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This study developed a prototype of a wire-plate air bubbling plasma reactor that can be easily scaled up for wastewater treatment. The electrical characteristics, including the discharge current and average power consumed, of the developed reactor were deeply investigated at different operating parameters and solution conductivities. The performance of the reactor was examined on the basis of energy efficiency and methylene blue (MB) decoloration efficiency. Moreover, the removal of the total organic carbon and the changes of the physicochemical properties of solution, including pH, conductivity, and temperature, were evaluated. The analysis of current discharge and average power consumed showed that the discharge mode in the present reactor is a filamentary streamer. Interestingly, the solution conductivity had no effect on the average power consumed at low applied voltages, due to confinement of the discharge in a small area surrounding the discharge electrode in the gas phase. However, at relatively high voltages, the effect of conductivity on the average power consumed was noticeable, yet it had no effect on the decoloration efficiency at the same average power. The present reactor showed a high energy-efficiency value of 42 g/kWh at 50% decoloration of 30 mg/l MB solution, but it dropped to 14 g/kWh at 97% decoloration. A first-order kinetics model described well the decoloration reaction rates and the overall rate constant correlated linearly to the average power. [ABSTRACT FROM AUTHOR]

The lower hybrid current drive (LHCD) plays an important role in the long pulse and high performance experiments on the EAST Tokamak, using LHW systems with frequencies of 2.45 GHz and 4.6 GHz. With the initial parallel refractive index mostly peaking at n ∥ ∼ 1.8 − 2.1 , it is difficult to have on-axis LHCD due to the accessibility conditions which prevents the LHW from propagating into the plasma core. However, according to the investigation of HXR diagnostics, LHW did provide an on-axis current drive in an EAST experiment. To interpret this on-axis LHCD phenomenon, various physics effects that give rise to variations in parallel wave numbers, thus influencing the propagation and the absorption of the LHW, have been taken into account, such as toroidal effects, full wave effects with focusing and diffraction, and scattering effects due to density fluctuations. Numerical tools including ray-tracing and full wave codes that contain one or two of the above physics effects have been used to model the heating and current drive of the LHW on EAST. Linear Landau damping and quasi-linear Landau damping have been compared by using the coupling between ray-tracing and the Fokker-Planck codes. Convergence studies have been performed for the full wave modeling, the maximum poloidal modes in the full wave have been scanned, and the results are compared with each other. The factors that characterize the amplitude, the radial thickness, and the location of the density fluctuations have been studied and scanned. The measurement of HXR diagnostics has been compared with synthetic diagnostics by reconstructing the HXR data from both the standard GENRAY/CQL3D LHCD modelling and the modeling taking the scattering effects into account. [ABSTRACT FROM AUTHOR]

In this paper, we report the results of ion cyclotron resonance frequency (ICRF) heating in the central cell of a fully axisymmetric tandem mirror. With a total power of 100 kW radiated by double half-turn and half-turn antennas, the plasma diamagnetism increases by 15-fold, with a corresponding peak β ⊥ ∼2%, density ∼ 1.5 × 10 18 m − 3 , and total temperature ∼60 eV. The effects of the magnetic configuration on resonance heating and wave emission are studied by varying the magnetic fields at the midplane and at the location of the antennas, respectively; the results confirm that the magnetic beach configuration is key to successful ICRF heating. The axial phase speed measurements suggest that the excited wave is a slow wave in the plasma core and a fast wave at the edge. [ABSTRACT FROM AUTHOR]

A systematic investigation of the expansion dynamics of plasma plumes generated by two Q-switched Nd:YAG lasers at 1064 nm wavelength operating on a silicon target was undertaken for the inter-pulse delay times of 0, 100, 200, and 400 ns using a technique involving fast-gated intensified charge-coupled device imaging. Our results indicate that the plasmas exhibit free expansion in a vacuum environment at an inter-pulse delay time of 0 ns. With increasing inter-pulse delay time, the plasma front becomes sharpened and an interaction boundary is formed. Moreover, using the radiation intensity distribution along the plasma axis of symmetry, the formation and evolution mechanism of the plasmas generated by the double pulses was analyzed at different inter-pulse delay times. Finally, the experimental results of the expansion of the plasma core and front were compared with a radiation hydrodynamics model and a drag model, and were found to be generally in good agreement. [ABSTRACT FROM AUTHOR]

ENEA and Ansaldo Nucleare S.p.A. are currently working on the fabrication of full scale prototypes of inner vertical target component for ITER (International Thermonuclear Experimental Reactor). The requirements is to manufacture a component by means of a qualified technology which uses armour and cooling pipe materials defined by ITER organization specification. A dedicated new Hot Radial Pressing facility was designed and finally installed in ENEA for the fabrication of the full scale Plasma Facing Units of the inner vertical target component prototype. HRP technology was widely tested with small mock-ups and medium qualification prototypes but its applicability to fabricate full scale units has to be anyway demonstrated and, therefore, their joint quality and also dimensions and shape has to be properly checked. The compliance of the joint quality with the acceptance criteria is then performed by ultrasonic water gap technique, using the qualified ENEA testing equipment. Dimensional check is performed as well by analyzing acquired data points compared to the reference drawings and 3D model. [ABSTRACT FROM AUTHOR]

The plasma in the tokamak JT-60SA is initiated mainly by operating the four Switching Network Units (SNUs) inserted in the four modules of the Central Solenoid. In the framework of the “Broader Approach” agreement, these four SNUs were procured by the European Union. This paper presents the final assembly of the SNU system and the main tests performed in the last years before shipping it to Japan. The experimental results demonstrated the capabilities of the SNUs to comply with the JT-60SA requirements, even with better performances. [ABSTRACT FROM AUTHOR]

The F4E, Amec Foster Wheeler and INL comprehensive methodology for fusion breeding blanket accident analysis starts with the selection of reference accident scenarios, the development of detailed accident analysis specifications and the assessment of analysis codes. Models of each TBS are then constructed using the selected codes (MELCOR and RELAP5-3D) and modelling approaches. The models are qualified according to a test matrix including comparison with TBM finite element design analyses, code-to-code comparisons for both TBS normal operation and transient cases, and sensitivity studies for accident scenarios. The qualification test cases that are executed gradually move from models of separate systems to complete TBS models, and from the simulation of steady-state and normal plasma pulse operation to consideration of power excursions, operational transients and accident events. Finally, both of the qualified models are used to analyse a selected accident scenario (a 32 h loss-of-offsite power) together with sensitivity studies dedicated to the evaluation of uncertainties. This step completes the qualification process. The results obtained in the qualification of the EU HCLL TBS models are reported in the paper. [ABSTRACT FROM AUTHOR]

The realization of the 19.6 m 2 highly heat loaded part of the divertor of Wendelstein 7-X (W7-X) requires the installation of 890 target elements. A target element is made of a CuCrZr copper alloy heat sink armored with carbon fibre reinforced carbon CFC NB31 tiles. The industrial production of the target elements by the Austrian company PLANSEE SE needed 5 years. The successful delivery of a total of 973 target elements (armored with ∼16,200 tiles) was based on an efficient quality assurance throughout the production by the manufacturer: 44 different quality examinations for 82 manufacturing steps. It was followed by an intensive quality assessment by IPP: visual inspections, dynamic pressure tests, He-leak testing in vacuum oven, high heat flux testing. The quality of the delivered elements, and in particular the reliability of the bonding between CFC tiles and heat sink, was confirmed by high heat flux testing on the basis of a statistical approach. The essential recovery of CuCrZr properties after ageing processes was confirmed by the measurement of hardness and electrical conductivity. 104 target elements (10.7%) were accepted after repair. [ABSTRACT FROM AUTHOR]

ASDEX Upgrade (AUG) is the only tokamak in Europe to have low activation ferritic steel as the inner vessel wall facing component. Together with the massive tungsten tiles in the lower divertor, AUG is the tokamak with the closest DEMO wall. The project is a first step towards the extensive use of ferritic steel in future fusion reactors. For example, the test blanket module of ITER is planned to have a ferritic steel wall and thick tungsten tiles as a plasma facing component. The ‘ad hoc’ ferritic steel built with low activation capability is known as Eurofer. As the low activation property is not a requirement for AUG, the material selected for the project is the martensitic steel P92 which is the most similar material to Eurofer from a magnetic point of view. The purpose of the project is to improve understanding of the magnetic perturbation of the ferritic steel both on the plasma and magnetic probes, evaluating and controlling these effects. Additionally, the effect of the additional forces on the supporting structure has been addressed. Bearing this in mind, in 2013 a step wise program has been started and part of the W coated graphite tiles in the region of the inner column were replaced by steel tiles [1]. The first campaign did not suffer any particular issue related to the new material. According to the calculations, the plasma was almost unperturbed, thanks also to the toroidal symmetry of the tiles inside the vessel, and the magnetic probe measurements were properly corrected [2]. Inspection of the machine pointed out some hardware problems. The graphite tiles adjacent to the steel tiles were damaged. The graphite tiles had broken edges in 5 from 64 positions and notches in many others. The coating of the graphite and steel tiles, made of tungsten and TiO respectively, was damaged. At first glance it was clear that the steel tiles were moving but it was definitely unexpected. In understanding the process, the location of the damage was the crucial hint. In fact all failures were located at the boundary between 2 vacuum vessel octants. To justify this failure mode inside the vessel, a hypothesis (about current flowing in the heat shield supporting structure) was made and FEM analyses were carried out in this direction. With extreme caution, in 2015 just one additional row of steel tiles was added together with diagnostics that confirmed the hypothesis. Now that a clear understanding of the problem has been reached, the project to add further rows of steel tiles can be continued. For the next campaign it is planned to replace all the tiles in the middle region of the heat shield together with stiffening and modification of the supporting structure. In this paper the learning process from the damage of the tiles and its causes, from the FEM analysis results to the data diagnostics will be reported. The future plans for steel tiles in AUG will be discussed. [ABSTRACT FROM AUTHOR]

In the framework of the EUROfusion DEMO project, studies are conducted in several European institutions for designing the tokamak magnet systems. In order to generate the high magnetic fields required for the plasma confinement and control, the reactor should be equipped with superconducting magnets, the reference design being based on Cable-In-Conduit Conductors (CICC) cooled at cryogenic temperatures by forced circulation of supercritical helium. In order to propose a toroidal field (TF) winding pack (WP) design compatible with DEMO requirements, CEA has developed several tools addressing the different areas related to magnet dimensioning. An accurate calculation of magnetic field along the conductors is provided by the TRAPS code, and conductor design is performed by using an integrated macroscopic home design code based on simplified models accounting for superconducting properties, mechanics and thermal. This multi-physic tool gives a realistic but not assessed design. Indeed it is based on an assumed operating temperature that must be validated with an elaborate code, since it is linked with temperature margin design criterion (1.5 K). A dedicated modelling tool was developed by coupling the THEA code for 1D thermo-hydraulics in cables and the Cast3M code for 2D transverse thermal diffusion in a limited number of coil cross-sections, enhancing the accuracy of the outputs as being a quasi-3D approach. This tool allows a better assessment of the flux exchange between WP and casing, and the modelling of inter-turn and inter-pancake thermal coupling. The coupling methodology is described, as well as its validation on the simulation of a heat exchanger. A calculation was performed on the CEA proposal for DEMO TF coil in a burn (steady state) scenario, and finally providing a realistic assessment of the temperature margin. [ABSTRACT FROM AUTHOR]

In this paper, ethanol vapor up to 50% is added to an argon, air or nitrogen dielectric barrier discharge at medium pressure to profoundly investigate the effect of ethanol addition on the surface modification of low density polyethylene (LDPE). Water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) measurements show that the ethanol vapor addition effect on the LDPE surface depends on the used carrier gas. Adding ethanol to an argon plasma has no significant effect on the wettability nor on the chemical composition of LDPE compared to a pure argon plasma treatment. Ethanol addition does however slightly increase the LDPE surface roughness. Addition of small amounts of ethanol vapor to an air plasma makes it possible to incorporate additional nitrogen and oxygen groups on the LDPE surface, resulting in an extra decrease of 11% in WCA value. Moreover, the LDPE surface roughness is slightly increased due to the ethanol vapor addition. The most significant effect of ethanol addition is however observed when nitrogen is used as carrier gas. After an N 2 /2% ethanol plasma treatment, an 85% reduction in WCA value to 8.5° is found compared to a pure N 2 plasma treatment. This very hydrophilic LDPE surface is obtained due to a significantly high incorporation of oxygen and nitrogen groups on the surface with an O/C and N/C ratio reaching 32% and 53% respectively. FTIR measurements also reveal that the observed extremely high wettability of LDPE is not the result of plasma activation but is due to plasma polymerization effects occurring on the surface resulting into the deposition of a plasma polymer containing ketones, amides as well as C N groups. In addition, ageing studies have also been conducted and these studies reveal that for all carrier gases, ethanol addition to the discharge gas significantly suppresses the ageing effect. All the above mentioned conclusions therefore indicate that ethanol vapor based plasmas can be an excellent tool to increase the surface energy of polymers. [ABSTRACT FROM AUTHOR]

In this work, CO 2 reforming with methane in the form of biogas over Ni/γ-Al 2 O 3 catalysts was carried out in a coaxial dielectric barrier discharge (DBD) non-thermal plasma reactor. The effects of various process parameters (biogas flow rate, discharge power, CO 2 /CH 4 molar ratio and Ni loading) and their interactions on the hybrid plasma-catalytic biogas reforming were evaluated using response surface methodology through a four-factor, five-level central composition design. Quadratic regression models were developed to gain a better understanding of the relationships between these process parameters (independent variables) and the biogas conversion, syngas yield and energy efficiency (responses) of the plasma reforming process. The results indicated that biogas flow rate was the most significant factor affecting the conversion of CO 2 and CH 4 and syngas yield, while the CO 2 /CH 4 molar ratio was the leading process parameter determining the energy efficiency of the process. In addition, there was a trade-off between the biogas conversion and energy efficiency of the process at different specific energy inputs (SEI). The process optimization suggested that the optimal process performance was achieved at a biogas flow rate of 56.1 ml/min, a discharge power of 60.0 W, a CO 2 /CH 4 molar ratio of 1.03 and a Ni loading of 9.5 wt.%, which was demonstrated by the reproducibility of the experimental results. Moreover, the carbon deposition on the spent catalyst was only 3.9% after running the plasma biogas reforming process for 150 min under the optimal experimental conditions. [ABSTRACT FROM AUTHOR]

Unsteady loading rates can affect the proper operation of a biofilter. In addition, biofiltration is known to be less effective when dealing with poorly soluble substances, like some volatile organic compounds (VOCs). A non-thermal plasma (NTP) produced with a dielectric barrier discharge (DBD) was studied as an option to pre-treat an air stream contaminated by a mixture of VOCs. Therefore, the plasma reactor was operated upstream of a laboratory-scale biofilter. Air admixed with toluene, n -heptane, p -xylene, ethylbenzene and benzene with average concentrations of 95.6, 49.4, 60.8, 47.3 and 36.6 ppm, respectively, was used as a model polluted gas, as these contaminants represent the air stripped by an oil-refinery wastewater treatment plant. Peaks of loading rates at the inlet of the biofilter were simulated by the increase of the flow rates of VOCs. The operation of NTP, with specific energy densities between 92 J L −1 and 256 J L −1 allowed reducing the VOC concentrations down to the level of optimal biofilter operation. In addition, non-water soluble VOCs were converted to more soluble compounds by the plasma treatment. In this first attempt to investigate the synergies between NTP and biofiltration, NTP reveals as a promising option to pre-treat effluents upstream of biofilters for optimized operation. [ABSTRACT FROM AUTHOR]

SUMMARY Ethylene gas was decomposed using packed-bed type dielectric barrier discharge (PBDBD) plasma reactor to keep freshness of fruits. The ethylene gas was diluted with gas mixture of nitrogen, oxygen, and carbon dioxide as simulated gas in the transportation container. The PBDBD plasma was generated by a pulse switching power supply, which consisted of MOS-FET switching devices, capacitors, and pulse transformers. The Ag nanoparticle-loaded zeolite as catalyst has high activity and good performance for reduction of ozone and oxidizing carbon monoxide at room temperature. The Ag nanoparticle-loaded zeolite pellets enhanced ethylene removal efficiency and reduced ozone and carbon monoxide produced by the plasma treatment. It was confirmed that the carbon monoxide in the gas simulated dry air composition was oxidized using Ag nanoparticle-loaded zeolite with plasma treatment. [ABSTRACT FROM AUTHOR]

We have developed and fielded x-ray penumbral imaging on the National Ignition Facility in order to enable sub-10 μm resolution imaging of stagnated plasma cores (hot spots) of spherically shock compressed spheres and shell implosion targets. By utilizing circular tungsten and tantalum apertures with diameters ranging from 20 μm to 2 mm, in combination with image plate and gated x-ray detectors as well as imaging magnifications ranging from 4 to 64, we have demonstrated high-resolution imaging of hot spot plasmas at x-ray energies above 5 keV. Here we give an overview of the experimental design criteria involved and demonstrate the most relevant influences on the reconstruction of x-ray penumbral images, as well as mitigation strategies of image degrading effects like over-exposed pixels, artifacts, and photon limited source emission. We describe experimental results showing the advantages of x-ray penumbral imaging over conventional Fraunhofer and photon limited pinhole imaging and showcase how internal hot spot microstructures can be resolved. [ABSTRACT FROM AUTHOR]

The concept of the tokamak is a very good candidate to lead to a fusion reactor. In fact, certain regimes of functioning allow today the tokamaks to attain performances close to those requested by a reactor. Among the various scenarios of functioning nowadays considered for the reactor option, certain named ‘advanced scenarios’ are characterized by an improvement of the stability and confinement in the plasma core, as well as by a modification of the current profile, notably thank to an auto-generated ‘bootstrap’ current. The general frame of this paper treats the perspective of a real-time control of advanced regimes. Concrete examples will underline the impact of diagnostics on the identification of plasma models, from which the control algorithms are constructed. Several preliminary attempts will be described. [ABSTRACT FROM AUTHOR]

Neutron noise methods are well established and known techniques for the experimental analysis and surveillance of nuclear reactors. One of these methods, the variance to mean ratio or α -Feynman, is based on the measurement of the histogram of the number of counts of a detector in a subcritical reactor driven by a external neutron source. The method uses the first and second moments of the distribution of counts. As a further step in the full characterization of the distribution we compute, in addition, third and fourth moments showing the limitations of approximated counts distributions. [ABSTRACT FROM AUTHOR]

Fuel Coolant Interactions (FCIs) are important issues in nuclear reactor severe accident analysis, which have drawn much attention by experts all over the world for many years. The boundary layer stripping is one of the mechanisms that result in hydrodynamic fragmentation during FCIs, and has been studied for many years. However, the results and trends predicted by the existing fragmentation rate models based on such a mechanism are still very different from the experimental data. In this study, in order to develop a fragmentation rate model of a liquid droplet, induced by boundary layer stripping, a new velocity distribution in boundary layer is proposed, which covers two very significant parameters. Then, based on theoretical modeling and experimental data, semi-empirical correlations which can predict the fragmentation rate and the average size of fragments are established, which are verified by typical experimental data and are compared with previous model predictions. The result shows that the fragmentation rate calculated by the present model and the certain range of average fragment size are in good agreement with the experimental data, which proves that the two new parameters involved can reflect the velocity distribution in boundary layers of both the melt and coolant more appropriately and reliably. With the help of the model from IFCI and CULDESAC codes, there is reason to believe the present hydrodynamic fragmentation model could be applied in FCI codes in the future. [ABSTRACT FROM AUTHOR]

A renewed interest in experimental research on Accelerator-Driven Systems (ADS) has been initiated by the global attempt to produce energy from thorium as a safe(r), clean(er) and (more) proliferation-resistant alternative to the uranium-fuelled thermal nuclear reactors. The ADS research has been actively pursued at the Joint Institute for Nuclear Research (JINR), Dubna, since decades. Most recently, the emission of fast neutrons was experimentally investigated at the massive ( m = 512 kg) natural uranium spallation target QUINTA . The target has been irradiated with the relativistic deuteron beams of energy from 0.5 AGeV up to 4 AGeV at the JINR Nuclotron accelerator in numerous experiments since 2011. Neutron production inside the target was studied through the gamma-ray spectrometry measurement of natural uranium activation detectors. Experimental reaction rates for ( n,γ ), ( n,f ) and ( n ,2 n ) reactions in uranium have provided valuable information about the neutron distribution over a wide range of energies up to some GeV. The experimental data were compared to the predictions of Monte Carlo simulations using the MCNPX 2.7.0 code. The results are presented and potential sources of partial disagreement are discussed later in this work. [ABSTRACT FROM AUTHOR]

Thermo-mechanical behavior of fuel rod is of great importance for safety assessment of nuclear reactors. This paper deals essentially with the mechanical description of pressurized water reactor (PWR) fuel rods under long-term burnups. The main goal of the work is generation of a numerical code for study of pellet–cladding interaction (PCI) as long-term phenomena in Bushehr nuclear power plant (BNPP). In this way, a basic modeling hypothesis with particular attention being paid to the numerical treatment of stress relaxation and interaction of fuel swelling and clad creep down have been implemented. In this model, the mechanical equilibrium equations are integrated on principle of virtual work with generalized plane strain assumption and the numerical algorithm is based on finite element method. Afterward, the generated code, IR-FRA (Iranian Fuel Rod Analysis), is developed for long-term behavior study of fuel rods. For validating the IR-FRA code, the pellet–cladding interaction results in some test cases are compared with the FROBA, BISON codes and experimental data. These comparisons demonstrated the accuracy and capability of the presented code for prediction of fuel rods thermo-mechanical behavior. Eventually, the fuel and cladding mechanical interaction during long-term burnup of WWER1000 for the BNPP is simulated and results show good agreement with experimental and published data. [ABSTRACT FROM AUTHOR]

The article is devoted to the problem of creating a system of automated control with boron regulation for reactor WWER-1000 series. Using the boron regulation to control WWER-1000 allows to extend its maximum output operation period, ensuring the economic efficiency of the power unit, as well as to maintain the reactor facility within relevant safety limits that prevents from emergencies occurrence and development. The results of this problem solution, related to the process simulation, optimization and prediction, were used at further development of computer-integrated control system increasing the efficiency of decisions, taken by operational staff at reactor control. [ABSTRACT FROM AUTHOR]

By arranging the particle first banana orbits to pass near a distant detector, the light ion beam probe (LIBP) utilizes orbital deflection to probe internal fields and field fluctuations. The LIBP technique takes advantage of (1) the in situ, known source of fast ions created by beam-injected neutral particles that naturally ionize near the plasma edge and (2) various commonly available diagnostics as its detector. These born trapped particles can traverse the plasma core on their inner banana leg before returning to the plasma edge. Orbital displacements (the forces on fast ions) caused by internal instabilities or edge perturbing fields appear as modulated signal at an edge detector. Adjustments in the q-profile and plasma shape that determine the first orbit, as well as the relative position of the source and detector, enable studies under a wide variety of plasma conditions. This diagnostic technique can be used to probe the impact on fast ions of various instabilities, e.g., Alfvén eigenmodes (AEs) and neoclassical tearing modes, and of externally imposed 3D fields, e.g., magnetic perturbations. To date, displacements by AEs and by externally applied resonant magnetic perturbation fields have been measured using a fast ion loss detector. Comparisons with simulations are shown. In addition, nonlinear interactions between fast ions and independent AE waves are revealed by this technique. [ABSTRACT FROM AUTHOR]

Oscillations of a plasma column in a longitudinal magnetic field are considered. It is found that eigenmodes with frequencies close to the ion cyclotron frequency can be excited in columns the radii of which are smaller than the characteristic wavelength of magnetosonic oscillations predicted by the theory of homogeneous plasma. The eigenmodes have the form of waves running around the column axis in the direction of electron gyration in the magnetic field. Magnetosonic oscillations can be excited as a side effect when using helical antennas for ion cyclotron resonance heating of plasma. These oscillations should enhance electron heating in the plasma core, as well as both electron and ion heating at the periphery of the plasma column. The spectrum of eigenmodes of inhomogeneous plasma columns includes oscillations of different nature. Comparative analysis of their properties performed in the present paper is useful for understanding the full picture of the physical processes occurring during ion cyclotron resonance heating and clarifying the characteristic features of the magnetosonic oscillations under study. [ABSTRACT FROM AUTHOR]

Plasma/material interactions is a critical scientific issue for fusion power, with major potential limitations on plasma core and edge operating parameters. Gaining understanding and predictive capability in this area will require simultaneously addressing complex and diverse physics occurring over a wide range of lengths (angstroms to meters) and times (femtoseconds to days). This requires further development and validation of detailed physics models and computational strategies at each of these scales. The overriding numerical need is for petascale real-time coupling between 3-D material response/evolution/trapping codes, plasma edge/SOL codes, and impurity transport codes. We discuss selected science and modeling/computational challenges in this area and our ideas for achieving these goals; this from the standpoint of our existing simulation codes. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The simulation study of nonlocal transport from edge to core in tokamak plasmas is performed using the 4-field reduced MHD model. A toroidally-elongated cylindrical particle source is applied in the plasma edge, after saturation of the resistive ballooning turbulence is attained. After a short time, the source is switched off and plasma response is investigated in detail. The nonlocal transport appears at the location far from the edge source. It is found that the particle source induces (0,0) and (±1, 0) modes of density fluctuations, where ( m, n) indicates the set of poloidal mode number m and the toroidal mode number n. These modes interact with each other by the nonlinear and/or toroidal couplings. The symmetry of (±1, 0) modes breaks after switching-off the source and the formation of the spiral structure with poloidal rotation is observed, which yields a connection between core and edge regions. In this simulation, the convective cell mode such as (1,0) mode contributes the nonlocal transport. The simulation result indicates that two dimensional transport plays an essential role to produce the nonlocal transport. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Investigations of runaway electrons (REs) during induced disruptions are performed at the TEXTOR tokamak. The synchrotron radiation generated by REs in the plasma core is detected using an infrared camera. The measurements enable the observation of the structure and dynamics of the runaway beam. In particular, the runaway beam is investigated as a function of the vertical and horizontal control fields. From the plasma current a runaway number of 4.33 × 1016 was calculated. The number of REs with energies exceeding 25 MeV is 6.4 × 1015 according to the synchrotron measurement at the end of the current quench phase. The mean pitch angle of the >25 MeV runaways is found to be 52 mrad which is smaller than in the low density discharge scenario. In addition, the synchrotron measurements show for the first time that a significant number of the high energy REs can survive after the end of the current plateau phase. In order to understand this, runaway orbit calculations have been performed which are in good agreement with the measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] Various plasma reactors available for water remediation are addressed. [•] Combination of plasma with catalysts for pollutant removal is reviewed. [•] Some factors in pulsed electrical discharge are systematically discussed. [•] Further researches and challenges for plasma technology are presented. [Copyright &y& Elsevier]

The paper presents results of a first analysis of the divertor performance during the L–H transition in ITER. The integrated model consists of the SOLPS4.3 code suite for the SOL and divertor, and the ASTRA code for the core and pedestal regions. The results of SOLPS4.3 are parametrized and used as the boundary conditions for ASTRA, ensuring a consistent description of the plasma core and the edge. Boundary conditions switch from those for wide (L-mode) to narrow (H-mode) SOL once the transition criterion is met. The results show that, for conditions for which a full-power operational space with acceptable power loading of the targets exists, a transition from the initial L-mode operation to H-mode can be found for the same assumptions, i.e. the full-power H-mode regime is accessible. [ABSTRACT FROM AUTHOR]

In the Large Helical Device (LHD) operated with a metallic (stainless steel) first wall, it is found that the iron density, nFe, at the plasma core is fairly low (nFe ≤ 108 cm-3) in general neutral beam (NB)-heated discharges, while the iron quickly increases with the appearance of impurity accumulation when a multi-hydrogen ice pellet is injected or the NB input power is largely reduced. Although the highest iron density (nFe ≤ 1010 cm-3) at the plasma centre in the LHD is observed from such discharges, it suggests a still low iron concentration (nFe/ne < 10-3). Therefore, the edge iron transport in the ergodic layer, which determines the iron influx to the core plasma, is studied to clarify why the iron density in the core plasma is low. A line ratio of Fe XV located in the vicinity of the last closed flux surface to Fe VIII (or Fe IX) located in the ergodic layer decreases with density. The two-dimensional (2D) edge iron emission of Fe XVI and Fe IX is enhanced in the vicinity of the X-point with a larger number of magnetic field lines directly connected to divertor plates, which suggests that iron ions from the first wall move downstream. The density of edge Fe15+ ions giving the iron influx to the core plasma is analysed with the 2D distribution. The analysis also shows that the iron influx to the core plasma decreases with density. These results clearly indicate that the screening effect developed in the ergodic layer works well for iron ions coming from the first wall. A three-dimensional edge transport simulation with EMC3-EIRENE can also predict an effective impurity screening for heavy impurities compared to light impurities. [ABSTRACT FROM AUTHOR]

We show that the self-organized single-helical-axis (SHAx) and double-axis (DAx) states in reversed field pinches can be reproduced in a minimally constrained equilibrium model using only five parameters. This is a significant reduction on previous representations of the SHAx which have required an infinite number of constraints. The DAx state, which has a nontrivial topology, has not previously been reproduced using an equilibrium model that preserves this topological structure. We show that both states are a consequence of transport barrier formation in the plasma core, in agreement with experimental results. We take the limit of zero pressure in this work, although the model is also valid for finite pressure. [ABSTRACT FROM AUTHOR]

Plasmas with internal transport barriers (ITBs) are a potential and attractive route to steady-state operation in ITER. These plasmas exhibit radially localized regions of improved confinement with steep pressure gradients in the plasma core, which drive large bootstrap current and generate hollow current profiles and negative magnetic shear. This work examines the formation and sustainment of ITBs in ITER with electron cyclotron heating and current drive. The time-dependent transport simulations indicate that, with a trade-off of the power delivered to the equatorial and to the upper launcher, the sustainment of steady-state ITBs can be demonstrated in ITER with the baseline heating configuration. [ABSTRACT FROM AUTHOR]

A novel non-equilibrium atmospheric-pressure-plasma generation system is proposed. The system discussed in this study is specifically designed for nitrogen oxide (NOx) gas treatment. A plasma is generated by a high-voltage radio-frequency (RF) electric field formed in the system that accumulates electromagnetic energy by resonance provided by a low-voltage power supply. With an input RF voltage of 100-200V, a high voltage of 4k-8 kV at the same frequency can be formed on the powered electrode of the system under the resonance conditions. The plasma generator also serves as a plasma reactor, in which nitric oxide (NO) can be efficiently oxidized to form nitrogen dioxide (NO2) in the presence of oxygen (O2) at atmospheric pressure. It has been shown that, in terms of NO oxidation efficiency, the resonant plasma reactor proposed in this study is comparable or even superior to some of the previously proposed NO oxidation systems. [ABSTRACT FROM AUTHOR]

We studied the effect of saturated kink-like instabilities on the redistribution of W impurities. A numerical code that follows the exact trajectories of the impurity ions in the total fields and includes collisions was employed. The code is written in CUDA C and runs in graphical processing units, allowing simulations with a large number of particles with modest resources. The total electric and magnetic fields are calculated as the sum of a simple analytical equilibrium (large aspect ratio, circular cross section) plus the fields of the kink mode. Our simulations show that when the W ions have a thermal velocity distribution, with zero mean velocity, the kink has no effect on the W density. However, when we include the plasma rotation and the drag on the impurities, the kink can affect the W density. When the average passing frequency of the W ions is similar to the frequency of the kink mode, the expulsion of W ions from the plasma core is maximized and the W density profile shows a hollow structure. This could have implications for the mitigation of W accumulation. [ABSTRACT FROM AUTHOR]

The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell pellets are being investigated as a possible new path toward achieving tokamak disruption mitigation with both low conducted wall heat loads and slow current quench. Conventional disruption mitigation injects radiating impurities into the outer edge of the tokamak plasma, which tends to result in poor impurity assimilation and creates a strong edge cooling and outward heat flow, thus requiring undesirable high-Z impurities to achieve low conducted heat loads. The shell pellet technique aims to produce a hollow temperature profile by using a thin, low-ablation shell surrounding a dispersive payload, giving a greatly increased impurity ablation (and radiation) rate when the payload is released in the plasma core. This principle was demonstrated successfully using 3.6 mm outer diameter, 40 μm thickness diamond shells holding boron powder. The pellets caused rapid (<10 ms) discharge shutdown with low conducted divertor heat fluence (~0.1 MJ/m²). Confirmation of massive release of the boron powder payload into the plasma core was obtained spectroscopically. Some evidence for the formation of a hollow temperature profile during the shutdown was observed. These first results open a new avenue for disruption mitigation research, hopefully enabling development of highly effective methods of avoiding disruption wall damage in future reactor-scale tokamaks. [ABSTRACT FROM AUTHOR]

Measuring the value of the safety factor (q) in the core during sawtooth cycles is still an open issue. A new method to measure q in Tore Supra plasma core is presented here. It relies on the analysis of the time evolution of a set of MHD modes detected after the sawtooth crashes. These modes are in the frequency range of previously observed Beta-induced Alfvén Eigenmodes, but with a frequency declining in time. The mode frequency analysis shows that the q profile is reversed when we have ICRH, after the sawtooth crash. In high current discharges ( MA), the q-profile remains reversed for a longer time compared with lower plasma current discharges. Non-linear 3D MHD simulations of sawteeth performed with the XTOR-2F code (Lütjens and Luciani 2010 J. Comput. Phys. 229 8130–43) exhibit features that are similar to these observations. [ABSTRACT FROM AUTHOR]

Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n  =  2 RMP maintaining good confinement . Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes. [ABSTRACT FROM AUTHOR]

Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B0  =  0.95 T, 〈R〉  =  1.5 m, 〈a〉  =  0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (PNBI  ⩽  1.0 MW, ENBI  =  32 keV, PECRH  ⩽  0.6 MW). In low-density plasmas in the range   =  (0.3–1.5)  ×  1019 m−3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz  <  fAE  <  380 kHz. In experiments in which the vacuum rotational transform is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of intervals within which the AEs studied are chirping or steady-state is determined. [ABSTRACT FROM AUTHOR]

The wide applicability of capacitively coupled plasma (CCP) deposition has increased the interest in developing comprehensive numerical models, but CCP imposes a tremendous computational cost when conducting a transient analysis in a three-dimensional (3D) model which reflects the real geometry of reactors. In particular, the detailed flow features of reactive gases induced by 3D geometric effects need to be considered for the precise calculation of radical distribution of reactive species. Thus, an alternative inclusive method for the numerical simulation of CCP deposition is proposed to simulate a two-dimensional (2D) CCP model based on the 3D gas flow results by simulating flow, temperature, and species fields in a 3D space at first without calculating the plasma chemistry. A numerical study of a cylindrical showerhead-electrode CCP reactor was conducted for particular cases of SiH4/NH3/N2/He gas mixture to deposit a hydrogenated silicon nitride (SiNxHy) film. The proposed methodology produces numerical results for a 300 mm wafer deposition reactor which agree very well with the deposition rate profile measured experimentally along the wafer radius. [ABSTRACT FROM AUTHOR]

A fast 2D axisymmetric fluid-analytical multifrequency capacitively coupled plasma (CCP) reactor code is used to study center high nonuniformity in a low pressure electronegative chlorine discharge. In the code, a time-independent Helmholtz wave equation is used to solve for the capacitive fields in the linearized frequency domain. This eliminates the time dependence from the electromagnetic (EM) solve, greatly speeding up the simulations at the cost of neglecting higher harmonics. However, since the code allows up to three driving frequencies, we can add the two most important harmonics to the CCP simulations as the second and third input frequencies. The amplitude and phase of these harmonics are estimated by using a recently developed 1D radial nonlinear transmission line (TL) model of a highly asymmetric cylindrical discharge (Lieberman et al 2015 Plasma Sources Sci. Technol. 24 055011). We find that at higher applied frequencies, the higher harmonics contribute significantly to the center high nonuniformity due to their shorter plasma wavelengths. [ABSTRACT FROM AUTHOR]

In this computational study, a gliding arc plasma reactor with a reverse-vortex flow stabilization is modelled for the first time by a fluid plasma description. The plasma reactor operates with argon gas at atmospheric pressure. The gas flow is simulated using the k-ε Reynolds-averaged Navier–Stokes turbulent model. A quasi-neutral fluid plasma model is used for computing the plasma properties. The plasma arc movement in the reactor is observed, and the results for the gas flow, electrical characteristics, plasma density, electron temperature, and gas temperature are analyzed. [ABSTRACT FROM AUTHOR]

The synthesis of nanocrystalline Nd2O3 through an inductively coupled radiofrequency thermal plasma route is reported. Unlike in conventional synthesis processes, plasma-synthesized nanoparticles are directly obtained in a stable hexagonal crystal structure with a faceted morphology. The synthesized nanoparticles are highly uniform with an average size around 20 nm. The nanoparticles are characterized in terms of phase formation, crystallinity, morphology, size distribution, nature of chemical bonds and post-synthesis environmental effects using standard characterization techniques. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy are used for structural and morphological studies. The thermo-gravimetric technique, using a differential scanning calorimeter, is used to investigate the purity of phase. Fourier transform infrared spectroscopy is used to investigate the nature of existing bonds. The optical response of the nanoparticles is investigated through the electronic transition of Nd3+ ions in its crystalline structure via UV–visible spectroscopy. The presence of defect states and corresponding activation energies in the nanocrystalline Nd2O3 compared to those of the precursors are studied using thermoluminescence. [ABSTRACT FROM AUTHOR]

Ion temperature gradient (ITG) and trapped electron modes (TEM) are two important micro-instabilities in the plasma core region of fusion devices (). They usually coexist in the same range of spatial scale (around ), which makes their discrimination difficult. To investigate them, one can perform gyrokinetic simulations, transport analysis and phase velocity estimations. In Tore Supra, the identification of trapped electron modes (TEM) is made possible due to measured frequency fluctuation spectra. Indeed, turbulent spectra generally expected to be broad-band, can become narrow in case of TEM turbulence, inducing ‘quasi-coherent’ (QC) modes named QC-TEM. Therefore the analysis of frequency fluctuation spectra becomes a possible tool to differentiate TEM from ITG. We have found indications that the TEM can have a QC signature by comparing frequency fluctuation spectra from reflectometry measurements, gyrokinetic simulations and synthetic diagnostic results. Then the scope of the analysis of QC-TEM are discussed and an application is shown, namely transitions between TEM turbulence and MHD fluctuations. [ABSTRACT FROM AUTHOR]

The ITER baseline scenario, with 500 MW of DT fusion power and Q = 10, will rely on a Type I ELMy H-mode, with ΔW = 0.7 MJ mitigated edge localized modes (ELMs). Tungsten (W) is the material now decided for the divertor plasma-facing components from the start of plasma operations. W atoms sputtered from divertor targets during ELMs are expected to be the dominant source under the partially detached divertor conditions required for safe ITER operation. W impurity concentration in the plasma core can dramatically degrade its performance and lead to potentially damaging disruptions. Understanding the physics of plasma-wall interaction during ELMs is important and a primary input for this is the energy of incoming ions during an ELM event. In this paper, coupled Infrared thermography and Langmuir Probe (LP) measurements in JET-ITER-Like-Wall unseeded H-mode experiments with ITER relevant ELM energy drop have been used to estimate the impact energy of deuterium ions (D+) on the divertor target. This analysis gives an ion energy of several keV during ELMs, which makes D+ responsible for most of the W sputtering in unseeded H-mode discharges. These LP measurements were possible because of the low electron temperature (Te) during ELMs which allowed saturation of the ion current. Although at first sight surprising, the observation of low Te at the divertor target during ELMs is consistent with the ‘Free-Streaming’ kinetic model which predicts a near-complete transfer of parallel energy from electrons to ions in order to maintain quasi-neutrality of the ELM filaments while they are transported to the divertor targets. [ABSTRACT FROM AUTHOR]