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in creator/contributor: "Barnes, D.C."

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Approximate model for toroidal force balance in the high-beta stellarator

A simple model for estimating the body force acting on a diffuse plasma confined in a three-dimensional, high-beta stellarator geometry is given. The equilibrium is treated by an asymptotic expansion about a straight theta pinch with diffuse, circular cross section. The expansion parameter delta is the strength of the applied helical fields. This expansion leads to an inconsistent set of equations for the equilibrium in second order. Nevertheless, by averaging the equilibrium equations over the… more

Date: March 1, 1979

Creator: Barnes, D. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Three-dimensional, nonlinear magnetohydrodynamic computations of the postimplosion dynamics of the Los Alamos scyllac

The Scyllac experiment is designed to produce high-beta plasmas in toroidal equilibrium by adding l = 0 and l = 1 perturbations to the basic theta pinch fields. The Scyllac experiment is being studied by means of the numerical solution of nonlinear, time-dependent equations with appropriate boundary conditions. Some calculations of the post-implosion phase are discussed. (MOW)

Date: January 1, 1976

Creator: Barnes, D. C. & Brackbill, J. U.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Application of the 3D Iced-Ale method to equilibrium and stability problems of a magnetically confined plasma

A numerical study of the equilibrium and stability properties of the Scyllac experiment at Los Alamos is described. The formulation of the numerical method, which is an extension of the ICED-ALE method to magnetohydrodynamic flow in three dimensions, is given. The properties of the method are discussed, including low computational diffusion, local conservation, and implicit formulation in the time variable. Also discussed are the problems encountered in applying boundary conditions and computin… more

Date: January 1, 1977

Creator: Barnes, D. C. & Brackbill, J. U.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Compact torus experiments and theory

Two types of compact toroids have been studied: spheromaks and field-reversed configurations (FRC). Spheromaks, which contain both toroidal and poloidal fields, have been formed with a magnetized coaxial injector and trapped in both prolate and oblate flux conservers. As expected from theory, the prolate configuration always tilts, but the oblate configuration can be made stable even in the presence of a guide field. Observations include 150..mu..s lifetimes, <n> approx. 10/sup 14/ cm/sup -3/, … more

Date: January 1, 1980

Creator: Armstrong, W. T.; Barnes, D. C. & Bartsch, R. R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Recent results of an internal tilt mode calculation in FRCs

Recent theoretical results on the stability of FRCs to the internal tilt mode are presented. An approximate treatment of collisions shows that collisions have a small effect on the growth rate of the mode until the plasma becomes very collisional (lambda/sub ii/ less than or equal to r/sub s/2). Finite Larmor radius theory predicts that the growth rate of the instability normalized to that of MHD depends only on the combination anti s/e, where e is the plasma elongation. However, a full Vlasov … more

Date: January 1, 1985

Creator: Barnes, D. C.; Schwarzmeier, J. L. & Lewis, H. R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Compact torus theory: MHD equilibrium and stability

Field reversed theta pinches have demonstrated the production and confinement of compact toroidal configurations with surprisingly good MHD stability. In these observations, the plasma is either lost by diffusion or by the loss of the applied field or is disrupted by an n = 2 (where n is the toroidal mode number) rotating instability only after 30 to 100 MHD times, when the configuration begins to rotate rigidly above a critical speed. These experiments have led one to investigate the equilibri… more

Date: January 1, 1979

Creator: Barnes, D. C.; Seyler, C. E. & Anderson, D. V.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Ion kinetic effects on the tilt mode in FRCs

Theory and simulations have shown that field reversed configurations (FRG's) should be unstable magnetohydrodynamically to the tilting mode, yet tilting seldom is seen in the experiments. Profile effects (within MHD) and ion finite larmor radius (FLR) effects have been prosed to explain the observed stability of FRC's. The present work seeks to test both of these effects.

Date: January 1, 1981

Creator: Schwarzmeier, J. L.; Seyler, C. E. & Barnes, D. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Analytical and numerical calculations of field-reversed theta-pinch equilibria based on a generalized Hill's vortex model

We have been investigating methods for numerically extending the analytic solutions of field reversed theta pinch equilibria so that the results may be used in various stability and dynamics studies. We have used generalizations of elliptical Hill's vortex equilibria which accomodate separatrices with more rectangular shapes and which allow plasma to exist outside the separatrix. Although the equilibria are specified analytically inside the plasma surface, numerical techniques are required to g… more

Date: October 1, 1981

Creator: Anderson, D. V.; Hammer, J. H. & Barnes, D. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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New results in high beta MHD theory

New results are described in the following three areas of high MHD theory: (1) equilibrium and stability of diffuse high-..beta.. stellarators, (2) MHD equilibrium and stability of minimum-B mirror traps, and (3) simulation of simple and reversed field mirror machines.

Date: January 1, 1978

Creator: Barnes, D. C.; Brackbill, J. U. & Cayton, T. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Implicit-particle simulation of magnetized plasmas

A second-order accurate, direct method for the simulation of magnetized, multi-dimensional plasmas is developed. A time decentered particle push is combined with the direct method for implicit plasma simulation to include finite sized particle effects in an absolutely stable algorithm. A simple iteration (renormalized Poisson equation) is used to solve the field corrector equation. Details of the two-dimensional, electrostatic, constant magnetic field, periodic case are given. Numerical results… more

Date: September 1, 1982

Creator: Barnes, D. C.; Kamimura, T.; Leboeuf, J. N. & Tajima, T.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Accurate, finite-volume methods for 3D MHD on unstructured Lagrangian meshes

Previous 2D methods for magnetohydrodynamics (MHD) have contributed both to development of core code capability and to physics applications relevant to AGEX pulsed-power experiments. This strategy is being extended to 3D by development of a modular extension of an ASCI code. Extension to 3D not only increases complexity by problem size, but also introduces new physics, such as magnetic helicity transport. The authors have developed a method which incorporates all known conservation properties i… more

Date: October 1, 1998

Creator: Barnes, D. C. & Rousculp, C. L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Profile stabilization of tilt mode in a Field Reversed Configuration

The possibility of stabilizing the tilt mode in Field Reversed Configurations without resorting to explicit kinetic effects such as large ion orbits is investigated. Various pressure profiles, P({Psi}), are chosen, including ``hollow`` profiles where current is strongly peaked near the separatrix. Numerical equilibria are used as input for an initial value simulation which uses an extended Magnetohydrodynamic (MHD) model that includes viscous and Hall terms. Tilt stability is found for specific… more

Date: June 1, 1993

Creator: Cobb, J. W.; Tajima, T. & Barnes, D. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Tilting mode in field-reversed configurations

Field Reversed Configurations (FRCs) experimentally have exhibited remarkable stability on the magnetohydrodynamic (MHD) timescale, despite numerous MHD calculations showing FRCs to be unstable. It is easy to believe that local modes are stabilized by finite Larmor radius (FLR) effects, but more puzzling is the apparent stability of FRCs against global modes, where one would expect FLR effects to be less important. In this paper we study the tilting mode, which MHD has shown to be a rapidly gro… more

Date: January 1, 1982

Creator: Schwarzmeier, J. L.; Barnes, D. C.; Lewis, H. R.; Seyler, C. E. & Shestakov, A. I.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Observation of tilt asymmetries in field-reversed configurations

In recent years, part of the experimental effort on the FRX-C/LSM device has been devoted to understanding why good FRC confinement is observed only in a narrow window of the operating parameter space (fill pressures less than 5 mtorr and bias fields less than 0.8--0.9 kG). The transition from good to bad confinement has been shown for some time to correlate with strong axial shocks, suggesting a formation or stability problem. More recently, FRC magnetic asymmetries have been observed whenever… more

Date: January 1, 1989

Creator: Tuszewski, M.; Barnes, D. C.; Klingner, P. & Ng, Chun

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Beyond the Brillouin limit with the Penning fusion experiment

Several years ago, it was proposed that a dense nonneutral plasma could be produced in a Penning trap. Nonneutral plasmas have excellent confinement. Thus, such a dense plasma might produce simultaneously high density and good confinement (as needed for fusion). Recently, this theoretical conjecture has been demonstrated in a small (3 mm radius) electron experiment (PFX). Densities up to 35 times the Brillouin density (limiting number density in a static trap) have been inferred from the observ… more

Date: November 9, 1996

Creator: Barnes, D. C.; Mitchell, T. B. & Schauer, M. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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US-Japan workshop on field-reversed configurations with steady-state high-temperature fusion plasmas and the 11th US-Japan workshop on compact toroids

The US-Japan Workshop on Field-Reversed Configurations with Steady-State High-Temperature Fusion Plasma and the 11th US-Japan Workshop on Compact Toroids were held at Los Alamos National Laboratory, Los Alamos, New Mexico on November 7--9, 1989. These proceedings contain the papers presented at the workshops as submitted by the authors. These papers have been indexed separately.

Date: May 1, 1990

Creator: Barnes, D. C.; Fernandez, J. C. & Rej, D. J. (comps.)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Multi-Level iterative methods in computational plasma physics

Plasma physics phenomena occur on a wide range of spatial scales and on a wide range of time scales. When attempting to model plasma physics problems numerically the authors are inevitably faced with the need for both fine spatial resolution (fine grids) and implicit time integration methods. Fine grids can tax the efficiency of iterative methods and large time steps can challenge the robustness of iterative methods. To meet these challenges they are developing a hybrid approach where multigrid… more

Date: March 1, 1999

Creator: Knoll, D. A.; Barnes, D. C.; Brackbill, J. U.; Chacon, L. & Lapenta, G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Analytic and numerical studies of Scyllac equilibrium

The results of both numerical and analytic studies of the Scyllac equilibria are presented. Analytic expansions are used to derive equilibrium equations appropriate to noncircular cross sections, and compute the stellarator fields which produce toroidal force balance. Numerical algorithms are used to solve both the equilibrium equations and the full system of dynamical equations in three dimensions. Numerical equilibria are found for both l = 1,0 and l= 1,2 systems. It is found that the stellar… more

Date: January 1, 1976

Creator: Barnes, D. C.; Brackbill, J. U.; Dagazian, R. Y.; Freidberg, J. P.; Schneider, W.; Betancourt, O. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The Los Alamos Intense Neutron Source

The Intense Neutron Source (INS) is an Inertial Electrostatic Confinement (IEC) fusion device presently under construction at Los Alamos National Laboratory. It is designed to produce 10{sup 11} neutrons per second steady-state using D-T fuel. Phase 1 operation of this device will be as a standard three grid IEC ion focus device. Expected performance has been predicted by scaling from a previous IEC device. Phase 2 operation of this device will utilize a new operating scheme, the Periodically O… more

Date: October 1, 1997

Creator: Nebel, R. A.; Barnes, D. C.; Bollman, R.; Eden, G.; Morrison, L.; Pickrell, M. M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effects of beam ions on the FRC tilt mode

In this paper, we present new theoretical results on stabilizing the internal tilting mode in a FRC which contains a minority energetic ion component. In contrast to previous results obtained in various asymptotic limits of geometry, mode structure, or beam parameters, the present results include all magnetoinductive effects self-consistently in a 3-D calculation representing a realistic FRC. 2 figs.

Date: January 1, 1989

Creator: Barnes, D.C. (Los Alamos National Lab., NM (USA)) & Mikic, Z. (Science Applications International Corp., Albuquerque, NM (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Recent theoretical studies of internal structure and stability of field-reversed configurations

In this paper we present the results of recent examinations of the low frequency, large scale stability of the field-reversed configurations (FRC). We also examined the ability to accurately infer internal transport quantities (e.g., field null resistivity) in an FRC. 7 refs., 5 figs.

Date: January 1, 1988

Creator: Webster, R. B.; Lewis, H. R.; Staudenmeier, J. L.; Milroy, R. D.; Barnes, D. C.; Bishop, R. C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Theory and simulation of fishbone-type instabilities in beam-heated tokamaks

Energetic trapped particles are shown to introduce a new unstable solution to the internal kink and ballooning modes in tokamaks. Both the real frequencies and growth rates of the instabilities are comparable to the trapped-particle precession frequency. Simulations including the excitation and particle-loss mechanisms of the internal kink mode are found to reproduce essential features of the fishbones. Furthermore, the energetic trapped particle-induced ballooning modes are shown to be consist… more

Date: September 1, 1984

Creator: Chen, L.; White, R. B.; Cheng, C. Z.; Romanelli, F.; Weiland, J.; Hay, R. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Review of the Los Alamos FRX-C experiment

The FRX-C device is a large field-reversed theta pinch experiment, with linear dimensions twice those of its FRX-A and FRX-B predecessors. It is used to form field-reversed configurations (FRCs), which are high-beta, highly prolate compact toroids. FRX-C has demonstrated an R/sup 2/ scaling for particle confinement in FRCs, indicating particles are lost by diffusive processes. Particle losses were also observed to dominate the energy balance. FRC lifetimes exceeding 300 ..mu..s were observed wh… more

Date: January 1, 1985

Creator: Siemon, R. E.; Armstrong, W. T.; Barnes, D. C.; Bartsch, R. R.; Chrien, R. E.; Cochrane, J. C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The tilt mode, turbulence and transport in field-reversed configurations

An outstanding theoretical problem of great importance in research on field-reversed configurations (FRCs) is the explanation of the observed stability of FRCs to the internal tilt mode. For example, in the Los Alamos FRX-C experiment, FRCs showed no evidence of the internal tilt mode during experimental lifetimes of up to 300 ..mu..s, which is over an order of magnitude longer than the expected ideal MHD growth time. Finite-Larmor-radius (FLR) theory is inappropriate for the FRC configuration … more

Date: January 1, 1988

Creator: Lewis, H. R.; Barnes, D. C.; Bishop, R. C.; Krall, N. A.; Mikic, Z.; Milroy, R. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department