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Convective cells and transport in toroidal plasmas

Description: The properties of convective cells and the diffusion resulting from such cells are significantly influenced by an inhomogeneity in the extermal confining magnetic field, such as that in toroidal plasmas. The convective diffusion in the presence of a field inhomogeneity is estimated. For a thermal background, this diffusion is shown to be substantially smaller than classical collisional diffusion. For a model nonthermal background, the diffusion is estimated, for typical parameters, to be at most of the order of collisional diffusion. The model background employed is based on spectra observed in numerical simulations of drift-wave-driven convective cells.
Date: December 1, 1978
Creator: Hassam, A.B. & Kulsrud, R.M.
Partner: UNT Libraries Government Documents Department

Time evolution of mass flows in a collisional tokamak

Description: The time evolution, due to dissipative processes, of an initial pattern of poloidal and toroidal mass flows in a tokamak is considered. The calculation is applicable to a collisional, low ..beta.., axisymmetric tokamak of arbitrary minor cross section. Time rates of change of poloidal flows which are subsonic but larger than the diamagnetic speed are given according to the magnitude of the flow and the collisionality of the plasma. Over most of parameter space for typical tokamaks, the poloidal rotation is strongly damped by magnetic pumping at the rate (l/qR)/sup 2/..nu../sub ii/, where l is the mean free path, qR the ''connection length,'' and ..nu../sub ii/ the ion-ion collision frequency. At higher speeds, even stronger damping is effected by electron thermal conduction. The toroidal rotation is determined largely by the conservation of toroidal angular momentum. A heuristic explanation of the damping due to magnetic pumping is given.
Date: April 1, 1978
Creator: Hassam, A.B. & Kulsrud, R.M.
Partner: UNT Libraries Government Documents Department

Plasma rotation and the radial electric field during off-axis NBI in the DIII-D tokamak

Description: Experiments have been carried out on the DIII-D tokamak to investigate whether off-axis NBI can: (a) drive significant perpendicular flow to lead to increased suppression of turbulence and improved confinement, and (b) be used to control the radial electric field profile. Measurements of both impurity ion poloidal and toroidal rotation profiles were made using charge exchange recombination spectroscopy. These experiments used a low current, low elongation (I{sub p} = 0.5 MA, {kappa} = 1.2) plasma whose magnetic axis was shifted 36 cm vertically upward from the vessel midplane and then shifted downward to be centered on the midplane later in the discharge. 10.7 MW of beam power was applied to maximize NBI effect while operating at low target densities and high temperature to minimize poloidal damping. Results from these experiments show a slight increase in impurity ion poloidal rotation velocity during the vertical shifted phase of off-axis NBI discharge. The toroidal rotation profile is more peaked during off-axis NBI. Both these effects lead to a change in the V x B contribution to the radial electric field during off-axis NBI.
Date: December 1, 1995
Creator: Gohil, P.; Burrell, K.H.; Osborne, T.H. & Hassam, A.B.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics and plasma transport

Description: In this paper we summarize the progress made over the last year in three different areas of research: (a) shear flow generation and reduced transport in fluids and plasma, (b) nonlinear dynamics and visualization of 3D flows, and (c) application of wavelet analysis to the study of fractal dimensions in experimental and numerical data.
Date: January 1, 1992
Creator: Antonsen, T. M., Jr.; Drake, J. F.; Finn, J. M.; Guzdar, P. N.; Hassam, A. B. & Sagdeev, R. Z.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics and plasma transport. Progress report, September 15, 1991--September 14, 1992

Description: In this paper we summarize the progress made over the last year in three different areas of research: (a) shear flow generation and reduced transport in fluids and plasma, (b) nonlinear dynamics and visualization of 3D flows, and (c) application of wavelet analysis to the study of fractal dimensions in experimental and numerical data.
Date: June 1, 1992
Creator: Antonsen, T. M. Jr.; Drake, J. F.; Finn, J. M.; Guzdar, P. N.; Hassam, A. B. & Sagdeev, R. Z.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics and plasma transport

Description: This progress report details work done on a program in nonlinear dynamical aspects of plasma turbulence and transport funded by DOE since 1989. This program has been in cooperation with laboratories in theUSSR [now Russia and the Confederation of Independent States (CIS)]. The purpose of this program has been: To promote the utilization of recent pathbreaking developments in nonlinear science in plasma turbulence and transport. To promote cooperative scientific investigations between the US and CIS in the related areas of nonlinear science and plasma turbulence and transport. In the work reported in our progress report, we have studied simple models which are motivated by observation on actual fusion devices. The models focus on the important physical processes without incorporating the complexity of the geometry of real devices. This allows for a deeper analysis and understanding of the system both analytically and numerically.
Date: January 1, 1993
Creator: Antonsen, T.M. Jr.; Drake, J.F.; Finn, J.M.; Guzdar, P.N.; Hassam, A.B. & Sageev, R.Z.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics and plasma transport. Progress report, September 15, 1992--September 14, 1993

Description: This progress report details work done on a program in nonlinear dynamical aspects of plasma turbulence and transport funded by DOE since 1989. This program has been in cooperation with laboratories in theUSSR [now Russia and the Confederation of Independent States (CIS)]. The purpose of this program has been: To promote the utilization of recent pathbreaking developments in nonlinear science in plasma turbulence and transport. To promote cooperative scientific investigations between the US and CIS in the related areas of nonlinear science and plasma turbulence and transport. In the work reported in our progress report, we have studied simple models which are motivated by observation on actual fusion devices. The models focus on the important physical processes without incorporating the complexity of the geometry of real devices. This allows for a deeper analysis and understanding of the system both analytically and numerically.
Date: May 1, 1993
Creator: Antonsen, T. M. Jr.; Drake, J. F.; Finn, J. M.; Guzdar, P. N.; Hassam, A. B. & Sageev, R. Z.
Partner: UNT Libraries Government Documents Department