The appeal of trait‐based approaches for assessing environmental vulnerabilities arises from the potential insight they provide into the mechanisms underlying the changes in populations and community ...structure. Traits can provide ecologically based explanations for observed responses to environmental changes, along with predictive power gained by developing relationships between traits and environmental variables. Despite these potential benefits, questions remain regarding the utility and limitations of these approaches, which we explore focusing on the following questions: (a) How reliable are predictions of biotic responses to changing conditions based on single trait–environment relationships? (b) What factors constrain detection of single trait–environment relationships, and how can they be addressed? (c) Can we use information on meta‐community processes to reveal conditions when assumptions underlying trait‐based studies are not met? We address these questions by reviewing published literature on aquatic invertebrate communities from stream ecosystems. Our findings help to define factors that influence the successful application of trait‐based approaches in addressing the complex, multifaceted effects of changing climate conditions on hydrologic and thermal regimes in stream ecosystems. Key conclusions are that observed relationships between traits and environmental stressors are often inconsistent with predefined hypotheses derived from current trait‐based thinking, particularly related to single trait–environment relationships. Factors that can influence findings of trait‐based assessments include intercorrelations of among traits and among environmental variables, spatial scale, strength of biotic interactions, intensity of habitat disturbance, degree of abiotic stress, and methods of trait characterization. Several recommendations are made for practice and further study to address these concerns, including using phylogenetic relatedness to address intercorrelation. With proper consideration of these issues, trait‐based assessment of organismal vulnerability to environmental changes can become a useful tool to conserve threatened populations into the future.
Traits of organisms are frequently used to explain the changes in populations and communities in response to environmental conditions. Using the example of stream invertebrates and climatic variables, we demonstrate inconsistencies in the relationships between individual traits and selected environmental variables. This variation may be attributable to multiple factors including trait intercorrelations, biotic interactions, and community‐assembly processes. We discuss how these factors could be considered in trait–environment analyses to be useful for conservation and bioassessment.
Experiments in JET with carbon-based plasma-facing components have been carried out in preparation of the ITER-Like Wall with beryllium main chamber and full tungsten divertor. The preparatory work ...was twofold: (i) development of techniques, which ensure safe operation with the new wall and (ii) provision of reference plasmas, which allow a comparison of operation with carbon and metallic wall. (i) Compatibility with the W divertor with respect to energy loads could be achieved in N2 seeded plasmas at high densities and low temperatures, finally approaching partial detachment, with only moderate confinement reduction of 10%. Strike-point sweeping increases the operational space further by re-distributing the load over several components. (ii) Be and C migration to the divertor has been documented with spectroscopy and QMBs under different plasma conditions providing a database which will allow a comparison of the material transport to remote areas with metallic walls. Fuel retention rates of 1.0–2.0×1021Ds−1 were obtained as references in accompanied gas balance studies.
The lifetime of the beryllium first wall in ITER will depend on erosion and redeposition processes. The physical sputtering yields for beryllium (both deuterium on beryllium (Be) and Be on Be) are of ...crucial importance since they drive the erosion process. Literature values of experimental sputtering yields show an order of magnitude variation so predictive modelling of ITER wall lifetimes has large uncertainty. We have reviewed the old beryllium yield experiments on JET and used current beryllium atomic data to produce revised beryllium sputtering yields. These experimental measurements have been compared with a simple physical sputtering model based on TRIM.SP beryllium yield data. Fair agreement is seen for beryllium yields from a clean beryllium limiter. However the yield on a beryllium divertor tile (with C/Be co-deposits) shows poor agreement at low electron temperatures indicating that the effect of the higher sputtering threshold for beryllium carbide is important.
Chemical erosion of carbon can be described as function of the incident ion flux, the ion energy and the surface temperature. Spectroscopy on the hydrocarbon break-up products CH and C2 is applied to ...determine in-situ hydrocarbon fluxes and quantify the chemical erosion by means of hydrocarbon injection. Present-day knowledge on critical issues concerning the erosion yield and its determination is presented: Effective inverse photon efficiencies are measured in TEXTOR for different hydrocarbon species and compared with calculations from HYDKIN. The underlying database for the methane break-up, used in different erosion/deposition models, has been put to test. The chemical erosion yield related to higher hydrocarbons is determined to be lower in the JET outer divertor than measured in previous experiments. In ASDEX Upgrade and DIII-D first in-situ calibrations of hydrocarbon fluxes in the detached outer divertor are performed.
The impact of large ELMs on JET Pitts, R.A.; Arnoux, G.; Beurskens, M. ...
Journal of nuclear materials,
06/2009, Letnik:
390
Journal Article, Conference Proceeding
Recenzirano
To ensure sufficient divertor target lifetime, the loss in plasma stored energy due to ELMs in ITER should be restricted to Δ
W
ELM
⩽
1
MJ. Only in JET, by virtue of its size, can such energies be ...approached. This contribution examines the impact of large, Type I ELMs in high current H-mode JET discharges with ITER-relevant pedestal characteristics. The ELMs provoke strong radiation losses, mostly confined to the inner divertor volume. Although the data are scattered, the average magnitude of this loss is Δ
E
RAD
∼
0.5Δ
W
ELM, for Δ
W
ELM
<
0.55
MJ. For higher Δ
W
ELM, greater fractional radiation losses occur, reaching ∼0.7Δ
W
ELM at Δ
W
ELM
∼
0.9
MJ, indicating enhanced impurity release. Even at the highest ELM energies, peak divertor target surface temperatures are too low for carbon sublimation, suggesting that thermal decomposition and/or ablation of thick co-deposited layers on the inner target may be occurring. On average, across the range of energies studied, ELMs are found to deposit between 3–4.5% of Δ
W
ELM on main wall limiters. When applied to the data for a specific discharge in the series, the model of ELM filament parallel energy losses developed at JET requires radial ELM velocities in the interval 0.1–0.65
km
s
−1 to explain these deposited energy fractions.
► A new wide angle view camera system has been installed at JET. ► The system helps to protect the ITER-like wall plasma facing components from damage. ► The coverage of the vessel by camera ...observation systems was increased. ► The system comprises an in-vessel part with parabolic and flat mirrors. ► The required image quality for plasma monitoring and wall protection was delivered.
A new wide angle view camera system has been installed at JET in preparation for the ITER-like wall campaigns. It considerably increases the coverage of the vessel by camera observation systems and thereby helps to protect the – compared to carbon – more fragile plasma facing components from damage. The system comprises an in-vessel part with parabolic and flat mirrors and an ex-vessel part with beam splitters, lenses and cameras. The system delivered the image quality required for plasma monitoring and wall protection.
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