CN112163365B - Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath - Google Patents
Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath Download PDFInfo
- Publication number
- CN112163365B CN112163365B CN202011050311.0A CN202011050311A CN112163365B CN 112163365 B CN112163365 B CN 112163365B CN 202011050311 A CN202011050311 A CN 202011050311A CN 112163365 B CN112163365 B CN 112163365B
- Authority
- CN
- China
- Prior art keywords
- plasma
- distribution
- plasma sheath
- target
- equivalent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/25—Design optimisation, verification or simulation using particle-based methods
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
- G06F30/15—Vehicle, aircraft or watercraft design
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/28—Design optimisation, verification or simulation using fluid dynamics, e.g. using Navier-Stokes equations or computational fluid dynamics [CFD]
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/08—Fluids
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/10—Nuclear fusion reactors
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- General Physics & Mathematics (AREA)
- Geometry (AREA)
- Evolutionary Computation (AREA)
- General Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
- Mathematical Analysis (AREA)
- Mathematical Optimization (AREA)
- Pure & Applied Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mathematical Physics (AREA)
- Computing Systems (AREA)
- Algebra (AREA)
- Automation & Control Theory (AREA)
- Aviation & Aerospace Engineering (AREA)
- Computational Mathematics (AREA)
- Plasma Technology (AREA)
Abstract
The invention provides a terahertz wave transmission characteristic equivalent measurement method and device in a plasma sheath. The method comprises the following steps: acquiring the electron density and distribution of a target plasma sheath in a Langmuir probe mode; according to the electron density and distribution of the target plasma sheath, performing simulation modeling on the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge; and equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the equivalent plasma generated by high-voltage discharge. The invention solves the technical bottleneck that the terahertz wave energy is weak at present and the terahertz wave transmission characteristic experimental data in the plasma sheath can not be directly obtained. The equivalent measurement purpose of fully developing the transmission characteristic of the terahertz wave in the plasma sheath is realized.
Description
Technical Field
The invention relates to the technical field of terahertz wave transmission characteristics, in particular to an equivalent measurement method and device for terahertz wave transmission characteristics in a plasma sheath.
Background
The electromagnetic wave is attenuated by being absorbed by the plasma sheath in the propagation process, and has the effects of deflection, delay, phase shift and the like, and the phenomenon of 'black obstacle' appears when the situation is serious, so that the occurrence of the phenomenon of 'black obstacle' brings great difficulty to measurement and control communication and guidance of the high-speed aircraft. The plasma is invisible to radar waves, and the root cause is that the electric field of the microwave band electromagnetic wave accelerates charged particles in the plasma, and the charged particles collide with neutral particles, so that energy absorbed from the microwave electromagnetic wave is transferred. Because the frequency of the terahertz wave is far greater than the oscillation frequency of the plasma, charged particles in the plasma do not respond to the change of the electromagnetic field of the terahertz wave, that is to say, the charged particles in the plasma consume the energy of the terahertz wave without the acceleration effect of an electric field, so that a technical approach of penetrating the terahertz wave into the plasma sheath from a physical mechanism is feasible.
The application requirements of effectively searching for the communication black barrier, plasma stealth and stealth prevention and a seeker radar transmission plasma sheath are all urgent to develop the research of terahertz wave propagation characteristic measurement technology in plasma.
The existing common plasma sheath is generated by friction between high-speed air flow in a wind tunnel and a target body, because the existing time of the plasma sheath is short and only has millisecond-level residence time, the existing time is difficult to capture, a terahertz transmission system is often complex, terahertz signals are weak, the plasma sheath in the wind tunnel is difficult to directly study, the plasma sheath is required to be equivalent according to main indexes of plasma, the plasma sheath can be miniaturized at the same time, and the plasma sheath can be placed in a complex terahertz transmission measurement system so as to facilitate the long-term stable scientific study.
Disclosure of Invention
The invention aims at least partially solving the problems, and provides a terahertz wave transmission characteristic equivalent measurement method and device in a plasma sheath, which solve the technical bottleneck that the terahertz wave energy is weak at present and the terahertz wave transmission characteristic experimental data in the plasma sheath cannot be directly obtained. The purpose of fully researching the transmission characteristics of terahertz waves in plasmas with different densities is achieved.
The invention discloses an equivalent measurement method of terahertz wave transmission characteristics in a plasma sheath, which comprises the following steps:
acquiring the electron density and distribution of a target plasma sheath in a Langmuir probe mode;
according to the electron density and distribution of the target plasma sheath, performing simulation modeling on the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
and equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the equivalent plasma generated by high-voltage discharge.
Preferably, obtaining the target plasma sheath electron density and its distribution by langmuir probe means comprises:
placing the warhead or the return cabin in a high enthalpy shock tunnel, setting the air flow rate in the tunnel according to the flying speed of the warhead or the return cabin, and determining the air injection pulse time and duration to generate a target plasma sheath;
langmuir probes with different heights and in stepped distribution are placed at different positions of the target plasma sheath, and electron density values of different layer points of the target plasma sheath are obtained through detection.
Preferably, performing simulation modeling on the target plasma sheath according to the target plasma sheath electron density and the distribution thereof comprises:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of a warhead or a return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the target plasma sheath.
Preferably, simulating the target plasma sheath using an equivalent plasma generated by a high voltage discharge comprises:
generating simulated plasmas corresponding to the electron density and the distribution of the target plasma sheath by utilizing a high-voltage discharge mode;
passing the collimated terahertz light beam through the simulated plasma from a side window of a plasma generator, so that the terahertz light beam vertically passes through the simulated plasma to obtain the spatial distribution condition of the density of the simulated plasma;
when the space distribution condition of the simulated plasma density is matched with the electron density of the target plasma sheath and the distribution of the electron density, the simulated plasma is used as equivalent plasma;
when the spatial distribution of the simulated plasma density is not matched with the electron density and the distribution of the electron density of the target plasma sheath, the spatial distribution of the simulated plasma density is changed by adjusting the voltage and the gas density of high-voltage discharge until the spatial distribution of the newly generated simulated plasma density is matched with the electron density and the distribution of the electron density of the target plasma sheath, and the newly generated simulated plasma is taken as equivalent plasma.
Preferably, equivalently measuring the transmission characteristics of the terahertz wave in the target plasma sheath according to the transmission characteristics of the terahertz wave in the plasma generated by the high-voltage discharge includes:
and interferometry is carried out on electron density distribution in the equivalent plasma, one beam of light passing through the Mach-Zehnder interferometer passes through the equivalent plasma and is coherent with the light transmitted by the other beam of free space, and according to interference fringes with alternating brightness and darkness formed by phase differences caused by the equivalent plasma, the refractive index and electron density in the equivalent plasma are obtained through analysis and processing of the interference fringes.
Preferably, obtaining the refractive index and the electron density in the equivalent plasma by analyzing the processing interference fringes includes:
and obtaining the refractive index distribution of the equivalent plasma through Abbe transformation on the phase difference distribution of the interference fringes, and inverting the two-dimensional interference image into three-dimensional information of the equivalent plasma refractive index according to the axisymmetry of the equivalent plasma distribution.
Preferably, equivalently measuring the transmission characteristics of the terahertz wave in the target plasma sheath according to the transmission characteristics of the terahertz wave in the plasma generated by the high-voltage discharge includes:
transmitting the equivalent plasma by using a terahertz time-domain spectrum, and placing a region where the equivalent plasma is positioned as a measured target in a terahertz wave transmission region for transmission experiments;
comparing the terahertz wave transmission spectrum with the free space terahertz wave transmission spectrum to obtain a spectrum of terahertz waves penetrating through the equivalent plasma;
and determining the transmission characteristic of the terahertz waves in the target plasma sheath through data processing of the transmission spectrum.
On the other hand, the invention also discloses a terahertz wave transmission characteristic equivalent measurement device in the plasma sheath, which comprises:
the detection module is used for acquiring the electron density and the distribution of the target plasma sheath in a Langmuir probe mode;
the simulation module is used for performing simulation modeling on the target plasma sheath according to the electron density and the distribution of the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
and the processing module is used for equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the plasma generated by high-voltage discharge.
Preferably, the simulation module performs simulation modeling on the target plasma sheath according to the electron density and the distribution of the target plasma sheath, including:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of a warhead or a return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the plasma sheath.
Preferably, the processing module equivalently measures the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the plasma generated by high-voltage discharge, and the method comprises the following steps:
and one beam of light passing through the Mach-Zehnder interferometer is coherent with the light transmitted by the other beam of free space through the equivalent plasma, and the refractive index and the electron density in the equivalent plasma are obtained through analysis and processing of interference fringes according to the light-dark alternating interference fringes formed by the phase difference caused by the equivalent plasma.
Compared with the prior art, the invention has the following advantages:
the invention solves the technical bottleneck of how to indirectly obtain the terahertz wave transmission characteristic experimental data in the plasma sheath through an equivalent experiment under the condition of weak terahertz wave energy at present. The Langmuir probe is used for acquiring plasma density first-hand experimental data of a plasma sheath of a target body in a wind tunnel due to high-speed air flow, and the equivalent transition of the plasma sheath is achieved by designing small plasmas with the same plasma density and similar distribution as the target plasma sheath, so that the transmission characteristic of terahertz waves in the equivalent plasmas is further studied indirectly by researching the transmission characteristic of the terahertz waves in the target plasma sheath.
The invention can skillfully overcome the experimental defects that terahertz waves are weak and the millisecond-level flash plasma sheath in the wind tunnel cannot be rapidly captured, and can realize the purpose of stably researching the transmission characteristics of the terahertz waves in the plasma for a long time in a complex terahertz transmission system by using an equivalent method, thereby increasing the reliability of experimental data.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate and do not limit the invention.
Fig. 1 is a flowchart of an equivalent measurement method of terahertz wave transmission characteristics in a plasma sheath according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an equivalent measurement device for terahertz wave transmission characteristics in a plasma sheath according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of the establishment of an equivalent plasma model according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of an experimental apparatus for generating plasma by high-voltage discharge ionization according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of an exemplary Mach-Zehnder interferometer according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an Abbe's transformation integration path according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a terahertz transmission spectrum testing system according to an embodiment of the invention;
in fig. 7: 1: a terahertz wave transmitting antenna; 2: a first parabolic mirror; 3: a second parabolic mirror; 4: a sample to be tested; 5: a third parabolic mirror; 6: a fourth parabolic mirror; 7: a silicon wafer; 8: an electro-optic crystal; 9: a quarter wave plate; 10: a focusing lens; 11: a wollaston prism; 12: differential photodetectors.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be arbitrarily combined with each other.
The steps illustrated in the flowchart of the figures may be performed in a computer system, such as a set of computer-executable instructions. Also, while a logical order is depicted in the flowchart, in some cases, the steps depicted or described may be performed in a different order than presented herein.
Example 1
Fig. 1 is a flowchart of an equivalent measurement method of terahertz wave transmission characteristics in a plasma sheath according to an embodiment of the present invention, and the equivalent measurement method of terahertz wave transmission characteristics in a plasma sheath according to an embodiment of the present invention may include:
s101, acquiring the electron density and distribution of a target plasma sheath in a Langmuir probe mode;
s102, according to the electron density and the distribution of the target plasma sheath, performing simulation modeling on the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
s103, equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the equivalent plasma generated by high-voltage discharge.
In the embodiment of the present invention, step S101 of obtaining the electron density of the target plasma sheath and the distribution thereof by using the langmuir probe method includes:
placing the warhead or the return cabin in a high enthalpy shock tunnel, setting the air flow rate in the tunnel according to the flying speed of the warhead or the return cabin, and determining the air injection pulse time and duration to generate a target plasma sheath;
langmuir probes with different heights and in stepped distribution are placed at different positions of the target plasma sheath, and electron density values of different layer points of the target plasma sheath are obtained through detection.
In the embodiment of the present invention, step S102, performing simulation modeling on the target plasma sheath according to the target plasma sheath electron density and the distribution thereof includes:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of a warhead or a return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the target plasma sheath.
In the embodiment of the present invention, step S102, simulating the target plasma sheath by using the equivalent plasma generated by the high-voltage discharge includes:
generating simulated plasmas corresponding to the electron density and the distribution of the target plasma sheath by utilizing a high-voltage discharge mode;
passing the collimated terahertz light beam through the simulated plasma from a side window of a plasma generator, so that the terahertz light beam vertically passes through the simulated plasma to obtain the spatial distribution condition of the density of the simulated plasma;
when the space distribution condition of the simulated plasma density is matched with the electron density of the target plasma sheath and the distribution of the electron density, the simulated plasma is used as equivalent plasma;
when the spatial distribution of the simulated plasma density is not matched with the electron density and the distribution of the electron density of the target plasma sheath, the spatial distribution of the simulated plasma density is changed by adjusting the voltage and the gas density of high-voltage discharge until the spatial distribution of the newly generated simulated plasma density is matched with the electron density and the distribution of the electron density of the target plasma sheath, and the newly generated simulated plasma is taken as equivalent plasma.
In the embodiment of the present invention, step S103, equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the plasma generated by high-voltage discharge includes:
and interferometry is carried out on electron density distribution in the equivalent plasma, one beam of light passing through the Mach-Zehnder interferometer passes through the equivalent plasma and is coherent with the light transmitted by the other beam of free space, and according to interference fringes with alternating brightness and darkness formed by phase differences caused by the equivalent plasma, the refractive index and electron density in the equivalent plasma are obtained through analysis and processing of the interference fringes.
In the embodiment of the present invention, step S103 includes the steps of:
and obtaining the refractive index distribution of the equivalent plasma through Abbe transformation on the phase difference distribution of the interference fringes, and inverting the two-dimensional interference image into three-dimensional information of the equivalent plasma refractive index according to the axisymmetry of the equivalent plasma distribution.
In the embodiment of the present invention, step S103 equivalently measures the transmission characteristics of the terahertz wave in the target plasma sheath according to the transmission characteristics of the terahertz wave in the plasma generated by the high-voltage discharge, where the step S103 includes:
transmitting the equivalent plasma by using a terahertz time-domain spectrum, and placing a region where the equivalent plasma is positioned as a measured target in a terahertz wave transmission region for transmission experiments;
comparing the terahertz wave transmission spectrum with the free space terahertz wave transmission spectrum to obtain a spectrum of terahertz waves penetrating through the equivalent plasma;
and determining the transmission characteristic of the terahertz waves in the target plasma sheath through data processing of the transmission spectrum.
Example two
As shown in fig. 2, the embodiment of the present invention further provides an equivalent measurement device for terahertz wave transmission characteristics in a plasma sheath, including:
the detection module 100 is configured to acquire the electron density of the target plasma sheath and the distribution thereof in a Langmuir probe mode;
the simulation module 200 is configured to perform simulation modeling on the target plasma sheath according to the electron density and the distribution of the target plasma sheath, and simulate the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
the processing module 300 is configured to equivalently measure the transmission characteristics of terahertz waves in the target plasma sheath according to the transmission characteristics of the terahertz waves in the plasma generated by the high-voltage discharge.
In the embodiment of the present invention, the simulation module 200 performs simulation modeling on the target plasma sheath according to the electron density and the distribution thereof, including:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of a warhead or a return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the plasma sheath.
In the embodiment of the present invention, the equivalent measurement of the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the plasma generated by the high-voltage discharge by the processing module 300 includes:
and one beam of light passing through the Mach-Zehnder interferometer is coherent with the light transmitted by the other beam of free space through the equivalent plasma, and the refractive index and the electron density in the equivalent plasma are obtained through analysis and processing of interference fringes according to the light-dark alternating interference fringes formed by the phase difference caused by the equivalent plasma.
Example III
The embodiment of the invention illustrates an equivalent measurement process of terahertz wave transmission characteristics in a plasma sheath: the electron density and the distribution of the plasma sheath are obtained through a Langmuir probe mode, the electron density and the distribution of the equivalent plasma device are obtained through an interferometry mode, the Abbe density is inverted, and the equivalent transmission of the plasma is measured through a terahertz wave time-domain spectrum transmission measurement system.
(1) Langmuir probe mode for obtaining electron density of plasma sheath and distribution thereof
Placing the warhead/return cabin shell target in a high enthalpy shock tunnel, setting the air flow rate in the tunnel according to the actual flight speed of the warhead/return cabin, and determining the proper air jet pulse time and duration so as to generate a plasma sheath around the warhead/return cabin shell target model. Probes with different heights and step distribution are placed at different positions on the surface of a measured target in a conventional mode, so that electron density values of different layer points of the plasma sheath are obtained through detection, and a plasma sheath density distribution model is constructed.
(2) Modeling simulation of plasma sheath and axisymmetric plasma
The plasma sheath is simulated and modeled by using fluid software and combining a plasma density distribution model obtained by the probe and the appearance of the warhead/return cabin. On the basis, as shown in fig. 3, the plasma sheath model is equivalently transited to an axisymmetrically distributed non-uniform plasma model so as to generate plasma consistent with the model from an actual plasma generator, thereby facilitating the subsequent terahertz transmittance experimental study. Meanwhile, the characteristics of the plasma sheath can be mastered through modeling simulation.
(3) Axisymmetric plasma generation
The plasma is essentially a mixture of charged ions, electrons and neutral particles, so that after the composition and distribution characteristics of the plasma are known through simulation, equivalent plasma which is easy to study can be generated through a laboratory construction plasma generator. The density of the plasma generated by laser ionization or high-voltage discharge is distributed in a gradient manner, namely the plasma has certain non-uniformity and axial symmetry, so that the simulation link needs to consider how to transition to simulate the real sheath situation. Fig. 4 is a schematic diagram of an apparatus for generating plasma by high-voltage discharge to be adopted. Terahertz beams can be used to pass through the plasma from a plastic window, and can also pass vertically through the plasma to simulate the situation of truly passing through the sheath.
In the test, in order to simulate the transmission influence of the plasma on the terahertz wave under the real condition, the collimated planar terahertz wave can be transmitted and tested from the axial direction of the glass tube in fig. 4, and the transmission and test can also be performed from the direction vertical to the axial direction of the glass tube.
(4) Interferometric method for obtaining electron density and distribution of equivalent plasma device
Interferometry is based on the principle of light wave interference superposition, interference fringes with alternating brightness and darkness are formed in a superimposed field, and related information to be measured is obtained by analyzing and processing the interference fringes. The Mach-Zehnder interferometer is adopted to measure the plasma density in the experiment, and mainly has certain advantages in the aspects of sensing and detecting the refractive index change. The mach-zehnder interferometer is an amplitude-splitting interferometer that is approximately doubled in luminous flux utilization compared to the michelson interferometer because half of the luminous flux in the michelson interferometer will be returned to the direction of the light source, whereas the mach-zehnder interferometer does not have such a return light source. A typical mach-zehnder interferometer is shown in fig. 5. It is composed of two plane spectroscopes P1 and P2 and two plane reflecting mirrors M1 and M2. In fig. 5, S is a point light source, and L is a collimating mirror. The object to be measured in phase can be placed in the light path formed by the elements P1, M1 and P2, and P1, M1 and P2 are called measuring arms; the optical path composed of original P1, M2 and P2 is used as reference arm, and features that two interference beams are separated far and the localization position of stripe can be regulated separately. The method can adjust the localized position to the vicinity of the flow field to be detected so as to obtain clearer interference fringes, and the light beam only passes through the detected medium once (the light beam in other interferometers passes through the detected medium twice in a round-trip manner), so that the method is particularly suitable for researching the condition of rapid change of the gas density.
(5) Abeli (abel) transformation
The interference image obtained by measuring the plasma density by the laser interferometry is a two-dimensional plane image, in practice, the plasma is a three-dimensional area, the problem of inversion of data of three-dimensional plasma parameters analyzed from the two-dimensional interference image is in important connection with the shape and distribution of the plasma, and if the shape distribution of the plasma is uncertain, the accurate inversion data can be influenced. The refractive index distribution of the plasma can be obtained from the phase difference distribution of the fringes by the abel transformation. For plasma distribution of a plasma generator to be measured by our experiments, the plasma with columnar axisymmetric distribution or spherical symmetric distribution can be used for inverting three-dimensional information of the refractive index of the plasma from a two-dimensional interference image through Abbe transformation. From the Abbe's transformation we can derive the following expression for the radial distribution of the refractive index of the plasma.
(6) Research on terahertz wave transmission in plasma through terahertz time-domain spectral transmission measurement system
And the terahertz time-domain spectrum transmission system is used for measuring terahertz transmission characteristics by taking plasma generated by the plasma generator as a medium, and then processing transmission spectrum data, so that the transmission characteristics of terahertz waves in the plasma can be obtained.
Example IV
The embodiment illustrates an equivalent measurement process of terahertz wave transmission characteristics in a plasma sheath:
(1) Langmuir probe mode for obtaining electron density of plasma sheath and distribution thereof
Through the collaborative research of the institute of mechanics of Chinese sciences, high enthalpy wind tunnel experiments are carried out on the HTV-2 aircraft, and the electron density data of the plasma sheath are obtained by using the technical means of probe measurement. Experiments show that the electron density of the plasma sheath obtained by wind tunnel experiments is between 10 in most areas 10 -10 11 cm -3 Between them.
The length of the model body is 397 mm, and the model body is as follows: 10, the diameter of the probe used is 0.3 mm, and the length of the probe acquisition part is 8 mm. At an angle of attack of 0 degrees, the first position was at a horizontal distance of 59.5 mm from the model head, on which two measurement probe sets, four probes each, were mounted. The axis of the probe is parallel to the model surface generatrix. The first probe above was 4 mm from the wall of the mold, and the spacing between each two probes was 4 mm. The largest measurement position is 16 mm from the model (vertical direction). The first probe below was also 4 mm from the wall of the mold, with a spacing of 4 mm between each two probes. The largest measurement position is 16 mm from the surface of the model (vertical direction); the horizontal distance from the second measuring position to the head of the model is 139.5 mm, and the mounting position of the probe is the same as that of the first group of probes; the horizontal distance between the third measuring position and the head of the model is 277 millimeters, and the mounting position of the probe is the same as that of the first group of probes; the fourth set of measurement locations was closely attached to the bottom wall of the mold at a horizontal distance of 397 mm from the head of the mold with the axis of the probe parallel to the surface generatrix of the mold. In the fourth measurement position, a total of 12 probes were mounted. The fifth set of measurement locations were 100 mm from the bottom wall of the mold and were located at a horizontal distance of 497 mm from the head of the mold. The axis of the probe is parallel to the axis of the model strut. In the fifth measurement position, a total of 12 probes were also mounted.
Through wind tunnel experiments of airflow Mach number 15 and total temperature 8000K, the electron density of a plasma sheath formed by standing points at different distances from the wall surface of the model at five different positions under two attack angles (0 degree and 10 degrees) is respectively obtained.
(2) Modeling simulation of plasma sheath and axisymmetric plasma
As shown in fig. 3, on the basis of experimental acquisition of plasma sheath experimental data of the surface of the target body in the wind tunnel, the plasma sheath model is equivalently transited to an axisymmetrically distributed non-uniform plasma model in a simulation modeling mode. So as to generate the plasma consistent with the model from the actual plasma generator, thereby facilitating the subsequent terahertz transmittance experimental study. Meanwhile, the characteristics of the plasma sheath can be mastered through modeling simulation.
(3) High voltage discharge plasma generation
There are various ways of generating plasma, and the plasma densities obtained by different ways of generating plasma are greatly different. In the embodiments of the present invention, to obtain a plasma with a density comparable to that of the plasma sheath, we use a high-voltage discharge to generate the plasma. FIG. 4 is a schematic diagram of an apparatus for generating plasma by high-voltage discharge according to an embodiment of the present invention. The terahertz light beam passes through the plasma from polytetrafluoroethylene windows at two ends and can also vertically pass through the plasma to simulate the situation of actually passing through the sheath layer.
In the test, in order to simulate the transmission influence of the plasma on the terahertz wave under the real condition, the collimated planar terahertz wave can be transmitted and tested from the axial direction of the glass tube in fig. 4, and the transmission and test can also be performed from the direction vertical to the axial direction of the glass tube.
(4) Interferometric method for obtaining electron density and distribution of equivalent plasma device
When the phase difference of the two beams is
Light wave E of (2) 1 expi (ωt) and E 2 After the addition of expi (ωt), the total light field intensity is
In the formula, the light wave field intensity consists of a direct current component and a cosine change component, and the light wave field intensity is expressed as fringes with alternate brightness and darkness on an interference pattern.
Phase difference of two optical paths in Mach-Zehnder interferometer
Can be expressed as
Wherein n is i 、n j Medium refractive indexes of two optical paths of the interferometer respectively; l (L) i 、l j The geometrical paths of two light paths of the interferometer are respectively.
When one branch of Mach-Zehnder interferometer is inserted into the plasma to be detected, after the detected light passes through the plasma, the phase difference of two paths of light rays of the interferometer will change, and the changed phase shift is written into an integral form, so that the detection light has the following characteristics
Where N is the refractive index of the plasma and l is the distance through the plasma.
The formula is given by
Carry-in
If the density of the plasma is much smaller than the critical electron density determined by the laser frequency, n e ＜＜n c The refractive index may be approximated as:
the expression (2) is brought into the expression (1) to obtain
Assuming that the interference fringes move D, then
Can obtain
∫n e dl＝2Dn c λ (3)
At the same time, the refractive index satisfies
∫(N-n 0 )dl＝Dλ (4)
In n 0 Is the ambient refractive index;
from the above deduction, as long as the amount of movement of the interference fringes of the plasma region is determined, the refractive index and electron density of the plasma can be determined according to the formulas (3) (4).
(5) Abeli (abel) transformation
As shown in fig. 6, consider a column symmetry amount f (r), the Z axis is a rotational symmetry axis, the Y axis is an integration axis, the X axis is perpendicular to the Y axis, the X axis is an image plane horizontal axis, the X axis is parallel to the X axis, the Z axis is an image plane vertical axis, the Z axis is parallel to the Z axis, and the Y axis are the same. F (x) is the integrated intensity along the y-axis:
the integral of variable y is converted into an integral of variable r, and the symmetry of the integral is taken into account, which can be obtained:
the Abbe transform of F (x) in the formula (6) is called F (r), and the inverse transform of F (x) is called F (r), and the expression is:
f (x) and F (r) in the above transformation are written as D (x) lambda, N (lambda) -N, respectively 0 The formulas (6), (7) can be rewritten as the following formula, where n 0 Is the ambient refractive index.
Wherein R is the radial direction of the plasma, x is the direction of the background fringe, and R is the radius of the interference fringe disturbance area. Based on the relationship between the refractive index of the plasma and the density of the plasma, the spatial distribution of the density of the plasma can be obtained
(6) Research on terahertz wave transmission in plasma through terahertz time-domain spectral transmission measurement system
As shown in fig. 7, with a conventional terahertz time-domain spectroscopy transmission measurement system, a region where a plasma is located in a plasma generator is placed as a measured object in a terahertz wave transmission region for transmission experiments, the spectrum of the terahertz wave transmitted through the plasma can be easily obtained through comparison with the free space terahertz wave transmission spectrum, and the terahertz wave transmission characteristics in the plasma can be studied in detail through data processing of the transmission spectrum.
Those of ordinary skill in the art will appreciate that all or some of the steps, systems, functional modules/units in the apparatus, and methods disclosed above may be implemented as software, firmware, hardware, and suitable combinations thereof. In a hardware implementation, the division between the functional modules/units mentioned in the above description does not necessarily correspond to the division of physical components; for example, one physical component may have multiple functions, or one function or step may be performed cooperatively by several physical components. Some or all of the components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software may be distributed on computer readable media, which may include computer storage media (or non-transitory media) and communication media (or transitory media). The term computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, as known to those skilled in the art. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computer. Furthermore, as is well known to those of ordinary skill in the art, communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media.
Claims (9)
1. The equivalent measurement method of the terahertz wave transmission characteristics in the plasma sheath is characterized by comprising the following steps of:
acquiring the electron density and distribution of a target plasma sheath in a Langmuir probe mode;
according to the electron density and distribution of the target plasma sheath, performing simulation modeling on the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the equivalent plasma generated by high-voltage discharge;
simulating the target plasma sheath using an equivalent plasma generated by a high voltage discharge includes:
generating simulated plasmas corresponding to the electron density and the distribution of the target plasma sheath by utilizing a high-voltage discharge mode;
passing the collimated terahertz light beam through the simulated plasma from a side window of a plasma generator, so that the terahertz light beam vertically passes through the simulated plasma to obtain the spatial distribution condition of the density of the simulated plasma;
when the space distribution condition of the simulated plasma density is matched with the electron density of the target plasma sheath and the distribution of the electron density, the simulated plasma is used as equivalent plasma;
when the spatial distribution of the simulated plasma density is not matched with the electron density and the distribution of the electron density of the target plasma sheath, the spatial distribution of the simulated plasma density is changed by adjusting the voltage and the gas density of high-voltage discharge until the spatial distribution of the newly generated simulated plasma density is matched with the electron density and the distribution of the electron density of the target plasma sheath, and the newly generated simulated plasma is taken as equivalent plasma.
2. The method for equivalently measuring terahertz wave transmission characteristics in a plasma sheath according to claim 1, wherein obtaining the target plasma sheath electron density and its distribution by a langmuir probe method includes:
placing the warhead or the return cabin in a high enthalpy shock tunnel, setting the air flow rate in the tunnel according to the flying speed of the warhead or the return cabin, and determining the air injection pulse time and duration to generate a target plasma sheath;
and placing Langmuir probes with different heights and in stepped distribution at different positions of the target plasma sheath, and detecting to obtain electron density values of different layer points of the target plasma sheath.
3. The method for equivalently measuring terahertz wave transmission characteristics in a plasma sheath according to claim 2, wherein performing simulation modeling on the target plasma sheath according to the target plasma sheath electron density and distribution thereof comprises:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of the warhead or the return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the target plasma sheath.
4. The method for equivalently measuring transmission characteristics of terahertz waves in a plasma sheath according to claim 3, wherein equivalently measuring the transmission characteristics of terahertz waves in a target plasma sheath from the transmission characteristics of terahertz waves in plasma generated by high-voltage discharge comprises:
and interferometry is carried out on electron density distribution in the equivalent plasma, one beam of light passing through the Mach-Zehnder interferometer passes through the equivalent plasma and is coherent with the light transmitted by the other beam of free space, and according to interference fringes with alternating brightness and darkness formed by phase differences caused by the equivalent plasma, the refractive index and electron density in the equivalent plasma are obtained through analysis and processing of the interference fringes.
5. The method for equivalent measurement of terahertz wave transmission characteristics in a plasma sheath according to claim 4, wherein obtaining the refractive index and electron density in the equivalent plasma by analyzing and processing interference fringes comprises:
and obtaining the refractive index distribution of the equivalent plasma through Abbe transformation on the phase difference distribution of the interference fringes, and inverting the two-dimensional interference image into three-dimensional information of the equivalent plasma refractive index according to the axisymmetry of the equivalent plasma distribution.
6. The method for equivalently measuring transmission characteristics of terahertz waves in a plasma sheath according to claim 3, wherein equivalently measuring the transmission characteristics of terahertz waves in a target plasma sheath from the transmission characteristics of terahertz waves in plasma generated by high-voltage discharge comprises:
transmitting the equivalent plasma by using a terahertz time-domain spectrum, and placing a region where the equivalent plasma is positioned as a measured target in a terahertz wave transmission region for transmission experiments;
comparing the terahertz wave transmission spectrum with the free space terahertz wave transmission spectrum to obtain a spectrum of terahertz waves penetrating through the equivalent plasma;
and determining the transmission characteristic of the terahertz waves in the target plasma sheath through data processing of the transmission spectrum.
7. The terahertz wave transmission characteristic equivalent measurement device in the plasma sheath is characterized by comprising:
the detection module is used for acquiring the electron density and the distribution of the target plasma sheath in a Langmuir probe mode;
the simulation module is used for performing simulation modeling on the target plasma sheath according to the electron density and the distribution of the target plasma sheath, and simulating the target plasma sheath by adopting equivalent plasma generated by high-voltage discharge;
the processing module is used for equivalently measuring the transmission characteristic of the terahertz wave in the target plasma sheath according to the transmission characteristic of the terahertz wave in the plasma generated by high-voltage discharge;
in the simulation module, the simulation of the target plasma sheath by using the equivalent plasma generated by high-voltage discharge comprises the following steps:
generating simulated plasmas corresponding to the electron density and the distribution of the target plasma sheath by utilizing a high-voltage discharge mode;
passing the collimated terahertz light beam through the simulated plasma from a side window of a plasma generator, so that the terahertz light beam vertically passes through the simulated plasma to obtain the spatial distribution condition of the density of the simulated plasma;
when the space distribution condition of the simulated plasma density is matched with the electron density of the target plasma sheath and the distribution of the electron density, the simulated plasma is used as equivalent plasma;
when the spatial distribution of the simulated plasma density is not matched with the electron density and the distribution of the electron density of the target plasma sheath, the spatial distribution of the simulated plasma density is changed by adjusting the voltage and the gas density of high-voltage discharge until the spatial distribution of the newly generated simulated plasma density is matched with the electron density and the distribution of the electron density of the target plasma sheath, and the newly generated simulated plasma is taken as equivalent plasma.
8. The apparatus according to claim 7, wherein the simulation module performs simulation modeling on the target plasma sheath according to the target plasma sheath electron density and distribution thereof, the simulation modeling including:
and (3) utilizing fluid software to obtain electron density values of different layer points of the target plasma sheath and the appearance of the warhead or the return cabin by combining detection, performing simulation modeling on the target plasma sheath, and constructing a plasma model with axisymmetric density distribution according to the plasma density distribution characteristics of the plasma sheath.
9. The apparatus according to claim 7, wherein the processing module equivalently measures the transmission characteristics of the terahertz wave in the target plasma sheath according to the transmission characteristics of the terahertz wave in the plasma generated by the high-voltage discharge, comprising:
and one beam of light passing through the Mach-Zehnder interferometer is coherent with the light transmitted by the other beam of free space through the equivalent plasma, and the refractive index and the electron density in the equivalent plasma are obtained through analysis and processing of interference fringes according to the light-dark alternating interference fringes formed by the phase difference caused by the equivalent plasma.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011050311.0A CN112163365B (en) | 2020-09-29 | 2020-09-29 | Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011050311.0A CN112163365B (en) | 2020-09-29 | 2020-09-29 | Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN112163365A CN112163365A (en) | 2021-01-01 |
| CN112163365B true CN112163365B (en) | 2023-06-02 |
Family
ID=73860670
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202011050311.0A Active CN112163365B (en) | 2020-09-29 | 2020-09-29 | Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN112163365B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112992387B (en) * | 2021-02-01 | 2023-10-13 | 大连理工大学 | Terahertz microwave interference array for measuring two-dimensional electron density profile based on time delay method |
| CN113038678B (en) * | 2021-03-09 | 2023-01-20 | 北京环境特性研究所 | Plasma density measurement method based on terahertz time-domain spectroscopy |
| CN113156172B (en) * | 2021-04-20 | 2022-07-29 | 核工业西南物理研究院 | Multi-step type electrostatic probe |
| CN113329553B (en) * | 2021-06-11 | 2022-09-06 | 北京环境特性研究所 | Detection method and detection device for plasma density distribution |
| CN114071849B (en) * | 2021-11-15 | 2023-11-14 | 上海无线电设备研究所 | Ultra-high sound velocity target ablation diffuser plasma generator |
| CN114689267B (en) * | 2022-05-30 | 2022-08-05 | 中国空气动力研究与发展中心超高速空气动力研究所 | Seven-channel microwave interferometer data processing method for plasma electron density distribution |
| CN114698218A (en) * | 2022-05-30 | 2022-07-01 | 中国空气动力研究与发展中心超高速空气动力研究所 | Seven-channel microwave interferometer measuring method for transient plasma electron density distribution |
| CN115728242B (en) * | 2022-11-24 | 2024-04-19 | 北京环境特性研究所 | Method for measuring influence of terahertz full-band plasma cladding on reflectivity of material |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105651385A (en) * | 2016-01-13 | 2016-06-08 | 南京邮电大学 | Terahertz spectrum measuring device based on interference effect and measuring method thereof |
| CN109030406A (en) * | 2018-10-12 | 2018-12-18 | 北京环境特性研究所 | Terahertz spectrum calibration system and method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007079342A2 (en) * | 2005-12-27 | 2007-07-12 | Rensselaer Polytechnic Institute | Method of analyzing a remotely-located object utilizing an optical technique to detect terahertz radiation |
-
2020
- 2020-09-29 CN CN202011050311.0A patent/CN112163365B/en active Active
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105651385A (en) * | 2016-01-13 | 2016-06-08 | 南京邮电大学 | Terahertz spectrum measuring device based on interference effect and measuring method thereof |
| CN109030406A (en) * | 2018-10-12 | 2018-12-18 | 北京环境特性研究所 | Terahertz spectrum calibration system and method |
Non-Patent Citations (5)
| Title |
|---|
| Deng haochuan等.Estimation of the parameters of Cold Unmagnetized Plasma Media Based on Time-Domain Inverse Scattering Technique.《IEEE》.2019,1-2. * |
| 任宁 ; 奚斌 ; 李晓斐 ; .黑障抑制技术的发展现状与研究难点.导弹与航天运载技术.2018,(第01期),122-126. * |
| 孙金海等. ZnTe晶体对太赫兹波的电光响应及极化匹配.红外与激光工程 .2019,第48卷(第16期),166-170. * |
| 延凯悦.太赫兹应用分析和展望.《邮电设计技术》.2020,(第4期),6-10. * |
| 马平 ; 秦龙 ; 石安华 ; 陈伟军 ; 赵青 ; 黄洁 ; .毫米波与太赫兹波在等离子体中传输特性.强激光与粒子束.2013,(第11期),2965-2970. * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN112163365A (en) | 2021-01-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN112163365B (en) | Equivalent measurement method and device for terahertz wave transmission characteristics in plasma sheath | |
| Gente et al. | Scaled bistatic radar cross section measurements of aircraft with a fiber-coupled THz time-domain spectrometer | |
| CN102323445B (en) | Method for measuring flowing velocity of recycle gas in multiple laser cavity | |
| Benitez et al. | Focused laser differential interferometry with contoured tunnel windows | |
| CN204631269U (en) | High precision absolute gravimeter optics frequency multiplier type laser interference system and application | |
| Bichal et al. | On the application of background oriented schlieren for wavefront sensing | |
| Zhang et al. | Dependence of interferogram phase on incident wavenumber and phase stability of Doppler asymmetric spatial heterodyne spectroscopy | |
| Liu et al. | A method for noise attenuation of straightness measurement based on laser collimation | |
| CN104808254A (en) | Optical multiple-frequency laser interference system for high-precision absolute gravity meter and application thereof | |
| CN109724532A (en) | A kind of precise testing device and method of complexity optical surface geometry parameter | |
| Menkirch | 2. Density sensitive flow visualization | |
| CN106018345A (en) | System and method for measuring refractive index of optical plate glass based on short coherence | |
| CN101435880B (en) | Static wide field aberration and temperature difference eliminating multi-direction real time simultaneous probing method for upper atmosphere wind field | |
| Briozzo et al. | Analytical expressions for pulse profile of neutron stars in plasma environments | |
| CN205003080U (en) | Refracting index and thickness synchronous measurement system based on spectral domain interferometer | |
| Wilcox et al. | Digital holography wavefront sensing with a supersonic wind tunnel | |
| CN109684690A (en) | A kind of emulated computation method obtaining laser shade, schlieren and shear interference image | |
| Oesch et al. | Aggregate behavior of branch points: characterization in wave optical simulation | |
| Shi et al. | Analysis and experiment of polarization characteristics of Off-axis freeform optical system | |
| Wu et al. | Research on a wide-angle diagnostic method for shock wave velocity at SG-III prototype facility | |
| Tian et al. | Testability of six-intersection detection area measurement method based on photoelectric detection | |
| Wang et al. | High-gradient index of refraction measurements with a quadrature fringe imaging interferometer | |
| Trolinger | Aero-optical characterization of aircraft optical turrets by holography, interferometry and shadowgraph | |
| Dhabal et al. | Optics alignment of a balloon-borne far-infrared interferometer BETTII | |
| CN204808718U (en) | Extension light source interferometry collimating system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |