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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Closing in on critical net-baryon fluctuations at LHC energies: Cumulants up to third order in Pb–Pb collisions

Fluctuation measurements are important sources of information on the mechanism of particle production at LHC energies. This article reports the first experimental results on third-order cumulants of the net-proton distributions in Pb–Pb collisions at a center-of-mass energy $\sqrt{s_{NN}}$ = 5.02 TeV recorded by the ALICE detector. The results on the second-order cumulants of net-proton distributions at $\sqrt{s_{NN}}$ = 2.76 and 5.02 TeV are also discussed in view of effects due to the global and local baryon number conservation. The results demonstrate the presence of long-range rapidity correlations between protons and antiprotons. Such correlations originate from the early phase of the collision. The experimental results are compared with HIJING and EPOS model calculations, and the dependence of the fluctuation measurements on the phase-space coverage is examined in the context of lattice quantum chromodynamics (LQCD) and hadron resonance gas (HRG) model estimations. The measured third-order cumulants are consistent with zero within experimental uncertainties of about 4% and are described well by LQCD and HRG predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Electro-Optical Characterization of Arsenic-Doped CdSeTe and CdTe Solar Cell Absorbers Doped in-situ During Close Space Sublimation

Most contemporary device models predict that an acceptor concentration of at least 10^16 cm^-3 is required to reach an open circuit voltage of 1 V in polycrystalline CdTe-based solar cells. While copper has traditionally been used as the de facto p-type dopant in polycrystalline cadmium telluride (CdTe) and cadmium selenide telluride (CdSeTe), reaching high acceptor concentrations has proved to be challenging in such devices due to significant dopant compensation. The acceptor concentration in copper-doped CdTe and CdSeTe typically ranges from 10^13 to 10^15 cm^-3 and routinely exhibit low external radiative efficiencies below 0.01%, limiting their implied voltage (i.e., quasi-Fermi level splitting) to approximately 900 mV. As an alternative to copper, this work explores the use of arsenic as a p-type dopant for CdTe and CdSeTe. Using a novel technique in which a thin layer of arsenic-containing material is deposited and used as a reservoir for arsenic to diffuse into a front layer of previously undoped material, this contribution demonstrates that high external radiative efficiencies are achievable, a direct result of combined high acceptor concentrations and long minority-carrier lifetimes in the absorber. This leads to improved implied voltages, and indicates that As-doping represents a promising pathway towards improving the external voltage of CdSeTe/CdTe solar cells.

cadmium telluride↗
DOE OSTI2024

Close roof-mounted system temperature estimation for compliance to IEC TS 63126

When photovoltaic (PV) modules are installed on rooftops, the module temperature depends primarily on the geographic location and the mounting configuration. If the mounting structure does not provide sufficient airflow in a hot environment, the 98th percentile temperature will exceed 70°C, which according to IEC TS 63126 ED. 1, requires higher levels of thermal stability testing. However, there is no clear way to determine the temperature level needed for a particular location and system design. Here, in this work, we identify a relationship between the module standoff to the rooftop and the module temperature and propose methods to describe a minimum standoff for typical PV modules in a simple mounting configuration installed in a given location. For more complex system designs, we show how to determine an equivalent “effective standoff” that can be applied to generic calculations. Lastly, we show measurements and calculations from several systems to demonstrate how this method could work.

14 SOLAR ENERGY↗
DOE OSTI2020

Impurity temperature screening in stellarators close to quasisymmetry

Impurity temperature screening is a favourable neoclassical phenomenon involving an outward radial flux of impurity ions from the core of fusion devices. Quasisymmetric magnetic fields lead to intrinsically ambipolar neoclassical fluxes that give rise to temperature screening for low enough $\unicode[STIX]{x1D702}^{-1}\equiv d\ln n/d\ln T$ . In contrast, neoclassical fluxes in generic stellarators will depend on the radial electric field, which is predicted to be inward for ion-root plasmas, potentially leading to impurity accumulation. Here, we examine the impurity particle flux in a number of approximately quasisymmetric stellarator configurations and parameter regimes while varying the amount of symmetry breaking in the magnetic field. For the majority of this work, neoclassical fluxes have been obtained using the SFINCS drift-kinetic equation solver with electrostatic potential $\unicode[STIX]{x1D6F7}=\unicode[STIX]{x1D6F7}(r)$ , where $r$ is a flux-surface label. Results indicate that achieving temperature screening is possible, but unlikely, at low-collisionality reactor-relevant conditions in the core. Thus, the small departures from symmetry in nominally quasisymmetric stellarators are large enough to significantly alter the neoclassical impurity transport. A further look at the magnitude of these fluxes when compared to a gyro-Bohm turbulence estimate suggests that neoclassical fluxes are small in configurations optimized for quasisymmetry when compared to turbulent fluxes.

Physics↗
DOE OSTI2020

Closing the Gap Between Experiment and Theory: Reactive Scattering of HCl from Au(111)

Accurate simulation of molecules reacting on metal surfaces, which can help in improving heterogeneous catalysts, remains out of reach for several reactions. For example, a large disagreement between theory and experiment for HCl reacting on Au(111) still remains, despite many efforts. In this work, the dissociative chemisorption of HCl on Au(111) is investigated with a recently developed MGGA density functional (MS-RPBEl) and a high-dimensional neural network potential. Additionally, previous experimental sticking probabilities are re-examined. A considerably improved agreement between experiment and theory is obtained, although theory still overestimates experimental sticking probabilities by a factor of 2-7 at the highest incidence energy. Computed and measured vibrational transition probabilities are also in improved agreement. Several dynamical effects such as angular steering and energy transfer from the molecule to the surface are found to play an important role.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗