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The relation between the macroscopic input power required at ASDEX Upgrade to access the H-mode and the microscopic shear has been investigated via fast charge-exchange recombination spectroscopy (CXRS) measurements at various toroidal magnetic fields, different electron densities, and in both hydrogen and deuterium plasmas. For the H-mode onset, a threshold in the minimum, an approximation of the shear, has been found. This identifies and not Er as the important player for the L-H transition. A database of measurements including CXRS, Doppler reflectometry measurements and comparison to neoclassical approximations shows a threshold of (6.7 ± 1.0) km/s ranging over a factor of three in. Using these findings, a simple derivation of the scaling is proposed giving a physics interpretation of the Bt, density and surface dependence of. [ABSTRACT FROM AUTHOR]

A first attempt to observe a nuclear-elastic-scattering (NES) effect caused by energetic protons on deuteron slowing-down behaviour was made on the Large Helical Device located at the National Institute for Fusion Science. The NES effect on the slowing-down of fast ions can influence the confinement of fast ions, ion heating, fusion reaction rate coefficient, etc. An intense hydrogen beam was injected into a deuterium plasma to create a knock-on tail, i.e. a non-Maxwellian energetic component in the deuteron velocity distribution function. We conducted two types of experiment: (1) observation of the slowing-down of the knock-on tail and (2) observation of the NES effect on the slowing-down time of fast ions. The phenomena are discussed in terms of the difference in the decay process of the D(d,n)3He neutron generation rate after neutral beam heating is terminated between the cases when the knock-on effect is influential and not influential, and also from the difference in the neutron decay times. The results of a series of experiments indicate that the NES effect caused by energetic protons can have an impact on the slowing-down of fast deuterons. [ABSTRACT FROM AUTHOR]

Two sets of pure deuterium plasmas are simulated using UEDGE, one including atoms and molecules and the other including atoms only as separate fluid species. Simulation results in one and two dimensions are reported to assess the role of molecules in tokamak plasmas. It is shown that thermal coupling of the molecules to the plasma can be relevant for the onset of detachment under highly collisional conditions in simple geometries, but play a modest role at low collisionality. Ion‐molecule equipartition presents an additional ion energy loss channel, dissipating ion energy that would otherwise heat the electrons by equipartition. The resulting reduced electron temperature increases the ion‐electron recombination by an order of magnitude as the plasma density is increased, yielding earlier and deeper detachment. [ABSTRACT FROM AUTHOR]

The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma (flux ∼ 3.71 × 1021 D/m2⋅s, energy ∼ 25 eV, and fluence up to 1.3 × 1026 D/m2) are studied. The results show that the total amount of deuterium released from W–2%Y2O3 is 5.23 × 1020 D/m2(2.5 K/min), about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra (TDS) at different heating rates (2.5 K/min–20 K/min) reveal that both W and W–2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV (grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV (vacancy) in W and 1.73 eV (vacancy) in W–2%Y2O3. [ABSTRACT FROM AUTHOR]

We report the results of an investigation of the main energy parameters of a plasma jet from a coaxial accelerator with a conical insert in the charge-formation region. We have obtained the dependences of the pressure and the jet diameter of the deuterium plasma on the distance to the accelerator, as well as on its length and the voltage polarity at the electrodes. It is shown that plasma jet energy is a quadratic function of voltage. Among all tested modifications, an accelerator with a length not exceeding 220 mm, a negative polarity of the voltage at the central electrode, and a focusing conical insert at the beginning of the outer electrode is found to be most effective. At the source output, a deuterium plasma with an ionization front velocity exceeding 100 km/s and a pressure exceeding 1 MPa is obtained. We describe a method for measuring the jet pressure with the help of a deflecting screen and an FLIR SC7300M infrared camera. [ABSTRACT FROM AUTHOR]

A continuous pellet fueling system (CPFS) is currently being designed at the Oak Ridge National Laboratory (ORNL) for the long pulse operation of the Wendelstein 7-X (W7-X) stellarator. The purpose of the CPFS is to provide deep continuous fueling for feedback-controlled high-density operation and mitigation of predicted hollow density profiles. The system will provide the capability to inject cylindrical pellets of solid hydrogen or deuterium into the plasma core, with flexibility to vary the pellet size, velocity, and injection frequency. Pellets are nominally of 3 mm in diameter and have a length between 1 and 4 mm. The heart of the CPFS is a vertically oriented, twin-screw extruder, cooled by three Gifford-McMahon cryocoolers in parallel, designed to form a continuous filament of hydrogen or deuterium. The filament width, which determines the pellet length, can be adjusted by means of a variable nozzle driven by a linear actuator at the base of the extruder. Coupled to the nozzle is a solenoid-operated gas gun and cutter assembly. A pneumatic propellant valve pulses a burst of ~60 bar helium to accelerate the cut pellet into W7-X. Three gaps in the guide tubes provide pumping locations to remove the helium propellant before it reaches the plasma. The maximum velocity of the pellet is limited by its ability to survive navigating the guide tube trajectory intact. A microwave cavity located within the guide tube provides the capability to measure the pellet size and velocity. The mechanical and thermal designs of the W7-X extruder, adjustable nozzle, and gun and cutter assembly design are described. A guide tube design and experimental pellet survivability test results are presented. [ABSTRACT FROM AUTHOR]

The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma (flux ∼ 3.71 × 1021 D/m2⋅s, energy ∼ 25 eV, and fluence up to 1.3 × 1026 D/m2) are studied. The results show that the total amount of deuterium released from W–2%Y2O3 is 5.23 × 1020 D/m2(2.5 K/min), about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra (TDS) at different heating rates (2.5 K/min–20 K/min) reveal that both W and W–2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV (grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV (vacancy) in W and 1.73 eV (vacancy) in W–2%Y2O3. [ABSTRACT FROM AUTHOR]

The influence of magnetic field curvature on the intermittency in density and potential fluctuations in drift-wave turbulence has been investigated in the stellarator TJ-K in the framework of an extended Hasegawa–Wakatani model. A structure function analysis was used to estimate the intermittency level of poloidally resolved drift-wave turbulence measurements of a deuterium plasma in TJ-K. Potential fluctuations were found to be broadly self-similar, whereas density fluctuations were found to be more intermittent in the region with negative normal and positive geodesic curvatures. This behavior could be understood by comparing the data to two-dimensional extended Hasegawa–Wakatani simulations that retain gradients in the magnetic field strength, giving rise to curvature effects. The model is able to reproduce the trends in the experimental data if both normal and geodesic curvature effects are accounted for, as well as the local anisotropy of turbulent length scales. The analysis indicates the importance of local magnetic geometry as a factor in the decoupling of density and potential fluctuations, leading to intermittency in drift-wave turbulence. [ABSTRACT FROM AUTHOR]

W-SiC composite material is a promising plasma-facing material candidate alternative to pure W due to the low neutron activation, low impurity radiation, and low tritium diffusivity of SiC while leveraging the high erosion resistance of the W armor. Additionally, W and SiC have high thermomechanical compatibility given their similar thermal expansion rates. The present study addresses the synthesis and performance of compositionally graded W-SiC films fabricated by pulsed-DC magnetron sputtering. Compositional gradients were characterized using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), and crystallographic information was obtained using electron diffraction and X-ray diffraction (XRD). Samples were exposed to L-mode deuterium plasma discharges in the DIII-D tokamak using the Divertor Material Evaluation System (DiMES). Post-mortem characterizations were performed using scanning electron microscopy (SEM) and XRD. Electron diffraction and XRD showed that the compositionally graded W-SiC films were composed of polycrystalline W and amorphous SiC with amorphous W+SiC interlayers. No macroscopic delamination or microstructural changes were observed under mild exposure conditions. This study serves as a preliminary examination of W-SiC compositionally graded composites as a potential candidate divertor material in future tokamak devices. [ABSTRACT FROM AUTHOR]

• Some silicide materials are found out as insert materials for the fabrication of W/CFC blocks. WSi 2 do not exceed but are the same level as insert material as that of SiC + additives. • Zr and V behave as insert materials for W/CFC bonding, but the thermal stability of specimens is not enough. • The bonding strength near edge of an expected size of mono-block is not enough. It needs to be fabricated as a larger size block with 40 MPa of pressure and removed its near-edge parts. The construction of a satellite tokamak, JT-60SA, was completed in 2020. JT-60SA is expected to contribute the research of ITER and developments for DEMO. JT-60SA employs carbon and carbon fiber strengthened carbon (CFC) composites divertors. The divertors will be set on an actively cooled cassette and be remotely handled because of human access restriction into the vacuum vessel due to the radioactivation caused by repeated deuterium plasma operations. An important mission of JT-60SA is high-β steady state plasma research, and during the mission, the use of carbon divertors will be continued. The possibility of metal wall experiments after the complete of high-β steady state plasma research is under discussion. Then the use of remote handled divertor cassette will be a condition, therefore, high performance and appropriate weight divertors are convenient for the operation. One idea is to use clad plates of tungsten and CFC. In previous researches revealed that a sinter bonding method using an insert material of SiC powders + additives was able to join W and CFC. But the research accidentally found out the insert material without explore of the other materials and the size of specimens was small. In present research, some candidates for the insert material were investigated and also the uniformity of strength on a W/CFC block of the expected size were evaluated. [ABSTRACT FROM AUTHOR]

Tungsten (W) film was prepared by magnetron sputtering, and the coarse crystalline W bulk was used as reference samples. All the samples were exposed to deuterium plasma with the exposure fluence of 1.67 × 1024 D/m2. The films were annealed in-situ at 723 K during deposition and hillocks were found on all film surfaces. Focused ion beam analysis of the subsurface structure of hillocks provides data support for the growth mechanism of hillocks. The formation of hillocks suggested that the underlying force is released the intrinsic compressive stress caused by thermal cycling during the magnetron sputtering. After deuterium plasma exposure, the W bulk showed obvious stepped high-dome deuterium blisters. The micrographs revealed the microscopic morphology characteristics of deuterium blisters and hillocks, and analyzed the similarities and differences between hillocks and surface deuterium blisters. By comparing the growth mechanism of hillocks on the W film with the surface blistering on the W bulk, the stress growth model of deuterium blisters on the surface of coarse crystalline W bulk is proposed. This work provides a new perspective for the transverse stress model of deuterium-induced surface blistering. [ABSTRACT FROM AUTHOR]

• We studied the erosion (and deposition) effect on the SiC mirror sample caused by high-energy neutral particles for the expected environmental condition of the field mirror of ITER divertor VUV spectrometer. • By ZEMAX software with a simplified entrance duct model, the flux of neutral particles reaching the first mirror (the field mirror) was calculated based on the particle flux in the first wall. The total depth of erosion on the first mirror of ITER divertor VUV spectrometer was calculated to be around 9 nm using the input particle flux from SOLPS-ITER code. • The erosion resistance test was performed on the SiC mirror sample using the laboratory-scale plasma device to assess the mirror surface damage by erosion from the charge exchange neutral particles of ITER. • In the experiment, the SiC mirror sample was exposed to H + and D + plasmas upto the total erosion depth of 650 nm, and this value is larger than the expected total erosion depth in the first mirror. The surface roughness change of Δ ∼ 0.7 nm was measured, and this mirror degradation is within the allowable level considering the expected initial mirror roughness of the first mirror ∼ 1 nm. A series of tests have been performed to validate the resistance of the Silicon Carbide (SiC) mirror as the first mirror material of ITER VUV spectrometers to all ITER environmental conditions. In the present paper, we focused on the erosion (and deposition) of the SiC mirror sample caused by high-energy neutral particles. The flux of neutral particles reaching the first mirror was calculated using the ZEMAX software with a simplified entrance duct model. In the calculation, the particle flux reaching the first wall is necessary and the previously reported values derived from the SOLPS calculations were used. Based on this estimated particle flux, the erosion resistance tests were performed to check the erosion effect due to the high-energy neutral particles on the first mirror of ITER divertor VUV spectrometer. In the experiment, erosion was induced by exposing the SiC mirror sample to hydrogen and deuterium plasmas (and ions). The target fluence of incident ions in experiment is based on the estimation of the flux of neutral particles in ITER. The surface shape, composition, erosion depth, and surface roughness were measured to check the damage of the mirror surface after erosion test. Based on simulations and erosion resistance tests, it was concluded that the SiC mirror can be used as the first mirror of ITER divertor VUV spectrometer. [ABSTRACT FROM AUTHOR]

Four sets of targets were used in this study: (1) Fe targets surrounded with 304 type stainless steel composed of mid-Z elements: Fe, Cr, Ni, and Mn (designated as Fe[304SS] targets), (2) Fe targets surrounded with high-Z tungsten (designated as Fe[W] targets), (3) Cu targets surrounded with mid-Z copper (designated as Cu[Cu] targets), and (4) Cu targets surrounded with high-Z tungsten (designated as Cu[W] targets). The targets were exposed to low-energy (140 and 200eV), high-flux (about 1022 D/m2s) deuterium (D) plasmas at various temperatures in the range from 355 to 740K. The surface morphology of the Fe and Cu targets is found to be dependent strongly on atomic number of re-deposited species and on the exposure temperature. For the Fe[W] and Cu[W] targets, due to formation of the W-enriched nano-sized structures on the target surfaces, the sputtering erosion yield is lower than that for the Fe[304SS] and Cu[Cu] targets, respectively. For the Fe[304SS], Fe[W], and Cu[W] targets, the sputtering erosion yield is increased distinctly as the exposure temperature rises from 355 to 740K.

Transport dynamic 2D simulations for supersonic molecular beam injection (SMBI) fueling into H-mode deuterium plasmas on the Experimental Advanced Superconducting Tokamak (EAST) is first simulated using a seven-field two-fluid model in the BOUT++ framework. The SMB is assumed to be injected into plasma from the midplane at the low field side with a fixed width and constant molecular flux. The different densities and injection velocities of SMBI are investigated within the upper single-null geometry of EAST. The simulations indicate that the SMBI has a self-shielding effect on molecules' inward transport into the plasma, and the deposition of SMBI leads to a large increase in plasma density and decrease in plasma temperature. There is a velocity threshold for SMB penetrating the pedestal and depositing at the top of density pedestal. However, the deposition point would be back toward the plasma boundary after SMB arriving at the deepest penetration position. Comparing the different molecular injection velocities and densities, the outcomes demonstrate that the depth of deposition is closely related to the injection velocity rather than the molecular density. The simulated results show good agreement with the EAST experiments by comparing the electron density profiles obtained by simulation and experiment, respectively. These results will be helpful for guiding future experiments, as well as the design of the SMBI system. [ABSTRACT FROM AUTHOR]

Using transient grating spectroscopy, we measure thermal diffusivity and surface acoustic wave speed in tungsten exposed to different fluences of deuterium plasma. Scanning electron microscopy (SEM) shows the formation of surface blisters that have similar morphology for all fluences considered. A significant reduction in thermal diffusivity and surface acoustic wave speed occurs as a result of plasma exposure. A saturation of the thermal diffusivity reduction with fluence is seen. Deuterium ion flux density appears to play a more important role in thermal diffusivity reduction than exposure time. These observations have important implications for plasma facing components in future fusion reactors. Unlabelled Image [ABSTRACT FROM AUTHOR]

An injector of fast deuterium atoms for plasma heating was designed and installed at the Tokamak à Configuration Variable (TCV). The neutral beam can deliver 1 MW power to the plasma in 2 s pulses. An ion beam of the injector is formed by a triode multislit ion-optical system with spherical electrodes which provide ballistic focusing. Tests at TCV revealed that the total angular divergence of the neutral beam across the slits exceeded the expected value more than twice. It was finally established that this increase in divergence was caused by the asymmetry of the chamfers at the slit edges of the plasma electrode. The redesigned shape of the slits of the plasma grid together with precise machining significantly improved the beam quality. Experimental testing proved that the neutral beam profile in the direction across the grid slits became very close to the expected value. [ABSTRACT FROM AUTHOR]

The effect of the isotope content of plasma (hydrogen/deuterium) on energy confinement time was studied at the FT-2 tokamak. A strong isotope effect is discovered, which is manifested in the deuterium plasma in high-density regimes. A correlation is shown between the improvement of the energy confinement in deuterium and the drop in the turbulence level at the plasma periphery. [ABSTRACT FROM AUTHOR]

This work focuses on the production of negative-ions on graphite and diamond surfaces bombarded by positive ions in a low pressure (2 Pa) low power (20 W) capacitively coupled deuterium plasma. A sample is placed opposite a mass spectrometer and negatively biased so that surface produced negative ions can be self-extracted from the plasma and measured by the mass spectrometer. The ratio between negative-ion counts at mass spectrometer and positive ion current at sample surface defines a relative negative-ion yield. Changes in negative-ion production yields versus positive ion energy in the range 10–60 eV are analysed. While the negative-ion production yield is decreasing for diamond surfaces when increasing the positive ion impact energy, it is strongly increasing for graphite. This increase is attributed to the onset of the sputtering mechanisms between 20 and 40 eV which creates negative ions at rather low energy that are efficiently collected by the mass spectrometer. The same mechanism occurs for diamond but is mitigated by a strong decrease of the ionization probability due to defect creation and loss of diamond electronic properties. [ABSTRACT FROM AUTHOR]

The surface of a liquid wall (cathode) in contact with plasma is subjected to the electric field and to the bombardment of plasma particles, mostly ions. The stability of electrocapillary waves at the wall surface is considered. In the first part of the paper, the motion of ions inside the sheath and its influence on the electric field distribution are considered in a self-consistent way. The stress exerted on the liquid surface by ions and the electric field is found. This stress is used to describe the liquid motion in the second (hydrodynamic) part of the paper. It allows us to obtain the dispersion relation of the electrocapillary waves and to find the most dangerous wavenumbers and corresponding instability increments. It is shown that disturbances with wavenumbers less than some critical value κ0 = kλ (λ is the Debye length) do not grow. Shorter disturbances grow if E, the electric field, at the wall exceeds a specific Ecrit number. Expressions for κ0 and Ecrit are obtained. The increment of instability for κ > κ0 and E > Ecrit is calculated. It is shown that the instability takes place within an interval of wavenumbers. The higher the electric field, the wider this interval and the higher the increment of the most dangerous instability. Calculations were performed for the liquid wall at floating potential bordering hydrogen and deuterium plasmas. It is shown that the instability takes place in a wider range of wavelengths and has a higher increment in the case of deuterium plasma than in the case of hydrogen plasma. [ABSTRACT FROM AUTHOR]

Deuterium plasma operations using a large fusion test device have been carried out since 2017 at the National Institute for Fusion Science. A small amount of tritium was produced by the fusion reaction, d(d, p)t. Then, a part of the tritium was released into the environment. Thus, monitoring the level of tritium in the environment around the fusion test facility is important. This is done before starting the deuterium plasma experiment. The environmental tritium concentrations indicated that they are at background levels in Japan. After starting the deuterium plasma experiment, the environmental tritium around the fusion test facility was within the range of environmental variation. This suggests that there was no impact of tritium on the environment during the first deuterium plasma experimental campaign. [ABSTRACT FROM AUTHOR]

Monthly precipitation samples have been collected at Toki, Japan, from November 2013 to March 2017. In this report, selected data were analysed to identify the regional hydrogen and oxygen isotope compositions. Tritium (3H) concentration in the precipitation ranged from 0.10 to 0.61 Bq L−1 and higher 3H concentrations were observed in spring rather than in other seasons. This range was similar to values reported in Chiba City, Japan. 3H concentration and the ratio d-excess, and δD values were roughly clustered according to each separate season. These regional hydrogen and oxygen isotope compositions will be used for environmental assessments of effects of the deuterium plasma experiments of the large fusion test device. [ABSTRACT FROM AUTHOR]

• In the Large Helical Device (LHD) of the National Institute for Fusion Science, the experiments using deuterium plasma were performed from March 2017. • The evaluation of the neutron flux in the torus hall as well as the LHD body is very important for designing the decommissioning of the LHD in the future, and the radiation shielding for workers and components around the LHD. • In this study, we performed the activation experiments using multiple activation foils and experimentally obtained the neutron spectrum in the vacuum vessel of the LHD for the first time. In the Large Helical Device (LHD) of the National Institute for Fusion Science, the experiments using deuterium plasma were performed from March 2017. Neutrons with the energy of 2.45 MeV are generated by d (d, n) 3He reactions. The evaluation of the neutron flux in the torus hall as well as the LHD vessel is very important for designing the decommissioning of the LHD in the future, and the radiation shielding for workers and components around LHD. In this study, we performed the activation experiments using multiple activation foils to obtain a neutron spectrum in the vacuum vessel of the LHD. The reaction rate of each activation foil was generally consistent with the calculation result by MCNP6. As a result of the unfolding with SAND-II code, we experimentally obtained the neutron spectrum in the vacuum vessel of the LHD for the first time. [ABSTRACT FROM AUTHOR]

This work aims to investigate the effects of 800 keV argon ions pre-damage on the following deuterium plasma irradiation behavior in tungsten-tantalum alloy (5 wt% tantalum dopant). The un-damaged and pre-damaged W–5%Ta were exposed to 60 eV deuterium plasma at a fluence of 1.944 × 1026 D/m2 in the linear plasma device. The results suggest that pre-damaged induced by Ar8+ ions can effectively mitigate deuterium-induced blistering, while the deuterium retention is significantly higher as compared to the un-damaged W–5%Ta. According to the transmission electron microscopic (TEM) analysis, a large number of defects can be observed clearly after irradiation by 800 keV Ar8+ ions, such as vacancies and dislocation loops, which eventually affect the surface blistering and deuterium retention in W–5%Ta. Furthermore, we also compared the deuterium retention in pre-damaged pure W, which was significantly increased by a factor of 15 than in pre-damaged W–5%Ta. • Pre-damages induced by Ar8+ ions can effectively mitigate deuterium-induced blistering in W-5%Ta. • Higher deuterium retention within the range of 300–1200 K in the pre-damaged W-5%Ta. • The damages induced by Ar8+ ions can lead to the irradiation harden of W-5%Ta. • The deuterium retention in pre-damaged pure W was increased by a factor of 15 than in pre-damaged W-5%Ta. [ABSTRACT FROM AUTHOR]

Tungsten and tungsten-tantalum alloy with tantalum concentration of 10 wt%, sintered by spark plasma sintering, were exposed to deuterium plasma at ∼500 K with flux of 1 × 1021–1 × 1022 D m−2s−1, an ion energy of 40 eV and fluence of 1 × 1025–1 × 1026 D m−2. After exposure, a large number of blisters with an average size of 1–2 μm form on the surface of tungsten, and the area density of blisters increases with increasing irradiation fluence. However, the dominant morphology on the surface of tungsten-tantalum alloy is characterized by the striped microstructure, and exhibits a strong grain-orientation dependence. TDS results show two major desorption peaks located at ∼650 K and ∼770 K for tungsten and tungsten-tantalum alloy, respectively. Furthermore, the deuterium retention in tungsten is 4–6 times more than that in the tungsten-tantalum alloy. It is suggested that tantalum alloying can be expected to suppress the surface blistering and reduce the deuterium retention in tungsten. [ABSTRACT FROM AUTHOR]

Results of experimental studies of toroidal Alfvén eigenmodes (TAEs) in the Globus-M spherical tokamak (R = 36 cm, a = 24 cm) are reported. The experiments were carried out in a wide range of plasma parameters at a magnetic field of up to 0.5 T and plasma current of up to 250 kA. Auxiliary plasma heating was performed by tangential injection of a deuterium beam with a power of Pb= 0.75 MW and particle energy of Eb = 28 keV into deuterium plasma. The experiments have shown that the TAE-induced loss of fast particles decreases with increasing plasma current and magnetic field. Using multifrequency Doppler backscattering diagnostics, it is established that the TAEs are localized at the plasma periphery. Results of simulations of the Alfvén continuum and TAE structure by means of the modified KINX and CAXE codes agree satisfactory with the experimental data on the TAE frequencies and localization. [ABSTRACT FROM AUTHOR]

We discuss the possibility of determining the evolution of the isotopic composition of plasma by the frequency of Alfvén oscillations in ohmic discharges in the compact TUMAN-3M tokamak with pulsed deuterium puffing into a hydrogen plasma and hydrogen puffing into a deuterium plasma. The isotopic ratios, i.e., relative concentrations of hydrogen nH/(nH + nD) and deuterium nD/(nH + nD) in the mixed hydrogen–deuterium plasma obtained by this method are in qualitative agreement with the results of spectroscopic measurements and neutral particle analysis data. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) emission diagnostics for studying differences of electron impact processes in hydrogen and deuterium plasmas are presented. The method is applied to study a filament driven multicusp arc discharge negative ion source by comparing the VUV-emission intensities of different emission bands and extracted currents of H−/D− ions and electrons. It was found that the ratio of coextracted electrons to extracted ions is four times higher for deuterium than for hydrogen. No significant differences of the VUV-spectra or volumetric rates of ionization, excitation, production of high vibrational states, and dissociation were found between the plasmas of the two isotopes. The volumetric rates of these electron impact processes are presented for both discharges. It is concluded that in the filament ion source, the observed difference of H−/D− production through dissociative electron attachment is due to different diffusion rates across the magnetic fields of the tandem-type discharge chamber rather than the production rate of ground state molecules at their vibrational levels. [ABSTRACT FROM AUTHOR]

The self-consistent core-pedestal prediction model of a combination of EPED1 type pedestal prediction and a simple stiff core transport model is able to predict Type I ELMy (edge localized mode) pedestals of a large JET-ILW (ITER-like wall) database at the similar accuracy as is obtained when the experimental global plasma β is used as input. The neutral penetration model [R. J. Groebner et al., Phys. Plasmas 9, 2134 (2002)] with corrections that take into account variations due to gas fueling and plasma triangularity is able to predict the pedestal density with an average error of 15%. The prediction of the pedestal pressure in hydrogen plasma that has higher core heat diffusivity compared to a deuterium plasma with similar heating and fueling agrees with the experiment when the isotope effect on the stability, the increased diffusivity, and outward radial shift of the pedestal are included in the prediction. However, the neutral penetration model that successfully predicts the deuterium pedestal densities fails to predict the isotope effect on the pedestal density in hydrogen plasmas. [ABSTRACT FROM AUTHOR]

The results of experiments and simulations of the transport of heat and particles in the Globus-M spherical tokamak are presented. Investigations were carried out in the ohmic mode in hydrogen and deuterium plasma. It is shown that in the phase of current growth under the same initial conditions, as long as the condition is met at which the minimum of the safety factor exceeds unity, two scenarios of discharge development are possible: with an electron temperature dive or with an electron density peak. After the safety factor reaches the value of 1, the differences are no longer observed. Modeling of transport processes using the ASTRA code showed that the dive of the electron temperature and density is a consequence of the decrease in the transport of heat and particles in the plasma core (i.e., the presence of internal transport barriers). [ABSTRACT FROM AUTHOR]

Surface morphology and deuterium retention in tungsten have been examined after exposure to a low-energy deuterium plasma with an ion fluence of 6.0 × 1024 D/m2 at various temperatures. Optical differential interference contrast microscope and scanning electron microscope equipped with focused ion beam were applied for surface observations. D (3He, p) 4He nuclear reaction at 3He energies varying from 0.5 to 4.5 MeV was used to determine the deuterium depth distributions within the depth of 8.0 μm. The thermal desorption spectroscopy was applied for deuterium retention measurement. The observed surface blistering and deuterium retention are found to strongly depend on the exposure temperature. At 230 K, many small blisters are formed on the tungsten surface. As the exposure temperature increases to 370 K, the blisters become sparser and larger. At 520 K no blisters appear. The deuterium retention is 1.4 × 1020 D/m2 at 230 K. Then it increases to 1.1 × 1021 D/m2 as the exposure temperature rises to 370 K, and decreases to 2.3 × 1020 D/m2 at 520 K. [ABSTRACT FROM AUTHOR]

The boron-doped diamond thin films were growth in deuterium rich microwave plasma in CVD process. The mechanism of influence of plasma composition on boron doping level was studied using optical emission spectroscopy. Deuterium rich plasma results in an increased dissociation of B 2 H 6 precursor and intense boron-radicals' production. In consequence, a higher doping level of diamond films was observed by means of Laser Induced Breakdown Spectroscopy and Raman spectroscopy. Deuterium species modify the mechanism of boron incorporation into thin films leading to increased boron concentration. Lower concentrations of sp 2 phases and CH defects have been noticed in the films deposited in the plasma with deuterium than with hydrogen. Moreover, all BH x (x = 0–3) species can bind to radical sites on the diamond {100} surface to form stable complexes. The enhanced boron doping is attributed to the lower energy of B H bond at the growth surface, when compared to C H bond. The hydrogen abstraction from B H site is providing dangling bond for diamond growth and boron incorporation. This effect plays a main role due to extended dissociation caused by deuterium rich plasma. The increase in the carrier concentration and the decrease in the Hall mobility for the BDD samples grown in deuterium was registered. Unlabelled Image • Boron-doped diamond films were grown in deuterium rich plasma CVD. • D 2 rich microwave plasma leads to enhanced boron doping. • Lower concentrations of sp 2 phases and CH defects have been noticed in deuterium grown diamond. • Hydrogen abstraction from B H site is enhanced by deuterium rich plasma providing dangling bond for diamond growth. [ABSTRACT FROM AUTHOR]

The experiments on deuterium plasma-driven permeation through liquid Ga and Li were conducted in a linear plasma device VEHICLE-1. Deuterium transport parameters such as diffusivity and surface recombination coefficient for Ga and Li were measured from the experiments. By using the measured transport parameters, deuterium dynamic retentions in Ga and Li under steady-state plasma bombardment were evaluated with the DIFFUSE code. It has been found that the deuterium dynamic retention in Ga is ~five orders of magnitude lower than that in Li under present experimental conditions. After exposed to the steady-state deuterium plasma at temperatures from 78 °C to 360 °C, deuterium static retentions in liquid Ga are measured by the thermal desorption spectroscopy. It has been found that the deuterium static retentions in Ga are close to the dynamic retentions when the exposure temperatures are below 250 °C. [ABSTRACT FROM AUTHOR]

In this study the fuel retention and erosion of different reduced-activation ferritic martensitic (RAFM) steels exposed to deuterium (D) plasma were investigated. D plasma exposure was performed in a linear experimental plasma system (LEPS) with the incident ion energy between 30 and 180 eV per D, fluence from 1023 to 1025 D/m2 and sample temperature between 300 and 500 K. After D plasma exposure, erosion structure development of surface topography was observed, but no significant difference was seen among various RAFM steels within the examined conditions. W-enriched surface is formed for all investigated RAFM steels with little difference. RAFM steels exhibited similarities in D erosion and dependence on D plasma energy or fluence. Thermal desorption spectroscopy reveals in all steel samples only one broaden releasing peak from 450 to 800 K and total D inventory of 1018–1020 D/m2. Similar D retention behavior of five RAFM steels was found that it decreases with increasing incident fluence or ion energy. Moreover, different cutting treatment along rolling direction leads to different erosion structure and D releasing behaviors. [ABSTRACT FROM AUTHOR]

The authors present the results of numerical simulation of the kinetic processes in deuterium microwave-resonator plasmas with electron–cyclotron resonance at a nonuniform distribution of the magnetic and electric fields. For the actual configuration of the resonator module, the authors show the optimal magnetic field distribution in terms of energy efficiency. The solution of the kinetic scheme of the microwave discharge in deuterium plasmas makes it possible to relate the gas-discharge plasma properties with the parameters of the deuterium-ion source: the residual gas pressure, the gas flow into the microwave resonator, the charged particle flows on the wall and into the ion-optical system, the electrical and magnetic field strength and distribution in the resonator, and the power input into it. The results make it possible to reveal and implement generator operation modes with the highest characteristics ever recorded. [ABSTRACT FROM AUTHOR]

High density (≥6 × 1019 m−3), low temperature (2–6 eV) helicon discharges in the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) are analyzed with the coupled multifluid plasma, kinetic neutrals code B2.5-Eirene. The interpretative analyses are constrained by data from multiple diagnostics, including Langmuir probes, Mach probes, filterscopes, infrared TV system, Thomson scattering, and baratrons. The objectives of the transport simulations include: investigation of the effects of heating, fueling, and plasma production; pumping, and assumed radial transport models on the calculated density and temperature distributions; plasma flow profiles and power balance. The primary objective in this report is to investigate the effects of the radial transport model in full plasma (the entire length of the plasma column in Proto-MPEX) data-constrained simulations. Results from three assumed forms of the radial transport coefficients are presented, including spatially constant, radially decreasing, and Bohm (D,χ ∼ Te/|B|). The results from each of the three transport coefficient sets agree qualitatively with the core (near axis) data. With the implicit Te dependence, the Bohm coefficients tend to decrease as functions of radius, although not as strongly as the centrally peaked set. The axial variation in the Bohm coefficients is largely due to the axial structure of the magnetic field. The agreement of the simulations and the diagnostic data with the Bohm set indicates that transport in the plasma column of Proto-MPEX is dominated by Bohm diffusion. [ABSTRACT FROM AUTHOR]

The article presents research on neutral beam current drive in Globus-M compact spherical tokamak. The experiments were performed in the plasma current range of 0.17–0.20 MA with a 0.4- or 0.5‑T toroidal magnetic field. The injection impact parameter was 33 cm. The variable parameters included compositions of plasma and the heating beam (hydrogen, deuterium), plasma density, and vertical displacement of the plasma column. The simultaneous increase in the plasma current and drop in the loop voltage were used to determine the neutral beam current drive. The injection of a hydrogen/deuterium beam into deuterium or hydrogen plasma resulted in a significant and reproducible drop in the loop voltage (up to 0.5 V). In order to process the obtained data, the authors developed an ASTRA code-based model, which allows one to calculate the neutral beam-driven current and bootstrap current. The share of noninductive currents as a function of plasma density during the injection of a hydrogen beam (28 keV, 0.5 MW) into the deuterium plasma was calculated. The authors analyze the results of experiments on off-axis beam injection achieved by vertical displacement of the plasma column and the effect of increasing the toroidal magnetic field on the consumption of the poloidal magnetic flux in discharges with atomic beam injection. [ABSTRACT FROM AUTHOR]

Capillary-porous systems (CPS) with liquid lithium are considered as a prospective alternative to traditional structural materials (W, Be, CFC) during the production of in-vessel elements contacting plasma of stationary thermonuclear reactors. The behavior of CPS with liquid lithium under the impact of pulsed deuterium plasma flows is considered. The basic processes determining the high stability of CPS against damage are revealed and the critical parameters defining the CPS resistance are specified. The behavior of the tungsten-lithium CPS after its interaction with atmospheric gases is studied in experiments on a plasma facility at the Ioffe Physical-Technical Institute. The irradiated samples of the CPS were studied by optical and scanning electronic microscopy and local X-ray spectral and X-ray diffraction analyses. The surface temperature was measured using a bicolored pyrometer during deuterium plasma irradiation. The outcome of the plasma effect on the heavily oxidized CPS surface substantially differs from that for a pure surface: there is damage to the CPS structure. The specific power of the plasma flow was 22–41 GW/m2, and the number of pulses per irradiated target was 100. [ABSTRACT FROM AUTHOR]

• The absence of an oxide layer on the downstream surface of the membrane enhances the plasma-driven permeation flux. • The plasma incident flux is a more crucial factor in enhancing the plasma-driven permeation flux than temperature. • The maximum plasma-driven permeation flux reaches 4.54 × 1018 D/(m2 s) at a radio frequency power of 500 W. The process of particle exhaust based on the cryopump in fusion reactor presents a severe issue of deuterium and tritium retention. However, the metal foil permeation pump represents an effective means to solve the problem of deuterium and tritium retention during the particle exhaust process. How to enhance the permeability performance of metal films to meet the requirements of practical engineering applications of fusion reactor is the main content of the research. This article focuses on the simulation and experimental investigation of V membrane, aiming to explore methods for enhancing membrane permeation flux. Through simulation analysis, the influence of thickness, membrane surface state, and temperature on both plasma-driven and gas-driven permeation has been studied. Among these, the downstream surface condition is changed during the PDP process, resulting in an almost twofold increase in permeation flux. Based on the permeation experiments the influence of temperature on permeation was proved and the impact of plasma source power on permeation was also studied. It was found that the permeation flux increased more than two orders of magnitude when the radio frequency power changed from 0 to 500 W, which indicates that plasma incident flux serves as a more effective means to enhance permeation flux compared to temperature. [ABSTRACT FROM AUTHOR]

This paper is devoted to experiments on testing of the Sn-Li capillary porous system (CPS) under conditions of deuterium plasma irradiation, carried out at a plasma-beam installation (PBI). As a metal CPS matrix, molybdenum mesh was used. The paper presents a detailed description of the development of technology and procedure for the fabrication of the investigated sample, intended for plasma testing, as well as experiments on irradiation of Sn-Li CPS with deuterium plasma. As a result of the experiments performed, the dependences of the temperature of the investigated sample on the energy of the plasma contacting with the CPS, time dependence of the gas phase composition in the PBI chamber during irradiation of Sn-Li CPS with deuterium plasma, optical spectra depending on the temperature were obtained. Post-experimental material science studies with a sample of Sn-Li CPS were also performed and the results of microstructure, thermal and X-ray phase analysis were obtained. Analysis of the experimental data obtained showed that the energy of deuterium plasma precipitated on the Sn-Li alloy is re-emitted into the energy of optical radiation on the evaporating neutral atoms of lithium and tin. A complete evaporation of the alloy from CPS, during interacting with deuterium plasma, leads to partial destruction of the metal matrix of molybdenum. [ABSTRACT FROM AUTHOR]

Abstract Deuterium (D) plasma-driven permeation (PDP) experiments for a Chinese reduced activation martensitic/ferritic steel CLF-1 have been performed. The effects of implantation flux, sample temperature and ion incident energy have been studied. The steady state PDP flux is found to be proportional to the square root of the implantation flux, indicating that the permeation takes place in recombination-limited regime for the upstream surface and diffusion-limited regime for the downstream surface (RD). The PDP flux and flux ratio (PDP flux/implantation flux) decrease with the increase of ion incident energy, which may be due to the enhancement of D recombination coefficient at the upstream surface. [ABSTRACT FROM AUTHOR]

In the large helical device (LHD) deuterium plasma experiment, the neutron emission rate and the shot-integrated neutron yield are measured with the neutron flux monitor (NFM) and the neutron activation system (NAS), respectively, where the neutron emission is assumed to be isotropic in the plasma. The differential cross section of the D(d,n)3He reaction has a large anisotropy for the forward direction of the incident deuteron direction. LHD has intensive tangential neutral beam injectors (NBIs), which may cause an anisotropic neutron emission in the plasma. The angular distribution of the neutron emission is calculated from the fast-ion distribution function evaluated by a code that solves Fokker–Plank equations for the 180-keV tangential NBI. The effect of the anisotropic neutron emission on the NFM and NAS measurements is estimated by a general-purpose Monte Carlo N-particle (MCNP) code calculations. Also, the effect is confirmed experimentally. The neutron emission rate measured with the NFM near the equatorial port is about 10% larger than that with the NFM at the top of the LHD center axis. The shot-integrated neutron yield measured with NAS is 25% larger than that with NFM at the top of the LHD center axis in the case of the tangential neutral beam injection, which is consistent with the MCNP calculation. [ABSTRACT FROM AUTHOR]

The vertical neutron camera (VNC) has been developed to measure neutron emission profile in deuterium plasmas of the large helical device (LHD). The experiment on spatial resolution evaluation for VNC was carried out in November 2016 by using a 252Cf neutron source of 800 MBq. The neutron source was introduced into the LHD vacuum vessel through an aluminum pipe from an upper diagnostics port to the equatorial plane. The source was placed at the following two positions. The first position is just on the cylindrical collimator axis, and the second position is in the middle of two neighboring collimator axes. The stilbene scintillation detectors are aligned radially at the collimator end to detect unscattered fast-neutrons generated in a deuterium plasma. The 3-D neutron transport calculations by using a general-purpose Monte Carlo N-particle code 6 reproduced the experimentally obtained neutron counting rate, indicating that VNC has sufficient spatial resolution and the crosstalk between two neighboring collimators is a fairly small fraction. It is expected that the VNC on LHD will function as a tool for the study on the radial transport of energetic ions. [ABSTRACT FROM AUTHOR]

From the recent experiments on liquid metal plasma-facing components, convection appears to play an important role in maintaining reduced recycling conditions. Either it is natural or forced convection, the transport of the implanted particle is accelerated in the depth direction whereby the surface saturation would be delayed or avoided. Reviewed in this paper are some of the recent studies on particle recycling from liquid metals under plasma bombardment with the emphasis on liquid convection effects. Natural convection has been observed to enhance deuterium plasma-driven permeation. In addition, the effects of $J \times B$ forced convection on particle recycling have been extensively studied under steady-state hydrogen, deuterium, helium, and argon plasma bombardment. Also, preliminary fluid dynamics analysis has been conducted to interpret these experimental observations. [ABSTRACT FROM AUTHOR]

It is well known that the influence of nuclear force, e.g., nuclear elastic scattering (NES), appears in an ion scattering process when ion energy increases. NES caused by high-energy particles forms the non-Maxwellian component in the ion distribution function. The non-Maxwellian component is named knock-on tail. The knock-on tail gives various effects on fusion plasma. Therefore, it is important to conduct an experiment in order to understand the impact of the NES effects. The NES effects are affected by the “shape and size” of the knock-on tail and the “shape and size” of the knock-on tail depends on plasma conditions. Therefore, we newly propose the method to observe the correlation between the NES effects and the plasma conditions by using Doppler effects for the $\gamma$ -ray-generating reaction, i.e., 6Li(d, p)7Li nuclear reaction, in ITER-like deuterium plasma. We can capture the impact of the NES effect caused by the change in the plasma conditions, i.e., electron temperature, deuteron density, proton beam power, and proton beam energy by capturing the change in the $\gamma$ -ray spectrum. On the basis of the Boltzmann–Fokker–Planck model, we showed the validity of the method by simulation. [ABSTRACT FROM AUTHOR]

The effect of deuterium plasma on tungsten with high levels of radiation damage was studied experimentally. Tungsten was examined as a candidate plasma-facing material for a fusion reactor. The effect of damage accumulation in a material irradiated with fusion neutrons was simulated using high-energy ions. Primary radiation defects of 1-100 dpa were produced in tungsten irradiated with He2+ and C3+ ions accelerated to 3-10 MeV in the cyclotron at the Kurchatov Institute with a fluence of 1017-1019 ion/cm2. The irradiated material was exposed to deuterium plasma at the LENTA linear plasma facility operated in the continuous regime and providing a plasma flux of 1021-1022 D/cm2. The erosion dynamics, the development of surface microstructure, and the accumulation of deuterium in tungsten were studied. Enhanced retention of deuterium was observed in the samples damaged both by helium and carbon ions at room temperature (ERDA). The effect of deuterium retention was suppressed in the damaged tungsten samples processed at a temperature of 500°C. [ABSTRACT FROM AUTHOR]