CN114423137A - Resonance laser interferometer for diagnosing particle number density in plasma of divertor - Google Patents
Resonance laser interferometer for diagnosing particle number density in plasma of divertor Download PDFInfo
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Abstract
The invention discloses a resonant laser interferometer for diagnosing the number density of particles in a plasma of a divertor. The interferometer comprises a frequency stabilized 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, an 1/2 wave plate, an optical fiber jumper, a cage bar and a signal acquisition and processing system. The traditional spectral measurement technology needs calibration for determining the absolute value of the number density of neutral particles. The invention adopts a resonance interferometer to obtain the phase shift dispersion relation of hydrogen atoms in a specific energy state by frequency sweeping by utilizing the dispersion effect of atoms on laser, and can give the absolute density of the hydrogen atoms. Furthermore, lasers and light path components with different frequencies can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of the number density of various other particles, and the spatial array of the multi-beam laser can realize the spatial resolution measurement of the number density of the particles in the plasma.
Description
Technical Field
The invention belongs to the technical field of plasma diagnosis, and particularly relates to a resonant laser interferometer for diagnosing the number density of particles in plasma of a divertor.
Background
The divertor is the key plasma component that bears the steady state heat and particle flow in the tokamak to direct the charged particles of the central plasma sheath toward the divertor target plate to reduce the thermal load on the first wall. The plasma in this region has a reduced energy and ionization rate, and charged particles recombine to produce a large number of neutral particles. The diagnosis of plasma parameters in the tokamak divertor area is the fundamental work for realizing the off-target of the divertor and understanding the physics of the divertor. The existing divertor plasma diagnostic methods are roughly divided into two categories: electrostatic probe method, optical diagnostic method.
The electrostatic probe belongs to invasive measurement, can generate disturbance to plasma, and also needs to consider damage caused by strong current and strong heat load when being applied to plasma diagnosis of a divertor. The optical diagnosis method comprises emission spectroscopy, absorption spectroscopy, laser-induced fluorescence spectroscopy and laser interferometry. Emission spectroscopy studies plasma parameters by measuring the emission lines of particles in the plasma. However, resolution of the spectral lines is very difficult due to the complexity of the plasma environment. On the basis of an emission spectrometry, the laser-induced fluorescence spectrometry utilizes laser to disturb the population number of particles, measures the intensity of scattered light, and has high spatial resolution and sensitivity. Absorption spectroscopy uses the absorption of laser light of a particular frequency by particles to diagnose plasma parameters. A common difficulty with spectroscopic methods for diagnosing plasma population density is that optical intensity calibration is required.
The laser interferometry can directly give the absolute number density of the particles without calibration, and the numerical value is more accurate. The conventional laser interferometry is mainly 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 a plasma of a divertor, and particularly relates to a dual-wavelength resonance heterodyne laser interferometer for diagnosing the number density of neutral hydrogen atoms in the 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 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 wavemeter. And 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 a plasma measuring module. And the 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 mirror, a first narrow-band filter plate, a second narrow-band filter plate, a first photoelectric detector, a second photoelectric detector and a signal acquisition and processing system. The laser source module and the plasma measuring module, and the plasma measuring module and the interference module are connected through optical fiber jumpers. The acousto-optic modulation driver and the acousto-optic crystal are connected by 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 and 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 the sequence shown in the attached figure 1, and the relative positions of the devices are fixed by using cage rods and cage plates.
In the traditional spectrum measurement technology, the absolute value of the number density of neutral particles needs to be calibrated. The absolute number density of particles is measured by adopting an interference method without calibration; different from non-resonance interference which can only measure the electron number density, the resonance interference method utilizes the dispersion effect of atoms on laser to obtain the phase shift dispersion relation of hydrogen atoms in a specific energy state through frequency sweeping to give the hydrogen number density. The laser source module, the plasma measuring module and the interference module which form the whole interferometer are connected through optical fibers, are simple and convenient to install and are suitable for complex measuring application scenes. The resonance interference method used by the invention measures the hydrogen atom number density by utilizing the resonance effect when the laser frequency is close to the transition frequency of the hydrogen atoms in a specific energy state. A path of frequency stabilized helium-neon laser and a beam of tunable laser are used in the measurement. The frequency (wavelength) of the tunable laser is varied to sweep around the characteristic spectral line of the atom in the specified energy state. The dispersion of free electrons to two laser beams with similar wavelengths is approximate, and the dispersion of hydrogen atoms in a specified energy state to tunable laser is obvious. The phase shift difference of the two laser paths has information of hydrogen atoms in the designated energy state, and the number density of neutral particles in the designated energy state is obtained by analyzing a phase shift dispersion curve.
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 the number density of various other particles, and the spatial array of the multi-beam laser can realize the spatial resolution measurement of the number density of the particles in the plasma.
The invention adopts the following technical scheme:
a resonance laser interferometer for diagnosing the number density of particles in a 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 (1), a frequency stabilized laser (2), a polarizer (3), a first beam splitting and combining mirror (4), a reflector (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). The frequency stabilized laser can be selected from, but not limited to, a frequency stabilized helium-neon laser. One path of laser output by the frequency stabilized laser (2) is emitted to a first beam splitting and combining mirror (4) through a polaroid (3) and a reflector (5); the tunable laser (1) outputs one path of laser to a first beam splitting and combining mirror (4); the two laser beams are combined at a first beam splitting and combining mirror (4), and then split into two laser beams to be output. The two paths of output laser comprise laser output by the tunable laser (1) and the frequency stabilized laser (2). One of the two paths of laser is incident to a wavemeter (6); and the other path of the light beam passes through a Faraday isolator (7) and enters an acousto-optic crystal (8). Two paths of laser are emitted from the acousto-optic crystal (8), wherein one path of laser is incident to a first optical fiber coupler (10); the other path is incident to a second optical fiber coupler (11). The tunable laser (1) and the frequency stabilized laser (2) are fixed on an optical platform, and the polaroid (3), the first beam splitting and combining mirror (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 with a fixed relative position by cage bars.
Further, 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 light emitted from the third optical fiber coupler (12) passes through the plasma to be tested (16) and then enters the fourth optical fiber coupler (13). One path of laser light emitted from the fifth optical fiber coupler (14) enters the sixth optical fiber coupler (15).
Preferably, the fifth optical fiber coupler (14) and the sixth optical fiber coupler (15) are fixed on the optical platform after being connected with the fixed relative position by using cage bars; the third optical fiber coupler (12) and the fourth optical fiber coupler (13) are fixed with the plasma source to be measured through a clamp. The plasma source to be measured generates a plasma to be measured (16).
Further, 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 mirror (20), a first narrow-band filter plate (21), a second narrow-band filter plate (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 a second beam splitting and combining mirror (20) through a half-wave plate; one path of laser emitted from the eighth optical fiber coupler (18) enters a second beam splitting and combining mirror (20); the two laser beams are combined and interfered at a second beam splitting and combining mirror (20), and then split into two laser beams to be output. One path of the light passes through a first narrow-band filter (21) and is emitted to a first photoelectric detector (22); the other path of the light beam passes through a second narrow-band filter (23) and is emitted to a second photoelectric detector (24). And the seventh optical fiber coupler (17), the eighth optical fiber coupler (18), the half-wave plate (19), the second beam splitting and combining mirror (20), the two narrow-band filters and the two photodetectors are connected by cage bars, and are fixed on the optical platform after fixed in position.
Furthermore, the frequency stabilized laser, the polaroid, the reflector, the tunable laser, the first beam splitting and combining mirror, the Faraday isolator, the acousto-optic crystal, the acousto-optic modulation driver, the first optical fiber coupler, the second optical fiber coupler and the wavelength meter jointly form the laser source module.
Furthermore, 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 jointly form the plasma measuring module.
Furthermore, 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 mirror, a first narrow-band filter plate, a second narrow-band filter plate, a cage bar, a first photoelectric detector, a second photoelectric detector and a signal acquisition and processing system.
Further, the laser source module and the plasma measuring module are connected through an optical fiber jumper. The plasma measuring module is connected with the interference module through an optical fiber jumper. The acousto-optic modulation driver and the acousto-optic crystal are connected by 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 and 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 the sequence shown in the attached figure 1, and the relative positions of the devices are fixed by using cage rods and cage plates.
Further, the laser source module emits two laser beams through the first optical fiber coupler and the second optical fiber coupler, one laser beam serves as probe light, and the other laser beam serves as reference light. Each laser beam contains two laser frequencies, wherein the tunable laser frequency 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 achieve multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of the number density of various other particles, and the spatial array of the multi-beam laser can realize the spatial resolution measurement of the number density of the particles in the plasma.
Furthermore, a third optical fiber coupler and a fourth optical fiber coupler in the plasma measurement module form a probe arm to guide probe beam laser to pass through plasma.
Further, the fifth optical fiber coupler and the sixth optical 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 suitable for the module.
Further, the tunable laser 1 located in the laser source module outputs a beam of linearly polarized light with a frequency ω. The frequency stabilized laser 2 outputs a beam with frequency omegaHThe polarization direction of the linearly polarized light is adjusted by the polaroid 3, and the frequency after adjustment is omegaHIs aligned with said linearly polarized polarization direction of frequency omega, then frequency omegaHThe linearly polarized light is combined and sub-divided with the linearly polarized light with the frequency omega through a first beam splitting and combining mirror 4, one path of the combined light is incident to a wavelength meter 6, and the laser frequency is monitored in real time; and the other path passes through a Faraday isolator 7 to an acousto-optic crystal 8. The acousto-optic modulation driver 9 provides a modulation voltage to the acousto-optic crystal 8. The acousto-optic crystal 8 outputs 0-order light and-1-order light of the difference frequency. The 0-level light as detection light 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 in sequence. The-1-order light 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 in sequence, and then interferes with the 0-order light exiting from the half-wave plate 19 at the second beam splitting and combining mirror 20.
Has the advantages that:
the absolute number density of hydrogen atoms is obtained by measuring the phase shift by adopting a resonance interference method, and calibration is not needed; unlike non-resonance interference which can only measure the electron number density, the resonance interference method utilizes the dispersion effect of atoms on laser to obtain the phase shift dispersion relation of hydrogen atoms in specific energy states through frequency sweeping. Furthermore, lasers and optical path components with different frequencies (or frequency ranges) can be selected to realize multi-beam and multi-frequency laser output. The output of the multi-frequency laser can realize the measurement of the number density of various other particles, and the spatial array of the multi-beam laser can realize the spatial resolution measurement of the number density of the particles in the plasma. The three modules forming the whole interferometer are connected through optical fibers, so that the interferometer is simple and convenient 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 number density of electrons. The invention can be used for interference diagnosis of H (n-2) atomic absolute density of divertor plasma. The measurement principle of the invention can be used for measuring the number 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.
The meanings of the figure numbers in figure 1 are as follows: 1-tunable laser, 2-frequency stabilized laser, 3-polaroid, 4-first beam splitting and combining mirror, 5-reflector, 6-wavelength meter, 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 tested (the position is shown between the third optical fiber coupler and the fourth optical fiber coupler, the object to be tested is, except that the third optical fiber coupler and the fourth optical fiber coupler are connected on a device window for generating the plasma to be tested through clamps, the rest is not limited), 17-seventh optical fiber coupler, 18-an eighth optical fiber coupler, 19-a half-wave plate, 20-a second beam splitting and combining mirror, 21-a first narrow-band filter (central wavelength 632.8nm), 22-a first photoelectric detector, 23-a second narrow-band filter (central wavelength 656nm), 24-a second photoelectric detector, 25-a first optical fiber jumper, 26-a second optical fiber jumper, 27-a third optical fiber jumper and 28-a fourth optical fiber jumper. The thin line optical path indicates that the laser light propagates in the form of spatial light, and the thick line indicates that the laser light propagates in the optical fiber jumper. The three modules that make up the interferometer are indicated by dashed boxes.
FIG. 2 different αjiLinear function of value P (u)ji,αji)。
Detailed Description
The invention is described in detail below with reference to the figures and the embodiments. The following examples are only for explaining the present invention, the scope of the present invention shall include the full contents of the claims, and the full contents of the claims of the present invention can be fully realized by those skilled in the art through the following examples.
The method aims at neutral hydrogen atoms of plasma of the tokamak divertor, adopts dual-wavelength resonance heterodyne laser interferometry to measure the number density of first excited-state particles, 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 comprises 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 stabilized laser 2, a polaroid 3, a first beam splitting and combining mirror 4, a reflector 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 stabilized laser 2 is emitted to a first beam splitting and combining mirror 4 through a polaroid 3 and a reflector 5 in sequence; the tunable laser 1 outputs a path of laser to the first beam splitting and combining mirror 4; the two laser beams are combined at the first beam splitting and combining lens 4 and then split into two laser beams to be output. The two paths of output laser comprise the laser output by the tunable laser 1 and the frequency stabilized laser 2. One of the two laser beams enters a wavemeter 6; and the other path of the light passes through a Faraday isolator 7 and enters an acousto-optic crystal 8. Two paths of laser are emitted from the acousto-optic crystal 8, wherein one path of laser is incident into a first optical fiber coupler 10; the other path enters the second fiber coupler 11.
The tunable laser 1 and the frequency stabilized laser 2 are both fixed on an optical platform. The polaroid 3, the first beam splitting and combining mirror 4, the Faraday isolator 7, the acousto-optic crystal 8, the first optical fiber coupler 10 and the second optical fiber coupler 11 are connected by cage bars, and are fixed on an optical platform after the relative positions are fixed. The acousto-optic modulation driver 9 and the acousto-optic crystal 8 are connected by a wire. The plasma measuring module is composed of 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 light emitted from the third optical fiber coupler 12 passes through the plasma 16 to be tested and then enters the fourth optical fiber coupler 13. One path of laser light emitted from the fifth optical fiber coupler 14 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 position is fixed. The third optical fiber coupler 12 and the fourth optical 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 divertor area 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 mirror 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 a second beam splitting and combining mirror 20 through a half-wave plate 19; one path of laser emitted from the eighth optical fiber coupler 18 enters a second beam splitting and combining mirror 20; the two laser beams are combined and interfered at the first beam splitting and combining mirror 20, and then split into two laser beams to be output. One path of the light passes through the first narrow-band filter 21 and is emitted to the first photoelectric detector 22; the other path passes through a second narrow-band filter 23 and is directed to a second photodetector 24. The signal acquisition processing system is respectively connected with the computer, the first photoelectric detector 22 and the second photoelectric detector 24.
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 mirror 20, the two narrow-band filters and the two photodetectors are connected by cage bars, and are fixed on the optical platform after fixed phase positions.
The laser source module and the plasma measuring module, and the plasma measuring module and the interference module are connected through optical fiber jumpers. The acousto-optic modulation driver 9 is connected with the acousto-optic crystal 8 by a lead; the third optical fiber coupler 12 and the fourth optical fiber coupler 13 are fixed with a plasma source to be measured (located between the third optical fiber coupler and the fourth optical fiber coupler as shown in the figure, and is an object to be measured, except that the third optical fiber coupler and the fourth optical fiber coupler are connected with a device window for generating plasma to be measured through a clamp, the rest is not limited). The plasma source to be measured generates a plasma 16 to be measured. The signal acquisition processing system is respectively connected with a computer and the first photoelectric detector 22 and the second photoelectric detector 24. The electrical signal detected by the first photodetector 22 is transmitted to a signal acquisition and processing system, and the signal acquisition and processing system phase-discriminates the electrical signal into a phase signal and transmits the phase signal to a computer. The electrical signal detected by the second photodetector 24 is transmitted to a signal acquisition and processing system, and the signal acquisition and processing system phase-discriminates the electrical signal into a phase signal and transmits the phase signal to a computer. All other devices are fixed on the optical platform according to the positions and the sequence shown in the attached figure 1, and the relative positions of the devices are fixed by using cage rods and cage plates.
The tunable laser 1 located in the laser source module outputs a beam of linearly polarized light with frequency ω. The frequency stabilized laser 2 outputs a beam with frequency omegaHThe polarization direction of the linearly polarized light is adjusted by the polaroid 3, and the frequency after adjustment is omegaHIs aligned with said linearly polarized polarization direction of frequency omega, then frequency omegaHThe linearly polarized light is combined and sub-divided with the linearly polarized light with the frequency omega through a first beam splitting and combining mirror 4, one path of the combined light is incident to a wavelength meter 6, and the laser frequency is monitored in real time; and the other path passes through a Faraday isolator 7 to an acousto-optic crystal 8. The acousto-optic modulation driver 9 provides a modulation voltage to the acousto-optic crystal 8. The acousto-optic crystal 8 outputs 0-level light and-1-level light of difference frequency, the 0-level light as detection light 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 in sequence, and then interferes with-1-level light emitted from the eighth optical fiber coupler 18 at the second beam splitting and combining mirror 20.
The-1-order light 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 in sequence, and then interferes with the 0-order light exiting from the half-wave plate 19 at the second beam splitting and combining mirror 20. The half-wave plate 19 aligns the probe light passing through the plasma with the polarization angle of the-1 st order reference light. The reference light and the detection light are combined, interfered and emitted by a second beam splitting and combining mirror 20, and one path of the reference light and the detection light passes through a beam splitter with the central wavelength of lambda1The first 632.8nm narrow band filter 21 is received by the first photodetector 22; the other path has a central wavelength of lambda2A second narrow band filter 23 of 656nm is received by a second photodetector 24.
The laser source module emits two laser beams through the first optical fiber coupler 10 and the second optical fiber coupler 11, one laser beam serves as probe light, and the other laser beam serves as reference light. Each laser beam contains two laser frequencies, wherein the tunable laser frequency can be varied. Alternatively, 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 the number density of various other particles, and the spatial array of the multi-beam laser can realize the spatial resolution measurement of the number density of the particles in the plasma.
The third optical fiber coupler 12 and the fourth optical fiber coupler 13 in the plasma measurement module form a probe arm to guide probe beam laser to pass through plasma.
The fifth optical fiber coupler 14 and the sixth optical fiber coupler 15 form a reference arm compensation reference beam laser optical path.
The interference module adopts but is not limited to a Mach-Zehnder interferometer optical path, and other general interference optical paths are suitable for 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 sent to a signal acquisition and processing system for digital filtering, phase discrimination is carried out, and phase signals obtained by the phase discrimination are sent to a computer; the phase discrimination algorithm specifically adopts a discrete Hilbert transform mode to obtain the complex amplitude of the measured electric signal, and then obtains a frequency-stabilized laser phase signal
And tunable laser phase signal
Changing tunable laser frequency, recording phase signal difference of two lasers under different tunable laser frequencies by the signal acquisition processing system, and processing data according to the measurement principle to obtain the hydrogen atom number density n in the plasma to be measuredi。
The measurement principle is as follows:
frequency stabilized He-Ne laser wavelength
Tunable laser wavelength
May vary from 656.1nm to 656.5 nm. Wherein ω isHFor the frequency of the frequency stabilized He-Ne laser, the unit is s-1Omega is tunable laser frequency and the unit is s-1And c is the speed of light in vacuum, with the unit of m.s-1。
For the acquired phase signal
And
can be expressed as:
wherein formula (1) represents the collected phase signal corresponding to the tunable laser
In units of rad, the first term on the right side of formula (1) is associated with a particular energy state hydrogen atom characteristic; the formula (2) represents the collected phase signal corresponding to the frequency stabilized He-Ne laser
The unit is rad. In the formula of omegaHFor the frequency of the frequency stabilized He-Ne laser, the unit is s-1Omega is the tunable laser frequency in s-1，niFor a selected particle number density, in m-3，fjiL is the length of the path traveled by the laser in the plasma, in m,
for Doppler broadening, in units of s-1In the Doppler spread expression, ωijFor a transition frequency from a particular lower energy level i to a corresponding upper energy level j, the unit is s-1C is the speed of light in vacuum, in m.s-1，kBDenotes the Boltzmann constant, TiIs the temperature of the hydrogen atoms in a specific energy state, in K, M being the mass of the selected particles, in kg,
is a linear function, in the expression of the linear function, r0Is a classical electron radius, in m,
to normalize incident light frequency, in units of s-1，
For normalized full width at half maximum, gammajiFor broadening by collision, in units of s-1。
Is the sum of the other components (mainly free electrons)The off-resonance phase shift, in rad, is generally much smaller than the resonance phase shift and the dispersion is small.
The phase shift, in rad, caused by various vibrations is mainly concentrated in the low frequency region.
Will phase signal
And
taking the difference, the phase difference φ (ω) associated only with hydrogen atoms in a particular energy state is obtained:
wherein ω isHFor the frequency of the frequency stabilized He-Ne laser, the unit is s-1Omega is the tunable laser frequency in s-1，niFor a selected particle number density, in m-3，fjiL is the length of the path traveled by the laser in the plasma, in m,
for Doppler broadening, in units of s-1In the Doppler spread expression, ωijFor a transition frequency from a particular lower energy level i to a corresponding upper energy level j, the unit is s-1C is the speed of light in vacuum, in m.s-1，kBDenotes the Boltzmann constant, TiIs the temperature of the hydrogen atoms in a specific energy state, in K, M being the mass of the selected particles, in kg,
is a linear function, in the expression of the linear function, r0Is a classical electron radius, in m,
to normalize incident light frequency, in units of s-1，
For normalized full width at half maximum, gammajiFor broadening by collision, in units of s-1。
FIG. 2 shows the difference αjiLinear function of value P (u)ji,αji). When alpha isjiWhen the condition < 1 is satisfied, it can be observed that the Pmax always occurs at ujiAt-1. Experimentally measured frequency omega of occurrence of phase shift maximamaxAnd center frequency omega0The difference between the two can be used to estimate betajiThe value of (c).
The plasma in the tokamak divertor area has the characteristics of high temperature and low air pressure, and the gamma is widened by collisionjiMuch less than the Doppler broadening βjiSatisfies the assumed conditions
Changing the frequency omega of the tunable laser 1 to obtain the corresponding
And
the difference is made to obtain a phase shift-frequency relationship phi (omega). At αjiUnder the condition of < 1, the frequency omega corresponding to the maximum phase shiftmaxAnd center frequency omega0To give betajiAn estimate of (d). Will betajiThe estimated value of (2) is brought back to the formula (3), and the parameter alpha is obtained by utilizing the phase shift dispersion relation phi (omega) obtained by measurement to fitjiAnd a number density n of hydrogen atom specific energy state particlesi。
The method is used for measuring the number density of the first excited state of the hydrogen atoms of the plasma of the tokamak divertor, and the measuring principle and the measuring method can be suitable for measuring other energy levels of the H atoms; while also giving the free electron number density. The invention can realize the space resolution measurement of the number density of various other particles of the plasma through multi-frequency and multi-beam laser output. The invention has not been described in detail and is part of the common general knowledge of a person skilled in the art. The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and the preferred embodiments are not exhaustive and do not limit the invention to the precise embodiments described. Various modifications and improvements of the technical solution of the present invention may be made by those skilled in the art without departing from the spirit of the present invention, and the technical solution of the present invention is to be covered by the protection scope defined by the claims.
Claims (9)
1. A resonance laser interferometer for diagnosing the number density of particles in a plasma of a 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.
2. Interferometer according to claim 1, wherein the laser source module comprises a tunable laser (1), a frequency stabilized laser (2), a polarizer (3), a first beam splitting and combining mirror (4), a mirror (5), a wavemeter (6), a faraday isolator (7), an acousto-optic crystal (8), an acousto-optic modulation driver (9), a first fiber coupler (10) and a second fiber coupler (11);
one path of laser output by the frequency stabilized laser (2) is emitted to a first beam splitting and combining mirror (4) through a polaroid (3) and a reflector (5) in sequence; the tunable laser (1) outputs one path of laser to a first beam splitting and combining mirror (4); two beams of laser are combined at a first beam splitting and combining mirror (4), and then split into two paths of laser to be output, wherein the two paths of output laser comprise the laser output by a tunable laser (1) and a frequency stabilized laser (2), one path of the two paths of laser enters a wavelength meter (6), and the other path of laser enters an acousto-optic crystal (8) through a Faraday isolator (7); two paths of laser are emitted from the back of the acousto-optic crystal (8), wherein one path of laser enters a first optical fiber coupler (10), and the other path of laser enters a second optical fiber coupler (11);
preferably, the tunable laser (1) and the frequency stabilized laser (2) are respectively fixed on an optical platform, and the polaroid (3), the first beam splitting and combining mirror (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 with a fixed relative position by cage bars; the acousto-optic modulation driver (9) and the acousto-optic crystal (8) are connected by a wire.
3. The interferometer of claim 1, wherein the plasma measurement module comprises a third fiber coupler (12), a fourth fiber coupler (13), a fifth fiber coupler (14), a sixth 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 tested and then enters the fourth optical fiber coupler (13); one path of laser emitted from the fifth optical fiber coupler (14) enters a sixth optical fiber coupler (15);
preferably, the fifth optical fiber coupler (14) and the sixth optical fiber coupler (15) are fixed on the optical platform after being connected with the fixed relative position by using cage bars; the third optical fiber coupler (12) and the fourth optical fiber coupler (13) are respectively fixed with the plasma source to be measured through clamps.
4. The interferometer according to claim 1, wherein the interference module comprises a seventh fiber coupler (17), an eighth fiber coupler (18), a half-wave plate (19), a second beam splitting and combining mirror (20), a first narrow-band filter (21), a second narrow-band filter (23), cage bars, a first photodetector (22), a second photodetector (24) and a signal acquisition and processing system; one path of laser emitted from the seventh optical fiber coupler (17) enters a second beam splitting and combining mirror (20) through a half-wave plate (19); one path of laser emitted from the eighth optical fiber coupler (18) enters a second beam splitting and combining mirror (20); the two paths of laser are combined and interfered at a second beam splitting and combining mirror (20), and then split into two paths of laser to be output, wherein one path of laser is emitted to a first photoelectric detector (22) through a first narrow-band filter (21), and the other path of laser is emitted to a second photoelectric detector (24) through a second narrow-band filter (23); the signal acquisition and processing system is respectively connected with a computer, a first photoelectric detector (22) and a second photoelectric detector (24);
preferably, the seventh optical fiber coupler (17), the eighth optical fiber coupler (18), the half-wave plate (19), the second beam splitting and combining mirror (20), the two narrow-band filters and the two photodetectors are connected by using a cage bar, and are fixed on the optical platform after the relative position is fixed.
5. The interferometer of claim 1, wherein the laser source module and the plasma measurement module are connected by fiber jumpers, and the plasma measurement module and the interference module are connected by fiber jumpers.
6. The interferometer of claim 2, wherein the laser source module emits two laser beams through the first fiber coupler (10) and the second fiber coupler (11), one as probe light and one as reference light.
7. Interferometer according to claim 6, wherein each laser beam comprises two laser frequencies, wherein the tunable laser frequency can be varied.
8. Interferometer according to claim 2, characterised in that the number of frequency-stabilized lasers (2) and/or the number of tuneable lasers (1) are each independently a plurality, and that both the frequency of the output laser light of the frequency-stabilized lasers and the frequency range of the output laser light of the tuneable lasers can be varied.
9. Interferometer according to claim 3, wherein the third (12) and fourth (13) fiber couplers of the plasma measurement module form a probe arm for guiding the probe beam laser through the plasma, and the fifth (14) and sixth (15) fiber couplers form a reference arm for compensating the reference beam laser path.
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