High power ECRH and ECCD in moderately collisional ASDEX upgrade H-modes and status of EC system upgrade

This contribution deals with H-modes with significant heat exchange between electrons and ions, but which can still show large differences between electron and ion-temperatures especially inside half minor radius. These conditions are referred to as moderately collisional. A systematic study shows that an increasing fraction of electron heating increases the transport in the ion channel mainly due to the dependence of the ITG dominated ion transport on the ratio Te/Ti in agreement with modeling. The rotational shear in the plasmas under study was so small that it hardly influences ITG stability, such that variations of the rotation profile due to a change of the heating method were of minor importance. These findings connect to studies of advanced tokamak scenarios using ECCD as a tool to modify the q-profile. The electron heating connected to the ECCD tends to increase the transport in the ion channel quite in contrast to the goal to operate at reduced current but with increased confinement. The confinement only increases as the fraction of ion heating is increased by adding more NBI. An ITER case was modeled as well. Due to the larger value of νei ・ τE the ratio Te/Ti is only moderately reduced even with strong electron heating and the confinement reduction is small even for the hypothetic case of using only ECRH as additional heating. Finally the paper discusses the ongoing upgrade of the AUG ECRH-system

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Spatially resolved characterization of PEFCs using simultaneously neutron radiography and locally resolved impedance spectroscopy

A method for performing neutron radiography and locally resolved impedance spectroscopy simultaneously in Situ in all operating polymer electrolyte fuel cell (PEFC) is presented. The new method provides Concurrently spatially resolved information about the local cell performance, the locally limiting processes, and the liquid water distribution. Information about the impact of water oil cell performance and limiting processes call be gained in situ oil a local scale in all operating PEFC. The method was applied to a PEFC operated oil pure H-2/O-2 in co-flow mode under low humidity operating conditions. The results show that in co-flow mode strong flooding and severe drying can Occur at the very same time in different sections of a PEFC

Effect of inert gas flow on hydrogen underpotential deposition measurements in polymer electrolyte fuel cells

The effect of inert gas flow rate on hydrogen underpotential deposition (H-upd) measurements in polymer electrolyte fuel cells (PEFCs) was investigated using a novel experimental technique. The method combines local voltammetric measurements in PEFCs with the use of sectioned electrodes. The results give experimental proof that the high inert gas flow rate usually employed in voltammetric measurements in PEFCs at the working electrode results in high hydrogen reduction currents in both the cathodic and the anodic sweep, which hampers an accurate determination of the electrochemically active surface area (ECA). Strong spatial inhomogeneities occur at low potentials as a consequence of formation and accumulation of molecular hydrogen along the flow field. The results show that the flow of inert gas should be minimized or even stopped during a measurement to allow molecular hydrogen to accumulate at the working electrode and to provide uniform conditions along the flow field

Oscillations in gas channels. II. Unraveling the characteristics of the low frequency loop in air-fed PEFC impedance spectra

The effect of oxygen depletion along the cathode flow channels on the local impedance response of a polymer electrolyte fuel cell (PEFC) operated on air and pure hydrogen was investigated using a novel experimental approach. The method combines the use of sectioned electrodes and local ac measurements in PEFCs. The results shown here give experimental proof that oxygen concentration oscillations in the cathode gas channels generated as a consequence of ac current flow evoke the formation of a low frequency capacitive loop in local H-2/air-PEFC impedance spectra in downstream parts of the flow field. The loop shows positive or negative real parts at low frequencies depending on the air stoichiometry. The loop is not observed in the local spectrum when the ac current is applied locally and, consequently, the impact of upstream processes on the local impedance response is excluded. A mechanistic description of the processes occurring during ac measurements in H-2/air-PEFCs was developed and validated by experiments. The results show that processes occurring along the flow channels of a PEFC cannot be excluded from the interpretation of PEFC impedance spectra even at rather high air stoichiometries and are in fact the most important phenomena at low modulation frequencies (f(mod)< 10 Hz)