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in subjects: "Mhd Equilibrium"

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Eliminating Islands in High-pressure Free-boundary Stellarator Magnetohydrodynamic Equilibrium Solutions

Magnetic islands in free-boundary stellarator equilibria are suppressed using a procedure that iterates the plasma equilibrium equations and, at each iteration, adjusts the coil geometry to cancel resonant fields produced by the plasma. The coils are constrained to satisfy certain measures of engineering acceptability and the plasma is constrained to ensure kink stability. As the iterations continue, the coil geometry and the plasma simultaneously converge to an equilibrium in which the island … more

Date: November 19, 2002

Creator: Hudson, S. R.; Monticello, D. A.; Reiman, A. H.; Boozer, A. H.; Strickler, D. J.; Hirshman, S. P. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Workshop on Feedback Stabilization of MHD Stabilities

The feedback stabilization of MHD instabilities is an area of research that is critical for improving the performance and economic attractiveness of magnetic confinement devices. A Workshop dedicated to feedback stabilization of MHD instabilities was held from December 11-13, 1996 at the Princeton Plasma Physics Laboratory, Princeton NJ, USA. The resulting presentations, conclusions, and recommendations are summarized.

Date: December 31, 1996

Creator: McGuire, K.; Kugel, H.; La Haye, R.; Mauel, M.; Nevins, W. & Prager, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Stable bootstrap-current driven equilibria for low aspect ratio tokamaks

Low aspect ratio tokamaks can potentially provide a high ratio of plasma pressure to magnetic pressure {beta} and high plasma current I at a modest size, ultimately leading to a high power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current. A high value of the Troyon factor {beta}{sub N} and strong shaping are required to allow simultaneous operation at high {beta} and high bootstrap current fraction… more

Date: August 1, 1996

Creator: Miller, R. L.; Lin-Liu, Y. R.; Turnbull, A. D.; Chan, V. S.; Pearlstein, L. D.; Sauter, O. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Stability of tearing modes in tokamak plasmas

The stability properties of m {ge} 2 tearing instabilities in tokamak plasmas are analyzed. A boundary layer theory is used to find asymptotic solutions to the ideal external kink equation which are used to obtain a simple analytic expression for the tearing instability parameter {Delta}{prime}. This calculation generalizes previous work on this topic by considering more general toroidal equilibria (however, toroidal coupling effects are ignored). Constructions of {Delta}{prime} are obtained fo… more

Date: February 1, 1994

Creator: Hegna, C. C. & Callen, J. D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Spheromak reactor: Physics opportunities and issues

The spheromak is a magnetic confinement device with a more attractive fusion reactor potential than the leading geometry, the tokamak. This results in large part from the absence of a toroidal field coil and other structures linking the plasma along the geometric axis. However, because of the lack of a strong external magnetic field, the physics is more complex so that considerable research is required to learn how to achieve the reactor potential. Several critical physics issues am considered … more

Date: June 20, 1996

Creator: Hooper, E.B. & Fowler, T.K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Lithium pellet injection experiments on the Alcator C-Mod tokamak

A pellet enhanced performance mode, showing significantly reduced core transport, is regularly obtained after the injection of deeply penetrating lithium pellets into Alcator C-Mod discharges. These transient modes, which typically persist about two energy confinement times, are characterized by a steep pressure gradient ({ell}{sub p} {le} a/5) in the inner third of the plasma, indicating the presence of an internal transport barrier. Inside this barrier, particle and energy diffusivities are g… more

Date: June 1, 1996

Creator: Garnier, D.T.

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

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Theoretical issues in Spheromak research

This report summarizes the state of theoretical knowledge of several physics issues important to the spheromak. It was prepared as part of the preparation for the Sustained Spheromak Physics Experiment (SSPX), which addresses these goals: energy confinement and the physics which determines it; the physics of transition from a short-pulsed experiment, in which the equilibrium and stability are determined by a conducting wall (``flux conserver``) to one in which the equilibrium is supported by ex… more

Date: April 1, 1997

Creator: Cohen, R. H., Hooper, E.B., LoDestro, L.L., Mattor, N., Pearlstein, L.D., Ryutov, D.D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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MHD stability studies in reversed shear plasmas in TFTR

MHD phenomena in reversed shear plasmas in TFTR are described during each of the three phases of the evolution of these discharges: the current ramp, high power neutral beam heating and after the beam power has been reduced. Theoretical analysis of discharges which disrupted in the high-{beta} phase indicates that the {beta} - limit is set by the ideal n = 1 infernal/kink mode. The mode structure of the disruption precursor reconstructed from the electron temperature data compares favorably wit… more

Date: December 31, 1996

Creator: Manickam, J.; Fredrickson, E. & Chang, Z.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Pseudo-MHD ballooning modes in tokamak plasmas

The MHD description of a plasma is extended to allow electrons to have both fluid-like and adiabatic-regime responses within an instability eigenmode. In the resultant {open_quotes}pseudo-MHD{close_quotes} model, magnetic field line bending is reduced in the adiabatic electron regime. This makes possible a new class of ballooning-type, long parallel extent, MHD-like instabilities in tokamak plasmas for {alpha} > s{sup 2}(2 {sup 7/3}/9) (r{sub p}/R{sub 0}) or-d{radical}{Beta}/dr > (2{sup 1/6} /3… more

Date: August 1, 1996

Creator: Callen, J. D. & Hegna, C. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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The validity of the extended energy principle

A recent analysis of plasma stability based on modifications of the extended energy principle for magnetohydrodynamic stability led to conclusions that are too optimistic. The original interpretation of this principle is indeed applicable. The present analysis demonstrates explicitly the fallacy of using the wrong functional for {delta}W in the extended energy principle. It then shows that the original energy principle functional {delta}W{sub B} is also obtained for a model in which a surface m… more

Date: April 1, 1994

Creator: Chance, M. S.; Johnson, J. L. & Kulsrud, R. M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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High-{beta} disruption in tokamaks

Three dimensional MHD simulations of high-{beta} plasmas show that toroidally localized high-n ballooning modes can be driven unstable by the local pressure steepening which arises from the evolution of low-n modes. Nonlinearly, the high-n mode becomes even more localized and produces a strong local pressure bulge which destroys the flux surfaces resulting in a thermal quench. The flux surfaces then recover temporarily but now contain large magnetic islands. This scenario is supported by experi… more

Date: July 1, 1995

Creator: Park, W.; Fredrickson, E.D. & Janos, A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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3D simulation studies of tokamak plasmas using MHD and extended-MHD models

The M3D (Multi-level 3D) tokamak simulation project aims at the simulation of tokamak plasmas using a multi-level tokamak code package. Several current applications using MHD and Extended-MHD models are presented; high-{beta} disruption studies in reversed shear plasmas using the MHD level MH3D code, {omega}{sub *i} stabilization and nonlinear island saturation of TAE mode using the hybrid particle/MHD level MH3D-K code, and unstructured mesh MH3D{sup ++} code studies. In particular, three inte… more

Date: December 31, 1996

Creator: Park, W.; Chang, Z.; Fredrickson, E. & Fu, G. Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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High beta and second stability region transport and stability analysis. Final report

This report describes MHD equilibrium and stability studies carried out at Northrop Grumman`s Advanced Technology and Development Center during the period March 1 to December 31, 1995. Significant progress is reported in both ideal and resistive MHD modeling of TFTR plasmas. Specifically, attention is concentrated on analysis of Advanced Tokamak experiments at TFTR involving plasmas in which the q-profiles were non-monotonic.

Date: January 1, 1996

Creator: Hughes, M.H. & Phillips, M.W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Impact of MHD Equilibrium Input Variations on the High-Beta Stability Boundaries of NSTX

Ideal MHD stability limits of anticipated plasma configurations for the National Spherical Torus Experiment (NSTX) [Ono, M., et al., Nucl. Fusion 40 (2000) 557] and the dependence on the parameters defining the MHD equilibrium are evaluated. The study provides a quantitative computational evaluation of the stability limit variations induced by changes to the equilibrium of NSTX high-beta plasmas. The analysis is based on a reference free-boundary equilibrium with beta = 41.5%, monotonic safety … more

Date: March 20, 2001

Creator: Paoletti, F.; Sabbagh, S. A.; Manickam, J.; Menard, J.; Akers, R. J.; Gates, D. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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The Spheromak path to fusion energy

The spheromak is a simple and robust magnetofluid configuration with several attractive reactor attributes including compact geometry, no material center post, high engineering {beta}, and sustained steady state operation through helicity injection. Spheromak physics was extensively studied in the US program and abroad (especially Japan) in the 1980` s with work continuing into the 1990s in Japan and the UK. Scientific results included demonstration of self-organization at constant helicity, co… more

Date: April 1, 1998

Creator: Hooper, E. B.; Barnes, C. W. & Bellan, P. M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Stabilization of ballooning modes with sheared toroidal rotation

A new code demonstrates the stabilization of MHD ballooning modes by sheared toroidal rotation. A shifted-circle model is used to elucidate the physics and numerically reconstructed equilibria are used to analyze DIII-D discharges. In the ballooning representation, the modes shift periodically along the field line to the next point of unfavorable curvature. The shift frequency (d{Omega}/dq where {Omega} is the angular toroidal velocity and q is the safety factor) is proportional to the rotation… more

Date: November 1, 1994

Creator: Miller, R .L.; Waelbroeck, F. W.; Lao, L. L. & Taylor, T. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Stellarator-Spheromak

A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with v… more

Date: March 1, 1997

Creator: Moroz, P. E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Sawtooth mixing of alpha particles in TFTR D-T plasmas

Radially resolved confined alpha particle energy and density distributions are routinely measured on TFTR using two diagnostics: PCX and {alpha}-CHERS. The Pellet Charge-eXchange (PCX) diagnostic uses the ablation cloud formed by an impurity pellet (Li or B) for neutralization of the alphas followed by analysis of the escaping helium neutrals. PCX detects deeply trapped alpha particles in the energy range 0.5 - 3.8 MeV. The {alpha}-CHERS technique, were the alpha signal is excited by charge-exc… more

Date: December 31, 1996

Creator: Petrov, M.P.; Budny, R.V. & Chang, Z.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Reversed field pinch experiments. Final report, November 24, 1991--November 23, 1994

The Reversatron reversed field pinch (RFP) is an experiment to investigate the effect of boundary conditions on plasma confinement. Earlier RFP experiments, particularly ZT-40 and Los Alamos and Eta Beta II at Padua, had found an improvement in confinement when the vacuum chamber wall was surrounded by a conducting shell. The data showed a longer discharge duration and a reduction in the applied loop voltage. The latter determines the energy input to the plasma, thus a lower loop voltage (with … more

Date: March 1, 1995

Creator: Robertson, S.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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A filament model of MHD turbulence

Turbulence of ordinary fluid is recognized as chaotic motion with almost no linear features. It is well described in wavenumber space by Kolmogorov`s phenomenological theory in wave number k-space: The source of energy should exist in the region of small wavenumbers. Then isotropic energy flux is generated in k-space directed toward a larger k-region where the energy is absorbed by viscosity. The main characteristics of energy spectrum of Kolmogorov turbulence is universal and in good agreement… more

Date: November 1, 1996

Creator: Petviashvili, V.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Three-dimensional magnetospheric equilibrium with isotropic pressure

In the absence of the toroidal flux, two coupled quasi two-dimensional elliptic equilibrium equations have been derived to describe self-consistent three-dimensional static magnetospheric equilibria with isotropic pressure in an optimal ({Psi},{alpha},{chi}) flux coordinate system, where {Psi} is the magnetic flux function, {chi} is a generalized poloidal angle, {alpha} is the toroidal angle, {alpha} = {phi} {minus} {delta}({Psi},{phi},{chi}) is the toroidal angle, {delta}({Psi},{phi},{chi}) is… more

Date: May 1, 1995

Creator: Cheng, C. Z.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Wall stabilization of high beta plasmas in DIII-D

Detailed analysis of recent high beta discharges in the DIII-D tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to {beta}{sub T} = 12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted {open… more

Date: February 1, 1995

Creator: Taylor, T. S.; Strait, E. J.; Lao, L. L.; Turnbull, A. D.; Burrell, K. H.; Chu, M. S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Mode coupling trigger of neoclassical magnetohydrodynamic tearing modes in tokamaks

Numerical studies of the nonlinear evolution of coupled magnetohydrodynamic - type tearing modes in three-dimensional toroidal geometry with neoclassical effects are presented. The inclusion of neoclassical physics introduces an additional free-energy source for the nonlinear formation of magnetic islands through the effects of a bootstrap current in Ohm`s law. The neoclassical tearing mode is demonstrated to be destabilized in plasmas which are otherwise {Delta}{prime} stable, albeit once a th… more

Date: May 1, 1997

Creator: Gianakon, T. A.; Hegna, C. C. & Callen, J. D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Summary discussion: An integrated advanced tokamak reactor

The tokamak concept improvement workshop addressed a wide range of issues involved in the development of a more attractive tokamak. The agenda for the workshop progressed from a general discussion of the long-range energy context (with the objective being the identification of a set of criteria and ``figures of merit`` for measuring the attractiveness of a tokamak concept) to particular opportunities for the improvement of the tokamak concept. The discussions concluded with a compilation of res… more

Date: December 31, 1994

Creator: Sauthoff, N. R.

Item Type: Article

Partner: UNT Libraries Government Documents Department