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Integrated Model for Transport and Large Scale Instabilities in Tokamak Plasmas

2009
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Release : 2009
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Kind : eBook
Book Rating : 835/5 ( reviews)

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Book Synopsis Integrated Model for Transport and Large Scale Instabilities in Tokamak Plasmas by : Federico David Halpern

Download or read book Integrated Model for Transport and Large Scale Instabilities in Tokamak Plasmas written by Federico David Halpern. This book was released on 2009. Available in PDF, EPUB and Kindle. Book excerpt: Improved models for neoclassical tearing modes and anomalous transport are developed and validated within integrated modeling codes to predict toroidal rotation, temperature and current density profiles in tokamak plasmas. Neoclassical tearing modes produce helical filaments of plasma, called magnetic islands, which have the effect of degrading tokamak plasma confinement or terminating the discharge. An improved code is developed in order to compute the widths of multiple simultaneous magnetic islands whose shapes are distorted by the radial variation in the magnetic perturbation [F. D. Halpern, et al., J. Plasma Physics 72 (2006) 1153]. It is found in simulations of DIII-D and JET tokamak discharges that multiple simultaneous magnetic islands produce a 10% to 20% reduction in plasma thermal confinement. If magnetic islands are allowed to grow to their full width in ITER fusion reactor simulations, fusion power production is reduced by a factor of four [F. D. Halpern, et al., Phys. Plasmas 13 (2006) 062510]. In addition to improving the prediction of neoclassical tearing modes, a new Multi-Mode transport model, MMM08, was developed to predict temperature and toroidal angular frequency profiles in simulations of tokamak discharges. The capability for predicting toroidal rotation is motivated by ITER simulation results that indicate that the effects of toroidal rotation can increase ITER fusion power production [F. D. Halpern et al., Phys. Plasmas 15 (2008), 062505]. The MMM08 model consists of an improved model for transport driven by ion drift modes [F. D. Halpern et al., Phys. Plasmas 15 (2008) 012304] together with a model for transport driven by short wavelength electron drift modes combined with models for transport driven by classical processes. The new MMM08 transport model was validated by comparing predictive simulation results with experimental data for 32 discharges in the DIII-D and JET tokamaks. It was found that the prediction of intrinsic plasma rotation is consistent with experimental measurements in discharges with zero net torque. A scaling relation was developed for the toroidal momentum confinement time (angular momentum divided by net torque) as a function of plasma current and torque per ion.

Predictive Integrated Modeling of Low Aspect Ratio Tokamaks and Large Scale Instabilities in Tokamaks

2004 Tokamaks
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Release : 2004
Genre : Tokamaks
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Book Synopsis Predictive Integrated Modeling of Low Aspect Ratio Tokamaks and Large Scale Instabilities in Tokamaks by : Canh Ngoc Nguyen

Download or read book Predictive Integrated Modeling of Low Aspect Ratio Tokamaks and Large Scale Instabilities in Tokamaks written by Canh Ngoc Nguyen. This book was released on 2004. Available in PDF, EPUB and Kindle. Book excerpt: Models for large scale instabilities in tokamaks are developed, and they are tested together with models for transport and other physical processes by comparing the results of BALDUR integrated predictive modeling simulations with experimental data from tokamaks. Simulations are carried out for the low aspect ratio tokamaks, Mega Ampere Spherical Tokamak and the National Spherical Torus Experiment, to test the applicability of models that were developed for conventional tokamaks. The results indicate that neoclassical transport dominates over anomalous transport in the inner third of the plasma. Sawtooth oscillations, which are the result of an instability that periodically redistributes the central part of the plasma profiles, play a significant role by radially spreading the neutral beam injection heating profiles across the broad sawtooth mixing region. Two models for sawtooth oscillations, the Porcelli and the Kadomtsev models, are combined and tested against experimental data from the Joint European Torus and the Tokamak Fusion Test Reactor. Most of the sawtooth crashes are triggered by the m = 1 resistive internal kink mode in the semi-collisional regime. The median sawtooth period increases with increasing magnetic reconnection fraction. The best overall agreement with experimental data is obtained with a magnetic reconnection fraction of approximately 55%. Finally, plasma pressure effects are included in a quasi-linear model for saturated tearing modes, which are instabilities that produce magnetic islands. The model is used in a stand-alone code, and in the BALDUR code, to calculate the widths of saturated magnetic islands in tokamak plasmas with arbitrary cross-section and plasma pressure. The widths of tearing mode islands increase with decreasing aspect ratio and with increasing elongation. Also, the island widths increase when the gradient of the current density increases at the edge of the islands or when the current density inside the islands is suppressed. The widths oscillate in time in response to periodic sawtooth crashes. Local enhancements in the transport produced by magnetic islands have a noticeable effect on global plasma confinement in simulations of low aspect ratio, high beta tokamaks, where saturated tearing mode islands can occur with widths greater than 15% of the plasma minor radius.

Theory of Tokamak Plasmas

2017-01-31 Science
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Release : 2017-01-31
Genre : Science
Kind : eBook
Book Rating : 262/5 ( reviews)

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Book Synopsis Theory of Tokamak Plasmas by : R.B. White

Download or read book Theory of Tokamak Plasmas written by R.B. White. This book was released on 2017-01-31. Available in PDF, EPUB and Kindle. Book excerpt: This is a graduate textbook on tokamak physics, designed to provide a basic introduction to plasma equilibrium, particle orbits, transport, and those ideal and resistive magnetohydrodynamic instabilities which dominate the behavior of a tokamak discharge, and to develop the mathematical methods necessary for their theoretical analysis.

Advanced Tokamak Stability Theory

2014-04-01 Science
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Release : 2014-04-01
Genre : Science
Kind : eBook
Book Rating : 072/5 ( reviews)

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Book Synopsis Advanced Tokamak Stability Theory by : Linjin Zheng

Download or read book Advanced Tokamak Stability Theory written by Linjin Zheng. This book was released on 2014-04-01. Available in PDF, EPUB and Kindle. Book excerpt: This book describes the advanced stability theories for magnetically confined fusion plasmas, especially in tokamaks. As the fusion plasma sciences advance, the gap between the textbooks and cutting-edge researches gradually develops. This book fills in

Predictive Models for the Edge of Tokamak H-mode Plasmas

2004 Plasma (Ionized gasses)
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Release : 2004
Genre : Plasma (Ionized gasses)
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Book Synopsis Predictive Models for the Edge of Tokamak H-mode Plasmas by : Thawatchai Onjun

Download or read book Predictive Models for the Edge of Tokamak H-mode Plasmas written by Thawatchai Onjun. This book was released on 2004. Available in PDF, EPUB and Kindle. Book excerpt: High confinement (H-mode) discharges in tokamak experiments are characterized by a narrow region of steep pressure gradient called the "pedestal" that forms at the edge of the plasma, and often by an instability called an "Edge Localized Mode (ELM)" that periodically removes energy and particles from the edge of the plasma. The parameters at the top of the pedestal and the characteristics of ELMs have a strong influence on the performance of H-mode discharges. In this study, models for the pedestal are developed initially without including the effects of ELMs. The predictions from these pedestal models yield reasonable agreement with experimental data. These pedestal models are then used to provide boundary conditions in an integrated modeling code in order to simulate plasma profiles, such as temperature and density profiles, in existing H-mode experiments. The simulated profiles obtained using predictive boundary conditions and those obtained using experimental boundary conditions have similar agreement with experimental profiles. A more advanced pedestal model with a dynamic model for ELM crashes is developed using a concept of turbulence suppression at the edge of plasma. These pedestal and ELM models are coupled with a core transport model in an integrated modeling code. An advantage of this approach is that it allows for the evolution of plasma pressure and current profiles in the pedestal region, which can lead to an instability that triggers ELM crashes that limit the growth of the pedestal. Pressure-driven ballooning and current-driven peeling instabilities are considered as the possible instabilities that trigger ELM crashes. The combined core and pedestal models, with the effect of ELMs included, are used to study the dependence of triangularity and heating power on the pedestal. An MHD stability analysis is also performed to confirm the validity of these simulations. It is found that plasma edge stability improves as triangularity increases, as a result of access to the second stability region of ballooning modes. Finally, simulations yield a pedestal height with a dependence on heating power similar to that observed experimentally when the ELM crash model is extended to include ELMS triggered by current-driven peeling instabilities.

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