Method for measuring the spatio-temporal distribution of temperature and density of neutral fuel in a fusion device

Abstract

This invention discloses a method for measuring the spatiotemporal distribution of temperature and density of neutral fuel in a fusion device, belonging to the field of nuclear fusion technology. A solid-state laser pumps a dye laser, which is then third-harmonicized to generate ultraviolet laser light. This ultraviolet laser light is transmitted over a long distance via a vacuum pipe and introduced into the vacuum chamber of the fusion device, exciting neutral deuterium atoms to undergo photon transitions and emit 656 nm fluorescence signals. A collection optical system couples the fluorescence signals at different spatial locations along the laser path to multi-channel optical fibers. After spectroscopic detection by a precision spectrometer, the signals are converted into digital signals by the acquisition system and transmitted to an industrial control computer. The industrial control computer's built-in data processing software performs background subtraction, multi-peak linear fitting, Doppler broadening extraction, and temperature inversion on the fluorescence spectrum, and combines this with absolute density calibration to obtain the spatial distribution of temperature and density of neutral deuterium atoms. By setting the laser repetition frequency, pulse measurements at different times are achieved, obtaining the one-dimensional spatial distribution of temperature and density evolution over time.

Description

Technical Field

[0001] This invention relates to the field of nuclear fusion technology, specifically a method for measuring the spatiotemporal distribution of temperature and density of neutral fuel in a fusion device. Background Technology

[0002] Deuterium / tritium (D / T) is the fuel for plasma in nuclear fusion plasma devices. The spatial distribution of neutral atom density at the plasma edge is an important parameter for edge physics research. Various diagnostic methods exist to provide neutral hydrogen / deuterium atom density information, such as pressure gauges, Balmer or Lyman alpha spectroscopy, and neutral particle analyzers (NPAs). Balmer or Lyman alpha spectroscopy has been used to measure neutral hydrogen / deuterium atom densities in devices such as DIII-D, JET, EAST, and the Alcator C-Mod tokamak. Similarly, K. Bogar derived a neutral hydrogen / deuterium atom density profile in a mid-plane background on ASDEXUpgrade using a neutral particle analyzer (NPA). However, these diagnostic techniques are either the result of line integral measurements, and the spectroscopic methods rely on collisional radiation models (CRMs) with accurate electron density and temperature profiles. These inherent limitations prevent measurements of high spatiotemporal distributions. In addition to experimental measurements, the density of neutral atoms in fuels has also been studied through simulations using codes such as UEDGE and EMC3-EIRENE. In contrast, laser-induced fluorescence (LIF), an active spectroscopy technique that measures the density of neutral atoms in fuels by exciting specific atomic transitions with a laser, offers a potential alternative. This technique includes two methods: single-photon laser-induced fluorescence (LIF) and two-photon laser-induced fluorescence (TALIF).

[0003] LIF (Liquid Fiber Ionization) technology is used to measure the density of neutral hydrogen / deuterium atoms in tokamak devices such as FT-1, ASDEX, and TEXTOR-94. However, obtaining absolute density based on LIF still requires correction using a collisional radiation model, and faces technical challenges in practical applications, such as incident laser interference and low vacuum ultraviolet fluorescence collection efficiency. To overcome these limitations, two-photon absorption laser-induced fluorescence (TALIF) technology has emerged. The TALIF method places higher demands on the performance of the laser source (such as energy, linewidth, and stability). In recent years, with the continuous improvement of laser linewidth control and detection accuracy, the TALIF method has been successfully tested on experimental platforms abroad. However, for large-scale magnetic confinement fusion experimental devices (such as tokamaks), due to the strong magnetic field, high radiation background, and complex internal plasma environment during operation, the diagnostic system usually needs to be located in a shielded laboratory far from the device. TALIF technology cannot be implemented in engineering practice, and is also affected by plasma parameters, resulting in broadening of the fluorescence signal and confusion with the original plasma parameters. Signal. Therefore, to date, there is still no routine diagnostic method for directly measuring the neutral temperature and density of fusion fuel on large-scale fusion devices. The main problems include:

[0004] 1. There is a lack of ultraviolet laser sources that combine high pulse energy (millijoule level) and narrow linewidth (picometer level);

[0005] 2. Ultraviolet lasers need to be transmitted remotely to the device window via a long optical path, resulting in significant transmission loss and beam quality degradation.

[0006] 3. Laser-induced fluorescence signals are weak and, influenced by plasma parameters, can broaden, further obscuring the original plasma fluorescence signals. The signal cannot yet be effectively separated in strong background stray light (such as plasma radiation and wall reflection light);

[0007] 4. High-resolution measurement of fluorescence spectra with picometer-level linewidths, as well as precise signal acquisition and processing across a dynamic range of 3 to 4 orders of magnitude, place extremely high demands on the detection system. Summary of the Invention

[0008] To address the above technical problems, this invention provides a method and system for measuring the spatiotemporal distribution of temperature and density of neutral fuel in a fusion device. This approach focuses on overcoming key challenges such as the generation and long-distance transmission of pulsed high-energy, narrow-linewidth ultraviolet lasers, the extraction of fluorescence signals affected by plasma parameters and strong background light, and high-resolution spectral measurements with a large dynamic range, ultimately achieving reliable in-situ diagnosis of neutral atomic parameters in fusion fuels. The specific technical solution is as follows:

[0009] A method for measuring the spatiotemporal distribution of temperature and density of neutral fuel in a fusion device includes the following steps:

[0010] Step 1: Turn on the solid-state laser and output a 532 nm wavelength laser as the pump source for the dye laser.

[0011] Step 2: After receiving 532 nm pump light, the dye laser outputs 615 nm wavelength laser light, which is then converted into 205 nm ultraviolet laser light after being tripled.

[0012] Step 3: The 205 nm ultraviolet laser is transmitted through a vacuum pipe and introduced into the vacuum chamber of the fusion experimental device through the device window. During the discharge process of the fusion device, there is a certain concentration of neutral deuterium atoms in the vacuum chamber. The laser beam interacts with the neutral deuterium atoms, exciting them to undergo two-photon transitions. The atoms in the n=3 excited state then decay to the n=2 energy level and emit a 656.1 nm fluorescence signal.

[0013] Step four: The optical system collects fluorescence signals generated at different spatial locations along the laser path and couples them into the optical fibers of the corresponding spatial channels. The fluorescence signals are then transmitted to the precision spectrometer via the optical fibers.

[0014] Step 5: The precision spectrometer performs spectral dispersion and detection on the fluorescence signal, and the acquisition system converts the signal output by the spectrometer into a digital signal and transmits it to the industrial control computer.

[0015] Step six: The industrial control computer records and stores the fluorescence spectrum data through signal acquisition and data processing software for subsequent processing and analysis.

[0016] Step 7: Using a self-developed data processing flow and algorithm, the temperature and density of the neutral fuel are extracted from the measured fluorescence signal.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. This method can realize a complete diagnosis of the temperature and density spatial distribution of neutral deuterium atoms in fusion fuel on a magnetically confined nuclear fusion device;

[0019] 2. Solid-state lasers and precision spectrometers contain electrical components. Placing them in a laboratory far from the device avoids the effects of radiation and electromagnetic fields during device operation and ensures long-term operation of the equipment.

[0020] 3. Use 532nm laser emitted by a solid-state laser for long-distance transmission to reduce the transmission distance of ultraviolet lasers;

[0021] 4. Dye lasers do not require electrical control devices, which can be placed near the device, reducing the long-distance transmission of the ultraviolet laser beam. Furthermore, the use of a vacuum tube to transmit the ultraviolet laser beam improves efficiency and beam quality.

[0022] 5. To address the interference of plasma parameters and strong background light on fluorescence signals in fusion devices, a data processing flow and algorithm are proposed, which can effectively extract the temperature and density information of neutral fuel from the measurement signals;

[0023] 6. This invention provides a reliable, accurate, and engineering-feasible solution for diagnosing neutral atom parameters in fusion fuels. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method of the present invention;

[0025] Figure 2 This is a flowchart of the data processing of the present invention;

[0026] Figure 3The total signal and its components at different temperatures, including the D atom Zeeman triplet, H impurities (15%), and instrument broadening (20 pm).

[0027] Figure 4 The comparison between the true value of Doppler broadening and the value extracted by the algorithm shows an average error of 2.34%. The black squares represent the true values, and the red circles represent the values ​​fitted by the algorithm. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0029] The principle of temperature and density measurement of neutral deuterium atoms and isotopes: In TALIF technology, the energy level transition scheme of deuterium involves exciting the ground-state atom with a 205 nm ultraviolet laser. After absorbing two photons, the atom transitions from the n=1 energy level to the n=3 energy level. Due to the short lifetime of this excited state, the atom subsequently decays from the n=3 energy level to the n=2 energy level, emitting 656 nm fluorescence during this process. According to the energy level transition theory, the fluorescence signal of the deuterium atom under two-photon laser induction transitions from the 1s to 3d energy levels is... With the ground state density of neutral deuterium atoms The expression is as follows:

[0030] (1)

[0031] in, For the ratio, Collect solid angles for normalization (normalized to spherical solid angles). For launch volume, The photon counting factor is calculated (1 for a single beam and 2 for two incoherent beams). It is a two-photon absorption cross section. The statistical factor is 2 for phase-independent beams in spectral modes and 1 for mode-locked beams. The laser frequency, This represents laser intensity, measured in W / cm². This represents the ground-state density of neutral deuterium atoms. is Planck's constant. Plexus width, This refers to the laser linewidth.

[0032] Doppler broadening is caused by the random thermal motion of absorbing atoms, and its frequency... spectral intensity function at Represented as:

[0033] (2)

[0034] in, It is the center wavelength of the spectral line. It is the center frequency of the spectral line. Peak intensity at that location It is spectral Doppler broadening. In the frequency domain, Represented as:

[0035] (3)

[0036] in, It is the speed of light in a vacuum. is Boltzmann's constant, and T is the temperature of the neutral atom.

[0037] Laser linewidth ( ), observed fluorescence spectral broadening ( ) and Doppler broadening ( The relationship between them can be approximated as:

[0038] (4)

[0039] when At this time, the broadening of the fluorescence spectrum is mainly dominated by Doppler broadening. In the TALIF system, the linewidth of the ultraviolet laser source is 0.18 pm, while the Doppler broadening corresponding to a neutral deuterium atom at 1 eV is approximately 0.04 nm (i.e., 40 pm). Since the laser linewidth is much smaller than the Doppler broadening, the condition of broadening dominance is met. Therefore, the Doppler broadening component can be directly extracted from the measured fluorescence linewidth, using the relationship between the temperature of the neutral atom and the Doppler broadening (…). ) Calculate the temperature of neutral deuterium atoms.

[0040] According to formula (1), the fluorescence signal intensity is proportional to the density. The absolute density of neutral atoms can be obtained by measuring the integral intensity (area) of the fluorescence spectrum and performing absolute calibration. However, in actual measurements, the absolute intensity of the fluorescence signal is affected by various factors such as laser energy fluctuations, optical path alignment, and aging of optical components. Directly calculating the absolute density based on formula (1) will result in a large error. Therefore, the absolute density calibration method is required to obtain density data. The absolute density calibration method is as follows: Under the same experimental geometry, the TALIF signal intensity of the gas to be tested (deuterium) and the calibration gas of known concentration are measured respectively. The signal ratio of the two is used to eliminate the influence of common factors such as system constant and laser energy. When the relative detection sensitivity of the calibration gas and the gas to be tested is known, the absolute atomic density of the gas to be tested can be determined by the following formula:

[0041] (5)

[0042] in, This represents the absolute density (ground state density) of neutral deuterium atoms to be measured during discharge in the fusion device. The calibration gas introduced into the device in a plasma-free state The known absolute density, which is determined by barometer or temperature measurement. The integral intensity of the TALIF fluorescence signal of the neutral deuterium atom being measured during discharge in the fusion device. When the device is without plasma, it is filled with a calibration gas. The measured integrated intensity of the TALIF fluorescence signal, The relative TALIF detection sensitivity coefficients for the two gases (dimensionless, to be obtained through theoretical calculations or standard sample calibration).

[0043] To achieve the above calibration scheme, the selection of calibration gas is crucial. The calibration gas should meet the following conditions: (1) its laser absorption wavelength and fluorescence emission wavelength are similar to those of the gas to be tested, to ensure that the two have the same or highly consistent optical transmission characteristics and detection efficiency; (2) its TALIF excitation and emission spectra do not overlap with the spectral lines of the gas to be tested, to avoid signal interference. The TALIF measurement absorption wavelength of the inert gas krypton (Kr) is 204.13 nm, and its fluorescence wavelength is 826.5 nm, while the corresponding wavelengths of deuterium (D) are 205.08 nm and 656.1 nm, respectively. The absorption wavelengths of the two differ by only about 0.95 nm, and they can be excited sequentially using the same laser system without changing the optical components. The fluorescence wavelengths are all in the visible-near infrared band, and the detector sensitivity is good. In addition, Kr is chemically stable, non-toxic, and easy to quantitatively mix, making it an ideal calibration gas. Therefore, this diagnostic scheme intends to use Kr as the reference gas for absolute calibration.

[0044] Methods for analyzing and extracting fluorescence signals in magnetically confined nuclear fusion experimental devices. Fluorescence spectra in magnetically confined nuclear fusion experimental devices are affected by factors such as magnetic fields, electrons, and particles. Besides Doppler broadening, the spectral line shapes of absorbing atoms also include pressure broadening (collision broadening), saturation broadening, instrument broadening, natural linewidth, and Zeeman broadening, as well as the influence of hydrogen impurities. It is necessary to analyze and evaluate the impact of these broadening mechanisms on Doppler broadening based on plasma parameters. Taking the plasma parameters of the EAST tokama device as an example, the neutral deuterium atom temperature is in the range of 1 eV-100 E, and the magnetic field strength is 2 T. The calculated ratio of instrument broadening to Doppler broadening is in the range of 0.06-0.6, and the ratio of Zeeman effect to Doppler broadening is in the range of 0.13-1.32, while other effects are negligible. To accurately extract the fluorescence signal of neutral deuterium atoms from the complex spectrum containing Zeeman splitting, hydrogen impurities, and instrument broadening, we propose a spectral decomposition algorithm based on multi-peak Voigt fitting. The algorithm decomposes the measured spectrum into several spectral-resolved components with distinct physical meanings, each described by a Voigt linear shape (the convolution of a Gaussian function and a Lorentz function). Subsequently, nonlinear least-squares optimization is used to extract the fluorescence of deuterium atoms from the total signal.

[0045] A method for measuring the high spatiotemporal distribution of temperature and density of neutral deuterium atoms and isotopes in fusion fuel inside a fusion device:

[0046] Spatial distribution measurement: By injecting vacuum ultraviolet laser into plasma, the scattered light at different positions along the laser path is imaged onto the corresponding channel at the end of the fiber bundle using a collection optical system, thereby constructing a density spatial distribution profile along the radial direction.

[0047] Spatiotemporal distribution measurement: By controlling the timing of the laser, pulsed lasers are emitted at different times. The laser pulses can be 1Hz, 10Hz, 20Hz, or even 50Hz. Combined with the spatial distribution, the spatial distribution that evolves over time can be measured.

[0048] To achieve the above objectives, the specific implementation scheme of the present invention is as follows:

[0049] I. Components of the diagnostic system, such as Figure 1 As shown, it includes:

[0050] (a) Laser source system

[0051] A high-energy, high-frequency 532 nm Nd:YAG solid-state laser was used as the pump source and placed in a diagnostic laboratory far from the fusion experimental device to avoid interference from the strong magnetic field and radiation during the operation of the fusion device. The 532 nm laser output from this laser was transmitted through a light guide path to a dye laser placed in the device's main hall, serving as its pump source. After receiving the 532 nm pump light, the dye laser underwent dye oscillation and amplification to output a 615 nm wavelength laser. This laser was then third-harmonicized by a BBO crystal to generate a 205 nm ultraviolet laser, which was used to excite the 1s→3d two-photon transition of neutral deuterium atoms.

[0052] (II) Laser Transmission and Introduction System

[0053] The ultraviolet laser is transmitted to the window of the fusion experimental device via a vacuum pipe. Both ends of the vacuum pipe are sealed windows to isolate it from the outside world and maintain a certain degree of vacuum. The pipe maintains a vacuum environment similar to that of the device to avoid the strong absorption and loss of the ultraviolet laser when it propagates in air. After entering the vacuum chamber of the device through the window, the laser propagates along a predetermined path. At the end of the laser beam path, a laser energy absorber is installed inside the device to absorb any remaining tail light and prevent stray light interference caused by laser reflection from the device walls.

[0054] (III) Fluorescence signal collection and transmission system

[0055] A collecting optical system is installed in another window of the device, with its object plane positioned on the path of the dye laser beam transmission inside the device, and its image plane being the signal entry end face of multiple optical fibers. Each optical fiber corresponds to an image plane at a different spatial position on the laser path, enabling spatially resolved measurement of the laser-induced fluorescence signal. The collecting optical system includes a lens group, filters (to block stray components of the 205 nm excitation light), and fiber coupling components.

[0056] (iv) Signal detection and acquisition system

[0057] The other end of the optical fiber connects to a precision spectrometer (such as an echelle grating spectrometer or a Fabry-Pérot interferometer) placed in the diagnostic laboratory. The spectrometer disperses the fluorescence signal according to wavelength and converts it into an electrical signal. The spectrometer output is connected to a data acquisition system (such as an ICCD camera or a multi-channel photomultiplier tube array), which is then connected to an industrial control computer. The industrial control computer has signal acquisition and data processing software installed to record, store, and process the spectral data.

[0058] II. Work Process

[0059] Step 1: Turn on the high-energy, high-frequency 532 nm Nd:YAG solid-state laser to output 532 nm wavelength laser light as the pump source for the dye laser.

[0060] Step 2: After receiving 532 nm pump light, the dye laser outputs 615 nm wavelength laser light; this laser light is converted into 205 nm ultraviolet laser light after being tripled by a BBO crystal.

[0061] Step 3: A 205 nm ultraviolet laser is transmitted through a vacuum pipe and introduced into the vacuum chamber of the fusion experimental device through the device window. During the discharge process of the fusion device, there is a certain concentration of neutral deuterium atoms in the vacuum chamber. The laser beam interacts with the neutral deuterium atoms, exciting them to undergo a 1s→3d two-photon transition. The atoms in the n=3 excited state then decay to the n=2 energy level, emitting a 656.1 nm fluorescence signal.

[0062] Step 4: The optical system collects fluorescence signals generated at different spatial locations along the laser path and couples them into the optical fibers of the corresponding spatial channels. The fluorescence signals are then transmitted to the precision spectrometer via the optical fibers.

[0063] Step 5: The precision spectrometer performs spectral dispersion and detection on the fluorescence signal, and the acquisition system converts the signal output by the spectrometer into a digital signal and transmits it to the industrial control computer.

[0064] Step Six: The industrial control computer records and stores the fluorescence spectrum data through signal acquisition and data processing software for subsequent processing and analysis.

[0065] III. Data Processing Algorithms

[0066] The signal acquisition and data processing system built into the industrial control computer processes the fluorescence spectral data according to the following steps: Figure 2 As shown:

[0067] (a) Spectral preprocessing

[0068] Background intensity subtraction: Before and after each set of valid fluorescence signal acquisition, the background light signal of the detector when the laser is off is recorded. .definition For the corrected fluorescence signal, then It is from the original fluorescence spectrum signal The signal is subtracted from the background effects, including the signal that eliminates the influence of dark current in the detector and stray light radiation inside the fusion device.

[0069] Fluorescence broadening analysis: Based on plasma parameter analysis and evaluation, this study assesses the influence of pressure broadening (collision broadening), saturation broadening, instrumental broadening, natural linewidth, Zeeman broadening, and hydrogen impurities on Doppler broadening. Pressure broadening, also known as collision broadening, arises from collisions between atoms and surrounding particles, leading to energy level perturbations and changes in transition frequencies. In plasma, pressure broadening induced by the electric field of charged particles (especially electrons) is called Stark broadening. The calculation formula is:

[0070] (6)

[0071] in, For electron collision half-width parameters, Electron density (unit: cm) -3 ), The ion broadening parameter is dimensionless. Electron temperature (unit: eV).

[0072] Saturation broadening is an effect induced by high-intensity lasers. When the laser intensity is too high, a large number of ground-state atoms are pumped to excited states, leading to a decrease in the number of ground-state particles (i.e., "ground state depletion"), and the quadratic relationship between the fluorescence signal and the laser intensity no longer holds. This nonlinear effect can cause the measured signal to be suppressed or broadened. Experimentally, this needs to be determined by measuring the change in the integrated intensity of the fluorescence signal as a function of laser energy, confirming that the laser energy is in the unsaturated region, and ensuring that the signal is consistent with the laser intensity. Proportional.

[0073] The instrument broadening stems from the limited resolution of the measurement system and is mainly composed of the laser linewidth and the spectrometer resolution. Under high-temperature (e.g., >1 eV) fusion plasma conditions, the laser linewidth (0.18 pm in this system) is much smaller than the Doppler broadening (approximately 40 pm), and its contribution to the total spectral broadening is negligible. Similarly, if the spectrometer resolution is superior to the laser linewidth, its influence is also negligible.

[0074] The natural linewidth is determined by the Heisenberg uncertainty principle and reflects the finite lifetime of the excited state. The longer the lifetime of the excited state, the narrower its natural linewidth. For the 3d excited state of the deuterium atom, its lifetime is very short, so the natural linewidth is extremely small (on the order of MHz). Compared with Doppler broadening (on the order of GHz), its contribution is negligible.

[0075] Zeeman broadening is caused by the splitting of atomic energy levels in a strong magnetic field (such as that of a tokamak), leading to spectral broadening or splitting. This effect is more pronounced when the magnetic field is strong and the ion temperature is low. The extent of its effect depends on the comparison between the magnetic field strength and Doppler broadening. The formula for calculating the Zeeman effect is:

[0076] (7)

[0077] in, For Bohr magneton, The magnetic field strength, Landes for each energy level factor, is the magnetic quantum number of the total angular momentum. Represents the transition between the initial and final states. The difference in values.

[0078] In fact, the Zeeman effect in magnetic confinement fusion experimental devices is quite complex. The results calculated based on the parameters of the EAST tokamak device are described as follows:

[0079] when At eV: Doppler broadening (approximately 34-76 pm) is on the same order of magnitude as Zeeman splitting (45 pm). Measured fluorescence spectra show a three-peaked Zeeman structure (center...). Peak and symmetrical on both sides (Peak), in which the Zeeman effect plays a dominant role.

[0080] when At eV: Doppler broadening (approximately 107-152 pm) is greater than Zeeman splitting (45 pm). The three-peak splitting structure completely merges, appearing as a single broadened peak.

[0081] when At eV: Doppler broadening (>240 pm) is much greater than Zeeman splitting (45 pm). The three Zeeman components are almost completely submerged in the Doppler envelope, and the measured fluorescence spectrum is dominated by Doppler broadening.

[0082] To comprehensively evaluate the signals measured in the fusion experiment, we simulated the total TALIF fluorescence signal at different temperatures, taking into account the combined effects of Zeeman splitting, instrument dispersion, and isotope effects on the spectral profile. The total signal was modeled as a superposition of the following components: the Zeeman triplet of D atoms (π, σ... + σ - The intensity ratio was 1:0.5:0.5; the splitting distance was 22.5 pm; the H impurity signal (isotope shift of 180 pm) and instrument broadening (FWHM = 20 pm) were also measured. 2% random noise was added to simulate real-world conditions. The Zeeman effect was induced by a 2 T magnetic field, the instrument dispersion corresponded to a grating of 1800 lines / mm, and the hydrogen impurity concentration was set to an H:D ratio of 0.15:1. Figure 3 Simulation results of each component signal and the total signal at different temperatures are presented.

[0083] (II) Spectral line feature extraction

[0084] Peak identification: Set a peak search window near the target fluorescence wavelength (656.1 nm for deuterium) to locate the peak wavelength position.

[0085] Linear fitting: The measured spectrum is decomposed into several spectral-resolved components with clear physical meaning, each described by a Voigt line shape (the convolution of a Gaussian function and a Lorentz function). Subsequently, nonlinear least-squares optimization is used to extract the fluorescence of D atoms from the total signal. Since the peak shape of the total signal varies with temperature, differentiated fitting strategies are employed for different temperature ranges to obtain more accurate fitting values. The method used in this invention is as follows:

[0086] Low temperature (≤5 eV): With the Zeeman parameters fixed, the Zeeman-Doppler convolution model is used for fitting, that is, the three Zeeman components are convolved as a whole with the Doppler widening to accurately extract the temperature;

[0087] Intermediate temperature (5–30 eV): Add a hydrogen single peak to the constrained three-peak fitting;

[0088] High temperature (>30 eV): simplified to double Voigt fitting.

[0089] Based on the signal extraction algorithm, the error between theoretical Doppler broadening and fitted broadening was also calculated. Figure 4 The actual Doppler broadening and fitted Doppler broadening of D atoms at different temperatures are compared, with an average error of 2.34%. Black squares represent the true values, and red circles represent the algorithm-fitted values.

[0090] Temperature inversion: The Doppler broadening component is extracted from the measured spectral linewidth using formula (5). , ,in, The instrument linewidth (which includes the combined effects of laser linewidth and spectrometer resolution, and is determined in advance through calibration experiments) is then substituted into formula (4) to retrieve the neutral atom temperature:

[0091] ;

[0092] Signal integration area calculation: Numerical integration is performed on the fitted spectral peak function within the effective wavelength range. To avoid introducing excessive noise and ensure the validity of the integration results, the integration interval is taken as the center wavelength of each spectral peak component. Both sides The range (i.e., covering approximately 99.7% of the total spectral area) is used to obtain the integrated intensity of the fluorescence signal, which is the fluorescence signal intensity in formula (1), proportional to the ground state atom density.

[0093] (III) Spatial Multichannel Data Processing

[0094] For different spatial locations corresponding to multiple optical fibers ( ,in (total number of fiber channels), and perform the above spectral feature extraction respectively to obtain the neutral deuterium atom temperature at each spatial point along the laser beam path. and fluorescence signal integrated intensity (i.e., the fluorescence signal intensity of each spatial point obtained according to formula (1)) thereby obtaining the one-dimensional spatial distribution of temperature and density.

[0095] (iv) Solid-state lasers are pulsed lasers. By setting the repetition frequency of the laser and emitting laser pulses for different time periods, the above tests can be performed to obtain the characteristics of the one-dimensional spatial distribution of temperature and density evolving over time.

[0096] (v) Absolute density calibration

[0097] Based on formula (1), under the same experimental geometry and laser parameters, the ratio of the integrated fluorescence signal intensity of the analyte gas (deuterium) to that of the calibration gas (Kr) is equal to the ratio of their ground state densities multiplied by the relative detection sensitivity coefficient:

[0098] ;

[0099] in, This represents the absolute density (ground state density) of neutral deuterium atoms to be measured during discharge in the fusion device. The known absolute density of the calibration gas Kr, which is introduced into the device in a plasma-free state, is determined by a barometer or temperature measurement. The integral intensity of the TALIF fluorescence signal of the neutral deuterium atom being measured during discharge in the fusion device. This refers to the integrated intensity of the TALIF fluorescence signal measured when the device is filled with calibration gas Kr without plasma. The relative TALIF detection sensitivity coefficients for the two gases (dimensionless, to be obtained through theoretical calculations or standard sample calibration).

[0100] The absolute density calibration process is as follows:

[0101] Fill the fusion device with a known absolute density The concentration of Kr gas was determined by a precision barometer and temperature measurement.

[0102] The integrated intensity of the TALIF fluorescence signal of Kr was measured under the established experimental conditions (laser energy, optical path alignment, spectrometer parameters, etc. were completely consistent with those used in the formal measurement). The Kr gas was evacuated, and the system was switched to the plasma discharge condition to be tested. The integrated intensity of the TALIF signal of deuterium atoms was measured while keeping all system parameters constant. ,Will , , and relative sensitivity coefficient Substituting into the above equation, we can obtain the absolute density of neutral deuterium atoms:

[0103] ;

[0104] This invention, through the aforementioned system configuration, workflow, data processing algorithm, and absolute calibration process, constitutes a complete diagnostic scheme for the spatial distribution of neutral deuterium atom temperature and density in fusion devices. It can effectively solve key technical challenges such as the generation and long-distance transmission of high-energy, narrow-linewidth ultraviolet lasers, the extraction of weak fluorescence signals under strong background light, and the precise measurement of picometer-level linewidth and large dynamic range spectral signals.

Claims

1. A method for measuring the spatio-temporal distribution of the temperature and density of neutral fuel in a fusion device, characterized in that, Includes the following steps: Step 1: Turn on the high-energy solid-state laser and output a 532 nm wavelength laser as the pump source for the dye laser. Step 2: After receiving 532 nm pump light, the dye laser outputs 615 nm wavelength laser light, which is then converted into 205 nm ultraviolet laser light after being tripled. Step 3: The 205 nm ultraviolet laser is transmitted through a vacuum pipe and introduced into the vacuum chamber of the fusion experimental device through the device window. During the discharge process of the fusion device, there is a certain concentration of neutral deuterium / tritium atoms in the vacuum chamber. The laser beam interacts with the neutral deuterium atoms, exciting them to undergo two-photon transitions. The atoms in the n=3 excited state then decay to the n=2 energy level and emit a 656.1 nm fluorescence signal. Step four: The optical system collects fluorescence signals generated at different spatial locations along the laser path and couples them into the optical fibers of the corresponding spatial channels. The fluorescence signals are then transmitted via optical fibers to a precision spectrometer with a resolution of picometers. Step 5: The precision spectrometer performs spectral dispersion and detection on the fluorescence signal, and the acquisition system converts the signal output by the spectrometer into a digital signal and transmits it to the industrial control computer. Step six: The industrial control computer records and stores the fluorescence spectrum data through signal acquisition and data processing software for subsequent processing and analysis; Step 7: Based on the measured fluorescence spectral data, the temperature and density of the neutral fuel are extracted from the measured fluorescence signal through data processing procedures and algorithms. The data processing flow includes: first, spectral preprocessing, including background intensity subtraction and fluorescence broadening analysis; then, spectral feature extraction, including peak identification, line shape fitting, temperature inversion, and signal integration area calculation; and finally, spatial multi-channel data processing to obtain the temperature of neutral deuterium atoms and the integrated intensity of fluorescence signals at each spatial point along the laser beam path, thereby obtaining a one-dimensional spatial distribution of temperature and density. The data processing algorithm includes: decomposing the measured spectrum into several spectral resolution components with clear physical meaning, each component being described by a Voigt linear shape, and extracting the fluorescence of D atoms from the total signal through nonlinear least squares optimization; employing differentiated fitting strategies for different temperature ranges: when the temperature is ≤5 eV, fixing the Zeeman parameters and using a Zeeman-Doppler convolution model for fitting; when the temperature is 5–30 eV, adding a hydrogen single peak to the constrained three-peak fitting; and when the temperature is >30 eV, simplifying to a double Voigt fitting.

2. The method of claim 1, wherein, In the fluorescence broadening analysis, the effects of pressure broadening, saturation broadening, instrument broadening, natural linewidth, Zeeman broadening, and hydrogen impurities on Doppler broadening are evaluated based on plasma parameters. The Zeeman effect is calculated using the following formula: wherein, is the Bohr magneton, is the magnetic field strength, is the Lande g-factor for each energy level factor, is the magnetic quantum number for the total angular momentum, denotes the difference in the value of the value of the initial and final states of the transition.

3. The method according to claim 1, characterized in that, In the temperature inversion, the formula The Doppler broadening component is extracted from the measured spectral width Where The measured fluorescence spectral width, The instrument line width, and the formula is substituted ， The temperature of the neutral atoms in the inversion, where m is the atomic mass and c is the speed of light, is the Boltzmann constant, is the central wavelength of the spectral line.

4. The method of claim 1, wherein, The solid-state laser is a pulsed laser. By setting the laser repetition frequency, laser pulses of different time periods are emitted and measured separately to obtain the characteristics of the one-dimensional spatial distribution of temperature and density evolving over time, thereby realizing the measurement of spatiotemporal distribution.

5. The method of claim 1, wherein, The process also includes an absolute density calibration step: Under the same experimental geometry and laser parameters, the integrated intensity of the TALIF fluorescence signals of the deuterium gas to be tested and the calibration gas Kr are measured separately. The ratio of their signals is used to eliminate the influence of common factors such as system constants and laser energy. The absolute density of the neutral deuterium atom to be tested is determined by the following formula. ； wherein, is the absolute density of the neutral deuterium atoms to be measured during discharges in a fusion device, is the known absolute density of the calibration gas Kr filled in the device without plasma, is the integral intensity of the TALIF fluorescence signal of the neutral deuterium atoms to be measured during discharges in a fusion device, is the integral intensity of the TALIF fluorescence signal measured for the calibration gas Kr filled in the device without plasma, is the relative TALIF detection sensitivity coefficient of the two gases.

6. The method of claim 1, wherein, Both ends of the vacuum pipe are isolated from the outside world by sealed windows, and a vacuum environment is maintained inside the pipe. At the end of the laser beam path, a laser energy absorber is installed to absorb the remaining tail light.

7. The method according to claim 1, characterized in that, The collecting optical system is located in another window, with its object plane positioned on the path of the dye laser beam transmission inside the device, and its image plane being the signal entry end face of multiple optical fibers. Each optical fiber corresponds to the image plane at a different spatial position on the laser path, so as to realize the spatial resolution measurement of the laser-induced fluorescence signal. The collecting optical system includes a lens group, a filter for blocking stray components of 205 nm excitation light, and an optical fiber coupling assembly.

8. The method according to claim 1, characterized in that, The precision spectrometer is an echelle grating spectrometer or an interferometer, and the acquisition system is an ICCD camera or a multi-channel photomultiplier tube array.

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