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Results for “EIKONAL APPROXIMATION”

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 19 records
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DOE OSTI2013

Inverse bremsstrahlung heating rate in xenon clusters in the eikonal approximation

We report inverse bremsstrahlung (IB) heating rates in the eikonal approximation (EA). The present analysis is performed using the plasma-screened Rogers and Debye potentials for Xe clusters with two different charge states (6 and 10). We compare the eikonal results with the first Born approximation (FBA) and classical-simulation (CL-sim) (Moll et al., Phys. Plasmas 19, 033303 (2012)) calculations for clusters in infrared light. Calculations have been performed for the field strength of 2.6 Multiplication-Sign 10{sup 8} V/cm. We find that compared to the FBA and CL-sim methods, the IB heating rate in the EA is less sensitive to the choice of the two potentials considered here. The present EA calculation shows that the influence of the inner structure of atomic ion on the heating rate is more prominent for the smaller ion charge (Xe{sup 6+}). In the case of low laser field approximation based on the elastic transport cross sections, it is seen that in contrast to the FBA and classical methods, the heating rate predicted by the EA does not deviate much all over the range of mean kinetic energy of electrons (20-500 eV) considered here for both the charge states of xenon (Xe{sup 6+} and Xe{sup 10+}). Furthermore, for the Rogers potential, EA is found to be in closer agreement with the classical method than the FBA. We also compare the results of the IB heating rate using the present and low-field approximation approaches to the above three methods and observe that the magnitudes of the IB heating rate calculated in the low field approximation are, in general, higher than the corresponding values predicted by the present approach for both the electron-ion potentials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effects of first-order correction to eikonal approximation in the analysis of {sup 9}Be({sup 15}C,{sup 14}C + n){sup 9}Be stripping reaction

We have studied the effects of the first-order correction to the eikonal approximation for {sup 9}Be({sup 15}C,{sup 14}C + n){sup 9}Be stripping reactions at 54A MeV incident energy and have found that the correction term slightly changes the tail of the longitudinal momentum distribution of the core fragment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Small $x$ physics beyond eikonal approximation: an effective Hamiltonian approach

Understanding the spin structure of hadrons in the small x regime is an important direction to unravel the spin puzzle in hadronic physics. To include spin degrees of freedom in the small x regime requires going beyond the usual eikonal approximation in high energy QCD. We developed an effective Hamiltonian approach to study spin related observables in the small x regime using the shockwave formalism. The small-x effective Hamiltonian incorporates both quark and gluon propagators in the background fields and the background field induced interaction vertices up to next-to-eikonal order. A novel feature of sub-eikonal interactions is the background gluon field induced gluon radiation inside the shockwave. Its relation to chromo-electrically polarized Wilson line correlator is established both in small x helicity evolution and in longitudinal double-spin asymmetry for gluon production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Non-perturbative QCD amplitudes in quenched and eikonal approximations

Even though approximated, strong coupling non-perturbative QCD amplitudes remain very difficult to obtain. In this article, in eikonal and quenched approximations at least, physical insights are presented that rely on the newly-discovered property of effective locality. The present article also provides a more rigorous mathematical basis for the crude approximations used in the previous derivation of the binding potential of quarks and nucleons. Furthermore, the techniques of Random Matrix calculus along with Meijer G-functions are applied to analyze the generic structure of fermionic amplitudes in QCD. - Highlights: • We discuss the physical insight of effective locality to QCD fermionic amplitudes. • We show that an unavoidable delta function goes along with the effective locality property. • The generic structure of QCD fermion amplitudes is obtained through Random Matrix calculus.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Inverse bremsstrahlung heating rate for dense plasmas in laser fields

We report a theoretical analysis of inverse bremsstrahlung heating rate in the eikonal approximation. The present analysis is performed for a dense plasma using the screened electron-ion interaction potential for the ion charge state Z{sub i} = 1 and for both the weak and strong plasma screening cases. We have also compared the eikonal results with the first Born approximation (FBA) [M. Moll et al., New J. Phys. 14, 065010 (2012)] calculation. We find that the magnitudes of inverse bremsstrahlung heating rate within the eikonal approximation (EA) are larger than the FBA values in the weak screening case (κ = 0.03 a.u.) in a wide range of field strength for three different initial electron momenta (2, 3, and 4 a.u.). But for strong screening case (κ = 0.3 a.u.), the heating rates predicted by the two approximations do not differ much after reaching their maximum values. Furthermore, the individual contribution of photoemission and photoabsorption processes to heating rate is analysed for both the weak and strong screening cases. We find that the single photoemission and photoabsorption rates are the same throughout the field strength while the multiphoton absorption process dominates over the multiphoton emission process beyond the field strength ≈ 4×10{sup 8} V/cm. The present study of the dependence of heating rate on the screening parameter ranging from 0.01 to 20 shows that whereas the heating rate predicted by the EA is greater than the FBA up to the screening parameter κ = 0.3 a.u., the two approximation methods yield results which are nearly identical beyond the above value.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

A new approach to analytic, non-perturbative and gauge-invariant QCD

Following a previous calculation of quark scattering in eikonal approximation, this paper presents a new, analytic and rigorous approach to the calculation of QCD phenomena. In this formulation a basic distinction between the conventional 'idealistic' description of QCD and a more 'realistic' description is brought into focus by a non-perturbative, gauge-invariant evaluation of the Schwinger solution for the QCD generating functional in terms of the exact Fradkin representations of Green's functional G{sub c}(x,y|A) and the vacuum functional L[A]. Because quarks exist asymptotically only in bound states, their transverse coordinates can never be measured with arbitrary precision; the non-perturbative neglect of this statement leads to obstructions that are easily corrected by invoking in the basic Lagrangian a probability amplitude which describes such transverse imprecision. The second result of this non-perturbative analysis is the appearance of a new and simplifying output called 'Effective Locality', in which the interactions between quarks by the exchange of a 'gluon bundle'-which 'bundle' contains an infinite number of gluons, including cubic and quartic gluon interactions-display an exact locality property that reduces the several functional integrals of the formulation down to a set of ordinary integrals. It should be emphasized that 'non-perturbative' here refers to the effective summation of all gluons between a pair of quark lines-which may be the same quark line, as in a self-energy graph-but does not (yet) include a summation over all closed-quark loops which are tied by gluon-bundle exchange to the rest of the 'Bundle Diagram'. As an example of the power of these methods we offer as a first analytic calculation the quark-antiquark binding potential of a pion, and the corresponding three-quark binding potential of a nucleon, obtained in a simple way from relevant eikonal scattering approximations. A second calculation, analytic, non-perturbative and gauge-invariant, of a nucleon-nucleon binding potential to form a model deuteron, will appear separately. - Highlights: Black-Right-Pointing-Pointer An analytic, non-perturbative and gauge-invariant formulation for QCD processes. Black-Right-Pointing-Pointer A new property called Effective Locality appears in the QCD fermionic amplitudes. Black-Right-Pointing-Pointer An effective quark-antiquark and 3-quark binding potential is obtained. Black-Right-Pointing-Pointer A single 'gluon bundle' replaces the sum of an infinite number of Feynman graphs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Energy-Dependent microscopic optical potential for p+{sup 9}Be elastic scattering

The p+{sup 9}Be elastic scattering at an energy range up to 200 MeV/nucleon is analyzed using the single-folding model. The density- and isospin-dependent M3Y-Paris nucleon-nucleon (NN) interaction is used for the real part and the NN-scattering amplitude of the high-energy approximation for the imaginary one. The analysis reveals that the cross-section data are reproduced well at energies up to 100 MeV/nucleon by use of the partial-wave expansion. For higher energies, the eikonal approximation give results better than the partial-wave expansion calculations. The volume integrals of the optical-potential parts have systematic energy dependencies, and they are parameterized in empirical formulas.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

On the Contribution of the Long-Range Scattering Potential in the Process of Multiphoton Above-Threshold Ionization of Atoms in the Laser Field

Using the quantum mechanical analysis of stimulated bremsstrahlung of an electron on an electrostatic potential in the field of a strong electromagnetic wave in the generalized eikonal approximation, the simplified formula for the probability of multiphoton above-threshold ionization of a hydrogen-like atom in the laser field is obtained, taking into account the interaction of the photoelectron with the long-range Coulomb field of the residual ion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Analysis of orbital occupancy of valence neutron in {sup 15}C through Coulomb breakup reactions

The Coulomb breakup reactions {sup 208}Pb({sup 15}C, {sup 14}C + n){sup 208}Pb and {sup 181}Ta({sup 15}C, {sup 14}C + n){sup 181}Ta have been studied at 68 and 85 A MeV beam energies, respectively, within the framework of the eikonal approximation to investigate the orbital occupancy of valence neutron in the {sup 15}C nucleus. The outcomes of the present work favor 0{sup +} ⊗ 2s{sub 1/2} as the core-neutron coupling for the ground-state structure with 0.91 as a spectroscopic factor.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Stopping of Fast Structural Ions in a Substance by Means of Excitation of Their Own Electrons

The paper considers the theory of stopping of fast structural ions in a substance. Within the eikonal approximation, it develops a non-perturbative method for calculation of effective stopping of fast structural ions by means of excitation of their own electrons during collision with atoms. It shows that taking into account the interaction of atoms with the ion nucleus can make a considerable contribution into the value of the abovementioned effective stopping. It also examines the dependence of this contribution on the charge of the ion nucleus.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

On the importance of nonlinear couplings in large-scale neutrino streams

We propose a procedure to evaluate the impact of nonlinear couplings on the evolution of massive neutrino streams in the context of large-scale structure growth. Such streams can be described by general nonlinear conservation equations, derived from a multiple-flow perspective, which generalize the conservation equations of non-relativistic pressureless fluids. The relevance of the nonlinear couplings is quantified with the help of the eikonal approximation applied to the subhorizon limit of this system. It highlights the role played by the relative displacements of different cosmic streams and it specifies, for each flow, the spatial scales at which the growth of structure is affected by nonlinear couplings. We found that, at redshift zero, such couplings can be significant for wavenumbers as small as k=0.2 h/Mpc for most of the neutrino streams.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Optical properties of titanium dioxide nanotube arrays

We present experimental measurements and a theoretical analysis of the near UV to NIR optical properties of free standing titania nanotube arrays. An improved understanding of the optical physics of this type of nanostructure is important to several next generation solar energy conversion technologies. We measured the transmission, reflection, and absorption of the electromagnetic spectrum from 300 nm to 1000 nm (UV to NIR) of titania nanotube arrays. We measured the total, specular, and diffuse reflection and transmission using both single point detection and an integrating sphere spectrometer. We find that the transmission, but not the reflection, of light (UV to NIR) through the nanotube array is well-explained by classic geometric optics using an effective medium model taking into account the conical geometry of the nanotubes. For wavelengths shorter than ∼500 nm, we find the surprising result that the reflection coefficient for light incident on the open side of the nanotube array is greater than the reflection coefficient for light incident on the closed “floor” of the nanotube array. We consider theoretical models based on the eikonal approximation, photonic crystal band theory, and a statistical treatment of scattering to explain the observed data. We attribute the fact that light with wavelengths shorter than 500 nm is more highly reflected from the open than the closed tube side as being due to disorder scattering inside the nanotube array.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Proton radiography, nuclear cross sections and multiple Coulomb scattering

The principles behind proton radiography including multiple Coulomb scattering are discussed for a purely imaginary square well nucleus in the eikonal approximation. It is found that a very crude model can reproduce the angular dependence of the cross sections measured at 24 GeV/c. The largest differences are ~3% for the 4.56 mrad data, and ~4% for the 6.68 mrad data. The prospect of understanding how to model deterministically high-energy proton radiography over a very large range of energies is promising, but it should be tested more thoroughly.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Cusped light-like Wilson loops in gauge theories

We propose and discuss a new approach to the analysis of the correlation functions which contain light-like Wilson lines or loops, the latter being cusped in addition. The objects of interest are therefore the light-like Wilson null-polygons, the soft factors of the parton distribution and fragmentation functions, high-energy scattering amplitudes in the eikonal approximation, gravitational Wilson lines, etc. Our method is based on a generalization of the universal quantum dynamical principle by J. Schwinger and allows one to take care of extra singularities emerging due to lightlike or semi-light-like cusps. We show that such Wilson loops obey a differential equation which connects the area variations and renormalization group behavior of those objects and discuss the possible relation between geometrical structure of the loop space and area evolution of the light-like cusped Wilson loops.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗