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A study of the influence of plasma–molecule interactions on particle balance during detachment
No full textIn this work we provide experimental insights into the impact of plasma–molecule interactions on the target ion flux decrease during divertor detachment achieved through a core density ramp in the TCV tokamak. Our improved analysis of the hydrogen Balmer series shows that plasma–molecule processes are strongly contributing to the Balmer series intensities and substantially alter the divertor detachment particle balance. We find that Molecular Activated Recombination (MAR) ion sinks from H2+ (and possibly H−) are a factor ∼5 larger than Electron–Ion Recombination (EIR) and are a significant contributor to the observed reduction in the outer divertor ion target flux. Molecular Activated Ionisation (MAI) appears to be substantial during the detachment onset, but further research is required into its magnitude given its uncertainty. Plasma–molecule interactions enhance the Balmer line series emission strongly near the target as detachment proceeds. This indicates enhancements of the Lyman series, potentially affecting power balance in the divertor. As those enhancements vary spatially in the divertor and are different for different transitions, they are expected to result in a separation of the Lyβ and Lyα emission regions. This may have implications for the treatment and diagnosis of divertor opacity. The demonstrated enhancement of the Balmer series through plasma–molecule processes potentially poses a challenge to using the Balmer series for understanding and diagnosing detachment based only on atom–plasma processes
Use of Sodium Diethyldithiocarbamate to Enhance the Open-Circuit Voltage of CH3NH3PbI3 Perovskite Solar Cells
No full textPlasma modelling and prebiotic chemistry: a review of the state of the art and perspective
No full textWe review the recent progress in the modeling of plasmas or ionized gases, with compositions compatible with that of primordial atmospheres. The plasma kinetics involves elementary processes by which free electrons ultimately activate weakly reactive molecules, such as carbon dioxide or methane, thereby potentially starting prebiotic reaction chains. These processes include electron–molecule reactions and energy exchanges between molecules. They are basic processes, for example, in the famous Miller-Urey experiment, and become relevant in any prebiotic scenario where the primordial atmosphere is significantly ionized by electrical activity, photoionization or meteor phenomena. The kinetics of plasma displays remarkable complexity due to the non-equilibrium features of the energy distributions involved. In particular, we argue that two concepts developed by the plasma modeling community, the electron velocity distribution function and the vibrational distribution function, may unlock much new information and provide insight into prebiotic processes initiated by electron–molecule collisions
Two-temperature balance equations implementation, numerical validation and application to H2O-He microwave induced plasmas
No full textGlobal Models are widely used to study reaction kinetics in low-temperature plasma discharges. The governing conservative equations are simplified into a system of ordinary differential equations in order to provide computationally feasible conditions to study complex chemistries with hundreds of species and thousands of reactions. This paper presents a detailed two-temperature global model for a H2O-He mixture. The model developed in this work uses a statistical thermodynamics approach to solve the heavy particles energy equation self-consistently together with the electron energy and particles balance equations in order to improve the description of reactive plasma environments. Three analytical test cases are presented to validate and demonstrate the capability of this newly developed functionality embedded in PLASIMO software\u27s [1] global model module. The developed H2O-He models are compared with the reported results for a radio-frequency plasma [2] and then with experimental measured electron densities and gas temperature for a microwave induced plasma. In addition, conversion and energy efficiencies of hydrogen and hydrogen peroxide productions are compared with experimental values (only for hydrogen) for a pure H2O microwave induced plasma and with available literature results. This comparison underlines the challenges toward finding an optimal plasma configuration and conditions for production of hydrogen from water. The three analytical test cases for validation of the gas-temperature balance implementation in the PLASIMO global model and the detailed developed H2O-He model can be used as benchmarks for other global plasma models. The PLASIMO input files for the presented H2O-He model are available as supplementary materials (); for any future update, please consult the PLASIMO website
LIBS applicability for investigation of re-deposition and fuel retention in tungsten coatings exposed to pure and nitrogen-mixed deuterium plasmas of Magnum-PSI
Get PDFWe have investigated the applicability of Laser Induced Breakdown Spectroscopy (LIBS) for analyzing the changes in the composition and fuel retention of W and W-Ta coatings following exposure to D2 or mixed D2-N2 plasma beams in the linear plasma device Magnum PSI. The exposed samples were characterized by in situ ns-LIBS and complementary analysis methods Secondary Ion Mass Spectroscopy, Energy Dispersive x-ray spectroscopy and Nuclear Reaction Analysis. In agreement with the used complementary analysis methods, LIBS revealed the formation of up to 400 nm thick co-deposited surface layer in the central region of the coatings which contained a higher concentration of the main plasma impurities, such as N, and metals, such as Ta and Mo, the latter originating mainly from the substrate and from the plasma source. The deuterium retention on the other hand was highest outside from the central region of the coatings.</p
Dislocation Loops in Proton Irradiated Uranium-Nitrogen-Oxygen System
Get PDFIn this study, we investigated the type of dislocation loops formed in the proton-irradiated uranium-nitrogen-oxygen (U-N-O) system, which involves uranium mononitride (UN), uranium sesquinitride (α-U2N3), and uranium dioxide (UO2) phases. The dislocation loop formation is examined using specimens irradiated at 400°C and 710°C. Based on the detailed transmission-based electron microscopy characterization with i) the morphology-based on-zone and ii) the invisibility-criterion based two-beam condition imaging techniques, only a single type of dislocation loop in each phase is found: a/2⟨110⟩, a/2⟨111⟩, or a/3⟨111⟩ dislocation loops in UN, α-U2N3, and UO2 phases, respectively. Molecular statics calculations for the formation energy of perfect and faulted dislocation loops in the UN phase indicate a critical loop size of ∼6 nm, above which perfect loops are thermodynamically favorable. This could explain the absence of faulted loops in the experimental observation of the irradiated UN phase at two temperatures. This work will enhance the understanding of irradiation induced microstructural evolution for uranium mononitride as an advanced nuclear fuel for the next-generation nuclear reactors.</p
Inducing thermionic emission from lanthanum hexaboride probes in Magnum-PSI
No full textFor thermionic emission rates exceeding the incident plasma electron flux, recent theory proposes an inverse sheath regime, with promising properties for future application in fusion edge plasmas. With the aim of inducing thermionic emission in fusion-relevant plasma conditions, several lanthanum hexaboride probes were heated in the linear plasma generator Magnum-PSI. During exposures at low plasma power and additional pulsed laser heating, the probe’s floating potential was reduced by up to 12%, providing a possible indication of thermionic emission. However, these observations coincided with rapid erosion of probe material, attributed to enhanced lanthanum self-sputtering. During follow-up experiments with helium plasmas at electron temperatures around 1 eV, the lanthanum ion impact energy and sputtering yield were reduced, and rapid erosion was avoided, thus confirming the thesis of self-sputtering. A parameter scan of plasma power resulted in LaB6 surface temperatures up to 2450 °C, exceeding the theoretical inverse sheath threshold temperature by over 300 °C. However, the probe’s floating potential did not deviate from reference measurements using a probe with high electronic work function, indicating absence of strong thermionic emission. This apparent discrepancy is attributed to the effects of probe surface modifications as observed during these experiments: impurity deposition, erosion and cavity formation. These modifications possibly affected the LaB6 electronic work function, thereby keeping the inverse sheath threshold out of reach. In conclusion, although LaB6 has one of the lowest work functions available, the inverse sheath threshold conditions could not be reached with the present setup in Magnum-PSI. Surface modifications thus do form a limiting factor for the application of LaB6 in fusion-relevant plasma conditions. Moreover, the window of stable operation for LaB6 in dense hydrogen plasmas is limited below ~1.5 eV, and does not overlap with the conditions expected in the edge region of future fusion devices like ITER
High-Throughput Computational Screening of Cubic Perovskites for Solid Oxide Fuel Cell Cathodes
Get PDFIt is a present-day challenge to design and develop oxygen-permeable solid oxide fuel cell (SOFC) electrode and electrolyte materials that operate at low temperatures. Herein, by performing high-throughput density functional theory calculations, oxygen vacancy formation energy, Evac, data for a pool of all-inorganic ABO3 and A I 0.5 A II 0.5 BO3 cubic perovskites is generated. Using E vac data of perovskites, the area-specific resistance (ASR) data, which is related to both oxygen reduction reaction activity and selective oxygen ion conductivity of materials, is calculated. Screening a total of 270 chemical compositions, 31 perovskites are identified as candidates with properties that are between those of state-of-the-art SOFC cathode and oxygen permeation components. In addition, an intuitive approach to estimate Evac and ASR data of complex perovskites by using solely the easy-to-access data of simple perovskites is shown, which is expected to boost future explorations in the perovskite material search space for genuinely diverse energy applications.</p
Tailoring the Surface Chemistry of Anion Exchange Membranes with Zwitterions: Toward Antifouling RED Membranes
No full textMars in situ oxygen and propellant production by non-equilibrium plasmas
No full textIt has been recently advocated that Mars has excellent conditions for oxygen and fuel production directly from atmospheric CO2 using non-equilibrium plasmas. The Martian conditions would be favorable for vibrational excitation and/or enhanced dissociation by electron impact, two important pathways for CO2 plasma dissociation. Herein we confirm these theoretical predictions by measuring, for the first time, the vibrational temperatures of CO2 and the CO and CO2 concentrations in realistic Martian conditions. In situ Fourier transform infrared spectroscopy (FTIR) measurements are performed in experiments conducted in DC glow discharges operating at pressures p=1-5 Torr, discharge currents I=10-50 mA, initial gas temperatures of 220 K and 300 K, both in pure CO2 and in the synthetic Martian atmosphere 96% CO2-2% Ar-2% N2. To analyse and interpret the experimental results, we develop a detailed self-consistent kinetic model for pure CO2 plasmas, describing the coupled electron and heavy-particle kinetics. The simulation results are in very good agreement with the experimental data. It is shown that the low-temperature conditions may enhance the degree of vibrational non-equilibrium and that the Martian atmospheric composition has a positive effect on CO2 decomposition. Accordingly, the present investigation confirms the potential of plasma technologies for in-situ resource utilization (ISRU) on Mars