Porous metallic foams suffer from severe signal instability and matrix effects in laser-induced breakdown spectroscopy (LIBS) due to heterogeneous laser-material coupling and pore-driven plasma fluctuations, limiting accurate porosity discrimination. To address this challenge, we propose a novel multimodal strategy that integrates LIBS emission spectra and time-synchronized plasma plume image features, acquired simultaneously from a single laser pulse, to avoid spatiotemporal registration errors for plasma diagnostics and porosity classification. Porous nickel foams with four pore densities (40-100 PPI) and a dense Ni block were analyzed under high vacuum (5 & times; 10-5 mbar) to isolate pore structure effects. Plasma diagnostics confirmed local thermodynamic equilibrium (LTE) with electron densities ranging from 9.3 & times; 1016 to 1.76 & times; 1017 cm- 3 and plasma temperatures of 6500-9500 K, both increasing systematically with pore density. Classical machine learning (ML) models (SVM, RF, MLP, XGBoost) and deep learning architectures (1D-CNN for spectra, CNN-ResNet18 for images) were trained via five-fold stratified cross-validation. Standalone spectral models achieved a maximum accuracy of 69%, while image-based models reached 93%, demonstrating the superior discriminative power of morphology-driven features. A late-fusion model combining XGBoost-derived spectral features and CNNResNet18-extracted image features yielded an unprecedented classification accuracy of 98.2% with minimal variance, representing a 29.2% improvement over spectral-only models and 5.2% over the best unimodal approach. This work's innovations lie in: synchronized acquisition of complementary spectral and morphological data to eliminate cross-instrument registration errors; quantitative linking of pore density to plasma thermodynamic properties (temperature, electron density); and a physics-consistent fusion framework that harnesses compositional and structural information synergistically. The results validate a robust, data-driven approach for LIBS-based characterization of porous metallic foams, overcoming porosity-dependent plasma variability and enabling accurate assessment of structurally diverse porous materials.

The impurity information contained in the deposition layers on plasma-facing components (PFCs) is essential for understanding the plasma-wall interaction (PWI) processes in fusion devices. Although laser-induced breakdown spectroscopy (LIBS) has become a promising technology for in situ elemental analysis on PFCs, systematic investigations into the LIBS spectral characteristics of relatively thin deposition layers remain limited. In this study, tungsten (W) nanofilms of varying thicknesses were deposited on different substrates using arc ion plating to simulate the thin layers formed in fusion devices. LIBS measurements were performed at a pressure of 5 x 10-5 mbar to obtain the spectral signals from these nanofilms. The spectral features of W nanofilms with different thicknesses, deposited on various substrates and ablated by a one-shot laser, were systematically investigated. The properties of LIBS plasma for these nanofilms were analyzed, along with the relationship between spectral intensity and ablation volume, with special attention paid to the effects of localized surface plasmon resonance (LSPR). Results show that as the W nanofilms thickness and grain size decrease, the one-shot LIBS spectral intensity of W increases exponentially. For the thinnest films, the highest electron temperature and density were observed, attributed to LSPR effects near the interface. A numerical model was developed to qualitatively describe how spectral intensity varies with W nanofilm thickness, effectively decoupling multiple factors and aligning well with experimental data.

Boronization is a critical wall conditioning technique that improves the plasma performance of nuclear fusion devices by effectively reducing impurity levels. The team associated with the International Thermonuclear Experimental Reactor (ITER) has identified boronization as an effective means of mitigating the release of high-Z impurities. High-power long-pulse discharges conducted at the Experimental Advanced Superconducting Tokamak (EAST) have demonstrated the feasibility of ITER operations. A real-time monitoring of boron (B) layer thickness deposited on the first wall is crucial under these conditions. In this study, laser-induced breakdown spectroscopy (LIBS) has been applied to measure the thickness of ultra-thin boron films deposited on molybdenum (Mo) substrates at 5 x 10-5 mbar to simulate the EAST vacuum conditions. A series of boron films on Mo substrate samples with thicknesses ranging from 30 to 300 nm were produced by pulsed laser deposition (PLD). In ns-laser ablation, the first laser pulse penetrates the boron film and excites the underlying Mo substrate, producing stable spectral lines from boron (B II 703.19 nm) and molybdenum (Mo I 710.99 nm). A direct correlation is established between the intensity ratio of the B II 703.19 nm to Mo I 710.99 nm signals and the boron film thickness. A laser ablation model has been established and used to fit the experimental results, demonstrating consistency with the data. In addition, the relationship between the B/Mo signal intensity ratio and the relative amount of ablated material, calculated by calibration-free LIBS (CF-LIBS), has confirmed the validity of this approach. Based on experiments conducted using four different laser fluences, in-situ diagnostics of ultra--thin B film thickness in the 3.9-7.8 J/cm2 laser fluence range is recommended. The findings of this study have demonstrated the feasibility of LIBS technology for in-situ diagnostics of ultra-thin B layers as a means of monitoring the plasma-wall interaction (PWI) in fusion devices.

Laser-induced breakdown spectroscopy (LIBS) is a powerful in-situ diagnostic technique for real-time, multi-element analysis in extreme environments. In this work, copper (Cu) pellets were fabricated by compressing metallic powders under different compaction pressures (198 MPa – 1164 MPa), resulting in samples with varying densities (6.22–8.47 g/cm3). The influence of compaction pressure on laser-induced plasma characteristics was systematically investigated under vacuum conditions (6 × 10−5 mbar). The results show that the intensity of Cu I emission lines increases with increasing compaction pressure (corresponding to higher density) and approaches a saturation regime at high pressure levels. Meanwhile, the relative standard deviation decreases significantly from ∼20% to below 6%, indicating a substantial improvement in signal reproducibility. Plasma diagnostics based on Boltzmann plot and Stark broadening analyses reveal that the electron temperature remains nearly unchanged, whereas the electron density increases markedly (up to ∼3×) with increasing compaction pressure, with a more pronounced effect observed at lower laser fluence. Plasma imaging at a fixed delay shows enhanced plume expansion with increasing compaction pressure. In contrast, ablation crater analysis reveals a decreasing trend in crater depth for highly compacted samples. This behavior is likely associated with enhanced plasma shielding effects, which may reduce effective laser energy coupling to the target. These results indicate that compaction pressure plays a critical role in governing LIBS signal characteristics under vacuum conditions. Overall, this study provides a clearer understanding of matrix effects associated with compacted powder materials and offers useful guidance for improving LIBS diagnostics of porous and compacted materials in environments relevant to fusion applications.

Laser wavelength plays a critical role in laser-matter coupling, plasma formation, and the analytical sensitivity of laser-induced breakdown spectroscopy (LIBS). In this study, the influence of three laser wavelengths (1064, 532, and 355 nm) on emission characteristics, limits of detection (LoD) of trace elements, plasma parameters, and ablation volume of Al-Li alloy samples was systematically investigated under a vacuum of 5 & times; 10-5 mbar. At a constant laser fluence of 4 J cm-2, set according to the operating conditions of the in-situ LIBS system used for monitoring deposited impurities on the inner wall of the EAST tokamak, excitation with the 355 nm laser produced significantly stronger atomic emission signals, higher electron temperature (Te) and electron density (ne), and lower LoDs. This improvement is attributed to more efficient energy coupling between the laser and the sample surface at shorter wavelengths. Specifically, the LoDs of Mg, Cu, and Cr decreased from 0.253, 0.684, and 0.303 a.t. % at 1064 nm to 0.066, 0.142, and 0.018 a.t. % at 355 nm, respectively. In contrast, irradiation at 1064 nm resulted in a larger ablation volume and deeper craters, indicating that enhanced spectral signal intensity is not determined solely by the amount of ablated material but is also strongly governed by plasma excitation efficiency. These results demonstrate that LIBS at 355 nm offers significant potential for high-sensitivity, low-damage, in-situ detection of trace impurities in fusion-relevant materials.

Accurate helium (He) retention detection in plasma-facing components (PFCs) is critical for fusion reactor safety, efficiency, and longevity. Boron-molybdenum (B-Mo) coated tungsten mimicking real-world multilayered boronized PFCs in EAST/ITER-like tokamaks poses challenges for laser-induced breakdown spectroscopy (LIBS) due to weak He emission, matrix variability, and unoptimized laser parameters. This study addresses these limitations via systematic laser fluence optimization for He-I 587.56 nm detection. Key innovations include: (1) identification of an approximate helium emission threshold of 3.50 J/cm(2) and highest helium signal efficiency at 5.77 J/cm(2) for the present LIBS configuration, enabling sustained He signals across 7 consecutive ablation shots (1.5 & times; higher depth resolution than suboptimal fluences) with reproducible relative standard deviation (RSD = 4.2%); (2) revelation of distinct element-specific fluence responses, He signal exhibits apparent saturation above 8.75 J/cm(2) fluence during the first laser shot; however, when considering subsequent shots, the average intensity continues to increase with increasing fluence, while B emission intensifies monotonically providing a framework for multi-element depth profiling; (3) methodological rigor via calibrated laser spot size (1.206 +/- 0.008 mm) and beam mode preservation (M-2 < 1.1). Complementary validations confirm reliability: thermal desorption spectroscopy (TDS) quantifies He retention at 4.93 & times; 10(20) atoms/m(2), cross-sectional scanning electron microscopy (SEM) verifies defect-free multilayers (B: similar to 1.19 mu m, Mo: similar to 2.23 mu m). Plasma parameters were estimated assuming local thermodynamic equilibrium (LTE). This work advances LIBS as a transformative in-situ diagnostic for fusion reactors, offering a generalizable fluence-optimized protocol for complex nuclear materials and enabling precise He monitoring in realistic PFCs to support real-time wall conditioning and erosion assessment in ITER and future tokamaks.

A spectral matching algorithm based on the Saha–Boltzmann distribution is proposed to determine the spatio-temporal evolution of T e and n e in laser-ablated molybdenum plasma in vacuum.

The retention of hydrogen isotopes in the fusion device is critical due to safety concerns. In this work, the deuterium (D) and helium (He) retention features in the different marked tiles exposed to HL-2A tokamak discharge plasma were quantitatively characterized using long pulse laser induced desorption-quadrupole mass spectrometer (LID-QMS) combined with SEM and EDX. The D retention originates primarily from D plasma discharges of HL-2A during 2021 campaign, and the He retention comes primarily from the helium glow discharge cleaning (He-GDC). The marked tiles materials include pure bulk W, bulk stainless steel (S.S) and W-, C-, Fe-films deposited on titanium-zirconium-molybdenum alloy (TZM) or W substrates. The LID-QMS results indicate that the D and He retention distribution along the poloidal direction of HL-2A device exhibited an overall uniformity. The sequence of the D concentration trapped in the marked tiles is C-film > W-film > Fe-film/bulk S.S > bulk W, whereas the He retention is Fe-film > bulk S.S > W-film > bulk W > C-film. The D retention is higher than the He retention in all measured materials. And the D and He trapped in the film tiles are higher than those in bulk tiles. The probable reasons for the differences were discussed in combination with the changes of the surface micro-morphology and the elemental compositions of the marked tiles. This investigation would provide a reference for future in-situ application of LID-QMS to monitor the D and He retention in bulk tiles and deposited materials, and also gives the data support for fuel particle transport modelling.

In situ monitoring of helium (He) retention in plasma-facing materials of nuclear fusion devices is critical for understanding plasma–wall interactions (PWIs). This study introduces a transformative approach to optimize He detection in high- Z materials—tungsten (W) and molybdenum (Mo)—using laser-induced breakdown spectroscopy (LIBS) under vacuum conditions. The He I 587.56 nm spectral line was identified as the optimal analytical signal for LIBS due to its dominant intensity and resilience to spectral interference from high- Z elements. By systematically optimizing gate delay timing and leveraging spatial plasma emission characteristics, a threefold improvement in the signal-to-noise ratio was achieved through the exclusion of core plasma emissions, where bremsstrahlung background and matrix interference are most pronounced. Quantitative calibration curves were established using laser-induced desorption quadrupole mass spectrometry as a reference, with internal standardization reducing prediction errors to ⩽10%—significantly enhancing accuracy in the face of variable laser ablation rates. The achieved limits of detection for He in Mo and W co-deposited layers are 0.72 × 10 ^14 He mm ^−2 (0.09 at.%) and 0.84 × 10 ^14 He mm ^−2 (0.11 at.%), respectively, being the lowest reported values for high- Z materials to date. This work delivers critical calibration parameters and a robust methodology for in situ LIBS diagnostics, addressing the longstanding challenge of real-time He retention monitoring in fusion devices. The proposed approach paves the way for practical applications in tokamaks such as ITER and EAST, enabling precise characterization of PWIs and facilitating advancements in plasma-facing component design.

Tungsten impurities deposited on the plasma-facing components (PFCs) of the inner walls of tokamak devices pose a significant risk to steady-state operation and safety. Nevertheless, quantitative chemical analysis of the co-deposited layer on PFCs is a critical task. Laser-induced breakdown spectroscopy (LIBS) is a promising technique for assessing the deposition of impurities on PFCs, enabling in situ monitoring, real-time analysis, and simultaneous detection of all elements. However, the accuracy of the quantitative analysis is affected by the material matrix. Diffuse reflectance spectroscopy (DRS) provides complementary information about the material matrix, such as optical properties. Herein, we present a novel data fusion model of LIBS and DRS techniques, providing more accurate results compared to models based on each of these single methods. 66 standard samples were prepared to simulate the impurities deposited on PFCs in EAST. 15 samples were randomly selected as the prediction set, while the remaining 51 samples were used as the calibration set. The average relative errors of the data fusion model for W, Li, Fe, and O were 2.23, 1.95, 2.08, and 0.39%, respectively. Compared with the single LIBS data model, the root mean square errors of prediction (RMSEP) for the four elements W, Fe, Li, and O in the data fusion model were reduced by 19.4, 18.5, 21.4, and 20.9%, respectively. The results show that the fusion of LIBS and DRS data enables improved quantitative analysis of co-deposited impurities on PFCs.

The cascaded arc plasma source is a significant plasma-generating device capable of producing high-density, steady-state plasma in a low-pressure environment. The two most crucial physical parameters of the plasma are the electron density (ne) and electron temperature (Te). The laser Thomson scattering (LTS) technique provides an accurate method for measuring both ne and Te. In this study, we conducted diagnostic measurements of ne and Te for cascaded arc argon-helium (Ar-He) and argon-neon (Ar-Ne) mixture plasmas utilizing LTS technology. Furthermore, we explored the local thermodynamic equilibrium (LTE) state of the plasma by comparing the electron excitation temperature (Texc) obtained through optical emission spectroscopy (OES) with Te measured via LTS. Our results indicate that varying the dopant ratios of the gas mixtures, alongside the experimental currents and background pressures, influences both ne and Te. Specifically, these parameters are inversely proportional to the dopant ratio, while they are directly proportional to the background pressure and discharge current. Notably, at the same dopant ratios, ne and Te are slightly elevated in the presence of Ne dopants compared to those with He dopants. Additionally, the observed differences between Texc and Te suggest that the cascaded arc mixture plasma deviates significantly from the LTE state. This deviation is directly proportional to the dopant ratio and inversely proportional to the discharge current. The findings contribute to a deeper understanding of multicomponent plasmas and potentially enhance the applications of cascaded arc mixture plasmas.

The Thomson scattering (TS) spectrometer is a core diagnostic instrument for the precise measurement of electron temperature and electron density in plasmas. However, strong stray light is a significant problem in TS measurements. In this study, we designed a triple grating spectrometer (TGS) in a symmetric subtractive configuration to achieve a high rejection ratio (RR) of stray light. The triple-grating spectrometer (TGS) comprises three symmetric single-grating spectrometers. Among these, the first and second spectrometers, along with the mask, collectively form the notch filter module and serve as the primary components for stray light rejection. To investigate the influence of the system's three key spectrometer components-specifically the entrance slit, mask and exit slit-on the rejection ratio (RR), we conducted comprehensive and systematic experimental measurements of the TGS's RR using a semiconductor laser as the light source. The results indicate that the RR is positively correlated with the widths of the entrance and exit slits, while negatively correlated with the mask width. With the optimal parameter combination, the experimentally measured RR reaches as high as 9.033x10(-8). Additionally, we experimentally explored the stray light rejection capability under a wide range of parameter conditions, which provides design guidance for optimizing key parameters in Thomson scattering (TS) spectrometer systems.

The depth resolution of the deposited layer on the plasma-facing components (PFCs) is essential for understanding the plasma-wall interaction (PWI) processes. Laser-induced breakdown spectroscopy (LIBS) has been proven effective for the in situ diagnosis of the depth profile of the deposited layer on the first wall of a fusion device. However, the effect of focusing conditions on LIBS depth profiling requires further investigation. In this study, depth profiling of multilayer samples with a four-layer structure was performed in a vacuum by adjusting the distance from the focal point to the sample surface (Delta L). The impact of focusing conditions on LIBS depth resolution was investigated, and the resulting depth distribution profiles were modeled. The results indicated that the laser profile factor gradually decreases with increasing Delta L and the resolving ability of the Ni intermediate layer gradually decreases. According to the LPIR model, the depth profiles obtained under different focusing conditions were successfully simulated, and the interface positions between layers were quantitatively identified. The correlation coefficients between the modeling and experimental results for the depth distributions under different focusing conditions were greater than 0.99. Additionally, layer thicknesses were calculated and compared under different focusing conditions. Overall, the medium spot size obtained in the defocused state is beneficial for depth profiling of a complex multilayer sample, considering the layer-resolving ability of the Ni intermediate layer and the accuracy of the layer thickness. This study will be of great significance in optimizing the experimental conditions of the in situ LIBS system for fusion devices.

The spatio-temporal evolution of laser ablation W plasma under low-pressure conditions in a continuous Ar plasma ambient was investigated and compared to that in Ar gas ambient.

Fiber-Optic Laser-Induced Breakdown Spectroscopy (FO-LIBS) technology offers excellent remote diagnostic capabilities and flexibility in complex environments, making it highly promising for monitoring the elemental distribution in wall materials of future fusion devices. This study focused on the low-pressure conditions, where a FO-LIBS experimental system was developed to systematically analyze the temporal evolution of Cu and Mo plasma spectra under pressures ranging from 0.2 to 20 Pa. The results demonstrated that the intensities of key spectral lines, such as Cu I and Mo I, show linear growth with increasing laser energy within the specified pressure range. Additionally, the intensities of these characteristic spectral lines decrease significantly as pressure rises, becoming much weaker than at atmospheric pressure. The presence of an argon atmosphere further reduces these spectral line intensities. Time-resolved measurements indicate that plasma lifetimes are approximately 400 ns under 0.2 Pa, which happens earlier than under atmospheric pressure. Calculated electron densities, estimated using the Stark broadening method, correspond with the trends in spectral line intensity variations. This research provides optimized FO-LIBS parameter selection for in situ elemental diagnostics under low-pressure environments in fusion devices.

The species including atoms and multiply charged ions in the laser produced molybdenum (Mo) plasma are investigated in this work using optical emission spectroscopy and time-of-flight electrostatic energy analyzer (TOF-EEA). Nanosecond laser (5 ns, 1064 nm,) pulses were focused on the Mo target surface with a spot size of 0.4 mm2, energy of similar to 150 mJ/pulse (corresponding to a power density of similar to 7.5 GW cm(-2)) to generate the Mo plasma in vacuum environment. Time-resolved spectral analysis was carried out to investigate the temporal evolution of continuous background, atomic, and monovalent ionic spectral signals. The Saha-Boltzmann method is applied for spectral fitting, providing insight into the temporal evolution of electron temperature (T-e) and electron density (n(e)). Over the time from 40 ns to 500 ns, the T e decreases from 3.6 eV to 0.52 eV, and the n e decreases from 2.5 x 1020 cm(-3)-1.0 x 10(15) cm(-3). Linear fitting extrapolation predicts the T e and n e could be even up to 6.3 eV and 2.5 x 10(22) cm(-3), respectively, at the early stage of 10 ns. This indicates the generation of multiply charged ions during the laser ablation process. The multiply charged ions up to 6 charge states were observed by the TOF-EEA and the energy distributions for the different charged ions were also obtained. It was found the ion kinetic energy is positively related to the number of charge state indicates the existence of acceleration electric field. The equivalent accelerating potential is determined as approximately 570 V at the current laser power density. This research provides a significant reference for the establishment of models for laser ablation plasmas and a profound understanding of the underlying physical processes.

Laser-induced breakdown spectroscopy (LIBS) is a highly promising technique for the in-situ, real-time diagnosis of impurity deposits on the inner walls of tokamak devices. The deposited impurity on plasma-facing materials (PFCs) pose a significant risk to the steady-state operation of the tokamak. Under vacuum conditions, an accurate quantitative analysis of the thin co-deposition layers is a technical challenge. In this study, 30 co-deposited layer samples of tungsten (10.0-92.3 a.t.%), molybdenum (2.0-77.8 a.t.%), iron (2.9-12.1 a.t.%) and copper (1.2-18.7 a.t.%) were prepared to simulate the co-deposition layers found on PFCs in Experimental Advanced Superconducting Tokamak (EAST). A variation of the CF-LIBS algorithm, the so-called One Point Calibrated LIBS (OPC-LIBS), was employed to analyze these co-deposited layer samples under conditions of 5 × 10-5 mbar. It was found that the matrix matching degree among the measured samples and the selection of standard samples play a decisive role in the quantitative analysis capability of OPC-LIBS. In actual situations, the composition of the co-deposited impurity layers at different locations in the Tokamak will be quite different. We addressed this challenge by developing the Classified OPC-LIBS (COPC-LIBS) model, an enhanced version of OPC-LIBS with pre-classification to offset matrix effects in LIBS analysis. For tungsten in the co-deposition layers, the root mean square (RMSE) calculated by the CF-LIBS method was 14.7, the OPC-LIBS method was 11.5, and the newly invented COPC-LIBS was reduced to only 5.1. The COPC-LIBS method is a highly efficient technique that can precisely measure the distribution of co-deposited layers on the surface of inner wall materials. The diagnostic data obtained from this method will provide valuable insights into the interaction between plasma and wall materials during the operation of fusion devices.

ITER is designed for a burning plasma operation in which Tungsten (W) tiles are used as the first wall and diverter materials. Studying He dynamics in B-coated W wall is essential to understanding the effect of boronized plasma-facing components in fusion reactors, as these post-conditioning materials significantly influence helium retention and release. Plasma-wall interactions (PWI) are an important issue in ITER fusion reactors. PWI would lead to wall erosion and impurity redeposition. As a product of the D-T burning plasma, helium (He) ash would be retained or co-deposited on plasma-facing components (PFCs), affecting the stable operation of burning plasma. Laser-induced breakdown spectroscopy (LIBS) is proposed as a promising in-situ diagnostic approach for monitoring D/T and He retention and impurity deposition on PFCs of tokamak devices. In this study, the LIBS technique was used to investigate the helium retention feature in the boron (B) layer on tungsten substrate in 10-5-5 mbar. Five He-retention samples on the boron deposition layer on tungsten substrates were prepared by pulsed laser deposition (PLD) method at different ambient pressures in our lab. The investigations indicate that the atomic spectral line of helium (He-I 587.56 nm) was observed in the spectra of the first three laser shots. The depth profiles of He, B, and W in the boron-deposited layer on tungsten substrate were performed by LIBS to determine the co-deposition layer thickness. The concentration of He in the co-deposition layer samples measured by TDS is 7 x 1020 20 He/m2. 2 . The plasma parameters, such as plasma electron temperature and electron number density, were calculated to validate the local thermodynamic equilibrium. Machine learning (ML) algorithms are used to classify the co-deposits and substrates. The first three principal components (PC1, PC2 & PC3) of the unsupervised ML algorithm (PCA) give a classification accuracy of 91.7 %. The supervised ML algorithm neural network achieved training and testing accuracy of 100 % and 96.7 %, respectively.

This study investigates the impact of sample temperature Ts on Laser-Induced Breakdown Spectroscopy (LIBS) emission characteristics and Calibration-Free LIBS (CF-LIBS) quantitative analysis in vacuum and air. Using an aluminum-tin-copper alloy, we analyze spectral lines within a 20 degrees C to 170 degrees C temperature range. Evaluation encompasses emission line intensities, plasma parameters, expansion imagery, and laser ablation crater morphologies. CF-LIBS analysis underlines that elevated Ts maintains quantitative accuracy even for minor elements with weak lines. In atmospheric conditions, tin segregation occurs, yet CF-LIBS remains robust. These results highlight CF-LIBS's potential for varied applications by mitigating Ts-induced effects.