JPH0640102B2 - Laser gas velocity and temperature measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention measures the flow velocity and temperature of a gas in a plasma state individually or simultaneously using laser light, and determines the spatial distribution of those amounts inside the plasma. It concerns a method that can be measured.

(Prior Art) There are many methods for obtaining the gas flow velocity, but it can be applied even under severe conditions regarding gas temperature and pressure, such as the pressure region of plasma and intermediate flow, which are well known in the engineering field. The method of measurement was unknown. For example, the method of using the Pitot tube, which is one of the most commonly used ones, cannot be used in a spatially narrow place or a high temperature system, and has a drawback of disturbing the flow. Also, as a method of measuring the flow velocity using a laser beam, recently, a laser topler velocimeter has also been often used, but this requires solid fine particles to flow together with a fluid (Shokai Sho 62 No. 111663), it cannot be used at a low pressure such as an intermediate flow region, and there is a problem that plasma is greatly disturbed when solid fine particles are mixed into a system in a discharged state.

On the other hand, as a method for obtaining the temperature of a gas, a method using a probe such as a thermocouple or a resistance thermometer or a method for measuring thermal radiation is widely used. There is known a method of measuring the Doppler width of the spectrum line generated by the above or a method of obtaining the temperature from the relative intensity of the spectrum line by utilizing the heat distribution of the molecule to the rotational level or the molecular vibration level. However, the method using the probe has the drawback of disturbing the flow,
Further, the method using the spectrum has a drawback that it is necessary to correct the interference from the emission of plasma and the influence from the perturbation acting on the intramolecular energy level. Furthermore, these methods cannot simultaneously measure the gas flow velocity in the plasma state.

(Problems to be Solved by the Invention) In view of such a situation, the present invention can cope with plasma under severe conditions with respect to temperature and pressure of a gas, and can mix solid fine particles as a tracer without disturbing an object to be measured. Provided is a method capable of simultaneously measuring a flow velocity and a temperature for a spatially limited site.

(Means for Solving the Problems) The present invention irradiates a laser beam while sweeping the wavelength of a gas in a plasma state, and determines the intensity of laser-excited emission of gas atoms or molecules (hereinafter collectively referred to as molecules). Gas flow velocity measuring method by laser, characterized by calculating gas flow velocity from Doppler shift of excitation spectrum obtained by measurement, and gas temperature by laser characterized by calculating gas temperature from spectral width of excitation spectrum Measurement method, and the gas flow rate from the Doppler shift of the excitation spectrum, the gas flow rate and temperature measurement method by laser, which is characterized by simultaneously calculating the gas temperature from the spectral width of the excitation spectrum, further laser beam irradiation site and By moving the sampling position of the excitation spectrum, the flow rate of gas inside the plasma and A gas flow velocity and temperature measuring method using a laser, which is characterized by measuring a spatial distribution of temperature.

(Operation) In the present invention, gas molecules themselves in a plasma state are irradiated with laser light in order to avoid mixing of solid fine particles, and the flow velocity and temperature of the gas are calculated by utilizing the excitation spectrum. That is, the gas in the plasma state is in a state in which electrons are excited when it is irradiated with laser light. For example, when He gas is discharged into a plasma state, He atoms excited in a metastable state or an excited state are generated, and He ³ P ₀
The state is obtained. When this is irradiated with laser light while sweeping the wavelength, it excites to a ³ D ₁ state at a specific wavelength, and further emits light to transit to a stable state. Therefore, an excitation spectrum can be obtained by irradiating a gas in a plasma state with laser light while sweeping the wavelength and measuring the intensity of laser-excited emission of gas molecules.

On the other hand, it is known that the absorption and emission of light by gas molecules causes the spectrum to broaden due to the Doppler effect due to the thermal motion of molecules, that is, the effect that the frequency of the light wave absorbed or emitted by the molecules differs depending on the direction and speed of the motion. ing. If the molecules move in one direction as a group of molecules in addition to this random thermal motion, the peak position of the spectrum line should shift due to the Doppler effect due to the macroscopic motion. Therefore, in the present invention, the gas flow velocity is calculated from the Doppler shift of the excitation spectrum. Further, since the line width of the spectrum line reflects the statistical distribution of the thermal motion of the molecule, the width can be measured to calculate the temperature at the same time as the flow velocity.

Furthermore, the diameter of the laser beam is set to 0.1 by using a lens system.
Since the measurement area is limited by concentrating the light to less than 0.5 mm and limiting the size of the excitation spectrum sampling area to 0.5 mm or less using a condenser lens, the optical path of the laser beam and the position of the condenser lens are limited. By moving, the spatial distribution of flow velocity and temperature in the plasma can be measured and mapped.

(Example) In the example, a ring dye laser (line width: about 0.00067 cm) conventionally used for laser spectroscopy of low-pressure discharge of rare gas or molecular gas and its application experiment to plasma diagnosis.
^-1 ), the experiment was carried out paying attention to the fact that if the flow velocity is 100 m / sec or more, sufficient measurement is possible.
Proved it. That is, He is added to the capillary discharge tube.
A gas is caused to discharge to cause a discharge, and a wave number region corresponding to an optical transition from the He ³ P ₀ state to a ³ D ₁ state generated during the discharge is swept with the ring dye laser wave number, and this transition is excited by laser light. ³ by monitoring the intensity of the emitted light
The P ₀ → ³ D ₁ absorption spectrum (excitation spectrum) was observed, and the shift of the peak wave number was measured.

FIG. 2 shows a vacuum system to which a discharge tube is connected. The capillary discharge tube 1 is made of heat-resistant glass, and the inner diameter of the capillary portion is 1 mm and the length is 28 mm. The electrode used was a brass hollow cylindrical type having an inner diameter of 6.3 mm, an outer diameter of 11.7 mm and a length of 18 mm. The discharge tube 1 is connected to a gas supply system and an exhaust system, and a high voltage DC constant current power source 2 is used so that the upstream side becomes a cathode.
Connected to. Exhaust was performed by connecting the oil diffusion pump 3 and the oil rotary pump 4 in series. The flow rate of helium gas was controlled by the mass flow meter 5.

Since He atoms excited in a metastable state or an excited state are generated during the capillary discharge, the present invention is to monitor the emission generated by absorbing the laser light by these He atoms while sweeping the wavelength of the laser light. To obtain the absorption spectrum. As shown in FIG. 1, a ring dye laser 10 excited by an argon ion laser 9 was used as an excitation light source. The output beam of the ring dye laser 10 was intermittently modulated at about 1.3 kHz by the mechanical chopper 11 and then made incident on the discharge tube 1 in parallel with the flow of He gas. Laser-excited light emission from the capillary portion was focused on the iris 13 by the lens 12. Further, a colored glass filter 14 is arranged immediately before the iris 13 in order to remove stray light of the laser light. Light emitted from the capillary passes through the photodetector 15 and the lock-in amplifier 1
Phase-sensitive detection was performed by 6 and recorded by the recorder 18. At this time, the laser excitation spectrum of iodine was recorded in order to know the absolute frequency of the laser beam, and the interference fringes of the Fabry-Perot etalon with a fringe spacing of 500 MHz were recorded at the same time as the spectrum. It should be noted that the capillary discharge tube 1 and the laser-excited luminescence detection system 12, 13, 14, 15 are installed on a micrometer-driven moving table, and their positions are moved to move the respective positions of the laser light irradiation optical path and the laser-excited luminescence. The sampling position of was moved.

The obtained excitation spectrum line is shown in FIG. From the deviation from the original spectrum line, it was found that the average flow velocity was about 300 m / sec under the condition that the pressure difference between both ends of the capillary was about 20 Torr. Also, the gas temperature under a discharge current of 10 mA is 780 K at the upstream end of the capillary and 3.5 to 3.5
It was found that it was 1000K in the 7.5 mm interval and 1500K in the central part.

(Effect of the invention) As described above, the method of the present invention is suitable for simultaneous and three-dimensional measurement of the flow velocity and temperature in the flow velocity region of a general flow discharge, and the measurement method disturbs plasma without contact. Since it does not require as much laser power, it can not only solve the problem of disturbing the flow, which is a common drawback of the conventional methods, but it is also possible to simultaneously obtain the flow velocity and the temperature from the same measurement, In addition, three-dimensional information can be obtained by moving the measurement site.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus used for carrying out the method of the present invention, FIG. 2 is a diagram showing an example of a vacuum system, and FIG. 3 is a diagram showing an excitation spectrum. 1 ... Capillary discharge tube, 2 ... High voltage DC constant current power supply, 3 ... Oil diffusion pump, 4 ... Oil rotary pump, 5 ...
Mass flow meter, 6a, 6b ... Pirani pressure gauge,
7 ... helium gas cylinder, 8 ... oscilloscope,
9 ... Argon ion laser, 10 ... Ring dye laser, 11 ... Mechanical chopper, 12 ... Lens, 13 ... Iris, 14 ... Color glass filter,
15 ... Photodetector, 16 ... Lock-in amplifier, 17 ...
... preamplifier, 18 ... recorder, 19 ... iodine cell, 20 ... photomultiplier tube, 21 ... scanning controller.

Claims (4)

[Claims] 1. A gas flow velocity is calculated from a Doppler shift of an excitation spectrum obtained by irradiating a gas in a plasma state with a laser beam while sweeping a wavelength and measuring the intensity of laser-excited luminescence of an atom or a molecule of the gas. A method for measuring a gas flow velocity by a laser, which is characterized in that: 2. A gas temperature is calculated from the spectral width of an excitation spectrum obtained by irradiating a gas in a plasma state with a laser beam while sweeping the wavelength and measuring the intensity of laser-excited luminescence of an atom or a molecule of the gas. A method for measuring a gas temperature using a laser, which is characterized in that: 3. A gas flow velocity is excited from a Doppler shift of an excitation spectrum obtained by irradiating a gas in a plasma state with a laser beam while sweeping a wavelength and measuring the intensity of laser-excited emission of atoms or molecules of the gas. A gas flow velocity and temperature measuring method using a laser, wherein the gas temperature is calculated at the same time from the spectrum width of the spectrum. 4. The gas flow velocity by the laser according to claim 3, wherein the irradiation position of the laser light and the sampling position of the excitation spectrum are moved to measure the spatial distribution of the flow velocity and temperature of the gas inside the plasma. How to measure temperature.