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A feasibility study for the spherical torus experiment

Description: Oak Ridge National Laboratory (ORNL) proposes to build the Spherical Torus Experiment (STX), a very low aspect ratio toroidal confinement device. This proposal concentrates on tokamak operation of the experiment; however, it can in principle be operated as a pinch or reversed-field pinch as well. As a tokamak, the spherical torus confines a plasma that is characterized by high toroidal beta, low poloidal beta, large natural elongation, high plasma current for a given edge q, and strong paramagnetism. These features combine to offer the possibility of a compact, low-field fusion device. The figure below shows that when compared to a conventional tokamak the spherical torus represents a major change in geometry. The primary goals of the experiment will be to demonstrate a capability for high beta (20%) in the first stability regime, to extend our knowledge of tokamak confinement scaling, and to test oscillating-field current drive. The experiment will operate in the high-beta, collisionless regime, which is achieved in STX at low temperatures because of the geometry. At a minimum, operation of STX will help to resolve fundamental questions regarding the scaling of beta and confinement in tokamaks. Complete success in this program would have a significant impact on toroidal fusion research in that it would demonstrate solutions to the problems of beta and steady-state operation in the tokamak. The proposed device has a major radius of 0.45 m, a toroidai field of 0.5 T, a plasma current of 900 kA, and heating by neutral beam injection. We estimate 30 months for design, construction, and assembly. The budget estimate, including contingency and escalation, is $6.8 million.
Date: October 1, 1985
Creator: Lazarus, E & Peng, Yueng Kay Martin
Partner: UNT Libraries Government Documents Department

Trip Report-Visit to CERN July 5 to August 5, 1985

Description: The present visit to CERN was as a result of an invitation from Dr. Colin Johnson of the Antiproton Accumulator (AA) group. Two activities were planned for this visit. First, the second beam test of one of the original Fermilab lithium lenses (serial No.2). Second, the installation and beam tests for a new Fermilab lens of improved design (serial No.5). It should be mentioned here that CERN, after realizing the possible gains to be obtained, has started a considerable development effort in short focal length lenses. Presently they have 3 operational lithium lenses, transformers and power supplies for tests. They are in the process of constructing 3 other transformers and designing lenses of 4 cm diameter (twice the present Fermilab lenses). Fermilab should devote some added effort in the field to maintain the initiative. The first beam test of lens No.2 was performed during the summer of 1983, when the lens was used as an antiproton collecting lens. For this test the original lens was used as a strong focusing element in the 26 GeV proton beam in conjunction with a current carrying target Preliminary tests for this geometry were conducted during 1984, when the lens was exposed to over 2*E6 pulses at 320kAmps and 1.3*E13 protons per pulse. Lens No.5 was installed as an antiproton collecting lens, immediately following the AA production target, in a geometry similar to the one designed for the Tevatron 1 project at Fermilab. Targets of a different design than the one use normally at CERN were also required. After completion of the antiproton yield measurements and optimization the lens was left in the beam during regular operation for antiproton accumulation. During antiproton accumulation for the Lear accelerator new records were achieved on the accumulation yield and accumulation rate of antiprotons for the AA machine. ...
Date: September 13, 1985
Creator: Hogvat, C.
Partner: UNT Libraries Government Documents Department

Introduction to combinatorial geometry

Description: The combinatorial geometry package as used in many three-dimensional multimedia Monte Carlo radiation transport codes, such as HETC, MORSE, and EGS, is becoming the preferred way to describe simple and complicated systems. Just about any system can be modeled using the package with relatively few input statements. This can be contrasted against the older style geometry packages in which the required input statements could be large even for relatively simple systems. However, with advancements come some difficulties. The users of combinatorial geometry must be able to visualize more, and, in some instances, all of the system at a time. Errors can be introduced into the modeling which, though slight, and at times hard to detect, can have devastating effects on the calculated results. As with all modeling packages, the best way to learn the combinatorial geometry is to use it, first on a simple system then on more complicated systems. The basic technique for the description of the geometry consists of defining the location and shape of the various zones in terms of the intersections and unions of geometric bodies. The geometric bodies which are generally included in most combinatorial geometry packages are: (1) box, (2) right parallelepiped, (3) sphere, (4) right circular cylinder, (5) right elliptic cylinder, (6) ellipsoid, (7) truncated right cone, (8) right angle wedge, and (9) arbitrary polyhedron. The data necessary to describe each of these bodies are given. As can be easily noted, there are some subsets included for simplicity.
Date: January 1, 1985
Creator: Gabriel, T.A. & Emmett, M.B.
Partner: UNT Libraries Government Documents Department

Geometry-independent approach to coarse-mesh neutron diffusion calculations

Description: Powerful coarse-mesh and nodal methods have been recently developed to calculate accurate node-average fluxes and eigenvalues. The nodal methods solve for the node-average flux by reducing the multidimensional diffusion problem to a coupled system of 1-D equations. These schemes are mainly limited to rectangular (xyz) nodes and cannot easily be extended to other geometries. The polynomial-based coarse-mesh methods have been applied to thetaRZ and HEXZ geometries. This summary describes the development of a boundary coarse-mesh nodal method applicable to arbitrary geometries using the boundary integral technique coupled with nodal source expansion.
Date: June 1, 1985
Creator: Kohut, P.
Partner: UNT Libraries Government Documents Department

Influence of geometry on natural convection in buildings

Description: Strong free convection airflows occur within passive solar buildings resulting from elevated temperatures of surfaces irradiated by solar energy compared with the cooler surfaces not receiving radiation. The geometry of a building has a large influence on the directions and magnitudes of natural airflows, and thus heat transfer between zones. This investigation has utilized a variety of reduced-scale building configurations to study the effects of geometry on natural convection heat transfer. Similarity between the reduced-scale model and a full-scale passive solar building is achieved by having similar geometries and by replacing air with Freon-12 gas as the model's working fluid. Filling the model with Freon-12 gas results in similarity in Prandtl numbers and Rayleigh numbers based on temperature differences in the range from 10/sup 9/ to 10/sup 11/. Results from four geometries are described with an emphasis placed on the effects of heat loss on zone temperature stratification shifts.
Date: January 1, 1985
Creator: White, M.D.; Winn, C.B.; Jones, G.F. & Balcomb, J.D.
Partner: UNT Libraries Government Documents Department

Fractal geometry of two-dimensional fracture networks at Yucca Mountain, southwestern Nevada: proceedings

Description: Fracture traces exposed on three 214- to 260-m{sup 2} pavements in the same Miocene ash-flow tuff at Yucca Mountain, southwestern Nevada, have been mapped at a scale of 1:50. The maps are two-dimensional sections through the three-dimensional network of strata-bound fractures. All fractures with trace lengths greater than 0.20 m were mapped. The distribution of fracture-trace lengths is log-normal. The fractures do not exhibit well-defined sets based on orientation. Since fractal characterization of such complex fracture-trace networks may prove useful for modeling fracture flow and mechanical responses of fractured rock, an analysis of each of the three maps was done to test whether such networks are fractal. These networks proved to be fractal and the fractal dimensions (D) are tightly clustered (1.12, 1.14, 1.16) for three laterally separated pavements, even though visually the fracture networks appear quite different. The fractal analysis also indicates that the network patterns are scale independent over two orders of magnitude for trace lengths ranging from 0.20 to 25 m. 7 refs., 7 figs.
Date: December 31, 1985
Creator: Barton, C.C. & Larsen, E.
Partner: UNT Libraries Government Documents Department

Torsion and geometrostasis in covariant superstrings

Description: The covariant action for freely propagating heterotic superstrings consists of a metric and a torsion term with a special relative strength. It is shown that the strength for which torsion flattens the underlying 10-dimensional superspace geometry is precisely that which yields free oscillators on the light cone. This is in complete analogy with the geometrostasis of two-dimensional sigma-models with Wess-Zumino interactions. 13 refs.
Date: January 1, 1985
Creator: Zachos, C.
Partner: UNT Libraries Government Documents Department

Geometric perturbation theory and plasma physics

Description: Modern differential geometric techniques are used to unify the physical asymptotics underlying mechanics, wave theory and statistical mechanics. The approach gives new insights into the structure of physical theories and is suited to the needs of modern large-scale computer simulation and symbol manipulation systems. A coordinate-free formulation of non-singular perturbation theory is given, from which a new Hamiltonian perturbation structure is derived and related to the unperturbed structure. The theory of perturbations in the presence of symmetry is developed, and the method of averaging is related to reduction by a circle group action. The pseudo-forces and magnetic Poisson bracket terms due to reduction are given a natural asymptotic interpretation. Similar terms due to changing reference frames are related to the method of variation of parameters, which is also given a Hamiltonian formulation. These methods are used to answer a question about nearly periodic systems. The answer leads to a new secular perturbation theory that contains no ad hoc elements. Eikonal wave theory is given a Hamiltonian formulation that generalizes Whitham's Lagrangian approach. The evolution of wave action density on ray phase space is given a Hamiltonian structure using a Lie-Poisson bracket. The relationship between dissipative and Hamiltonian systems is discussed. A new type of attractor is defined which attracts both forward and backward in time and is shown to occur in infinite-dimensional Hamiltonian systems with dissipative behavior. The theory of Smale horseshoes is applied to gyromotion in the neighborhood of a magnetic field reversal and the phenomenon of reinsertion in area-preserving horseshoes is introduced. The central limit theorem is proved by renormalization group techniques. A natural symplectic structure for thermodynamics is shown to arise asymptotically from the maximum entropy formalism.
Date: April 4, 1985
Creator: Omohundro, S.M.
Partner: UNT Libraries Government Documents Department

New slab geometry radiation transport differencing scheme

Description: Considerable effort has been directed toward seeking an optimal spatial differencing scheme for the neutron transport equation. This search led to a best scheme (using specific criteria to define ''best''): the linear characteristic method. However, we have recently considered radiative transfer problems in which the same problem may have both optically thick and optically thin regions, with the maximum optical thicknesses being much greater than those generally encountered in neutron transport problems. Here, we describe the important features of these radiative transfer problems and a new differencing scheme which seems to have advantages for radiative transfer calculations relative to the older schemes.
Date: January 1, 1985
Creator: Larsen, E.W.; Morel, J.E. & Miller, W.F. Jr.
Partner: UNT Libraries Government Documents Department

SABRINA: an interactive solid geometry modeling program for Monte Carlo

Description: SABRINA is a fully interactive three-dimensional geometry modeling program for MCNP. In SABRINA, a user interactively constructs either body geometry, or surface geometry models, and interactively debugs spatial descriptions for the resulting objects. This enhanced capability significantly reduces the effort in constructing and debugging complicated three-dimensional geometry models for Monte Carlo Analysis.
Date: January 1, 1985
Creator: West, J.T.
Partner: UNT Libraries Government Documents Department

Seismic response of LMFBR tanks with imperfections

Description: This paper deals with seismic responses of imperfect circular tanks. Physical imperfection due to manufacturing tolerances and numerical imperfection due to finite element spatial discretization are described. Numerical imperfections produced by 4-node and 9-node Lagrangian shell elements are examined. A convergence study is performed in which the number of the shell elements required to capture the dominant ''out-of-roundness'' modes under seismic excitations is determined. The response of a shell with a cos4theta imperfection due to manufacturing tolerances is compared with that of a perfect circular shell to demonstrate the effects of imperfection on the axial stresses of the shell under seismic conditions. 3 refs., 4 figs., 2 tabs.
Date: January 1, 1985
Creator: Gvildys, J.; Ma, D.C. & Chang, Y.W.
Partner: UNT Libraries Government Documents Department