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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Photon Doppler Velocimetry to Spatially Resolve Plasma Density in a Power Flow Gap

The understanding of power flow plasmas is important as we look towards next generation pulsed power (NGPP) as current losses could prohibit the goals of that facility. Therefore, it is important to have accurate diagnostics of the plasma parameters on the current machines, which can be used to help inform and improve simulations. Having these plasma parameters will help validate models and simulations to provide confidence when they are expanded to conditions relevant to NGPP. One important plasma parameter that can be measured is the electron density, which can be measured by photonic Doppler velocimetry (PDV). A PDV system has several key advantages over other interferometers by measuring relatively low densities (> 1 × 10 15 cm -2 ) with both spatial and temporal resolution. Experiments were performed on the Mykonos pulsed power machine, which is a 1 MA sub scale machine in which recent platforms have been developed to explore current densities relevant to the inner magnetically insulated transmission line (MITL) on the Z machine. Experiments were performed on two different platforms, the thin foil platform and the Mykonos parallel plate platform (MP3). In addition, a combination of both single-point and multi-point measurements were used. The single-point measurements proved to be very promising, providing a clear increase in density at about 70 ns into the current rise on thin foil experiments up to about 5 × 10 17 cm -3 before the probe stopped providing signal. While we did also see returns from multi-point measurements on both platforms, the signals were not as easy to interpret due to strong background effects. However, they do show initial promise for this diagnostic to measure density at several points across a 1 mm gap. These measurements provide insights in how to improve the diagnostic so that it can provide useful information on power flow relevant experiments.

47 OTHER INSTRUMENTATION↗
NASA NTRS1978

Magnetospheric electrostatic emissions and cold plasma densities

A synoptic study of electric wave, magnetometer, and plasma data from IMP-6 was carried out for times when banded electrostatic waves are observed between harmonics of the electron gyrofrequency in the earth's outer magnetosphere. Four separate classes of such waves were previously identified. The spatial and temporal occurrences of waves in each class are summarized here, as are correlations of occurrence with geomagnetic activity. Most importantly, associations between the observations of waves of different classes and the relative portions of cold and hot electrons present at the position of the spacecraft are established. Finally, evidence for the signature of the loss cone is sought in the plasma data.

Hubbard, R. F.↗
NASA NTRS1979

Magnetospheric electrostatic emissions and cold plasma densities

A synoptic study of electric wave, magnetometer, and plasma data from Imp 6 has been carried out for times when banded electrostatic waves are observed between harmonics of the electron gyrofrequency in the earth's outer magnetosphere. Four separate classes of such waves have previously been identified by us. The spatial and temporal occurrences of waves in each class are summarized here, as are correlations of occurrence with geomagnetic activity. Most importantly, associations between the observations of waves of different classes and the relative portions of cold and hot electrons present at the position of the spacecraft are established. The cold to hot ratio varies in accordance with the predictions of our previous theoretical work, which models the emission as arising unstably from a hot loss cone distribution existing simultaneously with a cold isotropic electron component. Finally, evidence for the signature of the loss cone is sought in the plasma data.

Hubbard, R. F.↗
DOE OSTI2025

Addressing key physics problems in high-energy-density plasmas with a novel kinetic simulation capability

Many important physical processes in inertial confinement fusion (ICF) and dense Z-pinch (DZP) experiments require a kinetic (velocity-space-dependent) description. Conventional particle-in-cell (PIC) methods are poorly suited for high-energy-density (HED) plasmas, due to restrictive time-step constraints and the inability to conserve energy. In a previous LDRD (21-FS-048), we demonstrated that a fully implicit PIC formulation overcomes these limitations: it conserves energy even when coupled with Coulomb collision models and can be solved efficiently with large grid cells and large time steps. Thus, it is feasible to use this method to study kinetic effects in ICF and DZP plasmas on hydro-like time and spatial scales. In this follow-on LDRD, we advanced this methodology into a high-fidelity tool for production-scale simulations and used it to answer key questions relevant to ICF and DZP experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Magnetic-Field Effects in Unstable High-Energy-Density Plasmas

The influence of magnetic fields in high-energy-density (HED) systems is a widely unexplored field of research that can play an important role in magnetized inertial confinement fusion (ICF) and in astrophysical systems. Hydrodynamic instabilities are presently believed to be the dominant degradation mechanism in ICF implosions. Therefore, understanding the influence of an imposed B-field on RT growth is important for future mitigation strategies as well as fundamental physics of ICF implosions that utilize B-fields for enhanced performance. The Crab Nebula, one of the most observed objects in our universe, contains elongated spikes of material created by hydrodynamic instabilities, however these spikes do not break-up and become turbulent as they evolve late in time. One hypothesis for this behavior is that B-fields around these spikes prevent vortex generation typical in these types of systems.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Studies of particle transport in high-energy-density plasma in the presence of a megagauss magnetic field

Charged particle transport in a magnetic field is among the most fundamental phenomena in plasma physics. Magnetic fields are often introduced in conventional magnetized fusion devices to suppress particle and heat transport, a phenomenon that has been extensively studied. In contrast, particle and heat transport in magnetized high-energy-density (HED) plasmas remain relatively unexplored due to the challenges of generating an external magnetic field strong enough to significantly alter particle dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Radiative cooling of a low-density plasma

The paper extends and improves the radiative cooling coefficient calculations of Cox and Tucker (1969) and Cox and Daltabuit (1971) for a low-density optically thin plasma with no molecules or dust, of cosmic abundances in the range from 10,000 to 100,000,000 K. Earlier rates applied to a plasma containing H, He, C, N, O, Ne, Mg, Si, and S; the present study added Ca, Fe, and Ni. For the elements included, many individual lines are calculated which previously has been averaged together. The cooling processes considered are permitted, forbidden, and semiforbidden line transitions, including contributions from dielectronic recombination and bremsstrahlung, radiative recombination, and two-photon continua. The ionization balance is calculated in collisional equilibrium using an approximate auto-ionization following inner-shell excitation and the low-density limit for the dielectronic recombination rate. Cooling in various observational bands in the soft X-ray region is determined.

Raymond, J. C.↗
DOE OSTI2025

Particle-in-cell simulations of expanding high energy density plasmas with laser ray tracing

The design and analysis of high energy density (HED) laser experiments typically rely on radiation hydrodynamics simulations. However, some laser–plasma interaction regimes are not collisional and cannot be adequately modeled with hydrodynamics. For example, strongly driven magnetic reconnection and magnetized collisionless shock experiments possess extended hydrodynamic or even kinetic properties, necessitating first-principles kinetic simulations. In this paper, we present the benchmarking and first results obtained with a laser-ray-tracing and inverse bremsstrahlung absorption module implemented in the particle-in-cell code PSC. The simulation results are compared to radiation hydrodynamic simulations using the FLASH code as well as analytical estimates. We successfully benchmark the energy deposition model and overall hydrodynamic evolution of the systems. We also consider possible kinetic effects that may be expected from laser-target ablation in the HED regime, including non-local transport and two-temperature effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1979

Dielectronic recombination rates, ionization equilibrium, and radiative energy-loss rates for neon, magnesium, and sulfur ions in low-density plasmas

Results of detailed and systematic calculations are presented for the total dielectronic recombination rate coefficients for the ions of Ne, Mg, and S in a low-density predominantly hydrogen plasma. The new recombination rates are used to calculate solar corona ionization-equilibrium distributions of the ions. The most important effect of dielectronic recombination for ions in corona equilibrium is found to be a shift in the maximum-abundance temperatures toward higher temperatures, which are in some cases reduced from those predicted on the basis of the simple Burgess formula.

Jacobs, V. L.↗
DOE OSTI2023

Transition from ITG to MTM linear instabilities near pedestals of high density plasmas

Here, investigation of linear gyrokinetic ion-scale modes ( k θ ρ s = 0.3) finds that a transition from ion temperature gradient to microtearing mode (MTM) dominance occurs as the density is increased near the pedestal region of a parameterized DIII-D sized tokamak. H-modes profile densities, temperatures, and equilibria are parameterized utilizing the OMFIT PRO_create module. With these profiles, linear gyrokinetic ion-scale instabilities are predicted with CGYRO. This transition (nMTM) has a weak dependence on radial location in the region near the top of the pedestal ( ρ = 0.7 – 0.9), which allows simulating single radii to examine the approximate scaling of nMTM with global parameters. The critical nMTM is found to scale with plasma current. Additionally, increasing the minor radius by decreasing the aspect ratio and increasing the major radius are found to reduce nMTM. However, any relationship between nMTM and density limit physics remains unclear as nMTM increases relative to the Greenwald density with larger minor radius and with larger magnetic field, suggesting that the transport due to MTM may be less important for a reactor. Additionally, nMTM is sensitive to the pedestal temperature, the local electron and ion gradients, the ratio of ion to electron temperature T i / T e, and the current profile. MTMs are predicted to be the dominant instability in the core at similar Greenwald fractions for DIII-D, NSTX, and NSTX-U H-mode experiments, supporting the results of the parameterized study. Additionally, MTMs continue to be the dominant linear instability in a DIII-D L-mode after an H–L transition as the plasma approaches a density limit disruption despite the large change in plasma profiles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Charged-particle transport in high energy density plasmas

This Special Topic Collection grew out of two gatherings of researchers active in the high energy density (HED) physics community: a mini-conference on charged-particle transport in HED plasma held during the 64th annual meeting of the American Physical Society's Division of Plasma Physics (Spokane, WA, November 2022) and a dedicated charged-particle transport coefficient code comparison workshop (Livermore, CA, July 2023). These gatherings provided opportunities for theoretical, computational, and experimental researchers to discuss the state of the field, including current capabilities and methods, needs of hydrodynamic simulations, and frontiers for future research. Finally, this special issue collects a total of 13 research and review articles on charged-particle transport in HED plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2021

Magnetic Field and Plasma Density Observations of a Pressure Front by Voyager 1during 2020 in the Very Local Interstellar Medium

Voyager 1 has been moving through the very local interstellar medium (VLISM) from the time that it crossed the heliopause on 2012/DOY 238 to 2020/DOY 292. Three notable objects in the magnetic field of the VLISM have been observed: two shocks and one pressure front. This paper reports the observation of a fourth object observed near 2020/DOY 147. There were no upstream electron plasma oscillations of the type often observed ahead of shocks, abrupt increases in energetic particles, or fluctuations in the 48 s increments of the magnetic field associated with this feature, suggesting that it was probably not a shock. This feature was associated with a relatively large increase in the magnetic field strength(B2/B1=1.35)and in the electron density determined by the Plasma Wave Science experiment (N2/N1=1.36) using a new method described in this paper. This feature appears to be a pressure front associated with a compressive wave in the VLISM. The two shocks and the two pressure fronts were associated with the four largest maxima observed in B (t) between 2012/DOY 238 and 2020/DOY 292. Each feature was associated with a jump–ramp structure. The jump–ramp structures were separated by long relatively undisturbed quiet intervals.

Interstellar magnetic fields↗
DOE OSTI2023

A generalized approach to x-ray data modeling for high-energy-density plasma experiments

Accurate understanding of x-ray diagnostics is crucial for both interpreting high-energy-density experiments and testing simulations through quantitative comparisons. X-ray diagnostic models are complex. Past treatments of individual x-ray diagnostics on a case-by-case basis have hindered universal diagnostic understanding. Here, in this study, we derive a general formula for modeling the absolute response of non-focusing x-ray diagnostics, such as x-ray imagers, one-dimensional space-resolved spectrometers, and x-ray power diagnostics. The present model is useful for both data modeling and data processing. It naturally accounts for the x-ray crystal broadening. The new model verifies that standard approaches for a crystal response can be good approximations, but they can underestimate the total reflectivity and overestimate spectral resolving power by more than a factor of 2 in some cases near reflectivity edge features. We also find that a frequently used, simplified-crystal-response approximation for processing spectral data can introduce an absolute error of more than an order of magnitude and the relative spectral radiance error of a factor of 3. The present model is derived with straightforward geometric arguments. It is more general and is recommended for developing a unified picture and providing consistent treatment over multiple x-ray diagnostics. Such consistency is crucial for reliable multi-objective data analyses.

Nagayama, Taisuke↗
NASA NTRS1993

First in-situ observations of neutral and plasma density fluctuations within a PMSE layer

The NLC-91 rocket and radar campaign provided the first opportunity for high resolution neutral and plasma turbulence measurements with simultaneous observations of PMSE (Polar Mesospheric Summer Echoes). During the flight of the TURBO payload on August 1, 1991, Cornell University Portable Radar Interferometer (CUPRI) and European Incoherent Scattter facility (EISCAT) observed double PMSE layers located at 86 and 88 km altitude, respectively. Strong neutral density fluctuations were observed in the upper layer but not in the lower layer. The fluctuation spectra of the ions and neutrals within the upper layer are consistent with standard turbulence theories. However, we show that there is no neutral turbulence present in the lower layer and that something else must have been operating here to create the plasma fluctuations and hence the radar echoes. Although the in situ measurements of the electron density fluctuations are much stronger in the lower layer, the higher absolute electron density of the upper layer more than compensated for the weaker fluctuations yielding comparable radar echo powers.

Lubken, Franz-Josef↗
NASA NTRS2012

Deriving Plasma Densities and Elemental Abundances from SERTS Differential Emission Measure Analysis

We use high-resolution spectral emission line data obtained by the SERTS instrument during three rocket flights to demonstrate a new approach for constraining electron densities of solar active region plasma.We apply differential emission measure (DEM) forward-fitting techniques to characterize the multithermal solar plasma producing the observed EUV spectra, with constraints on the high-temperature plasma from the Yohkoh Soft X-ray Telescope. In this iterative process, we compare line intensities predicted by an input source distribution to observed line intensities for multiple iron ion species, and search a broad range of densities to optimize chi-square simultaneously for the many available density-sensitive lines. This produces a density weighted by the DEM, which appears to be useful for characterizing the bulk of the emitting plasma over a significant range of temperature. This "DEM-weighted density" technique is complementary to the use of density-sensitive line ratios and less affected by uncertainties in atomic data and ionization fraction for any specific line. Once the DEM shape and the DEM-weighted density have been established from the iron lines, the relative elemental abundances can be determined for other lines in the spectrum. We have also identified spectral lines in the SERTS wavelength range that may be problematic

corona↗
NASA NTRS2008

DEMETER Observations of Highly Structured Plasma Density and Associated ELF Electric Field and Magnetic Field Irregularities at Middle and Low Latitudes

The DEMETER spacecraft frequently encounters structured plasma and electric field irregularities associated with equatorial spread-F. However, during severe geo~nagnetic storms, the spacecraft detects broader regions of density structures that extend to higher latitudes, in some instances to the sub-auroral regions. In addition to the electric field irregularities, ELF magnetic field irregularities are sometimes observed. for example, on the walls of the density structures, and appear related to finely-structured spatial currents and/or Alfven waves. The mid-latitude irregularities are compared with those of equatorial spread-F as well as wit11 intense irregularities associated with the trough region observed at sub-auroral latitudes.

Pfaff, R.↗
NASA NTRS1992

X-ray emission-line spectra of photoionized plasmas - Density sensitivity of the Fe L-shell series

The circumsource environments of accretion-powered X-ray sources are likely to support relatively dense (greater than 10 exp 11/cu cm) photoionized X-ray emission-line regions. The Fe L-shell ions provide a versatile class of plasma diagnostics in this regime, their multielectron structures resulting in diverse spectral phenomena. Attention is given to the spectral response of Fe L-shell ions to variations in electron density over the range 10 exp 11 to 10 exp 16/cu cm. It is found that density-sensitive line ratios exist in the wavelength interval 12-17 A for the ions Fe XVII-XXI. The prominent role of radiative recombination in the population kinetics distinguishes the density-sensitive Fe lines in photoionized plasmas from those which operate in coronal equilibrium plasmas. The results of detailed atomic modeling of these ions are presented and applications to spectroscopic observations of accretion-driven X-ray sources are discussed.

Liedahl, Duane A.↗