Download or read book Gyrokinetic Simulation of Microtearing Turbulence written by Hauke Doerk and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Simulation Of Microtearing Turbulence In NSTX written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermal energy confinement times in NSTX dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future ST devices at much lower collisionality. Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport (≈98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E-B flows as experimental values of E-B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.

Download or read book Gyrokinetic Simulation of Pedestal Turbulence Using GENE written by Xing Liu (Ph. D. in physics) and published by . This book was released on 2018 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present here a study based on gyrokinetic simulations (using GENE) to model turbulence in the pedestals on several well-diagnosed shots: two H-modes on DIII-D and one I-mode on Alcator C-Mod. We match frequencies, power balance, and other transport characteristics in multiple channels with the observations. The observed quasi-coherent fluctuations on the DIII-D shots are identified as Micro Tearing Modes (MTM). The MTMs match frequency and power balance (together with heat loss from Electron Temperature Gradient (ETG) driven turbulence), and cause low transport in the particle, ion heat and impurity particle transport channels – consistent with observed inter-ELM evolution of ion and electron temperature, electron and impurity density or transport analysis of those channels. We find the Weakly Coherent Mode on C-Mod I-mode to be an electrostatic Ion Temperature Gradient/Impurity density gradient (ITG/Impurity) driven mode. The ITG/Impurity mode match frequency and the impurity confinement time observed on the I-mode. Electron scale turbulence, ETG, provides energy transport to match power balance. A novel concept called the transport fingerprints is used throughout this work, which greatly assists in identifying the instabilities. This work shows that the concept should be very valuable in many future investigations of pedestal turbulence.

Download or read book Gyrokinetic Simulation of Ion Temperature Gradient Driven Turbulence in 3D Toroidal Geometry written by W. W. Lee and published by . This book was released on 1993 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electromagnetic Transport From Microtearing Mode Turbulence written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This Letter presents non-linear gyrokinetic simulations of microtearing mode turbulence. The simulations include collisional and electromagnetic effects and use experimental parameters from a high beta discharge in the National Spherical Torus Experiment (NSTX). The predicted electron thermal transport is comparable to that given by experimental analysis, and it is dominated by the electromagnetic contribution of electrons free streaming along the resulting stochastic magnetic field line trajectories. Experimental values of flow shear can significantly reduce the predicted transport.

Download or read book Verhandlungen der ausserordentlichen Synode des Konsistorialbezirks Wiesbaden von 6 bis 26 September 1876 written by and published by . This book was released on 1876 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gyrokinetic Simulation of Ion Temperature Gradient Driven Turbulence in 3D Toroidal Geometry written by and published by . This book was released on 1993 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from a fully nonlinear three dimensional toroidal electrostatic gyrokinetic simulation of the ion temperature gradient instability are presented. The model has fully gyro-averaged ion dynamics, including trapped particles, and adiabatic electrons. Simulations of large tokamak plasma volumes are made possible due to recent advances in ?f methods and massively parallel computing. Linearly, a coherent ballooning eigenmode is observed, where the mode is radially elongated. In the turbulent steady-state, the spectrum peaks around k? ?{sub s} ∼ 0.1 with the ballooning structure reduced, but still prevalent.

Download or read book Progress in Gyrokinetic Simulations of Toroidal ITG Turbulence written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The 3-D nonlinear toroidal gyrokinetic simulation code PG3EQ is used to study toroidal ion temperature gradient (ITG) driven turbulence--a key cause of the anomalous transport that limits tokamak plasma performance. Systematic studies of the dependence of ion thermal transport on various parameters and effects are presented, including dependence on {rvec E} x {rvec B} and toroidal velocity shear, sensitivity to the force balance in simulations with radial temperature gradient variation, and the dependences on magnetic shear and ion temperature gradient.

Download or read book Dans les t n bres Le film complet cin roman written by and published by . This book was released on 1927 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gyrokinetic Simulations in General Geometry and Applications to Collisional Damping of Zonal Flows written by Zhihong Lin and published by . This book was released on 2000 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gyrokinetic Stability Studies of the Microtearing Mode in the National Spherical Torus Experiment H mode written by Redi M. H. Baumgaertel J. A. (Budny R. V.) and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Verification of Gyrokinetic delta f Simulations of Electron Temperature Gradient Turbulence written by and published by . This book was released on 2007 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The GEM gyrokinetic [delta]f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.

Download or read book Gyrokinetic Studies of Turbulence in Steep Gradient Region written by Taik Soo Hahm and published by . This book was released on 2004 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gyrokinetic Turbulence Simulation Compared with a High Ion Temperature Large Helical Device Experiment written by M. Nunami and published by . This book was released on 2011 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Collisional and Electromagnetic Physics in Gyrokinetic Models written by Paul Crandall and published by . This book was released on 2019 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most challenging problems facing plasma physicists today involves the modeling of plasma turbulence and transport in magnetic confinement experiments. The most successful model to this end so far is the reduced gyrokinetic model. Such a model cannot be solved analytically, but can be used to simulate the plasma behavior and transport with the help of present-day supercomputers. This has lead to the development of many different codes which simulate the plasma using the gyrokinetic model in various ways. These models have achieved a large amount of success in describing the core of the plasma for conventional tokamak devices. However, numerous difficulties have been encountered when applying these models to more extreme parameter regimes, such as the edge and scrape-off layer of the tokamak, and high plasma devices, such as spherical tokamaks. The development and application of the gyrokinetic model (specifically with the gyrokinetic code, GENE) to these more extreme parameter ranges shall be the focus of this thesis. One of the main accomplishments during this thesis project is the development of a more advanced collision operator suitable for studying the low temperature plasma edge. The previous collision operator implemented in the code was found to artificially create free energy at high collisionality, leading to numerical instabilities when one attempted to model the plasma edge. This made such an analysis infeasible. The newly implemented collision operator conserves particles, momentum, and energy to machine precision, and is guaranteed to dissipate free energy, even in a nonisothermal scenario. Additional finite Larmor radius correction terms have also been implemented in the local code, and the global code version of the collision operator has been adapted for use with an advanced block-structured grid scheme, allowing for more affordable collisional simulations. The GENE code, along with the newly implemented collision operator developed in this thesis, has been applied to study plasma turbulence and transport in the edge (tor = 0:9) of an L-mode magnetic confinement discharge of ASDEX Upgrade. It has been found that the primary microinstabilities at that radial position are electron drift waves destabilized by collisions and electromagnetic effects. At low toroidal mode numbers, ion temperature gradient driven modes and microtearing modes also seem to exist. In nonlinear simulations with the nominal experimental parameters, the simulated electron heat flux was four times higher than the experimental reconstruction, and the simulated ion heat flux was twice as high. However, both the ion and electron simulated heat flux could be brought into agreement with experimental values by lowering the input logarithmic electron temperature gradient by 40%. It was also found that the cross-phases between the electrostatic potential and the moments agreed well for the part of the binormal spectrum where the dominant transport occurred, and was fairly poor at larger scales where minimal transport occurred. Finally, a new scheme for evaluating the electromagnetic fields has been developed to address the instabilities occurring in nonlinear local and global gyrokinetic simulations at high plasma . This new scheme is based on evaluating the electromagnetic induction explicitly, and constructing the gyrokinetic equation based on the original distribution, rather than the modified distribution which implicitly takes into account the induction. This new scheme removes the artificial instability occurring in global simulations, enabling the study of high scenarios with GENE. The new electromagnetic scheme can also be generalized to a full-f implementation, however, it would require updating the field matrix every time-step to avoid the cancellation problem. The new scheme (including the parallel nonlinearity) does not remove the local instability, suggesting that that instability (caused by magnetic field perturbations shorting out zonal flows) is part of the physics of the local model.

Download or read book Progress in Simulating Turbulent Electron Thermal Transport in NSTX written by and published by . This book was released on 2013 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nonlinear simulations based on multiple NSTX discharge scenarios have progressed to help differentiate unique instability mechanisms and to validate with experimental turbulence and transport data. First nonlinear gyrokinetic simulations of microtearing (MT) turbulence in a high-beta NSTX H-mode discharge predict experimental levels of electron thermal transport that are dominated by magnetic flutter and increase with collisionality, roughly consistent with energy confinement times in dimensionless collisionality scaling experiments. Electron temperature gradient (ETG) simulations predict significant electron thermal transport in some low and high beta discharges when ion scales are suppressed by E x B shear. Although the predicted transport in H-modes is insensitive to variation in collisionality (inconsistent with confinement scaling), it is sensitive to variations in other parameters, particularly density gradient stabilization. In reversed shear (RS) Lmode discharges that exhibit electron internal transport barriers, ETG transport has also been shown to be suppressed nonlinearly by strong negative magnetic shear, s“0. In many high beta plasmas, instabilities which exhibit a stiff beta dependence characteristic of kinetic ballooning modes (KBM) are sometimes found in the core region. However, they do not have a distinct finite beta threshold, instead transitioning gradually to a trapped electron mode (TEM) as beta is reduced to zero. Nonlinear simulations of this "hybrid" TEM/KBM predict significant transport in all channels, with substantial contributions from compressional magnetic perturbations. As multiple instabilities are often unstable simultaneously in the same plasma discharge, even on the same flux surface, unique parametric dependencies are discussed which may be useful for distinguishing the different mechanisms experimentally.

Download or read book Comparisons of Gyrofluid and Gyrokinetic Simulations written by Michael Alan Beer and published by . This book was released on 1994 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: