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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Nonlinear resistivity for magnetohydrodynamical models

A new formulation of the plasma resistivity that stems from the collisional momentum-transfer rate between electrons and ions is presented. The resistivity computed herein is shown to depend not only on the temperature and density but also on all other polynomial velocity-space moments of the distribution function, such as the pressure tensor and heat flux vector. The full expression for the collisional momentum-transfer rate is determined and is used to formulate the nonlinear anisotropic resistivity. The new formalism recovers the Spitzer resistivity, as well as the concept of thermal force if the heat flux is assumed to be proportional to a temperature gradient. Furthermore, if the pressure tensor is related to viscous stress, the latter enters the expression for the resistivity. The relative importance of the nonlinear term(s) with respect to the well-established electron inertia and Hall terms is also examined. Lastly, the subtle implications of the nonlinear resistivity, and its dependence on the fluid variables, are discussed in the context of magnetized plasma environments and phenomena such as magnetic reconnection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Verification of long wavelength electromagnetic modes with a gyrokinetic-fluid hybrid model in the XGC code

As an alternative option to kinetic electrons, the gyrokinetic total-f particle-in-cell (PIC) code XGC1 has been extended to the MHD/fluid type electromagnetic regime by combining gyrokinetic PIC ions with massless drift-fluid electrons. Here, two representative long wavelength modes, shear Alfven waves and resistive tearing modes, are verified in cylindrical and toroidal magnetic field geometries.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

2D imaging of helium ion velocity in the DIII-D divertor

Two-dimensional imaging of parallel ion velocities are compared to fluid modeling simulations to understand the role of ions in determining divertor conditions and benchmark the UEDGE fluid modeling code. Pure helium discharges are used so that spectroscopic He+measurements represent the main-ion population at small electron temperatures. Electron temperatures and densities in the divertor match simulated values to within about 20-30% establishing the experiment/model match as being at least as good as those normally obtained in the more regularly simulated deuterium plasmas. He + brightness (HeII) comparison indicates that the degree of detachment is captured well by UEDGE, principally due to the inclusion of E x B drifts. Tomographically inverted Coherence Imaging Spectroscopy (CIS) measurements are used to determine the He + parallel velocities which display excellent agreement between model and experiment near the divertor target where He + is predicted to be the main-ion species and where electron-dominated physics dictates the parallel momentum balance. Upstream near the X-point where He + is a minority species and ion-dominated physics plays a more important role, there is an underestimation of the flow velocity magnitude by a factor of 2-3. These results indicate that more effort is required to be able to correctly predict ion momentum in these challenging regimes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Normal-mode-based analysis of electron plasma waves with second-order Hermitian formalism

The classic problem of the dynamic evolution and Landau damping of linear Langmuir electron waves in a collisionless plasma with Maxwellian background is cast as a second-order, self-adjoint problem with a continuum spectrum of real and positive squared frequencies. The corresponding complete basis of singular normal modes is obtained, along with their orthogonality relation. This yields easily the general expression of the time-reversal-invariant solution for any initial-value problem. Examples are then given for specific initial conditions that illustrate different behaviors of the Landau-damped macroscopic moments of the perturbations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Verification of local electrostatic gyrokinetic simulation of driftwave instability in field-reversed configuration

Local linear simulations of ion temperature gradient (ITG) instabilities using a gyrokinetic particle code GKD1D have been verified by comparing with the analytic dispersion relation in the slab geometry and by benchmarking with a global gyrokinetic code GTC-X in a realistic field-reversed configuration (FRC). Results of ITG simulations using either adiabatic or kinetic electrons exhibit excellent agreements between the two codes for linear frequencies, growth rates, and mode structures. The ITG modes in the FRC scrape-off layer region are mostly dominated by the poloidal m = 1 harmonic. Kinetic electrons enhance the subdominant m = 2 harmonic and the even parity dominates the ITG mode structure. Kinetic electrons increase the growth rates for the low-n modes, but decrease the growth rates for the high-n modes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Using statistical modeling to predict and understand fusion experiments

Over 300 cryogenic layered direct-drive inertial confinement fusion implosions have been successfully executed on the OMEGA Laser System in the last decade. However, extracting sufficient understanding from these experiments to develop new designs or to identify or mitigate degradation sources remains challenging. Recently, a statistical modeling approach was developed to successfully design and predict improved implosion experiments on OMEGA. Here, we show that one-dimensional simulations can be used to predict the outcomes of systematically perturbed three-dimensional simulations and that this statistical modeling approach can be used to identify or rule out physical mechanisms for some of the degradation sources observed on the OMEGA Laser System for direct-drive cryogenic inertial confinement fusion. In this instance, we investigate the fusion yield dependencies on the ion temperature asymmetries and laser beam size observed in experiments by comparing with trends in three-dimensional synthetic simulation databases. Using the statistical model on these systematically perturbed simulations, we find that the statistically inferred dependency on the measured ion temperature asymmetries is well explained by imposed ℓ =1 modes. However, we find that the dependency on the laser beam size is only dominated by the illumination non-uniformity for some extreme cases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Suppressing parametric instabilities in direct-drive inertial-confinement-fusion plasmas using broadband laser light

It has long been recognized that broadband laser light has the potential to control parametric instabilities in inertial-confinement-fusion (ICF) plasmas. Here, we use results from laser-plasma-interaction simulations to estimate the bandwidth requirements for mitigating the three predominant classes of instabilities in direct-drive ICF implosions: cross-beam energy transfer (CBET), two-plasmon decay (TPD), and stimulated Raman scattering (SRS). We find that for frequency-tripled, Nd:glass laser light, a bandwidth of 8.5 THz can significantly increase laser absorption by suppressing CBET, while ∼13 THz is needed to mitigate absolute TPD and SRS on an ignition-scale platform. None of the glass lasers used in contemporary ICF experiments, however, possess a bandwidth greater than 1 THz and reaching larger values requires the use of an auxiliary broadening technique such as optical parametric amplification or stimulated-rotational-Raman scattering. An arguably superior approach is the adoption of an argon-fluoride (ArF) laser as an ICF driver. Besides having a broad bandwidth of ∼10 THz, the ArF laser also possesses the shortest wavelength (193 nm) that can scale to the high energy/power required for ICF—a feature that helps to mitigate parametric instabilities even further. We show that these native properties of ArF laser light are sufficient to eliminate nearly all CBET scattering in a direct-drive target and also raise absolute TPD and SRS thresholds well above those for broadband glass lasers. The effective control of parametric instabilities with broad bandwidth is potentially a “game changer” in ICF because it would enable higher laser intensities and ablation pressures in future target designs.

Bates, J. W. (ORCID:0000000188087240)↗
DOE OSTI2024

Validation of MARS-F modeling of plasma response to RMPs using internal measurements on DIII-D

The linear resistive plasma response model is validated against the plasma internal measurement data from DIII-D edge-localized mode (ELM) control experiments with applied resonant magnetic perturbation (RMP). Considered are DIII-D discharges where the n = 1, 2, and 3 (n is the toroidal mode number) RMP field was applied. Experimental data for the plasma boundary displacement, as well as the three-dimensional (3D) pressure perturbation in the edge pedestal region, are deduced from the vertical Thomson scattering (TS) system and the horizontal charge exchange recombination (CER) system on DIII-D. The linear response model produces results that are in reasonable quantitative agreement with the DIII-D internal measurements. The plasma boundary displacement of up to 15 mm is modeled, with the pedestal pressure perturbation reaching 3 kPa. As an important insight, the larger plasma displacement measured by the vertical TS system, as compared to that measured by the horizontal CER system, is due to the contribution from the tangential component of the plasma displacement to the former. This mixing of displacement components is also found to influence the sensitivity of the CER measurement comparisons. The results of this study provide further confidence in the linear resistive plasma response model for analyzing ELM control experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Resistive hose modes in tokamak runaway electron beams

Beams of energetic runaway electrons are generated during disruptions in tokamaks, and fluid models are used to study their effects on macroscale dynamics. Linear computations of a massless, runaway electron beam coupled to MHD plasma show that resistive hose instabilities grow faster than tearing modes at large resistivity. Eigenvalue results with reduced models of the resistive hose instability are compared with results from the full MHD and beam system, showing that the resistive hose decouples from any plasma response. An estimate of plasma temperature at which growth of the resistive hose dominates tearing for post-disruption DIII-D plasma parameters is in a physically relevant regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Heavy ion beam probe for Wendelstein 7-X measurement capabilities as projected through its design

A heavy ion beam probe (HIBP) diagnostic is being developed for studies of plasma equilibrium and turbulence in the optimized Wendelstein 7-X (W7-X) stellarator. Operation of W7-X has experimentally demonstrated that its optimized magnetic field results in improved neoclassical particle confinement and, as a result, turbulence is the predominant cause of energy transport. The HIBP will have the unique ability to provide experimental data needed to complement models of both neoclassical and turbulent transport. It will acquire direct measurements in the W7-X plasma interior of the electric potential (needed for understanding ambipolar particle flux) and fluctuations of electron density and potential (needed for understanding turbulence). The HIBP for W7-X will inject singly charged ion beams with energies of up to 2 MeV and is designed to access the upper cross section of the W7-X plasma. We use trajectory simulations to illustrate the plasma coverage that the diagnostic can achieve in the reference magnetic configurations of W7-X. We calculate beam signal levels, discuss anticipated measurement sensitivity of broadband fluctuations of electron density and plasma potential, and show how they depend on plasma density. We also discuss the diagnostic sensitivity to equilibrium plasma potential.

Instruments & Instrumentation↗
DOE OSTI2025

Al–W gradient density materials—Processing and dynamic ramp compression

Materials with high-density gradients are desired for controlling loading paths in dynamic compression, important for studying material properties in extreme conditions and inertial confinement fusion. The large density difference between Al and W makes them ideal choices for producing gradient density materials, but their extremely different melting temperatures make them challenging to fabricate simultaneously. We report a method for producing Al–W porosity-free materials with a fourfold increase in density (2.7–11 g/cm 3 ) across the composition range, from Al-rich to W-rich, without intermetallic phase formation. This was achieved by understanding the aluminum-dominated densification behavior and examining the influence of pressure and temperature on the densification of Al–W composites. Dynamic compression experiments conducted with the Al–W gradient density material produced shock ramp compressions as expected based on the designed composition, and the performed hydrodynamics simulations showed excellent agreement with experimental results. The results demonstrate that current activated pressure-assisted densification allows for the easy and rapid fabrication of gradient density materials with significant density gradients and tailored compositions, facilitating precise control of the loading paths. These materials have the potential to create customized pressure drives for advancing the fields of material science in extreme environments and dynamic compression.

Alloys↗
DOE OSTI2020

Ion-Exchange Kinetics of Alpha-Zirconium Phosphate Nanoplatelets for Application in Targeted Alpha Therapy

The loading and kinetics of uptake for the inorganic ion-exchange material, α-zirconium phosphate, Zr(HPO 4 ) 2 •H 2 O, were investigated with ions relevant to targeted alpha therapy including natural Cs + (as a surrogate for 221 Fr), natural Bi 3+ (as a surrogate for 213 Bi), and natural La 3+ (as a surrogate for 225 Ac). The narrow interlayer spacing of the α-phase (d = 7.6 Å) was found not to be advantageous with respect to rapid ion exchange, while converting the material to the hydrated Na-phase (d = 12.2 Å) allowed ion exchange to proceed more quickly, reaching equilibrium in under an hour. High loading was achieved for all three ions, at 72 ± 4% for Cs + and 95 ± 5% for La 3+ at pH 3 and 108 ± 10% for Bi 3+ at pH 0.5. Leaching profiles of the loaded materials in a simulated human plasma environment of 10 mM carbonate buffer at pH 7.4 and 37°C, showed negligible release, with less than 1% in all cases. Furthermore, the ion-exchange properties and overall benign nature of zirconium phosphate highlight these materials as a promising platform for a targeted alpha therapy drug-delivery vehicle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

UBIQUITOUS NON-THERMALS IN ASTROPHYSICAL PLASMAS: RESTATING THE DIFFICULTY OF MAINTAINING MAXWELLIANS

This paper outlines the rather narrow conditions on a radiatively decoupled plasma where a Maxwell-Boltzmann (MB) distribution can be assumed with confidence. The complementary non-thermal distribution with non-perturbative kurtosis is argued to have a much broader purview than has previously been accepted. These conditions are expressed in terms of the electron Knudsen number, K{sub e} , the ratio of the electron mean free path to the scale length of electron pressure. Rather generally, f(v < v{sub 2}(K{sub e} )) will be Gaussian, so that MB atomic or wave particle effects controlled by speeds v < v{sub 2} {identical_to} w(15/8K{sub e} ){sup 1/4} will remain defensible, where w is the most probable speed. The sufficient condition for Spitzer-Braginskii plasma fluid closure at the energy equation requires globally K{sub e} (s) {<=} 0.01; this global condition pertains to the maximum value of K{sub e} along the arc length s of the magnetic field (to its extremities) provided that contiguous plasma remains uncoupled from the radiation field. The non-thermal regime K{sub e} > 0.01 is common in all main-sequence stellar atmospheres above approximately 0.05 stellar radii from the surface. The entire solar corona and wind are included in this regime where non-thermal distributions with kurtosis are shown to be ubiquitous, heat flux is not well modeled by Spitzer-Braginskii closure, and fluid modeling is qualitative at best.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

AN EXACT SOLUTION FOR MAGNETIC ANNIHILATION IN A CURVED CURRENT SHEET

An exact magnetohydrodynamic solution is presented for steady magnetic annihilation (merging) in an incompressible resistive viscous plasma. The merging, driven by an axisymmetric stagnation flow on a cylinder, takes place in a curved current sheet that is perpendicular to the plane in which the plasma flow stagnates. The new solution extends earlier models of flux pileup merging in a flat current sheet, driven by stagnation-point flows. The new solution remains valid in the presence of both the isotropic and anisotropic (parallel) plasma viscosity. The geometry of the solution may make it useful in modeling the photospheric flux cancellation on the Sun.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Measurement of the dispersion of radiation from a steady cosmological source

The 'missing baryons' of the near universe are believed to be principally in a partially ionized state. Although passing electromagnetic waves are dispersed by the plasma, the effect has hitherto not been utilized as a means of detection because it is generally believed that a successful observation requires the background source to be highly variable, i.e., the class of sources that could potentially deliver a verdict is limited. We argue in two stages that this condition is not necessary. First, by modeling the fluctuations on macroscopic scales as interference between wave packets, we show that, in accordance with the ideas advanced by Einstein in 1917, both the behavior of photons as bosons (i.e., the intensity variance has contributions from Poisson and phase noise) and the van-Cittert-Zernike theorem are a consequence of wave-particle duality. Nevertheless, we then point out that, in general, the variance on some macroscopic timescale τ consists of (1) a main contributing term ∝1/τ, plus (2) a small negative term ∝1/τ{sup 2} due to the finite size of the wave packets. If the radiation passes through a dispersive medium, this size will be enlarged well beyond its vacuum minimum value of Δt ≈ 1/Δν, leading to a more negative (2) term (while (1) remains unchanged), and hence a suppression of the variance wrt the vacuum scenario. The phenomenon, which is typically at a few parts in 10{sup 5} level, enables one to measure cosmological dispersion in principle. Signal-to-noise estimates, along with systematic issues and how to overcome them, will be presented.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

X-ray and EUV spectroscopy of various astrophysical and laboratory plasmas: Collisional, photoionization and charge-exchange plasmas

Several laboratory facilities were used to benchmark theoretical spectral models that are extensively used by astronomical communities. However, there are still many differences between astrophysical environments and laboratory miniatures that can be archived. Here we setup a spectral analysis system for astrophysical and laboratory plasmas to make a bridge between them, and we investigate the effects from non-thermal electrons and the contributions from a metastable level population on level populations and charge stage distribution for coronal-like, photoionized, and geocoronal plasmas. Test applications to laboratory measurement (i.e., electron beam ion trap plasma) and astrophysical observation (i.e., Comet, Cygnus X-3) are presented. A time evolution of the charge stage and level population are also explored for collisional and photoionized plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Forward modeling of gyrosynchrotron intensity perturbations by sausage modes

To determine the observable radio signatures of the fast sausage standing wave, we examine gyrosynchrotron (GS) emission modulation using a linear three-dimensional magnetohydrodynamic model of a plasma cylinder. Effects of the line-of-sight angle and instrumental resolution on perturbations of the GS intensity are analyzed for two models: a base model with strong Razin suppression and a low-density model in which the Razin effect was unimportant. Our finding contradicts previous predictions made with simpler models: an in-phase variation of intensity between low (f < f {sub peak}) and high (f > f {sub peak}) frequencies is found for the low-density model and an anti-phase variation for the base model in the case of a viewing angle of 45°. The spatially inhomogeneous character of the oscillating emission source and the spatial resolution of the model are found to have a significant effect on the resulting intensity.

79 ASTRONOMY AND ASTROPHYSICS↗