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Super-Resolution Mapping of a Chemical Reaction Driven by Plasmonic Near-Fields
No full textPlasmonic nanoparticles have recently emerged as promising photocatalysts for light-driven chemical conversions. Their illumination results in the generation of highly energetic charge carriers, elevated surface temperatures, and enhanced electromagnetic fields. Distinguishing between these often-overlapping processes is of paramount importance for the rational design of future plasmonic photocatalysts. However, the study of plasmon-driven chemical reactions is typically performed at the ensemble level and, therefore, is limited by the intrinsic heterogeneity of the catalysts. Here, we report an in situ single-particle study of a fluorogenic chemical reaction driven solely by plasmonic near-fields. Using super-resolution fluorescence microscopy, we map the position of individual product molecules with an ∼30 nm spatial resolution and demonstrate a clear correlation between the electric field distribution around individual nanoparticles and their super-resolved catalytic activity maps. Our results can be extended to systems with more complex electric field distributions, thereby guiding the design of future advanced photocatalysts
Ultralow dark current in near-infrared perovskite photodiodes by reducing charge injection and interfacial charge generation
No full textUnveiling the Symmetry Protection of Bound States in the Continuum with Terahertz Near-Field Imaging
No full textModel-based electron density profile estimation and control, applied to ITER
No full textIn contemporary magnetic confinement devices, the density distribution is sensed with interferometers and actuated with feedback controlled gas injection and open-loop pellet injection. This is at variance with the density control for ITER and DEMO, that will depend mainly on pellet injection as an actuator in feed-back control. This paper presents recent developments in state estimation and control of the electron density profile for ITER using relevant sensors and actuators. As a first step, Thomson scattering is included in an existing dynamic state observer. Second, model predictive control is developed as a strategy to regulate the density profile while avoiding limits associated with the total density (Greenwald limit) or gradients in the density distribution (e.g. neoclassical impurity transport). Simulations show that high quality density profile estimation can be achieved with Thomson Scattering and that the controller is capable of regulating the distribution as desired.</p
Advanced Self-Passivating Alloys for an Application under Extreme Conditions
No full textSelf-passivating Metal Alloys with Reduced Thermo-oxidation (SMART) are under development for the primary application as plasma-facing materials for the first wall in a fusion DEMOnstration power plant (DEMO). SMART materials must combine suppressed oxidation in case of an accident and an acceptable plasma performance during the regular operation of the future power plant. Modern SMART materials contain chromium as a passivating element, yttrium as an active element and a tungsten base matrix. An overview of the research and development program on SMART materials is presented and all major areas of the structured R&D are explained. Attaining desired performance under accident and regular plasma conditions are vital elements of an R&D program addressing the viability of the entire concept. An impressive more than 104-fold suppression of oxidation, accompanied with more than 40-fold suppression of sublimation of tungsten oxide, was attained during an experimentally reproduced accident event with a duration of 10 days. The sputtering resistance under DEMO-relevant plasma conditions of SMART materials and pure tungsten was identical for conditions corresponding to nearly 20 days of continuous DEMO operation. Fundamental understanding of physics processes undergone in the SMART material is gained via fundamental studies comprising dedicated modeling and experiments. The important role of yttrium, stabilizing the SMART alloy microstructure and improving self-passivating behavior, is under investigation. Activities toward industrial up-scale have begun, comprising the first mechanical alloying with an industrial partner and the sintering of a bulk SMART alloy sample with dimensions of 100 mm × 100 mm × 7 mm using an industrial facility. These achievements open the way to further expansion of the SMART technology toward its application in fusion and potentially in other renewable energy sources such as concentrated solar power stations.</p
B2.5-Eunomia simulations of Magnum-PSI detachment experiments: I. Quantitative comparisons with experimental measurements
Full text linkDetachment experiments have been carried out in the linear plasma device Magnum-PSI by increasing the gas pressure near the target. In order to have a proper detailed analysis of the mechanism behind momentum and power loss in detachment, a quantitative match is pursued between B2.5-Eunomia solutions and experimental data. B2.5 is a multi fluid plasma code and Eunomia is a Monte Carlo solver for neutral particles, and they are coupled together to provide steady-state solution of the plasma and neutral distribution in space. B2.5-Eunomia input parameters are adjusted to produce a close replication of the plasma beam measured in the experiments without any gas puffing in the target chamber. Using this replication as an initial condition, the neutral pressure near the plasma beam target is exclusively increased during simulation, matching the pressures measured in the experiments. Reasonable agreement is found between the electron temperature of the simulation results with experimental measurements using laser Thomson scattering near the target. The simulations also reveal the effect of increased gas pressure on the plasma current, effectively reducing the current penetration from the plasma source. B2.5-Eunomia is capable of reproducing detachment characteristics, namely the loss of plasma pressure along the magnetic field and the reduction of particle and heat flux to the target. The simulation results for plasma and neutrals will allow future studies of the exact contribution of individual plasma-neutral collisions to momentum and energy loss in detachment in Magnum-PSI.</p
Recent progress of thick tungsten coating prepared by chemical vapor deposition as the plasma-facing material
Full text linkChemical vapor deposition (CVD) is a promising technique for the preparation of W-based plasma-facing materials (PFMs). An overview of the microstructure, chemical composition, thermal conductivity, thermal stability, thermal shock performance under disruption-like and edge localized mode-like transient heat load, and neutron irradiation performance of CVD-W has been given in our previous work. However, for fusion applications, additional properties need to be assessed. To this end, deuterium (D) permeability, D plasma irradiation performance, and thermal fatigue resistance of CVD-W were investigated in this work. The results showed that the D permeability of CVD-W in the temperature range of 973–1173 K was larger than that of the commercial pure W, which was related to the columnar grain structure of CVD-W. Additionally, both CVD-W and commercial pure W were exposed to D plasma up to a fluence of 1 × 1026 m−2. Compared to commercial pure W, CVD-W exhibited a mitigated blistering behavior and lower D total retention, which could be attributed to its strong [001] crystallographic texture along the thickness direction and a lower number of defect density (e.g. grain boundaries). CVD-W and commercial pure W were also exposed to steady-state and transient heat load simultaneously, leading to a base surface temperature and surface temperature increase of about 953–1473 K and 250–300 K, respectively. A strong grain orientation dependence of the surface degradation induced by the combined heat load has been found. Consequently, CVD-W exhibited a much more uniform plastic deformation than pure W, and no surface cracks along grain boundaries were observed in CVD-W. Finally, the industrial-scale production of CVD-W-based PFMs and mockups was demonstrated. This work paves the way for the fusion applications of thick CVD-W coatings.</p
Noncovalent semiconducting polymer monolayers for high-performance field-effect transistors
No full textInfluence of hydrogen addition on methane coupling in a moderate pressure microwave plasma
Full text linkIn this paper, the effect of hydrogen addition on methane coupling in a microwave moderate pressure (55 mbar and 110 mbar) plasma reactor has been studied. The use of optical emission spectroscopy allowed the determination of the rotational temperature of heavy particles and showed it to be in the range of 3000–4000 K. Due to the high temperature in the discharge the dominant product was acetylene and it was concluded that the methane coupling process is mainly through thermal decomposition with a key role of H radicals. It was revealed that the addition of hydrogen can increase both methane conversion and acetylene and ethylene yield and selectivity. With the CH4:H2 ratio of 1:1, the methane conversion increased from 31.0% to 42.1% (55 mbar) and from 34.0% to 48.6% (110 mbar), when compared to pure methane plasma. Respectively, the yield of acetylene increased from 14.4% to 25.3% (55 mbar) and from 20.1% to 34.0% (110 mbar). Moreover, the addition of hydrogen decreased the output of the problematic soot-like product. These results indicate that hydrogen addition can be a simple yet effective method of increasing selectivity to desirable products in plasma reforming of CH4.</p
Initial TCV operation with a baffled divertor
Full text linkThe Tokamak à Configuration Variable (TCV) tokamak is in the midst of an upgrade to further its capability to investigate conventional and alternative divertor configurations. To that end, modular and removable gas baffles have been installed to decrease the coupling between the divertor and the plasma core. The baffles primarily seek to suppress the transit of recycling neutrals to closed flux surfaces. A first experimental campaign with the gas baffles has shown that the baffled divertor remains compatible with a wide range of configurations including snowflake and super-X divertors. Plasma density ramp experiments reveal an increase of the neutral pressure in the divertor by up to a factor ×5 compared to the unbaffled divertor and thereby qualitatively confirm simulations with the SOLPS-ITER code that were used to guide the baffle design. Together with a range of new and upgraded divertor diagnostics, the baffled TCV divertor is now used to validate divertor models for ITER and next step devices with particular emphasis on geometric variations.</p