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291. Study of liquid metal surface wave damping in the presence of magnetic fields and electrical currents

Author(s):
Fisher, A.E.; Hvasta, M.G.; Kolemen, E.
Abstract:
Experiments and predictions of surface wave damping in liquid metal due to a surface aligned magnetic field and externally regulated j × B force are presented. Fast-flowing, liquid-metal plasma facing components (LM-PFCs) are a proposed alternative to solid PFCs that are unable to handle the high heat flux, thermal stresses, and radiation damage in a tokamak. The significant technical challenges associated with LM-PFCs compared to solid PFCs are justified by greater heat flux management, self-healing properties, and reduced particle recycling. However, undesirable engineering challenges such as evaporation and splashing of the liquid metal introduce excessive impurities into the plasma and degrade plasma performance. Evaporation may be avoided through high-speed flow that limits temperature rise of the liquid metal by reducing heat flux exposure time, but as flow speed increases the surface may become more turbulent and prone to splashing and uneven surfaces. Wave damping is one mechanism that reduces surface disturbance and thus the chances of liquid metal impurity introduction into the plasma. Experiments on the Liquid Metal eXperiment Upgrade (LMX-U) examined damping under the influence of transverse magnetic fields and vertically directed Lorentz force.
Type:
Dataset
Issue Date:
March 2019

292. TRANSP-based closed-loop simulations of current profile optimal regulation in NSTX-Upgrade

Author(s):
Ilhan, Z.O.; Boyer. M.D.; Schuster, E.
Abstract:
Active control of the toroidal current density profile is critical for the upgraded National Spherical Torus eXperiment device (NSTX-U) to maintain operation at the desired high-performance, MHD-stable, plasma regime. Initial efforts towards current density profile control have led to the development of a control-oriented, physics-based, plasma-response model, which combines the magnetic diffusion equation with empirical correlations for the kinetic profiles and the non-inductive current sources. The developed control-oriented model has been successfully tailored to the NSTX-U geometry and actuators. Moreover, a series of efforts have been made towards the design of model-based controllers, including a linear-quadratic-integral optimal control strategy that can regulate the current density profile around a prescribed target profile while rejecting disturbances. In this work, the tracking performance of the proposed current-profile optimal controller is tested in numerical simulations based on the physics-oriented code TRANSP. These high-fidelity closed-loop simulations, which are a critical step before experimental implementation and testing, are enabled by a flexible framework recently developed to perform feedback control design and simulation in TRANSP.
Type:
Dataset
Issue Date:
March 2019

293. Supporting data for Baldwin et al 2019 "Temporally Compound Heat Waves and Global Warming: An Emerging Hazard"

Author(s):
Baldwin, Jane W; Dessy, Jay Benjamin; Vecchi, Gabriel A; Oppenheimer, Michael; Jia, Liwei; Gudgel, Richard G; Paffendorf, Karen
Abstract:
This data is compiled to support a publication in the journal Earth's Future: Baldwin et al 2019 "Temporally Compound Heat Waves and Global Warming: An Emerging Hazard". The GCM GFDL CM2.5-FLOR was used to produce the raw climate model data. The model code for FLOR is freely available and can be downloaded at https://www.gfdl.noaa.gov/cm2-5-and-flor/. Code used to calculate the derived heat wave statistics data and produce figures in the paper is available at https://github.com/janewbaldwin/Compound-Heat-Waves The heat wave statistics derived output for only one definition is provided (daily minimum temperature, 90th percentile threshold, temporal structure 3114) which is the definition used the most in the paper figures. Statistics for the other definitions can be created by running the HWSTATS code provided in the corresponding github folder, which includes python scripts which do the analysis and PBS job scheduling and submission scripts which show how to run the python scripts. For more information on this, please see the github readme.
Type:
Dataset
Issue Date:
17 February 2019

294. Application of transient CHI plasma startup to future ST and AT devices

Author(s):
Hammond, K.C.; Raman, R.; Jardin, S.C.
Abstract:
Employment of non-inductive plasma start-up techniques would considerably simplify the design of a spherical tokamak fusion reactor. Transient coaxial helicity injection (CHI) is a promising method, expected to scale favorably to next-step reactors. However, the implications of reactor-relevant parameters on the initial breakdown phase for CHI have not yet been considered. Here, we evaluate CHI breakdown in reactor-like configurations using an extension of the Townsend avalanche theory. We find that a CHI electrode concept in which the outer vessel wall is biased to achieve breakdown, while previously successful on NSTX and HIT-II, may exhibit a severe weakness when scaled up to a reactor. On the other hand, concepts which employ localized biasing electrodes such as those used in QUEST would avoid this issue. Assuming that breakdown can be successfully attained, we then apply scaling relationships to predict plasma parameters attainable in the transient CHI discharge. Assuming the use of 1 Wb of injector flux, we find that plasma currents of 1 MA should be achievable. Furthermore, these plasmas are expected to Ohmically self-heat with more than 1 MW of power as they decay, facilitating efficient hand-off to steady-state heating sources. These optimistic scalings are supported by TSC simulations.
Type:
Dataset
Issue Date:
February 2019

295. Methane emissions from oil and gas platforms in the North Sea.

Author(s):
Riddick, Stuart; Mauzerall, Denise
Abstract:
Since 1850 the concentration of atmospheric methane (CH4), a potent greenhouse gas, has more than doubled. Recent studies suggest that emission inventories may be missing sources and underestimating emissions. To investigate whether offshore oil and gas platforms leak CH4 during normal operation, we measured CH4 mole fractions around eight oil and gas production platforms in the North Sea which were neither flaring gas nor off-loading oil. We use the measurements from summer 2017, along with meteorological data, in a Gaussian plume model to estimate CH4 emissions from each platform. We find CH4 mole fractions of between 11 and 370 ppb above background concentrations downwind of the platforms measured, corresponding to a median CH4 emission of 6.8 g CH4 s-1 for each platform, with a range of 2.9 to 22.3 g CH4 s-1. When matched to production records, during our measurements individual platforms lost between 0.04% and 1.4% of gas produced with a median loss of 0.23%. When the measured platforms are considered collectively, (i.e. the sum of platforms’ emission fluxes weighted by the sum of the platforms’ production), we estimate the CH4 loss to be 0.19% of gas production. These estimates are substantially higher than the emissions most recently reported to the National Atmospheric Emission Inventory (NAEI) for total CH4 loss from United Kingdom platforms in the North Sea. The NAEI reports CH4 losses from the offshore oil and gas platforms we measured to be 0.13% of gas production, with most of their emissions coming from gas flaring and offshore oil loading, neither of which were taking place at the time of our measurements. All oil and gas platforms we observed were found to leak CH4 during normal operation and much of this leakage has not been included in UK emission inventories. Further research is required to accurately determine total CH4 leakage from all offshore oil and gas operations and to properly include the leakage in national and international emission inventories.
Type:
Dataset
Issue Date:
February 2019

296. Real-time capable modeling of neutral beam injection on NSTX-U using neural networks

Author(s):
Boyer, M.D.; Kaye, S.; Erickson, K.
Abstract:
A new model of heating, current drive, torque and other effects of neutral beam injection on NSTX-U that uses neural networks has been developed. The model has been trained and tested on the results of the Monte Carlo code NUBEAM for the database of experimental discharges taken during the first operational campaign of NSTX-U. By projecting flux surface quantities onto empirically derived basis functions, the model is able to efficiently and accurately reproduce the behavior of both scalars, like the total neutron rate and shine through, and profiles, like beam current drive and heating. The model has been tested on the NSTX-U real-time computer, demonstrating a rapid execution time orders of magnitude faster than the Monte Carlo code that is well suited for the iterative calculations needed to interpret experimental results, optimization during scenario development activities, and real-time plasma control applications. Simulation results of a proposed design for a nonlinear observer that embeds the neural network calculations to estimate the poloidal flux profile evolution, as well as effective charge and fast ion diffusivity, are presented.
Type:
Dataset
Issue Date:
February 2019

297. Physics design for a lithium vapor box divertor experiment on Magnum-PSI

Author(s):
Schwartz, Jacob; Emdee, Eric; Goldston, Robert; Jaworski, Michael
Abstract:
The lithium vapor box divertor is a potential solution for power exhaust in toroidal confinement devices. The divertor plasma interacts with a localized, dense cloud of lithium vapor, leading to volumetric radiation, cooling, recombination, and detachment. To minimize contamination of the core plasma, lithium vapor is condensed on cool (300°C to 400°C) baffles upstream of the detachment point. Before implementing this in a toroidal plasma device with a slot divertor geometry, we consider an experiment with a scaled baffled-pipe geometry in the high-power linear plasma device Magnum-PSI. Three 15 cm-scale open cylinders joined by 6 cm diameter ‘nozzles’ are positioned on the plasma beam axis upstream of a target. The central box may be loaded with several tens of grams of lithium, which can be evaporated at 650°C to produce a vapor predicted, using a simple plasma-neutral interaction model, to be dense enough to cause volumetric detachment in the plasma. The power delivered to the target and box walls as measured by increases in their temperatures after a 10 s plasma pulse can be compared to determine the effectiveness of the vapor in detaching the plasma. Direct Simulation Monte Carlo simulations are performed to estimate the flow rates of lithium vapor between the boxes and to estimate the trapping of H2 delivered by the plasma in the boxes, which could inadvertently lead to detachment. Details of the geometry, simulations, and possible diagnostic techniques are presented.
Type:
Dataset
Issue Date:
30 January 2019

299. Climate Impacts from Large Volcanic Eruptions in a High-resolution Climate Model: the Importance of Forcing Structure

Author(s):
Yang, Wenchang; Vecchi, Gabriel; Fueglistaler, Stephan; Horowitz, Larry; Luet, David; Muñoz, Ángel; Paynter, David; Underwood, Seth
Abstract:
Explosive volcanic eruptions have large climate impacts, and can serve as observable tests of the climatic response to radiative forcing. Using a high resolution climate model, we contrast the climate responses to Pinatubo, with symmetric forcing, and those to Santa Maria and Agung, which had meridionally asymmetric forcing. Although Pinatubo had larger global-mean forcing, asymmetric forcing strongly shifts the latitude of tropical rainfall features, leading to larger local precipitation/TC changes. For example, North Atlantic TC activity over is enhanced/reduced by SH-forcing (Agung)/NH-forcing (Santa Maria), but changes little in response to the Pinatubo forcing. Moreover, the transient climate sensitivity estimated from the response to Santa Maria is 20% larger than that from Pinatubo or Agung. This spread in climatic impacts of volcanoes needs to be considered when evaluating the role of volcanoes in global and regional climate, and serves to contextualize the well-observed response to Pinatubo.
Type:
Dataset
Issue Date:
2019