DIFFER: Publications
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Simulation of core turbulence measurement in Tore Supra ohmic regimes
No full textThis paper reports on a simulation of reflectometry measurement in Tore Supra ohmic discharges, for which the experimental observations as well as gyrokinetic non-linear computations predict a modification of turbulence spectrum between the linear (LOC) and the saturated ohmic confinement (SOC) regimes. Synthetic reflectometry simulations coupling full-wave computations with gyrokinetic data are carried out. This allows a direct comparison between the gyrokinetic non-linear predictions and experimental observations. The synthetic diagnostic results are found in a good agreement with the experimental findings; in particular, they reproduce well the quasi-coherent peak in the fluctuation spectrum of LOC regimes dominated by a trapped electron mode turbulence. It is also shown that such synthetic tools are valuable for (i) an enhanced interpretation of the reflectometry measurement (for instance, through the investigation of the 2D effects) and (ii) a better understanding of the turbulence properties (for instance, via the analysis of its poloidal asymmetry)
Early evolution of electron cyclotron driven current during suppression of tearing modes in a circular tokamak
No full textPlasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium
No full textThe plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement around the outboard midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the predictions from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components vertical bar m vertical bar > vertical bar nq vertical bar, whereas the poloidal mode structure of its displacement is almost resonant vertical bar m vertical bar approximate to vertical bar nq vertical bar. This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response.</p
Solar fuel production in a novel polymeric electrolyte membrane photoelectrochemical (PEM-PEC) cell with a web of titania nanotube arrays as photoanode and gaseous reactants
No full textA novel photoelectrochemical (PEC) cell design is proposed and investigated for H-2 production with gaseous reactants. The core of the cell is a membrane electrode assembly (MEA) that consists of a TiO2 nanotube arrays photoanode, a Pt/C cathode, a Pt/C reference electrode and a proton conducting polymeric electrolyte membrane (PEM), which serves both as compact reactor for water splitting and as gas separator. The design is inspired by PEM electrolysis technology and modified appropriately to allow light irradiation and to host a third electrode compartment, which enables the use of a hydrogen reference electrode. The titanium dioxide nanotube arrays (TNTAs) photoanodes were synthetized, for the first time, on a Ti-web of microfiber substrates by electrochemical anodization. The performance of TNTAs/Ti-web photoanodes were evaluated in both gaseous (i.e. PEM-PEC cell) and liquid media (conventional PEC cell). Due to the presence of the PEM-PEC reference electrode comparison of the results was possible. Gas phase operation with either He or air as carrier exhibits very promising photoefficiency in comparison with conventional PEC cells. Additionally the performance of our PEM-PEC cell was also investigated for simultaneous anodic air treatment and cathodic hydrogen evolution. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Collective Thomson scattering system for determination of ion properties in a high flux plasma beam
No full textA collective Thomson scattering system has been developed for measuring ion temperature, plasma velocity and impurity concentration in the high density magnetized Magnum-PSI plasma beam, allowing for measurements at low temperature (<5 eV) and high electron density >4 × 1020 m−3, while avoiding laser plasma heating caused by inverse Bremsstrahlung. The collective Thomson scattering system is based on the fundamental mode of a seeded Nd:YAG laser and equipped with an LIVAR M506 camera (EBABS technology). The first collective Thomson scattering measurements are taken at the linear plasma generator Pilot-PSI, 40 mm downstream of the cascaded arc source. At this location, the ion temperature is about equal to the electron temperature in the bulk of the plasma beam.</p
Interaction of adhered metallic dust with transient plasma heat loads
No full textThe first study of the interaction of metallic dust (tungsten, aluminum) adhered on tungsten substrates with transient plasma heat loads is presented. Experiments were carried out in the Pilot-PSI linear device with transient heat fluxes up to 550 MW m −2 and in the DIII-D divertor tokamak. The central role of the dust-substrate contact area in heat conduction is highlighted and confirmed by heat transfer simulations. The experiments provide evidence of the occurrence of wetting-induced coagulation, a novel growth mechanism where cluster melting accompanied by droplet wetting leads to the formation of larger grains. The physical processes behind this mechanism are elucidated. The remobilization activity of the newly formed dust and the survivability of tungsten dust on hot surfaces are documented and discussed in the light of implications for ITER.</p
