A plasma electron density measuring device

Abstract

The present invention discloses a plasma electron density measuring device, including a first terahertz solid source, a second terahertz solid source, an interferometer optical path and other devices; the interferometer optical path is used to output the light beam generated by the first solid source to the first detector; it is also used to output the light beam generated by the first solid source to the second detector; the interferometer optical path is used to output the light beam generated by the second solid source to the first detector; it is also used to output the light beam generated by the second solid source to the corner reflector passing through the plasma, so that the second detector receives the light beam returned by the corner reflector; the first detector and the second detector are used to obtain a combined beam signal, so that the device can calculate the plasma electron density according to the combined beam signal. The plasma electron density measuring device provided by the embodiment of the present invention has a compact layout, uses fewer optical devices, does not need to use a large bracket, is easy to design and install on a large plasma experimental device, has stable operation, and has low operation and maintenance costs.

Description

Technical Field

[0001] The invention relates to the field of optical technology, in particular to a plasma electron density measuring device. Background Art

[0002] In magnetic confinement fusion experimental devices and space plasma experimental simulation and research devices, plasma electron density is a crucial physical parameter. Almost all experimental devices require the ability to accurately and quickly measure plasma electron density in plasma physics experimental research.

[0003] In the prior art, far-infrared light sources are suitable for tokamak fusion experimental devices and are the most widely used light sources in interferometer systems at home and abroad. However, the light sources in this band have always used gas lasers with large volume and low output stability. For example, the HCN interferometer system developed on the EAST tokamak experimental device described in the article "Xu Qiang et al. 2008 Plasma Sci. Technol. 10 519" uses an HCN laser with a resonant cavity length of 3 meters. The laser is an electrically excited gas laser that uses a rotating grating to modulate the difference frequency signal. The entire laser system is large in size and requires a large experimental space. The power output of the laser is unstable and needs to be continuously adjusted during operation. In addition, the difference frequency modulated by the rotating grating is low, which makes the time resolution of the entire interferometer low. For example, the article "HQ Liu et al. 2013 JINST 8C11002”, an 11-channel polarization interferometer system was developed on the EAST Tokamak experimental device. The system uses three imported carbon dioxide-pumped formic acid lasers as light sources. The power output of the light source is relatively stable. Using the dual-laser principle, the difference frequency can reach the megahertz level, and the time resolution is also high. However, the entire laser system requires the construction of a large laser clean room with constant temperature and humidity vibration reduction effect. In addition, the system uses the dual-laser principle for difference frequency output, and the difference frequency output also needs to be adjusted by the staff at any time during the experiment, which increases the operating cost. The Space Plasma Environment Research Facility (SPREF) recently developed in China is expected to produce a plasma density that is also within the detection range of the interferometer in the far-infrared band. As shown in the article “QMXiao et al. 2020JINST 15P11026”, a set of HCN interferometer systems designed on the device is given. HCN lasers are also used as light sources, and a laser clean room is specially built for the system.

[0004] It can be seen that how to design a plasma electron density measurement device with a compact structure, small size and stable operation has become a technical problem that needs to be urgently solved by technical personnel in this field today. Summary of the invention

[0005] The present invention provides a plasma electron density measuring device to solve the above-mentioned defects. By designing the specific structure of the plasma electron density measuring device, a compact system layout is achieved, and reliable measurement data is provided for density measurement and experimental simulation research of space plasma.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a plasma electron density measuring device, including a first terahertz solid source, a second terahertz solid source, an interferometer optical path, plasma, a corner reflector, a first detector and a second detector;

[0007] The optical signal sending end of the first terahertz solid source is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the first terahertz solid source to the first detector; the interferometer optical path is also used to output the light beam generated by the first terahertz solid source to the second detector;

[0008] The optical signal sending end of the second terahertz solid source is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the second terahertz solid source to the first detector; the interferometer optical path is also used to output the light beam generated by the second terahertz solid source to the corner reflector passing through the plasma, so that the second detector receives the light beam returned by the corner reflector;

[0009] The first detector and the second detector are used to combine the light beams received by each detector to obtain a combined beam signal, so that the plasma electron density measuring device can calculate the plasma electron density according to the combined beam signal.

[0010] As one of the preferred solutions, the interferometer optical path includes a first focusing lens, a second focusing lens, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first plane reflector, a second plane reflector, a telescope optical path, and a 45-degree angle reflector;

[0011] The optical signal transmitting end of the first terahertz solid source is connected to the receiving end of the first detector through the first focusing lens, the first beam splitter and the second beam splitter in sequence; the optical signal transmitting end of the first terahertz solid source is connected to the receiving end of the second detector through the first focusing lens, the first beam splitter, the second plane reflector and the fifth beam splitter in sequence;

[0012] The optical signal transmitting end of the second terahertz solid source is connected to the receiving end of the corner reflector through the second focusing lens, the third beam splitter, the first plane reflector, the telescope optical path, the 45-degree angle reflector, the fourth beam splitter and the plasma in sequence, and the optical signal returning end of the corner reflector is connected to the receiving end of the second detector through the plasma, the fourth beam splitter and the fifth beam splitter in sequence; the optical signal transmitting end of the second terahertz solid source is connected to the receiving end of the first detector through the second focusing lens, the third beam splitter and the second beam splitter in sequence.

[0013] As one preferred solution, the telescope optical path includes a convex reflector and a concave reflector;

[0014] The first plane reflector sends the received light beam to the 45-degree angle reflector through the convex reflector and the concave reflector in sequence.

[0015] As one preferred solution, the first terahertz solid source is a variable frequency 340 GHz solid source, and the second terahertz solid source is a fixed frequency 340 GHz solid source.

[0016] As one of the preferred solutions, both the first detector and the second detector are AlGaN / GaN-HEMT field effect tube detectors.

[0017] As one of the preferred solutions, the plasma electron density measuring device also includes a flange bracket, a sleeve is provided on the flange bracket, the corner reflector is provided in the sleeve, the sleeve has an opening aligned with the corner reflector, and the opening is horizontally / vertically adjustable on the flange bracket.

[0018] As one of the preferred solutions, the corner reflector is made of gold-plated aluminum.

[0019] As one preferred solution, the plasma electron density measuring device further includes an optical platform;

[0020] The first terahertz solid source, the second terahertz solid source, the interferometer optical path, the first detector and the second detector are all arranged on the optical platform.

[0021] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0022] (1) Use a terahertz solid source with small size, compact structure, low environmental sensitivity and stable output signal.

[0023] (2) The interferometer optical path processes the laser beams emitted by the first terahertz solid source and the second terahertz solid source. The optical path is designed to pass through the plasma in the device as the detection path optical path, and the other optical path that does not pass through the plasma is the reference path optical path. After the plasma is generated, the detection path can detect the phase shift caused by the laser in the plasma. After heterodyning the detection path signal and the reference path signal, the plasma electron density can be calculated.

[0024] (3) The plasma electron density measuring device of the present invention has a compact layout, occupies a small space, uses relatively few optical devices, does not require the use of a large bracket, is easy to design and install on a large plasma experimental device, operates stably, and has low operating and maintenance costs. The system can realize two types of position measurements, vertical measurement and horizontal measurement, and can also be expanded into multiple channels to realize multi-channel line-integrated electron density measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of a plasma electron density measuring device in one embodiment of the present invention;

[0026] Figure 2 It is a schematic diagram of the principle of one embodiment of the present invention;

[0027] Figure 3 It is a schematic diagram of the installation structure of a corner reflector on a flange bracket in one embodiment of the present invention;

[0028] Figure 4 is a schematic diagram of a device in one embodiment of the present invention performing level measurement;

[0029] Reference numerals:

[0030] Among them, 1. a first terahertz solid source; 2. a second terahertz solid source; 3. plasma; 4. an angle reflector; 5. a first detector; 6. a second detector; 7. a first focusing lens; 8. a second focusing lens 8; 9. a first beam splitter; 10. a second beam splitter; 11. a third beam splitter; 12. a fourth beam splitter; 13. a fifth beam splitter; 14. a first plane reflector; 15. a second plane reflector; 16. a 45-degree angle reflector; 17. a convex reflector; 18. a concave reflector; 19. an optical platform; 411. a flange bracket; 412. a sleeve; M. a focusing lens assembly; N. other table optical paths. DETAILED DESCRIPTION

[0031] 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. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. 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.

[0032] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0033] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply 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. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0035] An embodiment of the present invention provides a plasma electron density measuring device. For details, see Figure 1 , Figure 1The figure shows a schematic structural diagram of a plasma electron density measuring device in one embodiment of the present invention, which includes a first terahertz solid source 1, a second terahertz solid source 2, an interferometer optical path, a plasma 3, a corner reflector 4, a first detector 5 and a second detector 6.

[0036] It should be noted that after studying terahertz technology, the inventors applied terahertz solid sources with small size, compact structure, low environmental sensitivity and stable output signal to the interferometer system. For example, the 340GHz terahertz solid source in this embodiment has a small size, a maximum output power of 10mW, and a stable difference frequency output. The interferometer system with two 340GHz solid sources as light sources, after using corner reflectors for double optical path design, eliminates the need for large optical brackets, can be compactly designed, and greatly reduces the space occupied by the entire interferometer system. The system is 1×10 17 m -3 ~1×10 18 m -3 It has excellent measurement accuracy within the plasma density range and can provide reliable measurement data for density measurements at the boundary of current tokamak experimental devices and for space plasma experimental simulation and research devices.

[0037] Preferably, in this embodiment, the first terahertz solid source 1 is a variable frequency 340 GHz solid source, and the second terahertz solid source 2 is a fixed frequency 340 GHz solid source. By using a dual laser method, the difference frequency between the two solid sources can be arbitrarily adjusted within the megahertz range to achieve high time resolution measurement.

[0038] The interferometer optical path in the embodiment of the present invention can be designed as a multi-channel measurement according to the optical path layout. Specifically, the optical signal sending end of the first terahertz solid source 1 is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the first terahertz solid source 1 to the first detector 5; the interferometer optical path is also used to output the light beam generated by the first terahertz solid source 1 to the second detector 6;

[0039] The optical signal sending end of the second terahertz solid source 2 is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the second terahertz solid source 2 to the first detector 5; the interferometer optical path is also used to output the light beam generated by the second terahertz solid source 2 to the corner reflector 4 passing through the plasma 3, so that the second detector 6 receives the light beam returned by the corner reflector 4.

[0040] In the above embodiment, the interferometer optical path is a heterodyne interferometer, and the adjustable frequency 340GHz solid source needs to be adjusted so that the laser has a frequency difference of the order of megahertz relative to the fixed frequency 340GHz solid source, so that the photosynthesized beams generated by the two lasers enter the detector, and a beat frequency signal of the order of megahertz can be obtained. In the optical path design, one optical path passing through the plasma in the device is designed as the detection path optical path, and the other optical path not passing through the plasma is designed as the reference path. After the plasma is generated, the detection path can detect the phase shift generated by the laser in the plasma, and after heterodyning the detection path signal and the reference path signal, the plasma electron density can be calculated.

[0041] Furthermore, in this embodiment, the interferometer optical path includes a first focusing lens 7, a second focusing lens 8 ( Figure 1 7 and 8 are uniformly shown as a focusing lens assembly M), a first beam splitter 9, a second beam splitter 10, a third beam splitter 11, a fourth beam splitter 12, a fifth beam splitter 13, a first plane reflector 14, a second plane reflector 15, a telescope optical path, and a 45-degree angle reflector 16;

[0042] The optical signal transmitting end of the first terahertz solid source 1 is connected to the receiving end of the first detector 5 through the first focusing lens 7, the first beam splitter 9 and the second beam splitter 10 in sequence; the optical signal transmitting end of the first terahertz solid source 1 is connected to the receiving end of the second detector 6 through the first focusing lens 7, the first beam splitter 9, the second plane reflector 15 and the fifth beam splitter 13 in sequence;

[0043] The optical signal sending end of the second terahertz solid source 2 is connected to the receiving end of the corner reflector 4 through the second focusing lens 8, the third beam splitter 11, the first plane reflector 14, the telescope optical path, the 45-degree angle reflector 16, the fourth beam splitter 12 and the plasma 3 in sequence, and the optical signal return end of the corner reflector 4 is connected to the receiving end of the second detector 6 through the plasma 3, the fourth beam splitter 12 and the fifth beam splitter 13 in sequence; the optical signal sending end of the second terahertz solid source 2 is connected to the receiving end of the first detector 5 through the second focusing lens 8, the third beam splitter 11 and the second beam splitter 10 in sequence.

[0044] For details, see Figure 2 , Figure 2 This is a schematic diagram of the principle of one embodiment of the present invention. Figure 2The optical path signal flow process in this embodiment is described in detail: the laser output by the fixed-frequency solid source 2 and the frequency-modulated (variable frequency) solid source 1 has a small beam waist and a large divergence, so it is necessary to change the beam waist to a suitable size after passing through the focusing lens assembly M in the table optical path. The laser emitted by the first terahertz solid source 1 passes through the first beam splitter 9 and the second beam splitter 10 and enters the first detector 5 (referred to as the first optical signal); the laser emitted by the second terahertz solid source 2 passes through the third beam splitter 11 and the second beam splitter 10 and enters the first detector 5, and is combined with the laser of the first optical signal to generate a reference track beat frequency signal.

[0045] The laser emitted by the second terahertz solid source 2 is split by the third beam splitter 11, and the other beam enters the telescope optical path through the first plane reflector 14. The wavelength of the 340GHz solid source is 882 microns, and the divergence is fast. The telescope optical path can keep the laser beam at a small diameter during the long propagation into the device, avoiding excessive power loss. The laser passing through the telescope optical path is vertically incident by the 45-degree angle reflector 16, passes through the plasma 3 in the device after passing through the fourth beam splitter 12, and then returns to the original path by the angle reflector 4 directly fixed on the top flange of the device, and enters the second detector 6 (referred to as the second optical signal) after passing through the fourth beam splitter 12 and the fifth beam splitter 13 in turn; the laser emitted by the first terahertz solid source 1, another beam split by the first beam splitter 9 passes through the second plane reflector 15 and the fifth beam splitter 13, enters the second detector 6, and is combined with the detection light of the above-mentioned second optical signal to generate a detection channel beat frequency signal.

[0046] The first detector 5 will receive two optical signals, combine them, and generate a reference channel beat signal; the second detector 6 will also receive two optical signals, combine them, and generate a detection channel beat signal. Since the detection channel can detect the phase shift generated by the laser in the plasma, the plasma electron density can be calculated by heterodyning the detection channel signal and the reference channel signal. It can be seen that if the light source power allows, as long as optical devices are added to split the main optical path detection beam, and optical design and reasonable layout are performed, the 340GHz solid source interferometer can be upgraded from one channel to multiple channels.

[0047] The telescope optical path can keep the laser beam at a small diameter during the long propagation into the device, thereby avoiding excessive power loss. Preferably, in this embodiment, the telescope optical path includes a convex reflector 17 and a concave reflector 18;

[0048] The first plane reflector 14 sends the received light beam to the 45-degree angle reflector 16 through the convex reflector 17 and the concave reflector 18 in sequence.

[0049] The first terahertz solid source 1 in this embodiment is a variable frequency 340 GHz solid source, so that the laser has a frequency difference of the order of megahertz relative to the second terahertz solid source 2 of fixed frequency, so that the photosynthesized beams generated by the two lasers enter the detector and a beat frequency signal of the order of megahertz can be obtained.

[0050] Furthermore, in the above embodiment, both the first detector 5 and the second detector 6 are AlGaN / GaN-HEMT field effect tube detectors. The AlGaN / GaN-HEMT field effect tube detectors are small in size and can be used at room temperature.

[0051] For details, see Figure 3 , Figure 3 The figure shows a schematic diagram of the installation structure of the corner reflector on the flange bracket in one embodiment of the present invention. The plasma electron density measuring device in this embodiment also includes a flange bracket 411. The flange bracket 411 is provided with a sleeve 412. The corner reflector 4 is provided in the sleeve 412. The sleeve 412 is provided with an opening aligned with the corner reflector 4. The opening is horizontally / vertically adjustable on the flange bracket 411. The corner reflector is fixed directly to the window to return the detection light path to its original path, thereby reducing the number of optical devices used. No large bracket support is required. According to the measurement requirements, two measurement schemes, vertical measurement and horizontal measurement, can be realized. For details, please refer to Figure 4 , Figure 4 A schematic diagram of a device for horizontal measurement in one embodiment of the present invention is shown. If the corner reflector 4 is fixed to the horizontal window, necessary optical reflectors are added to the other side, and the solid source interferometer optical platform and other table optical paths N are placed on the side of the device, horizontal measurement can be achieved.

[0052] Furthermore, in the above embodiment, the corner reflector 4 is made of gold-plated aluminum.

[0053] Furthermore, in the above embodiment, the plasma electron density measuring device also includes an optical platform 19; the first terahertz solid source 1, the second terahertz solid source 2, the interferometer optical path, the first detector 5 and the second detector 6 are all compactly fixed on the optical platform 19.

[0054] The plasma electron density measuring device provided in the embodiment of the present invention has the beneficial effects of at least one of the following:

[0055] (1) Use a terahertz solid source with small size, compact structure, low environmental sensitivity and stable output signal.

[0056] (2) The interferometer optical path processes the laser beams emitted by the first terahertz solid source and the second terahertz solid source. The optical path is designed to pass through the plasma in the device as the detection path optical path, and the other optical path that does not pass through the plasma is the reference path optical path. After the plasma is generated, the detection path can detect the phase shift caused by the laser in the plasma. After heterodyning the detection path signal and the reference path signal, the plasma electron density can be calculated.

[0057] (3) The plasma electron density measuring device of the present invention has a compact layout, occupies a small space, uses relatively few optical devices, does not require the use of a large bracket, is easy to design and install on a large plasma experimental device, operates stably, and has low operating and maintenance costs. The system can realize two types of position measurements, vertical measurement and horizontal measurement, and can also be expanded into multiple channels to realize multi-channel line-integrated electron density measurement.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A plasma electron density measuring device, characterized in that: It includes a first terahertz solid source, a second terahertz solid source, an interferometer optical path, a plasma, a corner reflector, a first detector and a second detector; The optical signal sending end of the first terahertz solid source is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the first terahertz solid source to the first detector; the interferometer optical path is also used to output the light beam generated by the first terahertz solid source to the second detector; The optical signal sending end of the second terahertz solid source is connected to the interferometer optical path, and the interferometer optical path is used to output the light beam generated by the second terahertz solid source to the first detector; the interferometer optical path is also used to output the light beam generated by the second terahertz solid source to the corner reflector passing through the plasma, so that the second detector receives the light beam returned by the corner reflector; The first detector and the second detector are used to combine the light beams received by each detector to obtain a combined beam signal, so that the plasma electron density measuring device can calculate the plasma electron density according to the combined beam signal.

2. The plasma electron density measuring device according to claim 1, characterized in that: The interferometer optical path includes a first focusing lens, a second focusing lens, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first plane reflector, a second plane reflector, a telescope optical path, and a 45-degree angle reflector; The optical signal transmitting end of the first terahertz solid source is connected to the receiving end of the first detector through the first focusing lens, the first beam splitter and the second beam splitter in sequence; the optical signal transmitting end of the first terahertz solid source is connected to the receiving end of the second detector through the first focusing lens, the first beam splitter, the second plane reflector and the fifth beam splitter in sequence; The optical signal transmitting end of the second terahertz solid source is connected to the receiving end of the corner reflector through the second focusing lens, the third beam splitter, the first plane reflector, the telescope optical path, the 45-degree angle reflector, the fourth beam splitter and the plasma in sequence, and the optical signal returning end of the corner reflector is connected to the receiving end of the second detector through the plasma, the fourth beam splitter and the fifth beam splitter in sequence; the optical signal transmitting end of the second terahertz solid source is connected to the receiving end of the first detector through the second focusing lens, the third beam splitter and the second beam splitter in sequence.

3. The plasma electron density measuring device according to claim 2, characterized in that: The telescope optical path includes a convex reflector and a concave reflector; The first plane reflector sends the received light beam to the 45-degree angle reflector through the convex reflector and the concave reflector in sequence.

4. The plasma electron density measuring device according to claim 1, characterized in that: The first terahertz solid source is a variable frequency 340 GHz solid source, and the second terahertz solid source is a fixed frequency 340 GHz solid source.

5. The plasma electron density measuring device according to claim 1, characterized in that: The first detector and the second detector are both AlGaN / GaN-HEMT field effect tube detectors.

6. The plasma electron density measuring device according to claim 1, characterized in that: The plasma electron density measuring device also includes a flange bracket, a sleeve is provided on the flange bracket, the corner reflector is arranged in the sleeve, the sleeve has an opening aligned with the corner reflector, and the opening is horizontally / vertically adjustable on the flange bracket.

7. The plasma electron density measuring device according to claim 1, characterized in that: The corner reflector is made of gold-plated aluminum.

8. The plasma electron density measuring device according to claim 1, characterized in that: The plasma electron density measuring device also includes an optical platform; The first terahertz solid source, the second terahertz solid source, the interferometer optical path, the first detector and the second detector are all arranged on the optical platform.

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