Full Radius Linear and Nonlinear Gyrokinetic Simulations for Tokamaks and Stellarators PDF Download
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Category :
Languages : en
Pages : 11
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Languages : en
Pages : 11
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Author: MITSURU KIKUCHI
Publisher: International Atomic Energy
ISBN:
Category : Antiques & Collectibles
Languages : en
Pages : 1158
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Humans do not live by bread alone. Physically we are puny creatures with limited prowess, but with unlimited dreams. We see a mountain and want to move it to carve out a path for ourselves. We see a river and want to tame it so that it irrigates our fields. We see a star and want to fly to its planets to secure a future for our progeny. For all this, we need a genie who will do our bidding at a flip of our fingers. Energy is such a genie. Modern humans need energy and lots of it to live a life of comfort. In fact, the quality of life in different regions of the world can be directly correlated with the per capita use of energy [1.1–1.5]. In this regard, the human development index (HDI) of various countries based on various reports by the United Nations Development Programme (UNDP) [1.6] (Fig. 1.1), which is a parameter measuring the quality of life in a given part of the world, is directly determined by the amount of per capita electricity consumption. Most of the developing world (~5 billion people) is crawling up the UN curve of HDI versus per capita electricity consumption, from abysmally low values of today towards the average of the whole world and eventually towards the average of the developed world. This translates into a massive energy hunger for the globe as a whole. It has been estimated that by the year 2050, the global electricity demand will go up by a factor of up to 3 in a high growth scenario [1.7–1.9]. The requirements beyond 2050 go up even higher.
Author: Justin Richard Ball
Publisher:
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Category :
Languages : en
Pages : 136
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Experiments and theory show that tokamak plasmas with strong toroidal rotation and rotation shear can suppress turbulent energy transport as well as allow violation of the Troyon [beta] limit. However, using external neutral beams to inject toroidal momentum, as is done in many current experiments, would require a prohibitive amount of energy in larger, reactor-sized devices. The most promising alternative to achieve significant mean plasma flow that scales to large devices is intrinsic rotation, the rotation that is observed in the absence of external momentum injection. Intrinsic rotation is observed in current experiments, but is generated by effects that are formally small in [pi]* =- [pi]i / a, the ratio of the ion gyroradius to the tokamak minor radius. These effects are insufficient in anticipated reactors because [pi]*, will be significantly smaller. Recent theoretical work concludes that up-down asymmetry in the poloidal crosssection of tokamaks can drive intrinsic rotation to lowest order in [pi]*, [1, 2]. In this thesis, we extend GS2, a local [delta] f gyrokinetic code that self-consistently calculates momentum transport, to permit up-down asymmetric configurations. MHD analysis shows that ellipticity is most effective at introducing up-down asymmetry throughout the plasma. Accordingly, tokamaks with tilted elliptical poloidal cross-sections were simulated in GS2 to determine nonlinear momentum transport. The results suggest that the current experimentally measured rotation levels can be generated in reactorsized devices using up-down asymmetry. Surprisingly, linear and nonlinear gyrokinetic simulations also suggest that tilted elliptical flux surfaces may naturally suppress turbulent energy transport. Using cyclone base case parameters [3] (except for an elongation K = 2), a 40% reduction in the linear turbulent growth rate was observed by tilting the flux surface [pi]/4 from vertical. However, this reduction of energy transport was not observed when the background temperature gradient was increased by 50%.
Author: Christoph Slaby
Publisher:
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Category : Fusion
Languages : en
Pages :
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This dissertation focusses on the numerical modelling of resonant destabilization of Alfvén eigenmodes by fast ions in fusion plasmas. It especially addresses non-linear simulations of stellarator plasmas in which particle collisions are retained. It is shown that collisions are required for a realistic description of Alfvén waves in plasmas relevant to nuclear fusion. We start by carefully verifying the implementation of the collision operators into the electromagnetic version of the gyro-kinetic delta-f particle-in-cell code EUTERPE. After these initial benchmarks are completed successfully, the code is in a position to be applied to realistic tokamak and stellarator scenarios. Since every collision operator needs to fulfil conservation laws, a momentum-conserving version of the pitch-angle scattering operator is implemented. This is in particular important for neoclassical transport simulations aimed at computing flux-surface variations of the electrostatic potential in stellarators. Using the simplified CKA-EUTERPE model (employing a fixed-mode-structure approximation), we perform non-linear simulations in tokamaks and stellarators. We show that the non-linear dynamics of fast-ion-driven Alfvén eigenmodes is significantly influenced by collisions. They have the potential to enhance the saturation level and to affect the frequency chirping of the modes. It is thus concluded that collisions play an essential role in determining Alfvén-eigenmode-induced fast-ion transport ...
Author:
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Category : Electronic journals
Languages : en
Pages : 504
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Category :
Languages : en
Pages : 10
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We present edge gyrokinetic neoclassical simulations of tokamak plasmas using the fully nonlinear (full-f) continuum code TEMPEST. A nonlinear Boltzmann model is used for the electrons. The electric field is obtained by solving the 2D gyrokinetic Poisson Equation. We demonstrate the following: (1) High harmonic resonances (n> 2) significantly enhance geodesic-acoustic mode (GAM) damping at high-q (tokamak safety factor), and are necessary to explain both the damping observed in our TEMPEST q-scans and experimental measurements of the scaling of the GAM amplitude with edge q95 in the absence of obvious evidence that there is a strong q dependence of the turbulent drive and damping of the GAM. (2) The kinetic GAM exists in the edge for steep density and temperature gradients in the form of outgoing waves, its radial scale is set by the ion temperature profile, and ion temperature inhomogeneity is necessary for GAM radial propagation. (3) The development of the neoclassical electric field evolves through different phases of relaxation, including GAMs, their radial propagation, and their long-time collisional decay. (4) Natural consequences of orbits in the pedestal and scrape-off layer region in divertor geometry are substantial non-Maxwellian ion distributions and flow characteristics qualitatively like those observed in experiments.
Author: Karla Kauffmann
Publisher:
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Category :
Languages : en
Pages : 0
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Author: Michael David John Cole
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Category :
Languages : en
Pages :
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Category :
Languages : en
Pages : 45
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A comprehensive study of transport in full-volume gyrokinetic (gk) simulations of ion temperature gradient driven turbulence in core tokamak plasmas is presented. Though this g̀̀yrokinetic tokamak ̀̀is much simpler than experimental tokamaks, such simplicity is an asset, because a dependable nonlinear transport theory for such systems should be more attainable. Toward this end, we pursue two related lines of inquiry. (1) We study the scalings of gk tokamaks with respect to important system parameters. In contrast to real machines, the scalings of larger gk systems (a/?{sub s} ≳ 64) with minor radius, with current, and with a/?{sub s} are roughly consistent with the approximate theoretical expectations for electrostatic turbulent transport which exist as yet. Smaller systems manifest quite different scalings, which aids in interpreting differing mass-scaling results in other work. (2) With the goal of developing a first-principles theory of gk transport, we use the gk data to infer the underlying transport physics. The data indicate that, of the many modes k present in the simulation, only a modest number (N{sub k} ∼ 10) of k dominate the transport, and for each, only a handful (N{sub p} ∼ 5) of couplings to other modes p appear to be significant, implying that the essential transport physics may be described by a far simpler system than would have been expected on the basis of earlier nonlinear theory alone. Part of this analysis is the inference of the coupling coefficients M{sub kpq} governing the nonlinear mode interactions, whose measurement from tokamak simulation data is presented here for the first time.
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Category :
Languages : en
Pages : 8
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OAK B202 COMPREHENSIVE GYROKINETIC SIMULATION OF TOKAMAK TURBULENCE AT FINITE RELATIVE GYRORADIUS. A continuum global gyrokinetic code GYRO has been developed to comprehensively simulate turbulent transport in actual experimental profiles and allow direct quantitative comparisons to the experimental transport flows. GYRO not only treats the now standard ion temperature gradient (ITG) mode turbulence, but also treats trapped and passing electrons with collisions and finite beta, and all in real tokamak geometry. Most importantly the code operates at finite relative gyroradius ([rho]*) so as to treat the profile shear stabilization effects which break gyroBohm scaling. The code operates in a cyclic flux tube limit which allows only gyroBohm scaling and a noncyclic radial annulus with physical profile variation. The later requires an adaptive source to maintain equilibrium profiles. Simple ITG simulations demonstrate the broken gyroBohm scaling depends on the actual rotational velocity shear rates competing with mode growth rates, direct comprehensive simulations of the DIII-D [rho]*-scaled L-mode experiments are presented as a quantitative test of gyrokinetics and the paradigm.
