Download or read book Experimental Measurement of Microwave Broadening by Fluctuations on the DIII D Tokamak written by Michael William Brookman and published by . This book was released on 2017 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Study of Electron Temperature Fluctuations in the DIII D Tokamak written by Anne Elisabeth White and published by . This book was released on 2008 with total page 592 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Studies of Turbulence and Flows in the DIII D Tokamak written by Jon Clark Hillesheim and published by . This book was released on 2012 with total page 307 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the turbulent transport of particles, momentum, and heat continues to be an important goal for magnetic confinement fusion energy research. The turbulence in tokamaks and other magnetic confinement devices is widely thought to arise due to linearly unstable gyroradius-scale modes. A long predicted characteristic of these linear instabilities is a critical gradient, where the modes are stable below a critical value related to the gradient providing free energy for the instability and unstable above it. In this dissertation, a critical gradient threshold for long wavelength ($k_{\theta} \rho_s \lesssim 0.4$) electron temperature fluctuations is reported, where the temperature fluctuations do not change, within uncertainties, below a threshold value in $L_{T_e}^{-1}=\nabla T_e / T_e$ and steadily increase above it. This principal result, the direct observation of a critical gradient for electron temperature fluctuations, is also the first observation of critical gradient behavior for \textit{any} locally measured turbulent quantity in the core of a high temperature plasma in a systematic experiment. The critical gradient was found to be $L_{T_e}^{-1}_{crit}=2.8 \pm 0.4 \ \mathrm{m}^{-1}$. The experimental value for the critical gradient quantitatively disagrees with analytical predictions for its value. In the experiment, the local value of $L_{T_e}^{-1}$ was systematically varied by changing the deposition location of electron cyclotron heating gyrotrons in the DIII-D tokamak. The temperature fluctuation measurements were acquired with a correlation electron cyclotron emission radiometer. The dimensionless parameter $\eta_e=L_{n_e}/L_{T_e}$ is found to describe both the temperature fluctuation threshold and a threshold observed in linear gyrofluid growth rate calculations over the measured wave numbers, where a rapid increase at $\eta_e \approx 2$ is observed in both. Doppler backscattering (DBS) measurements of intermediate-scale density fluctuations also show a frequency-localized increase on the electron diamagnetic side of the measured spectrum that increases with $L_{T_e}^{-1}$. Measurements of the crossphase angle between long wavelength electron density and temperature fluctuations, as well as measurements of long wavelength density fluctuation levels were also acquired. Multiple aspects of the fluctuation measurements and calculations are individually consistent with the attribution of the critical gradient to the $\nabla T_e$-driven trapped electron mode. The accumulated evidence strongly enforces this conclusion. The threshold value for the temperature fluctuation measurements was also within uncertainties of a critical gradient for the electron thermal diffusivity found through heat pulse analysis, above which the electron heat flux and electron temperature profile stiffness rapidly increased. Toroidal rotation was also systematically varied with neutral beam injection, which had little effect on the temperature fluctuation measurements. The crossphase measurements indicated the presence of different instabilities below the critical gradient depending on the neutral beam configuration, which is supported by linear gyrofluid calculations. In a second set of results reported in this dissertation, the geodesic acoustic mode is investigated in detail. Geodesic acoustic modes (GAMs) and zonal flows are nonlinearly driven, axisymmetric ($m=0,\ n=0$ potential) $E \times B$ flows, which are thought to play an important role in establishing the saturated level of turbulence in tokamaks. Zonal flows are linearly stable, but are driven to finite amplitude through nonlinear interaction with the turbulence. They are then thought to either shear apart the turbulent eddies or act as a catalyst to transfer energy to damped modes. Results are presented showing the GAM's observed spatial scales, temporal scales, and nonlinear interaction characteristics, which may have implications for the assumptions underpinning turbulence models towards the tokamak edge ($r/a \gtrsim 0.75$). Measurements in the DIII-D tokamak have been made with multichannel Doppler backscattering systems at toroidal locations separated by $180^{\circ}$; analysis reveals that the GAM is highly coherent between the toroidally separated systems ($\gamma> 0.8$) and that measurements are consistent with the expected $m=0,\ n=0$ structure. Observations show that the GAM in L-mode plasmas with $\sim 2.5-4.5$ MW auxiliary heating occurs as a radially coherent eigenmode, rather than as a continuum of frequencies as occurs in lower temperature discharges; this is consistent with theoretical expectations when finite ion Larmor radius effects are included. The intermittency of the GAM has been quantified, revealing that its autocorrelation time is fairly short, ranging from about 4 to about 15 GAM periods in cases examined, a difference that is accompanied by a modification to the probability distribution function of the $E \times B$ velocity at the GAM frequency. Conditionally-averaged bispectral analysis shows the strength of the nonlinear interaction of the GAM with broadband turbulence can vary with the magnitude of the GAM. Data also indicates a wave number dependence to the GAM's interaction with turbulence. Measurements also showed the existence of additional low frequency zonal flows (LFZF) at a few kilohertz in the core of DIII-D plasmas. These LFZF also correlated toroidally. The amplitude of both the GAM and LFZF were observed to depend on toroidal rotation, with both types of flows barely detectable in counter-injected plasmas. In a third set of results the development of diagnostic hardware, techniques used to acquire the above data, and related work is described. A novel multichannel Doppler backscattering system was developed. The five channel system operates in V-band (50-75 GHz) and has an array of 5 frequencies, separated by 350 MHz, which is tunable as a group. Laboratory tests of the hardware are presented. Doppler backscattering is a diagnostic technique for the radially localized measurement of intermediate-scale ($k_{\theta} \rho_s \sim 1$) density fluctuations and the laboratory frame propagation velocity of turbulent structures. Ray tracing, with experimental profiles and equilibria for inputs, is used to determine the scattering wave number and location. Full wave modeling, also with experimental inputs, is used for a synthetic Doppler backscattering diagnostic for nonlinear turbulence simulations. A number of non-ideal processes for DBS are also investigated; their impact on measurements in DIII-D are found, for the most part, to be small.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1994 with total page 1032 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.

Download or read book Experimental Characterization of Coherent Radially Sheared Zonal Flows in the DIII D Tokamak written by and published by . This book was released on 2002 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: A271 EXPERIMENTAL CHARACTERIZATION OF COHERENT, RADIALLY-SHEARED ZONAL FLOWS IN THE DIII-D TOKAMAK. Application of time-delay-estimation techniques to two-dimensional measurements of density fluctuations, obtained with beam emission spectroscopy in DIII-D plasmas, has provided temporally and spatially resolved measurements of the turbulence flow-field. Features that are characteristic of self-generated zonal flows are observed in the radial region near 0.85 {

Download or read book Experimental Study of Density Fluctuations in the STOR M Tokamak by Small angle Microwave Scattering written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1993 with total page 1058 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Plasma Science written by National Academies of Sciences Engineering and Medicine and published by . This book was released on 2021-02-28 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma Science and Engineering transforms fundamental scientific research into powerful societal applications, from materials processing and healthcare to forecasting space weather. Plasma Science: Enabling Technology, Sustainability, Security and Exploration discusses the importance of plasma research, identifies important grand challenges for the next decade, and makes recommendations on funding and workforce. This publication will help federal agencies, policymakers, and academic leadership understand the importance of plasma research and make informed decisions about plasma science funding, workforce, and research directions.

Download or read book Energy and Water Development Appropriations for 2009 Dept of Energy fiscal year 2009 justifications science environmental management defense nuclear waste disposal written by United States. Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development and published by . This book was released on 2008 with total page 1468 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Radio Frequency Power in Plasmas written by Donald B. Batchelor and published by American Institute of Physics. This book was released on 1992 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt: The proceedings of the Ninth Topical Conference on [title], held in Charleston, SC, August 1991, comprise invited and contributed papers on topics in the areas of electron cyclotron range of frequencies, lower hybrid range of frequencies, ion cyclotron range of frequencies, current drive, RF technol

Download or read book Government Reports Announcements Index written by and published by . This book was released on 1996 with total page 650 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book ERDA Energy Research Abstracts written by and published by . This book was released on 1989 with total page 848 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy and Water Development Appropriations for 2009 written by United States. Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development and published by . This book was released on 2008 with total page 1490 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nuclear Fusion written by and published by . This book was released on 1995-11 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book INIS Atomindex written by and published by . This book was released on 1995 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book China written by World Bank and published by World Bank Publications. This book was released on 1993 with total page 1422 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Republic of Korea's industrial policy has directed that nation's economy through nearly three decades of spectacular growth. But the authors of this paper maintain that this policy is showing signs of being outmoded. The time has come, the authors argue, for the Korean government to stop managing the economy's structural development and to redefine the responsibilities of business and government. Under this proposed compact, the allocation of resources would shift from the government to the private industrial and financial sectors. The transformation of the government bureaucracy from an ad hoc policy role to one of a transparent and predictable regulator is a key to the success of this undertaking. These new directions would present the government with enormous challenges. Greater competitive discipline and regulatory oversight would be required. While dealing with the complexities of the transition, the government would have to maintain macroeconomic stability and the momentum of savings and investment. For comparison, the study examines the industrial economies of France, Germany, Japan, and the United States, which underwent similar shifts.