Laser fiber polarizer system suitable for compact ring plasma

Abstract

The invention discloses a laser optical fiber polarizer system suitable for compact ring plasma, which comprises a laser, a first optical fiber coupler, a circularly polarized light generation module, a first collimator, a second collimator, a second optical fiber coupler, a second polarizer, a photoelectric converter and a data processing module, according to the laser fiber polarimeter system, non-contact elements for diagnosing and testing the compact ring plasma are reasonably arranged, so that high-precision testing of density and magnetic field information of the compact ring plasma is realized. According to the invention, the reference signal is compared with the measurement signal passing through the plasma, the phase difference between the signals can be extracted through phase demodulation, and then the density and magnetic field information can be obtained according to the Faraday effect; in addition, the use of open optical devices is reduced, the cost is greatly reduced, the platform building time is shortened, and meanwhile, the interference of the external environment in the experiment process is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of optical interference measurement, and in particular to a laser fiber polarimeter system suitable for compact ring plasma. Background Art

[0002] As a more advanced large-scale tokamak device in the future, the China Fusion Engineering Test Reactor has two main physical design goals, namely, achieving a steady-state fusion power of 1GW and tritium self-sustaining. Combined with the current research results, injecting fusion fuel directly into the core of the device can not only increase the fusion power of the core plasma, but also reduce the tritium multiplication rate, thereby achieving the goal of tritium self-sustaining. Therefore, core charging has become one of the core means of controlling fusion fuel plasma. In existing technologies, such as gas injection, supramolecular beam and projectile injection, it is difficult to achieve the injection of core plasma. With the progress of core charging experiments, compact ring injection is currently one of the most promising technologies for achieving core charging.

[0003] In order to evaluate the feeding efficiency of the compact ring injection device, it is very important to install a variety of diagnostic systems on it. The laser fiber polarimeter system described in the present invention is a diagnostic technology used to measure the density of the compact ring plasma. Plasma is called the "fourth state" of matter. It is often composed of a large number of charged particles and presents a quasi-neutral particle group as a whole. It can be understood as an ionized gas. The compact ring injection device uses the principle of an electromagnetic gun. First, the gas is broken down to form plasma through the instantaneous discharge of the capacitor, and then the plasma is accelerated and ejected through the Lorentz force. The plasma produced is called compact ring plasma or compact ring.

[0004] At present, the diagnostic methods for measuring plasma density are mainly divided into two categories: contact and non-contact. The contact diagnostic method, as the name implies, is to obtain plasma density information by directly contacting the plasma. Its disadvantages are obvious: it will destroy the structure of the plasma and introduce impurities. Non-contact diagnostic methods mainly include microwave measurement, laser measurement and spectral measurement. With the development of technology, microwave measurement is gradually replaced by laser measurement. Spectroscopic measurement is to infer plasma density information by measuring the intensity, displacement and other related physical quantities of plasma spectral lines. Of course, among the non-contact diagnostic methods, laser interferometry is one of the most concerned methods. Laser fiber polarimeter belongs to laser interferometry. Traditional laser fiber polarimeter basically adopts open optical path, which makes installation and debugging time-consuming and laborious, and the measurement accuracy and stability are low. In addition, the relevant interferometer system currently installed in the compact ring injection device can only measure density information, and there is a problem of being easily affected by the external environment. Summary of the invention

[0005] The object of the present invention is to provide a laser fiber polarimeter system suitable for compact ring plasma, so as to solve the problems in the above-mentioned background technology.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A laser fiber polarimeter system suitable for compact ring plasma, comprising a laser, a first fiber coupler, a circularly polarized light generating module, a first collimator, a second collimator, a second fiber coupler, a second polarizer, a photoelectric converter and a data processing module;

[0008] The laser is used to output a linearly polarized laser signal in a vertical direction;

[0009] The first optical fiber coupler is used to split the linearly polarized laser signal into a measurement signal and a reference signal, the measurement signal is sequentially output to the second optical fiber coupler through the circularly polarized light generating module, the first collimator, the plasma test area and the second collimator, and the reference signal is directly output to the second optical fiber coupler;

[0010] The second optical fiber coupler is used to output a beam interference signal, and the beam interference signal is output to the photoelectric converter through the second polarizer, and the photoelectric converter is used to convert the beam interference signal into a voltage signal;

[0011] The data processing module is used to collect and analyze the voltage signal to obtain density and magnetic field information of the compact ring plasma.

[0012] As a further solution of the present invention: there are two beams of measurement signals split by the first optical fiber coupler, and the two beams of measurement signals are converted into two circularly polarized light signals with opposite rotation directions when passing through the circularly polarized light generating module, and the two circularly polarized light signals with opposite rotation directions are sequentially output to the second optical fiber coupler through the first collimator, the plasma test area and the second collimator.

[0013] As a further solution of the present invention: the circularly polarized light generating module includes a first acousto-optic modulator, a second acousto-optic modulator, a half-wave plate, a first polarizer and a quarter-wave plate;

[0014] A beam of the measurement signal is output to the first collimator through the first acousto-optic modulator, the half-wave plate, the first polarizer and the quarter-wave plate in sequence, and the half-wave plate is used to convert the beam of the measurement signal into a linearly polarized laser signal in a horizontal direction;

[0015] Another beam of the measurement signal is output to the first collimator through the second acousto-optic modulator, the first polarizer and the quarter-wave plate in sequence;

[0016] Wherein, the quarter wave plate is used to convert the linearly polarized laser signal in the horizontal direction and / or the vertical direction into a circularly polarized light signal.

[0017] As a further solution of the present invention: the first optical fiber coupler is a 1×3 optical fiber coupler.

[0018] As a further solution of the present invention: the first acousto-optic modulator is an acousto-optic modulator with a frequency shift of 35 MHz; the second acousto-optic modulator is an acousto-optic modulator with a frequency shift of 50 MHz.

[0019] As a further solution of the present invention: the laser is a polarization-maintaining narrow-linewidth laser, the wavelength of the output laser signal is 1550nm, and the linewidth is less than 3kHz.

[0020] As a further solution of the present invention: the second optical fiber coupler is a 2×1 optical fiber coupler.

[0021] As a further solution of the present invention: when the light beam interference signal is output to the photoelectric converter through the second polarizer, the second polarizer is used to output the light beam interference signal to the photoelectric converter as a linearly polarized laser signal in a vertical direction.

[0022] As a further solution of the present invention: a compact ring injection device is provided between the first collimator and the second collimator, and the compact ring injection device is used to generate compact ring plasma in the plasma test area.

[0023] Beneficial effects of the present invention:

[0024] (1) The laser fiber polarimeter system can achieve high-precision testing of the density and magnetic field information of compact ring plasma by reasonably arranging non-contact elements for diagnosing and testing compact ring plasma. It is convenient to compare the reference signal with the measurement signal passing through the plasma, and extract the phase difference between the signals through phase demodulation, and then obtain the density and magnetic field information based on the Faraday effect.

[0025] (2) The laser fiber polarimeter system of the present application can reduce the use of open optical devices by using optical fiber devices such as fiber couplers, greatly reducing costs and platform construction time, while also reducing interference from the external environment during the experimental process;

[0026] (3) The advantage of the laser fiber polarimeter system of the present application is that polarization and interference signals can be obtained without the use of grating modulation, thus avoiding errors and signal instability introduced by modulation and optimizing measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1 It is a schematic diagram of the structure of the present invention;

[0029] Figure 2 It is a schematic structural diagram of a circularly polarized light generating module of the present invention;

[0030] Figure 3 It is a schematic diagram of collimators being arranged at the inlet and outlet ends of the compact ring injection device of the present invention.

[0031] In the figure: 1. laser; 2. first fiber coupler; 3. circularly polarized light generating module; 4. first collimator; 5. plasma test area; 6. second collimator; 7. second fiber coupler; 8. second polarizer; 9. photoelectric converter; 10. data processing module; 11. first acousto-optic modulator; 12. second acousto-optic modulator; 13. half-wave plate; 14. first polarizer; 15. quarter-wave plate; 16. compact ring injection device. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention; in the description of the present invention, the meaning of "multiple" and "several" is at least two, for example two, three, etc., unless otherwise clearly and specifically defined.

[0034] See also Figure 1 As shown, the present invention is a laser fiber polarimeter system suitable for compact ring plasma, comprising a laser 1, a first fiber coupler 2, a circularly polarized light generating module 3, a first collimator 4, a second collimator 6, a second fiber coupler 7, a second polarizer 8, a photoelectric converter 9 and a data processing module 10. The laser fiber polarimeter system reasonably arranges the non-contact elements for diagnosing and testing compact ring plasma to achieve high-precision testing of the density and magnetic field information of the compact ring plasma.

[0035] The laser 1 is used to output a linearly polarized laser signal in a vertical direction; the first optical fiber coupler 2 is used to split the linearly polarized laser signal into a measurement signal and a reference signal, the measurement signal is sequentially output to the second optical fiber coupler 7 through the circularly polarized light generating module 3, the first collimator 4, the plasma test area 5 and the second collimator 6, and the reference signal is directly output to the second optical fiber coupler 7; the second optical fiber coupler 7 is used to output a beam interference signal, the beam interference signal is output to the photoelectric converter 9 through the second polarizer 8, and the photoelectric converter 9 is used to convert the beam interference signal into a voltage signal; the data processing module 10 is used to collect and analyze the voltage signal to obtain the density and magnetic field information of the compact ring plasma.

[0036] During use of the laser fiber polarimeter system of the present application, the linearly polarized laser signal output by the laser 1 can be split into a measurement signal and a reference signal. The measurement signal of the linearly polarized laser can obtain a test signal after passing through the plasma test area 5, and interfere with the reference signal in the second fiber coupler 7 to generate a beam interference signal. The beam interference signal is converted into a voltage signal and transmitted to the data processing module 10, so as to facilitate data collection and data analysis through the data processing module 10 to obtain the density and magnetic field information of the compact ring plasma; in the present application, the reference signal and the measurement signal passing through the plasma are compared, and the phase difference between the signals can be extracted through phase demodulation, and then the density and magnetic field information can be obtained according to the Faraday effect.

[0037] The laser fiber polarimeter system of the present application can reduce the use of open optical devices by adopting optical fiber devices such as fiber couplers, greatly reducing costs and platform construction time, while also reducing interference from the external environment during the experiment.

[0038] In this specific embodiment, there are two measurement signals split by the first optical fiber coupler 2. The two measurement signals are converted into two circularly polarized light signals with opposite rotation directions when passing through the circularly polarized light generating module 3. The two circularly polarized light signals with opposite rotation directions are successively output to the second optical fiber coupler 7 through the first collimator 4, the plasma test area 5 and the second collimator 6; so that the two measurement signals can obtain two circularly polarized light signals with opposite rotation directions after passing through the plasma test area 5. In the following text, the two circularly polarized light signals with opposite rotation directions are respectively a right-handed polarized light signal and a left-handed polarized light signal.

[0039] In this specific implementation mode, combined with Figure 2As shown, the circularly polarized light generating module 3 includes a first acousto-optic modulator 11, a second acousto-optic modulator 12, a half wave plate 13, a first polarizer 14 and a quarter wave plate 15; a beam of measurement signals is sequentially output to the first collimator 4 through the first acousto-optic modulator 11, the half wave plate 13, the first polarizer 14 and the quarter wave plate 15, and the half wave plate 13 is used to convert the beam of measurement signals into a linearly polarized laser signal in the horizontal direction; another beam of measurement signals is sequentially output to the first collimator 4 through the second acousto-optic modulator 12, the first polarizer 14 and the quarter wave plate 15; wherein the quarter wave plate 15 is used to convert the linearly polarized laser signal in the horizontal direction and / or the vertical direction into a circularly polarized light signal.

[0040] The working principle of the circularly polarized light generating module 3 in the present application is as follows: a beam of measurement signal is converted into a horizontally polarized laser signal through the vertically polarized laser signal of the half wave plate 13, and the horizontally polarized laser signal and the vertical laser signal from the second acousto-optic modulator 12 are input into the first polarizer 14 together to synthesize a beam of light signal, and the first polarizer 14 then inputs the combined light signal into the quarter wave plate 15. At this time, the circularly polarized light output from the quarter wave plate 15 is the opposite rotation direction, and the circularly polarized light with the opposite rotation direction then passes through the first collimator 4, the plasma test area 5 and the second collimator 6 in sequence.

[0041] The working process of obtaining the test signal by passing the circularly polarized light with opposite rotation directions through the plasma test area 5 will be described in detail below.

[0042] The circularly polarized light signal enters the first collimator 4 to expand the beam and then propagates the light signal. The light signal passes through the plasma in the plasma test area 5 and enters the second collimator 6 to focus and then propagate out. The test signal and the reference signal from the second collimator 6 interfere at the second fiber coupler 7. The light beam interference signal enters the second polarizer 8 to select the linear polarized light in the vertical direction and output it to the photoelectric converter 9.

[0043] The photoelectric converter 9 transmits the electrical signal to the data processing module 10 for signal acquisition and data analysis.

[0044] When the data processing module 10 performs data acquisition and data analysis, the data processing module 10 demodulates the phase information φ; Among them, φ R is the phase shift of the right-hand polarized light signal, φ L is the phase shift of the left-hand polarized light signal.

[0045] The density information n of the compact ring plasma can be obtained by the following formula; Among them, n cis the cutoff density, λ is the wavelength of the optical signal generated by laser 1, l is the transmission path of the optical signal when it passes through the plasma, and dl is the differential representing l.

[0046] According to the Faraday effect, the Faraday rotation angle α can be obtained by the following formula: Then, the magnetic field information of the compact ring plasma can be obtained by the following formula, where the magnetic field information is the parallel component B of the poloidal field. ∥ , Where λ is the wavelength of the optical signal generated by laser 1, N R and N L are the refractive indices of right-handed and left-handed polarized light propagating in plasma, n e is the electron density, and l is the transmission path of the light signal when it passes through the plasma.

[0047] In summary, the laser fiber polarimeter system of the present application utilizes the three-wave method to demodulate the phase shift information. By comparing the phases of the optical signal of the reference path and the two optical signals of the measurement path, the phase shift information of the right and left polarized light can be obtained. At the same time, the laser fiber polarimeter system of the present application has the advantage that polarization and interference signals can be obtained without the use of grating modulation, thus avoiding errors introduced by modulation and signal instability, and optimizing measurement accuracy.

[0048] In addition, the laser fiber polarimeter system of the present application uses optical fiber devices, which reduces the use of open optical devices, greatly reduces costs and platform construction time, and reduces interference from the external environment during the experiment. It can also measure sub-information such as density and magnetic field.

[0049] In this specific implementation, the first optical fiber coupler 2 is a 1×3 optical fiber coupler.

[0050] In this specific implementation, the first AOM 11 is an AOM with a 35 MHz frequency shift; the second AOM 12 is an AOM with a 50 MHz frequency shift. The first AOM 11 and the second AOM 12 are used to enhance the corresponding measurement signal frequencies, respectively, which can enhance the signal resolution capability, thereby helping to improve the test accuracy.

[0051] In this specific implementation, the laser 1 is a polarization-maintaining narrow-linewidth laser 1, the wavelength of the output laser signal is 1550 nm, and the linewidth is less than 3 kHz.

[0052] In this specific implementation, the second optical fiber coupler 7 is a 2×1 optical fiber coupler.

[0053] In this specific implementation, when the light beam interference signal is output to the photoelectric converter 9 through the second polarizer 8, the second polarizer 8 is used to output the light beam interference signal to the photoelectric converter 9 as a linearly polarized laser signal in a vertical direction.

[0054] In this specific implementation mode, combined with Figure 3 As shown, a compact ring injection device 16 is provided between the first collimator 4 and the second collimator 6, and the compact ring injection device 16 is used to generate compact ring plasma in the plasma test area 5; when in use, the first collimator 4 and the second collimator 6 should be manually adjusted before the experiment to maximize the laser signal transmission efficiency; the plasma in the compact ring injection device 16 can be tested and diagnosed.

[0055] It should be understood that the working range of all the above-mentioned non-contact test elements should include the wavelength of the laser signal or the peak value of the electrical signal passing through it to ensure the integrity and accuracy of the plasma test.

[0056] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A laser fiber polarimeter system suitable for compact ring plasma, characterized in that: It comprises a laser (1), a first optical fiber coupler (2), a circularly polarized light generating module (3), a first collimator (4), a second collimator (6), a second optical fiber coupler (7), a second polarizer (8), a photoelectric converter (9) and a data processing module (10); The laser (1) is used to output a linearly polarized laser signal in a vertical direction; The first optical fiber coupler (2) is used to split the linearly polarized laser signal into a measurement signal and a reference signal, the measurement signal is sequentially output to the second optical fiber coupler (7) through the circularly polarized light generating module (3), the first collimator (4), the plasma test area (5) and the second collimator (6), and the reference signal is directly output to the second optical fiber coupler (7); The second optical fiber coupler (7) is used to output a light beam interference signal, and the light beam interference signal is output to the photoelectric converter (9) through the second polarizer (8), and the photoelectric converter (9) is used to convert the light beam interference signal into a voltage signal; The data processing module (10) is used to collect and analyze the voltage signal to obtain density and magnetic field information of the compact ring plasma.

2. A laser fiber polarimeter system suitable for compact ring plasma according to claim 1, characterized in that: The measurement signal split by the first optical fiber coupler (2) has two beams. The two measurement signals are converted into two circularly polarized light signals with opposite rotation directions when passing through the circularly polarized light generating module (3). The two circularly polarized light signals with opposite rotation directions are sequentially output to the second optical fiber coupler (7) through the first collimator (4), the plasma test area (5) and the second collimator (6).

3. A laser fiber polarimeter system suitable for compact ring plasma according to claim 2, characterized in that: The circularly polarized light generating module (3) comprises a first acousto-optic modulator (11), a second acousto-optic modulator (12), a half-wave plate (13), a first polarizer (14) and a quarter-wave plate (15); A beam of the measurement signal is output to the first collimator (4) through the first acousto-optic modulator (11), the half-wave plate (13), the first polarizer (14) and the quarter-wave plate (15) in sequence, and the half-wave plate (13) is used to convert the beam of the measurement signal into a linearly polarized laser signal in a horizontal direction; Another beam of the measurement signal is output to the first collimator (4) through the second acousto-optic modulator (12), the first polarizer (14) and the quarter-wave plate (15) in sequence; Wherein, the quarter wave plate (15) is used to convert the linearly polarized laser signal in the horizontal direction and / or the vertical direction into a circularly polarized light signal.

4. A laser fiber polarimeter system suitable for compact ring plasma according to claim 2, characterized in that: The first optical fiber coupler (2) is a 1×3 optical fiber coupler.

5. The laser fiber polarimeter system suitable for compact ring plasma according to claim 3, characterized in that: The first acousto-optic modulator (11) is an acousto-optic modulator with a 35 MHz frequency shift; the second acousto-optic modulator (12) is an acousto-optic modulator with a 50 MHz frequency shift.

6. A laser fiber polarimeter system suitable for compact ring plasma according to claim 1, characterized in that: The laser (1) is a polarization-maintaining narrow-linewidth laser (1), the wavelength of the output laser signal is 1550 nm, and the linewidth is less than 3 kHz.

7. The laser fiber polarimeter system suitable for compact ring plasma according to claim 1, characterized in that: The second optical fiber coupler (7) is a 2×1 optical fiber coupler.

8. The laser fiber polarimeter system suitable for compact ring plasma according to claim 1, characterized in that: When the light beam interference signal is output to the photoelectric converter (9) through the second polarizer (8), the second polarizer (8) is used to output the light beam interference signal to the photoelectric converter (9) as a linearly polarized laser signal in a vertical direction.

9. The laser fiber polarimeter system suitable for compact ring plasma according to claim 1, characterized in that: A compact ring injection device (16) is provided between the first collimator (4) and the second collimator (6), and the compact ring injection device (16) is used to generate compact ring plasma in the plasma test area (5).

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