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Interference-enhanced absorption of visible and near-infrared radiation in ultrathin film coatings
Full text linkWe report the interference-enhanced absorption of electromagnetic radiation in two-layer lossy coatings on metal substrates. The conditions for the complete absorption of monochromatic radiation are described in comparison with those in previously studied single-layer coatings. Proof-of-principle measurements of the interference-enhanced absorption in the near-infrared range are presented for silicon-on-germanium coatings on aluminum substrates. We also provide various examples of materials that can be used to create similar light-absorbing coatings for visible and near-infrared ranges. The proposed design can be applied to optical filters, optoelectronic devices, photodetectors, and light-emitting devices.</p
Monitoring of tritium and impurities in the first wall of fusion devices using a LIBS based diagnostic
Full text linkLaser-Induced Breakdown Spectroscopy (LIBS) is one of the most promising methods for quantitative in-situ determination of fuel retention in Plasma-Facing Components (PFCs) of fusion devices. The current state of understanding in LIBS development for fusion applications will be presented, based on a complete review of existing results and complemented with newly obtained data. The work has been performed as part of a research programme, set up in the EUROfusion Consortium, to address the main requirements for ITER: a) quantification of fuel from relevant surfaces with high sensitivity, b) the technical demonstration to perform LIBS with a remote handling system and c) accurate detection of fuel at ambient pressures relevant for ITER. The elemental composition of ITER-like deposits, including deuterium (D: as substitute for tritium (T)) or helium (He) containing W-Be, W, W-Al and Be-O-C coatings, was successfully determined: D surface densities below 1016 D/cm2 could be measured with an accuracy of ~30% (depth resolution 50-250 nm). A remote handling application was demonstrated inside the Frascati-Tokamak-Upgrade (FTU), where a compact, remotely controlled LIBS system was mounted on a multipurpose deployer providing an in-vessel retention monitor system. LIBS was performed at atmospheric pressure for measuring the composition and fuel content of different area of the FTU first wall and toroidal limiter. Concerning the capabilities of LIBS at pressure conditions relevant for ITER, quantitative determination of the composition of PFC materials at ambient pressures up to 100 mbar of N2, the D content could be determined with an accuracy of 25% (50% at 1 bar using single-pulse lasers). To improve the LIBS performance in atmospheric pressure conditions, a novel approach, based on an alternative LIBS detection timing scheme, is proposed. The application of double pulse LIBS at atmospheric pressure improved the distinguishability of H isotope lines significantly, but further research is required.</p
Topology of the Warm plasma dispersion relation at the second Harmonic Electron Cyclotron Resonance Layer
No full textThe Warm Plasma Dispersion Relation, for waves in the electron cyclotron resonance range of frequencies, can be cast into the form of a bi-quadratic equation for N⊥, where the coefficients are a function of N2⊥ and an iterative procedure is required to obtain a solution. However, this iterative procedure is not well understood and fails to converge towards a solution at the 2nd harmonic resonance layer, in particular at higher densities where the wave can couple to an electron Bernstein wave. This paper focuses on a solution to the poor convergence of the iterative method, enabling determination of the topology of the dispersion relation around the 2nd harmonic using a fully relativistic code for oblique waves. A feed-forward controller is proposed with the ability to adjust the rotation of a step of N2⊥ within the complex plane, while also limiting the step-size. It is shown that implementation of the controller stabilizes unstable solutions, while improving overall robustness of the iteration. This allows the evaluation of the coupling between the fast extraordinary mode and electron Bernstein waves at the 2nd harmonic electron cyclotron resonance layer, for non-perpendicularly propagating waves.</p
Measurement of the 2D emission profiles of hydrogen and impurity ions in the TCV divertor
No full textPlasma emission of hydrogen and impurities is measured with use of filtered camera imaging in TCV divertor. The measurement technique is discussed in detail including: selection choice of filters, the absolute calibration procedure and the tomographic inversion. The process is applied to an unseeded L-mode density ramp discharge in an unfavorable for H-mode access magnetic field direction with divertor baffles. Obtained poloidal emission profiles are used to split Balmer emission into excitation and recombination parts revealing a recombination emission maximum on the high field side. The optical emission is further studied by selecting radial profiles in cross sections of interest finding an opposite radial shift direction for high and low n Balmer line emission maxima in detached conditions
Advanced methods in control of the core density and divertor detachment in nuclear fusion devices
No full textMicrostructure study of pulsed laser beam welded oxide dispersion-strengthened (Ods) eurofer steel
No full textOxide dispersion-strengthened (ODS) Eurofer steel was laser welded using a short pulse duration and a designed pattern to minimise local heat accumulation. With a laser power of 2500 W and a duration of more than 3 ms, a full penetration can be obtained in a 1 mm thick plate. Material loss was observed in the fusion zone due to metal vaporisation, which can be fully compensated by the use of filler material. The solidified fusion zone consists of an elongated dual phase microstructure with a bimodal grain size distribution. Nano-oxide particles were found to be dispersed in the steel. Electron backscattered diffraction (EBSD) analysis shows that the microstructure of the heat-treated joint is recovered with substantially unaltered grain size and lower misorientations in different regions. The experimental results indicate that joints with fine grains and dispersed nano-oxide particles can be achieved via pulsed laser beam welding using filler material and post heat treatment
Efficient Solar Cells Based on a Polymer Donor with β-Branching in Trialkylsilyl Side Chains
No full textDetachment in conventional and advanced double-null plasmas in TCV
Full text linkDivertor detachment is investigated on the Tokamak à Configuration Variable (TCV) for conventional and alternative double-null (DN) magnetic geometries in L-mode, Ohmic density ramps and then compared to precisely matched single-null (SN) geometries. The poloidal flux expansion at the outer strikepoint(s) is varied by a factor 2 and the total flux expansion by 30% in lower single null (LSN) and DN configurations. Leg power sharing for DN and near-DN in attached conditions is in line with previous studies in other devices, with balanced power partition between upper and lower divertor achieved for |δRsep| ≲ λq/2. This results in a reduction in the lower outer target integral and peak heat flux compared to a LSN by 30%. Unlike previous studies, λq is fairly insensitive to δRsep. The detachment threshold in these geometries is investigated from target measurements with wall-embedded Langmuir probes and two-dimensional CIII line emissivity profiles across the two divertor regions. DN plasmas display clear benefits compared to their LSN counterparts. Transitioning from a LSN to DN shows a substantial reduction, of approx. 20%–25%, in the detachment threshold for the active divertor legs as well as a 50% higher radiated fraction at all (n e). The density limit is simultaneously reduced in DN by 10%–20%. Across the explored range, poloidal flux expansion has only a small effect on the detachment threshold in LSN (as seen in previous experiments), and no effect in DN, with similar observations for the total flux expansion. In general, no strong benefits of increased poloidal or total flux expansion are observed across the explored range.</p
Catalyst-assisted DBD plasma for coupling of methane: Minimizing carbon-deposits by structured reactors
No full textNon-oxidative coupling of methane has been performed in DBD plasma reactors with a catalytic layer with varying thickness loaded on the reactor wall. These structured reactors allow to study the effect of the thickness of the catalyst layer, including the blank plasma reactor, without significant modification of plasma properties, SEI and residence time. Moreover, it allows analysis of the catalytic effect of Pd/Al2O3. The catalyst layer decreases the methane conversion only mildly, which is attributed to hydrogenation of CHx radicals at the outer surface of the catalyst layer. This results in typically 34% methane conversion at 2.8 W at room temperature with 6% CH4 in Ar, independently of the layer thickness. In contrast, the thickness of the catalyst layer strongly influences the product distribution, assigned to hydrogenation of acetylenes at external and internal surfaces in the catalyst layer. The formation of undesired deposits is suppressed by a factor of 2 with value-added hydrocarbons selectivity of 70% and a carbon balance of 93%. In addition, catalytic-wall reactors was compared with packed bed reactors. The synergistic effect is much more evident in the structured reactor than in the packed bed reactor, independently of the position of the catalytic bed.</p
