Search

This paper presents progress made toward the overarching goal to adapt single-photon-counting microcalorimeters to magnetic fusion energy research and demonstrate the value of such measurements for fusion. Microcalorimeter spectrometers combine the best characteristics of x-ray instrumentation currently available on fusion devices: high spectral resolution similar to an x-ray crystal spectrometer and broad spectral coverage sufficient to measure impurity species from Be to W. As a proof-of-principle experiment, a NASA-built x-ray microcalorimeter spectrometer has been installed on the Madison Symmetric Torus (MST) at the Wisconsin Plasma Physics Laboratory. For fusion applications, microcalorimeters will provide multi-species impurity ion data and will also contribute to the measurements of impurity ion temperature and flow velocity, Zeff, and electron density. Here, improvements to the microcalorimeter setup at MST and spectra acquired with the upgraded system are presented. Four motor-controlled wheels, loaded with x-ray fluorescence targets for continuous gain-drift tracking and broad energy-scale calibration, filters, and apertures, were added to the diagnostic's beamline. A stronger 55Fe source was added as an additional x-ray source for calibration. The 55Fe source, targets, filters, and apertures can be moved into and out of the optical path. Several configurations are now accessible for shot-to-shot adjustments to the count rate and waveband, enabling the measurement of x-ray photons emitted by a variety of impurity ions in the majority deuterium plasma, including aluminum, carbon, and argon. [ABSTRACT FROM AUTHOR]

This paper examines the characteristics of nuclear reactions occurring in low-temperature magnetized deuterium plasma. It is demonstrated that considering the ionization-recombination dynamics of deuterium atoms in this plasma allows for the potential realization of efficient nuclear fusion at low thermal energies k T ≈ 10 − 20 e V. The study shows that these processes are linked to the formation of coherent correlated states of deuterons, accompanied by the generation of giant energy fluctuations δ E ≥ 10 − 50 k e V during each recurring ionization event of deuterium atoms. These findings align with known anomalies in the solar atmosphere, such as the sharp temperature increase above the Sun's surface and the observed excess concentration of helium-3 ions in the solar wind. Furthermore, this process may explain well-documented experimental results, such as neutron generation during electric discharges in gas. [ABSTRACT FROM AUTHOR]

The burning rate of pure deuterium (D-D) fuel in Z-pinch devices with magneto-inertial confinement was studied in this paper. The system of particle and energy balance equations for D-D fuel burning with a mixed D-T-3He fusion cycle (D-D, D-T, and D-3He reactions) was solved numerically, taking into account the densities of all reacted and produced ions (protons, deuterium, tritium, helium-3, and alpha-particles). The obtained results indicate that effective D-D fusion in Z-pinch devices can be successfully achieved under conditions of a hot, dense plasma with an initial temperature of 31 keV or higher. The initial ion density of deuterium and electron density were equal due to quasi-neutrality condition of the plasma, with both reaching 10 24 m−3. Although the obtained results show that the burning rate of D-D fuel is approximately 2.3 times slower and its power density notably lower than that of D-T fuel, pure deuterium plasma can be considered as a promising alternative to well-studied deuterium–tritium plasma, with potential future applications in magneto-inertial fusion (MIF) facilities. [ABSTRACT FROM AUTHOR]

In the progress of nuclear fusion development, environmental radiation monitoring in the vicinity of the facility would be an important issue. At the National Institute of Fusion Science (NIFS), the deuterium plasma experiment, which produces tritium and neutrons using d-d fusion reactions, was conducted from 2017 to 2022. Environmental radiation and tritium in environmental water were monitored before and during the deuterium plasma experiment for public acceptance. As a result, there was no significant change in the observed dose rate and tritium concentration in the rainwater, and no statistically significant difference was identified in the statistical analysis of the data observed before and during the deuterium plasma experiment. Therefore, the environmental impact of the deuterium plasma experiments at NIFS is considered to be negligible. [ABSTRACT FROM AUTHOR]

A time-resolved deuterium–deuterium (D–D) fusion-born triton confinement study, aimed at understanding alpha particle confinement ability, was performed in Experimental Advanced Superconducting Tokamak (EAST) deuterium plasmas for the first time. A scintillating fiber detector was developed for measuring the secondary deuterium–tritium (D–T) neutrons, which provide evidence of triton slowdown, in EAST. The D–D fusion-born triton confinement experiment was performed by measuring secondary D–T neutrons in D-beam-heated D plasma with a plasma current of 400 kA. The secondary D–T neutron signal and its time evolution were obtained using pulse height discrimination analysis. The D–T neutron rate was calculated using the classical energetic ion confinement model to clarify the D–T neutron measurements. The secondary D–T neutron emission rate obtained from the numerical simulation closely agrees with the experimentally obtained results when considering the prompt loss of the tritons. [ABSTRACT FROM AUTHOR]

Experiments using the OMEGA EP laser system were performed to study collisionless shock acceleration of ions driven by the interaction of a relativistically intense laser pulse with underdense plasma. The energy spectrum of accelerated ions in the direction transverse to laser propagation is measured to have several narrow-band peaks which are quasi-monoenergetic with a typical energy bandwidth of 3%. In deuterium plasmas, these ions generate a significant number of fast fusion neutrons. Particle-in-cell simulations confirm that these ions were accelerated by the interaction of transverse shocks and that the appearance of quasi-monoenergetic spectral features depends on the growth of an ion-electron two-stream instability during the interaction. [ABSTRACT FROM AUTHOR]

The latest version of the SONIC code with the extended thermal force model that is capable to treat collisionality dependence of the force has been applied to the interpretative simulation of L‐mode discharge of JT‐60 U to investigate the impact of kinetic correction of the thermal force on the scrape‐off layer (SOL) plasma properties. As a first attempt, we have selected an L‐mode attached discharge #39090 (Ip = 1.6 MA, Bt = 3.1 T, and PNBI = 4.5 MW), where n‾e$$ {\overline{n}}_e $$ = 2.08 × 1019 m−3, n‾e/nGr$$ {\overline{n}}_e/{n}_{Gr} $$ = 0.392 with deuterium plasmas. It has been found that the peak values of SOL impurity density are reduced by a factor of 2, with the kinetic correction, because the thermal force is reduced by the low collisionality of SOL plasma between the X‐point and the (inner and outer) midplane. On the other hand, the profiles near the divertor plates are unaffected by the kinetic correction due to the highly collisional condition. The kinetic correction is found more pronounced for the higher charge states impurity due to the charge dependence of the parallel impurity force balance. Overall effects due to the kinetic correction on the total impurity radiation and the divertor heat load are confirmed to be a few % in the present discharge condition of JT‐60U. [ABSTRACT FROM AUTHOR]

The SOLPS‐ITER3.0.8 code with new Grad‐Zhdanov module was applied for predictive modeling of tritium plasma and deuterium‐tritium mixture in tokamak JET. The moderate power scenario of shot JPN #85278 modeled earlier for deuterium plasma was taken as a starting point. Effect of puffing increase, which was applied in experiment, on divertor conditions and inter‐ELM tungsten sputtering for both working gases and on isotope separation in their mixture is analyzed. Both for attached and for semi‐detached outer targets, the tritium plasma shows moderate increase in SOL width compared to deuterium one. The tungsten sputtering at the outer target in the inter‐ELM period for tritium is an order of magnitude bigger than that for deuterium. The D–T separation in the D–T mixture is moderate. [ABSTRACT FROM AUTHOR]

The hydrogenic two‐point model (H‐2PM), an analytical model for the scrape‐off layer that predicts a common electron and ion temperature and density along a flux tube from a target temperature and density, is adapted to a single‐species helium (He) model, preserving the 2PM assumptions and analytical nature. Across a range of densities and heating powers, the predicted Te$$ {T}_e $$ is within 20eV$$ 20\kern0.3em \mathrm{eV} $$ of upstream measurements by high‐resolution Thomson scattering (HRTS) for low‐confinement He plasmas performed in JET ITER‐like wall (JET‐ILW). For high‐recycling conditions, He‐2PM predictions of ne$$ {n}_e $$ were within 10% of the Li‐beam diagnostic measurements, excluding the near‐SOL, when assuming Zeff=1$$ {Z}_{\mathrm{eff}}=1 $$, suggesting the divertor SOL was not fully ionised in the JET‐ILW He plasmas. [ABSTRACT FROM AUTHOR]

A COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak (COSMONAUT) has been developed for spectroscopy measurements of the 2.45 MeV neutron emission from deuterium plasmas at the ASDEX Upgrade. The instrument is based on a CLYC-7 inorganic scintillator, whereby the detection of fusion neutrons occurs via their interaction with 35Cl nuclei in the detector crystal, leading to a peak in the detector response function and providing excellent neutron/gamma-ray discrimination capabilities. The diagnostics is installed along a radial line of sight and makes use of a digital system to record time resolved data for the whole duration of the discharge. Measurements in ASDEX Upgrade plasmas with neutral beam injection have been carried out and are successfully interpreted using state-of-the-art modeling codes. Next step applications of the diagnostics are in experiments aimed at generating energetic particles by ion cyclotron resonance heating schemes. In these scenarios, COSMONAUT will provide unique information on the acceleration of deuterons beyond the beam injection energy and on their confinement, for comparison with modeling. [ABSTRACT FROM AUTHOR]

We show that in plasmas generated in deuterium in the presence of sputtered W surfaces, various molecular tungsten species are formed, whose chemical composition depends on the presence of gaseous impurities, namely, nitrogen, oxygen, and hydrogen. A magnetron discharge was used for plasma sustaining, and the species were investigated by mass spectrometry and optical emission spectroscopy. The identified tungsten-containing molecules are described by the chemical formula WOxNyDzHt, where x = 0–4, y = 0–3, z = 0–3, t = 0–5. Presumptively, even higher mass tungsten molecular species are present in plasma, which were not detected because of the limitation of the spectrometer measurement range to 300 amu. The presence of these molecules will likely impact the W particle balance and dust formation mechanisms in fusion plasmas. [ABSTRACT FROM AUTHOR]

The results of a study of the combined effect on the W–Cu pseudoalloy of pulsed flows of deuterium ions with a power density of qi ≈ 1 × 109 W/cm2 at an exposure duration of τi = 20 ns and deuterium plasma with parameters qpl ≈ 1 × 108 W/cm2 and τpl = 20 ns generated in the "Vikhr" Plasma Focus installation are presented. It is shown that in the implemented mode of irradiation the nature of the damage to the surface layer of the tested material depends on the state of the surface of the irradiated samples and the number of pulsed impacts of energy flows. The impact of pulsed irradiation on the polished surface of pseudoalloy samples leads to the appearance of extended copper drops on the tungsten surface and to the formation of many pores, which are observed both in Cu drops and in the W matrix. In addition, microcracks appear on the W surface, as well as islands of a copper film of arbitrary configuration. Repeated irradiation of samples of the studied material with an unpolished surface leads to the formation of chains of tungsten droplets located in the upper parts of extended ridges formed during grinding of the original samples. Bursting bubbles are also visible on the irradiated surface, which arise as a result of the boiling of copper inclusions and a copper film deposited on tungsten. Clusters of such bubbles are often localized along ridges on the tungsten surface. The results obtained are discussed using numerical calculations and analysis of the thermal effect on the considered pseudoalloy under pulsed irradiation. [ABSTRACT FROM AUTHOR]

Blister formation has been an emerging research topic for extreme ultraviolet (EUV) mirrors exposed to hydrogen plasmas. Similar to plasma-facing materials in nuclear fusion reactors, it has been reported that blister formation in EUV mirrors is initiated by hydrogen uptake due to hydrogen ion or atom bombardment. However, the research so far has focused on Mo/Si multilayers exposed to only hydrogen ions or atoms, while the EUV mirror typically has a Ru capping layer facing hydrogen plasmas. We present experimental work to measure plasma-induced hydrogen uptake of Ru films. We bombarded our designed Ru-capped target with a low-temperature deuterium plasma and measured the deuterium retention using elastic recoil detection. Contrary to ion-driven deuterium uptake, the deuterium uptake rate of the Ru film had no dependence on the deuterium ion flux or energy after a period of plasma exposure. A reaction–diffusion model has been built to calculate the time evolution of deuterium retention, which well fits the experimental data. Based on this model, we conclude that the surface composition of the Ru film is the limiting factor for the deuterium uptake, which is seriously weakened when the surface is covered by Ru oxide. After the Ru oxide is reduced by the plasma, the uptake rate is predominantly driven by the deuterium surface coverage on metallic Ru. Our model also indicates that at the deuterium-populated Ru surface, deuterium has a low absorption barrier to penetrate the surface, which is supported by previously reported computational work. [ABSTRACT FROM AUTHOR]

The influence of ion thermal motion on the Stark broadening of spectral lines in plasmas is investigated within the frequency fluctuation method (FFM). The method for the consistent calculation of the jumping frequency, which is the main FFM parameter, is suggested on the basis of the S. Chandrasekhar and J. von Neumann stochastic theory. The calculations of the neutral hydrogen spectra in plasmas are presented. These results are compared with the experimental data. The spectra of the Ar dopant in the deuterium plasma are calculated taking into account ion thermal motion. The effect of ion thermal motion on the dip in the Heβ spectral line of the He-like Ar ion is shown. The calculations of the Heβ lineshape of the He-like Ti ion are compared with experimental data. [ABSTRACT FROM AUTHOR]

The effect of collisions on the motion of magnetized ions in sheath and presheath plasma regions was investigated through the measurement of ion incident angle of a hydrogen ion at a graphite surface. The experiment was conducted in hydrogen and deuterium plasmas where the ion mean free path is 5–10 times larger than the ion gyro radius and with varying magnetic field angle ψ from 0° to 90° normal to the target surface. The hydrogen ions actively reacted with carbon, leading to the formation of conical tips with axes directed along the incident ion flow direction. The ion incident angle was measured from the etched graphite images taken by scanning electron microscopy. The measured angles were compared to those calculated using Ahedo's fluid magnetic sheath model. In addition, we adopted the nominal Bohm criterion at the electrostatic sheath edge due to the larger ion gyro radius than the sheath. The results show that the ion incident angle was inclined to the normal direction with respect to the magnetic field angle because of the effect of ion collisions on ion motion in the presheath. The collisional effect on the ion motion is drastic for an oblique magnetic field angle ψ > 85°. This study demonstrates that the collisional property of the ions is crucial to guide the ion motion in magnetic (pre)sheath and to determine the ion incidence angle at the surface, even in collisionless and weakly magnetized plasmas. [ABSTRACT FROM AUTHOR]

The sputtering and transport of tungsten (W) impurities in helium (He) and deuterium (D) plasma discharges are compared using the SOLPS-ITER code. To reduce the computational resources of modeling, W ions are treated using the bundled charge state model. The results show that the W erosion flux of He plasma is almost a factor of two higher than that of D plasma under the same upstream electron density and heating power due to the higher W sputtering yield in He plasma. Moreover, the W self-sputtering flux is significantly higher than the W flux sputtered by the main ions. The leakage and retention of W impurities in the divertor region is also analyzed. W ions mainly escape from the near scrape-off layer (SOL) region through the divertor entrance as the stagnation point of the average W impurity poloidal velocity is considerably closer to the target plates in the near SOL region. Furthermore, the leakage flux of W ions in He plasma is higher than that in D plasma, mainly because of the higher W sputtering level in He plasma, which results in a larger W density. W ions with low-lying charge states, mostly comprising the charge state of W10–12+, easily escape from the divertor through the near SOL flux tubes in both D and He plasmas. In addition, the effects of upstream electron density on W sputtering and retention in He and D plasma discharges are presented. [ABSTRACT FROM AUTHOR]

Experimental campaigns at the Joint European Torus with an ITER-like Be/W wall with pure deuterium (D), tritium (T), and deuterium–tritium (DT) were a unique opportunity to explore various aspects related to the ITER operation. One of the most important challenges in recent years was the development of the hybrid scenario for D-T, based on reference deuterium and tritium plasmas. This kind of scenario, one of the foreseen for ITER, is characterized by a low current plasma and a high normalized beta βN factor compared to the parallel optimized baseline scenario [Hobirk et al., Plasma Phys. Controlled Fusion 54, 095001 (2012)]. As the experiments have shown, controlling the plasma edge in the different phases of the hybrid scenario becomes more difficult with higher isotope mass, and therefore, are also in risk of impurity accumulation [Hobirk et al., Nucl. Fusion 63, 112001 (2023)]. For this reason, investigation of the impurity behavior, as well as their control, constituted the crucial issue. The present contribution aims to compare mid-Z and high-Z impurities behavior within H-mode hybrid discharges in D and T plasmas, as well as D and DT plasmas. Detailed analysis shows that in the H-mode regime in the hybrid scenario, higher impurity radiation is observed for DT in comparison to D plasmas, as well as for T compared to D plasmas. Additionally, it was noticed that the most significant contribution to the plasma radiated power comes from W and to a lesser extent from Ni (∼10%). Moreover, it was found that an earlier transition from small edge localized modes (ELMs) to ELM-free phase can result in the earlier increase in impurities. [ABSTRACT FROM AUTHOR]

Electromagnetic fluctuations between 300 and 500 kHz were observed in both ion saturation current and magnetic field measurements in the KAERI plasma beam irradiation facility where the applied-field magnetoplasmadynamic (MPD) thruster is used as a plasma source. In this study, the plasmas were ignited with deuterium gas and the plasma current (input power) was varied from 55 A (2 kW) to 155 A (6 kW). The electron temperature and density measured downstream of the MPD thruster plasma were ∼5 eV and (2–4) × 1012 cm−3, respectively. To identify the fluctuations, the dispersion relation and the phase velocity were experimentally obtained using the Beall method and were compared to the theoretical values under warm plasma conditions. It was revealed that the observed fluctuations were fast Alfvén waves with a circularly polarized magnetic field. In addition to the fast Alfvén waves, we also observed electrostatic fluctuations at a higher frequency that was similar to the lower-hybrid frequency. [ABSTRACT FROM AUTHOR]

The evaluation of activities from radionuclides inside a vacuum vessel is required for the safe maintenance and estimation of the activation level of fusion devices. The Large Helical Device (LHD), Toki, Japan, has been performing deuterium plasma experiments since 2017, and radionuclides have accumulated in components such as vacuum vessels. In this work, the gamma-ray spectrum and activity of each detected radionuclide in an LHD vacuum vessel were evaluated using portable high-purity germanium (P-HPGe) and numerical calculations of photon transport for comparison with the removed armor tiles to evaluate the occupational exposure in the maintenance of LHD experiments. Measurements using the P-HPGe detector were performed at 20 positions along the toroidal direction of the LHD, at each O port, and between each pair of adjacent O ports. Using the estimated efficiency of the photoelectronic effects inside the P-HPGe detector calculated by Monte Carlo N-particle code version 6.1, the activities of the radionuclides in the armor tiles attached to the vacuum vessel were evaluated. The estimated activity concentrations were compared with the measured activities of the armor tiles removed from the vacuum vessel. Gamma rays from 58Co, 54Mn, and 60Co were detected, and the measured activities of 58Co and 54Mn generated by fast neutrons in the armor tile were almost consistent with those obtained from the removed armor tiles. The radioactivity of 60Co in the armor tile was underestimated compared with the activity obtained from the removed armor tiles. The measurement of activation by fast neutrons is feasible, whereas activation by thermal neutrons requires more accurate calculations and surveys to be measured using this method. [ABSTRACT FROM AUTHOR]

The paper investigates the trapping and desorption of hydrogen isotopes under irradiation of zirconium alloy E110 with ions of deuterium plasma. It is established that, under the irradiation, hydrogen exchange between the alloy and the gaseous ambient occurs: part of deuterium from the irradiation flux is trapped by the alloy, and at the same time, hydrogen initially contained in the alloy is partially desorbed. In general, hydrogen exchange results in an increase in the content of hydrogen isotopes in the sample. Addition of 30 at % oxygen to the plasma-forming gas, as well as increasing the sample temperature from T = 450 K to T = 600 K, slows down deuterium trapping and accelerates hydrogen desorption, leading to a decrease in the content of hydrogen isotopes in the sample. Increasing the dose of irradiation of E110 alloy with deuterium plasma ions intensifies both deuterium trapping and hydrogen desorption. On the basis of the experimental results, the mechanism of hydrogen exchange between zirconium alloy and gaseous ambient under the ion irradiation is proposed. The process includes three stages: reactions on the oxidized surface of zirconium alloy (hydroxylation of surface oxide and formation of water molecules); reactions on the metal–oxide boundary; and transport of hydrogen isotopes through the surface oxide layer in both directions. Surface reactions initiated by irradiation trigger the hydrogen exchange process. [ABSTRACT FROM AUTHOR]

The effect of the thermal motion of ions on the spectra of multicharged ions in dense plasma is investigated. An analytical expression is obtained for the frequency of jumps in the amplitude of the ion micropole. A modification of the frequency-fluctuation model technique is proposed, which allows taking into account the dependence of the frequency of jumps of the ion microfield on the energy shift. A new approach to the diagnosis of plasma density by the area of the dip in the center of the spectral lines is presented. Calculations of the spectra of argon impurity in deuterium plasma are given. [ABSTRACT FROM AUTHOR]

In the plasma focus chamber of the PF-MOL facility, a pulse valve allows an inhomogeneous density of the working gas to be obtained. In the combined mode of operation (stationary filling and additional injection), it is possible to use different gases together in one run. The facility has a capacitive source with a maximum current of 750 kA. The chamber houses a system of magnetic probes. At currents of 700 kA in the normal mode of stationary filling with deuterium, the neutron yield Yn is (4–5) × 109 per pulse. The maximum yield Yn = 1.2 × 1010 was obtained with the additional pulsed deuterium resupply of the area of current sheath focusing. Experiments have been carried out with a helium current sheath that compresses the injected deuterium. At a current of 530 kA, the yield Yn ~ 2 × 109 was reproducibly recorded. Tests have been carried out that indicate the absence of a helium impurity in the deuterium pinch plasma. [ABSTRACT FROM AUTHOR]

In the current study, bulk tungsten material surfaces are exposed to hydrogen, deuterium, and helium plasmas in the radiofrequency domain (13.56 MHz) at an input power of 250 W using the hollow-cathode configuration. The ejected material is collected on titanium substrates at various distances (from 6 mm up to 40 mm). Therefore, the exposed tungsten materials are investigated for surface changes (blister occurrence, dust formation, or nano-structuration), along with the crystallinity, depending on the plasma's exposure times (from 30 min up to 120 min for each plasma type). Also, the collected materials are analyzed (morphological, structural, and statistical investigations) for dust and dust film-like appearance. Plasma discharges are analyzed using two methods: optical emission spectroscopy, and single Langmuir probes, to emphasize the nature of the used plasmas (cold discharges, ~2 eV), along with the presence of tungsten emission (e.g., WI 406.31 nm, WI 421.31 nm) during the plasma lifetime. By using a dedicated protocol, a method was established for obtaining fusion-relevant tungsten surfaces in the hydrogen and deuterium plasma discharges. By using the implemented method, the current paper introduces the possibility of obtaining a new tungsten morphology, i.e., the dandelion-like shape, by using helium plasma, in which the W18O49 compound can be found. [ABSTRACT FROM AUTHOR]

After the second Deuterium–Tritium Campaign (DTE2) in the JET tokamak with the ITER-Like Wall (ILW) and full tritium campaigns that preceded and followed after the DTE2, a sequence of fuel recovery methods was applied to promote tritium removal from wall components. The sequence started with several days of baking of the main chamber walls at 240 °C and at 320 °C. Subsequently, baking was superimposed with Ion-Cyclotron Wall Conditioning (ICWC) and Glow Discharge Conditioning (GDC) cleaning cycles in deuterium. Diverted plasma operation in deuterium with different strike point configurations, including a Raised Inner Strike Point (RISP) configuration, and with different plasma heating—Ion Cyclotron Resonance Frequency (ICRF) and Neutral Beam Injection (NBI)—concluded the cleaning sequence. Tritium content in plasma and in the pumped gas was monitored throughout the experiment. The applied fuel recovery methods allowed reducing the residual tritium content in deuterium NBI-heated plasmas to about 0.1% as deduced from neutron rate measurements. This value is well below the requirement of 1% set by the maximum 14 MeV fusion neutron budget allocated in the ensuing deuterium plasma campaign. The quantified tritium removal over the course of the experiment was 13.4 ± 0.7 × 10 22 atoms or 0.67 ± 0.03 g with ∼58% attributed to baking, ∼12.5% to ICWC, ∼26% to GDC, and ∼3.5% to first low power RISP plasmas. The experimentally estimated amount of removed tritium is in good agreement with long-term tritium accounting by the JET tritium reprocessing plant, in which the unaccounted amount was reduced by 0.71 g after the cleaning experiment. [ABSTRACT FROM AUTHOR]

Divertor power load is a major challenge towards a burning plasma in a next-step tokamak. Here, the first results of a divertor power load characterisation in tritium plasmas in type-I ELMy H-mode, obtained in the JET deuterium-tritium campaign (DTE2) performed in 2021, are presented. It is demonstrated that both, transient loads due to type-I ELMs as well as the power fall-off length, do not exhibit an explicit ion mass dependence, with remarkably similar values in the tritium plasmas and in the deuterium references. This gives an improved credence to published scaling law predictions, solely based on deuterium plasma experiments. Moreover, the type-I ELM impact on the inner divertor target is studied in deuterium discharges. A slightly increased parallel energy fluence on the inner target with a factor of 1.08 compared to the outer target is observed. This is explained by the smaller major radius of the inner target. [ABSTRACT FROM AUTHOR]

The work describes the pedestal structure, transport and stability in an effective mass (A eff) scan from pure deuterium to pure tritium plasmas using a type I ELMy H-mode dataset in which key parameters that affect the pedestal behaviour (normalized pressure, ratio of the separatrix density to the pedestal density, pedestal ion Larmor radius, pedestal collisionality and rotation) are kept as constant as possible. Experimental results show a significant increase of the density at the pedestal top with increasing A eff, a modest reduction in the temperature and an increase in the pressure. The variations in the pedestal heights are mainly due to a change in the pedestal gradients while only small differences are observed in the pedestal width. A clear increase in the pedestal density and pressure gradients are observed from deuterium to tritium. The experimental results suggest a reduction of the pedestal inter-edge localized mode (inter-ELM) transport from deuterium to tritium. The reduction is likely in the pedestal inter-ELM particle transport, as suggested by the clear increase of the pedestal density gradients. The experimental results suggest also a possible reduction of the pedestal inter-ELM heat transport, however, the large experimental uncertainties do not allow conclusive claims on the heat diffusivity. The clear experimental reduction of η e (the ratio between density and temperature gradient lengths) in the middle/top of the pedestal with increasing A eff suggests that there may be a link between increasing A eff and the reduction of electron scale turbulent transport. From the modelling point of view, an initial characterization of the behaviour of pedestal microinstabilities shows that the tritium plasma is characterized by growth rates lower than the deuterium plasmas. The pedestal stability of peeling-ballooning modes is assessed with both ideal and resistive magnetohydrodynamics (MHD). No significant effect of the isotope mass on the pedestal stability is observed using ideal MHD. Instead, resistive MHD shows a clear increase of the stability with increasing isotope mass. The resistive MHD results are in reasonable agreement with the experimental results of the normalized pedestal pressure gradient. The experimental and modelling results suggest that the main candidates to explain the change in the pedestal are a reduction in the inter-ELM transport and an improvement of the pedestal stability from deuterium to tritium. [ABSTRACT FROM AUTHOR]

The JET hybrid scenario has been developed from low plasma current carbon wall discharges to the record-breaking Deuterium-Tritium plasmas obtained in 2021 with the ITER-like Be/W wall. The development started in pure Deuterium with refinement of the plasma current, and toroidal magnetic field choices and succeeded in solving the heat load challenges arising from 37 MW of injected power in the ITER like wall environment, keeping the radiation in the edge and core controlled, avoiding MHD instabilities and reaching high neutron rates. The Deuterium hybrid plasmas have been re-run in Tritium and methods have been found to keep the radiation controlled but not at high fusion performance probably due to time constraints. For the first time this scenario has been run in Deuterium-Tritium (50:50). These plasmas were re-optimised to have a radiation-stable H-mode entry phase, good impurity control through edge Ti gradient screening and optimised performance with fusion power exceeding 10 MW for longer than three alpha particle slow down times, 8.3 MW averaged over 5 s and fusion energy of 45.8 MJ. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition tungsten (CVD-W) is a promising material for plasma-facing materials. This work evaluated CVD-W samples with a large grain size (CVD-L) and a small grain size (CVD-S) together with rolled W (ND-W) and recrystallized (Rec-W) samples for their performance under deuterium (D) plasma exposure with a flux of 1021 D m−2 s−1 and fluences up to 2 × 1025 D m−2 at a surface temperature of 500 K. Both CVD-L and CVD-S samples featured a columnar grain structure with a preferred orientation close to 〈001〉 || Z, with a more preferred orientation in CVD-L samples. Both CVD-L and CVD-S samples show good resistance to blistering and only few micron-diameter blisters were observed at fluences. In ND-W and Rec-W samples, the number and size of blisters increased with fluence. The D desorption spectra show two desorption peaks in both CVD-W samples at 520 K and 570–604 K. Whereas in ND-W and Rec-W samples, two peaks were at 520 K and 607–700 K. The total D retention in both CVD-L and CVD-S samples was less than 30 % of that in ND-W and Rec-W samples. The low D retention in CVD-W samples was attributed to the low desorption intensities with the peak at 570–604 K. It is suggested that the microstructure of the columnar grain and the 〈001〉 texture in CVD-W samples helps suppressing plasma-induced blistering, therefore reducing D retention. In terms of the stability of the surface integrity and hydrogen isotopes retention, CVD-W demonstrates a significant potential as a wall material for future fusion reactors.

In today's nuclear fusion devices, erosion of high-Z metallic plasma-facing materials (PFMs) is mainly caused by physical sputtering. That is, by the exchange of energy between plasma ions and the atoms in the walls. In most of the numerical codes currently in use impinging plasma is approximated as a fluid. By averaging the incident particles' energy distribution the high-energy population of the eroded material is underestimated. For heavy materials such as W, high-energy eroded particles tend to ionize far from the wall and they are less affected by the sheath electric field hence, not being attracted back to the wall, they have a higher chance to contaminate the core plasma. This could in turn result in an underestimation of the net erosion sources. In this work, a semi-analytical model was developed to include the energy distribution of the incident particles. Then, by Monte Carlo method, the net erosion of tungsten from a smooth PFM was calculated. The results show that the kinetic description in energy is important only for incident particles ionized once. For instance, it is particularly important for plasma ions such as Deuterium. It is seen that Deuterium contribution to the W net sources is not always negligible if compared to light impurities or to tungsten self-sputtering in the range of plasma parameters tested. Finally, results show that the difference between the fluid and kinetic models becomes more pronounced for high-screening plasma conditions. [ABSTRACT FROM AUTHOR]

Low-Z impurity injection is frequently used for divertor detachment operations in current tokamaks; however, the impurity effects on the main plasma are yet to be fully understood. In this paper, the impurity effects on the ion temperature gradient (ITG) modes in tokamak edge plasmas are investigated based on the Euler matrix eigenvalue method. The eigen-equations with multiple ion species are established from the fundamental gyrokinetic theory, in which each ion species is treated equally. A novel and efficient gyro-kinetic code is developed for this numerical study, and the code's availability to examine quasi-linear ITG modes is demonstrated by its comparison with existing results. At the pedestal top parameters in Experimental Advanced Superconducting Tokamak high- β p H-mode plasmas, the ITG mode behavior is investigated in pure deuterium plasmas and with impurities. Impurities can induce destabilizing or stabilizing effects on ITG modes, which are determined by the impurity density scale length. The inwardly peaked impurity density profile tends to reduce the ITG growth rate. The effect strength also increases with the impurity charge concentration. The effects of impurity species, including boron, carbon, neon and argon, are also evaluated. Numerical results show that the strength of destabilizing or stabilizing effect inverses with impurity ion charge at the same effective charge. [ABSTRACT FROM AUTHOR]

Studies of core toroidal rotation reversal phenomenology in C-Mod deuterium L-mode plasmas have been expanded to include details of the dependences on plasma current and toroidal magnetic field. Rotation reversal occurs at a critical density, and universal scaling indicates that the product of ncritq95R ∼ BT/2, with ncrit in 1020/m3, R in m, and BT in T. Measurements in H and He plasmas exhibit similar behavior, including a connection with the linear Ohmic confinement/saturated Ohmic confinement transition and the cutoff for non-diffusive heat transport. Electron density and ion cyclotron range of frequencies power modulation experiments suggest that the collisionality ν * is a unifying parameter. Strong impurity puffing causes the critical density to increase, indicating that the situation is more complicated than only collisionality, perhaps involving the details of the effects of dilution on ion temperature gradient mode stability. [ABSTRACT FROM AUTHOR]

The JET neutron camera is a well-established detector system at JET, which has 19 sightlines each equipped with a liquid scintillator. The system measures a 2D profile of the neutron emission from the plasma. A first principle physics method is used to estimate the DD neutron yield that is based on JET neutron camera measurements and is independent of other neutron measurements. This paper details the data reduction techniques, models of the neutron camera, simulations of neutron transport, and detector responses used to this end. The estimate uses a simple parameterized model of the neutron emission profile. The method makes use of the JET neutron camera's upgraded data acquisition system. It also accounts for neutron scattering near the detectors and transmission through the collimator. These components together contribute to 9% of the detected neutron rate above a 0.5 MeVee energy threshold. Despite the simplicity of the neutron emission profile model, the DD neutron yield estimate falls on average within 10% agreement with a corresponding estimate from the JET fission chambers. The method can be improved by considering more advanced neutron emission profiles. It can also be expanded to estimate the DT neutron yield with the same methodology. [ABSTRACT FROM AUTHOR]

In this work, we study the transport of lithium impurities as they are transported from the wall where they are sputtered into the core plasma of the experimental device Pi3 that uses solid lithium walls at General Fusion. We perform time-dependent full-orbit simulations of initially neutral lithium impurities entering a Pi3 deuterium plasma that evolve their charge states and follow their full-orbit dynamics in axisymmetric Pi3 plasmas. This is done by extending the capabilities of the KORC-T code [L. Carbajal et al., Phys. Plasmas 24, 042512 (2017); J. Martinell et al., Bulletin of the American Physical Society (American Physical Society, 2020), Vol. 65] to include atomic collisions of ionization, recombination, and charge-exchange (CX) with neutral hydrogenic species by interpolating rates of these atomic processes from OPEN-ADAS tables to local plasma conditions. We assess the effect of hydrogenic neutrals, initial energy of sputtered lithium impurities, and the inclusion of E × B drifts caused by a radial electric field obtained from a radial force balance equation. It is found that both penetration of lithium impurities into the core and electron energy losses are enhanced by the radial electric field, with a weaker dependence on initial energy with which neutral lithium is sputtered off the lithium wall. Hydrogenic neutrals are not found to have a visible effect on transport of lithium impurities. Also, it is shown that ionized lithium impurities are not thermalized with the background deuterium ions at the edge plasma of Pi3 in studied timescale. From an analysis of electron cooling and radiation losses driven by lithium impurities, we find that energy losses are not significant in these plasmas. [ABSTRACT FROM AUTHOR]

• The irradiated sample with higher W content shows swelling and melting for all discharges, the CrNbTaVW only shows blisters. • The effect of irradiation was more severe in CrNbTaVW 1.7 when compared to CrNbTaVW. • The deuterium retention was evidenced to be in a deeper depth between 1.3 and 3 μm. • Deuterium retention was higher for CrNbTaVW 1.7 when compared with CrNbTaVW for 3 discharges applied. CrNbTaVW x high-entropy alloys have been developed for plasma facing components to be applied in nuclear fusion reactors. The CrNbTaVW x (x = 1 and 1.7) compositions were prepared by ball milling and consolidated at 1600 °C under 90 MPa. To study the irradiation resistance of these materials, deuterium plasmas were used to irradiate the samples in the PF-1000U facility with 1 and 3 discharges. Structural changes before and after irradiation were analyzed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Nuclear reaction analysis was carried out with 1000 and 2300 keV 3He+ ion beams to evaluate the profile and amount of retained deuterium on the irradiated samples. After irradiation, the sample with higher W content revealed swelling and melting for all discharges, while in the case of CrNbTaVW only blisters were observed. The deuterium retention was higher for CrNbTaVW 1.7 when compared with CrNbTaVW for 3 discharges applied. [ABSTRACT FROM AUTHOR]

It has been demonstrated that the electron density, ne, and temperature, Te, are successfully evaluated from He I line intensity ratios coupled with machine learning (ML). In this paper, the ML-aided line intensity ratio technique is applied to deuterium (D) plasmas with 0.031 < ne (1018 m−3) < 0.67 and 2.3 < Te (eV) < 5.1 in the PISCES-A linear plasma device. Two line intensity ratios, Dα/Dγ and Dα/Dβ, are used to develop a predictive model for ne and Te separately. Reasonable agreement of both ne and Te with those from single Langmuir probe measurements is obtained at ne > 0.1 × 1018 m−3. Addition of the D2/Dα intensity ratio, where the D2 band emission intensity is integrated in a wavelength range of λ ∼ 557.4–643.0 nm, is found to improve the prediction of, in particular, ne, and Te. It is also confirmed that the technique works for D plasmas with 0.067 < ne (1018 m−3) < 6.1 and 0.8 < Te (eV) < 15 in another linear plasma device, PISCES-RF. The two training datasets from PISCES-A and PISCES-RF are combined, and unified predictive models for ne and Te give reasonable agreement with probe measurements in both devices. [ABSTRACT FROM AUTHOR]

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.%.

In this study, three different materials (pure tungsten and two tungsten alloys with Fe and Ni dopants), which have been irradiated with a high-temperature deuterium plasma of 20, 25 and 100 plasma shots, are considered. The multifractal characteristics obtained from SEM images are then compared for the same specimens by analysing the distribution of defects and non-defects (nondamaged areas). A valid tendency was found that the brighter the original input image, the more accurate the results obtained when examining a non-damaged surface using multifractal characteristics. [ABSTRACT FROM AUTHOR]

In this paper, results concerning hydrogen and deuterium plasma (RF, 13.56 MHz) interactions with tungsten surfaces, were reported. We used the Hollow-Cathode (HC) configuration for plasma–tungsten surface interaction experiments, along with the collection of tungsten dust, at different distances. Further on, the plasma-exposed tungsten surfaces and the collected dust were morphologically analyzed by contact profilometry, scanning electron microscopy, and energy dispersive spectroscopy measurements, along with chemical investigations by the X-ray photoelectron spectroscopy technique. The results showed that exposing the tungsten surfaces to the hydrogen plasma induces surface erosion phenomena along with the formation of dust and interconnected W structures. Herein, the mean ejected material volume was ~1.1 × 105 µm3. Deuterium plasma facilitated the formation of blisters at the surface level. For this case, the mean ejected material volume was ~3.3 × 104 µm3. For both plasma types, tungsten dust within nano- and micrometer sizes could be collected. The current study offers a perspective of lab-scaled plasma systems, which are capable of producing tungsten fusion-like surfaces and dust. [ABSTRACT FROM AUTHOR]

The isotope dependence of the low- to high confinement-mode (L- to H-mode) transition power threshold PLH presents significant challenges for the initial (non-nuclear) hydrogen operations phase of the international thermonuclear experimental reactor (ITER). Here, we examine the isotope dependence of turbulence and ExB flow correlation properties in the L-mode edge plasma, leading up to the L-H transition. Atmarginal auxiliary power (near PLH), turbulence is initially suppressed periodically during limit cycle oscillations (LCO) that precede the transition to sustained H-mode confinement. We present evidence that the long-range (toroidal) correlation of the ExB edge plasma flow across the LCO phase is much weaker in hydrogen than in deuterium in the DIII-D tokamak, congruent with the higher threshold power PLH required to access LCO and H-mode in hydrogen. Concomitantly, the time required to initially quench edge turbulence via localized edge ExB flow shear is significantly longer in hydrogen (1–1.5 ms) than in deuterium (approx. 100 μs). No toroidal long-range correlation of the turbulence amplitude is observed, in agreement with expectations based on the relatively short poloidal turbulence correlation length. Radial edge turbulence and flow correlation lengths are longer in deuterium than in hydrogen plasmas as one would expect from ‘naïve’ gyro-Bohm isotope transport scaling, despite the substantially higher thermal flux across the last closed flux surface in hydrogen before the L-H transition. [ABSTRACT FROM AUTHOR]

Laser-Induced Breakdown Spectroscopy (LIBS) is a promising technology for in-situ analysis of Plasma-Facing Components in magnetic confinement fusion facilities. It is of major interest to monitor the hydrogen isotope retention i.e. tritium and deuterium over many operation hours to guarantee safety and availability of the future reactor. In our studies we use ultraviolet femtosecond laser pulses to analyze tungsten (W) tiles that were exposed to a deuterium plasma in the linear plasma device PSI-2, which mimics conditions at the first wall. A high-resolution spectrometer is used to detect the Balmer- α transition of the surface from implanted hydrogen isotopes (H and D). We use Calibration Free CF-LIBS to quantify the amount of deuterium stored in W. This proof-of-principle study shows the applicability of femtosecond lasers for the detection of low deuterium concentration as present in first wall material of prevailing fusion experiments. [ABSTRACT FROM AUTHOR]

• Detailed surface and in-depth chemistry of four ITER-like plasma-facing units located in different regions of the divertor, exposed to the WEST tokamak environment after the C4 campaign, were analyzed using X-ray photoelectron spectroscopy. • Boron carbides, tungsten carbides, and tungsten borides dominated the re-deposit region. • A blended mixture of oxidized and metallic tungsten, followed by boron carbides within a 50 nm depth range, was formed in the erosion-dominant area. • The re-deposited mixture in the deposition-dominated area of the divertor, thicker than a hundred nanometers, may significantly modify the hydrogen fuel retention of the plasma-facing units. Four monoblocks coming from one ITER-like plasma-facing unit from the Q3B sector of the lower divertor, named as monoblock (MB)3, MB9, MB20, and MB30, were exposed to the deuterium and helium plasma mixture during the C3 (2018) and C4 (2019) campaigns of the Tungsten Environment in Steady-state Tokamak (WEST), followed by a detailed ex-situ X-ray photoelectron spectroscopy investigation. The surface and in-depth chemistry of the tungsten monoblocks indicated the formation of a re-deposited mixture in the deposition-dominated area of the divertor, thicker than 218 and 172 nm for MB3 and MB9, respectively. The redeposition layer was dominated by a mixture of boron carbides accompanied by tungsten carbides in MB3, while in MB9, the redeposition layer was dominated by tungsten borides. The remaining two monoblocks, MB20 and MB30, were collected from the erosion region and showed similar chemical behavior with a blended mixture of oxidized and metallic tungsten followed by boron carbides within a 50 nm depth range. Boron fixation in the layers is an expected consequence of the boronizations used during the operation, but the chemical status of redeposited elements was characterized for the first time in this work. [ABSTRACT FROM AUTHOR]

Edge engineering is important for both fundamental research and applications as the device size decreases to nanometer scale. This is especially the case for graphene because a graphene edge shows totally different electronic properties depending on the atomic structure and the termination. It has recently been shown that an atomically precise zigzag edge can be obtained by etching graphene and graphite using hydrogen (H) plasma. However, edge termination had not been studied directly. In this study, termination of edges created by H-plasma is studied by high-resolution electron energy loss spectroscopy to show that the edge is sp 2 bonded and the edge carbon atom is terminated by only one H atom. This suggests that an ideal zigzag edge, which is not only atomically precise but also sp 2 bonding, can be obtained by H-plasma etching. Etching of the graphite surface with plasma of a different isotope, deuterium (D), is also studied by scanning tunneling microscopy to show that D-plasma anisotropically etches graphite less efficiently, although it can make defects more efficiently, than H-plasma. [Display omitted] [ABSTRACT FROM AUTHOR]

Surface modification, sputtering erosion and deuterium (D) retention were investigated of tungsten (W) and W-1 wt.% La 2 O 3 (WL10) that were exposed to pure D plasma and D plasma with different impurities (He, N 2 , Ar). After the plasma exposure, the surface of WL10 is covered by blisters with various shapes, and their size and density increase with D fluence. When the fluence was higher than 8.6 × 1024 D m−2, the blister rupturing occurred causing a partially- and/or fully-opened lid features. The phase interface between La 2 O 3 grains and W matrix was served as the nucleation sites for blistering and large-scale crack propagation near the surface. Small blisters were preferentially appeared on the grains with surface orientation of nearly (111) and that originated from the intra-granular crack at depths much closer to the sample surface. Micro-sized pits were formed on the WL10 surface after exposure to high fluence plasma, which was due to a higher sputtering rate of La 2 O 3 grains during plasma exposure. For both materials, seeding He in D plasma can effectively inhibit the blister formation, and most serious blistering occurs with N seeding in D plasma. When exposed to Ar + D plasma, sparse small blisters were visible and most of blisters were ruptured for W, whereas there are some big blisters with long strip shape for WL10. The difference in blistering behavior between W and WL10 was attributed to the differences in microstructure, composition as well as ductility due to the presence of La 2 O 3 phases. The sputtering yields increased slightly with He seeding in D plasma. N 2 and Ar seeding in D plasma leaded to a significant increase in sputtering yields. As compared to the W, the WL10 exhibits a better sputtering erosion resistance in terms of the sputtering yield. The D retention in WL10 increases with D fluence and that was equal to or lower than that in W when exposed to the same conditions. • Both deuterium (D) retention and blistering showed a strong dependence on the exposure fluence and impurity gas. • The phase interfaces between La 2 O 3 and tungsten (W) grains served as the nucleation sites for blistering. • Compared to the W grains, the La 2 O 3 grains were sputtered preferentially during plasma exposure. • The W-1 wt.% La 2 O 3 alloy (WL10) displayed much higher sputtering erosion resistance than pure W. • The amount of D retained in WL10 was dominated by intrinsic bulk defects and that was lower than that in pure W. [ABSTRACT FROM AUTHOR]

Double-peaked distribution (DPD) of particle flux has only been observed on the outer divertor target in electron cyclotron resonance heating deuterium plasmas with B × ∇ B toward the X-point in the HL-2A tokamak using high spatiotemporal Langmuir probe arrays. The experimental results demonstrate that the formation of the DPD is mainly due to the enhanced poloidal E × B drift flow stimulated in the divertor region, which is dependent on the plasma density, heating power, and divertor structure. The experimental results are qualitatively consistent with the SOLPS simulation. The experiment also shows that the formation of the DPD might be related to the enhanced cross field transport in the far scrape-off layer. This experimental findings presented here reveal the crucial role played by the synergistic effect of poloidal E × B drift flow and the closed divertor structure in the redistribution of the particle flux, which provides a potential way for the control of high heat flux in future fusion devices. [ABSTRACT FROM AUTHOR]

Тhe results of an experimental study of tungsten as a coating material for the divertor and the first wall of a thermonuclear tokamak reactor are presented. A method for modeling radiation damage of a material by thermonuclear neutrons based on the use of accelerated protons has been developed. A technique for irradiating tungsten samples (PLANSEE) with protons is developed at the cyclotron of the National Research Center Kurchatov Institute. During irradiation, protons with an energy of 3.7 MeV and the total fluence of 1018 protons/cm2 are used. The samples irradiated (0.05 dpa) are studied in deuterium plasma on the LENTA device. The results of irradiation and plasma exposure on the surface and the accumulation of deuterium in the irradiated material are presented. [ABSTRACT FROM AUTHOR]

The effect of sheared E  ×  B flow on the blob dynamics in the scrape-off layer (SOL) of HL-2A tokamak has been studied during the plasma current ramp-up in ohmically heated deuterium plasmas by the combination of poloidal and radial Langmuir probe arrays. The experimental results indicate that the SOL sheared E  ×  B flow is substantially enhanced as the plasma current exceeds a certain value and the strong sheared E  ×  B flow has the ability to slow the blob radial motion via stretching its poloidal correlation length. The locally accumulated blobs are suggested to be responsible for the increase of plasma density just outside the Last Closed Flux Surface (LCFS) observed in this experiment. The results presented here reveal the significant role played by the strong sheared E  ×  B flow on the blob dynamics, which provides a potential method to control the SOL width by modifying the sheared E  ×  B flow in future tokamak plasmas. [ABSTRACT FROM AUTHOR]

Reduced-activation ferritic-martensitic steels (RAFMS) are considered not only as structural but also, under certain conditions, as plasma-facing materials for fusion installations. The base material of RAFMS is iron. These steels also contain 8–12 wt % Cr and 1–2 wt % W. In a certain energy range during ion irradiation of RAFMS, there are conditions under which iron and chromium are sputtered, but tungsten is not. This phenomenon is called selective sputtering. In this work, for the first time, the selective sputtering of the domestic RAFMS EK-181 (Rusfer) under irradiation with deuterium plasma with an ion energy of 100 eV has been studied in detail. The sputtering coefficient was determined from the weight loss of the samples. In the course of sputtering, outgrowths are formed on the surface, the height of which increases with increasing irradiation dose and reaches several hundred nanometers. Data were obtained on sputtering and relief formation at a sample temperature of 440 K in the irradiation dose range of 3 × 1024–7 × 1025 ion/m2, as well as in the temperature range of 350–700 K at a fixed irradiation dose of 3 × 1024 ion/m2. The distribution of elements over the surface and in the cross section of the sample obtained by energy dispersive X-ray spectroscopy (EDX) indicates a significant enrichment of the surface in tungsten, especially pronounced in the protruding parts of the surface. Studies of the elemental composition by Rutherford backscattering spectroscopy (RBS) also showed an increase in the concentration of tungsten in the surface layer with an increase in the radiation dose. At the maximum irradiation dose, the concentration of tungsten on the surface, averaged over the area of the analyzing beam of 1.7 mm2, increased by about 10 times and reached 4.5 at %. [ABSTRACT FROM AUTHOR]