Hydrogen Isotopes Retention Studies Using Laser and Microwave Induced Plasma Coupling

Hydrogen Isotopes Retention Studies Using Laser and Microwave Induced Plasma Coupling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Hydrogen Isotopes Retention Studies Using Laser and Microwave Induced Plasma Coupling Nikola Vujadinovic, Ivan Traparic, Biljana Duško Stankov, Dragan Rankovic, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5912220/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Apr, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract The detection of deuterium and tritium retention in fusion devices via optical emission spectroscopy (OES) faces significant challenges due to experimental limitations, particularly in resolving hydrogen isotope Balmer alpha lines (H α , D α , and T α ). In this study, we propose and evaluate the coupling of laser ablation and laser-induced desorption with microwave-induced plasma (MIP) as an approach to resolve this problem. This approach effectively meets the resolution requirements for Balmer alpha lines, overcoming limitations of standard laser-induced breakdown spectroscopy (LIBS) setups. Optimization of Nd:YAG laser ablation was performed using pure copper and tungsten targets, while desorption, including femtosecond (fs) laser-induced desorption, was studied on graphite powder mixed with heavy water and water. The results demonstrate a significant improvement in spectral resolution and analytical performances, highlighting the potential of this technique for tritium retention studies in plasma-facing components. Physical sciences/Physics/Plasma physics/Laser produced plasmas Physical sciences/Physics/Chemical physics Hydrogen isotopes retention laser ablation laser induced desorption microwave induced plasma plasma-facing components LIBS Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction Diagnostics of the fusion plasma reactors are critical for ensuring their safe and proper stable operation. Among these diagnostics, the hydrogen isotope retention, particularly tritium, in plasma facing components (PFC) are probably the most important ones [ 1 ]. Techniques such as ion beam analysis (IBA) and thermal desorption spectroscopy studies (TDS) are highly reliable and commonly used PFC diagnostics methods [ 2 – 5 ]. However, these methods are constrained to laboratory settings and require complex equipment. Consequently, sections of the PFC or test targets positioned on various places within the vacuum vessel must be demounted from the reactor wall [ 6 ] to be analyzed. To enable in-situ analysis of PFC, laser induced breakdown spectroscopy (LIBS) is used as an effective solution to overcome limitations of traditional methods. LIBS is a minimally invasive, non-contact technique suitable for multi-element analysis, including depth profiling, without requiring sample preparation. The technique is adaptable for vacuum or low-pressure gas environments and has been applied across diverse fields, such as nitrogen detection in soil [ 7 ], explosives detection [ 8 ], olive oil classification [ 9 ], cadmium detection in drinking water [ 10 ], and even the identification of malaria biomarkers [ 11 ], bacteria [ 12 ] or SARS [ 13 ]. LIBS is also commonly used for analyzing metal purity, alloys, jewelry [ 14 ], archaeological and other samples. Reviews [ 15 – 17 ] and recent studies [ 18 – 20 ] provide comprehensive insights into the advancements of LIBS for fusion applications, particularly its potential for in-situ diagnostics. The most important application of LIBS for plasma fusion reactor wall diagnostics is the study of hydrogen isotope retention, which relies on measurement of their Balmer alpha spectral lines. A significant challenge in this application is resolving the closely spaced lines caused by the small isotope shift. Even high-resolution spectrometers struggle to resolve these lines, due to significant Stark broadening under standard LIBS plasma conditions [ 21 ]. Partial resolving of a hydrogen and deuterium Balmer alpha lines (with isotope shift of 0.18 nm) has been achieved in studies using double-pulsed LIBS, where line fitting with a Voigt function was employed [ 17 , 22 – 23 ]. More recently, approaches based on femtosecond (fs) laser ablation [ 24 ] and fs LIBS [ 25 ] have been applied to hydrogen isotope retention diagnostics, demonstrating further advancements in this field [ 26 – 31 ]. The use of the TEA CO 2 lasers or Nd:YAG in He [ 32 – 34 ] or filament fs laser LIBS [ 26 , 29 ] demonstrates the possibility of LIBS to resolve H α and D α lines. However, resolving T α ​ lines presents a greater challenge due to the stricter requirements for low electron density [ 21 ]. In this study, we propose overcoming these challenges by coupling laser and microwave-induced plasma (MIP) to achieve the necessary plasma conditions. Two sample introduction methods are employed: laser ablation using an Nd:YAG laser and fs laser-induced desorption, both integrated with microwave-induced low-pressure plasma. 2. Experiment Microwave induced plasma is the primary method used in this research for excitation and resolution of hydrogen isotope lines. The combination of MIP and laser induced plasma was used earlier for the enhancement of the LIBS [ 35 , 36 ], where the addition of microwaves increased electron density, temperature, and plasma duration and dimensions. However, this enhancement also increased Stark broadening, making the method unsuitable for tritium retention studies. In contrast, MIP source operating at atmospheric pressure has plasma parameters [ 37 , 38 ] suitable for resolving D α and T α spectral lines, as analyzed in [ 21 ]. At low gas pressures, MIP achieves even smaller electron densities [ 39 ], minimizing Stark and Van der Waals broadening, making them negligible in comparison with other broadening mechanisms (Doppler and instrumental). For this study, a Beenakker resonator cavity with an 8 mm diameter and 14 cm long capillary tube was used, with an optical window and evacuation port mounted at the end. MIP was generated using an AHF Analysen Technik GMW 24–301 DR 2.45 GHz microwave generator with a maximum power of 100 W. Pressure within the tube was regulated by a needle valve, and a mechanical vacuum pump was used for evacuation before maintaining stable argon gas flow. The first method used for sample introduction was laser ablation, a widely used technique in analytical spectroscopy for introducing samples into excitation sources such as inductively coupled plasma (ICP), MIP, LIBS or mass spectrometry [ 40 – 42 ]. For this purpose, we used a laboratory made laser ablation cell, see Fig. 1 . This cell was constructed as an elongation of the capillary tube thus enabling the most efficient transport of the ablated material into the MIP. The target was placed in a custom built holder with vacuum feedthrough, allowing rotation to expose fresh target surface area to the laser beam. Ablation was performed using Quantel 450 Nd:YAG (1064 nm, 6 ns pulse duration, 10 Hz maximum repetition rate). Laser beam was focused with a f = 12.5 cm lens through the window and onto the target. Special cell design enables irradiation of the target at approximately 45 degrees. Small variation of incident angle enables irradiation at a variable distance from the center of the target. That way, laser induced plasma radiation, which always propagates normal to the target surface, does not reach detection system and enables recording of the radiation coming from the MIP only. The emitted light from the MIP was collected through an optical window at the end of the capillary using a collimator (COLL) and guided via fiber optic cable (OF) either to medium resolution spectrometer Andor Shamrock 303i (with grating 1200 g/mm) or high-resolution spectrometer SOL instruments MS7504i spectrometer (with grating 1800 g/mm). The Andor spectrometer was equipped with Andor iStar DH720-18F-63 ICCD camera (256 x 1024 pixels, 26 µm pixel size), while SOL instruments spectrometer was equipped with Andor iStar DH734-18F-63 ICCD camera (1024 x 1024 pixels, 13 µm pixel size), that were used as detectors. Delay and gating of cameras were controlled with external digital delay generator (DDG, Stanford Research SRS 535), which was triggered with the signal for opening of a Nd:YAG laser Q switch. It should be noted that the separation of the optical emission signals created by LIBS and by MIP can also be achieved by changing the delay and gate time of the camera exposure. The Nd:YAG laser, commonly used for plasma creation, is known to ablate a thick layer of material, making it unsuitable for analyzing thin films or surface-bound elements. For detecting hydrogen isotopes within thin surface layers, laser-induced desorption (LID) [ 43 – 45 ], often paired with quadrupole mass spectrometry (LID-QMS) [ 46 ], is a more suitable approach. To test the feasibility of using MIP as an alternative to the more complex QMS, a femtosecond Yb:YAG laser (Solar FX200, 1030 nm, 150 fs pulse duration, 105 nJ peak energy, 71 MHz repetition rate, 7 W average power) was employed for laser-induced desorption of hydrogen isotopes. In this setup, the detection system was triggered by the camera’s internal trigger with a variable exposure time. While this study utilized the femtosecond laser, laser-induced desorption can also be achieved with other lasers capable of heating the target without causing significant ablation. The selected targets for these studies included a copper target for the experiment optimization in terms of gas pressure, delay time, microwave power and laser energy. A tungsten target was then introduced to verify the optimized conditions for resolving Balmer alpha spectral lines. Finally, a pill composed of graphite powder mixed with water and heavy water (D 2 O), was prepared using a hydraulic press, as previously described in [ 21 ]. This pill was tested for both laser-induced desorption and vacuum-induced desorption. 3. Results In the investigation of MIP for hydrogen isotope detection, the initial task involved optimizing the transport and excitation of sample components. Due to the challenges associated with tritium's radioactivity, most previous research has focused on deuterated samples as a safer alternative. In this study, tungsten (W) samples containing incorporated deuterium were analyzed using laser ablation as the method for introducing samples into the MIP. 3.1. Laser ablation The investigation of Nd:YAG laser ablation as a method for introducing tungsten samples with incorporated deuterium into the MIP proved nearly impossible with our experimental setup. This was due to several factors: the high reflectivity of the polished samples, the shallow retention of the deuterium and high laser ablation rate. As a result, the application of MIP for hydrogen isotopes detection using laser ablation was limited to optimizing parameters for resolving hydrogen isotope Balmer alpha lines. According to [ 21 ], D α and T α spectral lines can be resolved only if full width at half maximum (FWHM) of lines is less than 0.056 or even 0.027 nm, depending on their intensity ratio (1:1 or 1:10, respectively). Furthermore, FWHMs of the neighbor spectral lines must also be smaller than the wavelength separation between them and hydrogen isotope lines. To obtain the best resolving results, using laser ablation, the signal to noise ratio (i.e., line intensities) has to be maximized by optimizing several experimental parameters, while keeping FWHM as minimal as possible. For MIP operation, microwave power and gas pressure are the most important parameters. The line intensities increase with microwave power, but the reflected power also increases. If the reflected power exceeds 15 W, there is a risk of damaging the microwave generator or overheating the discharge tube. Optimal gas pressure, which corresponds to the flow rate, must also be determined, as it dictates the time the sample remains within the MIP resonator cavity for excitation. Additionally, the dependence of spectral line intensities on laser energy was analyzed, as laser energy influences the ablation process, specifically the ablated mass and particle dimensions. Although higher energy increases the ablated mass, it is important to assess whether larger particle dimensions might affect MIP performance by altering microwave coupling to the plasma or causing particle deposition on the tube walls. 3.1.1. Optimization of gas pressure The optimal gas pressure range for stable MIP operation was determined by analyzing the maximal intensity of the Ar I line at 516.22 nm (3s²3p⁵(²P o ₃/₂)4p → 3s²3p⁵(²P o ₃/₂)6d), as shown in Fig. 2 a. The Ar I line was used to establish the optimal gas pressure range since its intensity is independent of the camera recording delay. In contrast, the intensities of the target lines, such as Cu I, depend on the gas flow rate, which determines when the ablated material reaches the plasma. From Fig. 2 b, the optimal gas pressure range for stable MIP operation was between 15 and 20 mbar. The optimal gas pressure can be determined using the most intense spectral line, the Cu I line at 521.82 nm (3d¹⁰4p → 3d¹⁰4d). Since this line is susceptible to self-absorption, its optical thickness was evaluated. The Cu I lines at 515.32 nm (λ 1 ) and 521.82 nm (λ 2 ) belong to the same multiplet (transition 3d¹⁰4p → 3d¹⁰4d) as shown in Fig. 2 a. To assess self-absorption of the 521.82 nm line, the intensity ratio R = I λ1 / I λ2 was compared at various pressures to the theoretical value of R = 0.53 (Table 1 ) [ 47 ]. Results indicated no significant self-absorption for all pressures except at 10 mbar, where the lines exhibited low intensity. Table 1 Experimental ratios of the intensities of Cu I spectral lines at various pressures. Pressure (mbar) R = I λ1 / I λ2 (exp.) 10 0.66 15 0.54 20 0.53 25 0.54 Since the Cu I line has a significantly higher intensity at 20 mbar, see Fig. 2 b, this line was used in optimization of several experimental parameters in all further investigations. 3.1.2. Optimization of material transport to the MIP Gas pressure and flow regulate the duration for which the ablated material remains in the discharge, thereby influencing the recording parameters (delay and gate times). The delay corresponds to the time required for the material to travel from the target to the resonator cavity, while the gate time determines the duration the material spends in the discharge zone. An analysis of the optimal delay time is presented in Fig. 3 . Based on Fig. 3 it was concluded that the delay time should be 20 ms and the gate time should be 10 ms. During these measurements, microwave power was set to 75 W and laser energy was 250 mJ. The final spectrum was the accumulated spectrum of 20 laser shots. 3.1.3. Optimization of ablated material quantity The amount of ablated material is directly influenced by the laser energy used. To optimize this parameter, the laser energy was adjusted by varying the delay between the triggering of the flash lamps and the opening of the laser Q switch (FLQS). Three energy values were tested: 130, 250 and 430 mJ. The resulting graph is shown in Fig. 4 . With the increase of the laser energy, the intensity of the Cu I line also increases. This is primarily due to the ablation rate, as when the energy of the laser is higher, the ablation rate is also higher, and more material is entering the discharge region. Here, optimal energy of 250 mJ was chosen, as for the higher energy, the mass of the incoming material was too large, which caused the MIP discharge to shut down. 3.1.4. Selection of microwave generator power Dependence of the line intensity on the microwave power supplied to the cavity (for optimal pressure, delay, gate and laser energy) was analyzed. Here, four powers were considered (50, 60, 75 and 90 W). Besides supplied power, the reflected power was also measured. The obtained dependance on the supplied power is shown in Fig. 5 . The results indicate that increasing the supplied power leads to a corresponding increase in line intensity. However, the reflected power also rises with higher input power. In Fig. 5 , a dashed vertical line marks the input power at which the reflected power reaches 15 W. Since exceeding this threshold could overheat the source, it is not advisable to operate beyond this limit. Consequently, 75 W was selected as the optimal power setting to ensure safe and reliable generator operation. 3.1.5. Optimization of spectral resolution for hydrogen isotopes retention studies After optimizing experimental parameters for laser ablation and MIP operation the potential of this setup for hydrogen isotopes retention studies was analyzed. For such analysis, the FWHM of Balmer alpha lines should be less than 0.027 nm if one wants to detect small amounts of tritium in the first wall of future fusion reactors. The first step in this direction was to assess the instrument broadening on the spectral lines’ widths. Given the negligible Stark broadening at low MIP gas pressures ( Ne ~ 10 12 cm − 3 ), and the electron temperature between 2000 and 3000 K, we can safely assume that the major influence in the line broadening comes from the Doppler and instrument broadening. To determine the FWHM of the Cu I line at 521.82 nm, the recorded spectrum (Fig. 5 ) was fitted with a Gaussian function. As can be seen in Fig. 6 , the resulting FWHM was 0.27 nm, which greatly exceeds the goal of having lines as narrow as 0.027 nm. This result is reasonable, considering that medium resolution Shamrock 303 imaging spectrograph with the entrance slit width of 50 µm equipped with Andor iStar DH720 ICCD camera was used for these measurements. To reduce the instrumental broadening of the lines, the high resolution MS7504i spectrometer with the entrance slit width of 30 µm equipped with Andor iStar DH734-18F-63 ICCD camera was used for recording spectral lines of tungsten. As part of the optimization of the optical system (selection of the spectrometer and slit width), W target was used to verify whether the W line FWHM is less than 0.04 nm, which corresponds to the wavelength separation between hydrogen Balmer alpha line at 656.28 nm and W I line at 656.32 nm. Gaussian fitting of the W I lines (Fig. 7 ) showed the FWHM of 0.024 nm at 429.46 nm and 0.025 nm at 430.21 nm, meeting the required resolution. This demonstrates that the setup is capable of enabling precise determination of the H α line intensity. 3.2. Desorption as a method for sample introduction in MIP To obtain the H α and D α FWHM values and to test whether resolving the D α and T α lines is possible in this configuration, and for previously determined optimal experimental parameters of 20 ms delay and 10 ms gate time, 75 W MIP input power and a 30 µm entrance slit width of the high resolution spectrometer, a mixture of graphite powder, heavy water and water, pressed into a pill, was used as the target. In section 3.2.1, the results of the MIP spectrum for desorption induced by the vacuuming alone are presented, while in section 3.2.2, the results of desorption induced by fs laser heating in combination with the vacuum pump are presented. 3.2.1. Desorption due to vacuuming Due to the composition of the target pill, water and heavy water were not fully bonded to the graphite, resulting in their evaporation from the target during vacuum pump outgassing. The corresponding MIP spectra with deuterium and hydrogen Balmer alpha lines is shown in Fig. 8 . As can be seen, the lines are narrow and fully resolved. 3.2.2. Laser induced desorption As a final step, we examined whether a 1030 nm fs laser with very low energy (100 nJ) could induce desorption of hydrogen isotopes from the target and introduce them into MIP. Two cycles of heating were performed and recorded. During target heating, an increase in the D α and H α line intensities was observed, without a corresponding increase in their FWHMs. MIP spectra, after turning off the laser following the second heating cycle, is shown in Fig. 9 . The effect of laser induced desorption is evident: during the cooling of the target, the line intensities gradually decrease to the levels seen in Fig. 8 , where desorption was induced by the vacuum pump alone. The time dependency of the D α line intensity during both cycles is shown in Fig. 10 . The effects of laser heating and laser induced desorption are clear. The intensity increased while the laser was active, peaking at the moments when the laser was turned off. After that, intensity decreased gradually. This confirms that the deuterium comes from laser induced desorption, rather than solely from outgassing due to the vacuum pump. It should be noted that the intensity from the first measurement is higher than it should be, because not enough time has passed for the target to cool from the previous test measurements. The starting value should be close to the one shown in Fig. 8 , as that was recorded before the laser heating. Before proceeding to the estimation of hydrogen isotope line widths, plasma parameters were estimated. The excitation temperature was estimated from the Boltzmann plot of Ar I lines to be 2600 K. Boltzmann plot is given in Fig. 11 . Complete data for the lines used to obtain the Boltzmann plot can be found in the Supplementary Table S1 . Given the expected low electron density and negligible Stark broadening for both hydrogen and argon lines, an attempt was made to estimate the upper limit for electron density. The merging of spectral lines of hydrogen is a suitable method for this estimation. If the final detectable spectral line of Balmer series is found, then the use of Inglis – Teller relation [ 48 ] $$\:\text{log}({N}_{e}+{N}_{i})=23.26-7.5\text{log}{n}_{max}+4.5\text{log}z$$ 1 can give the upper limit on the electron density. The final observed member of the Balmer series in this study was H-η (9 → 2, 383.5 nm), shown in Fig. 12 . Assuming N e = N i , and that for hydrogen atoms the effective nuclear charge (z) is 1, the upper limit of electron density Ne ~ 6.3 ∙ 10 15 cm − 3 was obtained. This value is a huge overestimation, since the upper members of the series couldn’t be detected due to the presence of different molecular bands. Another approach for determining the electron density is through the Stark broadening of the upper members of the Balmer series. Since the highest detected member of the Balmer series has the width close to the instrumental width, and considering the errors during the fitting procedure, it can be estimated that the Stark width of the Balmer alpha lines doesn’t exceed 0.01 nm. If this value is inserted into the formula for the estimation of line widths from the higher members of the Balmer series [ 49 ] $$\:{N}_{e}={8\cdot\:10}^{18}\cdot\:{\left(\frac{{w}_{S}\:\left(nm\right)}{{\alpha\:}_{1/2}^{n}}\right)}^{1.5}$$ 2 the resulting value, with α n 1/2 = 0.345 (for n = 9), would be N e = 1.25 ∙ 10 12 cm − 3 , which is a more realistic estimation than the one obtained by the Inglis – Teller equation. Finally, to confirm the necessary resolution for the hydrogen retention studies, both lines were fitted with a Voigt profile (Fig. 13 ). Gaussian fitting was also attempted, but Voigt profile showed better performance in terms of wing fitting. Approximative equation for Voigt profile FWHM [ 50 ] $$\:{W}_{V}\approx\:0.5346{W}_{L}+\sqrt{0.2166{W}_{L}^{2}+{W}_{G}^{2}}$$ 3 was used with coefficients obtained from Fig. 13 . The resulting line widths are 0.033 nm for D α line and 0.038 nm H α line. Although Voigt line widths are correct, the Gaussian and Lorentzian parts are off. Gaussian parts can be calculated using the equation $$\:{W}_{G}=\sqrt{\left({W}_{D}^{2}+{W}_{I}^{2}\right)},$$ 4 where \(\:{W}_{D}\) represents the Doppler line width and \(\:{W}_{I}\) is the instrumental line width. Doppler broadening FWHM can be calculated using the equation $$\:{W}_{D}=7.16*{10}^{-7}\lambda\:\sqrt{\frac{T}{M}},\:$$ 5 where M is the mass of the emitter, given in atomic mass units, and T is the temperature estimated using a Boltzmann plot of the Ar I lines (Fig. 11 ). Since the instrumental FWHM was estimated at 0.024 nm, based on FWHM of W I 429.46 nm line from Fig. 7 , Gaussian parts of the Voigt profiles are 0.029 nm and 0.034 nm for D α and H α , respectively. Lorentzian parts are then calculated using the Eq. ( 3 ), and they are 0.007 nm for both D α and H α . Finally, using the formula suggested in [ 21 ], the intensity ratio of T α and D α for which both lines could be resolved was obtained. The critical FWHM at which mentioned lines can be resolved relates to the intensity ratio R = T α /D α through the following formula [ 21 ]: $$\:FWH{M}_{cr}=0.0599-0.0388\times\:{e}^{-1.765\times\:R}$$ 6 Now, for the determined FWHM of D α 0.033 nm, the theoretical ratio of lines is R = 0.2. Therefore, our proposed method could resolve D α and T α lines up to the point where D α is five times more intense than T α , or vice versa. 4. Conclusion In this work, we explored the coupling of laser-induced desorption and laser ablation with microwave-induced plasma as an effective method for studying hydrogen isotope retention in plasma-facing components of fusion devices. The experimental setup was optimized to achieve high spectral resolution, enabling the separation of hydrogen, deuterium, and tritium Balmer alpha lines. The application of femtosecond laser for desorption demonstrated a controlled and efficient sample introduction mechanism, while low-pressure MIP conditions minimized broadening effects, ensuring precise isotopic analysis. This study presents a significant advancement in the diagnostics of tritium retention, offering a minimally invasive, high-resolution approach that addresses the limitations of traditional methods such as ion beam analysis and thermal desorption spectroscopy. The findings underscore the potential of this technique for in-situ applications in fusion research, contributing to the development of safer and more efficient plasma diagnostics systems. Future work will focus on scaling this approach for broader fusion reactor applications and extending it to analyze mixed material deposits. Declarations Acknowledgements This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (contract numbers: 451-03-47/2023-01/200024 and 451-03-47/2023-01/200146), the Science Fund of the Republic of Serbia through the NOVA2LIBS4fusion project (grant number: 7753287), within the IDEAS call and under the project: NIFS21KLPF087. We also acknowledge Stanko Milanović, our technical associate, who drew the schematic figure of the experimental setup. Author Contributions N. V. – Investigation, Formal Analysis, Visualization, Writing - Review & Editing I. 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H. et al. Quantitative analysis of deuterium using laser-induced plasma at low pressure of helium. Anal. Chem. 78 , 5768–5773 (2006). Kurniawan, K. H., Tjia, M. O. & Kagawa, K. Review of laser-induced plasma, its mechanism, and application to quantitative analysis of hydrogen and deuterium. Appl. Spectrosc. Rev. 49 , 323–434 (2014). Pardede, M. et al. High sensitivity hydrogen analysis in zircaloy-4 using helium-assisted excitation laser-induced breakdown spectroscopy. Sci. Rep. 11 , 21999 (2021). Ikeda, Y., Soriano, J. K., Ohba, H. & Wakaida, I. Laser ablation plasma expansion using microwaves. Sci. Rep. 13 , 13901 (2023). Ikeda, Y., Soriano, J. K., Ohba, H. & Wakaida, I. Analysis of gadolinium oxide using microwave-enhanced fiber-coupled micro-laser-induced breakdown spectroscopy. Sci. Rep. 13 , 4828 (2023). Jovicevic, S., Ivkovic, M., Pavlovic, Z. & Konjevic, N. Parametric study of an atmospheric pressure microwave-induced plasma of the mini MIP torch - I. Two-dimensional spatially resolved electron-number density measurements. Spectrochim Acta Part. B . 55 , 1879–1893 (2000). Jovicevic, S., Ivkovic, M. & Konjevic, N. Parametric study of an atmospheric pressure microwave-induced plasma of the mini MIP torch - II. Two-dimensional spatially resolved excitation temperature measurements. Spectrochim Acta Part. B . 56 , 2419–2428 (2001). Jovicevic, S., Ivkovic, M., Konjevic, N. & Popovic, S. and Vuskovic, L. Excessive Balmer line broadening in microwave-induced discharges. J. Appl. Phys. 95 , 24–29 (2004). Ciocan, A., Uebbing, J. & Niemax, K. Analytical application of the microwave induced plasma used with laser ablation of solid samples. Spectrochim Acta . 47B , 611–617 (1992). Matusiewicz, H. Design concept and characterization of a laser ablation - inductively coupled plasma/microwave induced plasma optical emission spectrometric system. Ecol. Chem. and Eng. S 16, No. S1 9–17 (2009). Brunnbauer, L. et al. Combined LA-ICP-MS/LIBS: powerful analytical tools for the investigation of polymer alteration after treatment under corrosive conditions. Sci. Rep. 10 , 12513 (2020). Yehia-Alexe, S. A. et al. Considerations on hydrogen isotopes release from thin films by laser induced ablation and laser induced desorption techniques. Spectrochim Acta Part. B . 208 , 106774 (2023). Zlobinski, M. et al. Laser-Induced Desorption of co-deposited Deuterium in Beryllium Layers on Tungsten. Nucl. Mater. Energy 19, 503–509 (2019). (2019). Zlobinski, M. et al. Efficiency of laser-induced desorption of D from Be/D layers and surface modifications due to LID. Phys. Scr. 014075 (2020). (2020). Zlobinski, M. et al. First results of laser-induced desorption - quadrupole mass spectrometry (LID-QMS) at JET. Nucl. Fusion . 64 , 086031 (2024). NIST Atomic Spectra Database. (2024). https://www.nist.gov/pml/atomic-spectra-database (last update to data content: November. Inglis, D. & Teller, E. Ionic depression of series limits. Astrophys. J. 90 , 439–448 (1939). Jovicevic, S., Ivkovic, M., Konjevic, N. & Review Low electron density diagnostics: development of optical emission spectroscopic techniques and some applications to microwave induced plasmas. Spectrochim Acta Part. B . 59 , 591–605 (2004). Olivero, J. J. & Longbothum, R. L. Empirical fits to the Voigt line width: A brief review. J. Quant. Spectrosc. Radiat. Transf. 17 , 233–236 (1977). Additional Declarations No competing interests reported. Supplementary Files Supplementarymaterial.pdf Cite Share Download PDF Status: Published Journal Publication published 12 Apr, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 03 Mar, 2025 Reviews received at journal 23 Feb, 2025 Reviews received at journal 16 Feb, 2025 Reviewers agreed at journal 14 Feb, 2025 Reviewers agreed at journal 12 Feb, 2025 Reviewers invited by journal 10 Feb, 2025 Editor assigned by journal 30 Jan, 2025 Editor invited by journal 30 Jan, 2025 Submission checks completed at journal 28 Jan, 2025 First submitted to journal 27 Jan, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5912220","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":409397977,"identity":"2628628c-5e54-4f98-932e-82e89cb8fbb5","order_by":0,"name":"Nikola Vujadinovic","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Nikola","middleName":"","lastName":"Vujadinovic","suffix":""},{"id":409397978,"identity":"80d0641e-601a-44f6-b8e4-1e5215debe4f","order_by":1,"name":"Ivan Traparic","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"","lastName":"Traparic","suffix":""},{"id":409397979,"identity":"4d74eb3f-b13a-43dd-b76c-87c3ea9123e7","order_by":2,"name":"Biljana Duško Stankov","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Biljana","middleName":"Duško","lastName":"Stankov","suffix":""},{"id":409397980,"identity":"f92f837a-41c3-48a3-86d8-73112f280bd5","order_by":3,"name":"Dragan Rankovic","email":"","orcid":"","institution":"University of Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Dragan","middleName":"","lastName":"Rankovic","suffix":""},{"id":409397981,"identity":"8859fbdf-b59e-4360-94c4-43daa1220f5f","order_by":4,"name":"Miroslav Kuzmanovic","email":"","orcid":"","institution":"University of Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Miroslav","middleName":"","lastName":"Kuzmanovic","suffix":""},{"id":409397982,"identity":"d14f301a-cfd0-4454-a6b8-58c51b351612","order_by":5,"name":"Milivoje Ivkovic","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqklEQVRIiWNgGAWjYBACNiBk+GDAkECaFsYZJGkBaWLmYSBFC59EWuJjm4I7eQzshx8wV/whxg6JtMPGOQbPihl40gwYz7YRo4XneJt0jsHhxAaGHAbGxgbitLT/tgBp4X/DwNhAlMPY244xM4C0SABtaWAjTkuyZA/QL2wSzwwONhLjF/lmNsMPP/7cyePnT374kCiHQcEBUCIAkiQAkhSPglEwCkbBSAMAo24w8cAPnMgAAAAASUVORK5CYII=","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":true,"prefix":"","firstName":"Milivoje","middleName":"","lastName":"Ivkovic","suffix":""}],"badges":[],"createdAt":"2025-01-27 12:23:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5912220/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5912220/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-96546-x","type":"published","date":"2025-04-12T16:05:03+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":75552263,"identity":"abbbcb9b-bb74-4e96-8cf2-354f98bf8faf","added_by":"auto","created_at":"2025-02-05 18:55:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":76699,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental setup for laser ablation (using Nd:YAG) and laser induced desorption (using fs Yb:YAG laser) as methods for sample introduction in microwave induced plasma (MIP). DSO - digital storage oscilloscope, DDG - digital delay generator, COLL - collimator of the emitted radiation into the fiber, OF - optical fiber, M - folding mirrors, VAC - vacuuming port, L - focusing lens, OW - optical windows.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/69f5530244f7d49571ca9892.png"},{"id":75552480,"identity":"eb6bf30c-bead-4136-8d90-bf385ed056c6","added_by":"auto","created_at":"2025-02-05 19:03:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":55607,"visible":true,"origin":"","legend":"\u003cp\u003ea) MIP spectra of a laser-ablated Cu target in Ar at various pressures. Experimental parameters: MIP power: 75 W, delay: 8 ms, gate: 10 ms, number of accumulations: 20. b) Selected Ar and Cu line intensities as a function of pressure.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/a515e0b9c2144c012f327857.png"},{"id":75551801,"identity":"cef2a650-d1b5-4224-8001-219adb6a7c9b","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":11694,"visible":true,"origin":"","legend":"\u003cp\u003eOptimization of the delay time between the laser pulse and camera triggering by maximizing intensity of the 521.82 nm Cu I line.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/5e375e8974f1e357ccfed423.png"},{"id":75551792,"identity":"2fc152d1-33e1-43dc-98ed-feee8c96c879","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":15658,"visible":true,"origin":"","legend":"\u003cp\u003eOptimization of energy for the optimal pressure, delay and gate time by maximizing intensity of the 521.82 nm Cu I line.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/1c7666cc0f0dad246bd843fc.png"},{"id":75551795,"identity":"63a0a6c8-8982-4ffc-b94e-8454dd31ecef","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":41814,"visible":true,"origin":"","legend":"\u003cp\u003eIntensity of the 521.82 nm Cu I line and microwave generator reflected power as a function of microwave generator input power.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/f48a03952ae1344a3907ad24.png"},{"id":75551793,"identity":"7e765d79-b2b3-49f0-8148-fd6ebe843b37","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":32551,"visible":true,"origin":"","legend":"\u003cp\u003eGaussian fit of the Cu I line at 521.82 nm, recorded with the medium resolution imaging spectrograph with a 50 µm entrance slit width.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/390c20317e7cd570a55bd090.png"},{"id":75552264,"identity":"dd9fb2ef-c183-4859-bc0c-6aa72d9d46b6","added_by":"auto","created_at":"2025-02-05 18:55:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":44485,"visible":true,"origin":"","legend":"\u003cp\u003eGaussian fit of W I lines recorded with high resolution spectrometer with a 30 µm entrance slit width.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/e11ec80aad539fe650b763f3.png"},{"id":75551797,"identity":"2b40bbf1-9464-4596-9a3e-f57c0a97b422","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":19627,"visible":true,"origin":"","legend":"\u003cp\u003eD\u003csub\u003e∝\u003c/sub\u003e and H\u003csub\u003e∝\u003c/sub\u003e lines from MIP when the vacuum pump is the sole contributor to the sample’s desorption.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/0ffcbc4305a38f7e9f9d558a.png"},{"id":75551810,"identity":"880f1ded-1bf8-4168-acdb-6bc8d8845b03","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":47681,"visible":true,"origin":"","legend":"\u003cp\u003eD\u003csub\u003e∝\u003c/sub\u003e and H\u003csub\u003e∝\u003c/sub\u003e line intensities after heating the target with the fs laser in the second cycle.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/e01bfc522213f63045a605b7.png"},{"id":75551808,"identity":"1a046c87-cab4-43c3-90b6-e0b3df708c2d","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":29009,"visible":true,"origin":"","legend":"\u003cp\u003eTime evolution of the D\u003csub\u003e∝\u003c/sub\u003e line intensity during two cycles of heating and cooling of the target.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/204390e20b9277c705875af6.png"},{"id":75552267,"identity":"0e8c2c30-25b2-424e-874c-d425927e6326","added_by":"auto","created_at":"2025-02-05 18:55:01","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":26830,"visible":true,"origin":"","legend":"\u003cp\u003eBoltzmann plot of the Ar I lines for excitation temperature estimation.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/c4d865b06ae888f33ae18b30.png"},{"id":75551843,"identity":"d7da6e67-8092-4762-8804-29637bac291a","added_by":"auto","created_at":"2025-02-05 18:47:03","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":39103,"visible":true,"origin":"","legend":"\u003cp\u003eBalmer Hη line at 383.5 nm recorded for estimation of electron density.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/1505499aacb5e64c24a01df9.png"},{"id":75551822,"identity":"cb6b3a36-922e-43bd-9c29-b5776667a760","added_by":"auto","created_at":"2025-02-05 18:47:02","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":45889,"visible":true,"origin":"","legend":"\u003cp\u003eVoigt profile fitting of the D\u003csub\u003e∝\u003c/sub\u003e and H\u003csub\u003e∝\u003c/sub\u003e lines for the measurement at time T, marked in Fig. 10.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/e8b4ce6322ec06c38bbc7054.png"},{"id":80558266,"identity":"1ac1a83c-b78b-4c5d-a2e2-ba605044f625","added_by":"auto","created_at":"2025-04-14 16:14:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1237777,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/251bf7ae-c986-4365-a20a-57b528b5cde5.pdf"},{"id":75551802,"identity":"bab20550-62c8-42c7-8008-bda98af73709","added_by":"auto","created_at":"2025-02-05 18:47:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":151211,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterial.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5912220/v1/0ad1b92dc6620f7497c99c92.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eHydrogen Isotopes Retention Studies Using Laser and Microwave Induced Plasma Coupling\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDiagnostics of the fusion plasma reactors are critical for ensuring their safe and proper stable operation. Among these diagnostics, the hydrogen isotope retention, particularly tritium, in plasma facing components (PFC) are probably the most important ones [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Techniques such as ion beam analysis (IBA) and thermal desorption spectroscopy studies (TDS) are highly reliable and commonly used PFC diagnostics methods [\u003cspan additionalcitationids=\"CR3 CR4\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, these methods are constrained to laboratory settings and require complex equipment. Consequently, sections of the PFC or test targets positioned on various places within the vacuum vessel must be demounted from the reactor wall [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] to be analyzed.\u003c/p\u003e \u003cp\u003eTo enable in-situ analysis of PFC, laser induced breakdown spectroscopy (LIBS) is used as an effective solution to overcome limitations of traditional methods. LIBS is a minimally invasive, non-contact technique suitable for multi-element analysis, including depth profiling, without requiring sample preparation. The technique is adaptable for vacuum or low-pressure gas environments and has been applied across diverse fields, such as nitrogen detection in soil [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], explosives detection [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], olive oil classification [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], cadmium detection in drinking water [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and even the identification of malaria biomarkers [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], bacteria [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] or SARS [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. LIBS is also commonly used for analyzing metal purity, alloys, jewelry [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], archaeological and other samples. Reviews [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and recent studies [\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] provide comprehensive insights into the advancements of LIBS for fusion applications, particularly its potential for in-situ diagnostics.\u003c/p\u003e \u003cp\u003eThe most important application of LIBS for plasma fusion reactor wall diagnostics is the study of hydrogen isotope retention, which relies on measurement of their Balmer alpha spectral lines. A significant challenge in this application is resolving the closely spaced lines caused by the small isotope shift. Even high-resolution spectrometers struggle to resolve these lines, due to significant Stark broadening under standard LIBS plasma conditions [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Partial resolving of a hydrogen and deuterium Balmer alpha lines (with isotope shift of 0.18 nm) has been achieved in studies using double-pulsed LIBS, where line fitting with a Voigt function was employed [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. More recently, approaches based on femtosecond (fs) laser ablation [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] and fs LIBS [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] have been applied to hydrogen isotope retention diagnostics, demonstrating further advancements in this field [\u003cspan additionalcitationids=\"CR27 CR28 CR29 CR30\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe use of the TEA CO\u003csub\u003e2\u003c/sub\u003e lasers or Nd:YAG in He [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] or filament fs laser LIBS [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] demonstrates the possibility of LIBS to resolve H\u003csub\u003eα\u003c/sub\u003e and D\u003csub\u003eα\u003c/sub\u003e lines. However, resolving T\u003csub\u003eα\u003c/sub\u003e​ lines presents a greater challenge due to the stricter requirements for low electron density [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In this study, we propose overcoming these challenges by coupling laser and microwave-induced plasma (MIP) to achieve the necessary plasma conditions. Two sample introduction methods are employed: laser ablation using an Nd:YAG laser and fs laser-induced desorption, both integrated with microwave-induced low-pressure plasma.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cp\u003eMicrowave induced plasma is the primary method used in this research for excitation and resolution of hydrogen isotope lines. The combination of MIP and laser induced plasma was used earlier for the enhancement of the LIBS [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], where the addition of microwaves increased electron density, temperature, and plasma duration and dimensions. However, this enhancement also increased Stark broadening, making the method unsuitable for tritium retention studies. In contrast, MIP source operating at atmospheric pressure has plasma parameters [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] suitable for resolving D\u003csub\u003eα\u003c/sub\u003e and T\u003csub\u003eα\u003c/sub\u003e spectral lines, as analyzed in [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. At low gas pressures, MIP achieves even smaller electron densities [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], minimizing Stark and Van der Waals broadening, making them negligible in comparison with other broadening mechanisms (Doppler and instrumental). For this study, a Beenakker resonator cavity with an 8 mm diameter and 14 cm long capillary tube was used, with an optical window and evacuation port mounted at the end. MIP was generated using an AHF Analysen Technik GMW 24\u0026ndash;301 DR 2.45 GHz microwave generator with a maximum power of 100 W. Pressure within the tube was regulated by a needle valve, and a mechanical vacuum pump was used for evacuation before maintaining stable argon gas flow.\u003c/p\u003e \u003cp\u003eThe first method used for sample introduction was laser ablation, a widely used technique in analytical spectroscopy for introducing samples into excitation sources such as inductively coupled plasma (ICP), MIP, LIBS or mass spectrometry [\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. For this purpose, we used a laboratory made laser ablation cell, see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This cell was constructed as an elongation of the capillary tube thus enabling the most efficient transport of the ablated material into the MIP. The target was placed in a custom built holder with vacuum feedthrough, allowing rotation to expose fresh target surface area to the laser beam. Ablation was performed using Quantel 450 Nd:YAG (1064 nm, 6 ns pulse duration, 10 Hz maximum repetition rate). Laser beam was focused with a \u003cem\u003ef\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12.5 cm lens through the window and onto the target. Special cell design enables irradiation of the target at approximately 45 degrees. Small variation of incident angle enables irradiation at a variable distance from the center of the target. That way, laser induced plasma radiation, which always propagates normal to the target surface, does not reach detection system and enables recording of the radiation coming from the MIP only.\u003c/p\u003e \u003cp\u003eThe emitted light from the MIP was collected through an optical window at the end of the capillary using a collimator (COLL) and guided via fiber optic cable (OF) either to medium resolution spectrometer Andor Shamrock 303i (with grating 1200 g/mm) or high-resolution spectrometer SOL instruments MS7504i spectrometer (with grating 1800 g/mm). The Andor spectrometer was equipped with Andor iStar DH720-18F-63 ICCD camera (256 x 1024 pixels, 26 \u0026micro;m pixel size), while SOL instruments spectrometer was equipped with Andor iStar DH734-18F-63 ICCD camera (1024 x 1024 pixels, 13 \u0026micro;m pixel size), that were used as detectors. Delay and gating of cameras were controlled with external digital delay generator (DDG, Stanford Research SRS 535), which was triggered with the signal for opening of a Nd:YAG laser Q switch. It should be noted that the separation of the optical emission signals created by LIBS and by MIP can also be achieved by changing the delay and gate time of the camera exposure.\u003c/p\u003e \u003cp\u003eThe Nd:YAG laser, commonly used for plasma creation, is known to ablate a thick layer of material, making it unsuitable for analyzing thin films or surface-bound elements. For detecting hydrogen isotopes within thin surface layers, laser-induced desorption (LID) [\u003cspan additionalcitationids=\"CR44\" citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], often paired with quadrupole mass spectrometry (LID-QMS) [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], is a more suitable approach. To test the feasibility of using MIP as an alternative to the more complex QMS, a femtosecond Yb:YAG laser (Solar FX200, 1030 nm, 150 fs pulse duration, 105 nJ peak energy, 71 MHz repetition rate, 7 W average power) was employed for laser-induced desorption of hydrogen isotopes. In this setup, the detection system was triggered by the camera\u0026rsquo;s internal trigger with a variable exposure time. While this study utilized the femtosecond laser, laser-induced desorption can also be achieved with other lasers capable of heating the target without causing significant ablation.\u003c/p\u003e \u003cp\u003eThe selected targets for these studies included a copper target for the experiment optimization in terms of gas pressure, delay time, microwave power and laser energy. A tungsten target was then introduced to verify the optimized conditions for resolving Balmer alpha spectral lines. Finally, a pill composed of graphite powder mixed with water and heavy water (D\u003csub\u003e2\u003c/sub\u003eO), was prepared using a hydraulic press, as previously described in [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. This pill was tested for both laser-induced desorption and vacuum-induced desorption.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003eIn the investigation of MIP for hydrogen isotope detection, the initial task involved optimizing the transport and excitation of sample components. Due to the challenges associated with tritium's radioactivity, most previous research has focused on deuterated samples as a safer alternative. In this study, tungsten (W) samples containing incorporated deuterium were analyzed using laser ablation as the method for introducing samples into the MIP.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Laser ablation\u003c/h2\u003e \u003cp\u003eThe investigation of Nd:YAG laser ablation as a method for introducing tungsten samples with incorporated deuterium into the MIP proved nearly impossible with our experimental setup. This was due to several factors: the high reflectivity of the polished samples, the shallow retention of the deuterium and high laser ablation rate. As a result, the application of MIP for hydrogen isotopes detection using laser ablation was limited to optimizing parameters for resolving hydrogen isotope Balmer alpha lines. According to [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], D\u003csub\u003eα\u003c/sub\u003e and T\u003csub\u003eα\u003c/sub\u003e spectral lines can be resolved only if full width at half maximum (FWHM) of lines is less than 0.056 or even 0.027 nm, depending on their intensity ratio (1:1 or 1:10, respectively). Furthermore, FWHMs of the neighbor spectral lines must also be smaller than the wavelength separation between them and hydrogen isotope lines.\u003c/p\u003e \u003cp\u003eTo obtain the best resolving results, using laser ablation, the signal to noise ratio (i.e., line intensities) has to be maximized by optimizing several experimental parameters, while keeping FWHM as minimal as possible. For MIP operation, microwave power and gas pressure are the most important parameters. The line intensities increase with microwave power, but the reflected power also increases. If the reflected power exceeds 15 W, there is a risk of damaging the microwave generator or overheating the discharge tube. Optimal gas pressure, which corresponds to the flow rate, must also be determined, as it dictates the time the sample remains within the MIP resonator cavity for excitation.\u003c/p\u003e \u003cp\u003eAdditionally, the dependence of spectral line intensities on laser energy was analyzed, as laser energy influences the ablation process, specifically the ablated mass and particle dimensions. Although higher energy increases the ablated mass, it is important to assess whether larger particle dimensions might affect MIP performance by altering microwave coupling to the plasma or causing particle deposition on the tube walls.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Optimization of gas pressure\u003c/h2\u003e \u003cp\u003eThe optimal gas pressure range for stable MIP operation was determined by analyzing the maximal intensity of the Ar I line at 516.22 nm (3s\u0026sup2;3p⁵(\u0026sup2;P\u003csup\u003eo\u003c/sup\u003e₃/₂)4p \u0026rarr; 3s\u0026sup2;3p⁵(\u0026sup2;P\u003csup\u003eo\u003c/sup\u003e₃/₂)6d), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. The Ar I line was used to establish the optimal gas pressure range since its intensity is independent of the camera recording delay. In contrast, the intensities of the target lines, such as Cu I, depend on the gas flow rate, which determines when the ablated material reaches the plasma.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, the optimal gas pressure range for stable MIP operation was between 15 and 20 mbar.\u003c/p\u003e \u003cp\u003eThe optimal gas pressure can be determined using the most intense spectral line, the Cu I line at 521.82 nm (3d\u0026sup1;⁰4p \u0026rarr; 3d\u0026sup1;⁰4d). Since this line is susceptible to self-absorption, its optical thickness was evaluated. The Cu I lines at 515.32 nm (λ\u003csub\u003e1\u003c/sub\u003e) and 521.82 nm (λ\u003csub\u003e2\u003c/sub\u003e) belong to the same multiplet (transition 3d\u0026sup1;⁰4p \u0026rarr; 3d\u0026sup1;⁰4d) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. To assess self-absorption of the 521.82 nm line, the intensity ratio \u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eI\u003c/em\u003e \u003csub\u003e\u003cem\u003eλ1\u003c/em\u003e\u003c/sub\u003e / \u003cem\u003eI\u003c/em\u003e \u003csub\u003e\u003cem\u003eλ2\u003c/em\u003e\u003c/sub\u003e was compared at various pressures to the theoretical value of \u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.53 (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Results indicated no significant self-absorption for all pressures except at 10 mbar, where the lines exhibited low intensity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental ratios of the intensities of Cu I spectral lines at various pressures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePressure (mbar)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eI\u003c/em\u003e \u003csub\u003e\u003cem\u003eλ1\u003c/em\u003e\u003c/sub\u003e / \u003cem\u003eI\u003c/em\u003e \u003csub\u003e\u003cem\u003eλ2\u003c/em\u003e\u003c/sub\u003e (exp.)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSince the Cu I line has a significantly higher intensity at 20 mbar, see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, this line was used in optimization of several experimental parameters in all further investigations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. Optimization of material transport to the MIP\u003c/h2\u003e \u003cp\u003eGas pressure and flow regulate the duration for which the ablated material remains in the discharge, thereby influencing the recording parameters (delay and gate times). The delay corresponds to the time required for the material to travel from the target to the resonator cavity, while the gate time determines the duration the material spends in the discharge zone. An analysis of the optimal delay time is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e it was concluded that the delay time should be 20 ms and the gate time should be 10 ms. During these measurements, microwave power was set to 75 W and laser energy was 250 mJ. The final spectrum was the accumulated spectrum of 20 laser shots.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3. Optimization of ablated material quantity\u003c/h2\u003e \u003cp\u003eThe amount of ablated material is directly influenced by the laser energy used. To optimize this parameter, the laser energy was adjusted by varying the delay between the triggering of the flash lamps and the opening of the laser Q switch (FLQS). Three energy values were tested: 130, 250 and 430 mJ. The resulting graph is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith the increase of the laser energy, the intensity of the Cu I line also increases. This is primarily due to the ablation rate, as when the energy of the laser is higher, the ablation rate is also higher, and more material is entering the discharge region. Here, optimal energy of 250 mJ was chosen, as for the higher energy, the mass of the incoming material was too large, which caused the MIP discharge to shut down.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4. Selection of microwave generator power\u003c/h2\u003e \u003cp\u003eDependence of the line intensity on the microwave power supplied to the cavity (for optimal pressure, delay, gate and laser energy) was analyzed. Here, four powers were considered (50, 60, 75 and 90 W). Besides supplied power, the reflected power was also measured. The obtained dependance on the supplied power is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results indicate that increasing the supplied power leads to a corresponding increase in line intensity. However, the reflected power also rises with higher input power. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, a dashed vertical line marks the input power at which the reflected power reaches 15 W. Since exceeding this threshold could overheat the source, it is not advisable to operate beyond this limit. Consequently, 75 W was selected as the optimal power setting to ensure safe and reliable generator operation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.5. Optimization of spectral resolution for hydrogen isotopes retention studies\u003c/h2\u003e \u003cp\u003eAfter optimizing experimental parameters for laser ablation and MIP operation the potential of this setup for hydrogen isotopes retention studies was analyzed. For such analysis, the FWHM of Balmer alpha lines should be less than 0.027 nm if one wants to detect small amounts of tritium in the first wall of future fusion reactors. The first step in this direction was to assess the instrument broadening on the spectral lines\u0026rsquo; widths. Given the negligible Stark broadening at low MIP gas pressures (\u003cem\u003eNe\u003c/em\u003e\u0026thinsp;~\u0026thinsp;10\u003csup\u003e12\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), and the electron temperature between 2000 and 3000 K, we can safely assume that the major influence in the line broadening comes from the Doppler and instrument broadening. To determine the FWHM of the Cu I line at 521.82 nm, the recorded spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) was fitted with a Gaussian function. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the resulting FWHM was 0.27 nm, which greatly exceeds the goal of having lines as narrow as 0.027 nm. This result is reasonable, considering that medium resolution Shamrock 303 imaging spectrograph with the entrance slit width of 50 \u0026micro;m equipped with Andor iStar DH720 ICCD camera was used for these measurements.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo reduce the instrumental broadening of the lines, the high resolution MS7504i spectrometer with the entrance slit width of 30 \u0026micro;m equipped with Andor iStar DH734-18F-63 ICCD camera was used for recording spectral lines of tungsten. As part of the optimization of the optical system (selection of the spectrometer and slit width), W target was used to verify whether the W line FWHM is less than 0.04 nm, which corresponds to the wavelength separation between hydrogen Balmer alpha line at 656.28 nm and W I line at 656.32 nm.\u003c/p\u003e \u003cp\u003eGaussian fitting of the W I lines (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) showed the FWHM of 0.024 nm at 429.46 nm and 0.025 nm at 430.21 nm, meeting the required resolution. This demonstrates that the setup is capable of enabling precise determination of the H\u003csub\u003eα\u003c/sub\u003e line intensity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Desorption as a method for sample introduction in MIP\u003c/h2\u003e \u003cp\u003eTo obtain the H\u003csub\u003eα\u003c/sub\u003e and D\u003csub\u003eα\u003c/sub\u003e FWHM values and to test whether resolving the D\u003csub\u003eα\u003c/sub\u003e and T\u003csub\u003eα\u003c/sub\u003e lines is possible in this configuration, and for previously determined optimal experimental parameters of 20 ms delay and 10 ms gate time, 75 W MIP input power and a 30 \u0026micro;m entrance slit width of the high resolution spectrometer, a mixture of graphite powder, heavy water and water, pressed into a pill, was used as the target. In section 3.2.1, the results of the MIP spectrum for desorption induced by the vacuuming alone are presented, while in section 3.2.2, the results of desorption induced by fs laser heating in combination with the vacuum pump are presented.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Desorption due to vacuuming\u003c/h2\u003e \u003cp\u003eDue to the composition of the target pill, water and heavy water were not fully bonded to the graphite, resulting in their evaporation from the target during vacuum pump outgassing. The corresponding MIP spectra with deuterium and hydrogen Balmer alpha lines is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. As can be seen, the lines are narrow and fully resolved.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Laser induced desorption\u003c/h2\u003e \u003cp\u003eAs a final step, we examined whether a 1030 nm fs laser with very low energy (100 nJ) could induce desorption of hydrogen isotopes from the target and introduce them into MIP. Two cycles of heating were performed and recorded. During target heating, an increase in the D\u003csub\u003eα\u003c/sub\u003e and H\u003csub\u003eα\u003c/sub\u003e line intensities was observed, without a corresponding increase in their FWHMs. MIP spectra, after turning off the laser following the second heating cycle, is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The effect of laser induced desorption is evident: during the cooling of the target, the line intensities gradually decrease to the levels seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, where desorption was induced by the vacuum pump alone.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe time dependency of the D\u003csub\u003eα \u003c/sub\u003eline intensity during both cycles is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The effects of laser heating and laser induced desorption are clear. The intensity increased while the laser was active, peaking at the moments when the laser was turned off. After that, intensity decreased gradually. This confirms that the deuterium comes from laser induced desorption, rather than solely from outgassing due to the vacuum pump. It should be noted that the intensity from the first measurement is higher than it should be, because not enough time has passed for the target to cool from the previous test measurements. The starting value should be close to the one shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, as that was recorded before the laser heating.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBefore proceeding to the estimation of hydrogen isotope line widths, plasma parameters were estimated. The excitation temperature was estimated from the Boltzmann plot of Ar I lines to be 2600 K. Boltzmann plot is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. Complete data for the lines used to obtain the Boltzmann plot can be found in the Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGiven the expected low electron density and negligible Stark broadening for both hydrogen and argon lines, an attempt was made to estimate the upper limit for electron density. The merging of spectral lines of hydrogen is a suitable method for this estimation. If the final detectable spectral line of Balmer series is found, then the use of Inglis \u0026ndash; Teller relation [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\text{log}({N}_{e}+{N}_{i})=23.26-7.5\\text{log}{n}_{max}+4.5\\text{log}z$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ecan give the upper limit on the electron density. The final observed member of the Balmer series in this study was H-η (9 \u0026rarr; 2, 383.5 nm), shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. Assuming \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e = \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e, and that for hydrogen atoms the effective nuclear charge (z) is 1, the upper limit of electron density \u003cem\u003eNe\u003c/em\u003e\u0026thinsp;~\u0026thinsp;6.3 ∙ 10\u003csup\u003e15\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e was obtained. This value is a huge overestimation, since the upper members of the series couldn\u0026rsquo;t be detected due to the presence of different molecular bands.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAnother approach for determining the electron density is through the Stark broadening of the upper members of the Balmer series. Since the highest detected member of the Balmer series has the width close to the instrumental width, and considering the errors during the fitting procedure, it can be estimated that the Stark width of the Balmer alpha lines doesn\u0026rsquo;t exceed 0.01 nm. If this value is inserted into the formula for the estimation of line widths from the higher members of the Balmer series [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{N}_{e}={8\\cdot\\:10}^{18}\\cdot\\:{\\left(\\frac{{w}_{S}\\:\\left(nm\\right)}{{\\alpha\\:}_{1/2}^{n}}\\right)}^{1.5}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ethe resulting value, with \u003cem\u003eα\u003c/em\u003e\u003csup\u003e\u003cem\u003en\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.345 (for \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;9), would be \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e = 1.25 ∙ 10\u003csup\u003e12\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, which is a more realistic estimation than the one obtained by the Inglis \u0026ndash; Teller equation.\u003c/p\u003e \u003cp\u003eFinally, to confirm the necessary resolution for the hydrogen retention studies, both lines were fitted with a Voigt profile (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e). Gaussian fitting was also attempted, but Voigt profile showed better performance in terms of wing fitting.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eApproximative equation for Voigt profile FWHM [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{W}_{V}\\approx\\:0.5346{W}_{L}+\\sqrt{0.2166{W}_{L}^{2}+{W}_{G}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewas used with coefficients obtained from Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. The resulting line widths are 0.033 nm for D\u003csub\u003eα\u003c/sub\u003e line and 0.038 nm H\u003csub\u003eα \u003c/sub\u003eline. Although Voigt line widths are correct, the Gaussian and Lorentzian parts are off. Gaussian parts can be calculated using the equation\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:{W}_{G}=\\sqrt{\\left({W}_{D}^{2}+{W}_{I}^{2}\\right)},$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{D}\\)\u003c/span\u003e\u003c/span\u003e represents the Doppler line width and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{I}\\)\u003c/span\u003e\u003c/span\u003e is the instrumental line width. Doppler broadening FWHM can be calculated using the equation\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{W}_{D}=7.16*{10}^{-7}\\lambda\\:\\sqrt{\\frac{T}{M}},\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eM\u003c/em\u003e is the mass of the emitter, given in atomic mass units, and \u003cem\u003eT\u003c/em\u003e is the temperature estimated using a Boltzmann plot of the Ar I lines (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). Since the instrumental FWHM was estimated at 0.024 nm, based on FWHM of W I 429.46 nm line from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, Gaussian parts of the Voigt profiles are 0.029 nm and 0.034 nm for D\u003csub\u003eα\u003c/sub\u003e and H\u003csub\u003eα\u003c/sub\u003e, respectively. Lorentzian parts are then calculated using the Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), and they are 0.007 nm for both D\u003csub\u003eα\u003c/sub\u003e and H\u003csub\u003eα\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eFinally, using the formula suggested in [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], the intensity ratio of T\u003csub\u003eα\u003c/sub\u003e and D\u003csub\u003eα\u003c/sub\u003e for which both lines could be resolved was obtained. The critical FWHM at which mentioned lines can be resolved relates to the intensity ratio \u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;T\u003csub\u003eα\u003c/sub\u003e/D\u003csub\u003eα\u003c/sub\u003e through the following formula [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]:\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\:FWH{M}_{cr}=0.0599-0.0388\\times\\:{e}^{-1.765\\times\\:R}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eNow, for the determined FWHM of D\u003csub\u003eα\u003c/sub\u003e 0.033 nm, the theoretical ratio of lines is \u003cem\u003eR\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.2. Therefore, our proposed method could resolve D\u003csub\u003eα\u003c/sub\u003e and T\u003csub\u003eα\u003c/sub\u003e lines up to the point where D\u003csub\u003eα\u003c/sub\u003e is five times more intense than T\u003csub\u003eα\u003c/sub\u003e, or vice versa.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, we explored the coupling of laser-induced desorption and laser ablation with microwave-induced plasma as an effective method for studying hydrogen isotope retention in plasma-facing components of fusion devices. The experimental setup was optimized to achieve high spectral resolution, enabling the separation of hydrogen, deuterium, and tritium Balmer alpha lines. The application of femtosecond laser for desorption demonstrated a controlled and efficient sample introduction mechanism, while low-pressure MIP conditions minimized broadening effects, ensuring precise isotopic analysis.\u003c/p\u003e \u003cp\u003eThis study presents a significant advancement in the diagnostics of tritium retention, offering a minimally invasive, high-resolution approach that addresses the limitations of traditional methods such as ion beam analysis and thermal desorption spectroscopy. The findings underscore the potential of this technique for in-situ applications in fusion research, contributing to the development of safer and more efficient plasma diagnostics systems. Future work will focus on scaling this approach for broader fusion reactor applications and extending it to analyze mixed material deposits.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (contract numbers: 451-03-47/2023-01/200024 and 451-03-47/2023-01/200146), the Science Fund of the Republic of Serbia through the NOVA2LIBS4fusion project (grant number: 7753287), within the IDEAS call and under the project: NIFS21KLPF087. We also acknowledge Stanko Milanović, our technical associate, who drew the schematic figure of the experimental setup.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eN. V. – Investigation, Formal Analysis, Visualization, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eI. T. – Investigation, Formal Analysis, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eB. D. S. – Investigation, Formal Analysis, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eD. R. – Investigation, Resources\u003c/p\u003e\n\u003cp\u003eM. K. – Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eM. I. – Conceptualization, Funding Acquisition, Methodology, Supervision, Writing - Original Draft, Project Administration\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that supports the findings of this study is available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBrezinsek, S. et al. Fuel Retention Studies with the ITER-like Wall in JET. \u003cem\u003eNucl. Fusion\u003c/em\u003e. \u003cb\u003e53\u003c/b\u003e, 083023 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRubel, M. et al. The role and application of ion beam analysis for studies of plasma-facing components in controlled fusion devices. \u003cem\u003eNucl. 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Transf.\u003c/em\u003e \u003cb\u003e17\u003c/b\u003e, 233\u0026ndash;236 (1977).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Hydrogen isotopes retention, laser ablation, laser induced desorption, microwave induced plasma, plasma-facing components, LIBS","lastPublishedDoi":"10.21203/rs.3.rs-5912220/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5912220/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe detection of deuterium and tritium retention in fusion devices via optical emission spectroscopy (OES) faces significant challenges due to experimental limitations, particularly in resolving hydrogen isotope Balmer alpha lines (H\u003csub\u003eα\u003c/sub\u003e, D\u003csub\u003eα\u003c/sub\u003e, and T\u003csub\u003eα\u003c/sub\u003e). In this study, we propose and evaluate the coupling of laser ablation and laser-induced desorption with microwave-induced plasma (MIP) as an approach to resolve this problem. This approach effectively meets the resolution requirements for Balmer alpha lines, overcoming limitations of standard laser-induced breakdown spectroscopy (LIBS) setups. Optimization of Nd:YAG laser ablation was performed using pure copper and tungsten targets, while desorption, including femtosecond (fs) laser-induced desorption, was studied on graphite powder mixed with heavy water and water. The results demonstrate a significant improvement in spectral resolution and analytical performances, highlighting the potential of this technique for tritium retention studies in plasma-facing components.\u003c/p\u003e","manuscriptTitle":"Hydrogen Isotopes Retention Studies Using Laser and Microwave Induced Plasma Coupling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-05 18:46:56","doi":"10.21203/rs.3.rs-5912220/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-03-03T10:07:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-02-23T05:29:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-02-16T13:22:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"258643395709465126052568211438770609128","date":"2025-02-14T05:57:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"191587062343152455909709207811853994868","date":"2025-02-12T13:49:33+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-02-10T07:36:45+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-01-30T08:56:59+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-01-30T07:26:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-01-28T09:57:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-01-27T12:19:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f158f210-2703-439a-a1f9-60734f2173bf","owner":[],"postedDate":"February 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":43902627,"name":"Physical sciences/Physics/Plasma physics/Laser produced plasmas"},{"id":43902628,"name":"Physical sciences/Physics/Chemical physics"}],"tags":[],"updatedAt":"2025-04-14T16:07:44+00:00","versionOfRecord":{"articleIdentity":"rs-5912220","link":"https://doi.org/10.1038/s41598-025-96546-x","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-04-12 16:05:03","publishedOnDateReadable":"April 12th, 2025"},"versionCreatedAt":"2025-02-05 18:46:56","video":"","vorDoi":"10.1038/s41598-025-96546-x","vorDoiUrl":"https://doi.org/10.1038/s41598-025-96546-x","workflowStages":[]},"version":"v1","identity":"rs-5912220","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5912220","identity":"rs-5912220","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}