DIFFER: Publications
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Equilibration of Photogenerated Charge Carriers in Plasmonic Core@ Shell Nanoparticles
Get PDFNoble metal nanoparticles support localized surface plasmon resonances (LSPRs), which are light-driven oscillations of free electrons. Thanks to their strong dependence on the metal’s electron density, these resonances can be used to optically probe the equilibration of photogenerated charge carriers at metal/semiconductor interfaces, a process of paramount importance in energy conversion and sensing applications. In practice, however, it is often difficult to obtain quantitative insight from the observed plasmonic effects, as the spectral position, intensity, and line width of LSPRs can be influenced by different competing contributions, such as particle size distribution, surface oxidation, and changes in the dielectric environment. Here, we develop a two-step synthesis of Ag@TiO2 and Au@TiO2 core@shell nanoparticles and measure their plasmon resonance shifts during UV irradiation and charge equilibration in the dark. We show that the observed optical response can be fully accounted for by an accumulation of photogenerated electrons in the TiO2 shells and that charge transfer to the metal cores is negligible. Our results challenge the established understanding of charge equilibration in hybrid metal@semiconductor nanostructures.</p
Status of the Final Design of the EC UPP Launcher
No full textFour EC H&CD (Electron Cyclotron Heating and Current Drive) launchers will be installed into the upper ports #12, #13, #15 and #16 in ITER. Beside plasma heating their main purpose is to counteract plasma instabilities by injecting up to 20 MW of microwave power at a frequency of 170 GHz at dedicated positions into the plasma. The microwave power is generated in 24 Gyrotrons outside the Tokamak and transmitted into the dedicated ports by 8 waveguide lines per launcher. After passing a CVD (Chemical Vapor Deposition) diamond window and another section of circular waveguides, the microwaves are quasi-optically guided into the plasma by an adjusted set of mirrors. These mirrors and also the foremost segments of the waveguides are mounted into the Upper Port Plug, which is a massive steel structure capable to dissipate up to 800 kW heat and to withstand heavy mechanical loads induced mainly from plasma disruptions. This paper presents the most recent status of the design of the EC H&CD Upper Port Plug (UPP), featuring the construction of the supporting structure and the BSM (Blanket Shield Module) with its plasma facing First Wall, the PHTS (Primary Heat Transfer System) water cooling layout, the shielding components engineering, the microwave system integration and comprehensive manufacturing strategies. Also correlated computational analyses to prove the final design of the launcheŕs structural system are given
Nonlinear Emission of Molecular Ensembles Strongly Coupled to Plasmonic Lattices with Structural Imperfections
No full textWe demonstrate nonlinear emission from molecular layers strongly coupled to extended light fields in arrays of plasmonic nanoparticles in the presence of structural imperfections. Hybrid light-matter states, known as plasmon-exciton polaritons (PEPs), are formed by the strong coupling of Frenkel excitons in molecules to surface lattice resonances. These resonances result from the radiative coupling of localized surface plasmon polaritons in silver nanoparticles enhanced by diffraction on the array. By designing arrays with different lattice constants, we show that the nonlinear emission frequency is solely determined by the relaxation of exciton polaritons through vibrational quanta in the molecules. We also observe long-range spatial coherence in the samples, which supports the explanation in terms of a nonlinear collective emission of strongly coupled PEPs. In contrast to recent observations of exciton-polariton lasing and condensation in organic systems, photonic modes play a minor role at the emission frequency in our system, and this emission has an undefined momentum because of the structural imperfections. This remarkable result reveals the rich and distinct physics of strongly coupled organic molecules to photonic cavities
The effects of electron cyclotron heating and current drive on toroidal Alfvén eigenmodes in tokamak plasmas
No full textDedicated studies performed for Toroidal AEs (TAEs) in ASDEX-Upgrade (AUG) discharges with monotonic q-profiles have shown that electron cyclotron resonance heating (ECRH) can make TAEs more unstable. In these AUG discharges, energetic ions driving TAEs were obtained by ion cyclotron resonance heating (ICRH). It was found that off-axis ECRH facilitated TAE instability, with TAEs appearing and disappearing on timescales of a few milliseconds when the ECRH power was switched on and off. On-axis ECRH had a much weaker effect on TAEs, and in AUG discharges performed with co- and counter-current electron cyclotron current drive (ECCD), the effects of ECCD were found to be similar to those of ECRH. Fast ion distributions produced by ICRH were computed with the PION and SELFO codes. A significant increase in Te caused by ECRH applied off-axis is found to increase the fast ion slowing down time and fast ion pressure causing a significant increase in the TAE drive by ICRH-accelerated ions. TAE stability calculations show that the rise in Te causes also an increase in TAE radiative damping and thermal ion Landau damping, but to a lesser extent than the fast ion drive. As a result of the competition between larger drive and damping effects caused by ECRH, TAEs become more unstable. It is concluded, that although ECRH effects on AE stability in present-day experiments may be quite significant, they are determined by the changes in the plasma profiles and are not particularly ECRH specific
Divertor power load studies for attached L-mode single-null plasmas in TCV
No full textThis paper investigates the power loads at the inner and outer divertor targets of attached, Ohmic L-mode, deuterium plasmas in the TCV tokamak, in various experimental situations using an Infrared thermography system. The study comprises variations of the outer divertor leg length and target flux expansion, the plasma current and a reversal of the magnetic field direction. The direct impact of the divertor magnetic geometry on scrape-off layer (SOL) transport -parameterised by the SOL power fall-off length lambda_{q, u}, the divertor spreading factor S u and the in-out power asymmetry- is reported for constant core properties. The in-out power asymmetry increases, either with the divertor leg length, or the target flux expansion. The SOL width lambda_{q, u} scales positively with divertor leg length, with a strength that depends on the field direction and differs between the inner and outer divertor. This implies a parametric dependence of lambda_{q, u} that is not explicitly included in current multi-machine scaling laws. The divertor spreading factor at the target S = S_u f_x , where f_x is the target flux expansion, appears unaffected by changes in the divertor geometry and in the plasma current, is independent of the magnetic field direction and is similar between inner and outer divertor. Possible interpretations of these observations using an ad-hoc analytical purely conductive model for the SOL, by ion drifts or by asymmetric turbulent cross-field transport in the divertor are presented. The observed values of lambda_{q, u} are related to existing L-mode and H-mode scaling laws and to similar studies in other tokamaks. Finally, potential implications of these findings for future larger fusion machines are discussed
Where to improve in human-in-the-loop tele-operated maintenance? A phased task analysis based on video data of maintenance at JET
No full textFor the planned teleoperated maintenance of the experimental fusion plant ITER the time performance will be critical. Telemanipulated task execution is however characterised by long execution times compared to similar tasks performed hands-on. There is little quantitative research on task performance of telemanipulated maintenance available to give insight into most effective areas for improvement. In this paper a detailed analysis of real world remote maintenance at fusion plant JET is performed with the aim to: i) identify bottlenecks in task completion time and ii) quantify the room for potential improvement. Video recordings of the installation of 50 tiles executed by the three official master-slave operators were analysed. The task execution was characterised by a large variation in time performance, between but also within operators. Reduction of this variation could theoretically result in time reduction up to 41%. Recurring tasks like ‘rough/fine approach’ and ‘retreat’ covered more than 50% of the total task completion time and were identified as most promising for further improvement. The results will be the base for further research on operator assistance with augmented visual or haptic guidance
New n‐Type Solution Processable All Conjugated Polymer Network: Synthesis, Optoelectronic Characterization, and Application in Organic Solar Cells
No full textThe efficient synthesis of a new solution‐processable n‐type conjugated polymer network (PNT1) is reported through palladium‐catalyzed Stille cross‐coupling reaction conditions following the A3 + B2 synthetic approach. A benzo[1,2‐b:3,4‐b′:5,6‐b″]trithiophene derivative is used as the A3 knot and an alkyl functionalized naphthalenediimide is utilized as the B2 linker. The thermal, optical, and electrochemical properties are examined in detail, showing high thermal stability, absorbance in the visible part of the solar spectrum, and reversible reduction characteristics similar to those of the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). PNT1 is employed as the electron acceptor in solution‐processed bulk heterojunction organic solar cells, demonstrating the potential of this new type of materials for optoelectronic applications
Room Temperature Chiral Coupling of Valley Excitons with Spin-Momentum Locked Surface Plasmons
No full textWe demonstrate room temperature chiral coupling of valley excitons in a transition metal dichalcogenide monolayer with spin-momentum locked surface plasmons. At the onset of the strong coupling regime, we measure spin-selective excitation of directional flows of polaritons. Operating under such conditions, our platform yields surprisingly robust intervalley contrasts (ca. 40%) and coherence (ca. 5–8%) as opposed to their total absence for the uncoupled valley excitons at room temperature. These results open rich possibilities, easy to implement, in the context of chiral optical networks
A detailed look into hydrogen electrochemical oxidation on ceria anodes
No full textUsing the Nernst-Planck-Poisson model and a detailed reaction mechanism, we studied the hydrogen electrochemical oxidation on a ceria anode. Resistances caused by surface kinetics, and bulk transport of oxide-ion vacancies and electrons are computed individually to identify the dominant resistive process. The effect of operating conditions like temperature and gas-phase composition on the polarization resistance is evaluated and compared with the experimental data obtained by Electrochemical Impedance Spectroscopy (EIS). The rate-determining step is found to be the charge-transfer reaction in which hydrogen adsorbs at the surface oxide ions and forms hydroxyls along with the charge-transfer to adjacent cerium ions. Based on the rate-determining step, the exchange-current density is also calculated and validated with the experimental data
