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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Nonequilibrium effects in high-gain inertial confinement fusion

Recent experimental demonstrations of ignition and target gain in inertial confinement fusion (ICF) have stimulated interest in exploring the fundamental physics of violent deuterium-tritium (DT) burn in high-gain ICF targets. A significant DT-burn fraction is a necessary condition for high energy gain and large neutron yields (>100MJ). Using classical molecular-dynamics (MD) simulations and a hybrid fluid-kinetic model, we examine how a large fraction of low-energy 𝛼 particles can kick D and T ions out of equilibrium in high-gain ICF targets. The MD results suggest that (1) temperatures of 𝑇 𝐷 and 𝑇 𝑇 can differ by as much as ∼20% of their mean temperature and (2) the deviation of the DT energy distribution from the Maxwell-Boltzmann function can exceed ∼30%. Some of these MD observations, such as the preferential heating of D ions by low-energy 𝛼 particles and the temperature separation, can be explained by a proposed hybrid fluid-kinetic model. Furthermore, the implication of such nonequilibrium effects on the DT reactivity is also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Streaked Sub-ps-resolution X-ray Line Shapes and Implications for Solid-density Plasma Dynamics

A high-resolution x-ray spectrometer was coupled with an ultrafast x-ray streak camera to produce time-resolved line shape spectra measured from hot, solid-density plasmas. A Bragg crystal was placed near a laser-produced plasma to maximize throughput; alignment tolerances were established by raytracing. The streak camera produced single-shot time-resolved spectra, heavily sloped due to photon time-of-flight differences, with sufficient reproducibility to accumulate photon statistics. The images are time-calibrated by the slope of streaked spectra and dewarped to generate spectra emitted at different times defined at the source. The streaked spectra demonstrate the evolution of spectral shoulders and other features on ps timescales, showing the feasibility of plasma parameter measurements on the rapid timescales necessary to study high-energy-density plasmas.

High-energy-density plasmas↗
NASA NTRS2004

Magnetic-Nozzle Studies for Fusion Propulsion Applications: Gigawatt Plasma Source Operation and Magnetic Nozzle Analysis

This project has been a multiyear effort to assess the feasibility of a key process inherent to virtually all fusion propulsion concepts: the expansion of a fusion-grade plasma through a diverging magnetic field. Current fusion energy research touches on this process only indirectly through studies of plasma divertors designed to remove the fusion products from a reactor. This project was aimed at directly addressing propulsion system issues, without the expense of constructing a fusion reactor. Instead, the program designed, constructed, and operated a facility suitable for simulating fusion reactor grade edge plasmas, and to examine their expansion in an expanding magnetic nozzle. The approach was to create and accelerate a dense (up to l0(exp 20)/m) plasma, stagnate it in a converging magnetic field to convert kinetic energy to thermal energy, and examine the subsequent expansion of the hot (100's eV) plasma in a subsequent magnetic nozzle. Throughout the project, there has been a parallel effort between theoretical and numerical design and modelling of the experiment and the experiment itself. In particular, the MACH2 code was used to design and predict the performance of the magnetoplasmadynamic (MPD) plasma accelerator, and to design and predict the design and expected behavior for the magnetic field coils that could be added later. Progress to date includes the theoretical accelerator design and construction, development of the power and vacuum systems to accommodate the powers and mass flow rates of interest to out research, operation of the accelerator and comparison to theoretical predictions, and computational analysis of future magnetic field coils and the expected performance of an integrated source-nozzle experiment.

Gilland, James H.↗
NASA NTRS1984

Drift wave instabilities in a high beta multispecies plasma

The dispersion relation for drift-Alfven waves in two-component (cold and hot), high beta inhomogeneous multispecies plasma containing protons, oxygen, and sulfur ions is solved numerically. The magnetic field is assumed to have a gradient in simple slab geometry configuration. The plasma ion composition consists of H, O, S, SO2, and Na ions. The effect of heavy ions and multiple charge states on the growth rates has been numerically estimated for assumed ion compositions. The numerical calculations of growth rates also have been performed by using ion composition and plasma parameters based on Voyager spacecraft in the magnetospheres of Jupiter and Saturn.

Patel, V. L.↗
NASA NTRS1991

Landau damping in space plasmas

The Landau damping of electrostatic Langmuir waves and ion-acoustic waves in a hot, isotropic, nonmagnetized, generalized Lorentzian plasma is analyzed using the modified plasma dispersion function. Numerical solutions for the real and imaginary parts of the wave frequency omega sub 0 - (i)(gamma) have been obtained as a function of the normalized wave number (k)(lambda sub D), where lambda sub D is the electron Debye length. For both particle distributions the electrostatic modes are found to be strongly damped at short wavelengths. At long wavelengths, this damping becomes less severe, but the attenuation of Langmuir waves is much stronger for a generalized Lorentzian plasma than for a Maxwellian plasma. It is concluded that Landau damping of ion-acoustic waves is only slightly affected by the presence of a high energy tail, but is strongly dependent on the ion temperature.

Thorne, Richard M.↗
NASA NTRS2010

The Abundance Pattern in the Hot ISM of NGC 4472: Insights and Anomalies

Important clues to the chemical and dynamical history of elliptical galaxies are encoded in the abundances of heavy elements in the X-ray emitting plasma. We derive the hot ISM abundance pattern in inner (0.2.3R(sub e)) and outer (2.3.4.6R(sub e)) regions of NGC 4472 from analysis of Suzaku spectra, supported by analysis of co- spatial XMM-Newton spectra. The low background and relatively sharp spectral resolution of the Suzaku XIS detectors, combined with the high luminosity and temperature in NGC 4472, enable us to derive a particularly extensive abundance pattern that encompasses O, Ne, Mg, Al, Si, S, Ar, Ca, Fe, and Ni in both regions. We apply simple chemical evolution models to these data, and conclude that the abundances are best explained by a combination of alpha-element enhanced stellar mass loss and direct injection of Type Ia supernova (SNIa) ejecta. We thus confirm the inference, based on optical data, that the stars in elliptical galaxies have supersolar [alpha/Fe] ratios, but find that that the present-day SNIa rate is approximately 4.6 times lower than the standard value. We find SNIa yield sets that reproduce Ca and Ar, or Ni, but not all three simultaneously. The low abundance of O relative to Ne and Mg implies that standard core collapse nucleosynthesis models overproduce O by approximately 2.

Loewenstein, Michael↗
NASA NTRS1990

Cold plasma heating in the plasma sheet boundary layer - Theory and simulations

Satellite observations in recent years have confirmed that the plasma sheet boundary layer is a permanent feature of the earth's magnetotail located between the lobe and central plasma sheet during both quiet and active magnetic periods. Distinct features of the boundary layer include field aligned ion beams and intense electrostatic emissions known as broadband electrostatic noise. Since the plasma sheet boundary layer is a spatial feature of the magnetotail, within it will occur thermal mixing of the resident warm boundary layer plasma with inflowing (convecting) cold ionospheric plasma. A theoretical study involving linear theory and nonlinear numerical particle simulations is presented which examines ion beam instabilities in the presence of a thermally mixed hot and cold background plasma. It is found that the free energy in the ion beams can heat the cool ionospheric plasma to ambient plasma sheet boundary layer temperatures via broadband electrostatic noise. These results, along with recent observational reports that ionospheric outflow can account for measured plasma sheet densities, suggest that the ionospheric role in plasma sheet dynamics and content may be as large as the solar wind.

Schriver, David↗
NASA NTRS1987

Ratio of oxygen to sulfur in the Io plasma torus

The relative concentrations of O and S ions in the hot dense region of the Io plasma torus (IPT) are investigated by means of model calculations based on collisional diffusive equilibrium. The spectroscopic constraints and uncertainties encountered in calculating the ion partitioning and the modeling procedures employed are discussed, and the results are presented in tables and graphs and compared with Voyager EUV data and the rocket observations of Skinner and Durrance (1986). It is found that the observed O and S emission from the IPT can be reproduced by models with approximately equal partitioning between O and S species. The assumptions and analyses leading to the conclusion (Moreno et al., 1985) that the IPT is S-dominated (by 3 to 1 or more) are analyzed in detail and rejected.

Shemansky, Donald E.↗
NASA NTRS1975

The spatial and temperature structure of vacuum spark plasmas

The spatial and temperature structures of the X-ray emitting components of low-inductance vacuum-spark plasmas are investigated. The plasmas produced by low-inductance vacuum sparks show striking resemblances to solar-flare plasmas. High-resolution photographs show that the spark plasmas are composed of hot (about 30 million K) compact sources (less than 20 microns) and cooler (about 10 million K) larger sources (of the order of 100 microns). Both types of sources may be produced by the same plasma at different times. The differences between the solar flare iron-line spectrum near 1.9 A and the spark iron-line spectrum are discussed and interpreted.

Feldman, U.↗
NASA NTRS2003

The X-ray Spectrum of the North Polar Spur

An analysis is presented of the soft X-ray background spectrum measured by the EPIC MOS cameras on XMM-Newton in three observations targeted on the North Polar Spur (NPS). Three distinct Galactic plasma components are identified, a cool Local Hot Bubble (LHB) component, T(sub lo) approx. 0.1 keV, a cool Galactic Halo component at a similar temperature and a hotter component, T(sub hi) approx. 0.26 keV, associated with the NPS itself. Using the new data in combination with the Rosat All-Sky Survey count rates measured in the 0.1-0.4 keV band, we estimate the emission measure of the LHB material to be 0.0040-0.0052 cm(exp -6) pc, which implies an electron density of 0.008-0.011 cm(exp -3) and pressure of approx. 22000 cm(exp -3) K. The halo and NPS components lie behind at least 50% of the line-of-sight cold gas for which the total Galactic column density is in the range (2 - 8) x 10(exp 20) cm(exp -2). Modelling the X-ray emitting superbubble as a sphere at distance 210 pc, radius 140 pc and center l(sub II) = 352 deg, b(sub II) = 15 deg, the implied electron density in the NPS is approx. 0.03 cm(exp -3) with pressure approx. 150000 cm(exp -3) K. The observed spectral line complexes from OVII, OVIII, FeXVII, NeIX, NeX and MgXI provide constraints on the composition of the plasma. The hot component in the NPS is depleted in oxygen, neon and, to some extent, magnesium and iron. Assuming the effective line of sight across the halo emission is 1 kpc, the electron density in the halo is 0.007-0.011 cm(exp -3) and the pressure is approx. 16500 cm(exp -3) K, conditions very similar to those in the LHB.

Willingale, Richard↗
NASA NTRS1994

Coronal Magnetic Structures Observing Campaign. 3: Coronal plasma and magnetic field diagnostics derived from multiwaveband active region observations

Simultaneous soft X-ray, microwave, and photospheric magnetic field observations were taken during the Coronal Magnetic Structures Observing Campaign (CoMStOC '87). The plasma electron temperature and emission measures determined from the X-ray data are used to predict the free-free emission expected at 20 and 6 cm. Comparing these predictions with the microwave observations, it is found that the predicted 20 cm brightness temperatures are higher than the observed, requiring cool absorbing material between the hot X-ray plasma and the observer. The model that is most consistent with all the observations and minimizes the required coronal fields indicates that this 20 cm emission is either free-free or a combination of free-free and fourth harmonic cyclotron emanating from the X-ray plasma with an electron temperature of approximately 3.1 x 10(exp 6) K and an emission measure of approximately 1.3 x 10(exp 29)/cm(exp 5). The observed 20 cm polarization requires a field strength of greater than or equal to 150 G. In addition, the 6 cm emission is free-free, emanating from cooler plasma with an electron temperature of approximately 1.5 x 10(exp 6) K and an emission measure of approximately 3-6 x 10(exp 29)/cm(exp 5). This model is consistent with the rather unusual combination of high 20 cm and low 6 cm polarization as well as the low extrapolated coronal fields.

Schmelz, J. T.↗
NASA NTRS1985

Electromagnetic electron beam instabilities - Hot, isotropic beams

This paper considers the linear theory of electromagnetic instabilities driven by an electron beam in a homogeneous, nonrelativistic, Vlasov plasma. The beam is relatively hot, isotropic in its own frame, and streams parallel or antiparallel to a magnetic field B. Numerical solutions of the full dispersion equation for propagation parallel or antiparallel to B are presented, and the linear properties of the whistler heat flux and electron beam firehose instabilities are exhibited and compared. Under a broad range of parmameters the former mode has the lower beam speed threshold, and the larger maximum growth rate. In addition, it is demonstrated that, for a sufficiently large relative beam density, relative beam temperature, and plasma beta the whistler heat flux instability has a much lower beam speed threshold than the electrostatic electron beam instability. The application of these instabilities to first-order Fermi acceleration of electrons at space plasma shocks is discussed.

Gary, S. P.↗
NASA NTRS2004

Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core

We detected three extremely embedded X-ray sources in the R Corona Australis (R CrA) star forming core, IRS 7 region. Two weak X-ray sources are associated with the VLA centimeter radio sources 10E & W, whereas the third brightest source detected in the two XMM-Newton observations on March 2003 has no counterpart at any wavelengths. The large K-band upper-limit (19.4m) measured with the University of Hawaii 88-inch Telescope and strong absorption derived in X-rays (N(sub H) approx. 2.8 x 10(exp 23)/sq cm equivalent to A(sub v) approx. 180 m) indicate that the source is younger than typical Class I protostars, i.e. a Class 0 protostar or an intermittent phase between Class 0 and Class I protostars. The X-ray luminosity was less than one thirtieth (log L(sub x) less than or approx. equals 29.3 ergs/s) in the former Chandra observation in October 2000, which suggests that the X-ray activity, probably generated by magnetic activity, is triggered by an intermittent mass accretion episode such as FU Ori type outbursts. Because the source was detected at high significance in the XMM-Newton observations (approx. 2,000 cnts), X-ray properties of such young protostars can be well investigated for the first time. The light curves were constant in the 1st observation and increased linearly by a factor of two during 30 ksec in the 2nd observation. Both spectra showed iron K lines originated in hot thin-thermal plasma and fluorescence by cold gas. They can be reproduced by an absorbed thin-thermal plasma model with a Gaussian component at 6.4 keV (kT approx. 3-4 keV, L(sub x) approx. 7-20 x 10(exp 30) ergs/s). The rising timescale of the light curves in the 2nd observation was too slow for magnetically generated X-ray flares, whereas large equivalent width of the fluorescence iron K line in the 1st observation (approx. 810 eV) requires strong partial covering of the X-ray source. These results suggest that a confined hot (perhaps accretion) spot on the protostellar core was behind the star in the 1st observation and just appeared in the 2nd observation due to the core rotation with period of greater than or approx. 22.8 days, which is much slower than the break-up velocity previously assumed for young protostars. This means that the source had quiescent X-ray activity during the observations with an order of magnitude stronger level than Class I (older) protostars. We also consider whether the X-ray source associated with 10E could be shock heated plasma by a collision of a jet emanating from the tentative Class 0 object.

Hamaguchi, Ken-Ji↗
NASA NTRS1992

Coronal Magnetic Structures Observing Campaign. II - Magnetic and plasma properties of a solar active region

Simultaneous soft X-ray, microwave, and photospheric magnetic field observations were taken during the Coronal Magnetic Structures Observing Campaign. The plasma electron temperatures and emission measures determined from the X-ray data are used to predict the intensity and structure of the thermal bremsstrahlung emission at 20 and 6 cm. Comparing these predictions with the microwave observations, it is found that the 20 cm structure is very similar to that expected from the X-rays, but a substantial amount of the 6 cm emission was resolved out. The predicted 20 cm brightness temperatures are higher than the observed, requiring cool absorbing material (not greater than 500,000 K) between the hot X-ray plasma and the observer. The absorption mechanism in the cool plasma at 20 cm is most likely thermal bremsstrahlung, requiring coronal magnetic fields as high as 150 G. 'Coronal Magnetograms', made by extrapolating the photospheric longitudinal field using the Sakurai code, show that appropriate values of the total field are reached at heights of 6000-10,000 km above the photosphere (at many but not all locations).

Schmelz, J. T.↗