CN116741612A - Continuous light high space-time resolution thomson scattering diagnosis system - Google Patents
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Abstract
The application discloses a continuous light high space-time resolution thomson scattering diagnosis system, which comprises: the laser support subsystem is used for outputting and modulating to obtain continuous high-power laser and focusing on a tested plasma diagnosis area to obtain a spectrum signal; the spectrum treatment subsystem is used for carrying out photoelectric conversion on spectrum signals obtained by removing impurities and extracting the spectrum signals in the tested plasma diagnosis area according to the space-time resolution form requirement; the phase-locked detection subsystem is in circuit connection with the spectrum treatment subsystem, and extracts TS scattering spectrum information from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology; the data processing subsystem is used for carrying out data processing on the wavelength and the scattered signal intensity of the obtained TS scattered spectrum information, calculating an electron velocity distribution function and calculating electron temperature and density; and the driving execution subsystem is used for carrying out cooperative driving control on the movable component of the diagnosis system to realize the position movement of the measuring point.
Description
Technical Field
The application relates to the technical field of low-temperature plasma diagnosis, in particular to a continuous light high-space-time resolution Thomson scattering diagnosis system.
Background
The laser tom Sun Sanshe (Thomson Scattering, TS) is a non-contact plasma electronic parameter diagnosis method, laser emitted by a pulse laser in the current tom scattering diagnosis system is focused in a measured plasma through a lens, a laser spot and free electrons in the plasma generate TS spectrum signals with the same frequency as incident light, the TS spectrum signals and other stray spectrum signals enter a monochromator through a collecting lens group, after the scattered signals are directionally selected in frequency by the monochromator, TS signals higher than background radiation noise are synchronously acquired through a detector (PMT or ICCD) arranged at the rear end of the monochromator, average noise reduction processing is carried out on the TS signals acquired through multiple measurements, and Electronic Energy Distribution Function (EEDF) data is obtained through data analysis and calculation. In the diagnosis scheme, the collision section of the laser TS is usually smaller, the generated TS spectrum signal is extremely weak, a high-power pulse laser is used as a laser source for improving the TS signal intensity, the purpose of increasing the transient laser power is achieved by compressing the laser pulse width, and then enough tom Sun Sanshe light quantum number is generated to improve the signal to noise ratio of the TS detection signal.
At present, a TS system based on the scheme system is widely applied to EEDF diagnosis researches of low-temperature plasmas such as high-temperature plasmas, atmospheric arc plasmas and radio-frequency plasmas of a magnetically confined Tokamak device. Particularly in tokamak core plasma diagnostic applications with ultra high temperatures (1 hundred million degrees celsius), are almost the only diagnostic means available for diagnosis of tokamak plasma electrical parameters. However, the TS system scheme based on pulsed laser has many limitations, and the general applicability of measurement is limited, mainly in aspects of limited energy resolution, contradiction between the cost of measurement time and economic cost, incapability of transient characteristic measurement, incapability of performing laser-induced excitation secondary discharge (Laser Induced Discharge, neutral gas secondary discharge), incapability of avoiding neutral gas secondary discharge effect, and the like, which specifically include:
when the pulse laser TS system scheme is adopted for measurement, the measured plasma is in a thermodynamic system with a certain pressure, scattered light with the same wavelength is generated in all directions of a propagation path due to the Rayleigh scattering effect when laser passes through the system, and diffuse reflection is generated when the laser passes through all optical interfaces, so that the light receiving and signal acquisition processes are inevitably subjected to strong interference of stray light, and the signal to noise ratio of TS signals is reduced. In order to eliminate stray light, stray light is generally filtered by adding a band-stop filter, however, the line width of the filter is usually 1-2 nm due to the limitation of the processing technology of the filter, so that TS spectrum signals of low-energy electrons in the measured plasma are almost completely filtered by the large line width, and diagnostic data information is lost. Whereas in low temperature plasmas, low energy electrons occupy an absolute majority of the plasma electrons, which tends to result in extremely limited EEDF information available in low temperature plasma applications based on thomson scattering diagnostics of current pulsed laser system regimes. In another commonly adopted technical scheme for removing stray light, two monochromators or a plurality of monochromators are cascaded to form a bicolor or a multi-monochromator system, and stray light is suppressed to 1×10 in a dispersion subtraction mode -9 Magnitude. If ICCD is used as detector, the resolution is limited by the limit of local noise of ICCD. And PMT is used as a detector, because of the limitation of pulse laser, the grating scanning time scale of monochromator is far greater than the laser pulse width, the resolution of measurement cannot be improved in a grating scanning mode, and the highest resolution of 0.1nm can be realized.
The power of pulsed lasers is generallyOn the order of 10MW-100MW, single laser pulse at a density of 10 19 m -3 The total scattered photons generated in the plasma of (a) are still on the order of millions to tens of millions of photons, while in a limited light collection space angle (6.5 f-number) there are also on the order of hundreds of thousands of photons, the scattered signal intensity is limited. Whereas the repetition rate of high power pulsed lasers is typically 10-100Hz, typically about 10 is required to obtain a stronger TS signal 4 The time required to complete a measurement is between 100 and 1000 seconds. Aiming at the problems that the scattered signal intensity is limited and the average mode time of multiple measurements is too long, the current technical solution is to integrate a plurality of pulse lasers in series, increase the number of laser pulses in unit time through time sequence control so as to obtain more measurement data for averaging, thereby achieving the purpose of obtaining higher signal-to-noise ratio intensity in shorter time. However, the cost of the solution, the space size of the system and the complexity of the laser light path are extremely high (all the light spots are required to be focused at the same measuring position), and the nonlinear trend is raised along with the increase of the number of lasers, so that the practical application of the solution is very limited. Furthermore, limited by the pulse laser pulse width (about 10 ns), the current pulse laser TS does not have any measurement capability for the effects of plasma wave instability with characteristic frequencies in the range of 1-100kHz, transient instability effects such as breathing mode of hall propellers and plasma turbulence.
In addition, in low-temperature plasmas with lower ionization degree, a larger proportion of neutral gas exists, and high-power pulse laser can excite the neutral gas to perform secondary discharge, so that the gas in the plasmas is ionized, and serious uncertain disturbance is generated on the original electron energy distribution state. In the high energy density plasmas such as full-ionized tokamak plasmas and helicon plasmas, the influence caused by the secondary discharge effect of neutral gas is not obvious, but in the low-temperature plasmas with low ionization degree, the secondary discharge of neutral gas becomes a key bottleneck problem for restricting the application of pulse TS, and related problems can be relieved only by reducing laser power. While decreasing the laser power necessarily results in a linear decrease in scattered signal intensity, which for low temperature plasmas, where the electron density is inherently low, will further decrease the already very limited scattered signal intensity. Therefore, TS based on pulsed laser is limited in the parameter interval and measurement accuracy applicable to low-temperature plasma diagnosis.
Disclosure of Invention
The embodiment of the application provides a continuous light high space-time resolution thomson scattering diagnosis system, which aims to solve the technical problems that the conventional thomson scattering diagnosis system is limited in universality, energy resolution is limited, measurement time cost and economic cost are contradictory, transient characteristic measurement cannot be performed, and laser-induced excited secondary discharge exists.
The technical scheme adopted by the application is as follows:
a continuous light high spatial-temporal resolution thomson scattering diagnostic system comprising:
the laser support subsystem is used for outputting and modulating continuous high-power laser and focusing the laser on a tested plasma diagnosis area to obtain a spectrum signal, the linewidth of the laser is 10kHz to 20GHz, and the laser power is 100W to 1000W;
the spectrum treatment subsystem is used for carrying out photoelectric conversion on spectrum signals obtained by removing impurities and extracting the spectrum signals in the tested plasma diagnosis area according to the space-time resolution form requirement;
the phase-locked detection subsystem is in circuit connection with the spectrum treatment subsystem, and extracts TS scattering spectrum information from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology;
the data processing subsystem is connected with the phase-locked detection subsystem circuit and is used for carrying out data processing on the wavelength of the obtained TS scattering spectrum information and the scattering signal intensity, calculating an electron velocity distribution function and calculating electron temperature and density;
and the driving execution subsystem is used for carrying out cooperative driving control on the movable component of the diagnosis system to realize the position movement of the measuring point.
Further, the laser support subsystem includes:
the continuous light laser is used for exciting the light source to output a high-power steady laser beam;
the optical modulation device is used for carrying out frequency pulse modulation on the high-power steady laser beam output by the continuous laser, and taking the frequency pulse modulation signal as a reference signal for phase-sensitive detection extraction scattering spectrum of the phase-locked amplifier;
and the optical beam focusing system is used for focusing the modulated laser beam on the measured plasma diagnosis area to obtain a spectrum signal.
Further, the optical modulation device adopts an optical fiber amplifier to carry out electronic modulation or adopts an optical chopper to carry out optical modulation.
Further, the optical fiber amplifier adopts an optical fiber conical amplifier.
Further, the spectral treatment subsystem comprises:
the laser cut-off device is arranged on a laser light path after laser passes through the plasma diagnosis area to be detected and is used for collecting and removing interference sources including laser and direct scattering generated by interface scattering;
the collecting light cut-off is opposite to the collecting lens group and is positioned at the other side of the tested plasma diagnosis area far away from the collecting lens group;
the collecting lens group is used for collecting spectrum signals obtained from the plasma diagnosis area to be tested to a plurality of monochromators;
the multi-monochromator is used for inhibiting laser stray light and Rayleigh scattered light interference generated in the laser propagation process of the spectrum signals collected by the collection lens group in a dispersion cancellation mode, so that the stray light is suppressed to the maximum extent, the signal-to-noise ratio of the scattered signals is improved, and the spectrum signals with different wavelengths are obtained;
and the photoelectric detector is used for converting the spectrum signals processed by the multiple monochromators into electric signals.
Further, the photodetector employs a photomultiplier tube.
Further, the multiple monochromator adopts a grating-adjustable multiple monochromator, and the photoelectric detector adopts a single photomultiplier.
Further, the multi-monochromator adopts a grating fixed multi-monochromator, the photoelectric detector adopts a photomultiplier array, and multi-wavelength synchronous extraction is realized between the grating fixed multi-monochromator and the photomultiplier array by adopting a fiber bundle multi-channel densely-distributed acquisition mode.
Further, the phase-locked detection subsystem includes:
the phase-locked amplifier is in circuit connection with the spectrum treatment subsystem, TS scattering spectrum information is extracted from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology, and a reference signal of the phase-locked amplifier is a frequency pulse modulation signal of the optical modulation device;
and the acquisition system is connected with the phase-locked amplifier circuit and is used for acquiring the extracted TS scattering spectrum information.
Further, the phase-locked detection subsystem further comprises:
the gating collector is arranged between the lock-in amplifier and the spectrum treatment subsystem, takes the fluctuation quantity related to the oscillation behavior in the plasma to be tested as a trigger signal of the hollow collector, and is used for directly obtaining time resolution electronic speed diagnosis and realizing a transient diagnosis function.
Compared with the prior art, the application has the following beneficial effects:
aiming at the measurement limitation of a pulse laser Thomson scattering diagnosis system, the application provides a continuous light high space-time resolution Thomson scattering diagnosis system, in particular to a Thomson scattering diagnosis system based on continuous laser and using a phase-locked detection technology for signal extraction. The scheme adopts a continuous and narrow linewidth fiber laser to replace a pulse laser, the transient laser power is suddenly reduced from about 10-100MW to 100-1000W, and the transient intensity is reduced to about 10 -4 -10 -6 The original scattered signal to noise ratio is reduced proportionally. Continuous TS spectrum signals are generated during measurement after laser replacement, but not pulse TS spectrum signals, ultra-high signal-to-noise ratio weak scattering spectrum signals with the signal-to-noise ratio of-100 dB or even below-110 dB can be extracted by adopting a phase-locked amplification technology, and then a single laser can be adopted to obtain the spectrum signal superior to the current pulse laser type ThomsonThe signal quality of the scattering diagnosis scheme greatly reduces the system cost and the measurement time; in addition, compared with pulse laser, continuous laser has the important characteristics of easy light spot compression and time operability, the accurate control of the size of a diagnosis domain can be realized by carrying out focusing compression on an incident light beam and focusing compression on scattered spectrum collection optics, the frequency and transient characteristics of plasma are reserved in a tom Sun Sanshe signal excited by the continuous laser, and the time domain operation is carried out on measurement in a high-speed gating acquisition and active frequency modulation mode, so that the high space-time resolution diagnosis capability of the current pulse laser type tomson scattering diagnosis scheme is realized. Because the phase-locked detection technology is adopted, the application can obtain higher signal to noise ratio by adopting continuous laser with relatively lower transient power (100W to 1000W), and the reduction of the laser power can effectively avoid the problem of secondary discharge of neutral gas during low-temperature plasma measurement.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:
FIG. 1 is a schematic diagram of the continuous-light high-spatial-temporal resolution Thomson scattering diagnostic system according to a preferred embodiment of the application.
FIG. 2 is a schematic diagram of the continuous-light high-spatial-temporal resolution Thomson scattering diagnostic system according to another preferred embodiment of the application.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.
Referring to fig. 1, a preferred embodiment of the present application provides a continuous light high spatial-temporal resolution thomson scattering diagnostic system comprising:
the laser support subsystem is used for outputting and modulating continuous high-power laser and focusing the laser on a tested plasma diagnosis area to obtain a spectrum signal, the linewidth of the laser is 10kHz to 20GHz, the continuous power of the laser is 100W to 1000W, and the transient power is 100W to 1000W;
the spectrum treatment subsystem is used for carrying out photoelectric conversion on spectrum signals obtained by removing impurities and extracting the spectrum signals in the tested plasma diagnosis area according to the space-time resolution form requirement;
the phase-locked detection subsystem is in circuit connection with the spectrum treatment subsystem, and extracts TS scattering spectrum information from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology;
the data processing subsystem is connected with the phase-locked detection subsystem circuit and is used for carrying out data processing on the wavelength of the obtained TS scattering spectrum information and the scattering signal intensity, calculating an electron velocity distribution function and calculating electron temperature and density;
and the driving execution subsystem is used for carrying out cooperative driving control on the movable component of the diagnosis system to realize the position movement of the measuring point.
The application provides a continuous light high space-time resolution Thomson scattering diagnosis system, in particular to a Thomson scattering diagnosis system based on continuous laser and using a phase-locked detection technology to extract signals. The scheme adopts a continuous and narrow linewidth fiber laser to replace a pulse laser, the transient laser power is suddenly reduced from about 10-100MW to 100-1000W, and the transient intensity is reduced to about 10 -4 -10 -6 The original scattered signal to noise ratio is reduced proportionally. The continuous TS spectrum signal is generated during the measurement after the laser is replaced, but not the pulse TS spectrum signal, the phase-locked amplification technology can be adopted to extract the ultra-high signal-to-noise ratio weak scattering spectrum signal with the power of-100 dB or even below-110 dB, and then the signal quality superior to the current pulse laser type thomson scattering diagnosis scheme can be obtained by adopting a single laser, so that the system cost and the measurement time are greatly reduced; in addition, the continuous light laser has important characteristics of easy light spot compression and time operability compared with the pulse laser, and can realize diagnosis by focusing compression of incident light beams and focusing compression of scattered spectrum collection opticsThe precise control of the size of the broken domain keeps the frequency and transient characteristics of plasma in the tom Sun Sanshe signal excited by continuous laser, and performs time domain manipulation on measurement in a high-speed gating acquisition and active frequency modulation mode, so that the high space-time resolution diagnosis capability of the far-beyond current pulse laser type thomson scattering diagnosis scheme is realized. Because the phase-locked detection technology is adopted, the application can obtain higher signal to noise ratio by adopting continuous laser with relatively lower power (100W to 1000W), and the problem of secondary discharge of neutral gas during low-temperature plasma measurement can be effectively avoided by reducing the laser power.
Preferably, the laser support subsystem includes:
the continuous light laser is used for exciting the light source to output a high-power steady laser beam;
the optical modulation device is used for carrying out frequency pulse modulation on the high-power steady laser beam output by the continuous laser, and taking the frequency pulse modulation signal as a reference signal for phase-sensitive detection extraction scattering spectrum of the phase-locked amplifier;
and the optical beam focusing system is used for focusing the modulated laser beam on the measured plasma diagnosis area to obtain a spectrum signal.
Preferably, as shown in fig. 1, the optical modulation device employs an optical fiber amplifier for electronic modulation.
Preferably, as shown in fig. 2, the optical modulation device employs an optical chopper for optical modulation.
Preferably, the optical fiber amplifier is an optical fiber taper amplifier.
Preferably, the spectral treatment subsystem comprises:
the laser cut-off device is arranged on a laser light path after laser passes through the plasma diagnosis area to be detected and is used for eliminating interference sources including laser and direct scattering generated by interface scattering;
the collecting light cut-off is opposite to the collecting lens group and is positioned at the other side of the tested plasma diagnosis area far away from the collecting lens group;
the collecting lens group is used for collecting spectrum signals obtained from the plasma diagnosis area to be tested to a plurality of monochromators;
the multi-monochromator is used for inhibiting laser stray light and Rayleigh scattered light interference generated in the laser propagation process of the spectrum signals collected by the collection lens group in a dispersion cancellation mode, so that the stray light is suppressed to the maximum extent, the signal-to-noise ratio of the scattered signals is improved, and the spectrum signals with different wavelengths are obtained;
and the photoelectric detector is used for converting the spectrum signals processed by the multiple monochromators into electric signals.
Preferably, the photodetector employs a photomultiplier tube.
Preferably, as shown in fig. 1, the multiple monochromator employs a grating tunable multiple monochromator, and the photodetector employs a single photomultiplier tube.
Preferably, as shown in fig. 2, the multi-monochromator adopts a grating fixed multi-monochromator, the photoelectric detector adopts a photomultiplier array, and multi-wavelength synchronous extraction is realized between the grating fixed multi-monochromator and the photomultiplier array by adopting a mode of optical fiber bundle multichannel densely-distributed acquisition.
Preferably, the phase-locked detection subsystem includes:
the phase-locked amplifier is in circuit connection with the spectrum treatment subsystem, TS scattering spectrum information is extracted from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology, and a reference signal of the phase-locked amplifier is a frequency pulse modulation signal of the optical modulation device;
and the acquisition system is connected with the phase-locked amplifier circuit and is used for acquiring the extracted TS scattering spectrum information.
Preferably, the phase-locked detection subsystem further comprises:
the gating collector is arranged between the lock-in amplifier and the spectrum treatment subsystem, takes the fluctuation quantity related to the oscillation behavior in the plasma to be tested as a trigger signal of the hollow collector, and is used for directly obtaining time resolution electronic speed diagnosis and realizing a transient diagnosis function.
The main function of the laser supporting subsystem of the embodiment is to generate narrow linewidth single-frequency modulated laser with high enough power and compress and focus laser spots to improve the power density of the laser, so that the quantum amount of laser tom Sun Sanshe meets the requirements for realizing phase-sensitive detection. Specifically, the system uses high power (the high power mentioned here and later is the power of the continuous laser with respect to the common narrow linewidth, the power of the continuous laser with respect to the pulse laser is still low), the narrow linewidth and the continuous laser as an excitation light source, adopts the electronic modulation of a laser fiber amplifier or the optical modulation means of a high-power optical chopper to carry out the precise frequency pulse modulation on the high-power steady laser beam, and the modulation signal is used as a reference signal for carrying out the phase-sensitive detection as a phase-locked amplifier to extract the weak scattering spectrum; then, focusing laser on a tested plasma diagnosis area through a high-power optical beam focusing system so as to obtain higher power density (effectively improving signal to noise ratio) and better spatial resolution; because the power of the incident laser is high, any possible laser stray light can submerge weak scattering spectrum signals, and interference sources possibly causing direct scattering of laser, such as main laser, interface scattering and the like, are eliminated by utilizing a laser cut-off device; the scheme innovation point of the subsystem is that the system can output continuous high-power laser, the linewidth of the laser is as low as 20GHz, and the laser can be further compressed to the level of 10kHz, which is far lower than the typical linewidth of the traditional YAG laser, so that the laser frequency/wavelength used as a test probe is more accurate. The low linewidth means that the stray laser light interferes with the scattered spectrum data only in a very narrow range, and thus the resolution of the measurement can be significantly improved.
The spectrum treatment subsystem of the embodiment mainly transmits the laser TS spectrum signal to the photoelectric detector for photoelectric conversion in a high-efficiency and reliable mode according to the requirement of a space-time resolution mode. The influence of the Rayleigh scattered light interference generated in the laser stray light and the laser propagation process on the optical signal is most remarkable, the stray light is radically suppressed by various means such as laser main beam polarization state interface control, application of a laser cut-off device and a collecting light cut-off device, and aperture stray light elimination of a spectrum collecting lens group, and the like, and the stray light is suppressed by adopting a multi-monochromator in a dispersion cancellation mode, so that the stray light is maximally suppressed and the signal to noise ratio of scattered signals is improved. Meanwhile, because continuous scattering signals are generated by adopting continuous laser, wavelength scanning of the scattering signals can be realized by driving the grating to rotate by a precise motor, and PMT (photomultiplier) is adopted as a detector, namely, high-resolution wavelength control with limit resolution precision higher than 0.01nm is realized, and further, the resolution far superior to that of a pulse laser TS diagnostic system (-0.1 nm) is realized. In addition, the dispersion is carried out by adopting a multi-monochromator with fixed gratings, the multi-wavelength synchronous extraction is realized by adopting a multi-channel densely-distributed collection mode of the optical fiber bundles, the second-level extraction analysis of the high-resolution full-wave spectrum can be realized on the basis of the phase locking time of the sub-second level, and the synchronous online measurement requirement is met.
The signals received by the photomultiplier tube (PMT) comprise tom Sun Sanshe signals, stray light signals and plasma background radiation signals generated by the action of plasma and modulated laser, and the phase-locked detection subsystem of the embodiment has the function of effectively extracting extremely weak laser-induced TS spectrum from high background noise. The signal extraction based on continuous laser and using phase-locked detection technology is the core innovation point of the application. The original signal to be analyzed input by the subsystem is an electric signal of which the scattering spectrum is converted by a photomultiplier PMT, and the compared signal is an active frequency modulation (electronic chopping or optical chopping) monitoring signal.
The driving execution subsystem is mainly responsible for the controllable operation of the moving parts of the continuous light high space-time resolution Thomson scattering diagnosis system, ensures the cooperative movement of the incident laser-laser cut-off device and the collecting lens group-collecting cut-off device, and ensures that the diagnosis domain acted by the incident laser coincides with the focus of the collecting lens group so as to realize one-dimensional, two-dimensional or three-dimensional measurement.
In addition to the above basic functions, the system scheme system of the application has the inherent advantages that the system scheme system can identify and process the strong transient high-frequency oscillation mode of the measured plasma, which cannot be realized in the traditional pulse TS diagnosis system. This is because: the frequency of the existing high-energy pulse YAG laser is 10Hz, the frequency cannot be improved due to the limitation of component materials such as optical crystals, the frequency is far lower than the level of transient modes such as ion acoustic wave oscillation and the like, and effective analysis data cannot be obtained from the aspect of informatics. The high-fidelity phase-sensitive and frequency-sensitive diagnosis can be carried out on the disturbance of the plasma EEDF by reducing the phase-locked detection frequency and adding a gating collector at the phase-locked front stage by adopting a high-frequency gating technology and combining a high-efficiency data processing method, so that the analysis of the strong transient mode of the plasma which cannot be processed in the past can be realized.
The continuous light high space-time resolution thomson scattering diagnosis system provided by the application can realize a high-universality plasma electron density and temperature application range, and fine electron energy resolution and space-time resolution. The diagnostic system is suitable for use with electron densities of 1 x 10 16 m -3 Up to 1X 10 22 m -3 Plasma measurement with electron temperature of 0.01eV to 10000 eV; when the plasma with the electron temperature of 1eV is monitored, the energy resolution is 0.2eV; the spatial resolution of diagnosis is better than 0.3mm; frequency identification or phase sensitivity diagnosis can be carried out on a plasma oscillation mode of 100Hz-10 kHz; the diagnosis system can realize the real-time on-line electronic parameter monitoring of the plasma of 0.1 to 1 second.
The specific implementation and performance analysis are as follows:
continuous optical Thomson scattering (CWTS) signal detection feasibility and signal-to-noise ratio: the cross-sectional constant of the electron Thomson scattering was 6.65X10 -29 m 2 With photon energy of hν=hc/λ laser Calculated, a 100 watt 532nm laser emits approximately 2.7X10 lasers per second 20 Individual photons, according to a 1X 10 17 m -3 Length estimation of density plasma, 1mm diagnostic space, gives a total photon number of 1.78X10 6 In consideration of the problem of the relative solid angle of the collecting light path and the scattering element, the effective luminous flux is 1.78X10 assuming that the light receiving efficiency is 1/100 4 At 532nm wavelength, the optical power is 6.64×10 -15 W. The light quantum effect of this level can be easily demodulated by phase-locked detection: taking a typical Binsong R928 PMT as an example, the cathode sensitivity is about 50mA/W at a wavelength of 532nm, and the typical gain is 1×10 calculated as a bias voltage of 500V 5 Then the anode response is: 5000A/W, at 6.64×10 -15 At W optical power, the effective signal scatter spectrum signal resulted in a current intensity of about 33.2pA. According to the research of the inventor and the experience of the Laser Induced Fluorescence (LIF) phase-locked detection technology which belongs to the category of laser induced spectrum, under the PMT parameters, the effective current of the LIF is generated to be more ideal to be 1nA (signal to noise ratio)>30dB, phase lock time of 100 ms); since the objects tested are identical, the LIF should be comparable to the CWTS in the background noise of the test. Thus, assuming the phase lock time is unchanged, the effective signal to noise ratio of CWTS will be-1/30 of LIF.
The diameter of the output light spot of the continuous optical fiber laser adopted in the scheme is about 2.5mm, M 2 <1.2, the beam quality is excellent, and the light spot can be compressed to about 0.3mm through the beam focusing system. At this point, the signal strength is reduced to 0.3 times the estimated value, the noise is reduced to 0.09 times (proportional to the area), and the SNR value of the final CWTS spectrum is improved by 3.3 times. According to the current available phase-locked amplification technology level and referring to LIF signal detection level and noise level, on the premise of not prolonging phase-locked time, the special phase-locked amplification system is designed to improve the test signal-to-noise ratio by about 1-2 orders of magnitude, thereby realizing a CWTS diagnosis system>30dB high quality signal to noise ratio.
The applicable electron density range: the above estimation process uses electron density of 1×10 17 m -3 The estimation is carried out, according to the current phase-locked amplification technology, the signal-to-noise ratio is expected to have a rise margin of 1 order of magnitude, and the lower limit of the density is expected to be at least as low as 1×10 under the assumption that the noise size is unchanged 16 m -3 The method comprises the steps of carrying out a first treatment on the surface of the The increase in density is such that the signal enhancement amplitude is always greater than the noise enhancement amplitude, so that the increase in density facilitates efficient signal detection for phase-locked detection when the density is from 1 x 10 17 m -3 Up to 1X 10 22 m -3 When the density is increased by 1×10 5 The PMT is twice as high as the typical gain obtained in the estimation, and the PMT is detected by the cathode current without bias, and the upper limit of detection for the density limit is 1 x 10, considering that PMT may be damaged (negative gain cannot be modulated) at greater light intensities 22 m -3 。
Electron temperature application scope:considering that the free electron spectrum reflected by Thomson scattering is caused by electron Doppler shift in the scattering process, and passing through a zero-order Doppler velocity shift formula v e ＝λ laser The delta v calculates the false width of the velocity distribution and the absolute velocity error caused by the wavelength error of each optical device. The laser line width is 20GHz (1064 nm,1000W laser) or 10kHz (532 nm,100W laser), the corresponding Doppler shift speed errors are about 20000m/s (1064 nm) and about 0.005m/s (532 nm), respectively, and the corresponding wavelength errors are 68pm and 8.9X10, respectively -6 pm, typically, the resolution of a spectrometer system that uses a fixed grating and that uses PMT for light reception is about 100pm (about 10pm under a movable grating, measured here in worse case), i.e. the linewidths of both lasers are sufficiently narrow that the resolution of the actual measurement is limited by the resolution of the monochromator. With this limitation, the minimum electron energy calculated is 0.002eV (1064 nm), 0.009eV (532 nm), both not exceeding 0.01eV. The upper limit of electron temperature measurement is mainly determined by the measurement amplitude of wavelength, electron temperature of 10000eV (about 1 hundred million degrees) can exist in the plasma at the same temperature, the corresponding wavelength acquisition needs to be covered to the width of about 600nm, the spectrum disposal scheme adopted in the application actively changes the photosensitive center of the PMT by rotating the grating, the grating can be driven by a motor to rotate to realize the wavelength coverage of any wave band, the width of about 600nm can be easily covered in one scanning, and meanwhile, the high resolution of the wavelength is maintained.
Electron temperature resolution: the resolution of the electron temperature is related to the measurement error of the wavelength or the minimum electron energy, the wavelength measurement error is 0.1nm, the minimum electron energy is 0.01eV, and the electron energy error is about 0.2eV (@ 1 eV) [ delta E= V (4E x delta E) min )]。
Diagnostic spatial resolution: the spatial resolution of the diagnosis depends on the size of the laser beam focus. Taking 532nm continuous-light fiber laser as an example, the output light spot is 2.5mm, M 2 <1.2, the beam quality is excellent. The theoretical compressible spot diameter d of the single lens is close to the diffraction limit value: d=1.22λ laser f/D, wherein f is a permeanceAnd the focal length of the lens, D is the caliber of the lens. Taking the f=1000 mm tele lens design, and the d=10 mm normal bore lens, the ideal spot diameter D calculated from this is 65 μm. Therefore, a spot of 0.3mm (300 μm) can be realized, and a large design margin is left. In the specific implementation process, some links such as beam expansion, collimation and the like are needed to further improve the quality of the light beam before focusing and compressing.
Plasma oscillation mode frequency identification range: according to the technical system of the current laser, a mode of electronic modulation is adopted by using a fiber amplifier, the laser modulation frequency range is not higher than 1kHz, and in a mode of identifying the plasma oscillation mode frequency, a gating collector which is far higher than the modulation frequency is arranged between a photomultiplier and a phase-locked amplifier to pick out phase information, and the available identification range is estimated to be 100Hz-10kHz in consideration of the need of more than 10 times of the modulation frequency of 10Hz-1 kHz.
Normal mode time resolution: the CWTS can work under the fastest working mode in a mode of fixed grating light splitting, linear arrangement fiber bundle parallel acquisition and multichannel CWTS synchronous phase locking detection. According to the calculation mode, the detection of high signal-to-noise ratio (30 dB) can be realized on a time constant of 100ms, and in the actual working process, a stable analysis time design is also required to be set, and is usually designed to be 1-10 times of phase locking time, so that the diagnosis system can realize real-time online electronic parameter monitoring of the plasma for 0.1-1 second.
The foregoing description of the preferred embodiments of the application is not intended to limit the application to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and principles of the application are intended to be included within the scope of the application.
Claims (10)
1. A continuous-light high-space-time resolution thomson scattering diagnostic system, comprising:
the laser support subsystem is used for outputting and modulating continuous high-power laser and focusing the laser on a tested plasma diagnosis area to obtain a spectrum signal, the linewidth of the laser is 10kHz to 20GHz, and the laser power is 100W to 1000W;
the spectrum treatment subsystem is used for carrying out photoelectric conversion on spectrum signals obtained by removing impurities and extracting the spectrum signals in the tested plasma diagnosis area according to the space-time resolution form requirement;
the phase-locked detection subsystem is in circuit connection with the spectrum treatment subsystem, and extracts TS scattering spectrum information from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology;
the data processing subsystem is connected with the phase-locked detection subsystem circuit and is used for carrying out data processing on the wavelength of the obtained TS scattering spectrum information and the scattering signal intensity, calculating an electron velocity distribution function and calculating electron temperature and density;
and the driving execution subsystem is used for carrying out cooperative driving control on the movable component of the diagnosis system to realize the position movement of the measuring point.
2. The continuous-light high-spatial-temporal-resolution thomson scattering diagnostic system of claim 1, wherein the laser support subsystem comprises:
the continuous light laser is used for exciting the light source to output a high-power steady laser beam;
the optical modulation device is used for carrying out frequency pulse modulation on the high-power steady laser beam output by the continuous laser, and taking the frequency pulse modulation signal as a reference signal for phase-sensitive detection extraction scattering spectrum of the phase-locked amplifier;
and the optical beam focusing system is used for focusing the modulated laser beam on the measured plasma diagnosis area to obtain a spectrum signal.
3. The continuous-light high-spatial-temporal-resolution thomson scattering diagnostic system according to claim 2, wherein the optical modulation means employs an optical fiber amplifier for electronic modulation or an optical chopper for optical modulation.
4. A continuous-light high-spatial-temporal-resolution thomson scattering diagnostic system according to claim 3, wherein said fiber amplifier employs a fiber cone amplifier.
5. A continuous-light high-spatial-temporal-resolution thomson scattering diagnostic system according to claim 3, characterized in that said spectral treatment subsystem comprises:
the laser cut-off device is arranged on a laser light path after laser passes through the plasma diagnosis area to be detected and is used for collecting and removing interference sources including laser and direct scattering generated by interface scattering;
the collecting light cut-off is opposite to the collecting lens group and is positioned at the other side of the tested plasma diagnosis area far away from the collecting lens group;
the collecting lens group is used for collecting spectrum signals obtained from the plasma diagnosis area to be tested to a plurality of monochromators;
the multi-monochromator is used for inhibiting laser stray light and Rayleigh scattered light interference generated in the laser propagation process of the spectrum signals collected by the collection lens group in a dispersion cancellation mode, so that the stray light is suppressed to the maximum extent, the signal-to-noise ratio of the scattered signals is improved, and the spectrum signals with different wavelengths are obtained;
and the photoelectric detector is used for converting the spectrum signals processed by the multiple monochromators into electric signals.
6. The continuous-light high-spatial-temporal resolution thomson scattering diagnostic system of claim 5, wherein the photodetectors employ photomultiplier tubes.
7. The continuous-light high spatial-temporal resolution thomson scattering diagnostic system of claim 5, wherein,
the multi-monochromator adopts a grating-adjustable multi-monochromator, and the photoelectric detector adopts a single photomultiplier.
8. The continuous-light high spatial-temporal resolution thomson scattering diagnostic system of claim 5, wherein,
the multi-monochromator adopts a grating fixed multi-monochromator, the photoelectric detector adopts a photomultiplier array, and multi-wavelength synchronous extraction is realized between the grating fixed multi-monochromator and the photomultiplier array by adopting a fiber bundle multi-channel densely-distributed acquisition mode.
9. The continuous-light high-spatial-temporal resolution thomson scattering diagnostic system of claim 1, wherein the phase-locked detection subsystem comprises:
the phase-locked amplifier is in circuit connection with the spectrum treatment subsystem, TS scattering spectrum information is extracted from an electric signal obtained by photoelectric conversion by adopting a phase-locked detection technology, and a reference signal of the phase-locked amplifier is a frequency pulse modulation signal of the optical modulation device;
and the acquisition system is connected with the phase-locked amplifier circuit and is used for acquiring the extracted TS scattering spectrum information.
10. The continuous-light high-spatial-temporal resolution thomson scattering diagnostic system of claim 9, wherein the phase-locked detection subsystem further comprises:
the gating collector is arranged between the lock-in amplifier and the spectrum treatment subsystem, takes the fluctuation quantity related to the oscillation behavior in the plasma to be tested as a trigger signal of the hollow collector, and is used for directly obtaining time resolution electronic speed diagnosis and realizing a transient diagnosis function.
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