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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Full-wave model for the lower hybrid wave electric field vector with synthetic turbulence on Alcator C-Mod

The effects of synthetic turbulence on lower hybrid (LH) wave field magnitude and polarization are studied on Alcator C-Mod. Three synthetic turbulence models are evaluated to assess the impact of filaments, holes, and periodic fluctuations on the LH wave electric fields. For all three cases, the synthetic turbulence can greatly impact the LH wave magnitude and polarization. Back scattering, interference and edge/SOL absorption of the LH wave is observed. This impact is shown to depend on the wavelength and amplitude of the fluctuations. The strongest effect appears for fluctuations at high amplitudes and wavelengths comparable to the LH wavelength. This synthetic turbulence model can be used as inputs into a synthetic diagnostic to calculate the lower hybrid wave field magnitude and direction measured by dynamic Stark effect spectroscopy. It will be shown that fluctuations at these high amplitudes and wavelengths may explain the experimentally measured results. Here, the effect of fluctuations on modifying LH polarization are also shown to be anti-correlated with SOL power losses, similar to recently observed experimental trends on Alcator C-Mod. These SOL losses may have detrimental impact on LHCD efficiency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Identifying heavy-flavor jets using vectors of locally aggregated descriptors

Abstract Jets of collimated particles serve a multitude of purposes in high energy collisions. Recently, studies of jet interaction with the quark-gluon plasma (QGP) created in high energy heavy ion collisions are of growing interest, particularly towards understanding partonic energy loss in the QGP medium and its related modifications of the jet shower and fragmentation. Since the QGP is a colored medium, the extent of jet quenching and consequently, the transport properties of the medium are expected to be sensitive to fundamental properties of the jets such as the flavor of the parton that initiates the jet. Identifying the jet flavor enables an extraction of the mass dependence in jet-QGP interactions. We present a novel approach to tagging heavy-flavor jets at collider experiments utilizing the information contained within jet constituents via the model architecture. We show the performance of this model in proton-proton collisions at center of mass energy √(s) = 200 GeV as characterized by common metrics and showcase its ability to extract high purity heavy-flavor jet sample at various jet momenta and realistic production cross-sections including a brief discussion on the impact of out-of-time pile-up. Such studies open new opportunities for future high purity heavy-flavor measurements at jet energies accessible at current and future collider experiments.

Instruments & Instrumentation↗
DOE OSTI2021

Progress towards understanding ultranonlocality through the wave-vector and frequency dependence of approximate exchange-correlation kernels

In the framework of time-dependent density functional theory (TDDFT), the exact exchange-correlation (xc) kernel f xc (n, q, ω) determines the ground-state energy, excited-state energies, lifetimes, and the time-dependent linear density response of any many-electron system. The recently developed MCP07 xc kernel f xc (n, q, ω) of A. Ruzsinszky et al. [Phys. Rev. B 101, 245135 (2020)] yields excellent uniform electron gas (UEG) ground-state energies and plausible plasmon lifetimes. As MCP07 is constructed to describe f xc of the UEG, it cannot capture optical properties of real materials. To verify this claim, we follow Nazarov et al. [Phys. Rev. Lett. 102, 113001 (2009)] to construct the long-range, dynamic xc kernel, lim q→0 f xc (n, q, ω) = -α(ω)e 2 /q 2 , of a weakly inhomogeneous electron gas, using MCP07 and other common xc kernels. The strong wavevector and frequency dependence of the “ultranonlocality” coefficient α(ω) is demonstrated for a variety of simple metals and semiconductors. We examine how imposing exact constraints on an approximate kernel shapes α(ω). Comparisons to kernels derived from correlated-wavefunction calculations are drawn.

36 MATERIALS SCIENCE↗