A magnetic field cutting plasma focus device

Abstract

The present application relates to the technical fields of nuclear fusion research and neutron source, and particularly relates to a poloidal magnetic field plasma focus device, which comprises a vacuum tube, a coaxial electrode assembly and a poloidal magnetic field generating assembly, the coaxial electrode assembly and the poloidal magnetic field generating assembly are arranged in the vacuum tube; the poloidal magnetic field generating assembly comprises a plurality of bar magnets, each of the bar magnets is distributed in a circumferential array around an axis of the vacuum tube, and each of the bar magnets is arranged at an outer periphery of the coaxial electrode assembly, the magnetization directions of adjacent bar magnets are opposite, so that the N poles of the bar magnets and the S poles of the bar magnets are arranged alternately along the circumference, thereby forming a poloidal magnetic field in a discharge region of the coaxial electrode assembly, and the technical problem of low energy utilization efficiency caused by large parasitic inductance of a discharge loop of a traditional plasma focus device is solved.

Description

Technical Field

[0001] This invention relates to the fields of nuclear fusion research and neutron source technology, specifically to a tangential magnetic field plasma focus device. Background Technology

[0002] Plasma focus devices utilize high-power pulsed discharges to ionize the working gas, forming a plasma current sheath. Driven by electromagnetic force, this sheath accelerates axially along coaxial electrodes, ultimately resulting in a radial implosion at the center, thus generating high-density, high-temperature plasma. These devices have important applications in fundamental nuclear fusion research, neutron sources, X-ray sources, and materials irradiation testing. Traditional devices typically consist of coaxial electrodes, a vacuum tube, a pulsed power supply, and a gas handling system. Typical examples include the Mather-type structure (invented and systematically studied by John W. Mather and his team at Los Alamos National Laboratory in the early 1960s) and the Filippov-type structure (invented independently by the NV Filippov team at the Kurchatov Atomic Energy Institute in the Soviet Union; this structure employs a short-diameter ratio, large-area plate-shaped electrode (the anode is typically a disk or flat-topped cylinder, and the cathode is a ring-shaped plate, placed parallel to each other). The electrode gap is short and wide. After the plasma current sheath forms, it mainly moves rapidly radially towards the central axis and implodes to form the focus. Its structural inductance is usually smaller, enabling the generation of extremely strong pulsed currents. However, existing technologies still face several key bottlenecks in practical operation: First, the formation of the initial plasma depends on surface discharge, a process significantly affected by the state of the insulating surface, gas distribution, and electric field uniformity, resulting in poor stability and repeatability of plasma sheath formation, directly impacting the focus formation quality and neutron yield consistency of each discharge. Second, the presence of significant parasitic inductance in the discharge circuit limits the current rise rate, causing some input energy to be consumed in the gas ionization and sheath formation stages, rather than being entirely used for plasma acceleration and compression, resulting in low overall energy utilization efficiency.

[0003] Therefore, in view of this, the inventors propose a magnetic field plasma focus device to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a plasma focus device that cuts through a magnetic field, aiming to solve the technical problem of low energy utilization efficiency caused by the large parasitic inductance of the discharge circuit in traditional plasma focus devices.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A plasma focusing device for cutting magnetic fields includes a vacuum tube, a coaxial electrode assembly, and a cutting magnetic field generating assembly, wherein the coaxial electrode assembly and the cutting magnetic field generating assembly are disposed inside the vacuum tube; The cross-cutting magnetic field generating component includes several bar magnets, each of which is arranged in a circular array around the axis of the vacuum tube and on the outer periphery of the coaxial electrode assembly. The magnetization directions of adjacent bar magnets are opposite, so that the N pole and S pole of the bar magnets are alternately arranged along the circumference, thereby forming a cross-cutting magnetic field in the discharge region of the coaxial electrode assembly.

[0006] Furthermore, the vacuum tube includes two flanges and a vacuum chamber, with both ends of the vacuum chamber being sealed and fixedly connected to the two flanges.

[0007] Furthermore, the coaxial electrode assembly includes an anode and a plurality of cathode rods; the anode is arranged along the axis of the vacuum tube and extends into the vacuum cavity through one of the flanges; the plurality of cathode rods are circumferentially distributed around the anode and are detachably connected to the flange.

[0008] Furthermore, it also includes an insulation component, which includes a high-temperature resistant ceramic tube. The high-temperature resistant ceramic tube has a hollow structure and passes through one of the flanges and is fixedly connected to the flange. The anode is disposed inside the high-temperature resistant ceramic tube.

[0009] Furthermore, the number of the bar magnets is even, and the magnetization direction of each bar magnet is perpendicular to the axis of the vacuum tube.

[0010] Furthermore, the bar magnet is a rare-earth permanent magnet with high remanence density.

[0011] Furthermore, it also includes an inflation system and an air extraction system. The inflation system includes an air pump and an air supply pipe. The air pump is connected to the air supply pipe, and the air supply pipe passes through one of the flanges to inject working gas into the vacuum tube. The air extraction system includes an air pump and an exhaust pipe. Another flange has an air extraction port, which is connected to the exhaust pipe, and the exhaust pipe is connected to the air pump.

[0012] Furthermore, it also includes a cooling system, which includes cooling pipes disposed outside the vacuum tube and a circulating water pump connected to the cooling pipes.

[0013] Furthermore, it also includes a pulsed power system, which includes a DC high-voltage power supply, a high-voltage switch, and an energy storage capacitor; the energy storage capacitor is connected in parallel with the coaxial electrode assembly and forms a discharge circuit through the high-voltage switch; the DC high-voltage power supply is used to charge the energy storage capacitor.

[0014] Furthermore, the energy storage capacitor has a capacitance of 40μF, and the peak value of the pulse discharge current generated by the discharge circuit is 300KA to 500KA.

[0015] The beneficial effects of this invention are: This invention effectively reduces the overall inductance of the discharge circuit by optimizing the distributed return path design of the coaxial electrode assembly (a circumferential array structure of the anode and multiple cathode rods). Compared with the traditional Mather and Filippov structures, it significantly improves the pulse current rise rate, enhances the electromagnetic force driving the plasma sheath motion, and efficiently converts more input energy into plasma kinetic energy, thereby improving energy utilization efficiency and solving the energy waste problem caused by excessive parasitic inductance in traditional devices.

[0016] The present invention utilizes a shearing magnetic field generation component to form a petal-shaped magnetic field configuration in the discharge region using bar magnets arranged in a circular array with alternating N / S poles. During the initial plasma formation stage, the shearing magnetic field uses the Lorentz force to cause charged particles to rapidly detach from the electrode surface, forming a symmetrical and stable plasma current sheath. During the axial acceleration stage, the radial magnetic field gradient force provides continuous magnetic confinement, suppressing fluid instabilities such as sheath distortion and expansion, maintaining structural integrity until radial implosion, and ultimately improving the stability of plasma density and temperature in the focal region as well as the consistency of neutron yield.

[0017] Other advantages, objectives, and features of this application will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from practice of this application. The objectives and other advantages of this application may be realized and obtained through the detailed embodiments described below. Attached Figure Description

[0018] Figure 1 This is a cross-sectional schematic diagram of the magnetic field plasma focus device of the present invention; Figure 2 This is a side view schematic diagram of the magnetic field plasma focus device of the present invention; Figure 3 This is a partial structural diagram of one direction of the magnetic field plasma focus device of the present invention; Figure 4 This is a partial structural diagram of another direction in the magnetic field plasma focus device of the present invention.

[0019] The components include: 1. Insulation component; 2. Gas filling system; 3. Flange; 4. Bar magnet; 5. Cathode; 6. Vacuum chamber; 7. Anode; and 8. Air extraction port. Detailed Implementation

[0020] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0021] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0022] This embodiment proposes a magnetic field plasma focus device, such as... Figures 1 to 4 As shown, the device includes a vacuum tube, a coaxial electrode assembly, and a cross-cutting magnetic field generating assembly, which are disposed inside the vacuum tube. The cross-cutting magnetic field generating assembly includes several bar magnets 4, which are arranged in a circular array around the axis of the vacuum tube and on the outer periphery of the coaxial electrode assembly. The magnetization directions of adjacent bar magnets 4 are opposite, so that the N pole and S pole of the bar magnets 4 are alternately arranged along the circumference, thereby forming a cross-cutting magnetic field in the discharge region of the coaxial electrode assembly.

[0023] In this embodiment, when the device is working, the vacuum tube is filled with an appropriate amount of working gas (such as deuterium) and a high-voltage pulse is applied to the coaxial electrode assembly. First, surface discharge occurs on the surface of the coaxial electrode assembly, generating initial plasma. At this time, the tangential magnetic field generated by the bar magnets 4, which are arranged in a circular array and have alternating N / S poles, immediately acts on these initial plasmas. Since the N pole and S pole of the bar magnets 4 are arranged alternately in a circular array, there is a certain angle between the direction of the magnetic field and the direction of plasma movement. This can apply a magnetic force (Lorentz force) perpendicular to the initial direction of movement to the charged particles. This force causes the initial plasma to detach from the surface of the coaxial electrode assembly quickly and orderly, thereby forming a plasma current sheath with improved stability and symmetry. Subsequently, driven by the self-generated magnetic field (J×B force) produced by the pulsed high current flowing through it, the current sheath accelerates along the coaxial electrode axis. Throughout this axial acceleration process, the external tangential magnetic field continuously provides a magnetic confinement effect, helping to suppress fluid instabilities such as twisting and expansion that may occur in the plasma sheath during high-speed motion, thus maintaining its structural integrity. When the plasma current sheath accelerates to the electrode tip (corresponding to...), Figure 1When the kinetic energy is converted into internal energy at the right end of the coaxial electrode assembly, rapid radial implosion compression occurs, eventually forming a plasma focus with extremely small scale, extremely high density and temperature at the axis.

[0024] In a preferred embodiment, the vacuum tube includes two flanges 3 and a vacuum chamber 6. The two ends of the vacuum chamber 6 are sealed and fixedly connected to the two flanges 3. The coaxial electrode assembly includes an anode 7 and a plurality of cathode rods 5. The anode 7 is arranged along the axis of the vacuum tube and extends into the vacuum chamber 6 through the flange 3 on the left side. The plurality of cathode rods 5 are distributed circumferentially around the anode 7 and are installed and connected to the flanges 3 by means of threaded connection.

[0025] Within the sealed vacuum chamber comprised of flange 3 and vacuum cavity 6, when a pulsed high voltage is applied to the coaxial electrode assembly, a highly axisymmetric radial electric field is formed between the anode 7 and each cathode 5 rod. This electric field couples with the axial non-uniform magnetic field generated by the tangential magnetic field generating assembly, acting together on the discharge region. Specifically, this electrode arrangement first ensures that the initial plasma generated by surface discharge can be uniformly excited in the axisymmetric electric field. More importantly, this structural design, with the anode 7 serving as the concentrated current inflow end and multiple cathode 5 rods forming a distributed current return path, reduces the overall inductance of the discharge circuit compared to existing model structures (Mather-type and Filippov-type structures). The low inductance allows the pulsed current to rise at an extremely high rate, thereby enhancing the electromagnetic force driving the plasma sheath and efficiently converting more energy into the kinetic energy of the plasma. Simultaneously, the detachable connection between the cathode 5 rods and flange 3 not only facilitates installation, alignment, and maintenance but also allows for the individual replacement of cathode 5 components that have degraded due to ablation after long-term operation, effectively improving the reliability and service life of the device.

[0026] In a preferred embodiment, an insulating component 1 is also included. The insulating component 1 comprises a high-temperature resistant ceramic tube, which is hollow and passes through and is fixedly connected to the flange 3 on the left side. The anode 7 is inserted inside the high-temperature resistant ceramic tube. As an insulating and supporting component, the high-temperature resistant ceramic tube first provides the anode 7 with stable mechanical positioning and highly reliable electrical insulation, ensuring that the anode 7 does not experience surface flashover or breakdown between itself and the vacuum chamber and flange 3 under high-voltage pulses (e.g., 30-100KV), thus ensuring effective loading of discharge energy. Secondly, the high-temperature resistance of the ceramic tube allows it to withstand the instantaneous high-temperature plasma and thermal radiation generated by pulse discharge at the root of the anode 7 and the insulating surface, preventing material cracking or performance degradation due to thermal stress. This ensures the stability and repeatability of the physical state at the surface discharge location during multiple discharges.

[0027] In a preferred embodiment, the number of bar magnets 4 is even, and the magnetization direction of each bar magnet 4 is perpendicular to the axis of the vacuum tube. The bar magnets 4 are rare-earth permanent magnets with high remanence. The bar magnets 4 are preferably bar Sm2Co17 magnets with length, width and height of 25×25×200mm respectively. After magnetization, the modulus of the residual magnetic flux density Br in the core is ≥1.2T. Here, Br refers to the residual magnetic flux density, and T is the unit in the International System of Units (SI) for measuring magnetic induction intensity or magnetic flux density.

[0028] The bar magnet 4 has a wide surface (25×200mm) as its magnetization surface. An even number of magnets are arranged with their magnetization direction perpendicular to the vacuum tube axis. When the bar magnets 4 are arranged in a circular array around the axis, with adjacent magnets having alternating polarities (N / S), the magnetic fields generated by each bar magnet 4 superimpose in the discharge region near the axis, forming a magnetic field configuration where the magnetic field lines are distributed in a "petal-like" pattern, the magnetic field strength is zero on the axis, and the magnetic field strength rapidly increases after leaving the axis. This configuration of the magnetic field is characterized by a central line with zero magnetic field (coinciding with the discharge axis) and a strong magnetic field region surrounding this central line. Rare-earth permanent magnets with high remanence (Br≥1.2T) (such as Sm2Co17) are selected to provide a sufficiently strong magnetic field. Strong magnetic fields offer the following advantages: a. In the initial plasma generation stage, the strong vertical magnetic field component exerts a significant Lorentz force on the charged particles generated by surface discharge, forcing them to rapidly detach from the insulating surface and move along specific magnetic field lines, thus forming an axisymmetric plasma current sheath and improving the stability and repeatability of the initial plasma; b. During the axial acceleration stage of the plasma sheath, the radial magnetic field gradient force (magnetic mirror effect or magnetic pressure) generated by the tangential magnetic field can exert additional radial constraint on the moving plasma column, helping to suppress plasma distortion, expansion, or premature disintegration caused by uneven current distribution or Rayleigh-Taylor instability, thereby maintaining the structural integrity of the sheath until effective implosion; c. Strong magnetic fields also help shorten the formation time of the plasma sheath and may reduce the equivalent inductance of the discharge circuit to some extent, thereby increasing the current rise rate and overall energy utilization efficiency, and improving the stability and repeatability of the plasma.

[0029] In a preferred embodiment, the system further includes an inflation system 2 and a vacuum system. The inflation system 2 includes an air pump and an air supply pipe. The air pump is connected to the air supply pipe, which passes through a flange 3 on the left side for injecting working gas into the vacuum tube. The vacuum system includes a vacuum pump and an exhaust pipe. An exhaust port 8 is provided on the flange 3 on the right side, which is connected to the exhaust pipe, which is also connected to the vacuum pump. The vacuum system is used to evacuate the inside of the vacuum tube to an extremely high vacuum level (e.g., 1.33 × 10⁻⁶). -3The purpose of the gas filling system (on the order of Pa) is to thoroughly remove residual air, water vapor, and other impurities from the vacuum tube, preparing it for the subsequent injection of pure working gas. More importantly, it eliminates the risk of impurities being ionized during discharge, consuming energy, interfering with plasma composition, and potentially generating interfering radiation (such as impurity spectral lines), thus ensuring that the input energy is used to ionize and accelerate the target working gas to the maximum extent. Subsequently, the gas filling system 2 is used to inject the working gas into the vacuum tube to a specific optimal pressure range (e.g., 133-665 Pa). Too low a pressure may lead to difficulties in initial ionization and insufficient formation of the plasma sheath, while too high a pressure will increase the gas load, causing the current sheath to experience excessive gas dynamic resistance during acceleration, affecting its acceleration efficiency and final implosion velocity, thereby reducing the plasma density and temperature in the focal region.

[0030] In a preferred embodiment, a cooling system (not shown) is also included. The cooling system comprises cooling pipes disposed outside the vacuum tube and a circulating water pump connected to the cooling pipes. During high-power pulsed discharge, a huge amount of instantaneous heat energy is generated inside the vacuum tube. The cooling system, by laying cooling pipes outside the vacuum tube and having a circulating water pump drive the cooling medium (usually deionized water) to circulate within them, achieves efficient and uniform heat dissipation from the vacuum chamber wall, removing most of the waste heat generated by the discharge, and strictly controlling the operating temperature of the vacuum chamber wall and related components within the range permitted by material safety and stable performance, thereby ensuring that the device can operate reliably for a long time at a high repetition frequency.

[0031] In a preferred embodiment, a pulsed power system is also included, comprising a DC high-voltage power supply, a high-voltage switch, and an energy storage capacitor. The energy storage capacitor is connected in parallel with a coaxial electrode assembly and forms a discharge circuit through the high-voltage switch. The DC high-voltage power supply is used to charge the energy storage capacitor. The capacitance of the energy storage capacitor is preferably 40 μF, and the peak value of the pulsed discharge current generated by the discharge circuit is 300 kA to 500 kA. The DC high-voltage power supply charges the energy storage capacitor to a specific high voltage (e.g., 30-100 kV), while the energy storage capacitor value is limited to 40 μF. At a given voltage, the capacitance value determines the total stored energy (E = 1 / 2 CV). 2A 40μF capacitor can store approximately 200kJ of energy at a maximum voltage of 100kV, providing the necessary energy foundation for generating high-parameter plasma. Simultaneously, this capacitance value, along with the total inductance of the discharge circuit (including electrode structure, connecting wires, etc.), determines the oscillation period and current waveform of the discharge. An optimized capacitance value helps match the system inductance, forming a rapidly rising, single-peak or quasi-single-peak current pulse, thereby efficiently coupling energy to the plasma in a short time. The rapid closing of the high-voltage switch (e.g., using a spark gap or semiconductor switch) triggers the discharge, forming a low-impedance path. High pulsed current is a direct guarantee for achieving strong electromagnetic drive: First, a strong current is a necessary condition for forming initial surface discharge, effectively ionizing the working gas, and establishing a plasma current sheath; second, the self-generated magnetic field (proportional to the current) and the Lorentz force (J×B force) generated by the interaction of the current are the power sources driving the axial acceleration of the plasma sheath. The higher the peak current, the stronger the acceleration force, the greater the final velocity of the plasma, and the higher its implosion kinetic energy; finally, the peak current and the rise rate directly affect the compressibility, final density, and temperature of the focal spot. By optimizing the distributed return path design of the coaxial electrode assembly (a circumferential array structure of anode 7 and multiple cathode 5 rods), the overall inductance of the discharge circuit is effectively reduced. Compared to traditional Mather-type and Filippov-type structures, this invention significantly improves the pulse current rise rate, enhances the electromagnetic force driving the plasma sheath motion, and efficiently converts more input energy into plasma kinetic energy, thereby improving energy utilization efficiency and solving the energy waste problem caused by excessive parasitic inductance in traditional devices. The shearing magnetic field generation component forms a petal-shaped magnetic field configuration in the discharge region through a circular array of bar magnets 4 with alternating N / S poles. In the initial plasma formation stage, the shearing magnetic field promotes the rapid detachment of charged particles from the electrode surface through the Lorentz force, forming a symmetrical and stable plasma current sheath. In the axial acceleration stage, the radial magnetic field gradient force provides continuous magnetic confinement, suppressing fluid instabilities such as sheath distortion and expansion, maintaining structural integrity until radial implosion, and ultimately improving the stability of plasma density and temperature in the focal region and the consistency of neutron yield. This application has high application value.

[0032] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A device for focusing a plasma in a cutting magnetic field, characterized in that, include: A vacuum tube, a coaxial electrode assembly, and a tangential magnetic field generating assembly are disposed inside the vacuum tube. The cross-cutting magnetic field generating component includes several bar magnets, each of which is arranged in a circular array around the axis of the vacuum tube and on the outer periphery of the coaxial electrode assembly. The magnetization directions of adjacent bar magnets are opposite, so that the N pole and S pole of the bar magnets are alternately arranged along the circumference, thereby forming a cross-cutting magnetic field in the discharge region of the coaxial electrode assembly.

2. The tangential magnetic field plasma focus device according to claim 1, characterized in that: The vacuum tube includes two flanges and a vacuum chamber, with both ends of the vacuum chamber being sealed and fixedly connected to the two flanges.

3. The tangential magnetic field plasma focus device according to claim 2, characterized in that: The coaxial electrode assembly includes an anode and a plurality of cathode rods; the anode is arranged along the axis of the vacuum tube and extends into the vacuum cavity through one of the flanges; the plurality of cathode rods are circumferentially distributed around the anode and are detachably connected to the flange.

4. The tangential magnetic field plasma focus device according to claim 3, characterized in that: It also includes an insulation component, which includes a high-temperature resistant ceramic tube. The high-temperature resistant ceramic tube has a hollow structure and passes through one of the flanges and is fixedly connected to the flange. The anode is disposed inside the high-temperature resistant ceramic tube.

5. The tangential magnetic field plasma focus device according to claim 4, characterized in that: The number of the bar magnets is even, and the magnetization direction of each bar magnet is perpendicular to the axis of the vacuum tube.

6. The tangential magnetic field plasma focus device according to claim 5, characterized in that: The bar magnet is a rare-earth permanent magnet with high remanence.

7. The tangential magnetic field plasma focus device according to claim 6, characterized in that: It also includes an inflation system and an air extraction system. The inflation system includes an air pump and an air supply pipe. The air pump is connected to the air supply pipe, and the air supply pipe passes through one of the flanges to inject working gas into the vacuum tube. The air extraction system includes an air extraction pump and an exhaust pipe. Another flange has an air extraction port, which is connected to the exhaust pipe, and the exhaust pipe is connected to the air extraction pump.

8. The tangential magnetic field plasma focus device according to claim 7, characterized in that: It also includes a cooling system, which includes cooling pipes disposed outside the vacuum tube and a circulating water pump connected to the cooling pipes.

9. The tangential magnetic field plasma focus device according to claim 8, characterized in that: It also includes a pulsed power system, which includes a DC high-voltage power supply, a high-voltage switch, and an energy storage capacitor; the energy storage capacitor is connected to the coaxial electrode assembly and forms a discharge circuit through the high-voltage switch; the DC high-voltage power supply is used to charge the energy storage capacitor.

10. The tangential magnetic field plasma focus device according to claim 9, characterized in that: The energy storage capacitor has a capacitance of 40μF, and the peak value of the pulse discharge current generated by the discharge circuit is 300KA to 500KA.

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