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Measurement of turbulent electron temperature fluctuations on the ASDEX Upgrade tokamak using correlated electron cyclotron emission
No full textDegenerate Bogdanov-Takens bifurcations in a one-dimensional transport model of a fusion plasma
No full textExperiments in tokamaks (nuclear fusion reactors) have shown two modes of operation: L-mode and H-mode. Transitions between these two modes have been observed in three types: sharp, smooth and oscillatory. The same modes of operation and transitions between them have been observed in simplified transport models of the fusion plasma in one spatial dimension. We study the dynamics in such a one-dimensional transport model by numerical continuation techniques. To this end the MATLAB package CL\_MATCONTL was extended with the continuation of (codimension-2) Bogdanov-Takens bifurcations in three parameters using subspace reduction techniques. During the continuation of (codimension-2) Bogdanov-Takens bifurcations in 3 parameters, generically degenerate Bogdanov-Takens bifurcations of codimension-3 are detected. However, when these techniques are applied to the transport model, we detect a degenerate Bogdanov-Takens bifurcation of codimension 4. The nearby 1- and 2-parameter slices are in agreement with the presence of this codimension-4 degenerate Bogdanov-Takens bifurcation, and all three types of L-H transitions can be recognized in these slices. The same codimension-4 situation is observed under variation of the additional parameters in the model, and under some modifications of the model. (C) 2016 Elsevier B.V. All rights reserved.</p
Silicon carbide-based membranes with high soot particle filtration efficiency, durability and catalytic activity for CO/HC oxidation and soot combustion
No full textWe report here the solution coatings of Diesel Particulate Filter (DPF) with allylhydridopolycarbosilane (AHPCS)-based polymers leading to supported silicon carbide (SiC)-based membranes with high temperature soot particle filtration efficiency, durability and catalytic activity. In a first part of the present study, our objective was to reduce the pore size of DPF to filtrate finer particles without altering filtration efficiency by coating DPF with an additional fine porous AHPCS-derived SiC membrane. The latter is produced by dip-coating AHPCS on DPF following by a pyrolysis of the AHPCS membrane-modified DPF at 1000 °C under argon. We investigated the influence of dip-coating parameters and viscosity of different AHPCS solutions on the SiC membrane-coated DPF by SEM, mercury porosimetry, XRD and high-temperature thermogravimetric analysis. The evolution of the filtration capacity has been determined with a synthetic gas bench. An additional fine SiC membrane (∼150 nm in thickness) prepared from a 10 vol% of AHPCS in THF deposited on DPF allowed maintaining filtration efficiency as high as the virgin DPF while the pore size of the SiC membrane coated-DPF decreased to filter finer particles. Results are confirmed using a commercially-available polysiloxane (Si–C–O precursor). Furthermore, the SiC membrane acted as a thermal barrier coating and provided a better durability to the DPF by preventing apparition of cracks after heat-treatment to 1500 °C under argon. The use of mixed oxide and metallic phases formed in-situ in SiC constitutes one of the solutions to generate new and effective catalytic performances to membranes. Within this context, in a second part of the study, we applied a reverse AHPCS-based microemulsion to combine SiC and oxide phases in the same additional porous membrane. As a proof of concept, we have prepared catalytically active Ce–O–Fe–Pt/SiC membrane coated DPF after dip-coating and pyrolysis under argon. These materials have been characterized and tested with regard to CO/HC oxidation and soot combustion. Ce–O–Fe–Pt/SiC membrane coated DPF showed an activity for CO conversion reaching a light-off temperature T50=270 °C and the presence of the catalytic phase allowed burning soot at 486 °C
Metallic nanostructures for efficient LED lighting
No full textLight-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light–matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination
Blistering on tungsten surface exposed to high flux deuterium plasma
No full textThe blistering behaviour of tungsten surfaces exposed to very high fluxes (1–2 × 1024/m2/s) of low energy (38 eV) deuterium plasmas was investigated as a function of ion fluence (0.2–7 × 1026 D/m2) and surface temperature (423–873 K). Blisters were observed under all conditions, especially up to temperatures of 873 K. The blister parameters are evaluated with blister size, blister density and surface coverage. The blister size always peaked at less than 0.5 μm and no blister larger than 10 μm is observed even at high fluence. The blister densities are found in high magnitude of 106 blisters/m2, with the surface coverages lower than 2%. The formation of cracks in the sub-surface region was observed by cross-section imaging. Changes in blister size and shape with fluence and temperature suggest processes of predominantly nucleation and subsequent growth of blisters. The smaller blister size is considered to be caused by a combination of flux-related effects such as enhanced defect formation in the near surface region, reduced deuterium diffusivity and relatively short exposure times
