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Morel, J.E.

Sandia National Labs., Albuquerque, NM (USA)

Sandia National Labs., Albuquerque, NM (USA)

AbstractAbstract

[en] A collocation method is developed for the solution of the one-dimensional neutron transport equation in slab geometry with both symmetric and polarly asymmetric scattering. For the symmetric scattering case, it is found that the collocation method offers a combination of some of the best characteristics of the finite-element and discrete-ordinates methods. For the asymmetric scattering case, it is found that the computational cost of cross-section data processing under the collocation approach can be significantly less than that associated with the discrete-ordinates approach. A general diffusion equation treating both symmetric and asymmetric scattering is developed and used in a synthetic acceleration algorithm to accelerate the iterative convergence of collocation solutions. It is shown that a certain type of asymmetric scattering can radically alter the asymptotic behavior of the transport solution and is mathematically equivalent within the diffusion approximation to particle transport under the influence of an electric field. The method is easily extended to other geometries and higher dimensions. Applications exist in the areas of neutron transport with highly anisotropic scattering (such as that associated with hydrogenous media), charged-particle transport, and particle transport in controlled-fusion plasmas. 23 figures, 6 tables

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Jan 1981; 185 p; Available from NTIS., PC A09/MF A01

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Report

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Numerical Data

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ALGORITHMS, ASYMPTOTIC SOLUTIONS, COMPARATIVE EVALUATIONS, DISCRETE ORDINATE METHOD, ITERATIVE METHODS, MONTE CARLO METHOD, NEUTRON DIFFUSION EQUATION, NEUTRON FLUX, NEUTRON TRANSPORT, NEUTRON TRANSPORT THEORY, NUMERICAL SOLUTION, ONE-DIMENSIONAL CALCULATIONS, ONE-GROUP THEORY, SLABS, THEORETICAL DATA

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Morel, J.E.

Sandia National Labs., Albuquerque, NM (USA)

Sandia National Labs., Albuquerque, NM (USA)

AbstractAbstract

[en] Tables of Lobatto quadrature sets for S/sub N/ calculations in one-dimensional cylindrical geometry are presented. The order of the sets varies from S

_{2}to S_{10}. Each S/sub N/ set is sufficiently accurate to be used in conjunction with Legendre cross-section expansions of degree N-1. These sets are particularly useful for calculations with normally incident sources and line sources and for adjoint calculations with plane-incident forward sources. 3 figures, 1 tablePrimary Subject

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Jan 1981; 20 p; Available from NTIS., PC A02/MF A01

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Morel, J.E.

Los Alamos National Lab., NM (USA)

Los Alamos National Lab., NM (USA)

AbstractAbstract

[en] The Boltzmann-Fokker-Planck (BFP) equation can be used to describe both neutral and charged-particle transport. Over the past several years, the author and several collaborators have developed methods for representing Fokker-Planck operators with standard multigroup-Legendre cross-section data. When these data are input to a standard S/sub n/ code such as ONETRAN, the code actually solves the Boltzmann-Fokker-Planck equation rather than the Boltzmann equation. This is achieved wihout any modification to the S/sub n/ codes. Because BFP calculations can be more demanding from a numerical viewpoint than standard neutronics calculations, we have found it useful to implement new quadrature methods ad convergence acceleration methods in the standard discrete-ordinates code, ONETRAN. We discuss our BFP cross-section representation techniques, our improved quadrature and acceleration techniques, and present results from BFP coupled electron-photon transport calculations performed with ONETRAN. 19 refs., 7 figs

Primary Subject

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1987; 16 p; Computational methods in high temperature physics; Los Alamos, NM (USA); 2-6 Feb 1987; CONF-8702113--2; Available from NTIS, PC A03/MF A01; 1 as DE88005393; Portions of this document are illegible in microfiche products.

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Morel, J.E.

Sandia Labs., Albuquerque, NM (USA)

Sandia Labs., Albuquerque, NM (USA)

AbstractAbstract

[en] The primary purpose of this work was to develop a method for using standard neutron transport codes to perform electron transport calculations. The method is to develop approximate electron cross sections which are sufficiently well-behaved to be treated with standard S/sub n/ methods, but which nonetheless yield flux solutions which are very similar to the exact solutions. The main advantage of this approach is that, once the approximate cross sections are constructed, their multigroup Legendre expansion coefficients can be calculated and input to any standard S/sub n/ code. Discrete-ordinates calculations were performed to determine the accuracy of the flux solutions for problems corresponding to 1.0-MeV electrons incident upon slabs of aluminum and gold. All S/sub n/ calculations were compared with similar calculations performed with an electron Monte Carlo code, considered to be exact. In all cases, the discrete-ordinates solutions for integral flux quantities (i.e., scalar flux, energy deposition profiles, etc.) are generally in agreement with the Monte Carlo solutions to within approximately 5% or less. The central conclusion is that integral electron flux quantities can be efficiently and accurately calculated using standard S/sub n/ codes in conjunction with approximate cross sections. Furthermore, if group structures and approximate cross section construction are optimized, accurate differential flux energy spectra may also be obtainable without having to use an inordinately large number of energy groups. 1 figure

Original Title

1.0 MeV

Primary Subject

Source

1979; 6 p; American Nuclear Society meeting; San Francisco, CA, USA; 12 - 16 Nov 1979; CONF-791103--13; Available from NTIS., PC A02/MF A01

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Report

Literature Type

Conference; Numerical Data

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Halbleib, J.A. Sr.; Morel, J.E.

Sandia Labs., Albuquerque, N.Mex. (USA)

Sandia Labs., Albuquerque, N.Mex. (USA)

AbstractAbstract

[en] A new version of the TIGER Monte Carlo electron/photon transport code that more accurately models the transport for problems where atomic-shell effects are important is documented. The new model includes both electron impact ionization and photoionization of the K, L1, L2, L3, M (average) and N (average) shells, as well as a description of the subsequent atomic relaxation cascade. The relevant physical theories are essentially equivalent to those currently being employed in the SANDYL code. Because these modifications are only incidentally affected by the problem geometry, they can easily be extended to other codes in the TIGER series

Original Title

Cross sections, tables, relaxation, binding energy

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Source

May 1978; 64 p; Available from NTIS., PC A04/MF A01

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Report

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Morel, J.E.; Nelson, W.E.

Sandia National Labs., Albuquerque, NM (USA)

Sandia National Labs., Albuquerque, NM (USA)

AbstractAbstract

[en] The purpose of this study was to determine if a production capability for discrete-ordinates coupled electron-photon transport calculations should be developed and, if so, to recommend how it should be done. It is concluded that such a capability should be developed. The purpose of this report is to detail reasons for making these conclusions, and further to make specific recommendations regarding the manner in which this dvelopment should be carried out. The discrete ordinates method is a deterministic method originally developed to solve the neutron transport equation. For this purpose, it has proven to be an accurate and efficient technique. In particular, it has proven to be much more efficient than Monte Carlo methods in one spatial dimension. All current production methods for coupled electron-photon transport calculations are based upon the condensed history method developed by Berger. This method is generally quite expensive for problems of interest to the weapons radiation effects community, even when the problems are limited to one spatial dimension. Thus, routine engineering design calculations involving coupled electron-photon transport must often be performed with rather crude and inaccurate methods due to cost constraints. The existence of this global deficiency is the main motivation for developing a discrete-ordinates coupled electron-photon transport capability. It has the potential of being as accurate as Monte Carlo yet efficient enough to be used in routine engineering design calculations

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May 1984; 16 p; Available from NTIS, PC A02/MF A01 as DE84012957

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Morel, J.E.; Wienke, B.R.

Los Alamos Scientific Lab., N.Mex. (USA)

Los Alamos Scientific Lab., N.Mex. (USA)

AbstractAbstract

[en] PLASMX generates effective multigroup macroscopic cross sections for discrete-ordinates calculations of neutral hydrogen atom transport in tokamak systems. The effective microscopic cross sections can be generated at the midpoint energies of the multigroup bin structure. Variable dimensioning presently restricts the number of energy groups to 22, the number of spatial regions to 10, and the number of Legendre polynomial moments to 7 (P

_{6})Primary Subject

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Jan 1977; 33 p; Available from NTIS. $4.00.

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Warsa, J.S.; Wareing, T.A.; Morel, J.E.

Los Alamos National Laboratory (United States). Funding organisation: US Department of Energy (United States)

Los Alamos National Laboratory (United States). Funding organisation: US Department of Energy (United States)

AbstractAbstract

[en] We investigate the degradation in performance of diffusion synthetic acceleration (DSA) methods in problems with discontinuities in material properties. A loss in the effectiveness of DSA schemes has been Observed before with other discretizations in two dimensions under certain conditions. We present more evidence in support of the conjecture that DSA effectiveness can degrade in multidimensional problems with discontinuities in total cross section, regardless of the particular physical configuration or spatial discretization. Through Fourier analysis and numerical experiments, we identify a set of representative problems for which established DSA schemes are ineffective, focusing on highly diffusive problems for which DSA is most needed. We consider a lumped, linear discontinuous spatial discretization of the S N transport equation on three-dimensional, unstructured tetrahedral meshes and look ata fully consistent and a 'partially consistent' DSA method for this discretization. We find that the effectiveness of both methods can be significantly degraded in the presence of material discontinuities. A Fourier analysis in the limit of decreasing cell optical thickness is shown that supports the view that the degraded effectiveness of a fully consistent DSA scheme simply reflects the failure of the spatially continuous DSA method in problems where material discontinuities are present. Key Words: diffusion synthetic acceleration, discrete ordinates, deterministic transport methods, unstructured meshes

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1 Jan 2002; 17 p; ANS Topical Meeting in Mathematics and Computations; Gatlinburg, TN (United States); 6-11 Apr 2003; Available from http://lib-www.lanl.gov/cgi-bin/getfile?00995615.pdf; PURL: https://www.osti.gov/servlets/purl/976407-cV3aol/

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Morel, J.E.; Allen, R.C.; Knief, R.A.

Sandia Labs., Albuquerque, NM (USA); New Mexico Univ., Albuquerque (USA)

Sandia Labs., Albuquerque, NM (USA); New Mexico Univ., Albuquerque (USA)

AbstractAbstract

[en] Little effort has been made to develop numerical transport methods which can treat differential scattering cross sections which depend explicitly upon vector Ω' and vector Ω, where vector Ω' and vector Ω denote the incident and emergent particle directions, respectively. Such cross sections are called asymmetric. As a first step in the development of a general technique a finite-element collocation method was developed for the solution of the one-dimensional transport equation in slab geometry with asymmetric scattering. One of the unexpected results is that the reflection coefficient can be less than unity for particles incident upon a non-absorptive semi-infinite slab. A set of calculations using both the new technique and a standard Monte Carlo technique were performed for a 100-mean-free-path-thick slab. The diffusion values and the discrete-ordinates values are in excellent agreement with the Monte Carlo values. It is concluded that the discrete-ordinates method is a valid one with potential application to the transport of neutral atoms in anisotropic plasmas. 1 table

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1978; 6 p; ANS meeting; Washington, DC, USA; 12 - 17 Nov 1978; CONF-781105--25; Available from NTIS., PC A02/MF A01

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Morel, J.E.; Halbleib, J.A. Sr.

Sandia Labs., Albuquerque, NM (USA)

Sandia Labs., Albuquerque, NM (USA)

AbstractAbstract

[en] A collocation method is presented for the calculation of electron slowing-down spectra. The primary advantage of this approach is its versatility. Unlike the well-known Spencer-Fano technique, this method does not require an analytically integrable expression which closely approximates the scattering kernel in the region of small energy transfers. Calculational results are given which demonstrate the effectiveness of the technique. User instructions for a computer program which implements the collocation method are given in Appendix A

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May 1979; 34 p; Available from NTIS., PC A03/MF A01

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