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Simulations Of Reversed Shear Alfven Eigenmodes In Fusion Plasmas
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Book Synopsis Simulations of Reversed Shear Alfvén Eigenmodes in Fusion Plasmas by : Wenjun Deng
Download or read book Simulations of Reversed Shear Alfvén Eigenmodes in Fusion Plasmas written by Wenjun Deng and published by LAP Lambert Academic Publishing. This book was released on 2012-07 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: In fusion plasmas, generated from heating sources or fusion products, energetic particles can excite Alfven eigenmodes, which undermines energetic particle confinement. To reduce or avoid this problem, behaviors of energetic particles and Alfven eigenmodes need to be studied in detail. In this book, a nonlinear gyrokinetic simulation model, which recovers the ideal magnetohydrodynamic (MHD) theory in the linear long-wavelength regime, is formulated for studying kinetic MHD processes in magnetized plasmas. This comprehensive formulation enables gyrokinetic simulation of both pressure gradient-driven and current-driven instabilities including ideal and kinetic ballooning modes, kink modes, and shear Alfven waves, as well as their nonlinear interactions in multi-scale simulations. Implemented in the gyrokinetic toroidal code (GTC), the new formulation is verified in simulations of reversed shear Alfven eigenmode (RSAE). The verified model is then applied to studying the linear properties of RSAE driven by density gradient of neutral beam injected fast ions in a well-diagnosed DIII-D tokamak experiment.
Book Synopsis Gyrokinetic Particle Simulations of Reversed Shear Alfvén Eigenmodes in Fusion Plasmas by : Wenjun Deng
Download or read book Gyrokinetic Particle Simulations of Reversed Shear Alfvén Eigenmodes in Fusion Plasmas written by Wenjun Deng and published by . This book was released on 2011 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: A nonlinear gyrokinetic simulation model, which recovers the ideal magnetohydrodynamic (MHD) theory in the linear long-wavelength regime is formulated for studying kinetic MHD processes in magnetized plasmas. This comprehensive formulation enables gyrokinetic simulation of both pressure gradient-driven and current-driven instabilities including ideal and kinetic ballooning modes, kink modes, and shear Alfvén waves, as well as their nonlinear interactions in multi-scale simulations. Implemented in the gyrokinetic toroidal code (GTC), the new formulation is verified in simulations of reversed shear Alfvén eigenmode (RSAE) in fusion plasmas. The antenna excitation of RSAE provides verifications of its mode structure, frequency and damping rate from the initial perturbation simulation with kinetic thermal ions. When excited by fast ions, their non-perturbative contributions modify the mode structure relative to the ideal MHD theory. With inclusion of thermal plasma pressure, the mode frequency increases due to the elevation of the Alfvén continuum by the geodesic compressibility. The GTC simulations have been benchmarked with extended hybrid MHD-gyrokinetic simulations. The verified gyrokinetic simulation model is applied to studying the linear properties of RSAE driven by density gradient of neutral beam injected fast ions in a well-diagnosed DIII-D tokamak experiment (discharge #142111). GTC simulations find that weakly damped RSAE exists due to toroidal coupling and other geometric effects. Various damping and driving mechanisms are identified and measured in the simulations, which shows that accurate damping and growth rate calculation requires true mode structure from non-perturbative, fully self-consistent simulation. The mode structure has no up-down symmetry mainly due to the radial symmetry breaking by the radial variation of fast ion density gradient, as measured in the experiment by electron cyclotron emission imaging. The RSAE frequency up-sweeping and the mode transition from RSAE to toroidal Alfvén eigenmode are in good agreement with the experimental results when scanning the values of the minimum safety factor in simulations. Good agreements in frequencies, growth rates, and mode structures are obtained among simulations of gyrokinetic codes GTC and GYRO, and an MHD-hybrid code TAEFL, which provide further verification and validation of the gyrokinetic model for simulating the kinetic MHD processes. As a prelude to nonlinear simulations of RSAE and associated fast ion transport, properties of microturbulence in reversed shear plasmas are also studied.
Book Synopsis A Study of Reversed Shear Alfvén Eigenmodes in Alcator C-Mod with Phase Contrast Imaging by : Eric Matthias Edlund
Download or read book A Study of Reversed Shear Alfvén Eigenmodes in Alcator C-Mod with Phase Contrast Imaging written by Eric Matthias Edlund and published by . This book was released on 2009 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shear Alfvén waves are a fundamental mode of magnetized plasma oscillation and may exist in tokamak plasmas as eigenmodes with a global structure and discrete frequencies. The inhomogeneity of the plasma profiles in conjunction with tokamak geometry tends to focus the Alfvén waves in regions of near uniformity defined by local extrema in the Alfvén continuum, a quantity which describes the local Alfvén resonance frequency for particular mode numbers. Modes excited in the vicinity of these near uniform regions may be weakly damped and excited by energetic ions. The reversed shear Alfvén eigenmode (RSAE), localized deep in the plasma core, is typically associated with a minimum in q in reversed magnetic shear configurations. RSAEs have proven especially useful for MHD spectroscopy, that is the inference of plasma equilibrium properties through their frequency spectra, due to their high sensitivity to the value of qmin. Reversed shear equilibria during the current ramp-up phase and sawtoothing phase are studied through the spatial and temporal characteristics of the RSAEs. Analysis of the spatial structures of RSAEs measured by phase contrast imaging, and interpreted with a synthetic diagnostic using numerical results from the ideal MHD code NOVA, provides constraints on the evolution of qmi,. Additional observations including mode coupling, mode tunneling, and minimum frequency scaling are discussed in light of theoretical and numerical models, with commentary on possible future experiments.
Download or read book Double Gap Alfvén Eigenmodes written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new type of global shear Alfvén Eigenmode is found in tokamak plasmas where the mode localization is in the region intersecting the Alfvén continuum. The eigenmode is formed by the coupling of two solutions from two adjacent gaps (akin to potential wells) in the shear Alfvén continuum. For tokamak plasmas with reversed magnetic shear it is shown that the toroidiciy-induced solution tunnels through the continuum to match the ellipticity-induced Alfvén eigenmode (TAE and EAE, respectively) so that the resulting solution is continuous at the point of resonance with the continuum. The existence of these Double Gap Alfvén Eigenmodes (DGAEs) allows for potentially new ways of coupling edge fields to the plasma core in conditions where the core region is conventionally considered inaccessible. Implications include new approaches to heating and current drive in fusion plasmas as well as its possible use as core diagnostic in burning plasmas.
Book Synopsis Energetic Particles in Tokamak Plasmas by : Sergei Sharapov
Download or read book Energetic Particles in Tokamak Plasmas written by Sergei Sharapov and published by CRC Press. This book was released on 2021-04-02 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of energetic particles in magnetic fusion plasmas is key to the development of next-generation "burning" plasma fusion experiments, such as the International Thermonuclear Experimental Reactor (ITER) and the Demonstration Power Station (DEMO). This book provides a comprehensive introduction and analysis of the experimental data on how fast ions behave in fusion-grade plasmas, featuring the latest ground-breaking results from world-leading machines such as the Joint European Torus (JET) and the Mega Ampere Spherical Tokamak (MAST). It also details Alfvenic instabilities, driven by energetic ions, which can cause enhanced transport of energetic ions. MHD spectroscopy of plasma via observed Alfvenic waves called "Alfvén spectroscopy" is introduced and several applications are presented. This book will be of interest to graduate students, researchers, and academics studying fusion plasma physics. Features: Provides a comprehensive overview of the field in one cohesive text, with the main physics phenomena explained qualitatively first. Authored by an authority in the field, who draws on his extensive experience of working with energetic particles in tokamak plasmas. Is suitable for extrapolating energetic particle phenomena in fusion to other plasma types, such as solar and space plasmas.
Book Synopsis Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes by :
Download or read book Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
Book Synopsis Exascale Scientific Applications by : Tjerk P. Straatsma
Download or read book Exascale Scientific Applications written by Tjerk P. Straatsma and published by CRC Press. This book was released on 2017-11-13 with total page 607 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes practical programming approaches for scientific applications on exascale computer systems Presents strategies to make applications performance portable Provides specific solutions employed in current application porting and development Illustrates domain science software development strategies based on projected trends in supercomputing technology and architectures Includes contributions from leading experts involved in the development and porting of scientific codes for current and future high performance computing resources
Book Synopsis Controlled Stabilization of Alfvén Eigenmodes in DIII-D and Validation of Theory and Simulations by : Shawn Tang
Download or read book Controlled Stabilization of Alfvén Eigenmodes in DIII-D and Validation of Theory and Simulations written by Shawn Tang and published by . This book was released on 2021 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the interaction between wave excitation and damping is essential in the advancement of research on magnetized plasmas in space, laboratory, and astrophysical settings. Alfv\'en waves can be excited across all of these settings, and in fusion research plasmas such as tokamak plasmas, they are present due to energetic particles from neutral beam injection and fusion reactions. The interplay between wave-particle interaction and damping processes is at the core of understanding wave excitation. \\ In the work presented in this dissertation, an experiment was designed to investigate high frequency Alfv\'en waves excited through Doppler-shifted cyclotron resonance with energetic particles from neutral beam injection in the DIII-D tokamak. These waves, compressional (CAE) and global (GAE) Alfv\'en eigenmodes, typically have frequencies close to the ion cyclotron frequency $f_{ci}$; the frequency and amplitude of these modes was measured with the Ion Cyclotron Emission (ICE) diagnostic. The experiment utilized the unique capability of the DIII-D neutral beams to separately control the energy and injection rate. A parametric scan across many magnetic fields and beam geometries was performed to study the dependencies of these modes on various plasma parameters.\\ An energetic ion density threshold was observed during a discharge in which the voltage of an off-axis co-injecting beam was held constant while the current was ramped down by $40\%$. During this discharge, a spectrum of high frequency AEs at $f=0.58f_{ci}$ was stabilized via a controlled energetic ion density ramp for the first time in a fusion research plasma. This observation demonstrates an important property of resonant AEs: that the growth rate of these waves is set by the balance between fast-ion drive and damping processes. The controlled stabilization of this mode also validates previous simulations done on high frequency AEs in which an instability threshold was observed by varying the beam density without changing the shape of the distribution. \\ The scaling of the amplitude of this wave with the beam injection rate was found to be consistent with predictions for single mode collisional saturation near marginal stability. Analytic theory found that for the observed beam injection rate threshold, the mode was near marginal stability throughout the entire beam ramp. This is notably different from previous simulations of CAEs/GAEs that were in the collisionless regime and often far from marginal stability. \\ Modeling codes such as TRANSP and ORB\_GC were used to model and analyze the fast-ion distribution for this discharge. This analysis found that the modes were likely excited by a high energy subset of the fast-ion population with strong gradients in parallel velocity space. Resonance analysis of this subset of the fast-ion population, in conjunction with considerations from dispersion relations, shows that the mode is likely a shear-polarized GAE. This marks the first identification of a GAE excited through Doppler-shifted cyclotron resonance with sub-Alfv\'enic energetic ions, a first in fusion research plasmas.
Book Synopsis Journal of the Physical Society of Japan by :
Download or read book Journal of the Physical Society of Japan written by and published by . This book was released on 2016 with total page 934 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Supercomputing by : Julian M. Kunkel
Download or read book Supercomputing written by Julian M. Kunkel and published by Springer. This book was released on 2013-06-12 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book constitutes the refereed proceedings of the 28th International Supercomputing Conference, ISC 2013, held in Leipzig, Germany, in June 2013. The 35 revised full papers presented together were carefully reviewed and selected from 89 submissions. The papers cover the following topics: scalable applications with 50K+ cores; performance improvements in algorithms; accelerators; performance analysis and optimization; library development; administration and management of supercomputers; energy efficiency; parallel I/O; grid and cloud.
Book Synopsis Experimental Measurements and Numerical Modeling of Fast-ion Distributions in the Alcator C-Mod Tokamak by : Aaron Craig Bader
Download or read book Experimental Measurements and Numerical Modeling of Fast-ion Distributions in the Alcator C-Mod Tokamak written by Aaron Craig Bader and published by . This book was released on 2012 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis we discuss measurements and modeling of minority heated fast-ion distributions in the Ion Cyclotron Range of Frequencies (ICRF) on the Alcator C-Mod tokamak. Analysis of fast-ions >100Te is important for both ITER and a future fusion reactor as both will have a significant population of 3.5 MeV alpha particles generated in fusion reactions. Fast particles in this energy range can drive unstable modes such as Toroidal Alfvén Eigenmodes (TAEs) and Reversed Shear Alfvén Eigenmodes (RSAEs). Furthermore, energetic ions may display plasma properties that differ from the bulk plasma. It is crucial to benchmark current simulation codes with measurements from highly energetic fast-ions on current devices. This thesis will focus on measurements of the fast-ion distribution made on C-Mod with an upgraded Compact Neutral Particle Analyzer (CNPA). Measurements of the fast-ion distributions will reveal strong dependences of the fast-ion effective temperature on both electron density and plasma current. For further analysis, we use the simulated distributions generated by the coupled full-wave spectral solver AORSA, with the zero orbit-width bounce-averaged Fokker-Planck code CQL3D. A new synthetic diagnostic integrated into CQL3D is used to make direct comparisons with the CNPA. We find that for plasmas that have a steady-state fast-ion distribution (df /dt = 0) the simulation and the experiment have good agreement. However, in simulations where the fast-ion distribution is evolving in time (df/dt =/ 0) we find a discrepancy between the simulation and the experimental results. The simulation is seen to evolve much slower than the experiment. Various reasons for the discrepancy are explored, including the possibility of a violation of the quasi-linear theory used in CQL3D.
Download or read book Fusion Nucléaire written by and published by . This book was released on 2005 with total page 714 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Gyrokinetic Simulation of TAE in Fusion Plasmas by : Zhixuan Wang
Download or read book Gyrokinetic Simulation of TAE in Fusion Plasmas written by Zhixuan Wang and published by . This book was released on 2014 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Linear gyrokinetic simulation of fusion plasmas finds a radial localization of the toroidal Alfvén eigenmodes (TAE) due to the non-perturbative energetic particles (EP) contribution. The EP-driven TAE has a radial mode width much smaller than that predicted by the magnetohydrodynamic (MHD) theory. The TAE radial position stays around the strongest EP pressure gradients when the EP profile evolves. The non-perturbative EP contribution is also the main cause for the breaking of the radial symmetry of the ballooning mode structure and for the dependence of the TAE frequency on the toroidal mode number. These phenomena are beyond the picture of the conventional MHD theory. Linear gyrokinetic simulation of the electron cyclotron heating (ECH) experiments on DIII-D successfully recover the TAE and RSAE. The EP profile, rather than the electron temperature, is found to be the key factor determining whether TAE or RSAE is the dominant mode in the system in our simulation. Investigation on the nonlinear gyrokinetic simulation model reveals a missing nonlinear term which has important contributions to the zonal magnetic fields. A new fluid-electron hybrid model is proposed to keep this nonlinear term in the lowest order fluid part. Nonlinear simulation of TAE using DIII-D parameters confirms the importance of this new term for the zonal magnetic fields. It is also found that zonal structures dominated by zonal electric fields are forced driven at about twice the linear growth rate of TAE in the linear phase. The zonal flows then limit the nonlinear saturation level by tearing the eigenmode structures apart. In the nonlinear phase of the simulation, the major frequency in the system chirps down by about 30% and stays there.
Book Synopsis Theory of Fusion Plasmas by : Olivier Sauter
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.
Book Synopsis Resonant Toroidal Alfven Eigenmodes (RTAEs) in Neutral Beam Heated Reverse Magnetic Shear Plasmas on TFTR. by :
Download or read book Resonant Toroidal Alfven Eigenmodes (RTAEs) in Neutral Beam Heated Reverse Magnetic Shear Plasmas on TFTR. written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonant Toroidal Alfven Eigenmodes (RTAEs) [1, 2] excited by neutral beam ions are observed in the region of the internal transport barrier in enhanced reverse shear (ERS) plasmas on TFTR. These modes occur in multiples of the same toroidal mode number in the range n=2-4 and appear as highly localized structures near the minimum in the q-profile with frequency near to that expected for TAEs. Unlike regular TAEs, these modes are observed in plasmas where the birth velocity of beam ions is well below the fundamental or sideband resonance condition. Theoretical analysis indicates that the Toroidicity induced Alfven Eigenmode (TAE) does not exist in these discharges due to strong pressure gradients (of the thermal and fast ions) which moves the mode frequency down into the lower Alfven continuum. However a new non-perturbative analysis (where the energetic particles are allowed to modify the mode frequency and mode structure) indicates that RTAEs can be driven by neutral beam ions in the weak magnetic shear region of ERS plasma, consistent with observations on TFTR. The importance of such modes is that they may affect the alpha particle heating profile or enhance the loss of energetic alpha particles in an advanced tokamak reactor where large internal pressure gradients and reverse magnetic shear operation are required to sustain large bootstrap current.
Book Synopsis Advanced Magnetohydrodynamics by : J. P. Goedbloed
Download or read book Advanced Magnetohydrodynamics written by J. P. Goedbloed and published by Cambridge University Press. This book was released on 2010-04-29 with total page 651 pages. Available in PDF, EPUB and Kindle. Book excerpt: Following on from the companion volume Principles of Magnetohydrodynamics, this textbook analyzes the applications of plasma physics to thermonuclear fusion and plasma astrophysics from the single viewpoint of MHD. This approach turns out to be ever more powerful when applied to streaming plasmas (the vast majority of visible matter in the Universe), toroidal plasmas (the most promising approach to fusion energy), and nonlinear dynamics (where it all comes together with modern computational techniques and extreme transonic and relativistic plasma flows). The textbook interweaves theory and explicit calculations of waves and instabilities of streaming plasmas in complex magnetic geometries. It is ideally suited to advanced undergraduate and graduate courses in plasma physics and astrophysics.
Download or read book Fusion Energy Update written by and published by . This book was released on 1980 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:
