TS diagnostic signal processing method for obtaining frequency-sensitive signal directly using spectrum analyzer

Abstract

The application discloses a TS diagnostic signal processing method for obtaining a frequency-sensitive signal directly by using a spectrum analyzer, and comprises the following steps: obtaining a Doppler spectrum corresponding to a complete EVDF by a continuous light high space-time resolution Thomson scattering diagnostic system; finding a maximum slope position in the Doppler spectrum, moving a target wavelength of a polychromator to a wavelength corresponding to a Doppler shift of an electron velocity of the maximum slope position, and stabilizing the frequency at the wavelength; connecting a Thomson scattering signal obtained by the polychromator to the spectrum analyzer for analysis, obtaining a corresponding Doppler spectrum signal, and obtaining an oscillation frequency signal of the EVDF affected by plasma instability. The application does not need to know the plasma oscillation frequency in advance, does not need to perform corresponding triggering work, and can perform TS diagnosis, and is especially effective for the diagnosis of a wide spectrum of plasma instability, and gives the possibility of obtaining information of the influence of plasma 10-100 kHz oscillation on the EVDF for the TS diagnosis.

Description

Technical Field

[0001] This application relates to the field of plasma diagnostic technology, and in particular, to a TS diagnostic signal processing method that directly uses a spectrum analyzer to obtain frequency-sensitive signals. Background Technology

[0002] Thomson scattering (TS) is currently the most direct non-contact, low-interference diagnostic method for obtaining the energy distribution of electrons in plasma. Its basic principle is to obtain the electron velocity distribution (EVDF) by elastically scattering electromagnetic radiation between laser-excited electromagnetic radiation and charged free particles, and by analyzing the Doppler spectrum of the scattered light.

[0003] Current Thomson scattering diagnostics, when used for frequency-sensitive diagnostics, rely on pulsed lasers. This means the diagnostic information is limited to a single point in time: the instant of laser emission. When diagnosing frequency-sensitive phenomena, information can only be obtained by synchronizing laser triggering with the phenomenon. This requires prior knowledge of the plasma's frequency and appropriate triggering. However, traditional Thomson scattering diagnostics cannot provide information about unknown frequencies or broad-spectrum instabilities, making it unsuitable for measuring broad-spectrum and other uncontrollable frequency plasma oscillations. Similarly, traditional Thomson scattering diagnostics cannot be used to detect the frequency of the frequency-sensitive phenomenon itself. Summary of the Invention

[0004] This application provides a TS diagnostic signal processing method that directly uses a spectrum analyzer to obtain frequency-sensitive signals, thereby solving the technical problem that existing technologies require prior knowledge of the plasma oscillation frequency and corresponding triggering operations when performing frequency-sensitive diagnostics, making them unsuitable for measuring plasma oscillations of the broad spectrum and other uncontrollable frequencies.

[0005] This application adopts the following technical solution:

[0006] A method for processing frequency-sensitive signals (TS) diagnostic signals directly using a spectrum analyzer, comprising the following steps:

[0007] First, the complete Doppler spectrum corresponding to the EVDF was obtained by using a continuous light high spatiotemporal resolution Thomson scattering diagnostic system.

[0008] Next, the position with the maximum slope is found in the Doppler spectrum, the target wavelength of the multi-monochromator is shifted to the wavelength after the Doppler shift corresponding to the electron velocity at the position with the maximum slope, and the frequency is stabilized at that wavelength;

[0009] Finally, the Thomson scattering signal obtained by the multi-monochromator is connected to the spectrum analyzer for analysis. When the signal averaging time is sufficient, the corresponding Doppler spectrum signal can be obtained, thereby obtaining the oscillation frequency signal of EVDF affected by plasma instability.

[0010] Furthermore, the continuous light high spatiotemporal resolution Thomson scattering diagnostic system includes:

[0011] The laser support subsystem is used to output and modulate a continuous high-power laser and focus it on the diagnostic region of the plasma under test to obtain a spectral signal. The linewidth of the laser is 10 kHz to 20 GHz and the laser power is 100 W to 1000 W.

[0012] The spectral processing subsystem is used to perform photoelectric conversion on the spectral signal obtained from the diagnostic region of the plasma under test after removing impurities and extracting the spectral signal according to the spatial-temporal resolution requirements.

[0013] The phase-locked detection subsystem is connected to the spectral processing subsystem circuit and uses phase-locked detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion.

[0014] The data processing subsystem is connected to the phase-locked detection subsystem circuit and is used to process the wavelength and scattering signal intensity of the obtained TS scattering spectrum information to calculate the electron velocity distribution function, electron temperature and density.

[0015] The drive execution subsystem is used to coordinate drive control of the moving parts of the diagnostic system to realize the position movement of the measurement points.

[0016] Furthermore, the laser support subsystem includes:

[0017] A continuous-wave laser is used to excite a light source to output a high-power steady-state laser beam.

[0018] An optical modulation device is used to frequency pulse modulate the high-power steady-state laser beam output from a continuous-wave laser, and the frequency pulse modulation signal is used as a reference signal for a lock-in amplifier to perform phase-sensitive detection to extract the scattering spectrum.

[0019] An optical beam-focusing system is used to focus a modulated laser beam onto the diagnostic region of the plasma under test to obtain a spectral signal.

[0020] Furthermore, the optical modulation device employs an optical fiber amplifier for electronic modulation, and the optical fiber amplifier is an optical fiber taper amplifier; or, the optical modulation device employs an optical chopper for optical modulation.

[0021] Furthermore, the spectral processing subsystem includes:

[0022] A laser cutoff is placed in the laser beam path after the laser passes through the diagnostic area of ​​the plasma under test. It is used to collect and eliminate interference sources, including direct laser scattering caused by laser beams and interface scattering.

[0023] The light-collecting cutoff is positioned opposite the collecting lens group and on the opposite side of the plasma diagnostic area being measured, away from the collecting lens group.

[0024] A collection lens group is used to collect the spectral signal obtained from the diagnostic region of the plasma under test into a multi-monochromatic instrument;

[0025] A multi-monochromatic meter is used to suppress stray laser light and Rayleigh scattering interference generated during laser propagation by using dispersion cancellation to collect spectral signals from the lens group. This maximizes the suppression of stray light and improves the signal-to-noise ratio of the scattered signal, thereby obtaining spectral signals of different wavelengths.

[0026] A photodetector is used to convert spectral signals processed by a multi-monochromatic instrument into electrical signals.

[0027] Furthermore, the photodetector employs a photomultiplier tube.

[0028] Furthermore, the multi-monochromator is a grating-tunable multi-monochromator, and the photodetector is a single photomultiplier tube.

[0029] Furthermore, the multi-monochromator is a grating-fixed multi-monochromator, the photodetector is a photomultiplier tube array, and the grating-fixed multi-monochromator and the photomultiplier tube array are connected by a multi-channel dense acquisition method using fiber bundles to achieve synchronous extraction of multiple wavelengths.

[0030] Furthermore, the phase-locked detection subsystem includes:

[0031] A lock-in amplifier is connected to the spectral processing subsystem circuit. It uses lock-in detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion. The reference signal of the lock-in amplifier is the frequency pulse modulation signal of the optical modulation device.

[0032] The acquisition system, connected to the lock-in amplifier circuit, is used to acquire the extracted TS scattering spectrum information.

[0033] Furthermore, the phase-locked detection subsystem also includes:

[0034] A gated acquisition unit is located between the lock-in amplifier and the spectral processing subsystem. It uses the fluctuation quantity related to the oscillation behavior in the measured plasma as the trigger signal for the gated acquisition unit to directly obtain time-resolved electron velocity diagnosis and realize transient diagnosis function.

[0035] Compared with the prior art, this application has the following beneficial effects:

[0036] This application provides a TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer. The method first obtains the complete Doppler spectrum corresponding to the EVDF using a continuous light high spatiotemporal resolution Thomson scattering diagnostic system. Next, it finds the position with the maximum slope in the Doppler spectrum, shifts the target wavelength of the multi-monochromator to the wavelength corresponding to the Doppler shift of the electron velocity at that position, and stabilizes the frequency at that wavelength. Finally, it connects the Thomson scattering signal obtained by the multi-monochromator to the spectrum analyzer for analysis. With sufficient signal averaging time, the corresponding Doppler spectrum signal can be obtained, thereby obtaining the oscillation frequency signal of the EVDF affected by plasma instability. The TS diagnostic signal processing method provided in this application, which directly obtains frequency-sensitive signals using a spectrum analyzer, relies on a continuous-light high spatiotemporal resolution Thomson scattering diagnostic system to obtain an accurate electron velocity distribution function (EVDF). Utilizing the characteristic that the point of maximum slope in the velocity distribution function is generally most susceptible to drift instability, an ultra-narrow linewidth laser is used to lock the wavelength at the position of maximum slope in the electron velocity distribution. The frequency-sensitive information of the EVDF is obtained by directly inputting the signal into a spectrum analyzer. The greatest advantage of this diagnostic method is that it does not require synchronization of transient phenomena, making it suitable for measuring broad-spectrum and other uncontrollable plasma oscillations. This application uses the wavelength after Doppler shift corresponding to the electron velocity at the position of maximum Doppler spectral slope as the target wavelength of the monochromator. Its greatest advantage is that it does not require prior knowledge of the plasma oscillation frequency or corresponding triggering operations for TS diagnosis. It is particularly effective for diagnosing broad-spectrum plasma instability, providing the possibility of obtaining information on the impact of 10-100kHz plasma oscillations on the EVDF in plasma oscillations of unknown frequencies, spectral frequencies, and other types where laser synchronization is impossible. This function is unprecedented in previous TS diagnostic methods.

[0037] In addition to the purposes, features, and advantages described above, this application provides other purposes, features, and advantages. The application will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 This is a schematic flowchart of a preferred embodiment of the TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer.

[0040] Figure 2 This is a schematic diagram of the complete Doppler spectrum corresponding to the EVDF obtained by a preferred embodiment of this application.

[0041] Figure 3 This is a schematic diagram of the location of the maximum Doppler spectral slope in a preferred embodiment of this application.

[0042] Figure 4 This is a schematic diagram of the composition of a continuous light high spatiotemporal resolution Thomson scattering diagnostic system according to a preferred embodiment of this application.

[0043] Figure 5 This is a schematic diagram of the composition of a continuous light high spatiotemporal resolution Thomson scattering diagnostic system according to another preferred embodiment of this application.

[0044] Figure 6 This is a schematic diagram illustrating the principle of adjusting the target wavelength of the multi-monochromator in the partial continuous light high spatiotemporal resolution Thomson scattering diagnostic system (with the phase-locked detector subsystem and optical modulation device turned off) of the preferred embodiment to the wavelength after the Doppler shift corresponding to the electron velocity at the position of maximum slope and connecting it to the spectrum analyzer.

[0045] Figure 7 This is a schematic diagram illustrating the principle of adjusting the target wavelength of the multi-monochromator in a partially continuous light high spatiotemporal resolution Thomson scattering diagnostic system (with the phase-locked detector subsystem and optical modulation device turned off) of another preferred embodiment to the wavelength after the Doppler shift corresponding to the electron velocity at the position of maximum slope and connecting it to the spectrum analyzer. Detailed Implementation

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] Reference Figure 1 A preferred embodiment of this application provides a TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer, comprising the following steps:

[0048] S1. First, the complete Doppler spectrum corresponding to the EVDF is obtained through a continuous light high spatiotemporal resolution Thomson scattering diagnostic system (see...). Figure 2 );

[0049] S2. Locate the position of maximum slope in the Doppler spectrum, shift the target wavelength of the multi-monochromator to the wavelength corresponding to the Doppler shift of the electron velocity at the position of maximum slope, and stabilize the frequency at that wavelength (see...). Figure 3 During implementation, EVDF can be used at a velocity of approximately 1 (T) from the center. e / m e ) 1 / 2 The feature with the largest slope is found in the Doppler spectrum, where T is the location of the largest slope. e Indicates electron temperature, m eThis indicates the electron temperature; thus, both drift and density oscillations will be reflected in the signal fluctuations at a significant amplitude.

[0050] S3. The Thomson scattering signal obtained by the multi-monochromatic instrument is connected to the spectrum analyzer for analysis. If the signal averaging time is sufficient, the corresponding Doppler spectrum signal can be obtained, thereby obtaining the oscillation frequency signal of EVDF affected by plasma instability.

[0051] This embodiment provides a TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer. The method first obtains the complete Doppler spectrum corresponding to the EVDF using a continuous light high spatiotemporal resolution Thomson scattering diagnostic system. Next, it finds the position with the maximum slope in the Doppler spectrum, shifts the target wavelength of the multi-monochromator to the wavelength corresponding to the Doppler shift of the electron velocity at that position, and stabilizes the frequency at that wavelength. Finally, it connects the Thomson scattering signal obtained by the multi-monochromator to the spectrum analyzer for analysis. With sufficient signal averaging time, the corresponding Doppler spectrum signal can be obtained, thereby obtaining the oscillation frequency signal of the EVDF affected by plasma instability.

[0052] This embodiment provides a TS diagnostic signal processing method that directly obtains frequency-sensitive signals using a spectrum analyzer. It relies on a continuous-light high-spatiotemporal-resolution Thomson scattering diagnostic system to obtain an accurate electron velocity distribution function (EVDF). Utilizing the characteristic that the point of maximum slope in the velocity distribution function is most susceptible to drift instability, an ultra-narrow linewidth laser is used to lock the wavelength at the position of maximum slope in the electron velocity distribution. The frequency-sensitive information of the EVDF is obtained by directly inputting the signal into a spectrum analyzer. The greatest advantage of this diagnostic method is that it does not require synchronization of transient phenomena, making it suitable for measuring broad-spectrum and other uncontrollable plasma oscillations. This embodiment uses the wavelength after Doppler shift corresponding to the electron velocity at the position of maximum Doppler spectral slope as the target wavelength for the monochromator. Its greatest advantage is that it does not require prior knowledge of the plasma oscillation frequency or corresponding triggering operations for TS diagnosis. It is particularly effective for diagnosing broad-spectrum plasma instability, providing the possibility of obtaining information on the impact of 10-100kHz plasma oscillations on the EVDF in plasma oscillations with unknown frequencies, spectral frequencies, and other plasma oscillations where laser synchronization is impossible. This function is unprecedented in previous TS diagnostic methods.

[0053] Reference Figure 4 The continuous light high spatiotemporal resolution Thomson scattering diagnostic system includes:

[0054] The laser support subsystem is used to output and modulate a continuous high-power laser and focus it on the diagnostic region of the plasma under test to obtain a spectral signal. The linewidth of the laser is 10 kHz to 20 GHz, the continuous power of the laser is 100 W to 1000 W, and the transient power is also 100 W to 1000 W.

[0055] The spectral processing subsystem is used to perform photoelectric conversion on the spectral signal obtained from the diagnostic region of the plasma under test after removing impurities and extracting the spectral signal according to the spatial-temporal resolution requirements.

[0056] The phase-locked detection subsystem is connected to the spectral processing subsystem circuit and uses phase-locked detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion.

[0057] The data processing subsystem is connected to the phase-locked detection subsystem circuit and is used to process the wavelength and scattering signal intensity of the obtained TS scattering spectrum information to calculate the electron velocity distribution function, electron temperature and density.

[0058] The drive execution subsystem is used to coordinate drive control of the moving parts of the diagnostic system to realize the position movement of the measurement points.

[0059] This embodiment proposes a continuous-wave high spatiotemporal resolution Thomson scattering diagnostic system, specifically a Thomson scattering diagnostic system based on continuous-wave laser and using phase-locked loop detector technology for signal extraction. This system not only greatly expands the versatility of Thomson scattering diagnosis but also significantly reduces system costs. The scheme replaces the pulsed laser with a continuous-wave, narrow-linewidth fiber laser, drastically reducing the laser transient power from approximately 10-100MW to 100-1000W, and weakening the transient intensity to approximately 10. -4 -10 -6The signal-to-noise ratio of the original scattered signal decreases proportionally. After the laser is replaced, the measurement generates a continuous Thomson scattering spectral signal, rather than a pulsed Thomson scattering spectral signal. Lock-in amplification technology can be used to extract weak scattered spectral signals with ultra-high signal-to-noise ratios below -100dB or even -110dB. Thus, a single laser can achieve signal quality superior to the current pulsed laser-based Thomson scattering diagnostic scheme, greatly reducing system cost and measurement time. In addition, compared with pulsed lasers, continuous lasers have the important characteristics of easy spot compression and time manipulation. By focusing and compressing the incident beam and the focusing and compression of the scattering spectrum collection optics, precise control of the diagnostic domain size can be achieved. The Thomson scattering signal excited by the continuous laser retains the frequency and transient characteristics of the plasma. Through high-speed gated acquisition and active frequency modulation, the measurement can be manipulated in the time domain, achieving a high spatiotemporal resolution diagnostic capability far exceeding the current pulsed laser-based Thomson scattering diagnostic scheme. Because of the use of phase-locked loop detector technology, this embodiment can obtain a high signal-to-noise ratio using a relatively low-power (100W to 1000W) continuous laser. The reduction in laser power can effectively avoid the problem of secondary discharge of neutral gas during low-temperature plasma measurement.

[0060] Preferably, the laser support subsystem includes:

[0061] A continuous-wave laser is used to excite a light source to output a high-power steady-state laser beam.

[0062] An optical modulation device is used to frequency pulse modulate the high-power steady-state laser beam output from a continuous-wave laser, and the frequency pulse modulation signal is used as a reference signal for a lock-in amplifier to perform phase-sensitive detection to extract the scattering spectrum.

[0063] An optical beam-focusing system is used to focus a modulated laser beam onto the diagnostic region of the plasma under test to obtain a spectral signal.

[0064] Preferably, such as Figure 4 As shown, the optical modulation device uses an optical fiber amplifier for electronic modulation.

[0065] Preferably, such as Figure 5 As shown, the optical modulation device uses an optical chopper for optical modulation.

[0066] Preferably, the fiber amplifier is a fiber tapered amplifier.

[0067] Preferably, the spectral processing subsystem includes:

[0068] A laser cutoff is placed in the laser beam path after the laser passes through the diagnostic area of ​​the plasma under test. It is used to eliminate interference sources, including the laser beam itself and direct laser scattering caused by interface scattering.

[0069] The light-collecting cutoff is positioned opposite the collecting lens group and on the opposite side of the plasma diagnostic area being measured, away from the collecting lens group.

[0070] A collection lens group is used to collect the spectral signal obtained from the diagnostic region of the plasma under test into a multi-monochromatic instrument;

[0071] A multi-monochromatic meter is used to suppress stray laser light and Rayleigh scattering interference generated during laser propagation by using dispersion cancellation to collect spectral signals from the lens group. This maximizes the suppression of stray light and improves the signal-to-noise ratio of the scattered signal, thereby obtaining spectral signals of different wavelengths.

[0072] A photodetector is used to convert spectral signals processed by a multi-monochromatic instrument into electrical signals.

[0073] Preferably, the photodetector is a photomultiplier tube.

[0074] Preferably, such as Figure 4 As shown, the multi-monochromator is a grating-tunable multi-monochromator, and the photodetector is a single photomultiplier tube.

[0075] Preferably, such as Figure 5 As shown, the multi-monochromator is a grating-fixed multi-monochromator, the photodetector is a photomultiplier tube array, and the grating-fixed multi-monochromator and the photomultiplier tube array are connected by a multi-channel dense acquisition method using fiber bundles to achieve synchronous extraction of multiple wavelengths.

[0076] Preferably, the phase-locked detection subsystem includes:

[0077] A lock-in amplifier is connected to the spectral processing subsystem circuit. It uses lock-in detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion. The reference signal of the lock-in amplifier is the frequency pulse modulation signal of the optical modulation device.

[0078] The acquisition system, connected to the lock-in amplifier circuit, is used to acquire the extracted TS scattering spectrum information.

[0079] Preferably, the phase-locked detection subsystem further includes:

[0080] A gated acquisition unit is located between the lock-in amplifier and the spectral processing subsystem. It uses the fluctuation quantity related to the oscillation behavior in the measured plasma as the trigger signal for the gated acquisition unit to directly obtain time-resolved electron velocity diagnosis and realize transient diagnosis function.

[0081] The main function of the laser support subsystem in the above embodiment is to generate a sufficiently high-power, narrow-linewidth, single-frequency modulated laser and to compress and focus the laser spot to improve the power density of the laser, so that the number of photons scattered by the laser Thomson scattering meets the requirements for phase-sensitive detection. Specifically, the system uses a high-power (high power here and thereafter refers to the power relative to a typical narrow-linewidth, continuous laser, but still low power relative to a pulsed laser), narrow-linewidth, continuous-wave laser as the excitation source. It employs either laser fiber amplifier electronic modulation or high-power optical chopper optical modulation to precisely pulse-modulate the high-power steady-state laser beam. The modulated signal serves as a reference signal for phase-sensitive detection by a lock-in amplifier to extract weak scattering spectra. Subsequently, a high-power optical focusing system focuses the laser onto the diagnostic region of the plasma under test to achieve higher power density (effectively improving the signal-to-noise ratio) and better spatial resolution. Due to the high power of the incident laser, any possible stray laser light could overwhelm the weak scattering spectrum signal. A laser cutoff is used to eliminate interference sources that could directly scatter the laser, such as the main laser beam and interface scattering. The innovation of this subsystem lies in its use of a high-power laser capable of continuous output, with a linewidth as low as 20 GHz, which can be further compressed to the ~10 kHz level, far lower than the typical linewidth of a traditional YAG laser, making the laser frequency / wavelength as a test probe more accurate. A low linewidth means that stray lasers only interfere with the scattering spectral data within a very narrow range, thus significantly improving the resolution of the measurement.

[0082] The spectral processing subsystem of the above embodiment mainly transmits the laser TS spectral signal to a photodetector for photoelectric conversion in a highly efficient and reliable manner, according to the spatial-temporal resolution requirements. Laser stray light and Rayleigh scattering interference generated during laser propagation have the most significant impact on the spectral signal. In this subsystem, stray light generation is suppressed at its source through various means, including laser main beam polarization state interface control, the application of laser and light-collecting cutoff devices, and stray light elimination by limiting the aperture of the spectral collecting lens group. A multi-monochromatic instrument is used to suppress stray light through dispersion cancellation, thereby maximizing stray light suppression and improving the signal-to-noise ratio of the scattered signal. Simultaneously, since a continuous laser generates a continuous scattered signal, wavelength scanning of the scattered signal can be achieved by driving the grating rotation with a precision motor. Using a PMT (photomultiplier tube) as the detector, high-resolution wavelength control with a limiting resolution higher than 0.01 nm is achieved, thus achieving a resolution far superior to that of pulsed laser TS diagnostic systems (~0.1 nm). Furthermore, a fixed-grating multi-monochromatic instrument is used for dispersion, and a multi-channel dense acquisition method using fiber bundles is employed to achieve synchronous extraction of multiple wavelengths. Based on sub-second phase-locked time, high-resolution full-wave spectrum extraction and analysis can be achieved at the second level, meeting the requirements for synchronous online measurement.

[0083] The signal received by the photomultiplier tube (PMT) includes Thomson scattering signals generated by the interaction of plasma and modulated laser, stray light signals, and plasma background radiation signals. The function of the phase-locked detection subsystem in the above embodiment is to effectively extract the extremely weak laser-induced TS spectrum from high background noise. The core innovation of this application is signal extraction based on continuous laser and using phase-locked detection technology. The original signal to be analyzed input to this subsystem is an electrical signal converted from the scattered spectrum by the PMT, and the signal being compared is an active frequency modulation (electronic chopper or optical chopper) monitoring signal.

[0084] The aforementioned drive execution subsystem is mainly responsible for the controllable operation of the moving parts of the continuous light high spatiotemporal resolution Thomson scattering diagnostic system, ensuring the coordinated movement of the incident laser-laser cutoff and the collecting lens group-collecting cutoff, so that the diagnostic domain of the incident laser coincides with the focal point of the collecting lens group, thereby realizing one-dimensional, two-dimensional or three-dimensional measurement.

[0085] In addition to the basic functions mentioned above, the system design in this application possesses inherent advantages, enabling it to identify and process strong transient high-frequency oscillation modes of the tested plasma—a capability impossible in traditional pulsed TS diagnostic systems. This is because existing high-energy pulsed YAG lasers operate at frequencies of ~10Hz, which cannot be increased due to limitations in optical crystal and other component materials, falling far below the ~kHz level of transient modes such as ion acoustic wave oscillations. From an informatics perspective, this makes it impossible to obtain effective analytical data. By reducing the phase-locked detection frequency and employing high-frequency gating technology to add a gated acquisition unit before the phase-locked stage, combined with highly efficient data processing methods, high-fidelity, frequency-sensitive diagnostics of plasma EEDF disturbances can be performed, enabling the analysis of previously unprocessable strong transient plasma modes.

[0086] The continuous-wave high spatiotemporal resolution Thomson scattering diagnostic system provided in this embodiment achieves a highly versatile applicable range of plasma electron density and temperature, along with fine electron energy resolution and spatial-temporal resolution. This diagnostic system is suitable for electron densities of 1×10⁻⁶. 16 m -3 Up to 1×10 22 m -3 The system can measure plasmas with electron temperatures ranging from 0.01 eV to 10,000 eV; when monitoring plasmas with an electron temperature of 1 eV, the energy resolution is 0.2 eV; the spatial resolution of the diagnostics is better than 0.3 mm; it can perform frequency identification or phase-sensitive diagnostics for plasma oscillation modes from 100 Hz to 10 kHz; the diagnostic system can achieve real-time online monitoring of plasma electronic parameters from 0.1 to 1 second.

[0087] The specific implementation and performance analysis are as follows:

[0088] Feasibility and signal-to-noise ratio of continuous-wave Thomson scattering (CWTS) signal detection: The cross-sectional constant of electron Thomson scattering is 6.65 × 10⁻⁶. -29 m 2 With photon energy hν=hc / λ laser Calculations show that a 100-watt 532nm laser emits approximately 2.7 × 10⁻⁶ ppm per second. 20 A photon, according to a 1×10 17 m -3 Based on the plasma density and the estimated length of the 1mm diagnostic space, the total number of photons was found to be 1.78 × 10⁻⁶. 6 Considering the relative solid angle between the collecting optical path and the scattering element, and assuming a light collection efficiency of 1 / 100, the effective luminous flux is 1.78 × 10⁻⁶. 4 The optical output per second (p / s) at a wavelength of 532 nm is 6.64 × 10⁻⁶. -15 W. This level of photonic quantum effect can be easily demodulated using phase-locked detection: taking a typical Hamamatsu R928 PMT as an example, at a wavelength of 532nm, the cathode sensitivity is approximately 50mA / W, and with a bias voltage of 500V, its typical gain is 1×10⁻⁶. 5 Therefore, the anode response is 5000 A / W, which corresponds to 6.64 × 10⁻⁶ A / W. -15 At W optical power, the current intensity caused by the effective signal scattering spectrum is approximately 33.2 pA. Based on the inventors' experience in researching laser-induced fluorescence (LIF) phase-locked detection technology, which also falls under the category of laser-induced spectroscopy, under the above PMT parameters, a relatively ideal effective LIF current is ~1 nA (signal-to-noise ratio >30 dB, phase-locked time 100 ms). Since the test objects are the same, the background noise of LIF and CWTS should be comparable. Therefore, assuming the phase-locked time remains constant, the effective signal-to-noise ratio of CWTS will be ~1 / 30 of that of LIF.

[0089] The continuous-beam fiber laser used in this design has an output spot diameter of approximately 2.5 mm. 2 With a beam density <1.2, the beam quality is excellent, and the beam spot can be compressed to approximately 0.3 mm using a focusing system. At this point, the signal intensity decreases to 0.3 times the previously estimated value, and the noise decreases to 0.09 times (proportional to area), ultimately improving the SNR value of the CWTS spectrum by 3.3 times. Based on the current achievable lock-in amplification technology and referring to the LIF signal detection and noise levels, without extending the lock-in time, a dedicated lock-in amplification system can be designed to improve the test signal-to-noise ratio by approximately 1-2 orders of magnitude, thereby achieving a high-quality signal-to-noise ratio >30 dB for the CWTS diagnostic system.

[0090] Applicable electron density range: The above estimation process is based on an electron density of 1×10⁻⁶. 17 m -3 Based on current lock-in amplification technology, the signal-to-noise ratio is expected to have a margin of improvement of one order of magnitude. Assuming the noise level remains constant, the lower limit of the density is expected to be at least 1×10⁻⁶. 16 m -3 The increase in density ensures that the signal enhancement is always greater than the noise enhancement, thus increasing density is beneficial for effective signal detection in phase-locked loop (PLL) detectors. When the density increases from 1×10... 17 m -3 Reaching 1×10 22 m -3 When the density increases by 1×10 5 This is equal to the typical gain obtained in the estimation. At this point, the PMT does not require a bias voltage and can achieve detection using only the cathode current. Considering that the PMT may be damaged at higher light intensities (due to the inability to modulate negative gain), the achievable density limit detection upper limit is 1×10⁻⁶. 22 m -3 .

[0091] The applicable range of electron temperature: Considering that the free electron spectrum reflected by Thomson scattering is caused by the electron Doppler shift during the scattering process, the zero-order Doppler velocity-displacement formula v is used. e =λ laser Δν is used to calculate the spurious width and absolute velocity error of the velocity distribution caused by wavelength errors of each optical component. For laser linewidths of 20 GHz (1064 nm, 1000 W laser) or 10 kHz (532 nm, 100 W laser), the corresponding Doppler displacement velocity errors are approximately 20000 m / s (1064 nm) and approximately 0.005 m / s (532 nm), respectively, with corresponding wavelength errors of 68 pm and 8.9 × 10⁻⁶ pm, respectively. -6Typically, the resolution of a spectrometer system with a fixed grating and a PMT (partial transducer) is approximately 100 pm (approximately 10 pm with a movable grating; this calculation is based on a less favorable scenario). This means that the linewidths of both lasers are sufficiently narrow, limiting the actual measured resolution to the monochromator's resolution. Under this limitation, the calculated minimum electron energies are 0.002 eV (1064 nm) and 0.009 eV (532 nm), both not exceeding 0.01 eV. The upper limit for electron temperature measurement is primarily determined by the wavelength measurement amplitude. In isothermal plasmas, electron temperatures may reach 10,000 eV (approximately 100 million degrees Celsius), requiring wavelength acquisition to cover a width of approximately 600 nm. The spectral processing scheme employed in this invention actively changes the PMT's photosensitive center by rotating the grating. This allows for arbitrary wavelength coverage by a motor-driven grating rotation, easily covering a width of approximately 600 nm in a single scan while maintaining high wavelength resolution.

[0092] Electron temperature resolution: The resolution of electron temperature is related to the measurement error of wavelength or the lowest electron energy. Based on the above calculations, a wavelength measurement error of 0.1 nm corresponds to a lowest electron energy of 0.01 eV. According to the square relationship between energy and velocity, the electron energy error can be calculated to be approximately 0.2 eV (@1 eV) [ΔE=√(4E×ΔE]]. min )).

[0093] Diagnostic spatial resolution: The spatial resolution of the diagnosis depends on the size of the laser beam. Taking a 532nm continuous-wave fiber laser as an example, the output spot size is ~2.5mm, M 2 <1.2, beam quality is excellent. The theoretically compressible spot diameter d of a single lens is close to the diffraction limit: d = 1.22λ laser f / D, where f is the lens focal length and D is the lens aperture. Taking a telephoto lens design with f = 1000mm and a standard aperture lens with D = 10mm as an example, the ideal spot diameter d is calculated to be 65μm. Therefore, a spot size of 0.3mm (300μm) can be achieved with a large design margin. In the actual implementation process, before focusing and compression, further steps such as beam expansion and collimation are needed to improve beam quality.

[0094] Plasma oscillation mode frequency identification range: Based on the current laser technology, using fiber optic amplifiers for electronic modulation, the modulated frequency range of the laser is no higher than 1kHz. In the plasma oscillation mode frequency identification method, a gated acquisition device with a frequency much larger than the modulation frequency is placed between the photomultiplier tube and the lock-in amplifier to pick phase information. Considering that it needs to be more than 10 times the modulation frequency of 10Hz-1kHz, the achievable identification range is estimated to be 100Hz-10kHz.

[0095] Normal mode time resolution: By using fixed grating beam splitting, parallel acquisition of linearly arranged fiber bundles, and synchronous phase-locked detection of multi-channel CWTS, the CWTS can operate at its fastest speed. Based on the aforementioned calculation model, high signal-to-noise ratio (>30dB) detection can be achieved with a time constant of 100ms. In actual operation, a stable resolution time design is also required, typically designed to be 1 to 10 times the phase-locked time. Therefore, the diagnostic system can achieve real-time online monitoring of plasma electronic parameters from 0.1 to 1 second.

[0096] In summary, in order to obtain the corresponding Doppler spectrum signal and thus the oscillation frequency signal of EVDF affected by plasma instability, this application first utilizes... Figure 4 or Figure 5 The complete continuous-light high spatiotemporal resolution Thomson scattering diagnostic system shown obtains, as Figure 2 The complete Doppler spectrum corresponding to the EVDF is shown; then, after finding the position of maximum slope in the Doppler spectrum, ... Figure 4 or Figure 5 The target wavelength of the multi-monochromatic instrument in the continuous light high spatiotemporal resolution Thomson scattering diagnostic system shown is shifted to the wavelength corresponding to the Doppler shift of the electron velocity at the position of maximum slope, and the frequency is stabilized at that wavelength (see...). Figure 3 Finally, Figure 4 or Figure 5 The phase-locked detector subsystem and optical modulation device of the continuous-light high spatiotemporal resolution Thomson scattering diagnostic system shown are turned off, and the multi-monochromator is connected to the spectrum analyzer. After restarting the continuous-light high spatiotemporal resolution Thomson scattering diagnostic system with the phase-locked detector subsystem and optical modulation device turned off, the Thomson scattering signal obtained by the multi-monochromator can be connected to the spectrum analyzer for analysis (see...). Figure 6 and Figure 7 Given sufficient signal averaging time, the corresponding Doppler spectrum signal can be obtained, thereby revealing the oscillation frequency signal of the EVDF affected by plasma instability. Since this application does not require prior knowledge of the plasma oscillation frequency or any corresponding triggering operation for TS diagnosis, it is particularly effective for diagnosing broad-spectrum plasma instability. It makes it possible to obtain information on the impact of 10-100kHz plasma oscillations on the EVDF in plasma oscillations of unknown frequencies, spectral frequencies, and other conditions where laser synchronization is not possible.

[0097] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for processing TS diagnostic signals by directly obtaining frequency-sensitive signals using a spectrum analyzer, characterized in that, Including the following steps: First, the complete Doppler spectrum corresponding to the EVDF is obtained by using a continuous light high spatiotemporal resolution Thomson scattering diagnostic system. Find the position with the maximum slope in the Doppler spectrum, shift the target wavelength of the multi-monochromator to the wavelength after the Doppler shift corresponding to the electron velocity at the position with the maximum slope, and stabilize the frequency at that wavelength. The Thomson scattering signal obtained by the multi-monochromator is connected to the spectrum analyzer for analysis. If the signal averaging time is sufficient, the corresponding Doppler spectrum signal can be obtained, thereby obtaining the oscillation frequency signal of EVDF affected by plasma instability.

2. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 1, characterized in that, The continuous light high spatiotemporal resolution Thomson scattering diagnostic system includes: The laser support subsystem is used to output and modulate a continuous high-power laser and focus it on the diagnostic region of the plasma under test to obtain a spectral signal. The linewidth of the laser is 10 kHz to 20 GHz and the laser power is 100 W to 1000 W. The spectral processing subsystem is used to perform photoelectric conversion on the spectral signal obtained from the diagnostic region of the plasma under test after removing impurities and extracting the spectral signal according to the spatial-temporal resolution requirements. The phase-locked detection subsystem is connected to the spectral processing subsystem circuit and uses phase-locked detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion. The data processing subsystem is connected to the phase-locked detection subsystem circuit and is used to process the wavelength and scattering signal intensity of the obtained TS scattering spectrum information to calculate the electron velocity distribution function, electron temperature and density. The drive execution subsystem is used to coordinate drive control of the moving parts of the diagnostic system to realize the position movement of the measurement points.

3. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 2, characterized in that, The laser support subsystem includes: A continuous-wave laser is used to excite a light source to output a high-power steady-state laser beam. An optical modulation device is used to frequency pulse modulate the high-power steady-state laser beam output by a continuous-wave laser, and the frequency pulse modulation signal is used as a reference signal for a lock-in amplifier to perform phase-sensitive detection to extract the scattering spectrum. An optical beam-focusing system is used to focus a modulated laser beam onto the diagnostic region of the plasma under test to obtain a spectral signal.

4. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 3, characterized in that, The optical modulation device uses an optical fiber amplifier for electronic modulation, and the optical fiber amplifier is an optical fiber tapered amplifier; or, the optical modulation device uses an optical chopper for optical modulation.

5. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 4, characterized in that, The spectral processing subsystem includes: A laser cutoff is placed in the laser beam path after the laser passes through the diagnostic area of ​​the plasma under test. It is used to collect and eliminate interference sources, including direct laser scattering caused by laser beams and interface scattering. The light-collecting cutoff is positioned opposite the collecting lens group and on the opposite side of the plasma diagnostic area being measured, away from the collecting lens group. A collection lens group is used to collect the spectral signal obtained from the diagnostic region of the plasma under test into a multi-monochromatic instrument; A multi-monochromatic meter is used to suppress stray laser light and Rayleigh scattering interference generated during laser propagation by using dispersion cancellation to collect spectral signals from the lens group. This maximizes the suppression of stray light and improves the signal-to-noise ratio of the scattered signal, thereby obtaining spectral signals of different wavelengths. A photodetector is used to convert spectral signals processed by a multi-monochromatic instrument into electrical signals.

6. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 5, characterized in that, The photodetector is a photomultiplier tube.

7. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 5, characterized in that, The multi-monochromator is a grating-tunable multi-monochromator, and the photodetector is a single photomultiplier tube.

8. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 5, characterized in that, The multi-monochromator is a grating-fixed multi-monochromator, and the photodetector is a photomultiplier tube array. The grating-fixed multi-monochromator and the photomultiplier tube array are connected by a multi-channel dense acquisition method using fiber bundles to achieve synchronous extraction of multiple wavelengths.

9. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 2, characterized in that, The phase-locked detection subsystem includes: A lock-in amplifier is connected to the spectral processing subsystem circuit. It uses lock-in detection technology to extract TS scattering spectral information from the electrical signal obtained by photoelectric conversion. The reference signal of the lock-in amplifier is the frequency pulse modulation signal of the optical modulation device. The acquisition system, connected to the lock-in amplifier circuit, is used to acquire the extracted TS scattering spectrum information.

10. The TS diagnostic signal processing method for directly obtaining frequency-sensitive signals using a spectrum analyzer according to claim 9, characterized in that, The phase-locked detection subsystem also includes: A gated acquisition unit is located between the lock-in amplifier and the spectral processing subsystem. It uses the fluctuation quantity related to the oscillation behavior in the measured plasma as the trigger signal for the gated acquisition unit to directly obtain time-resolved electron velocity diagnosis and realize transient diagnosis function.

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