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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Assessment of ceramic coatings for metal fuel melting crucible

The objective of this study is to develop a coating method and material for crucibles to prevent material interactions with the U-Zr/U-TRU-Zr fuels during the manufacturing of SFR fuels. Refractory coatings were applied to niobium substrates by vacuum plasma-spray coating method. Melt dipping tests conducted were the coated rods lowered into the fuel melt at 1600 C. degrees, and withdrawn and cooled outside the crucible in the inert atmosphere of the induction furnace. Melt dipping tests of the coated Nb rods indicated that plasma-sprayed Y{sub 2}O{sub 3} coating doesn't form significant reaction layer between fuel melt and coating layer. Melt dipping tests of the coated Nb rods showed that TiC, TaC, and Y{sub 2}O{sub 3} coatings exhibited the promising performance among other ceramic coatings. These materials could be promising candidate materials for the reusable melt crucible of metal fuel for SFR. In addition, in order to develop the vacuum plasma-spray coating method for re-usable crucible of metal fuel slugs to be overcome the issue of thermal expansion mismatch between coating material and crucible, various combinations of coating conditions were investigated to find the bonding effect on the substrate in pursuit of more effective ways to withstand the thermal stresses. It is observed that most coating methods maintained sound coating state in U-Zr melt. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2021

Electron energization during merging of self-magnetized, high-beta, laser-produced plasmas

Electron energization during merging of magnetized plasmas is studied using the OMEGA and OMEGA EP laser facilities by colliding two plasma plumes, each containing a Biermann-battery self-generated magnetic field. Two neighbouring plasma plumes are produced by intense laser beams, and the anti-parallel Biermann fields merge and reconnect in the process of the plumes’ expansion and collision. To isolate the merging as an acceleration source, the electron energy spectra obtained from two-plume collision shots are compared with the spectra from single-plume shots. Single-plume shots exhibit an energized electron tail with energies up to ${\sim }250\ \textrm {keV}$ . The electrons in merging experiments are additionally accelerated by ${\sim }50\text {--}100$ keV compared to single-plume shots.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Laser-induced plasmas in air studied using two-color interferometry

Temporally and spatially resolved density profiles of Cu atoms, electrons, and compressed air, from laser-induced copper plasmas in air, are measured using fast spectral imaging and two-color interferometry. From the intensified CCD images filtered by a narrow-band-pass filter centered at 515.32 nm, the Cu atoms expansion route is estimated and used to determine the position of the fracture surface between the Cu atoms and the air. Results indicate that the Cu atoms density at distances closer to the target (0–0.4 mm) is quite low, with the maximum density appearing at the edge of the plasma's core being ∼4.6 × 10{sup 24 }m{sup −3} at 304 ns. The free electrons are mainly located in the internal region of the plume, which is supposed to have a higher temperature. The density of the shock wave is (4–6) × 10{sup 25 }m{sup −3}, corresponding to air compression of a factor of 1.7–2.5.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

R-matrix calculations for opacities: I. Methodology and computations

Abstract An extended version of the R -matrix methodology is presented for calculation of radiative parameters for improved plasma opacities. Contrast and comparisons with existing methods primarily relying on the distorted wave approximation are discussed to verify accuracy and resolve outstanding issues, particularly with reference to the opacity project (OP). Among the improvements incorporated are: (i) large-scale Breit–Pauli R -matrix calculations for complex atomic systems including fine structure, (ii) convergent close coupling wave function expansions for the ( e + ion) system to compute oscillator strengths and photoionization cross sections, (iii) open and closed shell iron ions of interest in astrophysics and experiments, (iv) a treatment for plasma broadening of autoionizing resonances as function of energy-temperature-density dependent cross sections, (v) a ‘top-up’ procedure to compare convergence with R -matrix calculations for highly excited levels, and (vi) spectroscopic identification of resonances and bound ( e + ion) levels. The present R -matrix monochromatic opacity spectra are fundamentally different from OP and lead to enhanced Rosseland and Planck mean opacities. An outline of the work reported in other papers in this series and those in progress is presented. Based on the present re-examination of the OP work, opacities of heavy elements might require revisions in high temperature-density plasma sources.

Pradhan, A. K. (ORCID:0000000187753643)↗
DOE OSTI2013

Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer

Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Impedance of an intense plasma-cathode electron source for tokamak startup

In this study, an impedance model is formulated and tested for the ~1kV, ~1kA/cm 2 , arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma (n arc ≈ 10 21 m -3 ) within the electron source, and the less dense external tokamak edge plasma (n edge ≈ 10 18 m -3 ) into which current is injected at the applied injector voltage, V inj . Experiments on the Pegasus spherical tokamak show the injected current, I inj , increases with V inj according to the standard double layer scaling I inj ~ V inj 3/2 at low current and transitions to I inj ~ V inj 1/2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density n b ~ I inj /V inj 1/2 . For low tokamak edge density n edge and high I inj , the inferred beam density n b is consistent with the requirement n b ≤ n edge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, n b ~ n arc is observed, consistent with a limit to n b imposed by expansion of the double layer sheath. These results suggest that n arc is a viable control actuator for the source impedance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Radial variation of the solar wind proton temperature: Heat flow or addition?

The proton temperature profile of the asymptotic solar wind plasma can be modified by four different physical effects: PdV work, external heat deposition, ΔQ, divergence of heat, ∇⋅q, and collisional energy exchange with other species in the plasma. Suggestions in the literature that ΔQ heating is “required” to explain the proton profile have often been deduced while neglecting q{sub p} and energy exchange. Despite the adiabatic approximation q{sub p}=0 having no rigorous justification in low-density plasmas, the simultaneous neglect of energy exchange unnaturally forces the “need” for ΔQ to balance adiabatic cooling caused by the wind’s expansion. In this paper, the asymptotic wind proton heat flux is determined which balances the inner Heliosphere’s steady state entropy equation for the protons, ignoring heat addition and energy exchange. The solutions of the energy equation recover both the power-law trend and amplitude of the 5 year averaged Helios temperature profiles that were segregated by speed. The dimensionless skewness S of the heat flow is empirically shown to scale for all wind states below 600 km s{sup −1} as if it were equal to the Knudsen number determined by Coulomb collisions, a relation that is rigorously demonstrated for an infinitesimal Knudsen number, bridging the unusual adiabatic protons for U≃250 km s{sup −1} and the higher speed states of the winds that remain hotter over a wider radial domain. Higher speed states (U>650 km s{sup −1}) may require additional scattering beyond what Coulomb effects can provide, although the averaged profiles for these speeds are not as accurate as those below 600 km s{sup −1}.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Transverse particle acceleration and diffusion in a planetary magnetic field

A general model of particle acceleration by plasma waves coupled with adiabatic radial diffusion in a planetary magnetic field is developed. The model assumes that a spectrum of lower hybird waves is present to resonantly accelerate ions transverse to the magnetic field. The steady state Green's function for the combined radial diffusion and wave acceleration equation is found in terms of a series expansion. The results provide a rigorous demonstration of how a quasi-Maxwellian distribution function is formed in the absence of particle collisons and elucidate the nature of turbulent heating of magnetospheric plasmas. The solution is applied to the magnetosphere of Neptune for which a number of examples are given illustrating how the spectrum of pickup N(+) ions from Triton evolves.

Barbosa, D. D.↗
NASA NTRS1972

Quantum statistical mechanics of dense partially ionized hydrogen.

The theory of dense hydrogenic plasmas beginning with the two component quantum grand partition function is reviewed. It is shown that ionization equilibrium and molecular dissociation equilibrium can be treated in the same manner with proper consideration of all two-body states. A quantum perturbation expansion is used to give an accurate calculation of the equation of state of the gas for any degree of dissociation and ionization. In this theory, the effective interaction between any two charges is the dynamic screened potential obtained from the plasma dielectric function. We make the static approximation; and we carry out detailed numerical calculations with the bound and scattering states of the Debye potential, using the Beth-Uhlenbeck form of the quantum second virial coefficient. We compare our results with calculations from the Saha equation.

Dewitt, H. E.↗
DOE OSTI2015

Observation and interpretation of energy efficient, diffuse direct current glow discharge at atmospheric pressure

A diffuse direct-current glow discharge was realized with low energy consumption and high energy utilization efficiency at atmospheric pressure. The formation of diffuse discharge was demonstrated by examining and comparing the electrical properties and optical emissions of plasmas. In combination with theoretical derivation and calculation, we draw guidelines that appearance of nitrogen ions at low electron density is crucial to enhance the ambipolar diffusion for the expansion of discharge channel and the increasing ambipolar diffusion near the cathode plays a key role in the onset of diffuse discharge. An individual-discharge-channel expansion model is proposed to explain the diffuse discharge formation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Intricate structure of the plasma Rayleigh–Taylor instability in shock tubes

Spikes and bubbles grow on unstable interfaces that are accelerated in high-energy-density conditions. If a shock propagates ahead of the interface, the plasma can be heated to extreme conditions where conduction and radiation fluxes influence the hydrodynamics. For example, a National Ignition Facility experiment found reduced single-mode nonlinear mixed-width growth in conditions scaled from a supernova explosion. We present high-resolution two-dimensional radiation hydrodynamic simulations with the Flash code that quantitatively reproduce the experiment. Radiative fluxes are primarily responsible for ablating the spike and removing the mushroom caps. The ablated plasma increases the mixed mass and forms a low-density halo with spikes forming in both directions. This is considerably more complex than classical instability. The halo is sensitive to ablative physics, so radiographing it may aid in the verification of energy transport modeling. Although ablation changes the spike shape, it has little effect on the overall mixed width for these parameters. This is because ablation enhances the bubble velocity but it has the opposite effect on the spike. The radiation transport instead suppresses the growth via increasing the shocked foam density, thus decreasing the Atwood number. Furthermore, a terminal velocity model including the rarefaction expansion agrees with the experimental mixed-width growth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

An investigation of resonances in e{sup +}-H scattering embedded in Debye plasma

We carry out calculations for S-wave and P-wave resonances in e{sup +}-H scattering in weakly coupled Debye plasma in which the interaction between two charged particles is represented by a screened Coulomb potential. We employ the complex-scaling method with Hylleraas-type basis set to take correlation effects into account. In the complex-scaling treatment of the screened Coulomb potential, we first perform a Taylor series expansion for the exponential function that contains the distance r between two particles into a polynomial with various powers r{sup n}. We then make the complex scaling transformation of r→r e{sup iθ} in the expansion. The complex resonant eigenvalues are obtained by searching for stabilized points in the complex energy plane with respect to the changes of rotational angle θ and other parameters in the basis set.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Exploring the Inner Acceleration Region of Solar Wind: A Study Based on Coronagraphic UV and Visible Light Data

This work combined coronagraphic visible light (VL) and UV data to provide with an unprecedented view of the inner corona where the nascent solar wind is accelerated. The UV (H i Lyα) and VL (polarized brightness) images (reconstructed with SOHO/UVCS, LASCO, and Mauna Loa data) have been analyzed with the Doppler dimming technique to provide for the first time daily 2D images of the radial wind speed between 1 and 6 R {sub ⊙} over 1 month of observations. Results show that both polar and equatorial regions are characterized at the base of the corona by plasma outflows at speeds >100 km s{sup −1}. The plasma is then decelerated within ∼1.5 R {sub ⊙} at the poles and ∼2.0 R {sub ⊙} at the equator, where local minima of the expansion speeds are reached, and gently reaccelerated higher up, reaching speeds typical of fast and slow wind components. The mass flux is highly variable with latitude and time at the equator and more uniform and stable over the poles. The polar flow is asymmetric, with speeds above the south pole lower than those above the north pole. A correlation (anticorrelation) between the wind speed and its density is found below (above) ∼1.8 R {sub ⊙}. The 2D distribution of forces responsible for deceleration and reacceleration of solar wind is provided and interpreted in terms of Alfvén waves. These results provide a possible connection between small-scale outflows reported with other instruments at the base of the corona and bulk wind flows measured higher up.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

The Yaglom law in the expanding solar wind

We study the Yaglom law, which relates the mixed third-order structure function to the average dissipation rate of turbulence, in a uniformly expanding solar wind by using the two-scale expansion model of magnetohydrodynamic (MHD) turbulence. We show that due to the expansion of the solar wind, two new terms appear in the Yaglom law. The first term is related to the decay of the turbulent energy by nonlinear interactions, whereas the second term is related to the non-zero cross-correlation of the Elsässer fields. Using magnetic field and plasma data from WIND and Helios 2 spacecrafts, we show that at lower frequencies in the inertial range of MHD turbulence the new terms become comparable to Yaglom's third-order mixed moment, and therefore they cannot be neglected in the evaluation of the energy cascade rate in the solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PSEUDOSTREAMERS AS THE SOURCE OF A SEPARATE CLASS OF SOLAR CORONAL MASS EJECTIONS

Using white-light and extreme-ultraviolet imaging observations, we confirm that pseudostreamers (streamers that separate coronal holes of the same polarity) give rise to a different type of coronal mass ejection (CME) from that associated with helmet streamers (defined as separating coronal holes of opposite polarity). Whereas helmet streamers are the source of the familiar bubble-shaped CMEs characterized by gradual acceleration and a three-part structure, pseudostreamers produce narrower, fanlike ejections with roughly constant speeds. These ejections, which are typically triggered by underlying filament eruptions or small, flaring active regions, are confined laterally and channeled outward by the like-polarity open flux that converges onto the pseudostreamer plasma sheet from both sides. In contrast, helmet streamer CMEs are centered on the relatively weak field around the heliospheric current sheet and thus undergo greater lateral expansion. Pseudostreamer ejections have a morphological resemblance to white-light jets from coronal holes; however, unlike the latter, they are not primarily driven by interchange reconnection, and tend to have larger widths (∼20°–30°), lower speeds (∼250–700 km s{sup −1}), and more complex internal structure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Residual stress of controlled atmosphere plasma spray blended metal deposits measured via in-situ substrate curvature method

The preliminary use of the in-situ curvature measurement technique for analyzing the planar stress evolution of controlled atmosphere plasma spray (CAPS) refractory metal deposits was performed with SNL-NM org. 1834’s CAPS system. A porous refractory metal exemplar of Ta-Nb was sprayed onto Ni-200, Ti-6Al-4V, and Al 7075-T6 substrates using a constant plasma torch parameter setting and deposition toolpath. Residual stresses of the deposits were found to be largely influenced by the substrate coefficient of thermal expansion and were calculated to be 49, 90, and -136 MPa for Ni 200, Ti-6Al-4V, and Al 7075-T6, respectively. The “Evolving stress” of the Ta-Nb deposits, which more accurately describes the mean intrinsic splat quenching stress of the spray material during deposition, was calculated to be 67, 92, and 129 MPa for Ni-200, Ti-6Al-4V, and Al 7075-T6, respectively. Notable difference in curvature measurement for the 1st coating pass for the Al 7075- T6 substrate was observed, with interface micrograph evidence suggesting potential softening and/or melting of the Al 7075-T6 substrate surface during deposition. Substrate temperature measurements prior to Ta-Nb deposition were used to calculate thermal energy absorbed from the hot gas plume by the different substrates and were found to correlate to the substrate’s thermal effusively. These calculated thermal energies were also found to be ~10 to 15% of the calculated energy output from the plasma torch’s nozzle exit for these experimental conditions.

36 MATERIALS SCIENCE↗