A method of measuring the pitch angle of a magnetic field using rotating doppler microwave reflection

Abstract

This invention discloses a method for measuring the magnetic field pitch angle using rotating Doppler microwave reflection. A Doppler backscattering meter (DBS) simultaneously transmits X-mode and O-mode polarized microwave signals to the plasma and receives the scattered signals returning along the transmitted optical path. A beam splitter divides the received scattered signals into two paths: one path enters the original DBS, and the other enters a rotatable antenna to adjust the vibration direction of the received electric field component. Based on the steady-state discharge conditions of EAST, a high-speed rotating platform rotates the rotatable antenna 360° during the stable discharge period, completing the scanning of the vibration directions of the electric and magnetic field components of the scattered signal, thus obtaining the magnetic field pitch angle at the detection frequency cutoff layer. This method is low-cost, causes almost no interference to the plasma, and allows for real-time, interference-free measurement of the magnetic field pitch angle at a localized location within the core of a magnetic confinement fusion device.

Description

Technical Field

[0001] This invention relates to the field of magnetic field pitch angle measurement technology, and in particular to a method for measuring magnetic field pitch angle using rotating Doppler microwave reflection. Background Technology

[0002] Driven by the need to address climate change and achieve sustainable energy development, controlled nuclear fusion is considered one of the most promising clean energy solutions for the future. Fusion energy boasts advantages such as abundant fuel, zero carbon dioxide emissions, and long-term stable operation. Currently, the most promising path to its realization is the magnetic confinement fusion device. Magnetic confinement fusion devices rely on strong magnetic fields to confine high-temperature plasma, and their confinement performance and stability directly determine the feasibility of fusion energy. In magnetic confinement fusion physics, EFIT (Equilibrium Fitting Code, a computer program for reconstructing the two-dimensional equilibrium configuration of plasma) equilibrium reconstruction is the foundation for many subsequent analyses. Turbulent transport simulations, magnetohydrodynamic (MHD) stability calculations, and studies of fast ion behavior all require accurate magnetic field structures. However, EFIT obtains the tokamak magnetic field distribution by solving the Grad–Shafranov equations, which require experimental measurements for confinement. The magnetic field pitch angle is a key physical quantity used for EFIT equilibrium reconstruction in magnetic confinement fusion devices.

[0003] Among existing methods for measuring the pitch angle of the magnetic field in magnetic confinement fusion devices, Motional Stark Effect (MSE) spectroscopy can directly measure the pitch angle and has high spatiotemporal resolution. However, it requires injecting a high-energy neutral beam (~50-10 keV) into the magnetic confinement fusion device, resulting in complex equipment. Meanwhile, diagnostic systems such as Faraday Rotation Polarimetry, Magnetic Probes (Mirnov Coils), and Electron Cyclopolar Interval Measurement (ECEI / POINT) have low spatiotemporal resolution and rely on other diagnostic methods to indirectly measure the pitch angle. Summary of the Invention

[0004] The purpose of this invention is to provide a method for measuring the magnetic field pitch angle by rotating Doppler microwave reflection. This method is low-cost, causes almost no interference to the plasma, and can measure the magnetic field pitch angle of a localized location in the core of a magnetic confinement fusion device in real time without interference.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for measuring the pitch angle of a magnetic field using rotating Doppler microwave reflection, the method comprising:

[0007] Step 1: Simultaneously transmit X-mode and O-mode polarized microwave signals to the plasma through the Doppler backscattering meter diagnostic system (DBS), and receive the scattered signals returning along the transmitted optical path;

[0008] Step 2: The received scattered signal is split into two paths by a beam splitter. One path goes into the original DBS, and the other path goes into a rotatable antenna to adjust the vibration direction of the received electric field component.

[0009] Step 3: Based on the steady-state discharge conditions of the EAST tokamak device, during the stable discharge period, a high-speed rotating platform is used to rotate the rotatable antenna 360° to complete the scanning of the vibration direction of the electric field component and the magnetic field component of the scattered signal, and to obtain the magnetic field pitch angle θ at the detection frequency cutoff layer.

[0010] As can be seen from the technical solution provided by the present invention, the above method is low in cost, has almost no interference with plasma, and can measure the magnetic field pitch angle of the local position of the core of a magnetic confinement fusion device in real time without interference. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic flowchart of a method for measuring the pitch angle of a magnetic field using rotating Doppler microwave reflection, provided in an embodiment of the present invention.

[0013] Figure 2 This is a schematic diagram of the microwave circuit described in an embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram illustrating the process of measuring the magnetic field pitch angle in an example of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, and do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0016] like Figure 1 This is a schematic flowchart of a method for measuring the pitch angle of a magnetic field using rotating Doppler microwave reflection, provided in an embodiment of the present invention. The method includes:

[0017] Step 1: Simultaneously transmit X-mode and O-mode polarized microwave signals to the plasma through the Doppler backscattering meter diagnostic system (DBS), and receive the scattered signals returning along the transmitted optical path;

[0018] In this step, the Doppler Backscattering (DBS) diagnostic system controls the electric field component E of the emitted microwaves by setting the frequency of the microwaves emitted by the electronics system. i O-mode component E i sin(θ+β) penetrates the plasma; θ represents the magnetic field pitch angle to be measured, and β represents the electric field component of the emitted microwave and the poloidal magnetic field B. P The included angle;

[0019] The electric field component E of the emitted microwave i X-mode component E i cos(θ+β) is scattered at the cutoff layer, and the scattered signal that returns to the transmitting antenna along the transmitted light path and is received is called the backscattered signal. Among them, considering the propagation of microwaves in plasma, when the refractive index of microwaves becomes 0 or the wavenumber k approaches 0, microwaves are cut off in plasma and reflected at the cutoff point. For a tokamak device, such a cutoff point is a density profile with the same density and magnetic field, and is therefore called the cutoff layer.

[0020] The scattered signal received by the DBS optical front end along the emitted optical path is the X-mode signal E relative to the background magnetic field at the cutoff layer. i cos(θ+β), since the vibration direction of the electric field component of the X-mode signal is perpendicular to the direction of the background magnetic field at the cutoff layer, the vibration direction of the electric field component of the backscattered signal carries the information of the magnetic field pitch angle θ.

[0021] The Doppler backscattering diagnostic system (DBS) used in the specific implementation can be used to measure parameters such as local density fluctuations and radial distribution of velocity fluctuations.

[0022] Step 2: The received scattered signal is split into two paths by a beam splitter. One path goes into the original DBS, and the other path goes into a rotatable antenna to adjust the vibration direction of the received electric field component.

[0023] In this step, when the angle between the vibration direction of the electric field component of the rotatable antenna and the vibration direction of the electric field component of the backscattered signal is α, the scattered signal received by the rotatable antenna is determined by orthogonal decomposition as the cos(α) component of the electric field component of the returned backscattered signal, and the electromagnetic wave intensity calculation formula is used. Here, I is the average intensity of the electromagnetic wave; n is the refractive index of the medium, which can be considered a constant in this paper as the medium is plasma. is the dielectric constant in a vacuum; c is the speed of light in a vacuum. It is the peak value of the electric field intensity of electromagnetic waves, and it is a definite value when orthogonally decomposed;

[0024] Therefore, the electric field component intensity of the backscattered signal received by the rotatable antenna With (cos(α)) 2 Proportional, expressed as:

[0025] .

[0026] Step 3: Based on the steady-state discharge conditions of the EAST (Experimental Advanced Superconducting Tokamak) tokamak device, during the stable discharge period, a high-speed rotating platform is used to rotate the rotatable antenna 360° to complete the scanning of the vibration direction of the electric field component and the magnetic field component of the scattered signal, and to obtain the magnetic field pitch angle θ at the detection frequency cutoff layer.

[0027] In this step, the EAST steady-state discharge condition refers to the EAST device continuously and safely confining high-temperature, high-density plasma in a magnetic cage for hundreds or even thousands of seconds, and achieving effective heating and current drive. In this embodiment, the confinement time is greater than the time required for the rotatable antenna to rotate 360°.

[0028] During the stable discharge period, since the density distribution and magnetic field distribution can be approximated as constant, the position of the cutoff layer and the magnetic field pitch angle θ remain unchanged during the rotation of the rotatable antenna. Therefore, the magnetic field pitch angle θ at the cutoff layer position inside the device can be directly measured. The specific process is as follows:

[0029] The rotation start trigger of the rotatable antenna is connected to the data acquisition triggering system (meaning the EAST device sends a command to the data acquisition system when it starts discharging, and the data acquisition system only starts acquiring signals upon receiving the command), and the exact moment of start of rotation is recorded. and the point at which the rotation ends Combined with the rotational speed of the rotatable antenna The unit is degrees per second. The rotation angle corresponding to each time point T during the rotation process is calculated. And define the start time point of rotation. rotation angle ;

[0030] Before the EAST device discharges, a laser is used to initially calibrate the electric field direction of the rotatable antenna relative to the circumferential magnetic field B. T The directions are the same or opposite, and the rotation angle of the rotatable antenna is defined in this case. If the angle is 0°, then the angle between the electric field direction of the rotatable antenna and the electric field component of the returned backscattered signal is obtained. ;

[0031] Rotate the rotatable antenna 360° to obtain the angle between the electric field direction corresponding to the maximum value of the received signal intensity and the electric field component of the returned backscattered signal. Equal to 0° or 180°, and the angle between the electric field direction corresponding to the minimum value of the received signal strength of the rotatable antenna and the electric field component of the returned backscattered signal. It equals 90° or 270°; it is worth noting that, theoretically, the minimum signal strength received by a rotatable antenna is close to 0, but due to the presence of background noise, it is only a very small value and not 0.

[0032] For (cos(α)) 2 Perform a trigonometric transformation: (cos(α)) 2 =(1+cos(2α)) / 2, since the period of cos(2α) is 360°, then (cos(α)) / 2 2 The first period is from 0 to 360°, corresponding to an angle α of 0 to 180°; therefore, the rotation angle of the rotatable antenna is... From 0 to 180°, angle α also changes by 180°, (cos(α)) 2 The size changed over one cycle; because ,when At that time, the magnetic field screw pitch angle rotatable antenna receiving signal strength If there is a minimum value, the corresponding time point can be obtained. Calculate the minimum rotation angle of the rotatable antenna at this time. Then, the magnetic field pitch angle θ at the detection frequency cutoff layer is calculated and expressed as:

[0033] .

[0034] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0035] This invention also provides an electronic device, including a memory and a processor, wherein the memory stores a computer program and the processor is configured to run the computer program to perform the method.

[0036] This invention also provides a computer storage medium storing a plurality of instructions adapted for loading and executing the method by a processor.

[0037] The measurement method described in this embodiment of the invention will be illustrated below with specific examples. This example uses an integrated microwave system for receiving backscattered signals via E-band backscattering and selectable electric field component vibration direction as an example. Figure 2 The figure shows a schematic diagram of the microwave circuit described in an embodiment of the present invention. The part in rectangle (1) is the multi-channel microwave generation and transmission system, and the parts in rectangle (2) and rectangle (3) are the DBS and the selective backscattered electric field component vibration direction receiving system (rotatable antenna), respectively. The specific reference numerals are shown in Table 1 below:

[0038] Table 1 Names of each component

[0039]

[0040] In addition, a signal generator (No. 10) is used as a reference microwave signal due to its low cost, portability and good stability. The model used is LMS-183DX, an adjustable microwave source with a frequency range of 6-18GHz. A hollow rotating platform (No. 21) has a maximum rotation speed of 78° / s, a repeatability of 0.005°, can rotate 360°, and has a hollow diameter of 90mm. Therefore, this rotating platform is used as a fast rotating carrier to carry the receiving antenna to select the vibration direction of the backscattered signal electric field component. This is one of the keys to the measurement of the magnetic field pitch angle in this application.

[0041] The signal output is divided into three parts: the reference signal (LO) is mixed with the backscattered received signals in signal mixers (numbered 13 and 22) to obtain an intermediate frequency (IF) signal (which serves as the RF input of the I / Q mixer (numbered 15)); the reference signal is mixed with the transmitted signal in the reference mixer (numbered 12) to obtain an IF signal (which serves as the LO input of the I / Q mixer). In the microwave generation and transmission system, the microwave source (numbered 1) has an output frequency range of 1-2 GHz and a minimum adjustable frequency step of 1 MHz. In the experiment, the output of this signal source was set to 2.0 GHz. By using a bandpass filter (numbered 3) with a frequency range of 15-23 GHz, four specific frequencies of 16, 18, 20, and 22 GHz were selected from the output of the comb spectrum generator (numbered 2). Then, after passing through a frequency multiplier (number 5) and an EH tuner (number 6), these four fixed frequencies (16, 18, 20, 22 GHz) are further multiplied and optimized to reach a frequency range of 60-90 GHz (E-band, frequency interval Δf = 2.0 GHz). Therefore, 16 fixed-frequency microwaves are emitted in the plasma, all of which can be regarded as probe microwave beams.

[0042] In the receiving section (part 2) of the DBS, the transmitting antenna (number 9) also serves as the receiving antenna for the DBS. The received signal is then mixed with the reference signal in a backscattered signal mixer (number 13) to obtain the intermediate frequency (IF) signal. The down-converted IF signals from the reference mixer (number 12) and the signal mixer are both passed through a low-pass filter (0-2 GHz).

[0043] In the receiving section (3 parts) of the microwave system with selectable backscattered electric field component vibration direction, a separate antenna (number 20) is used to receive the backscattered signal. Its polarization direction can rotate with the rotating platform, thereby selecting the vibration direction of the electric field component of the backscattered signal. The received signal is then mixed with a reference signal in a scattered signal mixer (number 22) to obtain an intermediate frequency signal. In the specific implementation, Figure 2 The detection frequencies of the microwave system for the vibration direction of the selected backscattered electric field component in the DBS and the microwave system are respectively... and By changing To change the detection frequency.

[0044] The intermediate frequency signals from the reference path and the receiving path are demodulated into Acosφ and Asinφ (IQ signals, where A is the amplitude of the received backscattered signal and Φ is the phase of the backscattered signal) in the I / Q mixer (No. 15). The IQ signals are acquired by the high-speed data stream system (No. 17).

[0045] like Figure 3 The diagram shown is a schematic diagram of the process of measuring the magnetic field pitch angle in an example of the present invention. In the diagram, B... P This represents the poloidal magnetic field at the location of the microwave cutoff layer in a magnetic confinement fusion device; the arrow indicates its direction. T This represents the circumferential magnetic field at the location of the microwave cutoff layer in a magnetic confinement fusion device; the arrow indicates its direction. P and B T These are the components in two directions obtained by orthogonal decomposition of the magnetic field B0 at the cutoff layer; E i The arrow represents the electric field component of the emitted microwave, indicating the direction, and β represents the electric field component E of the emitted microwave. i With the polar magnetic field B P The angle between them. Figure 3 In (1), the dashed line indicates the direction of the polar magnetic field. DBS controls the transmitted microwave E by setting the frequency of the microwave emitted by the electronic system. i O-mode component E i sin(θ+β) breaks through the plasma, X-mode component E i cos(θ+β) is scattered at the cutoff layer; therefore, the scattered signal received by the optical front end of the DBS system is the X-mode signal E relative to the background magnetic field at the cutoff layer. i cos(θ+β).

[0046] Based on the DBS, the scattered signal is split into two paths by a beam splitter. One path enters the original DBS, and the other path enters a rotatable antenna to select the vibration direction of the received electric field component. When the vibration direction of the electric field component of the rotatable antenna is at an angle α with the vibration direction of the electric field component of the backscattered signal, according to the orthogonal decomposition and electromagnetic wave intensity calculation formula, the intensity of the scattered signal received by the rotatable antenna is related to (cos(α)). 2 Proportional, α is the relative circumferential magnetic field B of the rotatable antenna set in the experiment. T The angle.

[0047] The rotation start trigger of the rotatable antenna is connected to the data acquisition triggering system (meaning the EAST device sends a command to the data acquisition system when it starts discharging, and the data acquisition system only starts acquiring signals upon receiving the command), and the exact moment of start of rotation is recorded. and the point at which the rotation ends Combined with the rotational speed of the rotatable antenna The unit is degrees per second. The rotation angle corresponding to each time point T during the rotation process is calculated. And define the start time point of rotation. rotation angle ;

[0048] Depend on Figure 3 (2) It can be seen that before the EAST device discharges, the initial angle of the electric field direction of the rotatable antenna is calibrated using a laser to be relative to the circumferential magnetic field B. T The directions are the same or opposite, and the rotation angle of the rotatable antenna is defined in this case. If the angle is 0°, then the angle between the electric field direction of the rotatable antenna and the electric field component of the returned backscattered signal is obtained. ;

[0049] Rotate the rotatable antenna 360° to obtain the angle between the electric field direction corresponding to the maximum value of the received signal intensity and the electric field component of the returned backscattered signal. Equal to 0° or 180°, and the angle between the electric field direction corresponding to the minimum value of the received signal strength of the rotatable antenna and the electric field component of the returned backscattered signal. It equals 90° or 270°; it is worth noting that, theoretically, the minimum signal strength received by a rotatable antenna is close to 0, but due to the presence of background noise, it is only a very small value and not 0.

[0050] Based on (cos(α)) 2 The rotation angle of the rotatable antenna in the first cycle. From 0 to 180°, because ,when At that time, the magnetic field screw pitch angle rotatable antenna receiving signal strength If there is a minimum value, the corresponding time point can be obtained. Calculate the minimum rotation angle of the rotatable antenna at this time. Then, the magnetic field pitch angle θ at the detection frequency cutoff layer is calculated and expressed as:

[0051] .

[0052] In specific implementation, during the 360° rotation of the rotatable antenna, the intensity of the electric field component of the backscattered signal received by the rotatable antenna... With (cos(α)) 2 Proportional, therefore With (cos(θ+90°-γ)) 2 Proportional to the calculated magnetic field pitch angle θ, by substituting it into the curve, the theoretically received signal strength of the antenna as a function of time or angle during the 360° rotation of the rotatable antenna can be accurately plotted. This curve can then be compared with the processed experimental data curve of the received signal strength as a function of time or angle, which can serve as an auxiliary means to verify whether the method of this invention for measuring the magnetic field pitch angle θ is correct.

[0053] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for measuring the pitch angle of a magnetic field using rotating Doppler microwave reflection, characterized in that, The method includes: Step 1: Simultaneously transmit X-mode and O-mode polarized microwave signals to the plasma through the Doppler backscattering meter diagnostic system (DBS), and receive the scattered signals returning along the transmitted optical path; Step 2: The received scattered signal is split into two paths by a beam splitter. One path goes into the original DBS, and the other path goes into a rotatable antenna to adjust the vibration direction of the received electric field component. Step 3: Based on the steady-state discharge conditions of the EAST tokamak device, during the stable discharge period, a high-speed rotating platform is used to rotate the rotatable antenna 360° to complete the scanning of the vibration direction of the electric field component and the magnetic field component of the scattered signal, and to obtain the magnetic field pitch angle θ at the detection frequency cutoff layer. In step 3, during the stable discharge period, the position of the cutoff layer and the magnetic field pitch angle θ remain unchanged during the rotation of the rotatable antenna. Therefore, the magnetic field pitch angle θ at the cutoff layer position inside the device can be directly measured. The specific process is as follows: Connect the rotatable antenna to the data acquisition system to trigger its rotation, and accurately record the moment the rotation begins. and the point at which the rotation ends Combined with the rotational speed of the rotatable antenna The rotation angle corresponding to each time point T during the rotation process is calculated. And define the start time point of rotation. rotation angle ; Rotate the rotatable antenna 360° to obtain the angle between the electric field direction corresponding to the maximum value of the received signal intensity and the electric field component of the returned backscattered signal. Equal to 0° or 180°, and the angle between the electric field direction corresponding to the minimum value of the received signal strength of the rotatable antenna and the electric field component of the returned backscattered signal. It equals 90° or 270°; For (cos(α)) 2 Perform a trigonometric transformation: (cos(α)) 2 =(1+cos(2α)) / 2, since the period of cos(2α) is 360°, then (cos(α)) / 2 2 The first period is from 0 to 360°, corresponding to an angle α of 0 to 180°; therefore, the rotation angle of the rotatable antenna is... From 0 to 180°, angle α also changes by 180°, (cos(α)) 2 The size changed over one cycle; because ,when At that time, the magnetic field screw pitch angle rotatable antenna receives signal strength If there is a minimum value, the corresponding time point can be obtained. Calculate the minimum rotation angle of the rotatable antenna at this time. Then, the magnetic field pitch angle θ at the detection frequency cutoff layer is calculated and expressed as: 。 2. The method for measuring the pitch angle of a magnetic field using rotating Doppler microwave reflection according to claim 1, characterized in that, In step 1, the Doppler backscatter diagnostic system DBS controls the frequency of the emitted microwaves by setting the electronics system to emit microwaves with an electric field component E i of the O-mode component E i sin(θ+β) through the plasma; θ represents the magnetic field pitch angle to be measured, and β represents the angle between the electric field component of the emitted microwaves and the poloidal magnetic field B P . The electric field component E of the emitted microwave i X-mode component E i cos(θ+β) is scattered at the cutoff layer, and the scattered signal that returns along the transmitted light path to the transmitting antenna and is received is called the backscattered signal. The scattered signal received by the DBS optical front end along the emitted optical path is the X-mode component E relative to the background magnetic field at the cutoff layer. i cos(θ+β), since the vibration direction of the electric field component of the scattered signal of the X-mode component is perpendicular to the direction of the background magnetic field at the cutoff layer, the vibration direction of the electric field component of the backscattered signal carries the information of the magnetic field pitch angle θ.

3. The method for measuring the magnetic field pitch angle using rotating Doppler microwave reflection according to claim 1, characterized in that, In step 2, when the angle between the vibration direction of the electric field component of the rotatable antenna and the vibration direction of the electric field component of the backscattered signal is α, according to the orthogonal decomposition of the scattered signal received by the rotatable antenna as the cos(α) component of the electric field component of the returned backscattered signal, and the electromagnetic wave intensity calculation formula... Here, I is the average intensity of the electromagnetic wave; n is the refractive index of the medium. is the dielectric constant in a vacuum; c is the speed of light in a vacuum. It is the peak value of the electric field intensity of electromagnetic waves, and it is a definite value when orthogonally decomposed; Therefore, the electric field component intensity of the backscattered signal received by the rotatable antenna With (cos(α)) 2 Proportional, expressed as: 。 4. The method for measuring the magnetic field pitch angle using rotating Doppler microwave reflection according to claim 3, characterized in that, In step 3, before the EAST device discharges, a laser is used to initially calibrate the electric field direction of the rotatable antenna to be aligned with the circumferential magnetic field B. T The directions are the same or opposite, and the rotation angle of the rotatable antenna is defined in this case. If the angle is 0°, then the angle between the electric field direction of the rotatable antenna and the electric field component of the returned backscattered signal is obtained. .

5. An electronic device, comprising a memory and a processor, characterized in that, The memory stores a computer program, and the processor is configured to run the computer program to perform the method according to any one of claims 1 to 4.

6. A computer storage medium, characterized in that, The computer storage medium stores a plurality of instructions adapted for loading by a processor and executing the method of any one of claims 1 to 4.

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