Download or read book Reduced MHD modeling of tearing mode interactions in Tokamaks written by J. W. Eastwood and published by . This book was released on 1986 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Computational Modeling of Neoclassical and Resistive MHD Tearing Modes in Tokamaks written by and published by . This book was released on 1996 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tearing Mode Dynamics in Tokamak Plasmas written by Nikolaos Vergos and published by . This book was released on 2016 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most problematic instabilities in tokamak plasmas is tearing modes; they are driven by current and pressure gradients, and involve a reconfiguration of the magnetic and velocity fields localized into a narrow region located at a resonant magnetic surface. While the equilibrium magnetic field lines are located on concentric nested toroidal flux surfaces, the instability creates magnetic islands in which field lines connect flux tubes together, allowing for a high radial heat transport, and, thus, resulting in a loss of confinement, and, potentially, disruptions. In order for the magnetic field lines to break and reconnect, we need to take into account the resistivity of the plasma and solve the resistive magnetohydrodynamics (MHD) equations. The analytical solution consists of a boundary layer analysis (asymptotic matching) and takes advantage of the small radial width of the region where the perturbations vary significantly. Indeed, ideal magnetohydrodynamics can be used everywhere except in that narrow region where the full resistive problem must be solved. This dissertation addresses two related problems in the study of resistive tearing modes, and their interactions with externally induced resonant magnetic perturbations (error-fields). First, an in-depth investigation of the bifurcated states of a rotating, quasi-cylindrical, tokamak plasma in the presence of a resonant error-field is performed, within the context of constant-[greek letter psi] resistive MHD theory. The response of the rotating plasma is studied in both the linear, and the nonlinear regime. In general, there is a "forbidden band" of tearing mode rotation frequencies that separates a branch of high-frequency solutions from a branch of low-frequency solutions. When a high-frequency solution crosses the upper boundary of the forbidden band there is a bifurcation to a low-frequency solution, and vice versa. Second, the analysis is extended to include the study of braking and locking of tearing mode rotation by the interaction of the mode with an error-field. It is found that this interaction can brake the plasma rotation, suppress magnetic island evolution and drive locked modes.
Download or read book Computational Modeling of Neoclassical and Resistive MHD Tearing Modes in Tokamaks written by Thomas A. Gianakon and published by . This book was released on 1996 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reduced Equations for Finite Beta Tearing Modes in Tokamaks written by and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The equations of resistive magnetohydrodynamics (MHD) are recast in a form that is useful for studying the evolution of those toroidal systems where the fast magnetosonic wave plays no important role. The equations are exact and have nabla vector. B vector = O satisfied explicitly. From this set of equations it is a simple matter to derive the equations of reduced MHD to any order in the inverse aspect ratio epsilon of the torus, and for .beta. approx. epsilon or smaller. We demonstrate this by deriving a reduced set of MHD equations that are correct to 5th order in epsilon. These equations contain the exact equilibrium relation and as such can be used to find 3-D stellarator equilibria. In addition, if a subsidiary ordering in eta, the resistivity, is made, the equations of Glasser, Greene, and Johnson are recovered. This set of reduced equations has been coded by extending the initial value code, HILO. Results obtained, for both ideal and resistive linear stability, from the reduced equations are compared with those obtained by solving the full set of MHD equations in a cylinder. The agreement is shown to be excellent for both zero and finite beta calculations. Comparisons are also made with analytic theory illuminating the present limitations of the latter.
Download or read book 3 D Resistive MHD Calculations for Tokamak Plasmas written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerical studies of the resistive stability of tokamak plasmas in cylindrical geometry have been performed using: (1) the full set of resistive Magnetohydrodynamic (MHD) equations and (2) an extended version of the reduced set of resistive MHD equations including diamagnetic and electron temperature effects. In particular, the nonlinear interaction of tearing modes of many helicities has been investigated. The numerical results confirm many of the features uncovered previously using the simple reduced equations.
Download or read book Magnetohydrodynamic Stability of Tokamaks written by Hartmut Zohm and published by John Wiley & Sons. This book was released on 2015-02-09 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book bridges the gap between general plasma physics lectures and the real world problems in MHD stability. In order to support the understanding of concepts and their implication, it refers to real world problems such as toroidal mode coupling or nonlinear evolution in a conceptual and phenomenological approach. Detailed mathematical treatment will involve classical linear stability analysis and an outline of more recent concepts such as the ballooning formalism. The book is based on lectures that the author has given to Master and PhD students in Fusion Plasma Physics. Due its strong link to experimental results in MHD instabilities, the book is also of use to senior researchers in the field, i.e. experimental physicists and engineers in fusion reactor science. The volume is organized in three parts. It starts with an introduction to the MHD equations, a section on toroidal equilibrium (tokamak and stellarator), and on linear stability analysis. Starting from there, the ideal MHD stability of the tokamak configuration will be treated in the second part which is subdivided into current driven and pressure driven MHD. This includes many examples with reference to experimental results for important MHD instabilities such as kinks and their transformation to RWMs, infernal modes, peeling modes, ballooning modes and their relation to ELMs. Finally the coverage is completed by a chapter on resistive stability explaining reconnection and island formation. Again, examples from recent tokamak MHD such as sawteeth, CTMs, NTMs and their relation to disruptions are extensively discussed.
Download or read book Tearing Mode Analysis in Tokamaks Revisited written by and published by . This book was released on 1997 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Resistive MHD Mode Structures in a Tokamak written by Hwan-Young Che and published by . This book was released on 1993 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Coupling of Tearing Modes in Tokamaks written by J. Michael Finn and published by . This book was released on 1977 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Theory of Fusion Plasmas written by Olivier Sauter and published by American Institute of Physics. This book was released on 2008-12-02 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Joint Varenna-Lausanne International Workshop on Theory of Fusion Plasmas takes place every other year in a place particularly favorable for informal and in depth discussions. Invited and contributed papers present state-of-the art researches in theoretical plasma physics, covering all domains relevant to fusion plasmas. This workshop always allows a fruitful mix of experienced researchers and students, to allow for a better understanding of the key theoretical physics models and applications, such as: Theoretical issues related to burning plasmas; Anomalous Transport (Turbulence, Coherent Structures, Microinstabilities) RF Heating and Current Drive; Macroinstabilities; Plasma-Edge Physics and Divertors; Fast particles instabilities.
Download or read book Multi scale Interactions of Tearing Modes with Microturbulence and Itg Saturation channel Selection written by Taweesak Jitsuk and published by . This book was released on 2024 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Global tearing modes (TMs) can interact among themselves or with small-scale instabilities, exerting profound influence on fusion plasma performance. Experiments in reversed-field pinches (RFPs) demonstrate that TMs couple, cascade, and cause robust transport, while partial suppression of their activity can result in enhanced confinement. The presence of unstable drift waves during the TM cascade in the RFP allows interactions with microinstabilities. Local gyrokinetic simulations with externally imposed magnetic perturbations modeling TMs have demonstrated that the magnetic perturbations erode zonal flows that are nonlinearly generated by the microinstabilities, resulting in higher turbulence levels. Similarly, when resonant magnetic perturbations (RMPs) are applied to mitigate edge-localized modes in tokamaks, the RMPs suppress the zonal flows, which in turn can increase the heat flux. These phenomena highlight the importance of multi-scale interactions between large-scale magnetic fluctuations and zonal-flow-regulated microturbulence, an incompletely understood topic. For a comprehensive understanding of these interactions, self-consistent computations simultaneously evolving TMs and small-scale fluctuations are needed. Here, calculations are performed with the global gyrokinetic code GENE, which was modified to include a background current density. This provides the TM drive, and it is verified that the modified GENE code properly models global TMs. Working towards multi-scale simulations, a non-reversed RFP discharge is studied; linear simulations show that the non-reversed equilibrium is unstable to large-scale TMs, which dominate in the core region, while small-scale density-gradient-driven TEMs dominate near the plasma edge. Nonlinear simulations with only TMs show that large-scale TMs in the core are coupled and excite smaller-scale stable TMs. The latter resonates at rational surfaces closer to the edge, where TEMs are active, indicating that multi-scale interactions are possible. In nonlinear global TEM simulations, zonal flows dominate the saturated state, leading to negligible transport in the absence of TMs, consistent with local simulations. When TMs and TEMs are simultaneously included in nonlinear simulations, TMs partially erode zonal flows. This erosion of zonal flows disrupts energy mediation by zonal flows, leading to a significant increase in heat flux. However, the zonal flows remain a dominant characteristic of fluctuations, causing the transport fluxes to remain much smaller than in experiments. To quantitatively reproduce experiments in future work, higher density gradients are required to weaken the zonal flows, or a stronger TM drive is needed to intensify the magnetic perturbations. These multi-scale simulations offer valuable insights for understanding RFP experiments and studying potential interactions of MHD phenomena and microturbulence in tokamaks. In contrast to TEM behavior, static magnetic perturbations do not strongly affect the ITG-driven turbulence of RFPs. This is because the ITG in RFPs is characterized by a slab limit and does not rely as strongly on zonal flows for saturation; instead, it depends on marginal modes. Zonal flows, on the other hand, play a crucial role in toroidal-ITG saturation. This prompts the exploration of saturation-channel selection rules that capture the preference of the toroidal limit for zonal flows and of the slab limit for marginal modes. Nonlinear coupling quantities are determined, and the triplet correlation time and mode overlap results are presented. Combining these metrics allows for predicting the dominant saturation channel for a given physical-parameter scenario, providing a powerful new tool that will aid a deeper understanding of nonlinear interactions and may also be used to enhance reduced models of anomalous transport.
Download or read book Mode Coupling Trigger of Neoclassical Magnetohydrodynamic Tearing Modes in Tokamaks written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerical studies of the nonlinear evolution of coupled magnetohydrodynamic - type tearing modes in three-dimensional toroidal geometry with neoclassical effects are presented. The inclusion of neoclassical physics introduces an additional free-energy source for the nonlinear formation of magnetic islands through the effects of a bootstrap current in Ohm's law. The neoclassical tearing mode is demonstrated to be destabilized in plasmas which are otherwise[Delta][prime] stable, albeit once a threshold island width is exceeded. A possible mechanism for exceeding or eliminating this threshold condition is demonstrated based on mode coupling due to toroidicity with a pre-existing instability at the q= 1 surface.
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 INIS Atomindex written by and published by . This book was released on 1994 with total page 540 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 1990 with total page 852 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1976 with total page 612 pages. Available in PDF, EPUB and Kindle. Book excerpt:
