| 1. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 2. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 3. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 4. |
- Jiang, Mingkai, et al.
(författare)
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The fate of carbon in a mature forest under carbon dioxide enrichment
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 580:7802, s. 227-231
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1–5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3–5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7–10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7–11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.
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| 5. |
- Jackson, R B, et al.
(författare)
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Belowground consequences of vegetation change and their treatment in models
- 2000
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Ingår i: Ecological Applications. - 1051-0761. ; 10:2, s. 470-483
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Tidskriftsartikel (refereegranskat)abstract
- The extent and consequences of global land-cover and land-use change are increasingly apparent. One consequence not so apparent is the altered structure of plants belowground. This paper examines such belowground changes, emphasizing the interaction of altered root distributions with other factors and their treatment in models. Shifts of woody and herbaceous vegetation with deforestation, afforestation, and woody plant encroachment typically alter the depth and distribution of plant rests, influencing soil nutrients, the water balance, and net primary productivity (NPP). For example, our analysis of global soil data sets shows that the major plant nutrients C, N, P, and K are more shallowly distributed than are Ca, Mg, and Na, but patterns for each element vary with the dominant vegetation type. After controlling for climate, soil C and N are distributed more deeply in arid shrublands than in arid grasslands, and subhumid forests have shallower nutrient distributions than do subhumid grasslands. Consequently, changes in vegetation may influence the distribution of soil carbon and nutrients over time (perhaps decades to centuries). Shifts in the water balance are typically much more rapid. Catchment studies indicate that the water yield decreases 25-40 mm for each 10% increase in tree cover, and increases in transpiration of water taken up by deep roots may account for as much as 50% of observed responses. Because models are increasingly important for predicting the consequences of vegetation change, we discuss the treatment of belowground processes and how different treatments affect model outputs. Whether models are parameterized by biome or plant life form (or neither), use single or multiple soil layers, or include N and water limitation will all affect predicted outcomes. Acknowledging and understanding such differences should help constrain predictions of vegetation change.
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| 6. |
- Baxter, D., et al.
(författare)
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Recommended conventions for reporting results from direct dark matter searches
- 2021
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:10
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Tidskriftsartikel (refereegranskat)abstract
- The field of dark matter detection is a highly visible and highly competitive one. In this paper, we propose recommendations for presenting dark matter direct detection results particularly suited for weak-scale dark matter searches, although we believe the spirit of the recommendations can apply more broadly to searches for other dark matter candidates, such as very light dark matter or axions. To translate experimental data into a final published result, direct detection collaborations must make a series of choices in their analysis, ranging from how to model astrophysical parameters to how to make statistical inferences based on observed data. While many collaborations follow a standard set of recommendations in some areas, for example the expected flux of dark matter particles (to a large degree based on a paper from Lewin and Smith in 1995), in other areas, particularly in statistical inference, they have taken different approaches, often from result to result by the same collaboration. We set out a number of recommendations on how to apply the now commonly used Profile Likelihood Ratio method to direct detection data. In addition, updated recommendations for the Standard Halo Model astrophysical parameters and relevant neutrino fluxes are provided. The authors of this note include members of the DAMIC, DarkSide, DARWIN, DEAP, LZ, NEWS-G, PandaX, PICO, SBC, SENSEI, SuperCDMS, and XENON collaborations, and these collaborations provided input to the recommendations laid out here. Wide-spread adoption of these recommendations will make it easier to compare and combine future dark matter results.
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| 7. |
- Matthews, G. F., et al.
(författare)
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Overview of the ITER-like wall project
- 2007
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T128, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- Work is in progress to completely replace, in 2008/9, the existing JET CFC tiles with a configuration of plasma facing materials consistent with the ITER design. The ITER-like wall (ILW) will be created with a combination of beryllium ( Be), tungsten ( W), W-coated CFC and Be-coated inconel tiles, with the material depending on the local anticipated heat flux and geometry. It is part of an integrated package of JET enhancements whose aim is to develop an understanding of the ITER materials issues and develop the techniques required to operate with inductive and advanced scenarios as close as possible to ITER parameters. Over 4000 tiles will be replaced and the ILW will accommodate additional heating up to at least 50 MW for 10 s. This paper describes the scientific background to the project, the technical objectives, the material configuration selected, the R&D behind the practical realization of the objectives and the generic problems associated with the Be tiles ( power handling capacity and disruption induced eddy currents). One of the objectives is to maintain or improve the existing CFC tile power handling performance which has been achieved in most cases by hiding bolt holes, optimizing tile size and profile and introducing castellations on plasma facing surfaces.
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| 8. |
- Rasmussen, Pil U., et al.
(författare)
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The impact of dispersal, plant genotype and nematodes on arbuscular mycorrhizal fungal colonization
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 132, s. 28-35
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Tidskriftsartikel (refereegranskat)abstract
- While the majority of parasitic and mutualistic microbes have the potential for long-range dispersal, the high turnover in community composition among nearby hosts has often been interpreted to reflect dispersal constraints. To resolve this apparent contradiction, we need further insights into the relative importance of dispersal limitation, host genotype and the biotic environment on the colonization process. We focused on the important root symbionts, the arbuscular mycorrhizal (AM) fungi. We studied AM fungal colonization ability in a controlled mesocosm setting, where we placed Plantago lanceolata plants belonging to four different genotypes in sterile soil at 10, 30 and 70 cm from a central AM fungal inoculated P. lanceolata plant. In part of the mesocosms, we also inoculated the source plants with nematodes. AM fungi colonized receiver plants <1 m away over the course of ten weeks, with a strong effect of distance from source plant on AM fungal colonization. Plant genotype influenced AM fungal colonization during the early stages of colonization, while nematode inoculation had no effect on AM fungal colonization. Overall, the effect of both dispersal limitation and plant genetic variation may underlie the small-scale heterogeneity found in natural AM fungal communities.
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| 9. |
- Wörman, Anders, et al.
(författare)
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Spectral scaling of heat fluxes in streambed sediments
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39:23, s. L23402-
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Tidskriftsartikel (refereegranskat)abstract
- Advancing our predictive capabilities of heat fluxes in streams and rivers is important because of the effects on ecology and the general use of heat fluxes as analogues for solute transport. Along these lines, we derived a closed-form solution that relates the in-stream temperature spectra to the responding temperature spectra at various depths in the sediment through a physical scaling factor including the effective thermal diffusivity and the Darcy flow velocity. This analysis considers the range of frequencies in temperature fluctuations that occur due to diurnal and meteorological variation both in the long and short term. This approach provides insight regarding the key frequencies for analysing temperature responses at different depths within the sediment and also provides a simple and accurate method that offers quantitative insight into heat transport and surface water interactions with groundwater. We demonstrate for Sava Brook, Sweden, how the values of effective thermal diffusivities can be estimated based on the observed in-stream and sediment temperature time series and explain the temporal scaling of the heat transport as a function of a dimensionless frequency number. We find that the lower limit of periods of significance for the analysis increases with depth, and we recommend further research regarding appropriate frequency windows.
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