Turbulent Transport In Magnetized Plasmas (Second Edition)


Book Description

For a few seconds with large machines, scientists and engineers have now created the fusion power of the stars in the laboratory and at the same time find the rich range of complex turbulent electromagnetic waves that transport the plasma confinement systems. The turbulent transport mechanisms created in the laboratory are explained in detail in the second edition of 'Turbulent Transport in Magnetized Plasmas' by Professor Horton.The principles and properties of the major plasma confinement machines are explored with basic physics to the extent currently understood. For the observational laws that are not understood — the empirical confinement laws — offering challenges to the next generation of plasma students and researchers — are explained in detail. An example, is the confinement regime — called the 'I-mode' — currently a hot topic — is explored.Numerous important problems and puzzles for the next generation of plasma scientists are explained. There is growing demand for new simulation codes utilizing the massively parallel computers with MPI and GPU methods. When the 20 billion dollar ITER machine is tested in the 2020ies, new theories and faster/smarter computer simulations running in near real-time control systems will be used to control the burning hydrogen plasmas.




Aspects of Anomalous Transport in Plasmas


Book Description

Anomalous transport is a ubiquitous phenomenon in astrophysical, geophysical and laboratory plasmas; and is a key topic in controlled nuclear fusion research. Despite its fundamental importance and ongoing research interest, a full understanding of anomalous transport in plasmas is still incomplete, due to the complexity of the nonlinear phenomena involved. Aspects in Anomalous Transport in Plasmas is the first book to systematically consider anomalous plasma transport theory and provides a unification of the many theoretical models by emphasizing interrelations between seemingly different methodologies. It is not intended as a catalogue of the vast number of plasma instabilities leading to anomalous transport; instead it chooses a number of these and emphasizes the aspects specifically due to turbulence. After a brief introduction, the microscopic theory of turbulence is discussed, including quasilinear theory and various aspects of renormalization methods, which leads to an understanding of resonance broadening, mode coupling, trajectory correlation and clumps. The second half of the book is devoted to stochiastic tramsport, using methods based on the Langevin equations and on Random Walk theory. This treatment aims at going beyond the traditional limits of weak turbulence, by introducing the recently developed method of decorrelation trajectories, and its application to electrostatic turbulence, magnetic turbulence and zonal flow generation. The final chapter includes very recent work on the nonlocal transport phenomenon.













Impurity Transport in Tokamak Plasmas


Book Description

Impurity transport is an issue of utmost importance for tokamaks. Indeed high-Z materials are only partially ionized in the plasma core, so that they can lead to prohibitive radiative losses even at low concentrations, and impact dramatically plasma performance and stability. On-axis accumulation of tungsten has been widely observed in tokamaks.While the very core impurity peaking is generally attributed to neoclassical effects, turbulent transport could well dominate in the gradient region at ITER relevant collisionality. Up to recently, first principles simulations of corresponding fluxes were performed with different dedicated codes, implicitly assuming that both transport channels are separable and therefore additive. The validity of this assumption is questionned. Simulations obtained with the gyrokinetic code GYSELA have shown clear evidences of a neoclassical-turbulence synergy for impurity transport and allowed the identification of a mechanism that underly this synergy.An analytical work allows to compute the level and the structure of the axisymmetric part of the electric potential knowing the turbulence intensity. Two mechanisms are found for the generation of poloidal asymmetries of the electric potential: flow compressibility and the ballooning of the turbulence. A new prediction for the neoclassical impurity flux in presence of large poloidal asymmetries and pressure anisotropies has been derived. A fair agreement has been found between the new theoretical prediction for neoclassical impurity flux and the results of a GYSELA simulation displaying large poloidal asymmetries and pressure anisotropies induced by the presence of turbulence.




Transport Analysis in Tokamak Plasmas


Book Description

One of the least understood areas of the plasma particle or heat transport is the turbulent transport. In this work the main focus is on the development and data analysis of anomalous transport characteristics (transport coefficients and fluxes) under fusion conditions in large tokamaks. Fluid and gyro-kinetic models are used and obtained results are compared. A model based on fractional kinetics for the study of the SOL turbulent transport characteristics, where non-Gaussian PDFs are observed, is developed.




Fluctuations and Transport in Fusion Plasmas. Final Report


Book Description

The energy confinement in tokamaks in thought to be limited by transport caused by plasma turbulence. Three dimensional plasma particle-in-cell (PIC) codes are used to model the turbulent transport in tokamaks to attempt to understand this phenomena so that tokamaks can be made more efficient. Presently, hundreds of hours of Cray time are used to model these experiments and much bigger and longer runs are desired, to model a large tokamak with realistic parameters is beyond the capability of existing sequential supercomputers. Parallel supercomputers might be a cost effect tool for performing such large scale 3D tokamak simulations. The goal of the work was to develop algorithms for performing PIC codes on coarse-grained message passing parallel computers and to evaluate the performance of such parallel computers on PIC codes. This algorithm would be used in a large scale PIC production code such as the UCLA 3D gyrokinetic code.







Understand and Predict the Power Threshold Leading to Reduced Turbulent Transport at the Edge of Tokamak Plasma


Book Description

A model based on a model which natively contained turbulence and turbulence driven flow. It has been improved to include the diamagnetic effects, the magnetic fluctuations, and in this work, we study the parametric dependencies of the observed L-H transition power threshold with respect to the ion mass. By including the diamagnetic effects in our model, we allow the competition between the drift waves and the interchange instabilities. This competition is here studied using fixed gradient simulation. We show in this work that the diamagnetic effects are stabilizing for a resistivity close to experimental conditions. Electromagnetic effects lead to more unstable modes at realistic resistivities. Moreover, a quasilinear estimation of the turbulent flux is able to qualitatively grasp the competition between the drift waves and the interchange and the behaviour of the nonlinear electrostatic turbulent flux with resistivity and plasma beta. Another parametric dependency of the turbulence is studied, by changing the mass of the isotope. This is known as the isotope effect. We show here that the turbulence is reduced when the ion mass is increased. Finally, the characteristic times of the turbulence are studied.Magnetic fluctuations have a dramatic effect on correlation times of the turbulence, by drastically reducing them. Accounting for these results, we present in this work the auto-generation of a transport barrier with electromagnetic simulations of edge turbulence, when the heat power is higher than a threshold, using flux-driven simulations. We have then changed the isotope, and correspondingly to experiments, the power threshold is lower for higher isotope mass.