Sterilization mechanism of helium/helium–oxygen atmospheric-pressure pulsed dielectric barrier discharge on membrane surface

Pulsed dielectric barrier discharge (PDBD) exhibits several applications in different fields; however, the interaction of its components with substances remains a key issue. In this study, we employed experimental and numerical modeling to investigate the interactions between different PDBD components and substances in pure helium and a helium–oxygen mixture. A membrane comprising a Staphylococcus aureus strain was utilized as the treatment object to demonstrate the trace actions of the evolutions and distributions of certain components on the surface of the substance. The results revealed that the shapes and sizes of the discharging area and inhibition zone differed between groups. Under a pure helium condition, a discharge layer existed along the membrane surface, lying beside the main discharging channel within the electrode area. Further, an annulus inhibition zone was formed at the outer edge of the electrode in the pure helium group at 30 s and 1 min, and this zone extended to a solid circle at 2 min with a radius that was ∼50% larger than that of the electrode radius. Nevertheless, the discharging channel and inhibition zone in the helium–oxygen mixture were constrained inside the electrode area without forming any annulus. A 2D symmetrical model was developed with COMSOL to simulate the spatiotemporal distributions of different particles over the membrane surface, and the result demonstrated that the main components, which formed the annulus inhibition zone under the pure helium condition, contributed to the high concentration of the He+ annulus that was formed at the outer edge of the electrode. Moreover, O+ and ${{\rm{O}}}_{2}^{+}$ were the main components that killed the bacteria under the helium–oxygen mixture conditions. These results reveal that the homogenization treatment on a material surface via PDBD is closely related to the treatment time and working gas.     

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum–magnesium alloy

We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al–Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.     

Dynamics of deuterium retention and sputtering of Li–C–O surfaces

Chemistry as well as sputtering and reflection dynamics of lithiated carbon material, bombarded by slow hydrogen atoms are studied. We present a realistic method for computational simulation of the dynamics of the polar Li–C–O–H material dynamics. It is based on an approximate, semi-empirical quantum mechanics of electrons and classical mechanics of nuclei. Results are validated qualitatively by comparison with experiments and with a first principle DFT computations. In particular, we explain observed details of the hydrogen bonding chemistry in lithiated carbon, showing that incoming hydrogen interacts preferably with Li-C rather than C structures.     

Degradation and mineralization of ciprofloxacin by gas–liquid discharge non-thermal plasma

A typical quinolones antibiotic ciprofloxacin(CIP) in aqueous solution was degraded by a gas–liquid discharge non-thermal plasma system. The discharge plasma power and the emission intensity of the excited reactive species(RS) generated in the gas phase were detected by the oscilloscope and the optical emission spectroscopy. The effects of various parameters on CIP degradation, i.e. input powers, initial concentrations addition of radical scavengers and p H values were investigated. With the increase of discharge power, the degradation efficiency increased but the energy efficiency significantly reduced. The degradation efficiency also reduced under high concentration of initial CIP conditions due to the competitive reactions between the plasma-induced RS with the degradation intermediates of CIP. Different radical scavengers(isopropanol and CCl_4) on ·OH and H· were added into the reaction system and the oxidation effects of ·OH radicals have been proved with high degradation capacity on CIP.Moreover, the long-term degradation effect on CIP in the plasma-treated aqueous solution proved that the long-lived RS(H_2O_2 and O_3, etc) might play key roles on the stay effect through multiple aqueous reactions leading to production of ·OH. The degradation intermediates were determined by the method of electrospray ionization(+)-mass spectroscopy, and the possible degradation mechanism were presented.     

Vulcan: A steady-state tokamak for reactor-relevant plasma–material interaction science

An economically viable magnetic-confinement fusion reactor will require steady-state operation and high areal power density for sufficient energy output, and elevated wall/blanket temperatures for efficient energy conversion. These three requirements frame, and couple to, the challenge of plasma–material interaction (PMI) for fusion energy sciences. Present and planned tokamaks are not designed to simultaneously meet these criteria. A new and expanded set of dimensionless figures of merit for PMI have been developed. The key feature of the scaling is that the power flux across the last closed flux surface P/S ? 1 MW m^?2 is to be held constant, while scaling the core volume-averaged density weakly with major radius, n ～ R^?2/7. While complete similarity is not possible, this new “P/S” or “PMI” scaling provides similarity for the most critical reactor PMI issues, compatible with sufficient current drive efficiency for non-inductive steady-state core scenarios. A conceptual design is developed for Vulcan, a compact steady-state deuterium main-ion tokamak which implements the P/S scaling rules. A zero-dimensional core analysis is used to determine R = 1.2 m, with a conventional reactor aspect ratio R/a = 4.0, as the minimum feasible size for Vulcan. Scoping studies of innovative fusion technologies to support the Vulcan PMI mission were carried out for three critical areas: a high-temperature, helium-cooled vacuum vessel and divertor design; a demountable superconducting toroidal field magnet system; and a steady-state lower hybrid current drive system utilizing a high-field-side launch position.     

Experiments in support of the Gas Dynamic Trap based facility for plasma–material interaction testing

The power density along the field lines in the scrape-off layer plasma in machines of the class of ITER, Wendelstein 7-X, NSTX-U is in the range of few hundreds megawatt per square meter. It is crucial for the future of tokamaks and stellarators to develop the plasma science and component technology to handle such high plasma heat fluxes. It would be valuable to produce parallel plasma heat fluxes at these power densities, impinging on test components at very shallow angles, as planned in tokamaks. The primary objective of this work is the direct measurement of plasma heat fluxes in the mirror throat of a Gas Dynamic Trap device. Options to develop a facility for plasma–material interaction testing based on the Gas Dynamic Trap are discussed.     

Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques

The surface enrichment of archaeological silver–copper alloys has been recognized for many years. However, the origin of this enrichment is not well defined and many hypotheses have been put forward to account for this behaviour: segregation of the components during casting, deliberate thermal and/or chemical post-treatment, abrasion or corrosion. Among the hypotheses mentioned above, we have focused our study on the first step of coin manufacturing. Replications of silver–copper standards of various compositions ranging from 30% to 80% Ag, reflecting the composition of silver blanks, have been produced. Metallographic examination, PIXE and SEM–EDS have been used for the characterization of each sample. A model of the direct enrichment has been established. This model allows us to propose a relationship between the surface composition and the silver content of the core. Comparison with data of Roman coins from the Roman site of Châteaubleau (France) and from the literature and consequences for the analyses of ancient coins by surface methods are presented.     

Experimental studies of nonlinear laser－plasma interactions and hot electrons

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Experimental studies of nonlinear laser—plasma interactions and hot electrons

Observation shows that the stimulated Raman scattering (SRS) in a cavity target irradiated by 1.053um laser is the dominant mechanism in producing hot electrons.In cavity targets,stimulated Brillouin scattering (SBS) and SRS are main abnormal absorption processes,they can scatter about 0.4 of the laser light energy fraction.     

On the electron sheath theory and its applications in plasma–surface interactions

In this work, an improved understanding of electron sheath theory is provided using both fluid and kinetic approaches while elaborating on their implications for plasma–surface interactions. A fluid model is proposed considering the electron presheath structure, avoiding the singularity in electron sheath Child–Langmuir law which overestimates the sheath potential. Subsequently, a kinetic model of electron sheath is established, showing considerably different sheath profiles in respect to the fluid model due to non-Maxwellian electron velocity distribution function and finite ion temperature. The kinetic model is then further generalized and involves a more realistic truncated ion velocity distribution function. It is demonstrated that such a distribution function yields a super-thermal electron sheath whose entering velocity at the sheath edge is greater than the Bohm criterion prediction. Furthermore, an attempt is made to describe the electron presheath–sheath coupling within the kinetic framework, showing a necessary compromise between a realistic sheath entrance and the inclusion of kinetic effects. Finally, the secondary electron emissions induced by sheath-accelerated plasma electrons in an electron sheath are analysed and the influence of backscattering is discussed.     

Activated persulfate by DBD plasma and activated carbon for the degradation of acid orange Ⅱ

In this study, the effect of activated peroxydisulfate(PDS) by dielectric barrier discharge(DBD) plasma and activated carbon(HGAC) on the removal of acid orange Ⅱ(AOⅡ) was investigated. The effects of applied voltage, PDS dosage, HGAC dosage, initial pH value, and inorganic anions on the removal rate of AOⅡ were discussed. The main free radicals degrading azo dyes during the experiment were also studied. Experimental results show that the removal rate of AOⅡ in DBD/HGAC/PDS synergistic system is much higher than that in the single system. With the applied voltage of 16 kV, HGAC dosage of 1 g l-1, PDS and AOⅡ molar ratio of 200:1, initial pH value of 5.4 and concentration of AOⅡ solution of 20 mg l-1, the removal rate of AOⅡ reached 97.6% in DBD/HGAC/PDS process after 28 min of reaction.Acidic and neutral conditions are beneficial for AOⅡ removal. Sulfate and hydroxyl radicals play an important role in the removal of AOⅡ. Inorganic anions are not conducive to the removal of AOⅡ.     

A human–machine interaction design and evaluation method by combination of scenario simulation and knowledge base

A method of designing and evaluating HMI (human–machine interaction) is proposed for the design in supervisory control of fully digitalized I&C (instrumentation and control) and digitalized human–machine interface system, which is a large-scale complex system in the NPPs (nuclear power plants). The proposed method consists of plant accident scenario simulation, knowledge base establishment, and interaction simulation. The plant accident scenario simulation is to analyze the plant behavior and system sequences under the predefined conditions; the knowledge base is modeled based on the simulation results as human and machine roles; and the interaction simulation is to simulate the interactions such as between operator and plant, operator and technical advisor. The proposed method utilizes the object-oriented software named plant DiD (defense-in-depth) risk monitor with the combination of accident simulation by an advanced nuclear safety analysis code such as RELAP5/MOD4. The practical developments for the details are demonstrated using an example practice for the SBLOCA (small break loss of coolant accident) case of passive safety PWR (pressurized water reactor) AP1000.     

Microstructure and oxidation properties of 16Cr–5Al–ODS steel prepared by sol–gel and spark plasma sintering methods

The 16Cr–5Al oxide dispersion strengthened (ODS) ferritic steel was fabricated by sol–gel method in combination with hydrogen reduction, mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The phase characterization, microstructure and oxidation resistance of the 16Cr–5Al–ODS steel were investigated in comparison with the Al free 16Cr–ODS steel. X-ray diffraction (XRD) patterns showed that the Al free and Al added 16Cr–ODS steels exhibited typical ferritic characteristic structure. The microstructure analysis investigated by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) revealed that Y–Ti–O complexes with particle size of 10–30 nm were formed in the Al free matrix and Y–Al–O complexes with particle size of 20–100 nm were formed in the Al contained high-Cr ODS steel matrix. These complexes are homogeneously distributed in the matrices. The fabricated 16Cr–5Al–ODS steel exhibited superior oxidation resistance compared with the Al free 16Cr–ODS steel and the commercial 304 stainless steel owing to the formation of continuous and dense Al₂O₃ film on the surface.     

Measurement of the anisotropy parameters for the M X-rays of gold induced by 3–9 MeV carbon ions

The angular distribution of Au M X-rays induced by 3–9 MeV carbon ions has been measured with a Si(Li) detector and found to be strongly anisotropic. The measured values of the anisotropy parameters range between 10% and 38%. The implication of such high values of the anisotropy parameter for M X-ray production cross section measurements has been discussed.     

Micro-fabrication and surface modification of fluorinated polymers by means of synchrotron radiation

It is well-known that fluorinated polymers are very unique polymer materials because of their distinguished properties, such as high electrical resistivities, chemical and thermal stabilities, bio-compatibilities, etc. However,polytetrafluoroethylene (PTFE) is degraded by ionizing radiation with a low dose through main chain scission, and the mechanical properties are seriously deteriorated. In early 1990‘s, it was found that irradiation for PTFE at elevating temperature enhances recombination of radicals induced by ionizing radiation. Thus,     

Investigation of high-temperature-resistant rhenium–boron neutron shields by experimental studies and Monte Carlo simulations

In this study,novel rhenium–boron neutronshielding high-temperature-resistant materials were designed.The considered samples,Re60–B40,Re58–B42,Re50–B50,and Re40–B60,with different concentrations of rhenium and boron were investigated to elucidate their neutron-shielding performances,and compare them with well-known neutron-shielding materials such as the 316 LN quality nuclear steel.In addition to the experimental studies,Monte Carlo simulations were performed using the FLUKA and GEANT4 codes,where 4.5-MeV neutrons emitted by a ~(241)Am–Be source were employed.Experimental equivalent dose rates,simulated track lengths,energy balances,and neutron mass absorption cross sections were discussed in detail.     

Development and verification of molten corium–concrete interaction code

During a severe accident of Pressurized Water Reactor(PWR), the core materials was heated, melt located on the lower head of Reactor Pressure Vessel(RPV). With the temperature rise, the corium will melt through the lower head and discharge into the reactor cavity. Those corium will interact with the concrete and damage the integrity of the containment, so some coolability method should used to quench the corium. In order to investigate the progress of MCCI, a MCCI analysis code, that is MOCO, was developed. The MOCO includes the heat transfer behavior in axial and radial directions from the molten corium to the basemat and sidewall concrete, crust generation and growth, and coolability mechanisms reveal the concrete erosion and gas release, which are important for the interaction process. Cavity ablation depth, melt temperature, and gas release are the key parameters in the interaction research. The physical-chemistry reaction is also involved in MOCO code. In the present paper, the related MCCI experiment data were used to verify the models of the MOCO and the calculation results of MOCO were also compared with other MCCI analysis codes.     

Nucleation,growth and transport modelling of helium bubbles under nuclear irradiation in lead–lithium with the self-consistent nucleation theory and surface tension corrections

Helium (He) nucleation in liquid metal breeding blankets of a DT fusion reactor may have a significant impact regarding system design, safety and operation. Large He production rates are expected due to tritium (T) fuel self-sufficiency requirement, as both, He and T, are produced at the same rate. Low He solubility, local high concentrations, radiation damage and fluid discontinuities, among other phenomena, may yield the necessary conditions for He nucleation. Hence, He nucleation may have a significant impact on T inventory and may lower the T breeding ratio.A model based on the self-consistent nucleation theory (SCT) with a surface tension curvature correction model has been implemented in OpenFOAM^® CFD code. A modification through a single parameter of the necessary nucleation condition is proposed in order to take into account all the nucleation triggering phenomena, specially radiation induced nucleation. Moreover, the kinetic growth model has been adapted so as to allow for the transition from a critical cluster to a macroscopic bubble with a diffusion growth process.Limitations and capabilities of the models are shown by means of zero-dimensional simulations and sensitivity analyses to key parameters under HCLL breeding unit conditions. Results provide a good qualitative insight into the helium nucleation phenomenon in LM systems for fusion technology and reinforces the idea that nucleation may not be a remote phenomenon, may have a large impact on the system's design and reveals the necessity to conduct experiments on He cavitation.     

Degradation of antibiotic contaminants from water by gas–liquid underwater discharge plasma

Antibiotic contamination adversely affects human health and ecological balance.In this study,gasliquid underwater discharge plasma was employed to simultaneously degrade three antibiotics,sulfadiazine(SDZ),tetracycline(TC),and norfloxacin(NOR),to address the growing problem of antibiotic contaminants in water.The effects of various parameters on the antibiotic degradation efficiency were evaluated,including the discharge gas type and flow rate,the initial concentration and pH of the solution,and...