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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

An overview on incomplete fusion reaction dynamics at energy range ∼ 3-8 MeV/A

The information of ICF reaction has been obtained from the measurement of excitation function (EF) of ERs populated in the interaction of {sup 20}Ne and {sup 16}O on {sup 55}Mn, {sup 159}Tb and {sup 156}Gd targets. Sizable enhancement in the measured cross-sections has been observed in α-emitting channels over theoretical predictions, which has been attributed to ICF of the projectile. In order to confirm the findings of the measurements and analysis of EFs, the forward recoil range distributions of ERs populated in {sup 20}Ne+{sup 159}Tb (E ∼165MeV) and {sup 16}O+{sup 156}Gd (E ∼ 72, 82 and 93MeV) systems, have been measured. It has been observed that peaks appearing at different cumulative thicknesses in the stopping medium are related with different degree of linear momentum transfer from projectile to target nucleus by adopting the break-up fusion model consideration. In order to deduce the angular momentum involved in various CF and / or ICF reaction products, spin distribution and side-feeding intensity profiles of radio-nuclides populated via CF and ICF channels in {sup 16}O+{sup 160}Gd system at energy, E ∼ 5.6 MeV/A, have been studied. Spin distribution of ICF products are found to be distinctly different than that observed from CF products.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Theoretical model for plasma expansion generated by hypervelocity impact

The hypervelocity impact experiments of spherical LY12 aluminum projectile diameter of 6.4 mm on LY12 aluminum target thickness of 23 mm have been conducted using a two-stage light gas gun. The impact velocity of the projectile is 5.2, 5.7, and 6.3 km/s, respectively. The experimental results show that the plasma phase transition appears under the current experiment conditions, and the plasma expansion consists of accumulation, equilibrium, and attenuation. The plasma characteristic parameters decrease as the plasma expands outward and are proportional with the third power of the impact velocity, i.e., (T{sub e}, n{sub e}) ∝ v{sub p}{sup 3}. Based on the experimental results, a theoretical model on the plasma expansion is developed and the theoretical results are consistent with the experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Mutual colliding impact fast ignition

It is proposed to apply the well established colliding beam technology of high energy physics to the fast hot spot ignition of a highly compressed DT (deuterium-tritium) target igniting a larger D (deuterium) burn, by accelerating a small amount of solid deuterium, and likewise a small amount of tritium, making a head-on collision in the center of the target, projecting them through conical ducts situated at the opposite side of the target and converging in its center. In their head-on collision, the relative collision velocity is 5/3 times larger compared to the collision velocity of a stationary target. The two pieces have for this reason to be accelerated to a smaller velocity than would otherwise be needed to reach upon impact the same temperature. Since the velocity distribution of the two head-on colliding projectiles is with its two velocity peaks non-Maxwellian, the maximum cross section velocity product turns out to be substantially larger than the maximum if averaged over a Maxwellian. The D and T projectiles would have to be accelerated with two sabots driven by powerful particle or laser beams, permitting a rather large acceleration length. With the substantially larger cross section-velocity product by virtue of the non-Maxwellian velocity distribution, a further advantage is that the head-on collision produces a large magnetic field by the thermomagnetic Nernst effect, enhancing propagating burn. With this concept, the ignition of the neutron-less hydrogen-boron (HB{sup 11}) reaction might even be possible in a heterogeneous assembly of the hydrogen and the boron to reduce the bremsstrahlung-losses, resembling the heterogeneous assembly in a graphite-natural uranium reactor, there to reduce the neutron losses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Quantum diffraction and shielding effects on the low-energy electron-ion bremsstrahlung in two-component semiclassical plasmas

The quantum diffraction and shielding effects on the low-energy bremsstrahlung process are investigated in two-component semiclassical plasmas. The impact-parameter analysis with the micropotential taking into account the quantum diffraction and shielding effects is employed to obtain the electron-ion bremsstrahlung radiation cross section as a function of the de Broglie wavelength, density parameter, impact parameter, photon energy, and projectile energy. The result shows that the influence of quantum diffraction and shielding strongly suppresses the bremsstrahlung radiation spectrum in semiclassical plasmas. It is found that the quantum diffraction and shielding effects have broaden the photon emission domain. It is also found that the photon emission domain is almost independent of the radiation photon energy. In addition, it is found that the influence of quantum diffraction and shielding on the bremsstrahlung spectrum decreases with an increase of the projectile energy. The density effect on the electron-ion bremsstrahlung cross section is also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Asymmetry effects in fragment production

The production of different fragments has been studied by taking into account the mass asymmetry of the reaction and employing the momentum dependent interactions. Two different set of asymmetric reactions have been analyzed while keeping At{sub otal} fixed using soft momentum dependent equation of state. Our results indicate that the impact of momentum dependent interactions is different in lighter projectile systems as compared to heavier ones. The comparative analysis of IQMD simulations with the experimental data in case of heavier projectile and lighter target system for the reaction of {sup 197}Au+{sup 27}Al (η = 0.7) at E = 600 MeV/nucleon shows that with the inclusion of MDI we are able, upto some extent, to reproduce the experimental universality of rise and fall of intermediate mass fragments (IMFs).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Comparison of the secondary electrons produced by proton and electron beams in water

The secondary electrons produced in water by electron and proton beams are compared with each other. The total ionization cross section (TICS) for an electron impact in water is obtained by using the binary-encounter-Bethe model. Hence, an empirical equation based on two adjustable fitting parameters is presented to determine the TICS for proton impact in media. In order to calculate the projectile trajectory, a set of stochastic differential equations based on the inelastic collision, elastic scattering, and bremsstrahlung emission are used. In accordance with the projectile trajectory, the depth dose deposition, electron energy loss distribution in a certain depth, and secondary electrons produced in water are calculated. The obtained results for the depth dose deposition and energy loss distribution in certain depth for electron and proton beams with various incident energies in media are in excellent agreement with the reported experimental data. The difference between the profiles for the depth dose deposition and production of secondary electrons for a proton beam can be ignored approximately. But, these profiles for an electron beam are completely different due to the effect of elastic scattering on electron trajectory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

A curvature-based mechanism for the spontaneous emission of electromagnetic radiation at curved plasma–vacuum interfaces

In this work, we derive from first principles the dispersion relation for electromagnetic radiation that is spontaneously emitted at a 2D curved plasma–vacuum interface in the absence of both background and external electric and magnetic fields. This plasma geometry is motivated by plasmas generated through hypervelocity impact projectiles—an area that is of importance to satellite safety in the aerospace community, and may be of importance for the developing study of projectile impact-driven inertial confinement fusion. We find spontaneous radiation occurs when thermal surface waves propagate along the edge of a circular plasma, with a frequency lower than the plasma frequency and spatial decay proportional to 1/r. This is distinct from more well-known mechanisms of radiation, in which the radiation frequency is greater than or equal to the plasma frequency. This theory is validated against 2D, electromagnetic particle-in-cell simulations and shows reasonable agreement. Finally, we discuss the effects of plasma geometry and attribute the radiation generation mechanism to the acceleration of charged surface waves as they traverse azimuthally along a curved path.

Lau, Raymond (ORCID:0000000299318101)↗
DOE OSTI2017

Gas Gun Model and Comparison to Experimental Performance of Pipe Guns Operating with Light Propellant Gases and Large Cryogenic Pellets

Injection of multiple large (~10 to 30 mm diameter) shattered pellets into ITER plasmas is presently part of the scheme planned to mitigate the deleterious effects of disruptions on the vessel components. To help in the design and optimize performance of the pellet injectors for this application, a model referred to as “the gas gun simulator” has been developed and benchmarked against experimental data. The computer code simulator is a Java program that models the gas-dynamics characteristics of a single-stage gas gun. Following a stepwise approach, the code utilizes a variety of input parameters to incrementally simulate and analyze the dynamics of the gun as the projectile is launched down the barrel. Using input data, the model can calculate gun performance based on physical characteristics, such as propellant-gas and fast-valve properties, barrel geometry, and pellet mass. Although the model is fundamentally generic, the present version is configured to accommodate cryogenic pellets composed of H2, D2, Ne, Ar, and mixtures of them and light propellant gases (H2, D2, and He). The pellets are solidified in situ in pipe guns that consist of stainless steel tubes and fast-acting valves that provide the propellant gas for pellet acceleration (to speeds ~200 to 700 m/s). The pellet speed is the key parameter in determining the response time of a shattered pellet system to a plasma disruption event. The calculated speeds from the code simulations of experiments were typically in excellent agreement with the measured values. With the gas gun simulator validated for many test shots and over a wide range of physical and operating parameters, it is a valuable tool for optimization of the injector design, including the fast valve design (orifice size and volume) for any operating pressure (~40 bar expected for the ITER application) and barrel length for any pellet size (mass, diameter, and length). Key design parameters and proposed values for the pellet injectors for the ITER disruption mitigation systems are discussed.

Combs, Stephen Kirk↗
DOE OSTI2012

SIZE AND DENSITY ESTIMATION FROM IMPACT TRACK MORPHOLOGY IN SILICA AEROGEL: APPLICATION TO DUST FROM COMET 81P/WILD 2

A large number of cometary dust particles were captured with low-density silica aerogel during the NASA Stardust mission. The dust particles penetrated into the aerogel and formed various track shapes. To estimate the properties of the dust particles, such as density and size, based on the morphology of the tracks, we carried out systematic experiments testing impacts into low-density aerogel at 6 km s{sup -1} using projectiles of various sizes and densities. We found that the maximum track diameter and the ratio of the track length to the maximum track diameter in aerogel are good indicators of projectile size and density, respectively. Based on these results, we estimated the size and density of individual dust particles from comet 81P/Wild 2. The average density of the 'fluffy' dust particles and the bulk density of all dust particles were obtained as 0.35 {+-} 0.07 and 0.49 {+-} 0.18 g cm{sup -3}, respectively. These statistical data provided the content of monolithic and coarse grains in the Stardust particles, {approx}30 wt%. Combining this result with some mid-infrared observational data, we found that the content of crystalline silicates is {approx}50 wt% or more of non-volatile material.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

COLLISIONS BETWEEN GRAVITY-DOMINATED BODIES. I. OUTCOME REGIMES AND SCALING LAWS

Collisions are the core agent of planet formation. In this work, we derive an analytic description of the dynamical outcome for any collision between gravity-dominated bodies. We conduct high-resolution simulations of collisions between planetesimals; the results are used to isolate the effects of different impact parameters on collision outcome. During growth from planetesimals to planets, collision outcomes span multiple regimes: cratering, merging, disruption, super-catastrophic disruption, and hit-and-run events. We derive equations (scaling laws) to demarcate the transition between collision regimes and to describe the size and velocity distributions of the post-collision bodies. The scaling laws are used to calculate maps of collision outcomes as a function of mass ratio, impact angle, and impact velocity, and we discuss the implications of the probability of each collision regime during planet formation. Collision outcomes are described in terms of the impact conditions and the catastrophic disruption criteria, Q*{sub RD}-the specific energy required to disperse half the total colliding mass. All planet formation and collisional evolution studies have assumed that catastrophic disruption follows pure energy scaling; however, we find that catastrophic disruption follows nearly pure momentum scaling. As a result, Q*{sub RD} is strongly dependent on the impact velocity and projectile-to-target mass ratio in addition to the total mass and impact angle. To account for the impact angle, we derive the interacting mass fraction of the projectile; the outcome of a collision is dependent on the kinetic energy of the interacting mass rather than the kinetic energy of the total mass. We also introduce a new material parameter, c*, that defines the catastrophic disruption criteria between equal-mass bodies in units of the specific gravitational binding energy. For a diverse range of planetesimal compositions and internal structures, c* has a value of 5 {+-} 2; whereas for strengthless planets, we find c* = 1.9 {+-} 0.3. We refer to the catastrophic disruption criteria for equal-mass bodies as the principal disruption curve, which is used as the reference value in the calculation of Q*{sub RD} for any collision scenario. The analytic collision model presented in this work will significantly improve the physics of collisions in numerical simulations of planet formation and collisional evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Electronic excitation and charge transfer processes in collisions of H{sup +}, H{sub 2}{sup +}, and H{sub 3}{sup +} ions with carbon monoxide at typical solar-wind velocities

Luminescence in the 200-580 nm spectral region was observed in the collisions of H{sup +}, H{sub 2}{sup +}, and H{sub 3}{sup +} with CO in the 50-1000 eV projectile energy range. Using computer simulations, we have identified emission of the following products in the observed spectra: the CO{sup +}(A-X) comet-tail system, CO{sup +}(B-X) first negative system, CO{sup +}(B-A) Baldet-Johnson system, and CO(b-a) third positive system. Also, an emission from atomic hydrogen (H{sub β} line at 486nm) has been observed. From the analysis of the experimental spectra, we have determined the absolute emission cross-sections for the formation of the observed products. Computer simulations gave the excited-product population distributions over vibrational and rotational energy levels. The vibrational level distribution from the CO{sup +}(A-X) comet-tail system is compared with the data for CO excited by 100 eV electrons and extreme ultraviolet radiation (XUV) photons. We have used these data to analyze the excitation conditions in the comet Humason (1961e). From the vibrational population distributions observed in the comet, we found that this distribution can be reproduced if electrons produce 25%, protons 70%, and XUV photons produce 5% of the emitting molecules. We find that the ratio of the CO{sup +}(B-X) emission to the sum of two main emissions (CO{sup +}(A-X)+CO{sup +}(B-X)) is velocity dependent and does not depend on the projectile ion type. For small velocities (below 100 km s{sup –1}) the ratio is about 5%, while for higher velocities it increases to 30%. For these data, we have found an empirical formula that satisfactorily describes the experimental data: R = R {sub max}(1 – v {sub th}/v), (where R {sub max} = 33%, v {sub th} = 87 km s{sup –1}). This could be used to infer the velocity of ions producing the observed emission of CO{sup +} products.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Orientation and alignment effects in electron-induced ionization of a single oriented water molecule

We here report a theoretical study about the orientation effect on the total ionization cross sections for a single oriented water molecule. The theoretical description of the ionization process is performed within the first Born framework with a collisional system including an initial state composed of a projectile and a water target molecule described by a plane wave and an accurate one-center molecular wave function, respectively, and a final state constituted by a slow ejected electron represented by a Coulomb wave and a scattered (fast) electron projectile described by a plane wave. Secondary electron energetic distributions as well as total cross sections are then compared for particular target configurations pointing out strong alignment and orientation effects on the description of the ionization process.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Single and double ionization in C{sup 6+}+He collisions

Single- and double-ionization processes in C{sup 6+} collisions with the He atom at an incident energy of 100 MeV/amu are studied by direct solution of the time-dependent Schroedinger equation. A time-dependent close-coupling method based on an expansion of a one-electron three-dimensional wave function in the field of He{sup +} is used to calculate single-ionization cross sections. A time-dependent close-coupling method based on an expansion of a two-electron six-dimensional wave function in the field of He{sup 2+} is used to calculate single- and double-ionization cross sections. Electron energy and angle differential cross sections for single ionization are presented for various projectile impact parameters. For relatively large impact parameters, the differential cross sections are in qualitative agreement with ion-atom experiments. Electron energy and angle differential cross sections for double ionization are also presented for a relatively large projectile impact parameter.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Scattering-angle dependence of doubly differential cross sections for fragmentation of H{sub 2} by proton impact

We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV p + H{sub 2} collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Analysis of photon emission from 50--350-keV proton impact on H{sub 2}O

We have measured photon emission cross sections from neutral fragments produced by collisions of 50-350 keV protons with H{sub 2}O molecules. Balmer {alpha}-{delta} emissions from both the target and projectile were recorded. We also analyzed A {sup 2}{Sigma}{sup +}-X {sup 2}{Pi} (0,0) and (1,0) emission from the excited OH fragment produced during target dissociation. Trends in the cross sections revealed two key properties of the collision process: (1) The Bethe theory accurately describes target emission from both H and OH fragments and (2) the ratio of any two Balmer emission cross sections for both the target and projectile can be approximated by simple functions of the respective optical oscillator strengths. Finally, we provide the Bethe fit parameters necessary to calculate the target emission cross sections at all nonrelativistic impact energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Double ionization of helium by bare ions: Theoretical study of the fully differential cross sections

This work presents a theoretical study of fully differential cross sections (FDCSs) for the double ionization of an He target by ion impact within a distorted wave model. The initial atomic system is described by two approximated wave functions of different accuracy proposed by Bonham and Kohl. For the final channel several models are considered based upon improvements and simplifications of the well-known three-body Coulomb (3C) model. The influence of the receding projectile on the resulting fragments is also studied by implementing a model with effective charges that depend on the momenta of the four particles. The FDCSs resulting for different electron energy sharing are discussed. The sensitivity of the FDCSs to the projectile charge sign and magnitude is explored over the energy range 700 keV/amu through 6 MeV/amu.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Experimental and theoretical study of the energy loss of C and O in Zn

We present a combined experimental-theoretical study of the energy loss of C and O ions in Zn in the energy range 50-1000 keV/amu. This contribution has a double purpose, experimental and theoretical. On the experimental side, we present stopping power measurements that fill a gap in the literature for these projectile-target combinations and cover an extended energy range, including the stopping maximum. On the theoretical side, we make a quantitative test on the applicability of various theoretical approaches to calculate the energy loss of heavy swift ions in solids. The description is performed using different models for valence and inner-shell electrons: a nonperturbative scattering calculation based on the transport cross section formalism to describe the Zn valence electron contribution, and two different models for the inner-shell contribution: the shellwise local plasma approximation (SLPA) and the convolution approximation for swift particles (CasP). The experimental results indicate that C is the limit for the applicability of the SLPA approach, which previously was successfully applied to projectiles from H to B. We find that this model clearly overestimates the stopping data for O ions. The origin of these discrepancies is related to the perturbative approximation involved in the SLPA. This shortcoming has been solved by using the nonperturbative CasP results to describe the inner-shell contribution, which yields a very good agreement with the experiments for both C and O ions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Proton-beam stopping in hydrogen

The stopping cross section for protons passing through hydrogen is calculated for the energy range between 10 keV and 3 MeV. Both the positive and neutral charge states of the projectile are accounted for. The two-center convergent close-coupling method is used to model proton collisions with hydrogen. In this approach, electron-capture channels are explicitly included by expanding the scattering wave function in a basis of both target and projectile pseudostates. Hydrogen collisions with hydrogen are modeled using two methods: the single-center convergent close-coupling approach is used for the calculation of one-electron processes, while two-electron processes are calculated using the Born approximation. The aforementioned approaches are also applied to the calculation of the charge-state fractions. Furthermore, these are then used to combine the proton-hydrogen and hydrogen-hydrogen stopping cross sections to yield the total stopping cross section for protons passing through hydrogen.

74 ATOMIC AND MOLECULAR PHYSICS↗