The efficiency of deuterium (D) and 3He atoms removal from polycrystalline tungsten (W) by irradiation with 3 keV 4He ions at room temperature was investigated. It was shown that up to 90% of He isotopes are replaced by post-irradiation with another He isotopes in both directions when saturation with He atoms in W is achieved. There are at least four processes of He isotope exchange and D-He exchange, namely, (1) collision, (2) sputtering, (3) bubble bursting and (4) replacement of previously trapped atom by post-implanted atom. It was shown that the sputtering and bubble bursting play a minor role in the removal of D and He by 3 keV 4He ions in comparison with collision and replacement processes. In the case of He isotope exchange, the dominate process is most likely a replacement. Replacement occurs even at room temperature regardless on the binding energy of He with defects, probably, by decreasing of the binding energy of He or D atoms with defects when He atoms during sequential irradiation approach them. In the case of D-He exchange, both collision cascade and replacement play a main role in the D removal by 3 keV 4He ions. The mechanism of the D and He removal by He ions is still need further study.

In this work, hardness and micro- and nano-structure of W–10Cr–0.5Y alloy, which is a promising material for fusion reactors, before and after irradiation with Fe ions with an energy of 5.6 MeV at 500°C were studied. Nanoindentation for hardness measurement and transmission electron microscopy and atom probe tomography for structural changes were used. A formation of Cr clusters with the concentration of Cr in clusters of 52 ± 2 and 77 ± 3 at

Deuterium (D) trapping in the W-11.4Cr-0.6Y alloy manufactured by field assisted sintering technology (FAST) and pre-annealed at temperatures of 1050, 1250, 1473 K was studied by in-situ thermal desorption spectroscopy (TDS). D incorporation in W-11.4Cr-0.6Y alloy was carried out by irradiation with deuterium ions (670 eV/D+) to a fluence of 5 × 1019 D/m2. The change in Cr concentration in the bulk of the W-Cr-Y alloy was studied using energy dispersive spectroscopy (EDS). The elemental composition on the surface of alloy samples before and after annealing was investigated using low energy ion scattering spectroscopy (LEIS). The Cr concentration increases on the surface of alloy sample during annealing at 1000 and 1050 K due to intensive Cr segregation, while it decreases at temperatures of 1250 K and above by dominant Cr sublimation. Pre-annealing of W-Cr-Y alloy at 1050 K leads to a decrease in the D trapping in the alloy which is connected with an increase in the Cr concentration on the surface. At high annealing temperatures of 1250 K and above, the appearance of new phases and decomposition-induced grain refinement leads to new types of defects with high binding energy for D.

Irradiation of the promising self-passivating W-10wt%Cr-0.5wt%Y alloy suggested as the first wall material for demonstration power plant, DEMO, was performed with 5.9 MeV Co2+ ions at 300°C and 5.6 MeV Fe2+ ions at 500°C to a dose peak of 12 dpa (displacements per atom). Atom probe tomography and transmission electron microscopy were used to study the chemical compositions of this alloy at the atomic scale before and after irradiation. Before irradiation, the microstructure consists of a supersaturated bcc solid solution (αW,Cr) phase with an average grain size of about 1 µm. Cr-enriched nanoscale clusters with an average size of (2.0±0.4) with a density of (6.3±0.5) ×1024 m−3 and (1.8±0.4) nm with a density of (5.6±0.5) ×1024 m−3 were found in the damage range after irradiation at 300 and 500°C, respectively. The Cr concentration in the Cr-enriched clusters increased from 48 at.% to 78 at.% with increasing the irradiation temperature from 300 to 500°C, but the average size slightly decreased. This indicates that Cr clusters are embryos of a Cr-rich (αCr,W) phase. It was found that the Cr-enriched clusters play a dominant role in the radiation-induced hardening of the alloy. Beyond the damage range, no Cr clusters were observed. It was found that the formation of the Cr-enriched clusters in the W-10Cr-0.5Y alloy mitigates the formation of dislocation-type defects.A segregation of yttria particles in the form of platelets was observed at the grain boundaries under irradiation at 500°C. Although the average yttria particle size remains unchanged after irradiation, the size distribution becomes more uniform and shifts towards smaller sizes. Therefore, the beneficial effect of nanoscale yttria particles on the oxidation resistance and alloy strengthening is expected to remain unchanged after irradiation under current experimental conditions.

The interaction of deuterium (D) with defects produced by high heat flux (HHF) in tungsten relevant to Edge Localized Mode (ELM-like) transient events in ITER was studied using thermal desorption spectroscopy (TDS). Defects in tungsten were created by 10 pulses of D plasma HHF with a duration of 1 ms each. The energy density of the pulses was 0.7 and 1.7 MJ/m2, which is below and above the tungsten melting threshold, respectively. Using TDS up to 1800K, D was completely removed from HHF damaged samples, and then the remaining defects were decorated by D 3 + ion beam irradiation (667 eV/D+) to a fluence of 1022 D/m2 at a temperature of 470 K with sequential in-situ TDS. Deuterium retention after exposure to a power load of 1.7 MJ/m2 is almost two times higher than in the case of 0.7 MJ/m2. Cracks appear on the tungsten surface under a load of 1.7 MJ/m2, and closed cracks similar to elongated voids are found in deeper layers in the tungsten bulk. The formation of the cracked surface increases the effective surface area for D trapping after ion beam irradiation which leads to significant D retention by a factor of 8 compared to a crack-free surface. It is expected that after ELM-like events, D retention in tungsten will be increased during subsequent steady-state plasma operation.

The electrical parameters of a high-power impulse magnetron sputtering (HiPIMS) discharge operating in H2/He mixtures were studied using different values of the pulse width, repetition frequency, and power. Deposition of tungsten (W) coatings was carried out in a magnetron discharge with a thermally insulated W target in two regimes at different pulse widths (80 and 500 µs) and frequencies (2 and 0.5 kHz). The average discharge power was fixed at Pd = 1500 W. Fusion-relevant molecular deuterium/helium (He) and hydrogen/He gas mixtures with a 90/10 flow ratio were used in the experiments.

The retention of deuterium in tungsten-chromium-yttrium alloys, W-11.4Cr-0.6Y and W-10Cr-0.5Y, was investigated by means of in-situ thermal desorption spectroscopy (TDS). The first alloy was manufac-tured by field-assisted sintering technology (FAST), while W-10Cr-0.5Y alloy was produced by hot isostatic pressing followed by heat treatment (HIP + HT). Both alloys were irradiated with D 3 + ions (670 eV/D) and a fluence of 10 21 D/m2 at temperatures of 30 0, 60 0, 90 0 K. In the case of W-11.4Cr-0.6Y alloy, deuterium retention was investigated during sequential irradiation with helium (3 keV) and deuterium (670 eV/D) ions at room temperature with fluences of 10 19 -7 x 10 22 He/m2 and 10 21 D/m2, respectively. The material structure has a great influence on deuterium retention, as evidenced by the significantly increased deuterium trapping in W-11.4Cr-0.6Y alloy at both room and elevated irradiation temperatures due to the presence of high-energy trapping centers compared to W-10Cr-0.5Y alloy. In both alloys, the observed amount of deuterium released during TDS was higher than in pure tungsten. The general trend of helium influence on the deuterium retention in W-11.4Cr-0.6Y alloy is very sim-ilar to bare tungsten. Namely, deuterium retention increased until helium implantation reached a fluence of 1021He/m2, and then sharply decreased when the fluence exceeded this value.(c) 2023 Elsevier B.V. All rights reserved.

Porous tungsten coatings were prepared by magnetron deposition in He environment. The depositions were carried out in HiPIMS mode with a frequency of 1 kHz and a pulse duration of 300 μs. The tungsten target was thermally insulated from the water-cooled cathode. The samples were mounted on three different distances from the target. Temperature of each sample was measured with a dedicated thermocouple and recorded throughout the deposition process. The structure of resulting W-fuzz layers is analyzed and discussed. The deposition rate of tungsten fuzz in a hot-target magnetron system operated in HiPIMS mode is shown to be ~100 nm/min.

Using a beam-plasma discharge device operating on helium (He), tungsten with the fuzz on the surface (W f) has been formed by irradiating polycrystalline tungsten (W) samples with He ions with an energy of similar to 150 eV and the fluence of similar to 6 x10(24) He/m(2) at the temperature of 1273 K. The deuterium (D) retention in W f annealed at different temperatures was studied by thermal desorption spectroscopy (TDS). Before and after annealing at temperatures of 10 00,120 0,1400 and 1600 K, W f was irradiated at room temperature by 2 keV D-3 + (667 eV/D) ions with the fluence of 10(21) D/m(2), then in-situ TDS was performed after each irradiation. Annealing W above 1200 K clearly changes the retention mechanism of D: the TDS spectrum consisting of multiple peaks changes to an almost single-peak spectrum. Annealing at 1600 K leads to surface smoothing and the decrease of the D retention by a factor of two compared to the annealing at 100 0 K. This can be explained by an increase of the reflection coefficient for the flat W surface. However, the D retention in W-f is significantly higher compared to that in W without He plasma exposure even after annealing at 1600 K, because there are still He bubbles in W-f that effectively trap D (c) 2022 Elsevier B.V. All rights reserved.

In order to simulate ITER transient events with surface heat load parameters relevant to edge-localized-mode (ELM) impacts, tungsten samples were exposed to pulsed heat loads using pure deuterium (D) and with 10% helium (He) seeding plasmas in quasi-stationary high-current plasma gun QSPA-T. The pulse duration was 1 ms that is relevant to ELMs and number of pulses was varied from one to thirty. The power load was 0.7 MJ/m2 that is below the tungsten melting temperature (Tm). Two tungsten samples were used, namely, polycrystalline tungsten without (W) and with pre-existing He-induced W ‘fuzz’ (Wf). Similar to the steady state plasma, the presence of He in tungsten leads to a reduction of the D retention during transient events at temperature below Tm. We explained it as interruption of the D diffusion towards to the bulk of tungsten by (i) the strain field induced by He bubbles and (ii) the formation of interconnected He bubbles at high temperature which leads to an open porosity for accelerated D desorption, thus, decreasing the D influx into the tungsten bulk. But as the He retention in Wf decreases below 1019 He/m2, the effect of He on the D retention after the plasma gun irradiation disappears: the D retention in W and Wf is the same after 30 pulses of the exposure to pure D plasma. In both cases of pure D and He seeded D plasma gun exposures, the D retention is higher compared to the steady state plasma exposure at sample temperature above 600 K.

The helium (He) retention and the influence of He-induced defects on the deuterium (D) retention and migration in Eurofer97 were investigated by in-situ and ex-situ thermal desorption spectroscopy technique. Samples were pre-irradiated with 3 keV He ions in the fluence range of 10(19)-10(22)( ) He/m(2), then irradiation with 2 keV D-3(+) ions (667 eV/D) with a fluence of 10(21 )D/m(2) was performed. Experiments were carried out at the sample temperature of 300 K. It was shown that the D retention in Eurofer97 increases and decreases with pre-irradiation with He fluences below and above 10(21) He/m(2), respectively. However, in all cases of He pre-irradiation, the D retention is higher than that in Eurofer97 without He pre-irradiation. The effect of the reduction of the D retention at He fluences above 10(21) He/m(2) can be connected with either the formation of open porosity due to interconnected bubbles or the strain field induced by high pressurized He bubbles that preventing D penetration into the bulk of a metal. Both effects reduce the D diffusion towards the bulk of a metal and, therefore, lead to a decrease in the D retention. Our data of in-situ and ex-situ experiments revealed that HemVn complexes in the temperature range of 600-800 K are unstable and transformed in stable HemVn complexes in the temperature range of 900-1100 K after air exposure. Due to a formation of oxide layer during a contact with the atmosphere, ex-situ TDS of D leads to a shift of the D release temperature in the high-temperature range compared to in-situ TDS in both cases with and without He pre-irradiation. Finally, the presence of He in a metal lattice will have the dominant influence on the D retention in the future fusion devices together with neutron irradiation and high temperature gradient. In the case of He saturation, the similar D retention was measured in different bcc metals and their alloys.(c) 2022 Elsevier B.V. All rights reserved.

Кроме 20 докладов, представленных на 4-й Международной конференции по подкритическим гибридным системам синтеза-деления, одобренных рецензентами и публикуемых в настоящем выпуске

Tungsten (W) samples were pre-irradiated with low-energy helium (He) ions with an energy of 80 eV, flux of 10(21) He/m(2)s, at a sample temperature of 1200-1250 K in a inductively coupled plasma (ICP) source facility. Such irradiation conditions led to a formation of a nano-structured surface layer of tungsten, called 'fuzz'. These samples were then irradiated with D-3(+) ions with an energy of 2 keV and small doses of 10(19) D/m(2) at room temperature and in-situ thermal desorption analysis (TDS) was performed. It was found that the main factor determining the deuterium (D) retention in W samples pre-irradiated with helium is the concentration of helium below the surface, namely, the D retention was increased with decreasing the He concentration until the nanostructured W 'fuzz' was removed. The effect of nanostructured tungsten 'fuzz' is only in a decrease of the reflection coefficient of deuterium ions compared to a smoother surface, resulting in the increase of the D influx into W and, consequently, increase of the D retention. However, this increase has a minor effect on the D retention compared to the He concentration in the subsurface layer of W. (C) 2021 Elsevier B.V. All rights reserved.

The effect of He-induced defects in tungsten on the efficiency of trapping of deuterium ions in the subsurface layer was studied using thermal desorption spectroscopy (TDS). The W sample was pre-irradiated with 3 keV helium ions at room temperature and various fluences in the range of 10(19) - 5 x 10(21) He/m(2). Then, it was exposed to a probe fluence of 10(19) D/m(2) of 2 keV D-3(+) (670 eV/D) ions, and in-situ TDS was performed. The de-trapping energy for D atoms increased with the increase of the He pre-irradiation fluence. On the other hand, a strong decrease in the D retention was observed if the He fluence increased above 10(21) He/m(2). At the highest He fluence of 5 x 10(21) He/m(2) deuterium trapping was possible only after partial release of He atoms. By comparison of experimental TDS spectra with modeling, the de-trapping energies of D atoms from various defects were estimated. (C) 2021 Elsevier B.V. All rights reserved.

The paper presents new knowledge on primary defect formation in tungsten (W) and iron (Fe) irradiated by fission and high-energy neutrons at near-room temperature. Using a well-established method of positron-annihilation lifetime-spectroscopy (PALS), it was found that irradiation of W in the fission reactor and by high-energy neutrons from the p(35 MeV)-Be generator leads to the formation of small radiation-induced vacancy clusters with comparable mean size. In the case of Fe, smaller mean size of primary radiation-induced vacancy clusters was measured after irradiation with fission neutrons compared to irradiation with high-energy neutrons from the p(35 MeV)-Be generator. It was found that one of the reasons of the formation of the larger size of the defects with lower density in Fe is lower flux in the case of irradiation with high-energy neutrons from the p(35 MeV)-Be source. The second reason is enhanced defect agglomeration and recombination within the energetic displacement cascade at high energy primary knock-on-atoms (PKAs). This is consistent with the concept of the athermal recombination corrected (arc-dpa) model, although the measured dpa cross-section of both fission neutrons and wide-spectrum high-energy neutrons in W is between the conventional Norgett–Robinson–Torrens (NRT-dpa) and arc-dpa predictions. This means that the physics of the primary radiation effects in materials is still not fully known and requires further study through a combination of modeling and experimental efforts. The present data serve as a basis for the development of an improved concept of the displacement process.

Helium (He) is a product of deuterium-tritium (DT)-fusion reaction and will be a natural impurity in DT plasma in future fusion devices. He retention in tungsten irradiated by plasma and mass-separated ions in a wide temperature range (300-1200 K) was investigated by means of thermal desorption spectroscopy (TDS). He retention did not exceed the level of 1.5 x 10(21) He m(-2) for all investigated samples. A significant effect of air exposure on TDS spectra was demonstrated. In contrast to in situ TDS measurements, He release after interaction with the air started from similar to 400 K, even in the case of high temperature irradiation. Changes in surface morphology were analyzed by secondary electron microscopy. Blisters were found at the surface after ion irradiation at low temperatures. Acceleration of surface modification and more complex surface morphology was observed in the case of irradiation at temperatures above 1000 K.

Deuterium (D) retention in Tungsten (W) under plasma heat loads relevant to edge localized modes in ITER was experimentally investigated at the QSPA-T plasma gun facility. Samples were exposed to 1.0 ms D plasma pulses with different heat loads in the range of 0.4−3.7 MJm−2 (heat flux factor P√t = 13.3−123 MJm−2s−0.5). A significant D retention was observed already after one pulse. Moreover, the D retention grew up continuously with increasing the power load, although the surface was melted at highest loads (above 1.4 MJ m−2). The D retention was higher than that in the case of stationary plasma irradiation at 600–700 K, indicating possible significant contribution of ELM’s-like events to the total D retention. All stages of the experiments (irradiation, storage time and TDS) have been simulated using the TMAP 7 code.

The preliminary irradiation of a tungsten sample with low-energy helium ions (80 eV, flux of 1021 m−2 s−1) at a temperature of 1200–1250 K in a facility with an inductive RF discharge leads to the formation of a nanostructured tungsten surface layer, which is referred to as fuzz. After that, the sample is subjected to a set of annealing procedures and irradiations with $${\text{D}}_{3}^{ + }$$ ions with an energy of 2 keV (0.67 keV per D) at low fluences of 1019–1020 m−2. Deuterium retention at each stage is analyzed by in-situ thermal desorption spectroscopy. An increase in the helium concentration in the sample leads to a significant change of deuterium retention. At high helium concentrations, deuterium retention becomes low. Annealing in the temperature range of 1000–1400 K leads to helium desorption, modification of the surface layer and defects, and, as a consequence, an increase in the amplitude of the main deuterium desorption peak and a shift of the peak to higher temperatures. Annealing at a temperature of 1600 K leads to removal of the nanostructured fuzz from the tungsten surface and a decrease in the deuterium retention on account of an increase in the reflection coefficient from a smoother surface.