Deuterium Depth Profiles Research Articles

Proof-of-Concept Modeling for the Use of Neutron Reflectometry for the In Situ Diagnosis of Deuterium Accumulation in Tungsten and Dispersion-Strengthened Tungsten Alloys

The diagnosis of plasma-facing components in a fusion environment is challenging due to the limited number of measurement techniques that have been developed for in situ surface analysis. In this work, we assess the feasibility of using neutron reflectometry (NR) for the in situ diagnosis of deuterium accumulation in tungsten and dispersion-strengthened tungsten alloys. TRIM is used to simulate deuterium implantation at different energies to approximate the deuterium depth profiles in these materials in order to calculate the expected measurements from NR for various fluences. Our results suggest that NR should be an effective technique for testing hypotheses about the surface composition of materials under fusion-relevant fluences of deuterium irradiation.

Deuterium retention in helium-irradiated tungsten

Hot-rolled tungsten samples were first irradiated with helium ions with varying fluences or energies and then exposed to deuterium plasmas, and the influence of helium fluence (corresponding to damage levels of 0.12–2.3 dpa) and helium ion incident energy (50, 200, 400 keV) on deuterium retention were investigated. A significant increase of the total deuterium inventory was observed in the helium irradiated sample, and deuterium retention reaches saturation at 0.69–1.15 dpa. Radiation-induced defects and helium-vacancy complexes or helium bubbles contribute to the increase of deuterium inventory, and the effect of helium-vacancy complexes or helium bubbles is aggrandizement with the increase of damage level. Comparison of deuterium depth profiles of samples irradiated by helium ions with different incident energies reveals that the vast majority of deuterium is trapped in the helium accumulation region, and the depth of the maximum deuterium concentrations is consistent with the maximum helium concentrations rather than the damage levels. Furthermore, the total amount of deuterium increases with the increase of helium ions energy due to the deepening of the irradiation region.

Deuterium retention in reduced activation ferritic/martensitic steel EUROFER97 exposed to low-energy deuterium plasma

EUROFER97 steel samples were exposed to deuterium plasma in the linear plasma device PISCES-A with the ion energies of 90 and 140 eV at exposure temperatures between 360 and 773 K to deuterium ion fluences between 3.8 × 1023 and 6.3 × 1025 m−2. RBS analysis of these plasma-exposed samples showed that the uppermost surface layers were enriched with tungsten and tantalum. Deuterium depth profiles in the plasma-exposed samples were examined using the energy-scanning NRA technique allowing measurements of the deuterium depth profiles at depths of up to about 9 μm. With an increase in the exposure temperature from 360 to 773 K, the deuterium retention in the 1 µm thick sub-surface layer decreased almost monotonically from about 1 × 1019 D/m2 to 5 × 1017 D/m2. The deuterium concentration at a depth of 8 μm demonstrated a different temperature dependence - with an increase in the exposure temperature from 360 to 500 K, the deuterium concentration significantly decreased from about 4 × 10−3 to (4 ± 3) × 10−5 at.%. With a further increase in the temperature up to 773 K, the deuterium concentration at a depth of 8 μm became equal to or less than 5 × 10−5 at.%.

Deuterium and beryllium depth profiles into the W-coated JET divertor tiles after ITER-like wall campaigns

A number of 35 samples cored from JET divertor tiles exposed to JET plasmas in ILW1 (ITER Like Wall – first campaign), ILW2, ILW1 + ILW2 and ILW3 campaigns were analyzed using the Glow Discharge Optical Emission Spectrometry (GDOES) technique. The depth profiles of the elements contained in the surface layer of the tiles (W, Mo, Be, C, O and D) have been quantitatively determined up to a depth of 30–60 μm.The upper zone of Tile 3 (the lower vertical zone of the inner divertor) seems to be an erosion zone as it was demonstrated with a Mo marker layer in the ILW1 campaign. By increasing the input energy in the following campaigns this erosion did not increase, but it almost disappeared, probably due to significant amounts of Be that were transported from the main chamber and deposited on that area. The Be concentration increased in the upper zone of Tile3 in ILW2 and ILW3 by a factor of about 5 in comparison with the ILW1 campaign. It looks like the Be layer protects the tile surface from erosion.Depending on the amount of Be deposited on specific areas of the W-coated CFC (Carbon Fiber Composite) tiles, two mechanisms of D retention were identified. If the peak concentration of Be is less than ∼4.5 at.% D is mainly trapped into the defects of the W/Mo structure including W/Mo and Mo/C interfaces. When the peak concentration of Be exceeds ∼4.5 at.%, D is mainly retained in the Be deposits. The GDOES results were correlated with SEM analyses performed on the GDOES crater flanks and with the TDS (Thermal Desorption Spectroscopy), results obtained with the same samples after GDOES analyses. They are in good agreement with the corresponding results obtained by other authors using NRA (Nuclear Reaction Analysis), SIMS (Secondary Ion Mass Spectrometry) and TDS.

Comparing deuterium retention in heavy ion damaged tungsten measured by glow discharge optical emission spectroscopy, nuclear reaction analysis and thermal desorption spectroscopy

Hot-rolled tungsten specimen were irradiated with 5 MeV gold ion and loaded with deuterium plasma sequentially. Deuterium retention was examined by glow discharge optical emission spectroscopy, nuclear reaction analysis and thermal desorption spectroscopy. The deuterium depth profiles obtained by nuclear reaction analysis show that deuterium concentration increases significantly after irradiation, and damage region could uptake most of deuterium. The results of thermal desorption spectroscopy demonstrate that heavy ion damage can produce a large number of defects which could trap deuterium. Significant deuterium saturation was observed with damage level above 0.4 dpa. Furthermore, the depth profile and total inventory of deuterium show that the result measured by glow discharge optical emission spectroscopy is in good agreement with that by nuclear reaction analysis and thermal desorption spectroscopy.

Experiments and modelling of multiple sequential MeV ion irradiations and deuterium exposures in tungsten

Bulk tungsten samples were irradiated sequentially with 20 MeV tungsten ions and exposed to deuterium plasma. The experiments were performed in order to simulate the displacement damage that fusion neutrons will cause in a tungsten plasma-facing component of a future fusion device. To study the influence of the presence of hydrogen isotopes during the creation of displacement damage on the final defect density, tungsten irradiation and deuterium decoration cycles were performed up to three times. Deuterium depth profiling with 3He Nuclear Reaction Analysis and Thermal Desorption Spectroscopy showed that the deuterium concentration increased after each additional tungsten irradiation and deuterium exposure. After the third cycle, the deuterium concentration reached a maximum of 3.6 at.% at the given plasma exposure temperature of 370 K. We attribute this increase in retention to the stabilization of the displacement damage during the tungsten irradiation by the presence of deuterium. The experimental results were simulated using the MHIMS-R macroscopic rate-equation code, which was recently upgraded with a damage stabilization term to describe experiments where tungsten was irradiated with MeV tungsten ions and simultaneously exposed to low-energy deuterium ions. Using this novel model, it was possible to quantitatively describe also the present results for the sequential irradiation/exposure scheme, with model parameters that were congruent with parameters derived from the simultaneous experiment. Modelling shows that kinetic de-trapping of trapped deuterium takes place during irradiation However, it is not the dominant process that explains defect stabilization. In addition, the model facilitates the extrapolation of present experimental results to an even larger number of sequential tungsten irradiation and deuterium exposure cycles. The model predicts that after about five sequential irradiation and plasma exposure cycles, a stationary state is reached with an associated maximum trapped D concentration of 4.2 at.% for the given exposure temperature of 370 K.

Studies on the near-surface trapping of deuterium in implantation experiments

Surface-shifted deuterium profiles are re-examined in deuterium-ion irradiation experiments by using a combined experimental and modelling approach. Recrystallized tungsten foil samples were irradiated with energetic deuterium ions and the defect and deuterium depth profiles were studied using positron annihilation spectroscopy and secondary ion mass spectroscopy. We report direct experimental evidence of trapping of deuterium at the vacancies created by the deuterium ions themselves during the implantation by using positron annihilation studies. The deuterium profile is simulated using a Monte-Carlo diffusion model by taking into account the defect-aided diffusion of deuterium due to the local strain field created by the vacancies. The simulations also elucidate the role of the anisotropy in the diffusion and trapping of deuterium in ion-implantation experiments in metals.

A quantitative study of retention and release of deuterium and tritium during irradiation of γ-LiAlO2 pellets

This study reports on the quantification of deuterium in ion-irradiated γ-LiAlO2 pellets as a function of dose and temperature. The γ-LiAlO2 pellets were sequentially irradiated with He+ and D2+ ions to the same fluences of 5 × 1016, 1 × 1017 and 2 × 1017 He+ + D+/cm2 at 188 K. Additional irradiation was performed to 1 × 1017, 2 × 1017 and 4 × 1017 He+ + D+/cm2 at 573 K. A set of the pellets irradiated at 188 K was shipped and stored at low temperatures from 80 to 132 K and characterized using time-of-flight secondary ion mass spectrometry at ~173 K. The deuterium depth profiles show a Gaussian-like distribution in the low-temperature pellets. The total deuterium retention is found to be directly proportional to the ion fluence. About 27 at.% of the implanted deuterium atoms were released from the pellet irradiated to 2 × 1017 He+ + D+/cm2 at 188 K during storage at room temperature for ~1 month. The measured deuterium retention is found to increase initially with ion fluence and tend to saturate at high fluences during ion irradiation at 573 K. The amount of the released deuterium is observed to be quantitatively consistent with that of the released tritium from the standard pellets during neutron irradiation at 573 K.

Experimental measurement of deuterium concentration and depth profiling in tungsten by radio frequency glow discharge optical emission spectroscopy

For a detailed understanding of fuel retention characterization, especially in-depth profile analysis of plasma-facing materials, radio frequency glow discharge optical emission spectroscopy (RF-GDOES) method was applied to determine the deuterium depth concentration. Tungsten or titanium targets were co-deposited in deuterium atmosphere by magnetron sputtering, and these deposited films with different deuterium contents and film thicknesses were used as the standard samples for RF-GDOES measurement. Rutherford backscattering spectroscopy (RBS) and thermal desorption mass spectrometry (TDS) were used to measure the metal and deuterium concentrations in the standard films, respectively. After the standardization of deuterium concentration and sample sputtering rate when tested by RF-GDOES, deuterium concentration and depth profiling of deuterium-exposed tungsten samples were obtained and subsequently verified by compared with results by TDS. Results showed the deuterium concentration in deuterium-exposed tungsten has a high concentration peak about 0.002–0.013 at.fr. within 125 nm near-surface, and then reduced by two orders of magnitude from surface to depth with a minimum concentration of few 10−5at.fr. With increasing the incident deuterium fluence, deuterium concentration increased obviously in the first 6 μm near the surface. Under low incident fluence, the total released deuterium amounts obtained from RF-GDOES and TDS methods agree within the experimental error. However, the total released deuterium amounts measured by RF-GDOES were smaller than those of the TDS method under high fluence due to reason of the increasing diffusion depth and inhomogeneity of deuterium in tungsten.

Deuterium retention in solid and liquid tin after low-temperature plasma exposure

Recently, plasma-facing components based on liquid metals were proposed for a prospective nuclear fusion reactor in order to circumvent challenges that occur for solid metal components, such as erosion lifetime, neutron embrittlement or transient overloading. One candidate material is liquid tin. We present a systematic study of the behavior of solid and liquid tin exposed to a low-temperature deuterium plasma at temperatures between 300 and 515 K, focusing on deuterium retention and thermal release as well as on tin erosion and re-deposition. We find strong variations of deuterium depth profiles, deuterium release spectra, and tin erosion rates, which are correlated to dramatic changes in the surface morphology. In particular, we find evidence for massive gas bubble formation in tin, which can lead to the evolution of a thick, sponge-like layer for tin exposed to deuterium plasma just below the melting point, and to the rapid formation of a macroscopic gas pocket below liquid tin. We present evidence for strongly temperature-dependent chemical erosion of tin by deuterium plasma in the solid state. In the liquid state, a high tin erosion rate occurs, which is apparently induced by ejection of tin microdroplets. Furthermore, we observed strong plasma-assisted, low-temperature wetting of tin on tungsten near the melting point of tin. We tentatively propose the hypothesis that all of the observed effects may be influenced by tin-deuterium chemistry, e.g. the formation and de-composition of stannane molecules.

Gamma-ray irradiation effect on deuterium retention in reduced activation ferritic/martensitic steel and ceramic coatings

Tritium permeation and retention are serious problems in D-T fusion reactors from the viewpoint of fuel efficiency and radiological safety. Functional ceramic coatings have been intensively studied for the development of tritium permeation barriers for several decades, while reports about tritium retention in the ceramic coatings are scarce. Moreover, irradiation may affect tritium retention in fusion materials, which is important to precisely evaluate tritium inventory in the reactor. In this study, the gamma-ray irradiation effect on deuterium retention in reduced activation ferritic/martensitic steel and three kinds of ceramic coatings were investigated through deuterium exposure, gamma-ray irradiation using cobalt-60 gamma-ray sources and deuterium depth profile measurements. The amount of deuterium retention in yttrium oxide, silicon carbide, and zirconium oxide coatings decreased after the irradiation in the dose rate of 2.43 Gy s−1, while no clear change in the retention was observed at the lower dose rate. From these results, the gamma-irradiation effect on deuterium retention would have a threshold dose rate. Diffusion and desorption of deuterium would be accelerated by excitation of deuterium via energy transfer from electrons generated by Compton scattering.

IBA investigation on the effect of Ti-Mo interdiffusion on the D concentration in TiDx/Mo films

Ion Beam Analysis (IBA) which combines Rutherford backscattering (RBS), D(3He,p)4He nuclear reaction analysis (NRA) and chemical etching, is employed to detect the depth profiles of deuterium, titanium and molybdenum in metal hydride films (TiDx/Mo). Using this analysis technique, not only the depth resolutions of better than 70 nm for both Ti and Mo were achieved, but also there is no change in D content after the etching. Both secondary ion mass spectrometer (SIMS) and grazing incidence X-ray diffraction (GIXRD) have been also used to analyze the effect of Ti-Mo interdiffusion on the D concentration.

TEM investigation of the influence of dose rate on radiation damage and deuterium retention in tungsten

Tungsten targets were first irradiated with high energy W6+ ions (20 MeV) with different dose rates at 800 K and then loaded with deuterium at room temperature to decorate the displacement damage created in the first step. Detailed microstructure investigations were performed and compared with calculated damage profiles and deuterium depth profiles to link defect characteristics with the ability to retain hydrogen isotopes. Results directly indicate that depending on the used dose rate dislocation density and characteristics change. However, deuterium retention does not. Thus, we conclude that overall dislocation density does not affect deuterium retention significantly. Changes in D retention were observed as function of the depth of the damaged zone. Variations of dislocation density were also depth dependent. Consequently, we link changes in D retention with the dislocation presence, number of implanted tungsten ions and other point defects. The latter seem to affects D retention the most.

Comparison of LIBS results on ITER-relevant samples obtained by nanosecond and picosecond lasers

ITER foresees applying laser induced breakdown spectroscopy (LIBS) as a tool for quantitative assessment of fuel retention in the first walls. One open problem related to LIBS application is the choice of the laser type. Here we compare two Nd/YAG lasers with different pulse durations, 0.15 and 8 ns, working at λ = 1064 nm for LIBS studies of samples with D-doped W/Al coatings of ≈ 3 μm thickness (Al is used as a proxy of Be) on Mo. Low pressure argon was used as a background gas. Experiments were done in conditions where other factors (broadening of spectral lines, signal-to-noise ratio, limited thickness of coatings etc.) did not shadow the effect of laser pulse duration. For these reasons, low pressure argon was used as the background gas and fluences were kept at comparatively low values. Spectra of laser-produced plasma were recorded as a function of the number of laser pulses.Partially overlapping lines of hydrogen isotopes were fitted with Voigt contours, intensities were fitted and depth profiles of deuterium were reconstructed. The relative standard error of curve-fitting of spectra recorded with the laser of shorter pulse duration was two times smaller than that recorded by the longer pulse laser. The electron density was found from the Stark broadening of Hα line of the laser-produced plasma and the electron temperature of plasma was found on the basis W and Mo lines.It was found that in the case of ps laser an acceptable accuracy of the detection of deuterium was possible at considerably lower values of fluence. Steps needed for comparison of ps and ns lasers in ITER-relevant conditions were discussed.

Stabilization of defects by the presence of hydrogen in tungsten: simultaneous W-ion damaging and D-atom exposure

The possible mutual influence and synergistic effect between defect production and the presence of hydrogen isotopes in the crystal lattice of tungsten is studied. For this purpose, we perform modeling of experimental data where polycrystalline tungsten samples were in one case sequentially irradiated by 10.8 MeV tungsten ions followed by low-energy deuterium exposure and in the other case simultaneously irradiated by tungsten ions, while exposed to deuterium atoms. Modeling of the measured deuterium depth profiles and thermal-desorption spectra for different irradiation temperatures is performed by the MHIMS (migration of hydrogen isotopes in materials) code. A model of trap creation due to tungsten ion irradiation during the deuterium atom exposures is implemented. In both experimental series, the deuterium desorption peaks corresponding to defects induced by tungsten irradiation are described by the same two de-trapping energies of 1.83 and 2.10 eV. The experiments give unambiguous proof that the presence of deuterium increases the overall trap density. The modeling reveals that the two trap concentrations are affected differently by the temperature and presence of deuterium: the concentration of the low-energy trap is significantly higher in the case of simultaneous exposure compared to sequential exposure, especially at high temperature (2.2 times higher at 1000 K). The concentration of the high-energy trap is only weakly affected by the presence of hydrogen.

Analysis of retained deuterium on Be-based films: Ion implantation vs. in-situ loading

Pure Be, Be-O and Be-O-C thin coatings were deposited using high-power impulse magnetron sputtering (HiPIMS) with and without incorporation of deuterium. The coatings produced without deuterium were implanted afterwards with 15 keV 2H+ ion beams with a fluence limited to 2 × 1017 ion/cm2 in order to mitigate the damage imposed by ion irradiation and prevent a fast gas release. The as-deposited and as-implanted coatings were analysed by IBA techniques, namely by elastic and Rutherford backscattering spectrometries (EBS and RBS, respectively), nuclear reaction analysis (NRA) and by time-of-flight elastic recoil detection analysis (ToF-ERDA). Despite distinct deuterium depth profiles in the implanted samples, the results show that for the present ion implantation and deposition parameters, similar retained amounts are revealed in the films loaded by ion implantation or during the HiPIMS deposition, assuring ion implantation as a competitive and reliable method for fuel incorporation in thin Be-based films for retention studies in controlled conditions.

First GD-OES results on various deuterium ion fluences implanted in tungsten

Glow discharge optical emission spectroscopy (GD-OES) was used to investigate the deep depth profile of deuterium in tungsten exposed to deuterium ions at various fluences. Deuterium was found to continue to decrease in intensity at depths 10–20 µm, even at the lowest fluences, well beyond the probing depths of conventional deuterium measurement techniques. The detection sensitivity was sufficient to allow for definite separation in spectra for all fluences used in the present experiments. The integrated deuterium signal from GD-OES measurement was compared with total deuterium content for samples implanted with deuterium with fluences ranging from 1.0 × 1020 D/m2 to 1.0 × 1022 D/m2. The result showed a clear trend, where the intensity scales with implanted deuterium fluence to the 0.25 power. These results motivate further experiments and calibration of the system for future absolute retention measurements using GD-OES.

ToF-SIMS and ERDA study of hydrogen and deuterium in nickel-base alloys oxidized in water

The depth profiling of hydrogen and deuterium in polycrystalline and monocrystalline Nickel-base alloys (Ni-16Cr-8Fe, wt%) was performed by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Elastic Recoil Detection Analysis (ERDA) after oxidation in simulated primary medium conditions containing 9 at.% D2O. The use of deuterium isotopic tracer in ToF-SIMS has demonstrated the presence of deuterium in the oxide layer for oxidation times of 300 min and 100 h. The quantities of deuterium were determined by ERDA using a 2 MeV 4He ion beam. Finally, the penetration coefficient α was calculated, and ranged from 0.01 to 0.04.

Hydrogen diffusivity in oxide layers formed in Zr alloy in air or steam

The effect of the oxidation conditions on hydrogen diffusion in oxide layers in Zr alloy was experimentally studied. Samples of GNF-Ziron (high-iron Zircaloy-2-type alloy) sheets were oxidized in air or steam and then exposed to deuterium plasma to charge them with deuterium. Deuterium depth profiles in each sample were observed by nuclear reaction analysis during plasma exposure, and the deuterium diffusion coefficient D was estimated. The results showed that the D values of the steam-oxidized samples were high, whereas that of a steam-oxidized sample that was subsequently heated in vacuum was as low as those of air-oxidized samples. The difference in D was not attributed to the structure but is probably due to the presence of OH groups absorbed during steam oxidation.

Determination of deuterium depth profiles in fusion-relevant wall materials by nanosecond LIBS

The ablation and fuel-retention characteristics of aluminum–tungsten (AlW) and beryllium–tungsten (BeW) samples have been determined using Laser Induced Breakdown Spectroscopy (LIBS) and compared to results obtained using Secondary Ion Mass Spectrometry (SIMS). The measurements have been made both at vacuum (of the order of 10−4Pa) and at 50Pa of argon to especially enhance the intensities of the spectral lines of H and D. For reliable evaluation of the ablation rate of the samples the electron density ne and temperature Te of the LIBS plasma have been determined with the help of selected of spectral lines of Be, Al, and W. The electron density ne has been obtained from Stark broadening lines of Al I (308.7nm and 394.4nm) and Be I (457.3nm) and Te from the Saha–Boltzmann plot using W I and W II spectral lines having a higher value of the energy of upper states in order to prevent the influence of self-absorption on the results. The results indicate similar ablation characteristics between AlW (AlWD) and BeW (BeWD) samples but the inclusion of deuterium in the coating increases the ablation rate by a factor of 10 for both sample types. Concerning fuel retention more than one order of magnitude less D is retained in the AlWD sample than in BeWD. In the presence of background argon, the H and D lines were stronger and more easily distinguishable. This is a positive sign considering the real application in ITER where LIBS measurements are foreseen to be done during maintenance breaks. However the higher pressure gave a better signal, it is still far from the measurement conditions planned for ITER which need to be tested separately.