CN112135408A - Plasma parameter measuring method for plasma wind tunnel - Google Patents
Plasma parameter measuring method for plasma wind tunnel Download PDFInfo
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- CN112135408A CN112135408A CN202011018627.1A CN202011018627A CN112135408A CN 112135408 A CN112135408 A CN 112135408A CN 202011018627 A CN202011018627 A CN 202011018627A CN 112135408 A CN112135408 A CN 112135408A
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- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
- G01M9/06—Measuring arrangements specially adapted for aerodynamic testing
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- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/0006—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature
- H05H1/0087—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature by magnetic means
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Abstract
The invention provides a plasma parameter measuring method based on a plasma wind tunnel, which comprises the steps of firstly, before laminar plasma is input into the plasma wind tunnel, adjusting the same phase of a transmitting antenna and a receiving antenna through a vector network analyzer; after the plasma is input, a plasma beam current is formed in a wind tunnel between the transmitting antenna and the receiving antenna; measuring the diameter of the plasma beam and the phase difference between the receiving antenna and the transmitting antenna, and calculating the electron density of the plasma according to the phase difference and the diameter of the plasma beam; and measuring the offset of the characteristic spectral line of the plasma particles through a spectrometer, and calculating the beam current speed of the plasma according to the offset. The measurement error of the plasma electron density and the beam current speed measured by the method is less than 0.01mm, the associated resolution is less than 0.5 degrees, the comprehensive error is less than 0.16 percent, the plasma parameters are accurately measured on the premise of not interfering the plasma beam current, and the measurement precision is improved.
Description
Technical Field
The invention belongs to the field of plasma wind tunnel testing, and particularly relates to a plasma parameter measuring method of a plasma wind tunnel.
Background
The airflow in the plasma wind tunnel is formed by pure high-enthalpy plasma jet which stably runs for a long time, and the method can be used for researching the electromagnetic property of the plasma sheath of the hypersonic aircraft. On the plasma wind tunnel experimental device, a gas medium enters the quartz tube through the rotary air inlet device, plasma is generated through heating or radiation, and the plasma enters the vacuum test section through the spray pipe, so that plasma jet flow is formed. The key point for realizing the plasma wind tunnel is to obtain stable plasma jet for a long time. In order to ensure the stability of the plasma jet, the electron density and the beam current velocity of the plasma jet need to be measured in real time.
In the prior art, the electron density and the beam current velocity of the plasma wind tunnel are generally measured by a probe. Because the probe needs to intervene in the flow field to measure, the flow field is disturbed in different degrees, and errors are brought to measurement.
Disclosure of Invention
In view of the above defects or shortcomings in the prior art, the present invention aims to provide a non-intrusive plasma parameter measurement method for a plasma wind tunnel, wherein the electron density and the beam current speed in the plasma wind tunnel are measured based on a microwave interference method and a spectrum speed measurement method, the non-intrusive measurement avoids direct contact with the beam current, interference to the plasma is reduced, and the measurement result is more accurate.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
the embodiment of the invention provides a plasma parameter measuring method based on a plasma wind tunnel, which comprises the following steps:
step S1, before the laminar plasma is input into the plasma wind tunnel, the same phase of the transmitting antenna and the receiving antenna is adjusted through a vector network analyzer;
s2, controlling the laminar plasma source to input laminar plasma into the plasma wind tunnel by the laminar plasma source power/working medium input port, and forming plasma beam current in the wind tunnel between the transmitting antenna and the receiving antenna by the laminar plasma through the coil and the magnetic field;
step S3, measuring the diameter of the plasma beam;
step S4, the vector network analyzer measures the phase difference between the receiving antenna and the transmitting antenna after the laminar plasma is input; calculating the electron density of the plasma beam according to the phase difference and the diameter of the plasma beam;
and step S5, setting the jet direction of the collimating mirror of the spectrometer, which is opposite to the plasma beam, and the included angle between the jet direction of the collimating mirror of the spectrometer and the motion direction of the plasma beam to be theta, measuring the offset of the characteristic spectral line of the plasma particles by the spectrometer, and calculating the plasma beam speed according to the offset.
In the foregoing scheme, in step S4, the formula (1) is adopted for calculating the electron density of the plasma beam current:
in the formula (1), NeThe plasma beam current is electron density, f0Is the frequency of the microwave signal and,
for phase difference, L is the plasma beam diameter, i.e., the distance the microwave signal travels through the plasma.
In the above scheme, in step S5, the formula (2) is adopted to calculate the beam current velocity of the plasma according to the offset:
△λ＝(λvcosθ)/c (2)
in the formula (2), delta lambda is the wavelength variation, and lambda is the characteristic spectral line wavelength; v is the particle motion velocity, θ is the angle between the observation direction and the particle motion direction, and c is the speed of light.
In the scheme, the frequency range of the vector network analyzer is 10 MHz-43.5 GHz, the microwave signal adopts 30.5GHz central frequency and the bandwidth is 1 KHz.
In the scheme, the laminar plasma source is from an argon lamp light source;
the spectrometer measures offsets of 840.8nm and 842.4nm spectral lines of Ar I, calculates two beam velocities and averages the two beam velocities to obtain the final calculated beam velocity.
In the above scheme, the vector network analyzer communicates between the transmitting antenna and the receiving antenna by using microwave signals and/or radio frequency power input signals of a spiral wave discharge structure.
In the scheme, when a microwave signal and a radio frequency power input signal of a spiral wave discharge structure are adopted, the plasma density and the beam current speed under the two signals are respectively measured, and the average value of the two measurements is taken as a parameter measurement result.
According to the plasma parameter measuring method based on the plasma wind tunnel, a non-intrusive measuring method is adopted, the disturbance error of a flow field is reduced, the plasma parameter is accurately measured on the premise of not interfering the plasma beam current, the precision of wind tunnel parameter measurement is improved, the errors of the measured plasma electron density and the measured beam current speed are less than 0.01mm, the associated resolution is less than 0.5 degrees, and the comprehensive error is less than 0.16 percent.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings:
FIG. 1 is a schematic diagram illustrating a plasma parameter measurement principle of a plasma wind tunnel according to an embodiment of the present invention;
fig. 2 is a flowchart of a plasma parameter measuring method of a plasma wind tunnel according to an embodiment of the present invention.
Description of reference numerals:
1-laminar plasma source; 2-a coil; 3-a magnetic field; 4-a collimating mirror; 5-a receiving antenna; 6-a transmitting antenna; 7-plasma beam current; 8-laminar plasma source power/working medium input port; 9-a radio frequency input port; 10-a spectrometer; 11-vector network analyzer.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the present invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
The embodiment of the invention provides a parameter measuring method for low-pressure plasma, aiming at measuring parameters of a plasma wind tunnel and based on a microwave interference technology and a spectrum speed measurement. Fig. 1 shows the principle of plasma parameter measurement in the present embodiment. As shown in fig. 1, the plasma wind tunnel working environment is rough vacuumized, and the phases of the microwave signal of the receiving antenna 5 and the transmitting signal of the transmitting antenna 6 are reset to zero by adjusting through the network analyzer 11. The laminar plasma source 1 performs input control of power and air flow through a laminar plasma source power/working medium input port 8, a plasma beam 7 with a certain diameter is formed between the transmitting antenna 6 and the receiving antenna 5 through the coil 2 and the magnetic field 3, and a phase difference caused by plasma is generated between a microwave signal received by the receiving antenna 5 and the transmitting signal. The radio frequency input port 9 provides a magnetic field 3, the collimating mirror 4 of the spectrometer 10 faces away from the plasma beam injection direction, the included angle is theta, the vector network analyzer 11 monitors the phase difference between the receiving antenna 5 and the transmitting antenna 6 in real time, and the spectrometer 10 measures the offset of the particle characteristic spectral line. Calculating the electron density of the plasma through the phase difference; and calculating the beam current speed of the plasma through the offset of the particle characteristic spectral line.
FIG. 2 shows a flow chart of a plasma parameter measurement method of a plasma wind tunnel according to an embodiment of the invention. As shown in fig. 2, the plasma measuring method includes the following steps:
and step S1, before laminar plasma is input into the plasma wind tunnel, the same phase of the transmitting antenna and the receiving antenna is adjusted through the vector network analyzer.
In this step, the vector network analyzer communicates between the transmitting antenna and the receiving antenna by using a microwave signal as a first signal; the radio frequency power of the spiral wave discharge structure can be used for inputting signals to the transmitting antenna to serve as second signals.
In practical application, the first signal is adopted to calculate and obtain a first electron density and a first beam velocity; and calculating to obtain a second electron density and a beam current speed by adopting the second signal. The first electron density and the beam velocity are basically the same as the second electron density and the beam velocity, and errors of the first electron density and the beam velocity are caused by interference of signals. When the average value of the two is adopted, the obtained data is corrected data, and the plasma density and the beam current speed are more accurate. Preferably, in this embodiment, two measurements are taken and averaged.
And step S2, controlling the laminar plasma source to input laminar plasma into the plasma wind tunnel by the laminar plasma source power/working medium input port, and forming plasma beam current in the wind tunnel between the transmitting antenna and the receiving antenna through the coil and the magnetic field.
In this step, the laminar plasma source uses an argon lamp as a standard light source. The magnetic field is provided by a radio frequency input port.
And step S3, arranging a high-definition camera on the microwave interference path in the vacuum chamber of the wind tunnel, and reading the diameter of the plasma beam.
Step S4, the vector network analyzer measures the phase difference between the receiving antenna and the transmitting antenna after the laminar plasma is input; and calculating the electron density of the plasma beam according to the phase difference and the diameter of the plasma beam.
In this step, the electron density of the plasma beam is calculated by using the formula (1):
in the formula (1), NeIs the electron density of the plasma beam, f0Is the frequency of the microwave signal and,
for phase difference, L is the plasma beam diameter, i.e., the distance the microwave signal travels through the plasma.
The microwave interference is not in direct contact with the plasma, so that the plasma density can be measured accurately and effectively without intervention. The average linear density on the plasma propagation path is calculated by measuring the phase deflection of the microwave signal on the path.
Preferably, the vector network analyzer adopts an 11-PNA-X, N5244A vector network analyzer, the frequency range is 10 MHz-43.5 GHz, the microwave signal adopts 30.5GHz central frequency, and the bandwidth is 1 KHz.
And step S5, setting the jet direction of the collimating mirror of the spectrometer, which is opposite to the plasma beam, and the included angle between the jet direction of the collimating mirror of the spectrometer and the motion direction of the plasma beam to be theta, measuring the offset of the characteristic spectral line of the plasma particles by the spectrometer, and calculating the beam speed of the plasma according to the offset.
In the step, when the plasma comes from an argon lamp light source, the spectrometer measures the offsets of 840.8nm and 842.4nm spectral lines of Ar I, calculates two beam velocities and averages the two beam velocities to obtain the final calculated beam velocity.
The beam current velocity of the plasma is calculated according to the offset by adopting a formula (2):
△λ＝(λvcosθ)/c (2)
in the formula (2), Δ λ is a wavelength variation, namely offset, and λ is a characteristic spectral line wavelength; v is the particle motion velocity, θ is the angle between the observation direction and the particle motion direction, and c is the speed of light.
According to the doppler principle, when observing characteristic spectral lines of radiation from moving particles, if the particles move away from the observation point, the wavelength of the measured spectral line becomes longer (i.e. red shift phenomenon); conversely, if the particles move toward the observation point, the measured wavelength becomes shorter (i.e., blue shift phenomenon). The movement speed of the particles can be calculated by measuring the offset of the characteristic spectral line of the particles.
Preferably, the spectrometer uses Zolix λ 5008i, CCD model Ador Du-897D-C00-BV. The included angle theta between the observation direction and the particle motion direction is any angle.
By the plasma parameter measuring method of the plasma wind tunnel, the measured plasma electron density and beam velocity measuring error is less than 0.01mm, the associated resolution is less than 0.5 degrees, the comprehensive error is less than 0.16 percent, and the plasma parameters are accurately measured on the premise of not interfering the plasma beam.
The foregoing description is only exemplary of the preferred embodiments of the invention and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention herein disclosed is not limited to the particular combination of features described above, but also encompasses other arrangements formed by any combination of the above features or their equivalents without departing from the spirit of the invention. For example, the above features and (but not limited to) features having similar functions disclosed in the present invention are mutually replaced to form the technical solution.
Claims (7)
1. A plasma parameter measuring method based on a plasma wind tunnel is characterized by comprising the following steps:
step S1, before the laminar plasma is input into the plasma wind tunnel, the same phase of the transmitting antenna and the receiving antenna is adjusted through a vector network analyzer;
s2, controlling the laminar plasma source to input laminar plasma into the plasma wind tunnel by the laminar plasma source power/working medium input port, and forming plasma beam current in the wind tunnel between the transmitting antenna and the receiving antenna by the laminar plasma through the coil and the magnetic field;
step S3, measuring the diameter of the plasma beam;
step S4, the vector network analyzer measures the phase difference between the receiving antenna and the transmitting antenna after the laminar plasma is input; calculating the electron density of the plasma beam according to the phase difference and the diameter of the plasma beam;
and step S5, setting the jet direction of the collimating mirror of the spectrometer, which is opposite to the plasma beam, and the included angle between the jet direction of the collimating mirror of the spectrometer and the motion direction of the plasma beam to be theta, measuring the offset of the characteristic spectral line of the plasma particles by the spectrometer, and calculating the plasma beam speed according to the offset.
2. The method of claim 1, wherein in step S4, the calculating the electron density of the plasma beam current adopts formula (1):
in the formula (1), NeIs the electron density of the plasma beam, f0Is the frequency of the microwave signal and,
for phase difference, L is the plasma beam diameter.
3. The method of claim 1, wherein the step of calculating the beam current velocity of the plasma according to the offset in step S5 adopts formula (2):
△λ＝(λvcosθ)/c (2)
in the formula (2), Δ λ is an offset, λ is a characteristic spectral line wavelength, v is a particle motion speed, θ is an included angle between an observation direction and the particle motion direction, and c is a light speed.
4. The plasma parameter measurement method according to any one of claims 1 to 3, wherein the vector network analyzer has a frequency range of 10MHz to 43.5GHz, a microwave signal with a central frequency of 30.5GHz and a bandwidth of 1 KHz.
5. The plasma parameter measurement method according to any one of claims 1 to 3,
the laminar plasma comes from an argon lamp light source;
the spectrometer measures offsets of 840.8nm and 842.4nm spectral lines of Ar I, calculates two beam velocities and averages the two beam velocities to obtain the final calculated beam velocity.
6. A method as claimed in any one of claims 1 to 3, wherein the vector network analyser uses microwave signals and/or helical wave discharge structure rf power input signals for communication between the transmitting and receiving antennas.
7. The plasma parameter measurement method according to claim 6, wherein when a microwave signal and a helicon wave discharge structure radio frequency power input signal are adopted, plasma density and beam current velocity under the two signals are respectively measured, and an average value of the two measurements is taken as a parameter measurement result.
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| CN115683538A (en) * | 2022-11-25 | 2023-02-03 | 中国空气动力研究与发展中心低速空气动力研究所 | Wind tunnel dust environment simulation device and method based on plasma excitation |
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