Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator-CMOD H-modes PDF Download

Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 4

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Book Description

Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 4

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Book Description

Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 4

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Book Description

Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 8

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Book Description

Author: Redi M. H. Baumgaertel J. A. (Budny R. V.)
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Insight into plasma microturbulence and transport is being sought using linear simulations of drift waves on the National Spherical Torus Experiment (NSTX), following a study of drift wave modes on the Alcator C-Mod Tokamak. Microturbulence is likely generated by instabilities of drift waves, which cause transport of heat and particles. Understanding this transport is important because the containment of heat and particles is required for the achievement of practical nuclear fusion. Microtearing modes may cause high heat transport through high electron thermal conductivity. It is hoped that microtearing will be stable along with good electron transport in the proposed low collisionality International Thermonuclear Experimental Reactor (ITER). Stability of the microtearing mode is investigated for conditions at mid-radius in a high density NSTX high performance (H-mode) plasma, which is compared to the proposed ITER plasmas. The microtearing mode is driven by the electron temperature gradient, and believed to be mediated by ion collisions and magnetic shear. Calculations are based on input files produced by TRXPL following TRANSP (a time-dependent transport analysis code) analysis. The variability of unstable mode growth rates is examined as a function of ion and electron collisionalities using the parallel gyrokinetic computational code GS2. Results show the microtearing mode stability dependence for a range of plasma collisionalities. Computation verifies analytic predictions that higher collisionalities than in the NSTX experiment increase microtearing instability growth rates, but that the modes are stabilized at the highest values. There is a transition of the dominant mode in the collisionality scan to ion temperature gradient character at both high and low collisionalities. The calculations suggest that plasma electron thermal confinement may be greatly improved in the low-collisionality ITER.

Author: Juan Ruiz Ruiz (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 311

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In this thesis I perform an extensive validation study in an NSTX NBI-heated H-mode discharge, predicting that electron thermal transport can be entirely explained by shortwavelength electron-scale turbulence fluctuations driven by the electron temperature gradient mode (ETG), both in conditions of strong and weak ETG turbulence drive. For the first time, local, nonlinear gyrokinetic simulation carried out with the GYRO code [98] reproduce the experimental levels of electron thermal transport, the frequency spectrum of electron-scale turbulence, the shape of the wavenumber spectrum and the ratio of fluctuation levels between strongly driven and weakly driven ETG turbulence conditions. Ion thermal transport is very close to neoclassical levels predicted by NEO [215], consistent with stable ion-scale turbulence predicted by GYRO. Quantitative comparisons between high-k fluctuation measurements [65] and simulations are enabled via a novel synthetic high-k diagnostic implemented for GYRO in real-space. A new type of simulation resolving the full ETG spectrum in an unusually large domain (L[subscript r], L[subscript theta]) ~ (20, 20)[subscript rho subscript s] is required to quantitatively compare with the measured frequency spectra of the high-k density fluctuations. Simulations that best match all experimental observables predict that the measured high-k turbulence is closer to the streamer peak of the density fluctuation spectrum than was previously believed. The frequency spectra characteristics of electron-scale turbulence (spectral peak and width) can be consistently reproduced by the synthetic spectra, but these reveal not to be critical constraints on the simulations. The shape of the high-k wavenumber spectrum and the fluctuation level ratio between the strong and weak ETG conditions can also be simultaneously matched by electron-scale simulations within sensitivity scans about the experimental profile values, and result to be great discriminators of the simulations analyzed. Validation metrics are used to discriminate between simulations, are were able to isolate the effect of safety factor and magnetic shear to match the shape of the measured fluctuation wavenumber spectrum. Together, electron thermal transport comparisons and quantitative agreement of electron-scale turbulence spectra give the strongest experimental evidence to date supporting ETG-driven turbulence fluctuations as the main mechanism driving anomalous electron thermal transport in the outer-core of modest [beta] NSTX NBI-heated H-modes.

Author: M. H. Redi
Publisher:
ISBN:
Category : National Spherical Torus Experiment (Project).
Languages : en
Pages : 4

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Author: Martin Greenwald
Publisher:
ISBN:
Category :
Languages : en
Pages : 23

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Author:
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Category :
Languages : en
Pages :

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Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.

Author: Vladimir G. Ivancevic
Publisher: World Scientific Publishing Company Incorporated
ISBN: 9789814635868
Category : Science
Languages : en
Pages : 589

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Book Description
The book Complexity and Control: Towards a Rigorous Behavioral Theory of Complex Dynamical Systems is a graduate-level monographic textbook, intended to be a novel and rigorous contribution to modern Complexity Theory.This book contains 11 chapters and is designed as a one-semester course for engineers, applied and pure mathematicians, theoretical and experimental physicists, computer and economic scientists, theoretical chemists and biologists, as well as all mathematically educated scientists and students, both in industry and academia, interested in predicting and controlling complex dynamical systems of arbitrary nature.