line; one end of the electrode connecting line is connected with the other end of the test sample, and the other end of the electrode connecting line is connected with an external arc power supply.

[0018] Compared with the prior art, the embodiment of the present application has the following beneficial effects:

[0019] The first magnet coil and the second magnet coil are coaxially connected in series and are separated by a test gap, a stable and uniform background magnetic field is generated, the strict requirement of the magnetic field environment for arc test in a fusion device is met to provide a burning space, and space for sample insertion and observation is reserved; the fireproof piece arranged in the burning space and aligned with the test gap and the inner side wall of the two magnet coils forms a heat insulation space, and the sample insertion channel is arranged, which can protect the magnet from being directly affected by the high-temperature arc and improve the safety of the test; the first fixing piece for fixing the test sample inserted through the test gap and the sample insertion channel in sequence ensures the position stability of the test sample during the test, avoids the influence of sample shaking or position deviation on the test result, and improves the accuracy and reliability of the test; the magnet structure with a background magnetic field constructed by the application is suitable for various arc propagation characteristic researches in a fusion device, especially for fault arcs, and can be popularized to the fields of superconducting magnet safety design and failure mechanism evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the present application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 is a structural schematic diagram of a magnet structure with a background magnetic field provided by an embodiment of the present application;

[0022] Figure 2 is a schematic diagram of a magnet structure and a test sample installation structure provided by an embodiment of the present application;

[0023] Figure 3 is a schematic diagram of a magnet structure and a test sample installation structure provided by another embodiment of the present application;

[0024] Figure 4 is a layout diagram of a combustion chamber observation window provided by an embodiment of the present application;

[0025] Corresponding labels are as follows:

[0026] Among them, 1, magnet structure; 2, test sample; 3, burning space; 4, test platform; 20, fireproof piece; 30, sample fixing assembly; 50, series busbar; 60, electrode busbar; 70, electrode connecting wire; 80, cold water pipe; 101, first magnet coil; 102, second magnet coil; 301, clamp; 302, support frame; 401, forward observation window; 402, top observation window; 4011, combustion chamber front observation port; 4021, combustion chamber overhead observation port. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings and the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The purpose of providing these embodiments is to make the disclosure of the present application more thorough and complete. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0028] In the description of the present application, the terms "first", "second", "third" and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second", "third" and the like can be explicitly or implicitly included one or more features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0029] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. The terms "vertical", "horizontal", "left", "right", "up", "down" and similar expressions used in this paper are only for the purpose of description, and cannot be understood as indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. The term "and / or" used in this paper includes any and all combinations of one or more related listed items. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0030] In the description of the present application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art. The terms used in the description of the present application are only used to describe the specific embodiments, and are not intended to limit the present application. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0031] In an embodiment, as shown in Figure 1 The present application provides a magnet structure 1 with a background magnetic field, comprising a fireproof member 20, a first fixing member, and a first magnet coil 101 and a second magnet coil 102 connected in series with each other; wherein,

[0032] The first magnet coil 101 and the second magnet coil 102 are coaxially arranged, and a combustion space 3 inside the two forms a magnetic field; a test gap is arranged between the first magnet coil 101 and the second magnet coil 102;

[0033] The fireproof piece 20 is arranged in the combustion space 3, and a heat insulation space is formed between the inner side wall of the first magnet coil 101 and the inner side wall of the second magnet coil 102; a sample insertion channel aligned with the test gap is further arranged on the fireproof piece 20.

[0034] The first fixing assembly includes a plurality of clamps 301 for fixing the test sample 2 sequentially passing through the test gap and the sample insertion channel.

[0035] In view of the problem that the existing arc test platform only focuses on simulating arc phenomenon and cannot meet the test demand of the spatial propagation characteristics of fault arcs of a fusion device, the present application designs a magnet structure 1 with a background magnetic field, the resistance of which is 1.15Ω, and the weight of the magnet structure 1 with a skeleton structure is 1.773kg, which is used to provide a stable background magnetic field for the test of the fault arc in the fusion device simulated by the built arc test platform.

[0036] Specifically, the magnet structure 1 and the test sample 2 installation structure schematic diagram is as shown in Figure 2 , which is a front view, the magnet structure 1 and the test sample 2 installation structure schematic diagram is as shown in Figure 3 , which is a top view, and the combustion chamber observation window layout diagram is as shown in Figure 4 , please refer to Figures 1-4 , the magnet structure 1 includes a fireproof piece 20, a first fixing piece, and a first magnet coil 101 and a second magnet coil 102 connected in series.

[0037] The whole formed by the first magnet coil 101 and the second magnet coil 102 is a magnetic field generating structure, which is a hollow cylinder, including the first magnet coil 101 and the second magnet coil 102 coaxially arranged and connected in series, for generating a magnetic induction intensity of at least 2000 Gauss in the combustion space 3 surrounded by the two magnet coils, and the uniformity of the formed magnetic field is better than 10%, and meets the experimental conditions of stable propagation of the arc in the background magnetic field; the spatial range of the magnetic field is 500mm in radial direction and 600mm in axial direction, so that the whole process of arc propagation can be within the observation range.

[0038] The magnet structure 1 connects two magnet coils through a series busbar 50 (preferably made of red copper, high conductivity and small resistance), wherein the two ends of the series busbar 50 are connected with the same-named ends of the first magnet coil 101 and the second magnet coil 102 respectively, so that the first magnet coil 101 and the second magnet coil 102 form a series loop, and the magnetic fields generated by the two coils can be superimposed in the same direction in the combustion space 3; the busbar connection method adopted by the application simplifies the coil circuit structure (no need to connect the power supply separately), reduces the wiring complexity, and the thermal conductivity of the red copper material can assist the coil in dissipating heat, further controlling the temperature rise.

[0039] Meanwhile, the first magnet coil 101 and the second magnet coil 102 in the magnetic field generating structure are both wound by oxygen-free copper conductors, the cross section of the oxygen-free copper conductor is 8mm*8mm, and a water cooling hole with a diameter of 5mm is arranged in the conductor along the length direction of the conductor, the cooling hole is connected with the external water cooling equipment through the cooling water pipe 80 of the magnet structure 1, so that the temperature rise of the magnetic field generating structure under the input current of 200A is not more than 30K. In addition, the first magnet coil 101 and the second magnet coil 102 are both composed of 50 layers of windings, each layer has 10 turns, the single coil turn number-R is 10, and the single coil turn number-Z is 50; when the magnetic induction intensity of the background magnetic field generated by the structure reaches 2000 Gauss, the input current is 200A, and an insulating layer (preferably made of epoxy glass cloth material) with a thickness of 0.5mm is arranged between the adjacent two turns of the coil, which can withstand a breakdown voltage of not less than 10kV. In addition, the first magnet coil 101 and the second magnet coil 102 in the magnetic field generating structure are arranged oppositely, and there is a test gap between them, which is greater than 100mm, thereby providing an observation light path for the forward observation window 401, and facilitating the insertion of the test sample 2 and the collection of arc images.

[0040] The magnetic field generating structure in the magnet structure 1 adopts the design of coaxial series coil+test gap, which not only ensures the coaxial degree of the magnetic field, but also reserves space for sample insertion and observation; meanwhile, the magnetic field intensity and uniformity parameters are completely matched with the real background magnetic field environment in the fusion device, ensuring the consistency of the working conditions of the arc test, the magnetic field space range of 500mm*600mm covers the whole combustion space 3, ensures that the whole process from ignition to propagation to extinction of the fault arc is in a stable magnetic field, avoids experimental errors caused by magnetic field boundary effect; the design of oxygen-free copper conductor material and water cooling hole can effectively control the temperature rise of the magnet, ensure long-term stable operation under the current of 200A, and avoid the damage of the equipment due to overheating; the setting of the insulating layer can improve the electrical insulation performance of the coil, prevent breakdown in high voltage environment, and enhance the safety and durability of the system.

[0041] The fireproof piece 20 is a fireproof structure, which is a hollow cylindrical structure, a hollow cylindrical partition wall made of high-temperature resistant ceramic fiber plate (temperature resistance ≥ 1200 DEG C), which is sleeved in the inside of the combustion space 3 generated by the magnetic field generating structure, the inner diameter matches the outer diameter of the magnet coil, is fixed through the positioning support, and keeps a radial distance of 10 cm with the inner side wall of the two magnet coils, so as to form a heat insulation space with a thickness of 10 cm, and then effectively block the heat conduction between the combustion space 3 and the magnet structure 1 and the damage of the arc burning spatter to the device and the electrode; meanwhile, the fireproof piece 20 also includes a sample insertion channel (diameter 20 mm, and the center line thereof passes through the axis of the fireproof piece 20 and is aligned with the magnet middle space) arranged in the alignment test gap.

[0042] The fireproof structure in the magnet structure 1 adopts the design of hollow cylinder + radial distance, realizes heat insulation of the combustion space 3 and other parts of the structure, avoids high-temperature damage, and at the same time, the radial distance of 10 cm forms a composite heat insulation space of test gas + fireproof partition wall, which can block the high-temperature conduction of the combustion space 3 to the magnetic field generating structure (avoiding aging of the coil insulation layer), intercept the arc burning spatter (such as metal debris), prevent the arc burning spatter from adhering to the surface of the coil to cause short circuit, and at the same time, does not affect the magnetic field penetration (air and the material of the fireproof piece 20 have no obvious shielding effect on the magnetic field).

[0043] The magnet structure 1 also includes a fixing structure, i.e. a first fixing piece, which includes a plurality of clamps 301 (made of stainless steel or high-strength alloy) for fixing the test sample 2 passing through the test gap and the sample insertion channel in sequence, so as to suspend and fix the test sample 2 in the magnet structure 1, and make the test sample 2 be located in the combustion space 3 surrounded by the magnet coil. Among them, the clamps 301 are at least two, respectively fixing two ends of the test sample 2, and each clamp 301 is also provided with a fixing structure (such as a threaded hole, a clamping groove) matched with the test sample 2, so that the test sample 2 is fixed on the clamp 301 in a threaded connection or buckle clamping manner, one end of the clamp 301 is connected with the test sample 2, and the other end is connected with the test platform 4 (for collecting signals such as volt-ampere signals and electromagnetic wave signals, which is not the focus of the present application and will not be described here), so as to fix and install the whole magnet structure 1 on the test platform 4, and an insulating plate (preferably made of polytetrafluoroethylene material, insulation resistance ≥ 10 8 Ω) is arranged between the clamp 301 and the test platform 4, so as to realize electrical isolation.

[0044] Meanwhile, the magnet structure 1 further comprises a plurality of second fixing members for fixing the first magnet coil 101 and the second magnet coil 102, one end of each of the second fixing members is connected with the outer wall of the first magnet coil 101, and the other end of each of the second fixing members is connected with the outer wall of the second magnet coil 102. The second fixing members are support frames 302 (made of stainless steel or high-strength alloy, suitable for the weight of the magnet and the stability requirement of the experiment), at least four, for supporting the whole magnet structure 1, and the support frames 302 are uniformly distributed on the magnetic field generating structure, each of the support frames 302 is in a strip shape, and each of the support frames 302 is connected with the outer wall of the two magnet coils through bolt fastening or welding, so that the two magnet coils are coaxially aligned.

[0045] The fixing structure in the magnet structure 1 adopts the design of suspension fixing and path guiding, which ensures that the test sample 2 accurately falls into the combustion space 3 (the effective coverage range of the magnetic field), and improves the experimental repeatability. Meanwhile, the test sample 2 is fixed on the clamp 301, which can adapt to test samples 2 of different diameters and materials (such as copper-niobium titanium alloy pieces simulating superconducting magnet windings), and improves the versatility of the device. The connection of the support frame 302 and the two magnet coils can forcibly ensure that the two magnet coils are coaxially aligned (the coaxiality error is less than or equal to 0.5 mm), and the magnetic field uniformity is avoided to be reduced due to the coil deviation.

[0046] The magnet structure 1 further comprises an observation structure, which comprises a plurality of forward observation windows 401 (with a size of 150 mm*200 mm, uniformly distributed on the central axis of the fireproof member 20) arranged on the fireproof member 20 corresponding to the test gap and the combustion space 3, and a high-speed camera (such as Phantom VEO1010L) arranged outside the forward observation windows 401, which is arranged above the straight line connecting the axis centers of the first magnet coil 101 and the second magnet coil 102, and is aligned with a top observation window 402 (which can be a circular observation window with a DN250) arranged outside the top observation window 402 and an infrared thermal imager or an infrared camera (such as SPARK M200). Please refer to Figure 4 The forward observation windows 401 correspond to the front observation port 4011 of the combustion chamber, and the top observation window 402 corresponds to the top observation port 4021 of the combustion chamber, so that the observation structure can accurately observe the arc propagation phenomenon in the combustion space 3, so as to realize the comprehensive collection and analysis of the propagation morphology and thermal characteristics of the fault arc under multiple visual angles.

[0047] The observation structure in the magnet structure 1 breaks the limitation of the traditional single view angle, provides comprehensive data support for arc propagation characteristic analysis, and adopts a forward + top double-window design.

[0048] In addition, the magnet structure 1 further comprises an electrode busbar 60 (for example, a copper plate with a thickness of 10 mm) and an electrode connecting wire 70 (preferably a copper core cable with a current carrying capacity of greater than or equal to 10 kA); wherein one end of the electrode busbar 60 is connected to a non-opposite end of the first magnet coil 101 or a non-opposite end of the second magnet coil 102 (the non-opposite end herein can be understood as the side of the coil that is not connected to the series busbar 50), and the other end of the electrode busbar 60 is provided with a standard terminal for connecting to an external magnet power supply (a direct current stabilized power supply with a rated current of greater than or equal to 300 A, a rated voltage of greater than or equal to 250 V, and a stabilized current accuracy of less than or equal to 0.5%), thereby providing current for the first magnet coil 101 and the second magnet coil 102. One end of the electrode connecting wire 70 is connected to the other end of the test sample 2 away from the test gap and the sample insertion channel in sequence, and the other end of the electrode connecting wire 70 is connected to an external arc power supply (a direct current stabilized power supply that can simulate the current change in the magnet energy release process and output the load current through a remote input current change function, with a total power of 300 kW; the maximum output voltage is 125 V when the output current is 1200-2400 A; the maximum output voltage is 300 V when the output current is 0-1000 A), thereby providing electric energy for the test sample 2 to generate arc propagation phenomenon.

[0049] The magnet structure 1 provided by the application adopts the electrode busbar 60 to conveniently connect the external magnet power supply, without the need for on-site welding, thereby improving the device assembly efficiency; the busbar adopts a rigid structure and can withstand the electric force under a large current, thereby avoiding current fluctuations caused by vibration loosening at the wiring place and ensuring the stability of the magnetic field strength; the electrode connecting wire 70 can adapt to the large current output of the external arc power supply, thereby avoiding cable overheating and burning; one end of the connecting wire is connected to the test sample 2 through a quick connector, the test sample 2 can be quickly replaced, and the experimental interval is shortened; the other end is matched with the output end of the arc power supply, thereby ensuring the stability of arc ignition and improving the experimental success rate.

[0050] The magnet structure 1 designed in the application first integrates the four functions of magnetic field generation, heat protection, sample positioning and observation collection in the same structure, specifically: the stable and high uniformity background magnetic field can be provided in the closed combustion chamber to provide ideal experimental conditions for the arc propagation behavior research; the reasonable coil spacing and structure design enable the arc image to be accurately acquired by the high-speed camera equipment and infrared camera; the fireproof structure can effectively isolate heat and protect the magnet from being directly affected by the high-temperature arc, thereby improving the system safety; the problem of dispersed functions of the existing platform is solved, and the typical arc propagation scene in the fusion reactor is simulated, the collected images can be used to analyze the arc path, morphology and heat distribution and other parameters, thereby providing data support for subsequent magnet structure protection and fault diagnosis, the test of the arc propagation characteristics of the fault arc in the background magnetic field environment is realized, and the experimental method is safe and reliable; the overall structure is suitable for various arc propagation characteristic researches in the fusion device, especially the fault arc, and can be popularized to the fields of superconducting magnet safety design and failure mechanism evaluation. In addition, it should be noted that the device structure and its material and size described in the application are only one embodiment, which can be adjusted or realized by other schemes according to actual needs, and are not limited specifically herein.

[0051] In the embodiment of the application, based on the problem that the existing arc test platform cannot realize the test of the spatial propagation characteristics of the fault arc in the background field, a magnet structure with a background magnetic field is designed, the first magnet coil and the second magnet coil are coaxially connected in series and are separated by a test gap, a stable and uniform background magnetic field is generated, the strict requirement of the magnetic field environment for the arc test in the fusion device is met to provide a combustion space, and space is reserved for sample insertion and observation; the fireproof piece is arranged in the combustion space and forms a heat insulation space with the inner side wall of the two magnet coils, and the sample insertion channel is arranged in the test gap, the magnet is protected from being directly affected by the high-temperature arc, and the safety of the test is improved; the first fixing piece is used for fixing the test sample which passes through the test gap and the sample insertion channel in sequence, the position stability of the test sample in the test process is ensured, the influence of the test result caused by the shaking or position deviation of the sample is avoided, and the accuracy and reliability of the test are improved; the magnet structure with the background magnetic field constructed in the application is suitable for various arc propagation characteristic researches in the fusion device, especially the fault arc, and can be popularized to the fields of superconducting magnet safety design and failure mechanism evaluation.

[0052] In summary, the present application relates to the technical field of superconducting magnet fault arc test, and discloses a magnet structure with a background magnetic field, wherein the magnet structure comprises a fireproof part, a first fixing part, and a first magnet coil and a second magnet coil connected with each other in series; wherein the first magnet coil and the second magnet coil are coaxially arranged, and a combustion space inside the two forms a magnetic field; a test gap is arranged between the first magnet coil and the second magnet coil; the fireproof part is arranged in the combustion space, and a heat insulation space is formed between the fireproof part and the inner side wall of the first magnet coil and the inner side wall of the second magnet coil, and the fireproof part is further provided with a sample insertion channel aligned with the test gap; the first fixing part comprises a plurality of clamps for fixing test samples sequentially passing through the test gap and the sample insertion channel; the magnet structure can provide a stable background magnetic field for testing the spatial propagation characteristics of fault arcs in a simulated fusion device.

[0053] Each of the embodiments in the specification is described in a progressive manner, and the same or similar parts of each of the embodiments can be referred to each other, and each of the embodiments focuses on the difference from other embodiments. It should be noted that the technical features of the above-mentioned embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0054] The above-mentioned embodiments only express several preferred embodiments of the present application, and the description is more specific and detailed, but it should not be understood as the limitation of the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the technical principles of the present application, some improvements and replacements can be made, and these improvements and replacements should be considered as the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the protection scope of the claims.

Claims

1. A magnet structure with a background magnetic field for testing the spatial propagation characteristics of a fault arc in a fusion device, characterized in that, The fireproof part, the first fixing part, and the first magnet coil and the second magnet coil in series with each other are included. The first magnet coil and the second magnet coil are coaxially arranged, and a combustion space inside both forms a magnetic field. The fireproof part is a hollow cylindrical structure, which is arranged in the combustion space and forms a heat insulation space with a thickness of 10 cm between the inner side wall of the first magnet coil and the inner side wall of the second magnet coil, the heat insulation space is used to block the high temperature of the combustion space from conducting to the magnetic field generating structure and the damage of the arc burning spatter to the device and the electrode, the fireproof part is also provided with a sample insertion channel aligned with the test gap, and the center line of the sample insertion channel passes through the axis of the fireproof part and is aligned with the middle space of the magnet. The first fixing part includes a plurality of clamps for fixing the test sample sequentially passing through the test gap and the sample insertion channel, so that the test sample is suspended and fixed in the magnet structure, and the test sample is located in the combustion space surrounded by the magnet coil. The magnet structure also includes a series busbar, and the two ends of the series busbar are connected with the same name end of the first magnet coil and the same name end of the second magnet coil respectively, so that the first magnet coil and the second magnet coil form a series loop.

2. A magnet structure with a background magnetic field according to claim 1, characterized in that The magnetic induction intensity of the magnetic field is at least 2000 Gauss, and the spatial range of the magnetic field is 500 mm in the radial direction and 600 mm in the axial direction.

3. A magnet structure with a background magnetic field according to claim 1, characterized in that The test gap is greater than 100 mm.

4. The magnet structure with a background magnetic field according to claim 1, characterized in that, The fireproof part is also provided with a front observation window corresponding to the test gap and the combustion space.

5. A magnet structure with a background magnetic field according to claim 4, characterized in that The magnet structure also includes a top observation window arranged above the center line of the first magnet coil and the second magnet coil and aligned with the combustion space.

6. A magnet structure with a background magnetic field according to claim 5, characterized in that The magnet structure also includes a high-speed camera arranged outside the front observation window and an infrared thermal imager arranged outside the top observation window.

7. The magnet structure with a background magnetic field according to claim 1, characterized in that The magnet structure also includes a second fixing part for fixing the first magnet coil and the second magnet coil, and the two ends of the second fixing part are connected with the outer wall of the first magnet coil and the outer wall of the second magnet coil respectively, so that the first magnet coil and the second magnet coil are coaxially aligned.

8. The magnet structure with a background magnetic field of claim 1, wherein, The magnet structure also includes an electrode busbar, one end of the electrode busbar is connected with the non-same name end of the first magnet coil or the non-same name end of the second magnet coil, and the other end of the electrode busbar is connected with an external magnet power supply.

9. The magnet structure with a background magnetic field of claim 1, wherein, The magnet structure also includes an electrode connecting line, one end of the electrode connecting line is connected with the other end of the test sample, and the other end of the electrode connecting line is connected with an external arc power supply.

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