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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Plasma heating by electron cyclotron wave and the temperature effects on lower hybrid current drive on EAST

This paper presents the progress in the long—pulse operation of the electron cyclotron (EC) system and the achievements in high—electron temperature plasmas by the combined EC and lower hybrid (LH) waves heating since the EC system was built in 2015. An electron temperature of up to 12 keV with a duration over 100 s was realized by the simultaneous heating of EC and LH waves at the line-averaged density ${\bar n_{\text{e}}}$ ~1.8 × 10 19 m –3 . The plasma heating effect strongly depends on the location of EC power deposition. H-mode plasmas with solely EC wave auxiliary heating have been obtained on EAST for the first time. These H-mode discharges show an enhanced confinement factor H 98(y,2) around 1.0, which is higher than the previous H-mode using LH power alone (Xu et al 2011 Nucl. Fusion 51 072001). The total heating power is very close to the threshold value for L–H transition according to the international tokamak scaling. In addition to the temperature effects inside the separatrix, higher electron temperature produced by EC wave is found to reduce the LH power loss in the scrape-off layer due to collisional absorption, which is beneficial to further increase the LH current drive efficiency. Ray-tracing/Fokker–Planck modeling results indicate that higher electron temperature can shorten the LH wave propagation on EAST in a multiple-pass regime, thus decreasing the collisional dissipation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Scanning electrochemical probe microscopy investigation of two-dimensional materials

Research interests in two-dimensional (2D) materials have seen exponential growth owing to their unique and fascinating properties. The highly exposed lattice planes coupled with tunable electronic states of 2D materials have created manifold opportunities in the design of new platforms for energy conversion and sensing applications. Still, challenges in understanding the electrochemical (EC) characteristics of these materials arise from the complexity of both intrinsic and extrinsic heterogeneities that can obscure structure–activity correlations. Scanning EC probe microscopic investigations offer unique benefits in disclosing local EC reactivities at the nanoscale level that are otherwise inaccessible with macroscale methods. This review summarizes recent progress in applying techniques of scanning EC microscopy (SECM) and scanning EC cell microscopy (SECCM) to obtain distinctive insights into the fundamentals of 2D electrodes. We showcase the capabilities of EC microscopies in addressing the roles of defects, thickness, environments, strain, phase, stacking, and many other aspects in the heterogeneous electron transfer, ion transport, electrocatalysis, and photoelectrochemistry of representative 2D materials and their derivatives. Perspectives for the advantages, challenges, and future opportunities of scanning EC probe microscopy investigation of 2D structures are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Direct determination of the La 138 β -decay Q value using Penning trap mass spectrometry

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the 138 La $\beta$-decay $Q$ value with the beta-decay spectrum end-point energy measured by Quarati et al. using LaBr 3 detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the 138 La $\beta$-decay and electron capture (EC) $Q$ values to improve theoretical calculations of the $\beta$-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of 138 La, 138 Ce and 138 Ba ions from which beta-decay and EC Q values for 138 La were obtained.Results: The 138 La beta-decay and EC Q values were measured to be Q$_\beta$ = 1052.42(41) keV and $Q_{EC}$ = 1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the 138 La $\beta$-decay shape factor and EC probabilities. New determinations for the 138 Ce 2EC $Q$ value and the atomic masses of 138 La, 138 Ce, and 138 Ba are also reported. Conclusion: The 138 La $\beta$-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for 138 La $\beta$-decay using our new $Q$ value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.

138La↗
DOE OSTI2023

Exploring regular and turbulent flow states in active nematic channel flow via Exact Coherent Structures and their invariant manifolds

This work is a unified study of stable and unstable steady states of 2D active nematic channel flow using the framework of Exact Coherent Structures (ECS). ECS are stationary, periodic, quasiperiodic, or traveling wave solutions of the governing equations that, together with their invariant manifolds, organize the dynamics of nonlinear continuum systems. We extend our earlier work on ECS in the preturbulent regime by performing a comprehensive study of stable and unstable ECS for a wide range of activity values spanning the preturbulent and turbulent regimes. In the weakly turbulent regime, we compute more than 200 unstable ECS that co-exist at a single set of parameters, and uncover the role of symmetries in organizing the phase space geometry. We provide conclusive numerical evidence that in the preturbulent regime, generic trajectories shadow a series of unstable ECS before settling onto an attractor. Lastly, our studies hint at shadowing of quasiperiodic type ECS in the turbulent regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Flow Assisted Evaporative Cooling for Electric Motor

This paper examines a novel concept of flow assisted latent heat driven two-phase evaporative cooling (EC) confined in-between slot liner and active-winding of electric motor. Wicking micro-structure enhanced PDMS liner axially sucks coolant in the form of thin film between the PDMS liner and active-winding and eventually enables thin film evaporation on the outer surface of the active-winding. Therefore, EC based thermal management eliminates contact resistance between the winding and slot-liner and, enhances the heat extraction from the winding without compromising the electro-magnetic performance. Two-way coupled electro-magnetic (EM) – computational fluid dynamics/heat transfer (CFD/HT) and EM - lumped parameter thermal network (LPTN) models have been developed to assess the electro-thermal performance of the EC under steady and transient conditions. Taking a case study of a 125 kW jacket cooled BMW i3 motor and dielectric coolant FC-84, EC is shown to be capable of handling a maximum steady state rms current density of 26 A/mm2 at a evaporative heat transfer coefficient of 5,000 W/m2.K, which is about 78.7% higher compared to the traditional jacket cooling (JC). In case of EC, a maximum steady state and transient rms current density of 30 A/mm2 (106.2% higher compared to the JC), and 40.8 A/mm2 have been realized by using high thermal conductivity epoxy (1.9 W/m.K) impregnation material. Thermal performance of the EC is also assessed and compared with JC over a dynamic drive cycle. Lastly, a motorette testing has been performed to demonstrate the applicability of the proposed EC method and to validate the developed modeling framework.

42 ENGINEERING↗
DOE OSTI2018

Evaluating Emergent Constraints on Equilibrium Climate Sensitivity

Emergent constraints are quantities that are observable from current measurements and have skill predicting future climate. This study explores 19 previously proposed emergent constraints related to equilibrium climate sensitivity (ECS; the global-average equilibrium surface temperature response to CO 2 doubling). Several constraints are shown to be closely related, emphasizing the importance for careful understanding of proposed constraints. A new method is presented for decomposing correlation between an emergent constraint and ECS into terms related to physical processes and geographical regions. Using this decomposition, one can determine whether the processes and regions explaining correlation with ECS correspond to the physical explanation offered for the constraint. Shortwave cloud feedback is generally found to be the dominant contributor to correlations with ECS because it is the largest source of intermodel spread in ECS. In all cases, correlation results from interaction between a variety of terms, reflecting the complex nature of ECS and the fact that feedback terms and forcing are themselves correlated with each other. For 4 of the 19 constraints, the originally proposed explanation for correlation is borne out by our analysis. These four constraints all predict relatively high climate sensitivity. The credibility of six other constraints is called into question owing to correlation with ECS coming mainly from unexpected sources and/or lack of robustness to changes in ensembles. Another six constraints lack a testable explanation and hence cannot be confirmed. The fact that this study casts doubt upon more constraints than it confirms highlights the need for caution when identifying emergent constraints from small ensembles.

Caldwell, Peter M.↗
DOE OSTI2018

Evaluating Emergent Constraints for Equilibrium Climate Sensitivity

Emergent constraints are quantities that are observable from current measurements and have skill predicting future climate. Here, this study explores 19 previously proposed emergent constraints related to equilibrium climate sensitivity (ECS; the global-average equilibrium surface temperature response to CO 2 doubling). Several constraints are shown to be closely related, emphasizing the importance for careful understanding of proposed constraints. A new method is presented for decomposing correlation between an emergent constraint and ECS into terms related to physical processes and geographical regions. Using this decomposition, one can determine whether the processes and regions explaining correlation with ECS correspond to the physical explanation offered for the constraint. Shortwave cloud feedback is generally found to be the dominant contributor to correlations with ECS because it is the largest source of intermodel spread in ECS. In all cases, correlation results from interaction between a variety of terms, reflecting the complex nature of ECS and the fact that feedback terms and forcing are themselves correlated with each other. For 4 of the 19 constraints, the originally proposed explanation for correlation is borne out by our analysis. These four constraints all predict relatively high climate sensitivity. The credibility of six other constraints is called into question owing to correlation with ECS coming mainly from unexpected sources and/or lack of robustness to changes in ensembles. Another six constraints lack a testable explanation and hence cannot be confirmed. Lastly, the fact that this study casts doubt upon more constraints than it confirms highlights the need for caution when identifying emergent constraints from small ensembles.

58 GEOSCIENCES↗
DOE OSTI2023

Data and Scripts associated with: “Laboratory evaluation of open source and commercial electrical conductivity sensor precision and accuracy”

This data package is associated with the publication “Laboratory evaluation of open source and commercial electrical conductivity sensor precision and accuracy: How do they compare?” submitted to PLOS ONE and accepted for publication (Fulton, S.G. et al. 2023; doi not yet available).Variation in electrical conductivity (EC) of water is important to reveal environmental disturbance and natural dynamics, including factors such as anthropogenic salinization. This data package supports a study addressing the need for a robust performance assessment of open source (OS) EC sensors. We evaluated the accuracy (mean error, %) and precision (sample standard deviation) of OS EC sensors in the laboratory via comparison to EC calibration standards using three different OS and OS/commercial-hybrid (OS/C) EC sensors and data logger configurations and two commercial (C) EC sensors and data logger configurations. We also evaluated the effect of cable length (7.5 m and 30 m) and sensor calibration on OS sensor accuracy and precision. This data package presents the results from the different testing laboratory configurations. It also includes an R script for statistical analysis of the data and an Arduino IDE file used to calibrate and collect data with the OS Atlas EC sensor. File types are .csv, .pdf, .R, and .ino.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Permanent Magnet Synchronous Motors for Commercial Refrigeration (Final Report)

This report provides background information on various fractional-horsepower electric motor technologies used for evaporator fan applications in commercial refrigeration and summarizes data from a DOE-sponsored evaporator fan motor laboratory and field demonstration project. This report also extrapolates that data to project the potential economic and environmental benefits resulting from upgrading the current installed base of commercial refrigeration evaporator fan motors to permanent magnet synchronous (PMS) motors.Evaporator fan motors used in commercial refrigeration applications are fractional horsepower in size, responsible for moving air across the evaporator coil, and typically run at one speed. Historically, shaded-pole induction motors have been the most commonly used evaporator fan motors in commercial refrigeration equipment and beverage vending machines. These are the simplest and least expensive type of fractional-horsepower motor, with an efficiency of approximately 20%. Electronically commutated (EC) permanent magnet motors, also known as brushless DC motors, were initially commercialized in the late 1980s, and their use in commercial refrigeration applications has increased within the last 10 to 15 years because of economic incentives and regulatory requirements. State-of-the-art EC motors are approximately 66% efficient. Another induction motor type, the permanent split capacitor (PSC) motor, offers a mid-point between shaded-pole and EC motor price and efficiency levels. PSC motors are typically about 29% efficient.A permanent magnet synchronous (PMS) AC motor that can directly use grid-supplied AC current without the need to rectify to DC has recently been commercialized. This new motor exhibits a peak efficiency of 75% and has the potential to significantly reduce the energy consumption of evaporator fan motors in commercial refrigeration equipment. Laboratory evaluation of evaporator fan motor technologies was performed to quantify and compare the performance of shaded-pole, PSC, EC, and PMS evaporator fan motors in a controlled environment, so as to minimize the influence of external factors and anomalies. The laboratory evaluation included dynamometer testing of the fan motors and airflow testing of the motor/fan assemblies. It was found that the 6–12 W PMS motor exhibited a peak efficiency of 75% with a power factor of approximately 0.9 at a power output of 11 W. It was also found that a 38–50 W PMS motor exhibited a peak efficiency of 82% with a power factor of approximately 0.9 at a power output of 35 W.Airflow testing of shaded-pole, PSC, EC, and PMS motor/fan assemblies was performed using an airflow test chamber, which was designed in accordance with ANSI/AMCA Standard 210-16/ASHRAE Standard 51-16, to measure the performance of the subject motor/fan assembly and to determine the incumbent display case system impedance (AMCA 2016). A family of fan curves (static pressure vs airflow rate and electrical power input vs airflow rate) was generated for the 6–12 W PMS motor/fan assemblies with 8-inch fan blades pitched from 17 to 32 degrees. A similar set of curves was generated for the 38–50 W motors paired with 10 and 12-inch blades. Various incumbent motor/fan assemblies were also tested in the laboratory airflow test chamber and their fan curves were generated.Field evaluation of refrigerated display case evaporator fan motors was accomplished by performing side-by-side comparisons of 6–12 W PMS motors to 6–12 W shaded-pole and EC evaporator fan motors. It was found that, on average, a PMS motor consumes 79% less power and draws 82% less current than a shaded pole motor, and on average, 34% less power and 49% less current than an EC motor. In addition, the PMS motor exhibits an average power factor of approximately 0.82, which is on average 40% greater than that of existing evaporator fan motors.Two field test sites were selected to evaluate the performance of the larger 38 to 50 W PMS evaporator fan motors in walk-in cooler/freezer applications. At each supermarket, two walk-in units were selected for investigation: one walk-in dairy cooler and one walk-in freezer. A 61% decrease in fan motor power was measured when retrofitting existing evaporator fan motors with PMS motors in the walk-in cooler. In addition, a 48% decrease in fan motor power was measured when retrofitting existing evaporator fan motors with PMS motors in the walk-in freezer.The culmination of the field evaluation of fan motor technologies was a whole-store retrofit conducted at a supermarket. Pre- and post-retrofit measurement of evaporator fan motor power in medium- and low-temperature refrigerated display cases and walk-in coolers/freezers was performed. Overall for the whole-store retrofit, the current supplied to all monitored evaporator fan motors was reduced by 52%, the real power was reduced by 46% and the apparent power was reduced by 51% following the retrofit of the 262 evaporator fan motors that w

42 ENGINEERING↗
DOE OSTI2021

Evaluation of Electrical Resistivity Tomography to Monitor the Transport of Past Releases Beneath Tank Farms

Underground storage tanks at the Hanford Site, in southeastern Washington State, hold radioactive waste generated from four decades of plutonium production. The 149 single-shell tanks and the 28 double-shell tanks have all exceeded their initial design life of approximately 25 years. At least 67 tanks are assumed to have leaked in the past, resulting in radioactive releases into the vadose zone. Gamma ray logging within dry monitoring wells is currently the primary method for tracking the migration of leaked tank waste through the vadose zone. While this approach provides an accurate assessment of radioactive contamination, that information is only provided near (within ~1m) the borehole, leaving most of the vadose zone unmonitored, particularly the important region directly beneath the tank. This report describes a numerical study that investigates the feasibility and performance of time-lapse 3D electrical resistivity tomography (ERT) for long-term monitoring of a hypothetical tank waste location and migration through the vadose zone. ERT is a method of remotely imaging the bulk electrical conductivity (EC) of the subsurface, which is significantly impacted by the presence of conductive solid and liquid tank waste. The release of liquid tank wastes increases subsurface fluid conductivity and saturation over time, creating a target to use time-lapse ERT for long-term monitoring. Although the presence of metallic infrastructure can cause ERT interference, recent advancements in ERT data processing enable the deleterious effects of buried metallic infrastructure (e.g. pipes, wellbore casings, tanks) to be removed to better determine the liquid tank waste migration over time. Three hypothetical realistic scenarios were simulated in the ERT evaluation. The first two scenarios assume the same leak amount and rate (i.e., between 1/1/1951 and 12/31/1951 at the rate of 347 m 3 per year) but different leaky tanks. Scenario 1 assumes leaks under tank B-102, which is located on the edge of the B-tank farm and surrounded by a few metallic infrastructure including cased pipes/wells/tanks. Scenario 2 assumes leaks under tank B-108, which is located near the center of the B-tank farm and surrounded by larger amount of metallic infrastructure than B-102. Scenario 3 assumes the same metallic infrastructure as B-102, with a more recent contaminant leak that was simulated to have occurred between 1/1/2018 and 12/31/2023 at a rate of 1.89 m 3 per year. The leak time in Scenarios 1 and 2 corresponds to a historical overfill event in 1951 and Scenario 3 corresponds to a recent found tank leak in 2019. In each scenario, a “true” bulk EC model vs. time reflecting contaminant migration was generated. ERT data was simulated from these “true” bulk EC models and a time-lapse ERT inversion produced “imaged” bulk EC vs. time. Three electrode configurations in two, four and eight boreholes surrounding the leak tank were used in the ERT simulations in each scenario. These borehole configurations were considered logistically feasible and cost-effective for monitoring. The hypothetical ERT boreholes are assumed to have non-metallic casing. By comparing the “imaged” bulk EC with the “true” bulk EC, it was demonstrated that the three configurations of wells used (two, four, and eight wells) were able to successfully monitor the migration of tank leaks through the vadose zone, with bulk EC resolution increasing with the number of down borehole ERT arrays for all scenarios. Therefore, the use of eight boreholes to perform ERT monitoring beneath the tanks provided the best spatiotemporal information.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1996

Renal Response to Chronic Centrifugation in Rats

Previously reported effects of chronic centrifugation on renal function in mammals are contradictory. The present study was conducted as an effort to provide a comprehensive analysis of renal response to chronic centrifugation (12 days at +2 Gz). Sixteen male Sprague-Dawley rats (210-230 g) were used: eight centrifuged (EC) and eight off centrifuge controls (OCC). During centrifugation EC had lower body weight and food consumption. EC showed a decrease (72%) in water intake for the first two days (T1 and T2) followed by significant increases from T4-T6. EC urine output increased two-fold over the first four days, returning to baseline by T9. EC urea excretion was elevated on T3 through T5. Creatinine, Na(+), K(+), and osmolar excretion were lower than OCC over the last four days of the study. Assuming constant plasma osmolarity and creatinine levels, EC free water clearance (C(sub H2O)) was elevated significantly on T4 when the peak urine output was exhibited. EC also had a greater C(sub H2O) over the last four days, associated with a significantly lower osmolar clearance and GFR. The initial diuresis exhibited during centrifugation can be attributed to a reduced water resorption and increased urea excretion. This diuresis was mediated independent of changes in GFR over the first eight days. However, differences in excretion seen after eight days of centrifugation are probably GFR mediated which would imply animals established a new homeostatic setpoint by that time. Centrifugation elicites an acute alteration in fluid homeostasis followed by adaptation within a week.

Ortiz, Rudy M.↗
NASA NTRSDate not supplied

Magnetite in Matrix of Anomalous El3 Chondrite Northwest Africa (NWA) 8785

Enstatite chondrites (ECs) have generated considerable interest as having stable (O, Cr, Ti, Ni, Zn) isotope compositions that are similar to Earth-Moon [e.g., 1,2,3]. Studies of their volatiles have suggested that the ECs, although relatively dry, could have contributed considerably to Earth’s oceans [4,5]. The defining features of the ECs are their highly reduced mineral assemblages in which enstatite (near FeO-free) is the dominant silicate, abundant metal containing >2.5 wt. % Si in some ECs, elements that are generally lithophile occurring as sulfides, and the presence of nitrides, carbides and silicides [6,7,8]. Aside from certain EC clasts in the Kaidun breccia [9,10], most ECs lack evidence of hydrous minerals unlike other chondrite groups. Most ECs have low abundances of matrix (EH3s ~4-12 vol.%, EL3s ≤5 vol.% [11,12]). Here we describe NWA 8785, an anomalous EL3 with a high abundance of a magnetite-rich matrix [13]. Our goals are to understand the formation of the magnetite and its implications for understanding the origin of EL3 chondrites.

M. K. Weisberg↗
DOE OSTI2023

Model predictive current profile control in tokamaks by exploiting spatially moving electron cyclotron current drives

The plasma control systems in next-generation tokamaks like ITER will balance competing control objectives to achieve the desired level of performance in advanced scenarios while preventing magnetohydrodynamic instabilities and disruptions. During normal tokamak operation, the points of incidence of the electromagnetic waves generated by the electron cyclotron heating and current drives (EC H&CDs) are usually fixed in space. However, the points of incidence can be modified in real-time by changing the angles of the mirrors that reflect the EC H&CD waves. Altering the points of incidence, in turn, varies the ability of the plasma control system to regulate a plasma property. For instance, changing the EC H&CD wave incidence location may place the power demands necessary to achieve a particular plasma target within saturation limits. Therefore, using the EC H&CD deposition location, which is related to the EC H&CD mirror angle, as a supplementary controllable variable may facilitate access to a given target scenario. However, active scenario-control algorithms have not been designed so far to fully exploit this capability in real time. In this work, a model predictive controller that can handle actuation locations as control inputs is developed. In particular, the controller is designed to regulate both the auxiliary powers and the EC H&CD deposition locations in a pre-defined optimal sense to achieve the control objective of attaining and sustaining a target current profile. Further, the proposed controller is tested for a DIII-D tokamak scenario in nonlinear simulations using the Control Oriented Transport SIMulator (COTSIM).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Methane flux measurements in rice by static flux chamber and eddy covariance

Abstract Understanding methane (CH 4 ) fluxes from rice ( Oryza sativa L.) at the field scale is paramount to reducing environmental impacts while ensuring global food security. Greenhouse gas (GHG) measurements at the plot scale using static flux chambers (SFC) have long informed the understanding of flux dynamics and have largely been the basis of global flux estimates. However, in many parts of the world, the landscapes where agricultural fluxes are generated come from larger fields. Eddy covariance (EC) can measure trace gases on larger fields, but there are few studies available quantifying CH 4 emissions under typical practices at a field scale. Furthermore, few of these studies are from the U.S. Midsouth, the largest producer of U.S. rice. This study compares and quantifies field‐scale SFC and EC flux measurements on a large commercial system in northeastern Arkansas during the 2015 and 2016 growing seasons, following typical producer practices. Daily measured SFC CH 4 fluxes did not differ from EC‐daily CH 4 fluxes ( p = .108). Total season CH 4 emissions, calculated as the sum of daily fluxes ranged from 50 to 156 kg CH 4 ha −1 season −1 , with SFC reporting greater emissions than EC. Although SFC and EC‐daily flux measurements were similar early ( p = .382) and late ( p = .543) in the season, they differed mid‐season ( p < .001) with SFC consistently reporting greater fluxes than EC. The findings of this study help unify season long plot‐scale and field‐scale flux measurements and signify an advancement of our understanding of GHG fluxes from rice systems.

Reba, Michele L.↗
DOE OSTI2025

Dual‐Functional High‐Entropy Polymer Exhibiting Giant Cross‐Energy Couplings at Low Fields

A key component of cooling devices is the transfer of entropy from the cold load to heat sink. An electrocaloric (EC) polymer capable of generating both large electrocaloric effect (ECE) and substantial electroactuation can enable EC cooling devices to pump heat without external mechanisms, resulting in compact designs and enhanced efficiency. However, achieving both high ECE and significant electroactuation remains challenging. Herein, it is demonstrated that poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene‐double bond) [P(VDF‐TrFE‐CFE‐DB)] tetrapolymers can simultaneously generate high electrocaloric effects and electroactuations under low fields. These P(VDF‐TrFE‐CFE‐DB) tetrapolymers are synthesized through the dehydrochlorination of P(VDF‐TrFE‐CFE) terpolymer. By facile tuning the composition of the initial terpolymer to avoid pure relaxor state, tetrapolymers with optimal DB compositions are achieved, near the critical endpoint of normal ferroelectric phase with diffused phase transition. The nearly vanishing energy barriers between the nonpolar to polar phases result in a strong electrocaloric response and significant electroactuation. Specifically, the P(VDF‐TrFE‐CFE‐DB) tetrapolymer exhibits an EC entropy change Δ S of 100 J kg −1 K −1 under 100 MV m −1 : comparable to state‐of‐the‐art (SOA) EC polymers, while delivering nearly twice the electroactuation of the SOA EC polymers. This work presents a general strategy for developing EC materials that combine large electrocaloric effect and electroactuation at low electric fields.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Status of the ITER Electron Cyclotron Heating and Current Drive System

We present that the electron cyclotron (EC) heating and current drive (H&CD) system developed for the ITER is made of 12 sets of high-voltage power supplies feeding 24 gyrotrons connected through 24 transmission lines (TL), to five launchers, four located in upper ports and one at the equatorial level. Nearly all procurements are in-kind, following general ITER philosophy, and will come from Europe, India, Japan, Russia and the USA. The full system is designed to couple to the plasma 20 MW among the 24 MW generated power, at the frequency of 170 GHz, for various physics applications such as plasma start-up, central H&CD and magnetohydrodynamic (MHD) activity control. The design takes present day technology and extends toward high-power continuous operation, which represents a large step forward as compared to the present state of the art. The ITER EC system will be a stepping stone to future EC systems for DEMO and beyond.The development of the EC system is facing significant challenges, which includes not only an advanced microwave system but also compliance with stringent requirements associated with nuclear safety as ITER became the first fusion device licensed as basic nuclear installations as of 9 November 2012. Finally, since the conceptual design of the EC system was established in 2007, the EC system has progressed to a preliminary design stage in 2012 and is now moving forward toward a final design.

42 ENGINEERING↗
DOE OSTI2016

The value of soil respiration measurements for interpreting and modeling terrestrial carbon cycling

A recent acceleration of model-data synthesis activities has leveraged many terrestrial carbon (C) datasets, but utilization of soil respiration (RS) data has not kept pace with other types such as eddy covariance (EC) fluxes and soil C stocks. Here we argue that RS data, including non-continuous measurements from survey sampling campaigns, have unrealized value and should be utilized more extensively and creatively in data synthesis and modeling activities. We identify three major challenges in interpreting RS data, and discuss opportunities to address them. The first challenge is that when RS is compared to ecosystem respiration (RECO) measured from EC towers, it is not uncommon to find substantial mismatch, indicating one or both flux methodologies are unreliable. We argue the most likely cause of mismatch is unreliable EC data, and there is an unrecognized opportunity to utilize RS for EC quality control. The second challenge is that RS integrates belowground heterotrophic (RH) and autotrophic (RA) activity, whereas modelers generally prefer partitioned fluxes, and few models include an explicit RS output. Opportunities exist to use the total RS flux for data assimilation and model benchmarking methods rather than less-certain partitioned fluxes. Pushing for more experiments that not only partition RS but also monitor the age of RA and RH, as well as for the development of belowground RA components in models, would allow for more direct comparison between measured and modeled values. The third challenge is that soil respiration is generally measured at a very different resolution than that needed for comparison to EC or ecosystem- to global-scale models. Measuring soil fluxes with finer spatial resolution and more extensive coverage, and downscaling EC fluxes to match the scale of RS, will improve chamber and tower comparisons. Opportunities also exist to estimate RH at regional scales by implementing decomposition functional types, akin to plant functional types. We conclude by discussing the benefits that wide use of RS data will bring to model development, and database developments that will make RS data more robust, useful, and broadly available to the research community.

carbon cycle↗
DOE OSTI2017

Water requirements of short rotation poplar coppice: Experimental and modelling analyses across Europe

Poplars are among the most widely used short rotation woody coppice (SRWC) species but due to their assumed high water use, concerns have been raised with respect to large-scale exploitation and potentially detrimental effects on water resources. Here we present a quantitative analysis of the water requirements of poplar SRWC using experimental data and a soil water balance modelling approach at three different sites across Europe. We used (i) eddy covariance (EC) measurements (2004–2006) at an irrigated SRWC grown on a previous rice paddy in northern Italy, (ii) Bowen ratio and energy balance (BREB) measurements (2008–2015) and EC (2011–2015) at a SRWC in rain-fed uplands in the Czech Republic, and (iii) EC measurements (2010–2013) at a SRWC on a previous agricultural land with a shallow water table in Belgium. Without any calibration against water balance component measurements, simulations by the newly developed soil water balance model R-4ET were compared with evapotranspiration (ET) measurements by EC and BREB with a resulting mean root mean square error (RMSE) of 0.75 mm day -1 . In general, there was better agreement between EC and the model (RMSE = 0.66 mm day -1 ) when EC data were adjusted for lack of energy balance closure. A comparison of the simulated and measured soil water content yielded a mean RMSE of 0.03 m 3 m -3 . The mean annual crop coefficient, i.e. the ratio between actual and reference ET, was 0.82 (ranging from 0.65 to 0.95) while the monthly maxima reached 1.16. These values indicated that ET of poplar SRWC was significantly lower than ET of a well-watered grass cover at the annual time scale, but exceeded ET of the reference cover at shorter time scales during the growing season. We show that the model R-4ET is a simple, yet reliable tool for the assessment of water requirements of existing or planned SRWC. For very simple assessments on an annual basis, using a crop coefficient of 0.86 (adjusted to a sub-humid climate), representing an average value across the three sites in years with no evident drought stress, is supported by this analysis.

54 ENVIRONMENTAL SCIENCES↗