| 1. |
- Fenstermacher, M.E., et al.
(author)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Journal article (peer-reviewed)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. |
- Higgins, Charlotte, et al.
(author)
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Planning tools and methods for systems facing high levels of distributed energy resources
- 2023
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Conference paper (peer-reviewed)abstract
- It is important for utilities to plan for Distributed Energy Resources (DER) uptake by representing and modelling their characteristics using appropriate assumptions, methods and tools. Large-scale DER deployment impacts power flows and power system performance in various complex ways as well as potentially contributing to ancillary services. In this paper, we explore state of the art planning methods and tools being developed and deployed by utilities internationally, for systems facing high levels of distributed energy resources. This is part of technical working group C1 6.42 and our findings will be further expanded in the full technical brochure to be published in 2023. A survey of 17 international utilities was carried out to inform our study. In network planning, DER can broadly be treated similar to any other energy source. However, complexity arises particularly from several aspects: 1) how to model the impact of diverse, distributed DER at transmission and distribution network level and 2) how to model and characterise the impact of higher uncertainty from DER. This has led to a wider range of study conditions being considered using clustered time series and probabilistic methods to efficiently capture varying geospatial generation and demand during different times and seasons.Novel modelling approaches to representing DER in steady state and dynamic/transient studies have also been developed. These can have strengths and weaknesses and simulations of severe grid disturbances often fail to reproduce the widespread tripping of DER that can occur in reality, for example. Plant specific tuning for DER models and EMT modelling of high penetration networks are under development to better model behaviour under transient conditions. In order to provide greater whole-system representation, EMTP type numerical tools have been used to solve load flow problems with both transmission systems and distribution systems integrated into one network model. Hybrid/co-simulation approaches and dynamic phasor techniques are also being explored. More sophisticated and innovative statistical methods are also being applied to understand the impacts of DER and other uncertainty. Development of resilience standards and a more standardised approach to resilience modelling will support the improved consideration and contribution of DER in a resilient, decarbonised grid.
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| 3. |
- Li, Zhen, et al.
(author)
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Soil incubation methods lead to large differences in inferred methane production temperature sensitivity
- 2024
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In: Environmental Research Letters. - 1748-9326. ; 19:4
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Journal article (peer-reviewed)abstract
- Quantifying the temperature sensitivity of methane (CH4) production is crucial for predicting how wetland ecosystems will respond to climate warming. Typically, the temperature sensitivity (often quantified as a Q10 value) is derived from laboratory incubation studies and then used in biogeochemical models. However, studies report wide variation in incubation-inferred Q10 values, with a large portion of this variation remaining unexplained. Here we applied observations in a thawing permafrost peatland (Stordalen Mire) and a well-tested process-rich model (ecosys) to interpret incubation observations and investigate controls on inferred CH4 production temperature sensitivity. We developed a field-storage-incubation modeling approach to mimic the full incubation sequence, including field sampling at a particular time in the growing season, refrigerated storage, and laboratory incubation, followed by model evaluation. We found that CH4 production rates during incubation are regulated by substrate availability and active microbial biomass of key microbial functional groups, which are affected by soil storage duration and temperature. Seasonal variation in substrate availability and active microbial biomass of key microbial functional groups led to strong time-of-sampling impacts on CH4 production. CH4 production is higher with less perturbation post-sampling, i.e. shorter storage duration and lower storage temperature. We found a wide range of inferred Q10 values (1.2–3.5), which we attribute to incubation temperatures, incubation duration, storage duration, and sampling time. We also show that Q10 values of CH4 production are controlled by interacting biological, biochemical, and physical processes, which cause the inferred Q10 values to differ substantially from those of the component processes. Terrestrial ecosystem models that use a constant Q10 value to represent temperature responses may therefore predict biased soil carbon cycling under future climate scenarios.
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| 4. |
- Abbafati, Cristiana, et al.
(author)
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- 2020
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Journal article (peer-reviewed)
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