Heavy Impurities Research Articles

Comparison of the Level and Mechanisms of Toxicity of Carbon Nanotubes, Carbon Nanofibers, and Silicon Nanotubes in Bioassay with Four Marine Microalgae.

Nanoparticles (NPs) have various applications in medicine, cosmetics, optics, catalysis, environmental purification, and other areas nowadays. With an increasing annual production of NPs, the risks of their harmful influence to the environment and human health is rising. Currently, our knowledge about the mechanisms of interaction between NPs and living organisms is limited. Additionally, poor understanding of how physical and chemical characteristic and different conditions influence the toxicity of NPs restrict our attempts to develop the standards and regulations which might allow us to maintain safe living conditions. The marine species and their habitat environment are under continuous stress due to anthropogenic activities which result in the appearance of NPs in the aquatic environment. Our study aimed to evaluate and compare biochemical effects caused by the influence of different types of carbon nanotubes, carbon nanofibers, and silica nanotubes on four marine microalgae species. We evaluated the changes in growth-rate, esterase activity, membrane polarization, and size changes of microalgae cells using flow cytometry method. Our results demonstrated that toxic effects caused by the carbon nanotubes strongly correlated with the content of heavy metal impurities in the NPs. More hydrophobic carbon NPs with less ordered structure had a higher impact on the red microalgae P. purpureum because of higher adherence between the particles and mucous covering of the algae. Silica NPs caused significant inhibition of microalgae growth-rate predominantly produced by mechanical influence.

Statistical Model for Quasicontinuum of Heavy Ions in Hot Plasma

A statistical description is proposed for the shape of heavy impurity spectra observed in tokamaks and stellarators, corresponding to the quasicontinuous radiation distribution, and called the quasicontinuum. For the tungsten ions, in particular, it is located in the spectral range of ∼2 to 7 nm. The method is based on the statistical plasma model of atom, which allows expressing the quasicontinuum structure through the electron density distribution of multielectron ions. The Slater distribution is used as a model density distribution. The quasicontinuum is formed by the great number of closely spaced lines of heavy ions with different degrees of ionization, and its calculation is very complicated. A comparison of the results obtained within the statistical approach with the results of the level-by-level quantum mechanical calculations shows that such a model plausibly describes the envelopes of the individual line arrays in the ion spectra. In contrast to the level-by-level calculation codes, the statistical atom model is rather simple and it can be used by a large number of users. The quasicontinuum was simulated for the tungsten, gold, lead, and gadolinium ions, which are observed in plasmas of fusion facilities. The simulation results are in fairly good agreement with the experimental data. The studies of the tungsten quasicontinuum are of interest from the point of view of plasma diagnostics, as well as determination of the tungsten impurity density and its transport in fusion facilities.

Impurity charge state transport in tokamak and stellarator plasmas

The standard one-dimensional formulation of impurity transport has proved to be highly questionable for impurities with medium/high Z, and is unsuitable for tungsten. This allows to reveal an inconsistent interpretation of the coupling between particle transport and ionization/recombination processes. A discrete two-dimensional (2D) Fokker–Planck–Kolmogorov equation with charge and radius variables is proposed to study impurity equilibrium and transport in tokamak and stellarator plasmas. The impurity behaviour is consistently considered in terms of a 2D Markovian stochastic process, which has a complex structure according to probabilistic laws that include particle transport as part of a more general impurity charge state transport. It is found that a self-consistent 2D Markovian impurity equilibrium has the consequence that particle transport corresponding to the stationary state is governed by ionization and recombination processes, which are statistically independent of the particle motion. These generalised 2D coronal equilibrium conditions, usually observed for heavy impurities in experiments, turn out to be the stationary solution of the discrete 2D equation introduced and are justified in a discrete 2D grid model of impurity equilibrium. A complete analysis of the simplest discrete 2D equilibrium cell provides the basis for a general solution, while the grid model is reduced to a set of such local equilibrium cells using a pseudo-state technique.Modelling of the density profiles of carbon, argon and tungsten impurities is carried out by TICS (transport of impurity charge states) code developed using available experimental data. It is found that the introduced equilibrium function, which is a discrete profile of the ratios of reduced ionization and recombination rates, systematically predicts the central accumulation, equilibrium and radial transport of impurities in H- and L-mode and ion transport barrier plasmas, in agreement with the experimental data.

Atomic Data for Calculation of the Intensities of Stark Components of Excited Hydrogen Atoms in Fusion Plasmas

Motional Stark effect (MSE) spectroscopy represents a unique diagnostic tool capable of determining the magnitude of the magnetic field and its direction in the core of fusion plasmas. The primary excitation channel for fast hydrogen atoms in injected neutral beams, with energy in the range of 25–1000 keV, is due to collisions with protons and impurity ions (e.g., He 2 + and heavier impurities). As a result of such excitation, at the particle density of 10 13 –10 14 cm − 3 , the line intensities of the Stark multiplets do not follow statistical expectations (i.e., the populations of fine-structure levels within the same principal quantum number n are not proportional to their statistical weights). Hence, any realistic modeling of MSE spectra has to include the relevant collisional atomic data. In this paper we provide a general expression for the excitation cross sections in parabolic states within n = 3 for an arbitrary orientation between the direction of the motion-induced electric field and the proton-atom collisional axis. The calculations make use of the density matrix obtained with the atomic orbital close coupling method and the method can be applied to other collisional systems (e.g., He 2 + , Be 4 + , C 6 + , etc.). The resulting cross sections are given as simple fits that can be directly applied to spectral modeling. For illustration we note that the asymmetry detected in the first classical cathode ray experiments between the red- and blue-shifted spectral components can be quantitatively studied using the proposed approach.

Numerical study of magnetic particles mixing in waste water under an external magnetic field

Abstract The combination of nanotechnology and microfluidics may offer an effective water and wastewater treatment. A novel approach combines the use of magnetic particles which can capture heavy metal impurities in microfluidic ducts. The purpose of this study is to investigate the mixing mechanism of two water streams, one with magnetic particles and the other with wastewater. The optimum mixing is obtained when particles are uniformly distributed along the volume of water in the duct for the combined action of a permanent, spatially and temporally aligned magnetic field. Results showed that mixing is enhanced as the frequency of the magnetic field decreases or its amplitude increases, while magnetic gradient is found to play an insignificant role in the present configuration. Moreover, for simulations with low frequency, the mean concentration of particles is found to be twice as high as compared to the cases with higher frequency. Optimum distribution of particles inside the micromixer is observed for the combination of 0.6 T, 8 T/m and 5 Hz for the magnetic magnitude, gradient and frequency, respectively, where concentration reaches the optimal value of 0.77 mg/mL along the volume of the duct.

Energy and particle confinement in JET H-mode plasma

This work describes the behaviour of the global energy and particle confinement on JET observed in a massive database of H-mode plasmas covering almost the whole lifetime of JET operations, both with the carbon and metal wall. The analysis is focused on type I ELMy H-modes in stationary phases. It is shown that plasma density in that regime is determined mainly by the plasma current, edge safety factor, triangularity of the last closed flux surface and the hydrogenic isotope mass. Behaviour is consistent for the whole database regardless of divertor configuration or the plasma facing materials. On average, thermal energy confinement time in JET with the carbon wall (JET-C) is accurately predicted by the IPB98(y,2) scaling. For JET with the ITER-like wall (JET-ILW), the energy confinement is found to be lower than expected from the scaling. The difference is found to be much stronger in a divertor configuration with the outer strike point at a vertical target and the pumping throat at the private flux. Observed lower confinement in JET-ILW can partially be attributed to the additional operational constraints of the metal wall machine, i.e. the avoidance of heavy impurity accumulation via additional gas dosing, but not fully. The isotope effect on the energy confinement in the Meff = 1–2 range is found to be the same in JET-C and JET-ILW, thus is independent of the wall material, if correlation with plasma density is accounted for. The effect of the toroidal magnetic field on the confinement is between zero and slightly negative. Triangularity has a generally favourable effect on the energy confinement, but the magnitude changes across the database. The effect of triangularity on plasma density is always much stronger than on energy confinement however, therefore plasmas with high triangularity are in general more dense and colder than at lower triangularities. The work described in this paper is completed under the EUROfusion global confinement database project, and the data shown here will be available to EUROfusion collaborators shortly. The data are also either already included in the international H-mode confinement database, or will be in the future updated version.

Depth profiling of ion-implanted samples by high-energy electron scattering

For heavy ions implanted in low-Z targets it is possible to determine the depth and concentration of introduced heavy impurities by studying the energy spectra of electrons scattered from the surface. Here, we demonstrate this for the case of 30 and 300 keV Au implantation in SiO2. For high-energy incoming electrons the elastic peak splits up in different components as the recoil losses depends on the mass of the scattering atom. Heavy impurities also affect the partial intensities and hence changes in the shape of the energy loss spectra are observed. These effects are reproduced by a simple model that uses sample composition, atomic elastic scattering cross sections and target dielectric function as input.

Oscillatory convection of a colloidal suspension in a horizontal cell

The finite difference numerical simulations performed are for convection of a non-uniformly heated colloidal suspension (Hyflon MFA) filling a horizontal cell of finite length. The cell has solid and impermeable boundaries and is heated from below. A linear temperature distribution is maintained at the side walls. Due to the negative effect of thermodiffusion (Soret) and gravity sedimentation, a heavy impurity is collected at the hot lower boundary, and convection transfers it inside the cell. The stable and transient oscillatory convection modes observed experimentally are analyzed. If the initial distribution of the concentration is uniform, then stationary convection occurs in the cell. As the concentration inhomogeneities accumulate, oscillatory perturbations begin to increase. A modulated traveling wave may form in the layer. Stable traveling waves are observed when the Rayleigh number exceeds a certain critical value, which depends on the cell length. There is a good agreement between the experimental data [1] and the results of numerical research. The spatial structure of the concentration field and the time evolution of the convective characteristics of the colloid suspension are determined. The behavior of the colloidal suspension in the regimes of modulated traveling waves and transient flows near the threshold of convection, including localized traveling waves and waves that change their direction, is simulated and elucidated. By analyzing the behavior of the world lines of the vortices and the concentration field, the mechanism of formation of defects in the form of vortex coalescence is clarified. In the process of defect formation, two vortices with the opposite direction of rotation are involved.

Code/Code comparison of impurity transport in EMC3 and DIVIMP**Poster PB029.

Recently, the global impurity migration code WallDYN was coupled to the 3D edge transport code EMC3-Eirene in order to make WallDYN applicable to 3D, non-toroidally symmetric, geometries. As part of the coupling, a new impurity transport module was implemented, which, in contrast to the existing impurity module, takes the inertia of the impurity into account, making it more suitable for heavy impurities like W. This new ‘kinetic’ impurity transport module uses the same physics as the 2D trace impurity transport code DIVIMP and therefore, to check the correctness of the implementation, a code/code benchmark was performed comparing the transport of Be- and W-impurities in EMC3 and DIVIMP. The comparison was performed for toroidally symmetric plasma that could be handled both by EMC3 and DIVIMP. Both codes were setup such that they would treat the transport of the impurities as similar as possible. Then the re-distribution of Be and W launched from different positions around the poloidal circumference of the first wall was calculated in both codes. To compare the resulting material re-distribution data () and judge the significance of any differences, was used in WallDYN calculations that model the evolution of the first wall due to erosion, deposition, re-erosion and re-deposition. These WallDYN calculations, performed using the from EMC3 or DIVIMP, showed the same major erosion and deposition areas and it can therefore be concluded that the new kinetic impurity transport module is implemented correctly and now allows us to make DIVIMP-like transport calculations using EMC3 in 3D.

Evaluation of alcohols as substrates for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones under environmentally friendly conditions

The aim of this research was to develop a procedure for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones under environmentally friendly conditions using alcohols as the starting materials in aqueous media. The developed protocol resulted in 3,4-dihydropyrimidin-2(1H)-ones derivatives, which are relevant intermediates with therapeutic and pharmacological properties. Target products were synthetized in a tandem process, which meets the requirements of pharmaceutical chemistry. The influence of the reaction conditions was investigated, and as a result, various substituted 3,4-dihydropyrimidin-2(1H)-ones were obtained with a yield of up to 81%, free from heavy metal impurities.

Stratification of ferroparticles caused by gravitational and magnetic fields in soft ferronematics

In the framework of continuum theory we study the magnetic particles stratification caused by gravitational and magnetic fields in ferronematic, i.e., a highly dispersed suspension of ferroparticles in a nematic liquid crystal. We consider the so-called soft ferronematic, where the coupling energy between the liquid crystal and the particle surfaces is finite, which allows to consider the director and magnetization of the ferronematic as independent variables. We show how under the influence of an external uniform magnetic field due to the segregation effect heavy impurity ferromagnetic particles begin to float up in a lower-density fluid, moving opposite to the gravity field. As an example, several types of suspensions with material parameters corresponding to actually synthesized ferronematics with different ratios between the two competing mechanisms of separation of impurity particles (segregation and gravity) are considered.

Treated phosphogypsum as an alternative set regulator and mineral addition in cement production

Abstract Various treatments of phosphogypsum samples extracted in Huelva, Spain, curing conditions and incorporation ratios were studied to evaluate the viability of being used as set regulator or as supplementary cementitious material to improve the mechanical behaviour of cement mortars. The physical-chemical properties, mechanical behaviour and environmental impact of these phosphogypsum-based cement mortars were determined. It was concluded that the phosphogypsum treatments and curing conditions influence the mineralogical transformations of mortars and therefore also the mechanical behaviour of the mortars tested. Furthermore, the heavy metal impurities in the phosphogypsum were immobilized in the cement matrix, leading to a clear improvement of the technical properties of cement mortars made with this waste compared to the traditional use of natural gypsum.

Direct Observation of Heavy Metals and Impurities in Minerals Using Z-contrast Imaging

Direct Observation of Heavy Metals and Impurities in Minerals Using Z-contrast Imaging

Analysis of Natural Diamonds by Rutherford Backscattering

The method of Rutherford backscattering (RBS) of 4He ions is used to detect impurities in the surface region of natural diamond crystals. In order to decrease the influence of luminescence from the surface of diamond, the recording of scattered ions is performed by an annular detector, which decreases the statistical error and improves the measurement accuracy. The limit of impurity detection is 1014 at/cm2 for light impurities and 1012 at/cm2 for heavy impurities.

Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns

Data on erosion and melting of beryllium upper limiter tiles, so-called dump plates (DP), are presented for all three campaigns in the JET tokamak with the ITER-like wall. High-resolution images of the upper wall of JET show clear signs of flash melting on the ridge of the roof-shaped tiles. The melt layers move in the poloidal direction from the inboard to the outboard tile, ending on the last DP tile with an upward going waterfall-like melt structure. Melting was caused mainly by unmitigated plasma disruptions. During three ILW campaigns, around 15% of all 12376 plasma pulses were catalogued as disruptions. Thermocouple data from the upper dump plates tiles showed a reduction in energy delivered by disruptions with fewer extreme events in the third campaign, ILW-3, in comparison to ILW-1 and ILW-2. The total Be erosion assessed via precision weighing of tiles retrieved from JET during shutdowns indicated the increasing mass loss across campaigns of up to 0.6 g from a single tile. The mass of splashed melted Be on the upper walls was also estimated using the high-resolution images of wall components taken after each campaign. The results agree with the total material loss estimated by tile weighing (~130 g). Morphological and structural analysis performed on Be melt layers revealed a multilayer structure of re-solidified material composed mainly of Be and BeO with some heavy metal impurities Ni, Fe, W. IBA analysis performed across the affected tile ridge in both poloidal and toroidal direction revealed a low D concentration, in the range 1–4 × 1017 D atoms cm−2.

Observation of a fully non-inductive H-mode regime dominated by the sporadic-small edge-localized modes in EAST with a tungsten divertor

Here we report a fully non-inductive H-mode operation with a sporadic-small-edge-localized mode(ELM)-dominant pedestal realized in EAST with a tungsten divertor, where the normalized electron collisionality at the pedestal top is estimated below unity. This is regarded as the expansion and/or supplement of our previous research having been preliminarily reported (section 4.2 in (B N Wan et al 2017 Nucl. Fusion 57 102019)) in the EAST overview article contributed to the special issue on FEC 2016 summaries and overviews. In this operation, spontaneous avoidance of large ELMs is realized reproducibly, for the first time on EAST, at a lower collisionality (below unity) at the pedestal top, profiting from high heating power. Besides, this regime shows the well controlled bulk plasma density and light impurity concentration, good energy confinement with H98, (y2) ≃ 1, together with a loop voltage very close to zero. All of these features are considered critical to a steady-state operation with high performance, which EAST is on target to demonstrate in the near future in support to the International Thermonuclear Experimental Reactor (ITER). However, this operation regime suffers a continuous accumulation of medium-/high-Z impurities, which may seriously limit its sustainability. The resonant magnetic perturbation (RMP) with a dominant toroidal mode number n = 1 has been employed for assisting exhaust of heavy impurities, which is, unfortunately, not successful since the RMP with an effective poloidal spectrum always brings back large ELMs. This scenario transits to an ELM H-mode regime as plasma current is decreased, and elimination of large ELMs is well reproduced by ELITE simulation. Finally, we present a discussion on the potential mechanism eliminating large ELMs, which seems to highlight the LHW-induced profound change in edge magnetic topology.

Scenario development for D–T operation at JET

The JET exploitation plan foresees D–T operations in 2020 (DTE2). With respect to the first D–T campaign in 1997 (DTE1), when JET was equipped with a carbon wall, the experiments will be conducted in presence of a beryllium–tungsten ITER-like wall and will benefit from an extended and improved set of diagnostics and higher additional heating power (32 MW neutral beam injection + 8 MW ion cyclotron resonance heating). There are several challenges presented by operations with the new wall: a general deterioration of the pedestal confinement; the risk of heavy impurity accumulation in the core, which, if not controlled, can cause the radiative collapse of the discharge; the requirement to protect the divertor from excessive heat loads, which may damage it permanently. Therefore, an intense activity of scenario development has been undertaken at JET during the last three years to overcome these difficulties and prepare the plasmas needed to demonstrate stationary high fusion performance and clear alpha particle effects. The paper describes the status and main achievements of this scenario development activity, both from an operational and plasma physics point of view.

Application of RSM for Pb(II) and Cu(II) adsorption by bentonite enriched with [sbnd]SH groups and a binary system study

The aim of this study is to remove Pb(II) and Cu(II) ions in binary and single solutions with bentonite enriched with SH groups (BSH) and to optimize the adsorption conditions by using Response Surface Methodology (RSM). Some parameters (initial pH, initial metal concentration, adsorbent dosage and contact time) affecting the adsorption were optimized with Central Composite Design (CCD) under RSM. Optimum values for removal of Pb(II) and Cu(II) by BSH were obtained from the quadratic model generated from CCD. The optimal points for initial pH, initial concentration, adsorbent dosage and contact time obtained by the numerical analysis were 5.10, 32.98 mg/L, 146 mg and 146.01 min. for Pb(II), while these values were 4.52, 37.9 mg/L, 152.3 mg and 146.12 min. for Cu(II), respectively. At the optimum values, maximum Pb(II) and Cu(II) removal were obtained as 95.05% and 91.4%, respectively. Adsorption data for both metal ions were observed to conform with the pseudo-second order kinetic model and Freundlich isotherm model equation. In addition, owing to observation of the competitive effect in the removal of Pb(II) and Cu(II) ions by BSH, some binary system experiments were carried out under optimum conditions obtained for the single system. The selectivity adsorption order of BSH was determined as Pb(II) > Cu(II). Considering all this, it was shown that BSH has great potential applications for the removal of heavy metal impurities from aqueous solutions.

Investigation of cavitation and vibration processes in the technology of treatment of the contaminated liquids

This article considers the problems of treatment of contaminated liquids. Scientific works of home and foreign authors were analysed and according to this analysis it was made the conclusion. Experimental studies of the process of treatment of the contaminated liquids, in which the cavitation process in the technology of treatment of the contaminated media were investigated, as well as the process of treatment of the contaminated media in a vibration and centrifugal unit . As a result of the research, it was discovered that the cavitation method can be effectively used to treat water from heavy mechanical impurities, which makes it possible to carry out further filtration in fine filters. A vibration-rotary unit, developed in Belgorod State Technological University n.a. V G Shukhov, (Russia) at the Department of Technological Complexes, Machines and Mechanisms, was taken as a technical object, where experimental investigation of treatment of the contaminated liquids was carried out. It was also carried out the research of the stepwise process of treatment of the contaminated liquids in the developed unit. On the basis of these results the authors propose to use a stepwise method of treatment of liquid media: cavitation effect - for the preliminary phase of treatment and vibration-rotary effect – for the final stage of treatment.

Impurity transport driven by parallel velocity shear turbulence in hydrogen isotope plasmas

Turbulent impurity transport driven by parallel velocity shear (PVS) turbulence in hydrogen isotope plasmas is studied using the gyrokinetic theory in a slab configuration with weak magnetic shear. The quasi-linear impurity flux written in terms of diffusion and convection is analytically derived. It is found that PVS turbulence leads to an inward impurity convection. For high temperature helium ash from deuterium (D) and tritium (T) reaction, the turbulent impurity flux could be outward because the impurity diffusion dominates over the inward convection. Therefore, PVS turbulence might be beneficial for removing high temperature helium ash in future burning plasmas. Moreover, both the outward flux and diffusivity of helium ash are enhanced by increasing PVS, but reduced by decreasing the temperature of helium ash. For fully ionized light impurities with finite concentration and the trace heavy metal impurities, the stronger sheared parallel velocity as well as the steeper parallel velocity profile, the more serious accumulation of impurity. Thus, PVS turbulence might be a partial explanation for experimental observation of impurity accumulation in the neutral beam heated plasmas. While, the increase of the electron density gradient may be favorable for stabilizing the PVS mode and easing the accumulation of impurities from plasma-wall interaction or external injection. Furthermore, isotopic effects (increasing the effective hydrogen isotope mass number) are favorable for both removing helium ash and easing the accumulation of heavy metal impurities induced by PVS turbulence. More implications of these theoretical results to the future burning plasmas are discussed.