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The paper presents computer simulation studies of burst injection of carbon and tungsten dust particles in DIII-D-like edge plasmas. The injection causes a large transient influx of the low- and high-Z impurities associated with the dust ablation in the plasmas. The dust transport and the effects of the ablated impurities on the edge plasma dynamics in a modern mid-size tokamak geometry are investigated for low- and high-power plasma discharge conditions. The core plasma contamination with dust-ablated impurities and the factors affecting it are evaluated.

In this paper, we present a brief historic overview of the research on dust in fusion devices with carbon plasma-facing components and then highlight the most recent developments in the post-carbon era of the field. In particular, we consider how the metallic dust form, mobilize, and interact with fusion plasmas and plasma facing components. Achievements in wall conditioning and associated anomalous plasma transport modification, including ELM suppression, with the powder injection technique is another focus of the paper. Capabilities of the state-of-art simulation tools to describe different aspects of dust in fusion devices are exemplified and new directions for future dust studies are brought forward.

It is shown that stationary non-spherical dust grains immersed into stationary magnetized plasma can experience the [Formula: see text] force due to electric current flowing through the grain. The electric current can be caused by different patterns of electron and ion fluxes impinging on the grain.

Solutions of a 1D model of the scrape-off layer and a divertor plasma in a tokamak are analyzed on the basis of dimensionless parameters governing the physics of both plasma and neutral transport and atomic physics processes. Numerical simulations based on fluid plasma and Monte Carlo neutral modeling confirm earlier results obtained with simplified analytic considerations and numerical simulations performed with fluid neutral description and demonstrate bifurcation of plasma parameters. These simulations also confirm that the major physical reasons for the rollover of the plasma flux to the target, which is the key feature of the phenomenon of divertor plasma detachment, are the impurity radiation loss and plasma recombination. It is suggested that simulations of the edge plasma based on dimensionless parameters provide a powerful tool for checking the consistency of the physics incorporated in existing complex 2D codes used for edge plasma modeling.

Contrary to statements from some recent papers, the bifurcation of the scrape-off layer and divertor plasma parameters, as described within a 1D model, does exist. The analysis of both numerical simulations and experimental data shows that the real physical reasons that can cause a strong reduction of the plasma particle flux to the targetjdare impurity radiation loss and volumetric plasma recombination. Fitting the parameter describing the ‘plasma momentum removal’, based on the results of 2D numerical simulations, then using this fit in subsequent analytic expressions forjd, and finally interpreting the evolution ofjdas the result of elastic plasma-neutral interactions break the causality principle and lead to a wrong physical picture of divertor plasma detachment.

Divertor plasma detachment is analyzed from the viewpoint of energy and particle balance in the edge plasma. It is shown that volumetric recombination and impurity radiation losses are responsible for the transition to the detached plasma regime, whereas “momentum removal” plays although important, but auxiliary role providing conditions necessary for the first two to become efficient. A criterion of the local (on an isolated flux tube) detachment onset is studied for both pure and impurity-seeded plasmas. Keywords: Divertor, Detachment, Impurity, Recombination

The transport of hydrogen isotopes in solids is an important problem for a series of applications, in particular, for future thermonuclear reactors. The main processes determining transport are the diffusion of dissolved hydrogen and its interaction with lattice defects. It is known that vacancies in a metal can capture not only one hydrogen atom, but several at the same time. General equations describing hydrogen transport in this case are presented. Special attention is focused on the influence of this effect on the thermal desorption spectra. An experimental scheme making it possible to establish the capture of several atoms to traps is proposed.

In this paper we report on the ability of a compact current driver yielding 250 kA in 150 ns to produce counter-propagating plasma flows. The flows were produced by two vertically-opposed conical wire arrays separated by 1 cm, each comprised of 8 wires. With this array configuration, we were able to produce two supersonic plasma jets with velocities on the order of 100–200 km/s that propagate towards each other and collide. Aluminum wires were tested first; we observed a shock wave forming at the collision region that remained stationary for an extended period of time (∼50 ns) using optical probing diagnostics and Extreme Ultraviolet imaging. After this period, a bow shock is formed that propagates at 20 km/s towards the cathode of the array, likely due to small differences in the density and/or speed of the jets. The inter-jet ion mean free path was estimated to be larger than the shock scale length for aluminum, indicating that the shock is not mediated by collisions, but possibly by a magnetic field, whose potential sources are also discussed. Radiative cooling and density contrast between the jets were found to be important in the shock wave dynamics. We studied the importance of these effects by colliding jets of two different materials, using aluminum in one and copper in the other. In this configuration, the bow shock was observed to collapse into a thin shell and then to fragment, forming clumpy features. Simultaneously, the tip of the bow shock is seen to narrow as the bow shock moves at a similar speed observed in the Al–Al case. We discuss the similarity criteria for scaling astrophysical objects to the laboratory, finding that the dimensionless numbers are promising.

We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.

Increasing the quality of hydrojet cleaning can be provided by employment of additives, which provide dilatant properties to the water-abrasive pulp, i.e., increase viscosity with an increase in flow velocity. However, the use of any methods of hydrocleaning creates conditions for intense corrosion of a cleaned moist surface. The rate of development of corrosion centers of carbon steel after hydroabrasive and abrasive-dilatant cleaning and the influence of a series of corrosion inhibitors are analyzed. It is shown that optimal inhibitors are quite efficient and can decelerate the rate of formation and growth of corrosion centers by a factor of 10.

This article is devoted to the development of the production of 99Mo used in nuclear medicine. The stages in the development of the production of 99Mo and molybdenum-technetium generators are shown. Production has increased several-fold over the period 2009–2013 and meets the demand of domestic nuclear medicine. The problem of recycling the uranium from an irradiated target after 99Mo is extracted from the target is important and strongly influences the price of 99Mo. A technology for reprocessing uranium-containing tailings with the uranium obtained being returned into the 99Mo production cycle has been developed at the Scientific-Research Institute for Physical Chemistry. This has eliminated the need to purchase expensive high-enrichment uranium for targets and has made it possible to use the uranium remaining from the reprocessing of irradiated targets.

The problem of uranium regeneration from uranium-containing residues after irradiating a uranium target and isolating from it 99Mo for use in nuclear medicine is considered. It is shown to be possible to produce 99Mo of quality required for charging a 99mTc generator from the regenerated 235U. The service characteristics of the 99mTc generator based on secondary 99Mo fully meet the Technical Specifications for the standard 99mTc generator, and the quantitative characteristics of sodium pertechnetate meet the requirements of Russian and international pharmacopoeias.

The rate of corrosion damage development on steel after hydroabrasive and abrasive dilatant cleaning treatment, as well as the effect of some inhibitors on the rate of corrosion development on specimens cleaned by different methods have been studied. It has been shown that abrasive-dilatant treatment combined with inhibition efficiently hinders corrosion on freshly-cleaned surfaces and can slow down the formation and growth of corrosion sites by an order of magnitude.

An acoustic method for quality control of adhesive compounds of polymer coating on metal in the coating—positive system qualitatively characterizing the value of the adhesive bond is proposed. Ultrasonic measuring cell is considered as a resonant system, the parameters of which are determined by the properties of all the parameters of the layered structure at the same properties of the piezoelectric sensor and acoustic contact. The coating adhesion is evaluated on the basis of the parameters of the amplitude-frequency characteristics of the studied layered structure of the composite coating according to the humming dependences of the adhesion — reflection coefficient the wave. The technique allows to control the processes of polymerization of organic coatings in the process of their formation.

The rheological properties of bentonite clay-filled aqueous solutions of high-molecular-mass poly(ethylene oxide) (PEO) have been studied. The PEO solution is a typical polymer solution characterized by the highest Newtonian viscosity and the range of non-Newtonian flow. The addition of small amounts of bentonite to the PEO solution causes passage to a viscoplastic behavior that manifests itself as the appearance of the yield stress. Therewith, the flow at the highest Newtonian viscosity in the region of low shear stresses (rather than rates) remains possible. After passing through the yield stress, the effect of antithixotropy, i.e., an increase in the viscosity with the deformation rate in a certain shear rate region, has been observed for the multicomponent systems. The data obtained have been interpreted assuming that the addition of the solid filler to the polymer solution destroys the random network of entanglements between macromolecules, while the presence of the polymer in the clay suspension reduces the strength of the coagulation structure of bentonite.

Previous Staged Z-pinch experiments have demonstrated that gas liners (or puffs) can efficiently couple energy to a target plasma and implode uniformly, producing plasmas in High Energy Density (HED) regimes. In these experiments, a 50 kJ, 1.5 MA, 1 μs current driver was used to implode a magnetized, Kr liner onto a D+ target, producing 1010 neutrons per shot. Time-of-flight data suggested that primary and secondary neutrons were produced.

We discuss the design and characterization of a compact gas-puff nozzle and plasma gun assembly that will be used in Staged Z-pinch experiments1, where gas liners are imploded onto an on-axis target-plasma column. Previous work on the Staged Z-pinch demonstrated that gas liners can efficiently couple the energy and produce a uniform implosion on a target-plasma.2

Technological aspects of 99Mo production from 235U at the VVR-ts nuclear reactor are considered. The nuclear target design with which the formation of liquid and solid wastes is reduced to a minimum and the forced system for cooling of nuclear targets in experimental channels of the nuclear reactor are reported. Schemes of 99Mo isolation from 235U fission products and of 235U regeneration after 99Mo isolation are described. The 99Mo and, correspondingly, 99m Tc produced from the regenerated 235U fully meet the technical specification and pharmacopoeial monograph for sodium pertechnetate.

A one-dimensional model describing recycling of hydrogen isotopes in fusion reactors is proposed. The dispersion relation for thermal instability caused by plasma-wall interaction is derived, and conditions under which it develops are determined. It is shown analytically and numerically that this instability can develop under typical tokamak conditions.

The convective radial transport effects of SOL turbulence have been estimated using recent turbulence data from the gas puff imaging (GPI) camera diagnostic on Alcator C-Mod. The average radial turbulence speed within the region 1-2 cm outside the separatrix near the outer was calculated by a 2-0 cross-correlation technique to be V-t similar to 0.2-0.3 km/s. Assuming this to be the local convective plasma velocity, the density SOL width lambda(n) was evaluated using a simple convective model to be lambda(n) similar to 4-7 cm, which is similar to 2-3 times higher than that measured using a Langmuir probe. This convective velocity was also similar to 2-3 times lower than the velocities estimated from analytic blob models, but showed a similar scaling with plasma current at constant q(95). The measured blob speeds were lower than both the convective speeds and the analytic blob model speeds.

Autoscala was applied to ionograms recorded by the digital AIS-Parus ionosonde, built at the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, Russia, and installed in Moscow (55.5N, 37.5E). Some results in regard to the reliability of the foF2, foF1, and ftEs autoscaled characteristics are presented and discussed. The flexibility of Autoscala is illustrated based on its modular structure.

Resonant modes of multi-layer structures which contain the regions of negative epsilon material (such as a metal in the visible range) are analyzed. Existence of two separate classes of resonant modes is demonstrated. One is related to the excitation of the surface mode at the interface of the regions with opposite signs of the dielectric constant and involve energy transport by evanescent modes throughout the whole structure. The second class involves propagating modes (which form the resonant standing wave) in some regions and the evanescent waves in other layers with " < 0. It is shown that the resonant transmission is related to the existence of quasi-stationary leaky modes having a flnite life-time and characterized by large wave amplitude in the trapping region. It is shown that both types of

It is shown that turbulent interactions of two interpenetrating plasma clouds can cause seeding of the large scale-length magnetic field. This process becomes especially pronounced when clouds have the ions with different Z/M ratios.

Linear and nonlinear stability of blob propagation in the tokamak scrape off layer (SOL) and in the SOL/shadows of linear devices are studied. It is found that the most stable blobs, which can propagate as coherent structures for large distance, are the blobs with some specific spatial scale. Larger blobs are subject to the Rayleigh–Taylor (RT) instability, which breaks the blob apart and effectively reduces the scale of new structures. Smaller blobs evolve into mushroom structures typical for nonlinear stages of the RT and Richtmyer–Meshkov instabilities in fluids. Biasing of divertor targets can affect the dynamics of blob propagation. For a large magnitude of biasing potential, a strong deformation and even disintegration of the blob as a coherent structure were observed while the blob passes through the biased region.

We present the design of a gas-puff injector for liner-on-target experiments. The injector is composed of an annular high atomic number (e.g., Ar and Kr) gas and an on-axis plasma gun that delivers an ionized deuterium target. The annular supersonic nozzle injector has been studied using Computational Fluid Dynamics (CFD) simulations to produce a highly collimated (M > 5), ∼1 cm radius gas profile that satisfies the theoretical requirement for best performance on ∼1-MA current generators. The CFD simulations allowed us to study output density profiles as a function of the nozzle shape, gas pressure, and gas composition. We have performed line-integrated density measurements using a continuous wave (CW) He–Ne laser to characterize the liner gas density. The measurements agree well with the CFD values. We have used a simple snowplow model to study the plasma sheath acceleration in a coaxial plasma gun to help us properly design the target injector.

We report on counter-propagating plasma flows produced by two vertically opposing conical wire arrays using a compact, low inductance Linear Transformer Driver (LTD) “GenASIS” capable of producing 250 kA in about 150 ns. Laser interferometry and laser schlieren were performed with the use of a Nd:YAG 532 nm laser, with a pulse width of 5 ns. A shock wave formed by jet interaction was clearly observed and remained stationary for at least 50 ns. Interferometry data showed that the ion density of the jets prior to collision was of the order of 2×1017cm−3 and a jump in density of ∼ 5 was observed at the shock wave region. A lower limit of ∼ 100 km/s has been measured for the jet velocity. The ion mean free path has been estimated to be ∼ 12 mm, which is larger than the shock wave scale ∼ 5 mm, and hence the shock wave approaches the collisionless regime. Magnetic field advection, which can drastically modify the conditions for shock wave formation, will be discussed. Kinetic particle-in-cell modeling using LSP code has also been implemented and benchmarked against the experimental results in order to study the underlying physics of formation and evolution of the shock.

Ad hoc sinks and sources of turbulence are added in the two-dimensional (2D) magnetized plasma model to mimic excitation and damping of the modes. Depending on linear growth and damping rates and sink and source localizations, two kind of the turbulence and large scale flows evolution regimes were found: quasisteady state and dynamic. The quasisteady states with saturated averaged energy and enstrophy are characterized by strong large scale flows generated due to the inverse cascade in the nonlinear mode coupling. It is shown that for the adopted model there is not complete stabilization of high-k harmonics (microturbulence) by the generated zonal flows and convective cells. The dynamic regimes are characterized by nonvanishing energy and enstrophy fluctuations around averaged values and the energy spectrum has maximum, which corresponds to the turbulence source. The inverse cascades in these regimes are suppressed by the mode damping in the k-space sink region.

An analytical model of a magnetron glow discharge is considered, assuming classical electron and ion transport across the magnetic field lines. The theoretical volt-ampere characteristic of the discharge is obtained. The shape of this characteristic is similar to that found in experiments. However, the experimental current densities exceed the theoretical ones calculated with the present model. Possible reasons for this discrepancy between theoretical calculations and experimental results are discussed.

The nonlinear evolution of radiative modes with the effects of finite recombination time were studied in a uniformly magnetized quasi two-dimensional plasma. In the one-dimensional limit, it was found that a plasma in noncoronal equilibrium (impurities evolve at a slower rate than the temperature), radiative modes were modestly more stable and evolved at a slower rate. A new unstable state was found in which the plasma initially cooled, only to grow unstable to the radiative condensation mode. This nonlinearly unstable regime has a stability boundary an order of magnitude higher than that predicted by linear theory. For a parameter regime appropriate to the tokamak edge, the nonlinear condensation mode proved to be more unstable in noncoronal equilibrium than in coronal equilibrium. When two-dimensional effects were added, little difference was found in the behavior of the mode in coronal equilibrium, but in noncoronal equilibrium, a new state evolved in which the condensation initially grew, but then flattened as the plasma continued to heat at a constant rate. The results provide insight as to why condensations are observed in tokamaks when they are seemingly stable to condensation modes.

Plasma flow through the gas cloud in a tokamak divertor for ‘‘gas box’’ divertor geometry and Knudsen regime of neutral transport is investigated. It is shown that similar to the neutral models that have considered previously, (i) plasma parameters near the target is sensitive to the energy flux into the hydrogen recycling region and can change rapidly, resulting in bifurcation‐like behavior, which might be interpreted as a transition to detached regime, (ii) plasma flux onto the target starts to decrease at a very low plasma temperature near the target, while a strong pressure drop already occurs. At low plasma temperature near the target the recombination processes can significantly alter the plasma flux onto the target.

The role of edge turbulence in detached divertor plasmas is investigated. It is shown that the edge turbulence, through poloidal transport of parallel momentum, can produce a significant plasma pressure drop along the magnetic field lines toward the divertor plate, a feature that characterizes the detached divertor plasma regime.

The kinetics of neutral atoms in a plasma undergoing charge‐exchange, ionization, and recombination is considered. It is shown that if the mean‐free path divided by the macroscopic scale length is constant, it is possible to introduce self‐similar variables in the Boltzmann equation for the neutral particles. This equation is then solved analytically, and the nonlocal transport of heat and particles is calculated. Since the mean‐free path increases with increasing energy, a one‐sided, high‐energy tail is formed in the neutral distribution function. This tail may contribute significantly to the heat and particle fluxes. When this is the case, the fluid approximation of these quantities breaks down at arbitrarily short mean‐free paths.

The erosion of divertor targets caused by high heat fluxes during transients is a serious threat to ITER operation, as it is going to be the main factor determining the divertor lifetime. Under the influence of extreme heat fluxes, the surface temperature of plasma facing components can reach some certain threshold, leading to an onset of intense material evaporation. The latter results in formation of cold dense vapor and secondary plasma cloud. This layer effectively absorbs the energy of the incident plasma flow, turning it into its own kinetic and internal energy and radiating it. This so called vapor shielding is a phenomenon that may help mitigating the erosion during transient events. In particular, the vapor shielding results in saturation of energy (per unit surface area) accumulated by the target during single pulse of heat load at some level Emax. Matching this value is one of the possible tests to verify complicated numerical codes, developed to calculate the erosion rate during abnormal event...

The effect of the radial electric field on neoclassical orbits in a tokamak using the integrals of drift motion is considered. It is shown that for the most interesting case of high radial electric field shear, due to a dramatic change of the particle orbit topology at a distance of the order of one particle orbit width, it is not correct to apply local theory to describe neoclassical transport processes. For step‐like electrostatic potentials typical for the tokamak plasma periphery in the high (H) mode, the trajectories of the particles can be either squeezed or expanded depending on the location of the potential jump with respect to the unperturbed particle trajectories. The widening of the orbits decreases the threshold energy of suprathermal particles which can be promptly lost and enhances the ion prompt losses which might increase the amplitude of the potential step. It is shown that these effects are more pronounced for a diverted tokamak with the X point located at the inner side of the torus. Si...

A kinetic modelling of 1d collisional and 2d Vlasov magnetic SOL's using the W1 and W2 particle codes is presented. Deviation of the distribution function from the equilibrium one is shown, as well as the possibility of kinetic instability in diverted plasmas.

Preliminary results of the edge tokamak plasma simulation in the frame of 3D kinetic Vlasov-Fokker-Planck equations are presented. Currently two versions of the code are developed: one of them is based on a stochastic modeling method, another uses a finite difference approach via split techniques. In both versions, the self-consistent electric field may be calculated from the quasi-neutrality condition, while the sheath potential is obtained from the ambipolarity of plasma flux towards the neutralizing plate. Simplified equations, describing the dense SOL plasma parameters distributions and allowing the analytical solutions are obtained. It is shown, that for the high particle recycling in SOL, the radial scales of the temperature Δ T and densities Δ n are close to each other. The reversal flow is formed within a narrow layer near the separatrix magnetic surface.

Studies of submicron dust using Mie scattering from Nd:YAG lasers and video data of micron to sub‐millimeter sized dust on DIII‐D tokamak have provided the first data of dust sources and transport during tokamak discharges. During normal operation on DIII‐D dust observation rates are low, a few events per discharge or less. The net carbon content of the dust corresponds to a carbon atom density a few orders of magnitude below the core impurity density. Statistical analysis of Mie data collected over months of operation reveal correlation of increased dust rate with increased heating power and impulsive wall loading due to edge localized modes (ELMs) and disruptions. Generation of significant amounts of dust by disruptions is confirmed by the camera data. However, dust production by disruptions alone is insufficient to account for estimated in‐vessel dust inventory in DIII‐D. After an extended entry vent, thousands of dust particles are observed by cameras in the first 2–3 plasma discharges. Individual par...

Dust may have a large impact on ITER‐scale plasma experiments including both safety and performance issues. However, the physics of dust in fusion plasmas is very complex and multifaceted. Here, we discuss different aspects of dust dynamics including dust‐plasma, and dust‐surface interactions. We consider the models of dust charging, heating, evaporation/sublimation, dust collision with material walls, etc., which are suitable for the conditions of fusion plasmas. The physical models of all these processes have been incorporated into the DUST Transport (DUSTT) code. Numerical simulations demonstrate that dust particles are very mobile and accelerate to large velocities due to the ion drag force (cruise speed >100 m/s). Deep penetration of dust particles toward the plasma core is predicted. It is shown that DUSTT is capable of reproducing many features of recent dust‐related experiments, but much more work is still needed.

This paper considers impurity (helium) ion transport kinetics in a tokamak divertor along magnetic field lines, both analytically and numerically, for the case when the ratio of collisional mean-free-path to the characteristic length of plasma parameter variation is not too small. To obtain the numerical solution of the kinetics equation, the stochastic modeling method is used. For International Thermonuclear Experimental Reactor (ITER) divertor plasma conditions, the influence of thermal force on helium ions is expected to be decreased considerably. As a result, the helium ion flux toward the divertor plates may be significantly enhanced compared to that predicted by the hydrodynamics approach.