CN114423137B - Resonance laser interferometer for diagnosing particle number density in divertor plasma - Google Patents
Resonance laser interferometer for diagnosing particle number density in divertor plasma Download PDFInfo
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- CN114423137B CN114423137B CN202210180323.8A CN202210180323A CN114423137B CN 114423137 B CN114423137 B CN 114423137B CN 202210180323 A CN202210180323 A CN 202210180323A CN 114423137 B CN114423137 B CN 114423137B
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- H—ELECTRICITY
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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
- H05H1/0012—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry
- H05H1/0025—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry by using photoelectric means
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- H—ELECTRICITY
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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
- H05H1/0012—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry
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Abstract
The invention discloses a resonance laser interferometer for diagnosing the particle number density in a plasma of a divertor. The interferometer comprises a frequency stabilization laser, a tunable laser, a Faraday isolator, a beam splitting device, an acousto-optic crystal, an acousto-optic modulation driver, an optical fiber coupler, a beam combining device, a photoelectric detector, a narrow-band filter, a polaroid, a wavemeter, a 1/2 wave plate, an optical fiber jumper, a cage bar and a signal acquisition and processing system. The absolute value of the number density of neutral particles needs to be calibrated by the traditional spectrum measurement technology. The invention adopts a resonance interferometer to obtain the phase shift dispersion relation of hydrogen atoms in a specific energy state through frequency sweep by utilizing the dispersion effect of atoms on laser, and can give the absolute number density of the hydrogen atoms. Furthermore, lasers with different frequencies and optical path components can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of various other particle number densities, and the multi-beam laser is spatially arranged to realize the spatially resolved measurement of the particle number density in the plasma.
Description
Technical Field
The invention belongs to the technical field of plasma diagnosis, and particularly relates to a resonance laser interferometer for diagnosing the particle number density in a divertor plasma.
Background
The divertor is a critical plasma component that is subjected to steady state heat and particle flow in the tokamak for directing charged particles of the central plasma sheath toward the divertor target plate to reduce the thermal load of the first wall. The plasma in this region is reduced in energy and ionization rate, and the charged particles recombine to produce a large number of neutral particles. The plasma parameter diagnosis of the Tokamak divertor region is to realize the off-target of the divertor and understand the basic work of the divertor physics. Current divertor plasma diagnostic methods fall broadly into two categories: electrostatic probe method, optical diagnostic method.
The electrostatic probe belongs to invasive measurement, can generate disturbance to plasma, and is also required to consider damage caused by strong current and strong thermal load when being applied to the diagnosis of the divertor plasma. Optical diagnostic methods include emission spectroscopy, absorption spectroscopy, laser-induced fluorescence spectroscopy, and laser interferometry. The emission spectrometry is used for researching plasma parameters by measuring particle emission lines in the plasma. However, due to the complexity of the plasma environment, the resolution of the spectral lines is very difficult. On the basis of an emission spectrometry, the laser-induced fluorescence spectrometry utilizes the population of laser disturbance particles to measure the scattered light intensity, and has high spatial resolution and sensitivity. Absorption spectroscopy uses the absorption of a specific frequency laser by particles to diagnose a plasma parameter. A common difficulty in spectroscopically diagnosing plasma neutral particle number density is that a light intensity calibration is required.
The laser interferometry can directly give the absolute number density of particles, no calibration is needed, and the numerical value is more accurate. Conventional laser interferometry is primarily concerned with electron number density.
Disclosure of Invention
The invention aims to provide a resonance laser interferometer for diagnosing the number density of particles in plasma of a divertor, which is a dual-wavelength resonance heterodyne laser interferometer for diagnosing the number density of neutral hydrogen atoms in plasma of a tokamak divertor. The interferometer comprises a laser source module, a plasma measuring module and an interference module. The laser source module is composed of a frequency-stabilized laser, a tunable laser, a polaroid, a reflector, a first beam splitting and combining lens, a Faraday isolator, an acousto-optic crystal, an acousto-optic modulation driver, a first optical fiber coupler, a second optical fiber coupler and a wavelength meter. The third optical fiber coupler, the fourth optical fiber coupler, the fifth optical fiber coupler, the sixth optical fiber coupler, the cage bar and the clamp jointly form the plasma measuring module. The interference module is composed of a seventh optical fiber coupler, an eighth optical fiber coupler, a half wave plate, a second beam splitting and combining lens, a first narrow-band filter, a second narrow-band filter, a first photoelectric detector, a second photoelectric detector and a signal acquisition and processing system. The laser source module is connected with the plasma measuring module and the plasma measuring module is connected with the interference module through optical fiber jumpers. And the acousto-optic modulation driver is connected with the acousto-optic crystal by using a wire. The third optical fiber coupler and the fourth optical fiber coupler are fixed with the plasma source to be measured through a clamp. The signal acquisition processing system is connected with a computer and two photoelectric detectors; all other devices are fixed on the optical platform according to the positions and sequences shown in fig. 1, and the relative positions among the devices are fixed by using cage bars and cage plates.
In the conventional spectrum measurement technology, the absolute value of the number density of neutral particles needs to be calibrated. The absolute number density of particles is given by measuring the phase shift by adopting an interferometry method, and calibration is not needed; different from the fact that non-resonance interferometry can only measure electron number density, the resonance interferometry utilizes the dispersion effect of atoms on laser, and the phase shift dispersion relation of hydrogen atoms in a specific energy state is obtained through frequency sweeping, so that the number density of the hydrogen atoms is given. The laser source module, the plasma measuring module and the interference module which form the whole interferometer are connected through optical fibers, so that the interferometer is simple to install and is suitable for complex measuring application scenes. The resonance interferometry used in the invention utilizes the resonance effect when the laser frequency approaches the transition frequency of the hydrogen atoms in a specific energy state to measure the number density of the hydrogen atoms. One stable frequency helium-neon laser and one tunable laser are used in the measurement. The frequency (wavelength) of the tunable laser is changed, and the tunable laser sweeps around the atomic characteristic spectral line of the designated energy state. The free electrons are close to the laser dispersion of two paths of similar wavelengths, and the hydrogen atoms with the specified energy states are obvious to the dispersion of tunable laser. The phase shift difference of the two paths of lasers carries information of hydrogen atoms in a specified energy state, and the number density of neutral particles in the specified energy state is obtained through analysis of a phase shift dispersion curve.
The laser source module is not limited to two lasers, and can select lasers with different frequencies (or frequency ranges) and optical path components to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of various other particle number densities, and the multi-beam laser is spatially arranged to realize the spatially resolved measurement of the particle number density in the plasma.
The invention adopts the following technical scheme:
a resonance laser interferometer for diagnosing the particle number density in the plasma of a divertor comprises a laser source module, a plasma measuring module and an interference module; the laser source module is sequentially connected with the plasma measuring module and the interference module.
Further, the laser source module comprises a tunable laser, a frequency stabilization laser, a polaroid, a first beam splitting and combining mirror, a reflecting mirror, a wavelength meter, a Faraday isolator, an acousto-optic crystal, an acousto-optic modulation driver, a first optical fiber coupler and a second optical fiber coupler. Wherein the frequency stabilized laser may be selected from, but not limited to, a frequency stabilized helium-neon laser. One path of laser output by the frequency stabilization laser is emitted to the first beam splitting and combining lens through the polarizing plate and the reflecting mirror; the tunable laser outputs one path of laser to the first beam splitting and combining lens; the two laser beams are combined at the first beam splitting and combining lens, and then split into two paths of laser outputs. Both output lasers comprise lasers output by a tunable laser and a frequency stabilization laser. One of the two laser beams is incident to the wavemeter; the other path of the light passes through the Faraday isolator to be incident on the acousto-optic crystal. Two paths of laser are emitted from the acousto-optic crystal, and one path of laser is incident into the first optical fiber coupler; the other path is incident to the second optical fiber coupler. The tunable laser and the frequency-stabilized laser are fixed on an optical platform, and the polarizing plate, the first beam splitting and combining lens, the Faraday isolator, the acousto-optic crystal, the first optical fiber coupler and the second optical fiber coupler are fixed on the optical platform after being connected and fixed at relative positions by using cage bars.
Further, the plasma measurement module comprises a third optical fiber coupler, a fourth optical fiber coupler, a fifth optical fiber coupler, a sixth optical fiber coupler, a cage bar and a clamp. One path of laser emitted from the third optical fiber coupler passes through the plasma to be measured and then enters the fourth optical fiber coupler. And one path of laser is emitted from the fifth optical fiber coupler and enters the sixth optical fiber coupler.
Preferably, the fifth optical fiber coupler and the sixth optical fiber coupler are fixed on the optical platform after being connected and fixed in relative positions by using a cage bar; the third optical fiber coupler and the fourth optical fiber coupler are fixed with the plasma source to be measured through a clamp. The plasma source to be measured generates plasma to be measured.
Further, the interference module comprises a seventh optical fiber coupler, an eighth optical fiber coupler, a half-wave plate, a second beam splitting and combining lens, a first narrow-band filter, a second narrow-band filter, a cage bar, a first photoelectric detector, a second photoelectric detector and a signal acquisition and processing system; one path of laser emitted from the seventh optical fiber coupler enters the second beam splitting and combining lens through the half-wave plate; one path of laser is emitted from the eighth optical fiber coupler and enters the second beam splitting and combining lens; the two paths of laser beams are combined and interfered at the second beam splitting and combining lens, and then split into two paths of laser beams for output. One path of the light passes through the first narrow-band filter and irradiates the first photoelectric detector; the other path of the light passes through the second narrow-band filter plate and is shot to the second photoelectric detector. The seventh optical fiber coupler, the eighth optical fiber coupler, the half wave plate, the second beam splitting and combining lens, the two narrow-band filters and the two photoelectric detectors are connected by using cage bars, and are fixed on the optical platform after the relative positions are fixed.
Further, the laser source module is composed of a frequency stabilization laser, a polaroid, a reflecting mirror, a tunable laser, a first beam splitting and combining mirror, a Faraday isolator, an acousto-optic crystal, an acousto-optic modulation driver, a first optical fiber coupler, a second optical fiber coupler and a wavelength meter.
Further, the third optical fiber coupler, the fourth optical fiber coupler, the fifth optical fiber coupler, the sixth optical fiber coupler, the cage bar and the clamp jointly form the plasma measuring module.
Further, an interference module is formed by a seventh optical fiber coupler, an eighth optical fiber coupler, a half-wave plate, a second beam splitting and combining lens, a first narrow-band filter, a second narrow-band filter, a cage bar, a first photoelectric detector, a second photoelectric detector and a signal acquisition and processing system.
Further, the laser source module is connected with the plasma measuring module through an optical fiber jumper. The plasma measuring module is connected with the interference module through an optical fiber jumper. And the acousto-optic modulation driver is connected with the acousto-optic crystal by using a wire. The third optical fiber coupler and the fourth optical fiber coupler are fixed with the plasma source to be measured through a clamp. The signal acquisition processing system is connected with the computer and the two photoelectric detectors. All other devices are fixed on the optical platform according to the positions and sequences shown in fig. 1, and the relative positions among the devices are fixed by using cage bars and cage plates.
Further, the laser source module emits two laser beams through the first optical fiber coupler and the second optical fiber coupler, wherein one laser beam is used as detection light, and the other laser beam is used as reference light. Each laser contains two laser frequencies, where the tunable laser frequencies can be varied.
Further, the laser source module is not limited to two lasers, and lasers with different frequencies (or frequency ranges) and optical path components can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of various other particle number densities, and the multi-beam laser is spatially arranged to realize the spatially resolved measurement of the particle number density in the plasma.
Further, a detection arm is formed by a third optical fiber coupler and a fourth optical fiber coupler in the plasma measuring module to guide the detection beam laser to pass through the plasma.
Further, the fifth fiber coupler and the sixth fiber coupler form a reference arm to compensate the laser optical path of the reference beam. The interference module adopts, but is not limited to, a Mach-Zehnder interferometer optical path, and other general interference optical paths are applicable to the module.
Further, the tunable laser 1 located at the laser source module outputs a beam of linearly polarized light with a frequency ω. The frequency stabilized laser 2 outputs a beam of frequency omega H Is adjusted to have a frequency omega by adjusting the polarization direction of the linear polarization plate 3 H The polarization direction of the linear polarization is consistent with the polarization direction of the linear polarization with the frequency omega, and then the frequency omega H The linear polarized light with the frequency omega is combined with the linear polarized light with the frequency omega through the reflector 5 and then split through the first beam splitting and combining lens 4, and one path of the linear polarized light is incident to the wavemeter 6 to monitor the laser frequency in real time; the other path goes through Faraday isolator 7 to acousto-optic crystal 8. The acousto-optic modulation driver 9 supplies modulation voltage to the acousto-optic crystal 8. The acousto-optic crystal 8 outputs the 0 level light and the-1 level light of the difference frequency. The 0-level light as the detection light sequentially passes through the first optical fiber coupler 10, the first optical fiber jumper 25, the third optical fiber coupler 12, the plasma 16 to be detected, the fourth optical fiber coupler 13, the second optical fiber jumper 26, the seventh optical fiber coupler 17 and the half-wave plate 19. The level-1 light sequentially passes through the second optical fiber coupler 11, the third optical fiber jumper 27, the fifth optical fiber coupler 14, the sixth optical fiber coupler 15, the fourth optical fiber jumper 28 and the eighth optical fiber coupler 18 as reference light, and then is combined with the second half optical fiber couplerThe 0-order light emitted from the wave plate 19 interferes at the second beam splitting/combining mirror 20.
The beneficial effects are that:
the invention adopts a resonance interferometry to measure the phase shift to give the absolute number density of the hydrogen atoms, and no calibration is needed; unlike non-resonant interference, which can only measure electron number density, the resonant interference method uses the dispersive effect of atoms on laser and obtains the phase shift dispersion relation of hydrogen atoms in specific energy state through frequency sweep. Furthermore, lasers with different frequencies (or frequency ranges) and optical path components can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of various other particle number densities, and the multi-beam laser is spatially arranged to realize the spatially resolved measurement of the particle number density in the plasma. The three modules forming the whole interferometer are connected through optical fibers, so that the interferometer is simple to install and is suitable for complex measurement application scenes. The invention breaks through the limitation that the traditional laser interferometer can only measure the electron number density. The invention can be used for interference diagnosis of the absolute number density of the atomic number of the divertor plasma H (n=2). The measuring principle of the invention can be used for measuring the density of neutral particles with different energy states and different types.
Drawings
FIG. 1 is a schematic diagram of a dual wavelength heterodyne resonant laser interferometer apparatus.
Meaning of each figure number in fig. 1: 1-tunable laser, 2-stable frequency laser, 3-polarizer, 4-first beam splitting and combining mirror, 5-reflector, 6-wavemeter, 7-Faraday isolator, 8-acousto-optic crystal, 9-acousto-optic modulation driver, 10-first optical fiber coupler, 11-second optical fiber coupler, 12-third optical fiber coupler, 13-fourth optical fiber coupler, 14-fifth optical fiber coupler, 15-sixth optical fiber coupler, 16-plasma to be measured (position shown between third optical fiber coupler and fourth optical fiber coupler, for measuring object, except that the third optical fiber coupler and fourth optical fiber coupler are connected to device window for generating plasma to be measured by clamp, the rest is not limited), 17-seventh optical fiber coupler, 18-eighth optical fiber coupler, 19-half-waveplate, 20-second beam splitting and combining mirror, 21-first narrow band filter (center wavelength 632.8 nm), 22-first photoelectric detector, 23-second narrow band filter (center wavelength 656 nm), 24-second optical fiber coupler, second optical fiber jumper, 25-third optical fiber jumper, and fourth optical fiber jumper wire, 28-third optical fiber jumper wire. The thin line path en route indicates that the laser propagates in the form of spatial light, and the thick line indicates that the laser propagates within the fiber optic patch cord. The dashed boxes mark the three modules that make up the interferometer.
FIG. 2 different alpha ji Value linear function P (u) ji ,α ji )。
Detailed Description
The invention will now be described in detail with reference to the accompanying drawings and specific embodiments thereof. The following examples are intended to be illustrative only and the scope of the invention is to be construed as including the full breadth of the claims and by the recitation of the following examples, the full breadth of the claims can be fully set forth by those skilled in the art.
The method adopts dual-wavelength resonance heterodyne laser interferometry to measure the first excited state particle number density of the plasma of the tokamak divertor aiming at neutral hydrogen atoms of the plasma, and has the characteristics of strong anti-interference capability, no need of calibration, high spatial resolution and the like.
FIG. 1 is a schematic diagram of a dual wavelength heterodyne resonant laser interferometer apparatus. As shown in fig. 1, the dual-wavelength heterodyne resonant laser interferometer includes three parts, namely a laser source module, a plasma measurement module, and an interference module.
The laser source module is composed of a tunable laser 1, a frequency stabilization laser 2, a polaroid 3, a first beam splitting and combining lens 4, a reflecting lens 5, a wavemeter 6, a Faraday isolator 7, an acousto-optic crystal 8, an acousto-optic modulation driver 9, a first optical fiber coupler 10 and a second optical fiber coupler 11.
One path of laser output by the frequency stabilization laser 2 is emitted to the first beam splitting and combining lens 4 through the polaroid 3 and the reflecting mirror 5 in sequence; the tunable laser 1 outputs one path of laser to emit to the first beam splitting and combining lens 4; the two laser beams are combined at the first beam splitting and combining lens 4, and then split into two paths of laser outputs. Both the output laser beams comprise laser beams output by the tunable laser 1 and the frequency stabilization laser 2. One of the two laser beams is incident to the wavemeter 6; the other path of the light passes through the Faraday isolator 7 to be incident on the acousto-optic crystal 8. Two paths of laser are emitted from the acousto-optic crystal 8, and one path of laser is incident to the first optical fiber coupler 10; the other path is incident on the second fiber coupler 11.
The tunable laser 1 and the frequency stabilization laser 2 are both fixed on an optical platform. The polarizer 3, the first beam splitting and combining lens 4, the Faraday isolator 7, the acousto-optic crystal 8, the first optical fiber coupler 10 and the second optical fiber coupler 11 are all connected by using cage bars, and are fixed on an optical platform after the relative positions are fixed. A wire connection is used between the acousto-optic modulation driver 9 and the acousto-optic crystal 8. The third optical fiber coupler 12, the fourth optical fiber coupler 13, the fifth optical fiber coupler 14, the sixth optical fiber coupler 15, the cage bar and the clamp form a plasma measuring module together.
One path of laser light emitted from the third optical fiber coupler 12 passes through the plasma 16 to be measured and then enters the fourth optical fiber coupler 13. One path of laser light is emitted from the fifth optical fiber coupler 14 and enters the sixth optical fiber coupler 15. The fifth optical fiber coupler 14 and the sixth optical fiber coupler 15 are connected by using a cage bar, and are fixed on the optical platform after the relative positions are fixed. The third fiber coupler 12 and the fourth fiber coupler 13 are respectively fixed with the plasma source to be measured through clamps. In the present invention, the plasma 16 to be measured is a partial filter region plasma to be measured.
The interference module is composed of a seventh optical fiber coupler 17, an eighth optical fiber coupler 18, a half-wave plate 19, a second beam splitting and combining lens 20, a first narrow-band filter 21, a second narrow-band filter 23, a cage bar, a first photoelectric detector 22, a second photoelectric detector 24 and a signal acquisition and processing system.
One path of laser emitted from the seventh optical fiber coupler 17 enters the second beam splitting and combining lens 20 through the half-wave plate 19; one path of laser is emitted from the eighth optical fiber coupler 18 and enters the second beam splitting and combining lens 20; the two laser beams are combined and interfered at the second beam splitting and combining lens 20, and then split into two laser beams for output. One path of the light passes through the first narrow-band filter 21 and irradiates to the first photoelectric detector 22; the other path of the light passes through the second narrow-band filter 23 and is emitted to the second photoelectric detector 24. The signal acquisition processing system is connected with the computer, the first photoelectric detector 22 and the second photoelectric detector 24 respectively.
The first fiber coupler 10 is connected to the third fiber coupler 12 by a first fiber jumper 25. The fourth fiber coupler 13 is connected to the seventh fiber coupler 17 by a second fiber jumper 26. The second fiber coupler 11 is connected to the fifth fiber coupler 14 by a third fiber jumper 27. The sixth fiber coupler 15 is connected to the eighth fiber coupler 18 by a fourth fiber jumper 28.
The seventh optical fiber coupler 17, the eighth optical fiber coupler 18, the half-wave plate 19, the second beam splitting and combining lens 20, the two narrow-band filters and the two photodetectors are connected by using cage bars, and are fixed on the optical platform after the relative positions are fixed.
The laser source module is connected with the plasma measuring module and the plasma measuring module is connected with the interference module through optical fiber jumpers. The acousto-optic modulation driver 9 and the acousto-optic crystal 8 are connected by a wire; the third fiber coupler 12 and the fourth fiber coupler 13 are fixed with the plasma source to be measured (the position is shown between the third fiber coupler and the fourth fiber coupler, which are objects to be measured, except that the third fiber coupler and the fourth fiber coupler are connected with the window of the device for generating the plasma to be measured through the fixture, and the rest is not limited). The plasma source to be measured generates a plasma 16 to be measured. The signal acquisition processing system is connected to the computer and the first and second photodetectors 22 and 24, respectively. The electric signal measured by the first photodetector 22 is transmitted to a signal acquisition and processing system, and the signal acquisition and processing system converts the electric signal into a phase signal in a phase discrimination mode and then transmits the phase signal to a computer. The electrical signal measured by the second photodetector 24 is transmitted to a signal acquisition and processing system, and the signal acquisition and processing system converts the electrical signal into a phase signal by phase discrimination and then transmits the phase signal to a computer. All other devices are fixed on the optical platform according to the positions and sequences shown in fig. 1, and the relative positions among the devices are fixed by using cage bars and cage plates.
The tunable laser 1 at the laser source module outputs a beam of linearly polarized light of frequency ω. The frequency stabilized laser 2 outputs a beam of frequency omega H Is adjusted to have a frequency omega by adjusting the polarization direction of the linear polarization plate 3 H Is polarized in the direction of linear polarization and the frequencyThe linear polarization direction of the rate omega is consistent, and then the frequency omega H The linear polarized light with the frequency omega is combined with the linear polarized light with the frequency omega through the reflector 5 and then split through the first beam splitting and combining lens 4, and one path of the linear polarized light is incident to the wavemeter 6 to monitor the laser frequency in real time; the other path goes through Faraday isolator 7 to acousto-optic crystal 8. The acousto-optic modulation driver 9 supplies modulation voltage to the acousto-optic crystal 8. The acousto-optic crystal 8 outputs 0-level light and-1-level light of the difference frequency, and the 0-level light sequentially passes through the first optical fiber coupler 10, the first optical fiber jumper 25, the third optical fiber coupler 12, the plasma 16 to be measured, the fourth optical fiber coupler 13, the second optical fiber jumper 26, the seventh optical fiber coupler 17 and the half-wave plate 19 as detection light, and then interferes with the-1-level light emitted from the eighth optical fiber coupler 18 at the second beam splitting and combining lens 20.
The level 1 light then passes through the second fiber coupler 11, the third fiber jumper 27, the fifth fiber coupler 14, the sixth fiber coupler 15, the fourth fiber jumper 28 and the eighth fiber coupler 18 in this order as reference light, and then interferes with the level 0 light exiting from the half-wave plate 19 at the second beam splitting/combining mirror 20. The half wave plate 19 makes the polarization angle of the detection light passing through the plasma coincide with that of the-1 level reference light. The reference light and the detection light are combined, interfered and re-split by the second beam splitting and combining mirror 20, and one path passes through the center wavelength lambda 1 The first narrowband filter 21 is received by the first photodetector 22=632.8nm; the other path passes through the center wavelength lambda 2 A second narrow-band filter 23 of =656 nm is received by a second photodetector 24.
The laser source module emits two laser beams, one as probe light and one as reference light, through the first optical fiber coupler 10 and the second optical fiber coupler 11. Each laser contains two laser frequencies, where the tunable laser frequencies can be varied. Optionally, the laser source module is not limited to two lasers, and lasers with different frequencies and optical path components can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of various other particle number densities, and the multi-beam laser is spatially arranged to realize the spatially resolved measurement of the particle number density in the plasma.
In the plasma measuring module, a detection arm is formed by a third optical fiber coupler 12 and a fourth optical fiber coupler 13 to guide the laser of the detection beam to pass through plasma.
The fifth fiber coupler 14 and the sixth fiber coupler 15 form a reference arm compensating reference beam laser path.
The interference module adopts, but is not limited to, a Mach-Zehnder interferometer optical path, and other general interference optical paths are applicable to the module.
The first photoelectric detector 22 and the second photoelectric detector 24 respectively convert the interference light signals into electric signals, the electric signals are subjected to digital filtering by a signal acquisition processing system, then phase discrimination is performed, and phase signals obtained by phase discrimination are then transmitted to a computer; the phase discrimination algorithm specifically adopts a discrete Hilbert transformation mode to obtain the complex amplitude of the measured electric signal, and then obtains the frequency-stabilized laser phase signal
And a tunable laser phase signal->
Changing the tunable laser frequency, recording the phase signal difference of two lasers under different tunable laser frequencies by a signal acquisition processing system, and obtaining the number density n of hydrogen atoms in the plasma to be measured after data processing according to a measurement principle i 。
Measurement principle:
frequency stabilized helium-neon laser wavelength
Tunable laser wavelength +.>
Can vary from 656.1nm to 656.5 nm. Wherein omega H Is the frequency of the frequency-stabilized helium-neon laser, and has the unit of s -1 Omega is the tunable laser frequency and the unit is s -1 C is the speed of light in vacuum, the unit is m.s -1 。
For the acquired phase signal
And->
The respective terms can be expressed as:
wherein the formula (1) represents the phase signal of the collected corresponding tunable laser
The first term on the right side of formula (1) relates to the characteristic of a hydrogen atom in a specific energy state in rad; the formula (2) represents the collected phase signal of the corresponding frequency stabilized helium-neon laser
The unit is rad. Omega in H Is the frequency of the frequency-stabilized helium-neon laser, and has the unit of s -1 Omega is the tunable laser frequency and is given by s -1 ，n i For a selected particle number density, the unit is m -3 ，f ji L is the path length of laser in plasma for transition element intensity from specific lower energy level i to corresponding upper energy level j, and the unit is m, < >>
For Doppler spread, the unit is s -1 In the Doppler spread expression, ω ij To transition from a particular lower energy level i to a corresponding upper energy level j, the unit is s -1 C is the speed of light in vacuum, in m.s -1 ，k B Represents Boltzmann constant, T i Is the hydrogen atom temperature in the specific energy state, the unit is K, M is the mass of the selected particles, the unit is kg,/L>
Is a linear function, and r is expressed in the linear function expression 0 Is the classical electron radius, the unit is m, < >>
To normalize the frequency of incident light, the unit is s -1 ，/>
For normalized full width at half maximum, gamma ji For collision broadening, the unit is s -1 。/>
The total non-resonant phase shift in rad, which is the total non-resonant phase shift of the other components (mainly free electrons), is generally much smaller than the resonant phase shift and the dispersion is very small. />
The phase shift in rad, which is caused by various vibrations, is mainly concentrated in the low frequency region.
By applying phase signals
And->
By contrast, a phase difference Φ (ω) relating to only hydrogen atoms of a specific energy state is obtained:
wherein omega H Is the frequency of the frequency-stabilized helium-neon laser, and has the unit of s -1 Omega is the tunable laser frequency and is given by s -1 ，n i For a selected particle number density, the unit is m -3 ，f ji For the transition element intensity from a particular lower energy level i to the corresponding upper energy level j, L is the path length of the laser in the plasma, in m,
for Doppler spread, the unit is s -1 In the Doppler spread expression, ω ij To transition from a particular lower energy level i to a corresponding upper energy level j, the unit is s -1 C is the speed of light in vacuum, in m.s -1 ，k B Represents Boltzmann constant, T i Is the hydrogen atom temperature in the specific energy state, the unit is K, M is the mass of the selected particles, the unit is kg,/L>
Is a linear function, and r is expressed in the linear function expression 0 Is the classical electron radius, the unit is m, < >>
To normalize the frequency of incident light, the unit is s -1 ，/>
For normalized full width at half maximum, gamma ji For collision broadening, the unit is s -1 。
FIG. 2 shows a different alpha ji Linear function of value P (u ji ,α ji ). When alpha is ji When the condition < 1 is satisfied, it can be observed that Pmax always occurs at u ji At = -1. Experimental measurement of the frequency ω at which the maximum of the phase shift occurs max And a center frequency omega 0 The difference between them can be used to estimate beta ji Is a value of (2).
Tokamak divertor region plasma with high temperature and low pressure features, collision broadening gamma ji Much smaller than Doppler broadening beta ji Meets the assumption condition
The frequency omega of the tunable laser 1 is changed,obtain corresponding +.>
And->
The difference gives the phase shift-frequency relationship phi (omega). At alpha ji Under the condition of < 1, the frequency omega corresponding to the maximum phase shift max And a center frequency omega 0 Give beta ji Is used for the estimation of the estimated value of (a). Beta will be ji And (2) carrying back the estimated value of (3), and obtaining the parameter alpha by fitting the phase shift dispersion relation phi (omega) obtained by measurement ji And a hydrogen atom specific energy state particle number density n i 。
The method is used for measuring the first excited state number density of the plasma hydrogen atoms of the Tokamak divertor, and the measuring principle and the measuring method can be suitable for measuring other energy levels of the H atoms; at the same time, the free electron number density can be given. The invention can realize the spatial resolution measurement of a plurality of other particle number densities of plasmas through the output of multiple frequency and multiple laser beams. The present invention is not described in detail in part as being well known to those skilled in the art. The above examples are merely illustrative of preferred embodiments of the invention, which are not exhaustive of all details, nor are they intended to limit the invention to the particular embodiments disclosed. Various modifications and improvements of the technical scheme of the present invention will fall within the protection scope of the present invention as defined in the claims without departing from the design spirit of the present invention.
Claims (3)
1. The resonance laser interferometer for diagnosing the particle number density in the plasma of the divertor is characterized by comprising a laser source module, a plasma measuring module and an interference module; the laser source module is sequentially connected with the plasma measuring module and the interference module;
the laser source module comprises a tunable laser (1), a frequency stabilization laser (2), a polaroid (3), a first beam splitting and combining lens (4), a reflecting mirror (5), a wavelength meter (6), a Faraday isolator (7), an acousto-optic crystal (8), an acousto-optic modulation driver (9), a first optical fiber coupler (10) and a second optical fiber coupler (11);
one path of laser output by the frequency-stabilizing laser (2) is emitted to the first beam splitting and combining mirror (4) through the polaroid (3) and the reflecting mirror (5) in sequence; the tunable laser (1) outputs one path of laser to emit to the first beam splitting and combining lens (4); the two laser beams are combined at the first beam splitting and combining lens (4) and then split into two paths of laser beams to be output, the two paths of output laser beams comprise laser beams output by the tunable laser (1) and the frequency stabilization laser (2), one path of the two paths of laser beams enters the wavemeter (6), and the other path of laser beams enters the acousto-optic crystal (8) through the Faraday isolator (7); two paths of laser are emitted from the acousto-optic crystal (8), wherein one path of laser is incident to the first optical fiber coupler (10), and the other path of laser is incident to the second optical fiber coupler (11);
the tunable laser (1) and the frequency-stabilized laser (2) are respectively fixed on an optical platform, and the polarizer (3), the first beam splitting and combining lens (4), the Faraday isolator (7), the acousto-optic crystal (8), the first optical fiber coupler (10) and the second optical fiber coupler (11) are fixed on the optical platform after being connected and fixed at relative positions by using cage bars; the acousto-optic modulation driver (9) is connected with the acousto-optic crystal (8) by a wire;
the plasma measurement module comprises a third optical fiber coupler (12), a fourth optical fiber coupler (13), a fifth optical fiber coupler (14), a sixth optical fiber coupler (15), a cage bar and a clamp; one path of laser emitted from the third optical fiber coupler (12) passes through the plasma (16) to be detected and then enters the fourth optical fiber coupler (13); one path of laser is emitted from the fifth optical fiber coupler (14) and enters the sixth optical fiber coupler (15);
the fifth optical fiber coupler (14) and the sixth optical fiber coupler (15) are connected by using a cage bar to fix the relative positions and then are fixed on the optical platform; the third optical fiber coupler (12) and the fourth optical fiber coupler (13) are respectively fixed with a plasma source to be measured through clamps;
the interference module comprises a seventh optical fiber coupler (17), an eighth optical fiber coupler (18), a half-wave plate (19), a second beam splitting and combining lens (20), a first narrow-band filter (21), a second narrow-band filter (23), a cage bar, a first photoelectric detector (22), a second photoelectric detector (24) and a signal acquisition and processing system; one path of laser emitted from the seventh optical fiber coupler (17) enters the second beam splitting and combining lens (20) through the half-wave plate (19); one path of laser emitted from the eighth optical fiber coupler (18) enters the second beam splitting and combining lens (20); the two paths of laser beams are combined and interfered at the second beam splitting and combining lens (20), and then split into two paths of laser beams to be output, wherein one path of laser beam is emitted to the first photoelectric detector (22) through the first narrow-band filter (21), and the other path of laser beam is emitted to the second photoelectric detector (24) through the second narrow-band filter (23); the signal acquisition processing system is respectively connected with the computer, the first photoelectric detector (22) and the second photoelectric detector (24);
the seventh optical fiber coupler (17), the eighth optical fiber coupler (18), the half-wave plate (19), the second beam splitting and combining lens (20), the two narrow-band filter plates and the two photoelectric detectors are connected by using cage bars, and are fixed on an optical platform after the relative positions are fixed;
the laser source module is connected with the plasma measuring module through an optical fiber jumper, and the plasma measuring module is connected with the interference module through the optical fiber jumper.
2. Interferometer according to claim 1, characterized in that the number of frequency-stabilized lasers (2) and/or the number of tunable lasers (1) are each independently plural and that the frequency of the frequency-stabilized laser output laser and the frequency range of the tunable laser output laser can be varied.
3. Interferometer according to claim 1, characterized in that the third fiber coupler (12) and the fourth fiber coupler (13) in the plasma measurement module constitute a detection arm for guiding the detection beam laser through the plasma, and the fifth fiber coupler (14) and the sixth fiber coupler (15) constitute a reference arm for compensating the reference beam laser optical path.
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| US4183671A (en) * | 1978-03-14 | 1980-01-15 | The United States Of America As Represented By The United States Department Of Energy | Interferometer for the measurement of plasma density |
| US5694216A (en) * | 1996-04-25 | 1997-12-02 | University Of Central Florida | Scanning heterodyne acousto-optical interferometers |
| KR100978397B1 (en) * | 2008-06-20 | 2010-08-26 | 한국기초과학지원연구원 | System for analyzing plasma density |
| JP4925139B2 (en) * | 2008-10-31 | 2012-04-25 | 大学共同利用機関法人自然科学研究機構 | Dispersion interferometer and method for measuring physical quantity of object to be measured |
| KR101298990B1 (en) * | 2010-10-25 | 2013-08-23 | 서강대학교산학협력단 | Heterodyne interferometer using AOM |
| CN104931124B (en) * | 2015-06-12 | 2016-04-27 | 哈尔滨工业大学 | Based on dual-acousto-optic modulation and the Michelson heterodyne laser vialog of polarization spectro |
| CN105300274B (en) * | 2015-11-13 | 2018-06-12 | 山东神戎电子股份有限公司 | A kind of heterodyne interferometry system convenient for adjusting splitting ratio |
| CN207219136U (en) * | 2017-05-26 | 2018-04-10 | 中国工程物理研究院流体物理研究所 | Optical-fiber laser interference electron density measurement system based on mathematics method of comparison |
| KR102253837B1 (en) * | 2020-04-23 | 2021-05-20 | 한국핵융합에너지연구원 | Plasma density measuring apparatus using dispersion interferometer with single passing non-linear crystal and plasma density measuring method using the same |
| CN113970863A (en) * | 2021-11-15 | 2022-01-25 | 浙江大学 | Acousto-optic isolator based on Mach-Zehnder interferometer and application method thereof |
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