337 research outputs found
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Diagnostics for magnetically confined high-temperature plasmas
During the last 20 years, magnetically confined laboratory plasmas of steadily increasing temperatures and densities have been obtained, most notably in tokamak configurations, and now approach the conditions necessary to sustain a fusion reaction. Even more important to the goal of understanding the physics of such systems, remarkable advances in plasma diagnostics, the techniques for determining the properties of such plasmas, have accompanied these developments. More parameters can be determined with greater accuracy and finer spatial and temporal resolution. The magnetic configuration, the primary local thermodynamic quantities (density, temperature, and drift velocity), and other necessary quantities can now be measured with sufficient accuracy to determine particle and energy fluxes within the plasma and to characterize the basic transport processes. These plasmas are far from thermodynamic equilibrium. This deviation manifests itself in a variety of instabilities on several spatial and temporal scales, many of which are aptly described as turbulence. Many aspects of the turbulence can also be characterized. This article reviews the current state of diagnostics from an epistemoiogical perspective: the capabilities and limitations for measuring each important physical quantity are presented.Physic
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Plasma fluctuations as Markovian noise
Noise theory is used to study the correlations of stationary Markovian fluctuations that are homogeneous and isotropic in space. The relaxation of the fluctuations is modeled by the diffusion equation. The spatial correlations of random fluctuations are modeled by the exponential decay. Based on these models, the temporal correlations of random fluctuations, such as the correlation function and the power spectrum, are calculated. We find that the diffusion process can give rise to the decay of the correlation function and a broad frequency spectrum of random fluctuations. We also find that the transport coefficients may be estimated by the correlation length and the correlation time. The theoretical results are compared with the observed plasma density fluctuations from the tokamak and helimak experiments.Physic
Physical Acoustics
Contains reports on two research projects.U. S. Navy (Office of Naval Research) under Contract Nonr-1841-(42)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E
Physical Acoustics
Contains research objectives and reports on three research projects.U. S. Navy (Office of Naval Research) under Contract Nonr- 1841(42)National Science Foundation (Grant G-9330
Turbulence driven particle transport in Texas Helimak
We analyze the turbulence driven particle transport in Texas Helimak (K. W.
Gentle and Huang He, Plasma Sci. and Technology, 10, 284 (2008)), a toroidal
plasma device with one-dimensional equilibrium with magnetic curvature and
shear. Alterations on the radial electric field, through an external voltage
bias, change spectral plasma characteristics inducing a dominant frequency for
negative bias values and a broad band frequency spectrum for positive bias
values. For negative biased plasma discharges, the transport is high where the
waves propagate with phase velocities near the plasma flow velocity, an
indication that the transport is strongly affected by a wave particle resonant
interaction. On the other hand, for positive bias the plasma has a reversed
shear flow and we observe that the transport is almost zero in the shearless
radial region, an evidence of a transport barrier in this region.Comment: 8 pages, 11 figure
Constraints in Quantum Geometrodynamics
We compare different treatments of the constraints in canonical quantum
gravity. The standard approach on the superspace of 3--geometries treats the
constraints as the sole carriers of the dynamic content of the theory, thus
rendering the traditional dynamical equations obsolete. Quantization of the
constraints in both the Dirac and ADM square root Hamiltonian approaches leads
to the well known problems of time evolution. These problems of time are of
both an interpretational and technical nature. In contrast, the geometrodynamic
quantization procedure on the superspace of the true dynamical variables
separates the issues of quantization from the enforcement of the constraints.
The resulting theory takes into account states that are off-shell with respect
to the constraints, and thus avoids the problems of time. We develop, for the
first time, the geometrodynamic quantization formalism in a general setting and
show that it retains all essential features previously illustrated in the
context of homogeneous cosmologies.Comment: 36 pages, no figures, submitted to IJMPA, Rewording, Fixed Typo
Turbulence and Bias-Induced Flows in Simple Magnetized Toroidal Plasmas
Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three- dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows. These bias-induced vertical flows located in the gradient region appear to reduce the radial extent of turbulent structures, and thereby lower the radial plasma transport on the low field side
Physical Acoustics
Contains reports on four research projects.U. S. Navy (Office of Naval Research) under Contract Nonr-1841-(42)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E
Plasma Physics
Contains reports on three research projects.United States Atomic Energy Commission (Contract AT(30-1)-1842)United States Air Force, Electronic Systems Division (Contract AF19(604)-5992
Physical Acoustics
Contains reports on five research projects.U. S. Navy (Office of Naval Research) under Contract Nonr-1841(42
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