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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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High FEC or EMC content in LSEs will dominate salt ion coordination as contact-ion pairs and induce the de-coordination of the minor solvent. Therefore, a balance of both solvents is crucial to minimize free solvent formation for optimal performance.
The Kelvin–Helmholtz (KH) instability of a shear layer with an initially uniform magnetic field in the direction of flow is studied in the framework of 2D incompressible magnetohydrodynamics with finite resistivity and viscosity using direct numerical simulations. The shear layer evolves freely, with no external forcing, and thus broadens in time as turbulent stresses transport momentum across it. As with hydrodynamic KH, the instability here features a conjugate stable mode for every unstable mode in the absence of dissipation. Stable modes are shown to transport momentum up its gradient, shrinking the layer width whenever they exceed unstable modes in amplitude. In simulations with weak magnetic fields, the linear instability is minimally affected by the field, but enhanced small-scale fluctuations relative to the hydrodynamic case are observed. These enhanced fluctuations coincide with increased energy dissipation and faster layer broadening, with these features more pronounced in simulations with stronger fields. These trends result from the magnetic field reducing the effects of stable modes relative to the transfer of energy to small scales. As field strength increases, stable modes become less excited, thus transporting less momentum against its gradient. Furthermore, the energy that would otherwise transfer back to the driving shear because of the stable modes is instead allowed to cascade to small scales, where it is lost to dissipation. Approximations of the turbulent state in terms of a reduced set of modes are explored. While the Reynolds stress is well-described using just two modes per wavenumber at large scales, the Maxwell stress is not.
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LaCrGe 3 is an itinerant, metallic ferromagnet with a Curie temperature (T C ) of ~86 K. Whereas LaCrGe 3 has been studied extensively as a function of pressure as an example of avoided ferromagnetic quantum criticality, questions about its ambient pressure-ordered state remain: specifically, whether there is a change in the nature of the ferromagnetically ordered state below T C ~86 K. We present anisotropic M(H) isotherms, coupled with anisotropic AC susceptibility data, and demonstrate that LaCrGe 3 has a remarkable, low temperature coercivity associated with exceptionally sharp, complete magnetization reversals to and from fully polarized states. This coercivity is temperature dependent; it drops to zero in the 40–55 K region and reappears in the 70–85 K regions. Furthermore, at low temperatures LaCrGe 3 has magnetization loops and behavior that has been previously associated with micromagnetic/nanocrystalline materials, not bulk macroscopic samples.
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As an alternative inertial confinement fusion scheme, shock ignition requires a strong converging shock driven by a high-intensity laser pulse to ignite a pre-compressed fusion capsule. Understanding nonlinear laser-plasma instabilities is crucial to assess and improve the laser-shock energy coupling. Recent experiments conducted on the OMEGA EP laser facility have for the first time demonstrated that such instabilities can 100% deplete the first 0.5 ns of the high-intensity laser. Here, analyses of the observed laser-generated blast wave suggest that this pump-depletion starts at 0.02 critical density and progresses to 0.1-0.2 critical density, which is also confirmed by the time-resolved stimulated Raman backscattering spectra. The pump-depletion dynamics can be explained by the breaking of ion-acoustic waves in stimulated Brillouin scattering. Such pump-depletion would inhibit the collisional laser energy absorption but may benefit the generation of hot electrons with moderate temperatures for electron shock ignition.
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The linear growth and nonlinear energy transfer of the electron drift instability (EDI) are experimentally measured in the plume of a low-temperature, Hall effect discharge. A frequency-based bispectral analysis technique applied to fast ion density fluctuation measurements shows a growth rate function that is qualitatively similar to predictions from the linear instability dispersion relation, but an order of magnitude smaller. Calculation of the nonlinear transfer function indicates multiple three-wave interactions between high-frequency resonances of the instability in addition to an inverse energy cascade toward lower-frequency modes. Furthermore, these results are discussed in the context of recent theoretical, numerical, and experimental efforts on the EDI in Hall effect discharges and how the EDI may impact anomalous cross field transport.
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Strongly driven ion-scale turbulence in tokamak plasmas is shown to be regulated by a new propagating zonal flow mode, the toroidal secondary mode, which is nonlinearly supported by the turbulence. The mode grows and propagates due to the combined effects of zonal flow shearing and advection by the magnetic drift. Above a threshold in the turbulence level, small-scale toroidal secondary modes become unstable and shear apart turbulent eddies, forcing the turbulence level to remain near the threshold. This threshold condition is used to derive scaling laws for the turbulent heat flux, fluctuation spectra, and zonal flow amplitude, which are validated in nonlinear gyrokinetic simulations and explain previous experimental observations.