Theory and Transport of Nearly Incompressible Magnetohydrodynamic Turbulence
Energy Technology Data Exchange (ETDEWEB)
Zank, G. P.; Adhikari, L.; Hunana, P. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Shiota, D. [Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Bruno, R. [INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy); Telloni, D. [INAF—Astrophysical Observatory of Torino, Via Osservatorio 20, I-10025 Pino Torinese (Italy)
2017-02-01
The theory of nearly incompressible magnetohydrodynamics (NI MHD) was developed largely in the early 1990s, together with an important extension to inhomogeneous flows in 2010. Much of the focus in the earlier work was to understand the apparent incompressibility of the solar wind and other plasma environments, and the relationship of density fluctuations to apparently incompressible manifestations of turbulence in the solar wind and interstellar medium. Further important predictions about the “dimensionality” of solar wind turbulence and its relationship to the plasma beta were made and subsequently confirmed observationally. However, despite the initial success of NI MHD in describing fluctuations in the solar wind, a detailed application to solar wind turbulence has not been undertaken. Here, we use the equations of NI MHD to describe solar wind turbulence, rewriting the NI MHD system in terms of Elsässer variables. Distinct descriptions of 2D and slab turbulence emerge naturally from the Elsässer formulation, as do the nonlinear couplings between 2D and slab components. For plasma beta order 1 or less regions, predictions for 2D and slab spectra result from the NI MHD description, and predictions for the spectral characteristics of density fluctuations can be made. We conclude by presenting a NI MHD formulation describing the transport of majority 2D and minority slab turbulence throughout the solar wind. A preliminary comparison of theory and observations is presented.
Arendt, V.; Shalchi, A.
2018-06-01
We explore numerically the transport of energetic particles in a turbulent magnetic field configuration. A test-particle code is employed to compute running diffusion coefficients as well as particle distribution functions in the different directions of space. Our numerical findings are compared with models commonly used in diffusion theory such as Gaussian distribution functions and solutions of the cosmic ray Fokker-Planck equation. Furthermore, we compare the running diffusion coefficients across the mean magnetic field with solutions obtained from the time-dependent version of the unified non-linear transport theory. In most cases we find that particle distribution functions are indeed of Gaussian form as long as a two-component turbulence model is employed. For turbulence setups with reduced dimensionality, however, the Gaussian distribution can no longer be obtained. It is also shown that the unified non-linear transport theory agrees with simulated perpendicular diffusion coefficients as long as the pure two-dimensional model is excluded.
On the relation between neoclassical transport and turbulent transport
International Nuclear Information System (INIS)
Shaing, K.C.
2005-01-01
It is demonstrated through the flux-force relationship in the neoclassical theory that when neoclassical transport fluxes are improved, the damping rate of the radial electric field of the zonal flow is reduced. This, in turn, leads to improved turbulent transport fluxes. Thus, two seemingly unrelated transport fluxes are intimately connected through the momentum equation, and the neoclassical flux-force relation. This also implies a method to improve turbulent transport by improving neoclassical fluxes
International Nuclear Information System (INIS)
Edenstrasser, J.W.
1995-01-01
A multiple time-scale derivative expansion scheme is applied to the dimensionless Fokker--Planck equation and to Maxwell's equations, where the parameter range of a typical fusion plasma was assumed. Within kinetic theory, the four time scales considered are those of Larmor gyration, particle transit, collisions, and classical transport. The corresponding magnetohydrodynamic (MHD) time scales are those of ion Larmor gyration, Alfven, MHD collision, and resistive diffusion. The solution of the zeroth-order equations results in the force-free equilibria and ideal Ohm's law. The solution of the first-order equations leads under the assumption of a weak collisional plasma to the ideal MHD equations. On the MHD-collision time scale, not only the full set of the MHD transport equations is obtained, but also turbulent terms, where the related transport quantities are one order in the expansion parameter larger than those of classical transport. Finally, at the resistive diffusion time scale the known transport equations are arrived at including, however, also turbulent contributions. copyright 1995 American Institute of Physics
Statistical theory of resistive drift-wave turbulence and transport
International Nuclear Information System (INIS)
Hu, G.; Krommes, J.A.; Bowman, J.C.
1997-01-01
Resistive drift-wave turbulence in a slab geometry is studied by statistical closure methods and direct numerical simulations. The two-field Hasegawa endash Wakatani (HW) fluid model, which evolves the electrostatic potential and plasma density self-consistently, is a paradigm for understanding the generic nonlinear behavior of multiple-field plasma turbulence. A gyrokinetic derivation of the HW model is sketched. The recently developed Realizable Markovian Closure (RMC) is applied to the HW model; spectral properties, nonlinear energy transfers, and turbulent transport calculations are discussed. The closure results are also compared to direct numerical simulation results; excellent agreement is found. The transport scaling with the adiabaticity parameter, which measures the strength of the parallel electron resistivity, is analytically derived and understood through weak- and strong-turbulence analyses. No evidence is found to support previous suggestions that coherent structures cause a large depression of saturated transport from its quasilinear value in the hydrodynamic regime of the HW model. Instead, the depression of transport is well explained by the spectral balance equation of the (second-order) statistical closure when account is taken of incoherent noise. copyright 1997 American Institute of Physics
Theory of incremental turbulent transport in tokamaks
International Nuclear Information System (INIS)
Similon, P.L.
1991-01-01
The goal of this research is to understand how the various aspect of turbulent transport operate in tokamaks, in the presence of low frequency fluctuations such as drift waves or trapped electron modes
Theoretical studies of turbulence and anomalous transport in toroidal confinement devices
International Nuclear Information System (INIS)
Terry, P.W.
1990-01-01
The research performed under this grant during the current year has focused on key issues with respect to turbulence and transport in toroidal confinement devices. This work includes theoretical and computational studies of electron thermal confinement which have concentrated on the role of sheared poloidal flow in suppressing turbulence and transport, trapped ion convective cell turbulence and microtearing turbulence; analytical studies of anomalous particle transport and pinch mechanisms, and comparison with experimental measurement; development of the theory of self-consistent radial transport of field-aligned momentum in the tokamak and RFP; and work on other topics (ion temperature gradient driven turbulence, RFP fluctuation theory, coherent structures). Progress and publications in these areas are briefly summarized in this report. 20 refs
Dynamical theory of anomalous particle transport
International Nuclear Information System (INIS)
Meiss, J.D.; Cary, J.R.; Escande, D.F.; MacKay, R.S.; Percival, I.C.; Tennyson, J.L.
1985-01-01
The quasi-linear theory of transport applies only in a restricted parameter range, which does not necessarily correspond to experimental conditions. Theories are developed which extend transport calculations to the regimes of marginal stochasticity and strong turbulence. Near the stochastic threshold the description of transport involves the leakage through destroyed invariant surfaces, and the dynamical scaling theory is used to obtain a universal form for transport coefficients. In the strong-turbulence regime, there is an adiabatic invariant which is preserved except near separatrices. Breakdown of this invariant leads to a new form for the diffusion coefficient. (author)
Recent developments in plasma turbulence and turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Terry, P.W. [Univ. of Wisconsin, Madison, WI (United States)
1997-09-22
This report contains viewgraphs of recent developments in plasma turbulence and turbulent transport. Localized nonlinear structures occur under a variety of circumstances in turbulent, magnetically confined plasmas, arising in both kinetic and fluid descriptions, i.e., in either wave-particle or three-wave coupling interactions. These structures are non wavelike. They cannot be incorporated in the collective wave response, but interact with collective modes through their shielding by the plasma dielectric. These structures are predicted to modify turbulence-driven transport in a way that in consistent with, or in some cases are confirmed by recent experimental observations. In kinetic theory, non wavelike structures are localized perturbations of phase space density. There are two types of structures. Holes are self-trapped, while clumps have a self-potential that is too weak to resist deformation and mixing by ambient potential fluctuations. Clumps remain correlated in turbulence if their spatial extent is smaller than the correlation length of the scattering fields. In magnetic turbulence, clumps travel along stochastic magnetic fields, shielded by the plasma dielectric. A drag on the clump macro-particle is exerted by the shielding, inducing emission into the collective response. The emission in turn damps back on the particle distribution via Landau dampling. The exchange of energy between clumps and particles, as mediated by the collective mode, imposes constraints on transport. For a turbulent spectrum whose mean wavenumber along the equilibrium magnetic field is nonzero, the electron thermal flux is proportional to the ion thermal velocity. Conventional predictions (which account only for collective modes) are larger by the square root of the ion to electron mass ratio. Recent measurements are consistent with the small flux. In fluid plasma,s localized coherent structures can occur as intense vortices.
Turbulence closure for mixing length theories
Jermyn, Adam S.; Lesaffre, Pierre; Tout, Christopher A.; Chitre, Shashikumar M.
2018-05-01
We present an approach to turbulence closure based on mixing length theory with three-dimensional fluctuations against a two-dimensional background. This model is intended to be rapidly computable for implementation in stellar evolution software and to capture a wide range of relevant phenomena with just a single free parameter, namely the mixing length. We incorporate magnetic, rotational, baroclinic, and buoyancy effects exactly within the formalism of linear growth theories with non-linear decay. We treat differential rotation effects perturbatively in the corotating frame using a novel controlled approximation, which matches the time evolution of the reference frame to arbitrary order. We then implement this model in an efficient open source code and discuss the resulting turbulent stresses and transport coefficients. We demonstrate that this model exhibits convective, baroclinic, and shear instabilities as well as the magnetorotational instability. It also exhibits non-linear saturation behaviour, and we use this to extract the asymptotic scaling of various transport coefficients in physically interesting limits.
International Nuclear Information System (INIS)
Le Roux, J. A.
2011-01-01
Earlier work based on nonlinear guiding center (NLGC) theory suggested that perpendicular cosmic-ray transport is diffusive when cosmic rays encounter random three-dimensional magnetohydrodynamic turbulence dominated by uniform two-dimensional (2D) turbulence with a minor uniform slab turbulence component. In this approach large-scale perpendicular cosmic-ray transport is due to cosmic rays microscopically diffusing along the meandering magnetic field dominated by 2D turbulence because of gyroresonant interactions with slab turbulence. However, turbulence in the solar wind is intermittent and it has been suggested that intermittent turbulence might be responsible for the observation of 'dropout' events in solar energetic particle fluxes on small scales. In a previous paper le Roux et al. suggested, using NLGC theory as a basis, that if gyro-scale slab turbulence is intermittent, large-scale perpendicular cosmic-ray transport in weak uniform 2D turbulence will be superdiffusive or subdiffusive depending on the statistical characteristics of the intermittent slab turbulence. In this paper we expand and refine our previous work further by investigating how both parallel and perpendicular transport are affected by intermittent slab turbulence for weak as well as strong uniform 2D turbulence. The main new finding is that both parallel and perpendicular transport are the net effect of an interplay between diffusive and nondiffusive (superdiffusive or subdiffusive) transport effects as a consequence of this intermittency.
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Le Roux, J. A. [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
2011-12-10
Earlier work based on nonlinear guiding center (NLGC) theory suggested that perpendicular cosmic-ray transport is diffusive when cosmic rays encounter random three-dimensional magnetohydrodynamic turbulence dominated by uniform two-dimensional (2D) turbulence with a minor uniform slab turbulence component. In this approach large-scale perpendicular cosmic-ray transport is due to cosmic rays microscopically diffusing along the meandering magnetic field dominated by 2D turbulence because of gyroresonant interactions with slab turbulence. However, turbulence in the solar wind is intermittent and it has been suggested that intermittent turbulence might be responsible for the observation of 'dropout' events in solar energetic particle fluxes on small scales. In a previous paper le Roux et al. suggested, using NLGC theory as a basis, that if gyro-scale slab turbulence is intermittent, large-scale perpendicular cosmic-ray transport in weak uniform 2D turbulence will be superdiffusive or subdiffusive depending on the statistical characteristics of the intermittent slab turbulence. In this paper we expand and refine our previous work further by investigating how both parallel and perpendicular transport are affected by intermittent slab turbulence for weak as well as strong uniform 2D turbulence. The main new finding is that both parallel and perpendicular transport are the net effect of an interplay between diffusive and nondiffusive (superdiffusive or subdiffusive) transport effects as a consequence of this intermittency.
Turbulent transport in magnetized plasmas
Horton, Wendell
2012-01-01
This book explains how magnetized plasmas self-organize in states of electromagnetic turbulence that transports particles and energy out of the core plasma faster than anticipated by the fusion scientists designing magnetic confinement systems in the 20th century. It describes theory, experiments and simulations in a unified and up-to-date presentation of the issues of achieving nuclear fusion power.
Magnetic turbulent electron transport in a reversed field pinch
International Nuclear Information System (INIS)
Schoenberg, K.; Moses, R.
1990-01-01
A model of magnetic turbulent electron transport is presented. The model, based on the thermal conduction theory of Rechester and Rosenbluth, entails a Boltzmann description of electron dynamics in the long mean-free-path limit and quantitatively describes the salient features of superthermal electron measurements in the RFP edge plasma. Included are predictions of the mean superthermal electron energy, current density, and power flux asymmetry. A discussion of the transport model, the assumptions implicit in the model, and the relevance of this work to more general issue of magnetic turbulent transport in toroidal systems is presented. 32 refs., 3 figs
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Lasuik, J.; Shalchi, A., E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada)
2017-09-20
Recently, a new theory for the transport of energetic particles across a mean magnetic field was presented. Compared to other nonlinear theories the new approach has the advantage that it provides a full time-dependent description of the transport. Furthermore, a diffusion approximation is no longer part of that theory. The purpose of this paper is to combine this new approach with a time-dependent model for parallel transport and different turbulence configurations in order to explore the parameter regimes for which we get ballistic transport, compound subdiffusion, and normal Markovian diffusion.
Electron thermal transport in tokamak: ETG or TEM turbulences?
International Nuclear Information System (INIS)
Lin, Z.; Chen, L.; Nishimura, Y.; Qu, H.; Hahm, T.S.; Lewandowski, J.; Rewoldt, G.; Wang, W.X.; Diamond, P.H.; Holland, C.; Zonca, F.; Li, Y.
2005-01-01
This paper reports progress on numerical and theoretical studies of electron transport in tokamak including: (1) electron temperature gradient turbulence; (2) trapped electron mode turbulence; and (3) a new finite element solver for global electromagnetic simulation. In particular, global gyrokinetic particle simulation and nonlinear gyrokinetic theory find that electron temperature gradient (ETG) instability saturates via nonlinear toroidal couplings, which transfer energy successively from unstable modes to damped modes preferably with longer poloidal wavelengths. The electrostatic ETG turbulence is dominated by nonlinearly generated radial streamers. The length of streamers scales with the device size and is much longer than the distance between mode rational surfaces or electron radial excursions. Both fluctuation intensity and transport level are independent of the streamer size. These simulations with realistic plasma parameters find that the electron heat conductivity is much smaller than the experimental value and in contrast with recent findings of flux-tube simulations that ETG turbulence is responsible for the anomalous electron thermal transport in fusion plasmas. The nonlinear toroidal couplings represent a new paradigm for the spectral cascade in plasma turbulence. (author)
Introduction to turbulent transport in fusion plasmas
International Nuclear Information System (INIS)
Garbet, X.
2006-01-01
This introduction presents the main instabilities responsible for turbulence in tokamak plasmas, and the prominent features of the resulting transport. The usual techniques to construct reduced transport models are described. These models can be tested by analysing steady state and transient regimes. Another way to test the theory is to use a similarity principle, similar to the one used in fluid mechanics. Finally, the physics involved in the formation and sustainment of transport barriers is presented. (author)
Optimizing Stellarators for Turbulent Transport
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2010-01-01
Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.
Physics of turbulence control and transport barrier formation in DIII-D
International Nuclear Information System (INIS)
Doyle, E.J.; Burrell, K.H.; Carlstrom, T.N.
1996-10-01
This paper describes the physical mechanisms responsible for turbulence control and transport barrier formation on DIII-D as determined from a synthesis of results from different enhanced confinement regimes, including quantitative and qualitative comparisons to theory. A wide range of DIII-D data support the hypothesis that a single underlying physical mechanism, turbulence suppression via E x B shear flow is playing an essential, though not necessarily unique, role in reducing turbulence and transport in all of the following improved confinement regimes: H-mode, VH-mode, high-ell i modes, improved performance counter-injection L-mode discharges and high performance negative central shear (NCS) discharges. DIII-D data also indicate that synergistic effects are important in some cases, as in NCS discharges where negative magnetic shear also plays a role in transport barrier formation. This work indicates that in order to control turbulence and transport it is important to focus on understanding physical mechanisms, such as E x B shear, which can regulate and control entire classes of turbulent modes, and thus control transport. In the highest performance DIII-D discharges, NCS plasmas with a VH-mode like edge, turbulence is suppressed at all radii, resulting in neoclassical levels of ion transport over most of the plasma volume
Implications of Navier-Stokes turbulence theory for plasma turbulence
International Nuclear Information System (INIS)
Montgomery, David
1977-01-01
A brief discussion of Navier-Stokes turbulence theory is given with particular reference to the two dimensional case. The MHD turbulence is introduced with possible applications of techniques developed in Navier-Stokes theory. Turbulence in Vlasov plasma is also discussed from the point of view of the ''direct interaction approximation'' (DIA). (A.K.)
Numerical Test of Analytical Theories for Perpendicular Diffusion in Small Kubo Number Turbulence
Energy Technology Data Exchange (ETDEWEB)
Heusen, M.; Shalchi, A., E-mail: husseinm@myumanitoba.ca, E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada)
2017-04-20
In the literature, one can find various analytical theories for perpendicular diffusion of energetic particles interacting with magnetic turbulence. Besides quasi-linear theory, there are different versions of the nonlinear guiding center (NLGC) theory and the unified nonlinear transport (UNLT) theory. For turbulence with high Kubo numbers, such as two-dimensional turbulence or noisy reduced magnetohydrodynamic turbulence, the aforementioned nonlinear theories provide similar results. For slab and small Kubo number turbulence, however, this is not the case. In the current paper, we compare different linear and nonlinear theories with each other and test-particle simulations for a noisy slab model corresponding to small Kubo number turbulence. We show that UNLT theory agrees very well with all performed test-particle simulations. In the limit of long parallel mean free paths, the perpendicular mean free path approaches asymptotically the quasi-linear limit as predicted by the UNLT theory. For short parallel mean free paths we find a Rechester and Rosenbluth type of scaling as predicted by UNLT theory as well. The original NLGC theory disagrees with all performed simulations regardless what the parallel mean free path is. The random ballistic interpretation of the NLGC theory agrees much better with the simulations, but compared to UNLT theory the agreement is inferior. We conclude that for this type of small Kubo number turbulence, only the latter theory allows for an accurate description of perpendicular diffusion.
Numerical Test of Analytical Theories for Perpendicular Diffusion in Small Kubo Number Turbulence
International Nuclear Information System (INIS)
Heusen, M.; Shalchi, A.
2017-01-01
In the literature, one can find various analytical theories for perpendicular diffusion of energetic particles interacting with magnetic turbulence. Besides quasi-linear theory, there are different versions of the nonlinear guiding center (NLGC) theory and the unified nonlinear transport (UNLT) theory. For turbulence with high Kubo numbers, such as two-dimensional turbulence or noisy reduced magnetohydrodynamic turbulence, the aforementioned nonlinear theories provide similar results. For slab and small Kubo number turbulence, however, this is not the case. In the current paper, we compare different linear and nonlinear theories with each other and test-particle simulations for a noisy slab model corresponding to small Kubo number turbulence. We show that UNLT theory agrees very well with all performed test-particle simulations. In the limit of long parallel mean free paths, the perpendicular mean free path approaches asymptotically the quasi-linear limit as predicted by the UNLT theory. For short parallel mean free paths we find a Rechester and Rosenbluth type of scaling as predicted by UNLT theory as well. The original NLGC theory disagrees with all performed simulations regardless what the parallel mean free path is. The random ballistic interpretation of the NLGC theory agrees much better with the simulations, but compared to UNLT theory the agreement is inferior. We conclude that for this type of small Kubo number turbulence, only the latter theory allows for an accurate description of perpendicular diffusion.
Theoretical studies of turbulence and anomalous transport in toroidal confinement devices
International Nuclear Information System (INIS)
Terry, P.W.
1993-01-01
The research performed under this grant has focused on key issues with respect to turbulence and transport in toroidal confinement devices. Progress and publications in these areas are summarized in this report. This work includes analytical and numerical studies of spectral energy transfer and the saturation dynamics and transport of dissipative and collisionless trapped electron turbulence, the role of flow curvature in L-H mode transition physics, fully nonlinear calculations of the anomalous particle transport from the ion mixing mode, and the development of a theory for the drift wave frequency spectrum. Novel aspects of this work include an elucidation of the role of nonlinear frequency shifts in producing nonstationary saturated states, an identification of reverse and non-conserved flows in Hasegawa-Mima turbulence, and a description of the way incoherent emission affects the frequency of turbulent fluctuations
Energy Technology Data Exchange (ETDEWEB)
Sarazin, Y
2004-03-01
This document gathers the lectures made in the framework of a Ph.D level physics class dedicated to plasma physics. This course is made up of 3 parts : 1) collisions and transport, 2) transport and turbulence, and 3) study of a few exchange instabilities. More precisely the first part deals with the following issues: thermonuclear fusion, Coulomb collisions, particles trajectories in a tokamak, neo-classical transport in tokamaks, the bootstrap current, and ware pinch. The second part involves: particle transport in tokamaks, quasi-linear transport, resonance islands, resonance in tokamaks, from quasi to non-linear transport, and non-linear saturation of turbulence. The third part deals with: shift velocities in fluid theory, a model for inter-change instabilities, Rayleigh-Benard instability, Hasegawa-Wakatani model, and Hasegawa-Mima model. This document ends with a series of appendices dealing with: particle-wave interaction, determination of the curvature parameter G, Rossby waves.
Energy Technology Data Exchange (ETDEWEB)
Garbet, X
2001-06-01
The purpose of this work is to introduce the main processes that occur in a magnetized plasma. During the last 2 decades, the understanding of turbulence has made great progress but analytical formulas and simulations are far to produce reliable predictions. The values of transport coefficients in a tokamak plasma exceed by far those predicted by the theory of collisional transport. This phenomenon is called abnormal transport and might be due to plasma fluctuations. An estimation of turbulent fluxes derived from the levels of fluctuations, is proposed. A flow description of plasma allows the understanding of most micro-instabilities. The ballooning representation deals with instabilities in a toric geometry. 3 factors play an important role to stabilize plasmas: density pinch, magnetic shear and speed shear. The flow model of plasma gives an erroneous value for the stability threshold, this is due to a bad description of the resonant interaction between wave and particle. As for dynamics, flow models can be improved by adding dissipative terms so that the linear response nears the kinetic response. The kinetic approach is more accurate but is complex because of the great number of dimensions involved. (A.C.)
International Nuclear Information System (INIS)
Krommes, J.A.; Kim, Chang-Bae
1990-06-01
The fundamental problem in the theory of turbulent transport is to find the flux Γ of a quantity such as heat. Methods based on statistical closures are mired in conceptual controversies and practical difficulties. However, it is possible to bound Γ by employing constraints derived rigorously from the equations of motion. Brief reviews of the general theory and its application to passive advection are given. Then, a detailed application is made to anomalous resistivity generated by self-consistent turbulence in a reversed-field pinch. A nonlinear variational principle for an upper bound on the turbulence electromotive force for fixed current is formulated from the magnetohydrodynamic equations in cylindrical geometry. Numerical solution of a case constrained solely by energy balance leads to a reasonable bound and nonlinear eigenfunctions that share intriguing features with experimental data: the dominant mode numbers appear to be correct, and field reversal is predicted at reasonable values of the pinch parameter. Although open questions remain upon considering all bounding calculations to date one can conclude, remarkably, that global energy balance constrains transport sufficiently so that bounds derived therefrom are not unreasonable and that bounding calculations are feasible even for involved practical problems. The potential of the method has hardly been tapped; it provides a fertile area for future research. 29 refs
International Nuclear Information System (INIS)
Krommes, J.A.; Kim, C.
1990-01-01
The fundamental problem in the theory of turbulent transport is to find the flux Γ of a quantity such as heat. Methods based on statistical closures are mired in conceptual controversies and practical difficulties. However, it is possible to bound Γ by employing constraints derived rigorously from the equations of motion. Brief reviews of the general theory and its application to passive advection are given. Then, a detailed application is made to anomalous resistivity generated by self-consistent turbulence in a reversed-field pinch. A nonlinear variational principle for an upper bound on the turbulent electromotive force for fixed current is formulated from the magnetohydrodynamic equations in cylindrical geometry. Numerical solution of a case constrained solely by energy balance leads to a reasonable bound and nonlinear eigenfunctions that share intriguing features with experimental data: The dominant mode numbers appear to be correct, and field reversal is predicted at reasonable values of the pinch parameter. Although open questions remain, upon considering all bounding calculations to date it can be concluded, remarkably, that global energy balance constrains transport sufficiently so that bounds derived therefrom are not unreasonable and that bounding calculations are feasible even for involved practical problems. The potential of the method has hardly been tapped; it provides a fertile area for future research
Turbulent transport regimes and the SOL heat flux width
Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.
2014-10-01
Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks, and for seeking possible mitigation schemes. Simulation and theory results using reduced edge/SOL turbulence models have produced SOL widths and scalings in reasonable accord with experiments in many cases. In this work, we attempt to qualitatively and conceptually understand various regimes of edge/SOL turbulence and the role of turbulent transport in establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. Recent SOLT turbulence code results are employed to understand the roles of these considerations and to develop analytical scalings. We find a heat flux width scaling with major radius R that is generally positive, consistent with older results reviewed in. The possible relationship of turbulence mechanisms to the heuristic drift mechanism is considered, together with implications for future experiments. Work supported by US DOE grant DE-FG02-97ER54392.
Quasilinear theory of plasma turbulence. Origins, ideas, and evolution of the method
Bakunin, O. G.
2018-01-01
The quasilinear method of describing weak plasma turbulence is one of the most important elements of current plasma physics research. Today, this method is not only a tool for solving individual problems but a full-fledged theory of general physical interest. The author's objective is to show how the early ideas of describing the wave-particle interactions in a plasma have evolved as a result of the rapid expansion of the research interests of turbulence and turbulent transport theorists.
Effects of turbulent hyporheic mixing on reach-scale solute transport
Roche, K. R.; Li, A.; Packman, A. I.
2017-12-01
Turbulence rapidly mixes solutes and fine particles into coarse-grained streambeds. Both hyporheic exchange rates and spatial variability of hyporheic mixing are known to be controlled by turbulence, but it is unclear how turbulent mixing influences mass transport at the scale of stream reaches. We used a process-based particle-tracking model to simulate local- and reach-scale solute transport for a coarse-bed stream. Two vertical mixing profiles, one with a smooth transition from in-stream to hyporheic transport conditions and a second with enhanced turbulent transport at the sediment-water interface, were fit to steady-state subsurface concentration profiles observed in laboratory experiments. The mixing profile with enhanced interfacial transport better matched the observed concentration profiles and overall mass retention in the streambed. The best-fit mixing profiles were then used to simulate upscaled solute transport in a stream. Enhanced mixing coupled in-stream and hyporheic solute transport, causing solutes exchanged into the shallow subsurface to have travel times similar to the water column. This extended the exponential region of the in-stream solute breakthrough curve, and delayed the onset of the heavy power-law tailing induced by deeper and slower hyporheic porewater velocities. Slopes of observed power-law tails were greater than those predicted from stochastic transport theory, and also changed in time. In addition, rapid hyporheic transport velocities truncated the hyporheic residence time distribution by causing mass to exit the stream reach via subsurface advection, yielding strong exponential tempering in the in-stream breakthrough curves at the timescale of advective hyporheic transport through the reach. These results show that strong turbulent mixing across the sediment-water interface violates the conventional separation of surface and subsurface flows used in current models for solute transport in rivers. Instead, the full distribution of
Turbulent transport in low-beta plasmas
DEFF Research Database (Denmark)
Nielsen, A.H.; Pécseli, H.L.; Juul Rasmussen, J.
1996-01-01
Low-frequency electrostatic fluctuations are studied experimentally in a low-P plasma, with particular attention to their importance for the anomalous plasma transport across magnetic field lines. The presence of large coherent structures in a turbulent background at the edge of the plasma column...... is demonstrated by a statistical analysis. The importance of these structures for the turbulent transport is investigated. The study is extended by a multichannel conditional analysis to illustrate detailed properties and parameter dependences of the turbulent transport. (C) 1996 American Institute of Physics....
Transport barrier fluctuations governed by SOL turbulence spreading
International Nuclear Information System (INIS)
Ghendrih, Ph.; Sarazin, Y.; Ciraolo, G.; Darmet, G.; Garbet, X.; Grangirard, V.; Tamain, P.; Benkadda, S.; Beyer, P.
2007-01-01
Turbulence spreading, namely turbulent transport extending into a stable region is reported both for the flat density profiles in the far SOL and into a modeled H-mode barrier. It is shown that due to turbulence penetration, the pedestal width fluctuates and that its effective width is a factor 2 smaller than the linear predicted width. Turbulence overshooting throughout the pedestal leads to a non-vanishing turbulent transport within the barrier and provides a coupling of core and SOL turbulence despite the transport barrier
Statistical theory of turbulent incompressible multimaterial flow
International Nuclear Information System (INIS)
Kashiwa, B.
1987-10-01
Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of κ-ε modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy κ, and the rate of fluctuational energy dissipation ε, for each material. Hence a set of κ and ε equations must be solved, together with mean mass and momentum conservation equations, for each material. Both κ and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe
Linear and Nonlinear Theories of Cosmic Ray Transport
International Nuclear Information System (INIS)
Shalchi, A.
2005-01-01
The transport of charged cosmic rays in plasmawave turbulence is a modern and interesting field of research. We are mainly interested in spatial diffusion parallel and perpendicular to a large scale magnetic field. During the last decades quasilinear theory was the standard tool for the calculation of diffusion coefficients. Through comparison with numerical simulations we found several cases where quasilinear theory is invalid. On could define three major problems of transport theory. I will demonstrate that new nonlinear theories which were proposed recently can solve at least some to these problems
Turbulence introduction to theory and applications of turbulent flows
Westerweel, Jerry; Nieuwstadt, Frans T M
2016-01-01
This book provides a general introduction to the topic of turbulent flows. Apart from classical topics in turbulence, attention is also paid to modern topics. After studying this work, the reader will have the basic knowledge to follow current topics on turbulence in scientific literature. The theory is illustrated with a number of examples of applications, such as closure models, numerical simulations and turbulent diffusion, and experimental findings. The work also contains a number of illustrative exercises.
Mathematical and physical theory of turbulence
Cannon, John
2006-01-01
Although the current dynamical system approach offers several important insights into the turbulence problem, issues still remain that present challenges to conventional methodologies and concepts. These challenges call for the advancement and application of new physical concepts, mathematical modeling, and analysis techniques. Bringing together experts from physics, applied mathematics, and engineering, Mathematical and Physical Theory of Turbulence discusses recent progress and some of the major unresolved issues in two- and three-dimensional turbulence as well as scalar compressible turbulence. Containing introductory overviews as well as more specialized sections, this book examines a variety of turbulence-related topics. The authors concentrate on theory, experiments, computational, and mathematical aspects of Navier-Stokes turbulence; geophysical flows; modeling; laboratory experiments; and compressible/magnetohydrodynamic effects. The topics discussed in these areas include finite-time singularities a...
Influence of turbulence on bed load sediment transport
DEFF Research Database (Denmark)
Sumer, B. Mutlu; Chua, L.; Cheng, N. S.
2003-01-01
This paper summarizes the results of an experimental study on the influence of an external turbulence field on the bedload sediment transport in an open channel. The external turbulence was generated by: (1) with a horizontal pipe placed halfway through the depth, h; (2) with a series of grids......-bed experiments and the ripple-covered-bed experiments. In the former case, the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment...... correlated with the sediment transport rate. The sediment transport increases markedly with increasing turbulence level....
Effects of premixed flames on turbulence and turbulent scalar transport
Energy Technology Data Exchange (ETDEWEB)
Lipatnikov, A.N.; Chomiak, J. [Department of Applied Mechanics, Chalmers University of Technology, 412 75 Goeteborg (Sweden)
2010-02-15
Experimental data and results of direct numerical simulations are reviewed in order to show that premixed combustion can change the basic characteristics of a fluctuating velocity field (the so-called flame-generated turbulence) and the direction of scalar fluxes (the so-called countergradient or pressure-driven transport) in a turbulent flow. Various approaches to modeling these phenomena are discussed and the lack of a well-elaborated and widely validated predictive approach is emphasized. Relevant basic issues (the transition from gradient to countergradient scalar transport, the role played by flame-generated turbulence in the combustion rate, the characterization of turbulence in premixed flames, etc.) are critically considered and certain widely accepted concepts are disputed. Despite the substantial progress made in understanding the discussed effects over the past decades, these basic issues strongly need further research. (author)
Self-regulation of turbulence bursts and transport barriers
International Nuclear Information System (INIS)
Floriani, E; Ciraolo, G; Ghendrih, Ph; Sarazin, Y; Lima, R
2013-01-01
The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in magnetically confined plasmas. The turbulent bursts spread into the transport barriers and, depending on the competing magnitude of the burst and stopping capability of the barrier, can burn through. Simulations of two models of transport barriers are presented: a hard barrier where interchange turbulence modes are stable in a prescribed region and a soft barrier with external plasma biasing. The response of the transport barriers to the non-linear perturbations of the turbulent bursts, addressed in a predator–prey approach, indicates that the barriers monitor an amplification factor of the turbulent bursts, with amplification smaller than one for most bursts and, in some cases, amplification factors that can significantly exceed unity. The weak barriers in corrugated profiles and magnetic structures, as well as the standard barriers, are characterized by these transmission properties, which then regulate the turbulent burst transport properties. The interplays of barriers and turbulent bursts are modeled as competing stochastic processes. For different classes of the probability density function (PDF) of these processes, one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to the properties of the barriers. The main stochastic variables are the barrier width and the spreading distance of the turbulent bursts within the barrier, together with their level of correlation. One finds that in the case of a barrier with volumetric losses, such as radiation or particle losses as addressed in our present simulations, the stochastic model predicts a leaky behavior with an exponential PDF of escaping turbulent bursts in agreement with the simulation
Impact of large scale flows on turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Sarazin, Y [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Grandgirard, V [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Dif-Pradalier, G [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Fleurence, E [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Garbet, X [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Ghendrih, Ph [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Bertrand, P [LPMIA-Universite Henri Poincare Nancy I, Boulevard des Aiguillettes BP239, 54506 Vandoe uvre-les-Nancy (France); Besse, N [LPMIA-Universite Henri Poincare Nancy I, Boulevard des Aiguillettes BP239, 54506 Vandoe uvre-les-Nancy (France); Crouseilles, N [IRMA, UMR 7501 CNRS/Universite Louis Pasteur, 7 rue Rene Descartes, 67084 Strasbourg (France); Sonnendruecker, E [IRMA, UMR 7501 CNRS/Universite Louis Pasteur, 7 rue Rene Descartes, 67084 Strasbourg (France); Latu, G [LSIIT, UMR 7005 CNRS/Universite Louis Pasteur, Bd Sebastien Brant BP10413, 67412 Illkirch (France); Violard, E [LSIIT, UMR 7005 CNRS/Universite Louis Pasteur, Bd Sebastien Brant BP10413, 67412 Illkirch (France)
2006-12-15
The impact of large scale flows on turbulent transport in magnetized plasmas is explored by means of various kinetic models. Zonal flows are found to lead to a non-linear upshift of turbulent transport in a 3D kinetic model for interchange turbulence. Such a transition is absent from fluid simulations, performed with the same numerical tool, which also predict a much larger transport. The discrepancy cannot be explained by zonal flows only, despite they being overdamped in fluids. Indeed, some difference remains, although reduced, when they are artificially suppressed. Zonal flows are also reported to trigger transport barriers in a 4D drift-kinetic model for slab ion temperature gradient (ITG) turbulence. The density gradient acts as a source drive for zonal flows, while their curvature back stabilizes the turbulence. Finally, 5D simulations of toroidal ITG modes with the global and full-f GYSELA code require the equilibrium density function to depend on the motion invariants only. If not, the generated strong mean flows can completely quench turbulent transport.
Impact of large scale flows on turbulent transport
International Nuclear Information System (INIS)
Sarazin, Y; Grandgirard, V; Dif-Pradalier, G; Fleurence, E; Garbet, X; Ghendrih, Ph; Bertrand, P; Besse, N; Crouseilles, N; Sonnendruecker, E; Latu, G; Violard, E
2006-01-01
The impact of large scale flows on turbulent transport in magnetized plasmas is explored by means of various kinetic models. Zonal flows are found to lead to a non-linear upshift of turbulent transport in a 3D kinetic model for interchange turbulence. Such a transition is absent from fluid simulations, performed with the same numerical tool, which also predict a much larger transport. The discrepancy cannot be explained by zonal flows only, despite they being overdamped in fluids. Indeed, some difference remains, although reduced, when they are artificially suppressed. Zonal flows are also reported to trigger transport barriers in a 4D drift-kinetic model for slab ion temperature gradient (ITG) turbulence. The density gradient acts as a source drive for zonal flows, while their curvature back stabilizes the turbulence. Finally, 5D simulations of toroidal ITG modes with the global and full-f GYSELA code require the equilibrium density function to depend on the motion invariants only. If not, the generated strong mean flows can completely quench turbulent transport
The role of magnetic turbulence in astrophysical jet launching and cosmic ray transport
International Nuclear Information System (INIS)
Casse, Fabien
2001-01-01
The first part of my thesis shows how Keplerian discs can launch MHD jets, under some conditions. The key points of this first part are the adding of viscosity inside the disc and a relevant energy equation, In particular, I have shown both analytically and numerically that the angular momentum transport is constrained by the MHD turbulence properties. I have also shown that one must take into account a relevant energy equation in order to have a more realistic description of jets observed in the Universe. Moreover, some energy turbulent transport mechanisms cannot be described in a simple MHD approach. In order to better understand the interaction between a turbulent magnetic field and charged particles, I have undertaken a study dealing with spatial and angular diffusion of hadrons with a chaotic magnetic field generated by a magnetic turbulence. In this study, it clearly appears that the spatial diffusion coefficient along the mean magnetic field extrapolate the results of quasi-linear theory for weak turbulence. At the opposite, in the inertial range, the spatial diffusion coefficient across the mean magnetic field is inconsistent with such a theory. Indeed the spatial diffusion coefficient across the mean magnetic field has a behaviour that can be interpreted as a chaotic diffusion regime as the one predicted by Rechester and Rosenbluth. Moreover, outside this range, the behaviours of all spatial diffusion coefficients are different of those expected in the framework of quasi-linear theory. At last, it has been found that a Bohm diffusion regime never occurs whatever the magnetic chaos. (author) [fr
Weak turbulence theory for beam-plasma interaction
Yoon, Peter H.
2018-01-01
The kinetic theory of weak plasma turbulence, of which Ronald C. Davidson was an important early pioneer [R. C. Davidson, Methods in Nonlinear Plasma Theory, (Academic Press, New York, 1972)], is a venerable and valid theory that may be applicable to a large number of problems in both laboratory and space plasmas. This paper applies the weak turbulence theory to the problem of gentle beam-plasma interaction and Langmuir turbulence. It is shown that the beam-plasma interaction undergoes various stages of physical processes starting from linear instability, to quasilinear saturation, to mode coupling that takes place after the quasilinear stage, followed by a state of quasi-static "turbulent equilibrium." The long term quasi-equilibrium stage is eventually perturbed by binary collisional effects in order to bring the plasma to a thermodynamic equilibrium with increased entropy.
Instabilities, turbulence and transport in a magnetized plasma
International Nuclear Information System (INIS)
Garbet, X.
2001-06-01
The purpose of this work is to introduce the main processes that occur in a magnetized plasma. During the last 2 decades, the understanding of turbulence has made great progress but analytical formulas and simulations are far to produce reliable predictions. The values of transport coefficients in a tokamak plasma exceed by far those predicted by the theory of collisional transport. This phenomenon is called abnormal transport and might be due to plasma fluctuations. An estimation of turbulent fluxes derived from the levels of fluctuations, is proposed. A flow description of plasma allows the understanding of most micro-instabilities. The ballooning representation deals with instabilities in a toric geometry. 3 factors play an important role to stabilize plasmas: density pinch, magnetic shear and speed shear. The flow model of plasma gives an erroneous value for the stability threshold, this is due to a bad description of the resonant interaction between wave and particle. As for dynamics, flow models can be improved by adding dissipative terms so that the linear response nears the kinetic response. The kinetic approach is more accurate but is complex because of the great number of dimensions involved. (A.C.)
Holland, Christopher George
Studies of nonlinear couplings and dynamics in plasma turbulence are presented. Particular areas of focus are analytic studies of coherent structure formation in electron temperature gradient turbulence, measurement of nonlinear energy transfer in simulations of plasma turbulence, and bispectral analysis of experimental and computational data. The motivation for these works has been to develop and expand the existing theories of plasma transport, and verify the nonlinear predictions of those theories in simulation and experiment. In Chapter II, we study electromagnetic secondary instabilities of electron temperature gradient turbulence. The growth rate for zonal flow generation via modulational instability of electromagnetic ETG turbulence is calculated, as well as that for zonal (magnetic) field generation. In Chapter III, the stability and saturation of streamers in ETG turbulence is considered, and shown to depend sensitively upon geometry and the damping rates of the Kelvin-Helmholtz mode. Requirements for a credible theory of streamer transport are presented. In addition, a self-consistent model for interactions between ETG and ITG (ion temperature gradient) turbulence is presented. In Chapter IV, the nonlinear transfer of kinetic and internal energy is measured in simulations of plasma turbulence. The regulation of turbulence by radial decorrelation due to zonal flows and generation of zonal flows via the Reynolds stress are explicitly demonstrated, and shown to be symmetric facets of a single nonlinear process. Novel nonlinear saturation mechanisms for zonal flows are discussed. In Chapter V, measurements of fluctuation bicoherence in the edge of the DIII-D tokamak are presented. It is shown that the bicoherence increases transiently before a L-H transition, and decays to its initial value after the barrier has formed. The increase in bicoherence is localized to the region where the transport barrier forms, and shows strong coupling between well
Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Energy Technology Data Exchange (ETDEWEB)
Diamond, P.H.; Lin, Z.; Wang, W.; Horton, W.; Klasky, S.; Decyk, V.; Ma, K.-L.; Chames, J.; Adams, M.
2011-09-21
The three-year project GPS-TTBP resulted in over 152 publications and 135 presentations. This summary focuses on the scientific progress made by the project team. A major focus of the project was on the physics intrinsic rotation in tokamaks. Progress included the first ever flux driven study of net intrinsic spin-up, mediated by boundary effects (in collaboration with CPES), detailed studies of the microphysics origins of the Rice scaling, comparative studies of symmetry breaking mechanisms, a pioneering study of intrinsic torque driven by trapped electron modes, and studies of intrinsic rotation generation as a thermodynamic engine. Validation studies were performed with C-Mod, DIII-D and CSDX. This work resulted in very successful completion of the FY2010 Theory Milestone Activity for OFES, and several prominent papers of the 2008 and 2010 IAEA Conferences. A second major focus was on the relation between zonal flow formation and transport non-locality. This culminated in the discovery of the ExB staircase - a conceptually new phenomenon. This also makes useful interdisciplinary contact with the physics of the PV staircase, well-known in oceans and atmospheres. A third topic where progress was made was in the simulation and theory of turbulence spreading. This work, now well cited, is important for understanding the dynamics of non-locality in turbulent transport. Progress was made in studies of conjectured non-diffusive transport in trapped electron turbulence. Pioneering studies of ITB formation, coupling to intrinsic rotation and hysteresis were completed. These results may be especially significant for future ITER operation. All told, the physics per dollar performance of this project was quite good. The intense focus was beneficial and SciDAC resources were essential to its success.
Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
International Nuclear Information System (INIS)
Diamond, P.H.; Lin, Z.; Wang, W.; Horton, W.; Klasky, S.; Decyk, V.; Ma, K.-L.; Chames, J.; Adams, M.
2011-01-01
The three-year project GPS-TTBP resulted in over 152 publications and 135 presentations. This summary focuses on the scientific progress made by the project team. A major focus of the project was on the physics intrinsic rotation in tokamaks. Progress included the first ever flux driven study of net intrinsic spin-up, mediated by boundary effects (in collaboration with CPES), detailed studies of the microphysics origins of the Rice scaling, comparative studies of symmetry breaking mechanisms, a pioneering study of intrinsic torque driven by trapped electron modes, and studies of intrinsic rotation generation as a thermodynamic engine. Validation studies were performed with C-Mod, DIII-D and CSDX. This work resulted in very successful completion of the FY2010 Theory Milestone Activity for OFES, and several prominent papers of the 2008 and 2010 IAEA Conferences. A second major focus was on the relation between zonal flow formation and transport non-locality. This culminated in the discovery of the ExB staircase - a conceptually new phenomenon. This also makes useful interdisciplinary contact with the physics of the PV staircase, well-known in oceans and atmospheres. A third topic where progress was made was in the simulation and theory of turbulence spreading. This work, now well cited, is important for understanding the dynamics of non-locality in turbulent transport. Progress was made in studies of conjectured non-diffusive transport in trapped electron turbulence. Pioneering studies of ITB formation, coupling to intrinsic rotation and hysteresis were completed. These results may be especially significant for future ITER operation. All told, the physics per dollar performance of this project was quite good. The intense focus was beneficial and SciDAC resources were essential to its success.
Theory of anomalous transport in H-mode plasmas
International Nuclear Information System (INIS)
Itoh, S.; Itoh, K.; Fukuyama, A.; Yagi, M.
1993-05-01
Theory of the anomalous transport is developed, and the unified formula for the L- and H-mode plasmas is presented. The self-sustained ballooning-mode turbulence is solved in the presence of the inhomogeneous radial electric field, E r . Reductions in transport coefficients and the amplitude and decorrelation length of fluctuations due to E r ' are quantitatively analyzed. Combined with the E r -bifurcation model, the thickness of the transport barrier is simultaneously determined. (author)
Ion turbulence and thermal transport in laser-produced plasmas
International Nuclear Information System (INIS)
Barr, H.C.; Boyd, T.J.M.
1982-01-01
In the interaction of high-intensity lasers with target plasmas the transport of thermal energy from the region in which the radiation is absorbed, to the cold dense plasma in the interior of the target, is an issue of central importance. The role of ion turbulence as a flux limiter is addressed with particular regard to recent experiments in which target plasmas were irradiated by 1.06 μm neodymium laser light at irradiances of 10 15 W cm - 2 and greater. Saturation levels of the ion-acoustic turbulence driven by a combination of a suprathermal electron current and a heat flux are calculated on the basis of perturbed orbit theory. The levels of turbulence are found to be markedly lower than those commonly estimated from simple trapping arguments and too low to explain the thermal flux inhibition observed in the experiments used as a basis for the model. (author)
Reducing Turbulent Transport in Toroidal Configurations via Shaping
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2011-01-01
Recent progress in reducing turbulent transport in stellarators and tokamaks by 3D shaping using a stellarator optimization code in conjunction with a gyrokinetic code is presented. The original applications of the method focussed on ion temperature gradient transport in a quasi-axisymmetric stellarator design. Here, an examination of both other turbulence channels and other starting configurations is initiated. It is found that the designs evolved for transport from ion temperature gradient turbulence also display reduced transport from other transport channels whose modes are also stabilized by improved curvature, such as electron temperature gradient and ballooning modes. The optimizer is also applied to evolving from a tokamak, finding appreciable turbulence reduction for these devices as well. From these studies, improved understanding is obtained of why the deformations found by the optimizer are beneficial, and these deformations are related to earlier theoretical work in both stellarators and tokamaks.
Sogachev, Andrey; Kelly, Mark
2016-03-01
Displacement height ( d) is an important parameter in the simple modelling of wind speed and vertical fluxes above vegetative canopies, such as forests. Here we show that, aside from implicit definition through a (displaced) logarithmic profile, accepted formulations for d do not consistently predict flow properties above a forest. Turbulent transport can affect the displacement height, and is an integral part of what is called the roughness sublayer. We develop a more general approach for estimation of d, through production of turbulent kinetic energy and turbulent transport, and show how previous stress-based formulations for displacement height can be seen as simplified cases of a more general definition including turbulent transport. Further, we also give a simplified and practical form for d that is in agreement with the general approach, exploiting the concept of vortex thickness scale from mixing-layer theory. We assess the new and previous displacement height formulations by using flow statistics derived from the atmospheric boundary-layer Reynolds-averaged Navier-Stokes model SCADIS as well as from wind-tunnel observations, for different vegetation types and flow regimes in neutral conditions. The new formulations tend to produce smaller d than stress-based forms, falling closer to the classic logarithmically-defined displacement height. The new, more generally defined, displacement height appears to be more compatible with profiles of components of the turbulent kinetic energy budget, accounting for the combined effects of turbulent transport and shear production. The Coriolis force also plays a role, introducing wind-speed dependence into the behaviour of the roughness sublayer; this affects the turbulent transport, shear production, stress, and wind speed, as well as the displacement height, depending on the character of the forest. We further show how our practical (`mixing-layer') form for d matches the new turbulence-based relation, as well as
Stochastic Theory of Turbulence Mixing by Finite Eddies in the Turbulent Boundary Layer
Dekker, H.; Leeuw, G. de; Maassen van den Brink, A.
1995-01-01
Turbulence mixing is treated by means of a novel formulation of nonlocal K-theory, involving sample paths and a stochastic hypothesis. The theory simplifies for mixing by exchange (strong-eddies) and is then applied to the boundary layer (involving scaling). This maps boundary layer turbulence onto
DEFF Research Database (Denmark)
Diamond, P.H.; McDevitt, C.J.; Güran, Ö.D.
2009-01-01
Recent results in the theory of turbulent momentum transport and the origins of intrinsic rotation are summarized. Special attention is focused on aspects of momentum transport critical to intrinsic rotation, namely the residual stress and the edge toroidal flow velocity pinch. Novel results...
Statistical theory and transition in multiple-scale-lengths turbulence in plasmas
Energy Technology Data Exchange (ETDEWEB)
Itoh, Sanae-I. [Research Institute for Applied Mechanics, Kyushu Univ., Kasuga, Fukuoka (Japan); Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)
2001-06-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Nonlinear interactions in the same kind of fluctuations as well as nonlinear interplay between different classes of fluctuations are kept in the analysis. Nonlinear interactions are modelled as turbulent drag, nonlinear noise and nonlinear drive, and a set of Langevin equations is formulated. With the help of an Ansatz of a large number of degrees of freedom with positive Lyapunov number, Langevin equations are solved and the fluctuation dissipation theorem in the presence of strong plasma turbulence has been derived. A case where two driving mechanisms (one for micro mode and the other for semi-micro mode) coexist is investigated. It is found that there are several states of fluctuations: in one state, the micro mode is excited and the semi-micro mode is quenched; in the other state, the semi-micro mode is excited, and the micro mode remains at finite but suppressed level. New type of turbulence transition is obtained, and a cusp type catastrophe is revealed. A phase diagram is drawn for turbulence which is composed of multiple classes of fluctuations. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. Finally, the nonlocal heat transport due to the long-wave-length fluctuations, which are noise-pumped by shorter-wave-length ones, is analyzed and the impact on transient transport problems is discussed. (author)
Resistive drift wave turbulence and transport
International Nuclear Information System (INIS)
Wakatani, M.
1986-01-01
Our efforts for studying the properties of resistive drift wave turbulence by using model mode-coupling equations are shown. It may be related to the edge turbulence and the associated anomalous transport in tokamaks or in stellarator/heliotron. (author)
International Nuclear Information System (INIS)
Diamond, P.H.; Biglari, H.; Gang, F.Y.
1991-01-01
Recent advances in the theory of trapped particle pressure gradient driven turbulence are summarized. A novel theory of trapped ion convective cell turbulence is presented. It is shown that non-linear transfer to small scales occurs, and that saturation levels are not unphysically large, as previously thought. As the virulent saturation mechanism of ion Compton scattering is shown to result in weak turbulence at higher frequencies, it is thus likely that trapped ion convective cells are the major agent of tokamak transport. Fluid like trapped electron modes at short wavelengths (k θ ρ i > 1) are shown to drive an inward particle pinch. The characteristics of convective cell turbulence in flat density discharges are described, as is the stability of dissipative trapped electron modes in stellarators, with flexible magnetic field structure. The role of cross-correlations in the dynamics of multifield models of drift wave turbulence is discussed. (author). 32 refs, 8 figs, 1 tab
Turbulent transport in the atmospheric surface layer
Energy Technology Data Exchange (ETDEWEB)
Tagesson, Torbern [Dept. of Physical Geography and Ecosystem Science, Lund Univ., Lund (Sweden)
2012-04-15
In the modelling of transport and accumulation of the radioactive isotope carbon-14 (C-14) in the case of a potential release from a future repository of radioactive waste, it is important to describe the transport of the isotope in the atmosphere. This report aims to describe the turbulent transport within the lower part of the atmosphere; the inertial surface layer and the roughness sublayer. Transport in the inertial surface layer is dependent on several factors, whereof some can be neglected under certain circumstances. Under steady state conditions, fully developed turbulent conditions, in flat and horizontal homogeneous areas, it is possible to apply an eddy diffusivity approach for estimating vertical transport of C. The eddy diffusivity model assumes that there is proportionality between the vertical gradient and the transport of C. The eddy diffusivity is depending on the atmospheric turbulence, which is affected by the interaction between mean wind and friction of the ground surface and of the sensible heat flux in the atmosphere. In this report, it is described how eddy diffusivity of the inertial surface layer can be estimated from 3-d wind measurements and measurements of sensible heat fluxes. It is also described how to estimate the eddy diffusivity in the inertial surface layer from profile measurements of temperature and wind speed. Close to the canopy, wind and C profiles are influenced by effects of the surface roughness; this section of the atmosphere is called the roughness sublayer. Its height is up to {approx}3 times the height of the plant canopy. When the mean wind interacts with the canopy, turbulence is not only produced by shear stress and buoyancy, it is additionally created by wakes, which are formed behind the plants. Turbulence is higher than it would be over a flat surface, and the turbulent transport is hereby more efficient. Above the plant canopy, but still within the roughness sublayer, a function that compensates for the effect
Turbulent transport in the atmospheric surface layer
International Nuclear Information System (INIS)
Tagesson, Torbern
2012-04-01
In the modelling of transport and accumulation of the radioactive isotope carbon-14 (C-14) in the case of a potential release from a future repository of radioactive waste, it is important to describe the transport of the isotope in the atmosphere. This report aims to describe the turbulent transport within the lower part of the atmosphere; the inertial surface layer and the roughness sublayer. Transport in the inertial surface layer is dependent on several factors, whereof some can be neglected under certain circumstances. Under steady state conditions, fully developed turbulent conditions, in flat and horizontal homogeneous areas, it is possible to apply an eddy diffusivity approach for estimating vertical transport of C. The eddy diffusivity model assumes that there is proportionality between the vertical gradient and the transport of C. The eddy diffusivity is depending on the atmospheric turbulence, which is affected by the interaction between mean wind and friction of the ground surface and of the sensible heat flux in the atmosphere. In this report, it is described how eddy diffusivity of the inertial surface layer can be estimated from 3-d wind measurements and measurements of sensible heat fluxes. It is also described how to estimate the eddy diffusivity in the inertial surface layer from profile measurements of temperature and wind speed. Close to the canopy, wind and C profiles are influenced by effects of the surface roughness; this section of the atmosphere is called the roughness sublayer. Its height is up to ∼3 times the height of the plant canopy. When the mean wind interacts with the canopy, turbulence is not only produced by shear stress and buoyancy, it is additionally created by wakes, which are formed behind the plants. Turbulence is higher than it would be over a flat surface, and the turbulent transport is hereby more efficient. Above the plant canopy, but still within the roughness sublayer, a function that compensates for the effect of
Theory of self-sustained turbulence in confined plasmas
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.-I.; Fukuyama, A.; Yagi, M.
1996-01-01
This article reviews some aspects of recent theoretical activities in Japan on the problem of turbulent transport in confined plasmas. The method of self-sustained turbulence is discussed. The process of the renormalization is shown and the turbulent Prandtl number is introduced. Nonlinear destabilization by the electron momentum diffusion is explained. The nonlinear eigenmode equation is derived for the dressed-test-mode for the inhomogeneous plasma in the shear magnetic field. The eigenvalue equation is solved, and the least stable mode determines the anomalous transport coefficient. The formula of the thermal conductivity is presented for the system of bad average magnetic curvature (current diffusive interchange mode (CDIM) turbulence) and that for the average good magnetic curvature (current diffusive ballooning mode (CDBM) turbulence). The transport coefficient, scale length of fluctuations and fluctuation level are shown to be an increasing function of the pressure gradient. Verification by use of the nonlinear simulation is shown. The bifurcation of the electric field and improved confinement are addressed, in order to explain the H-mode physics. The improved confinement and dynamics such as ELMs are explained. Application to the transport analysis of tokamaks is also presented, including explanations of the L-mode confinement, internal transport barrier, and the role of the current profile control
International Nuclear Information System (INIS)
Biskamp, D.; Nuehrenberg, J.; Diamond, P.H.; Garbet, X.; Lin, Z.; Rogers, R.N.
2000-01-01
This IAEA Technical Committee Meeting on plasma transport theory was organized jointly by the Max-Planck-Institute for Plasma Physics, Garching, and the IAEA, Vienna. It took place on 21-23 June 1999 in Kloster Seeon, Germany. The topics were: 1. Turbulent transport in the tokamak core plasma; 2. Turbulence suppression, shear amplification and transport bifurcation dynamics; 3. Turbulence transport in the tokamak edge plasma; 4. Global aspects of turbulent transport in tokamak plasmas; 5. Neoclassical transport, in particular in stellarators
Turbulent momentum transport due to neoclassical flows
International Nuclear Information System (INIS)
Lee, Jungpyo; Barnes, Michael; Parra, Felix I; Belli, Emily; Candy, Jeff
2015-01-01
Intrinsic toroidal rotation in a tokamak can be driven by turbulent momentum transport due to neoclassical flow effects breaking a symmetry of turbulence. In this paper we categorize the contributions due to neoclassical effects to the turbulent momentum transport, and evaluate each contribution using gyrokinetic simulations. We find that the relative importance of each contribution changes with collisionality. For low collisionality, the dominant contributions come from neoclassical particle and parallel flows. For moderate collisionality, there are non-negligible contributions due to neoclassical poloidal electric field and poloidal gradients of density and temperature, which are not important for low collisionality. (paper)
Statistical analysis of anomalous transport in resistive interchange turbulence
International Nuclear Information System (INIS)
Sugama, Hideo; Wakatani, Masahiro.
1992-01-01
A new anomalous transport model for resistive interchange turbulence is derived from statistical analysis applying two-scale direct-interaction approximation to resistive magnetohydrodynamic equations with a gravity term. Our model is similar to the K-ε model for eddy viscosity of turbulent shear flows in that anomalous transport coefficients are expressed in terms of by the turbulent kinetic energy K and its dissipation rate ε while K and ε are determined by transport equations. This anomalous transport model can describe some nonlocal effects such as those from boundary conditions which cannot be treated by conventional models based on the transport coefficients represented by locally determined plasma parameters. (author)
Turbulent Transport in a Three-dimensional Solar Wind
Energy Technology Data Exchange (ETDEWEB)
Shiota, D. [Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Zank, G. P.; Adhikari, L.; Hunana, P. [Center for Space Plasma and Aeronomic Research (CSPAR), Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Telloni, D. [INAF—Astrophysical Observatory of Torino, Via Osservatorio 20, I-10025 Pino Torinese (Italy); Bruno, R., E-mail: shiota@isee.nagoya-u.ac.jp [INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy)
2017-03-01
Turbulence in the solar wind can play essential roles in the heating of coronal and solar wind plasma and the acceleration of the solar wind and energetic particles. Turbulence sources are not well understood and thought to be partly enhanced by interaction with the large-scale inhomogeneity of the solar wind and the interplanetary magnetic field and/or transported from the solar corona. To investigate the interaction with background inhomogeneity and the turbulence sources, we have developed a new 3D MHD model that includes the transport and dissipation of turbulence using the theoretical model of Zank et al. We solve for the temporal and spatial evolution of three moments or variables, the energy in the forward and backward fluctuating modes and the residual energy and their three corresponding correlation lengths. The transport model is coupled to our 3D model of the inhomogeneous solar wind. We present results of the coupled solar wind-turbulence model assuming a simple tilted dipole magnetic configuration that mimics solar minimum conditions, together with several comparative intermediate cases. By considering eight possible solar wind and turbulence source configurations, we show that the large-scale solar wind and IMF inhomogeneity and the strength of the turbulence sources significantly affect the distribution of turbulence in the heliosphere within 6 au. We compare the predicted turbulence distribution results from a complete solar minimum model with in situ measurements made by the Helios and Ulysses spacecraft, finding that the synthetic profiles of the turbulence intensities show reasonable agreement with observations.
Suprathermal ion transport in turbulent magnetized plasmas
International Nuclear Information System (INIS)
Bovet, A. D.
2015-01-01
Suprathermal ions, which have an energy greater than the quasi-Maxwellian background plasma temperature, are present in many laboratory and astrophysical plasmas. In fusion devices, they are generated by the fusion reactions and auxiliary heating. Controlling their transport is essential for the success of future fusion devices that could provide a clean, safe and abundant source of electric power to our society. In space, suprathermal ions include energetic solar particles and cosmic rays. The understanding of the acceleration and transport mechanisms of these particles is still incomplete. Basic plasma devices allow detailed measurements that are not accessible in astrophysical and fusion plasmas, due to the difficulty to access the former and the high temperatures of the latter. The basic toroidal device TORPEX offers an easy access for diagnostics, well characterized plasma scenarios and validated numerical simulations of its turbulence dynamics, making it the ideal platform for the investigation of suprathermal ion transport. This Thesis presents three-dimensional measurements of a suprathermal ion beam injected in turbulent TORPEX plasmas. The combination of uniquely resolved measurements and first principle numerical simulations reveals the general non-diffusive nature of the suprathermal ion transport. A precise characterization of their transport regime shows that, depending on their energies, suprathermal ions can experience either a super diffusive transport or a subdiffusive transport in the same background turbulence. The transport character is determined by the interaction of the suprathermal ion orbits with the turbulent plasma structures, which in turn depends on the ratio between the ion energy and the background plasma temperature. Time-resolved measurements reveal a clear difference in the intermittency of suprathermal ions time-traces depending on the transport regime they experience. Conditionally averaged measurements uncover the influence of
Group-kinetic theory and modeling of atmospheric turbulence
Tchen, C. M.
1989-01-01
A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.
Introduction to the theory of fluid and magnetofluid turbulence
International Nuclear Information System (INIS)
Montgomery, D.
1984-03-01
This set of notes was transcribed from the tape recording of three lectures given at the Institute of Plasma Physics, Nagoya University, in June, 1983. The lectures were intended to provide an introduction to the theory of magnetofluid turbulence which is a relatively new branch of plasma physics. It is related more closely to classic fluid dynamics than to the nonlinear theory of plasma oscillation. For this reason, fluid turbulence theory was reviewed as the background of the subject. The first lecture is on the origins of fluid and magnetofluid turbulence. The universal transition to turbulence takes place at sufficiently high Reynolds number, well above the critical threshold. The second lecture is on closures, attempt on dynamical theories. The Navier-Stokes case is discussed, and the attempt to reduce the number of the degrees of freedom, the importance of helicity in MHD, the direct interaction approximation (DIA) and others are explained. The third lecture is on the cascade and inverse cascade in fluid and magnetofluid. The idea of cascade was introduced into the theory of Navier-Stokes turbulence around 1941. The calculation of a form for inertial range energy spectra, the relation with dissipation rate, the tendency of migrating to long wavelength, the simulation of decaying turbulence, the numbers characterizing MHD and others are discussed. (Kako, I.)
Turbulent transport of large particles in the atmospheric boundary layer
Richter, D. H.; Chamecki, M.
2017-12-01
To describe the transport of heavy dust particles in the atmosphere, assumptions must typically be made in order to connect the micro-scale emission processes with the larger-scale atmospheric motions. In the context of numerical models, this can be thought of as the transport process which occurs between the domain bottom and the first vertical grid point. For example, in the limit of small particles (both low inertia and low settling velocity), theory built upon Monin-Obukhov similarity has proven effective in relating mean dust concentration profiles to surface emission fluxes. For increasing particle mass, however, it becomes more difficult to represent dust transport as a simple extension of the transport of a passive scalar due to issues such as the crossing trajectories effect. This study focuses specifically on the problem of large particle transport and dispersion in the turbulent boundary layer by utilizing direct numerical simulations with Lagrangian point-particle tracking to determine under what, if any, conditions the large dust particles (larger than 10 micron in diameter) can be accurately described in a simplified Eulerian framework. In particular, results will be presented detailing the independent contributions of both particle inertia and particle settling velocity relative to the strength of the surrounding turbulent flow, and consequences of overestimating surface fluxes via traditional parameterizations will be demonstrated.
Group-kinetic theory of turbulence
Tchen, C. M.
1986-01-01
The two phases are governed by two coupled systems of Navier-Stokes equations. The couplings are nonlinear. These equations describe the microdynamical state of turbulence, and are transformed into a master equation. By scaling, a kinetic hierarchy is generated in the form of groups, representing the spectral evolution, the diffusivity and the relaxation. The loss of memory in formulating the relaxation yields the closure. The network of sub-distributions that participates in the relaxation is simulated by a self-consistent porous medium, so that the average effect on the diffusivity is to make it approach equilibrium. The kinetic equation of turbulence is derived. The method of moments reverts it to the continuum. The equation of spectral evolution is obtained and the transport properties are calculated. In inertia turbulence, the Kolmogoroff law for weak coupling and the spectrum for the strong coupling are found. As the fluid analog, the nonlinear Schrodinger equation has a driving force in the form of emission of solitons by velocity fluctuations, and is used to describe the microdynamical state of turbulence. In order for the emission together with the modulation to participate in the transport processes, the non-homogeneous Schrodinger equation is transformed into a homogeneous master equation. By group-scaling, the master equation is decomposed into a system of transport equations, replacing the Bogoliubov system of equations of many-particle distributions. It is in the relaxation that the memory is lost when the ensemble of higher-order distributions is simulated by an effective porous medium. The closure is thus found. The kinetic equation is derived and transformed into the equation of spectral flow.
Renormalization theory of stationary homogeneous strong turbulence in a collisionless plasma
International Nuclear Information System (INIS)
Zhang, Y.Z.
1984-01-01
A renormalization procedure for the perturbation expansion of the Vlasov-Poisson equation is presented to describe stationary homogeneous turbulence. By using the diagramatic scheme the theory is shown to be renormalizable to any order. The expressions for the renormalized propagator, the renormalized dielectric function, and the intrinsically incoherent source are given. The renormalization leads to a complete separation of the fluctuating distribution function f/sub k/ into two parts, the coherent part, which is proved to represent the dielectric effect of the medium, and the intrinsically incoherent part, which represents the effect of nonlinear source. The turbulent collisional operator in the transport equation is proved equal to GAMMA 0 , the frequency broadening when k = 0
A new turbulence-based model for sand transport
Mayaud, Jerome; Wiggs, Giles; Bailey, Richard
2016-04-01
Knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes. While many aeolian studies have relied on time-averaged parameters such as wind velocity (U) and wind shear velocity (u*) to determine sediment flux, there is increasing evidence that high-frequency turbulence is an important driving force behind the entrainment and transport of sand. However, turbulence has yet to be incorporated into a functional sand transport model that can be used for predictive purposes. In this study we present a new transport model (the 'turbulence model') that accounts for high-frequency variations in the horizontal (u) and vertical (w) components of wind flow. The turbulence model is fitted to wind velocity and sediment transport data from a field experiment undertaken in Namibia's Skeleton Coast National Park, and its performance at three temporal resolutions (10 Hz, 1 Hz, 1 min) is compared to two existing models that rely on time-averaged wind velocity data (Radok, 1977; Dong et al., 2003). The validity of the three models is analysed under a variety of saltation conditions, using a 2-hour (1 Hz measurement resolution) dataset from the Skeleton Coast and a 5-hour (1 min measurement resolution) dataset from the southwestern Kalahari Desert. The turbulence model is shown to outperform the Radok and Dong models when predicting total saltation count over the three experimental periods. For all temporal resolutions presented in this study (10 Hz-10 min), the turbulence model predicted total saltation count to within at least 0.34%, whereas the Radok and Dong models over- or underestimated total count by up to 5.50% and 20.53% respectively. The strong performance of the turbulence model can be attributed to a lag in mass flux response built into its formulation, which can be adapted depending on the temporal resolution of investigation. This accounts for the inherent lag within the physical
Transport due to ion pressure gradient turbulence
International Nuclear Information System (INIS)
Connor, J.W.
1986-01-01
Turbulent transport due to the ion pressure gradient (or temperature drift) instability is thought to be significant when etasub(i)=d(ln Tsub(i))/d(ln n)>1. The invariance properties of the governing equations under scale transformations are used to discuss the characteristics of this turbulence. This approach not only clarifies the relationships between earlier treatments but also, in certain limits, completely determines the scaling properties of the fluctuations and the consequent thermal transport. (author)
Theory of neoclassical ion temperature-gradient-driven turbulence
Kim, Y. B.; Diamond, P. H.; Biglari, H.; Callen, J. D.
1991-02-01
The theory of collisionless fluid ion temperature-gradient-driven turbulence is extended to the collisional banana-plateau regime. Neoclassical ion fluid evolution equations are developed and utilized to investigate linear and nonlinear dynamics of negative compressibility ηi modes (ηi≡d ln Ti/d ln ni). In the low-frequency limit (ωB2p. As a result of these modifications, growth rates are dissipative, rather than sonic, and radial mode widths are broadened [i.e., γ˜k2∥c2s(ηi -(2)/(3) )/μi, Δx˜ρs(Bt/Bp) (1+ηi)1/2, where k∥, cs, and ρs are the parallel wave number, sound velocity, and ion gyroradius, respectively]. In the limit of weak viscous damping, enhanced neoclassical polarization persists and broadens radial mode widths. Linear mixing length estimates and renormalized turbulence theory are used to determine the ion thermal diffusivity in both cases. In both cases, a strong favorable dependence of ion thermal diffusivity on Bp (and hence plasma current) is exhibited. Furthermore, the ion thermal diffusivity for long wavelength modes exhibits favorable density scaling. The possible role of neoclassical ion temperature-gradient-driven modes in edge fluctuations and transport in L-phase discharges and the L to H transition is discussed.
Momentum-energy transport from turbulence driven by parallel flow shear
International Nuclear Information System (INIS)
Dong, J.Q.; Horton, W.; Bengtson, R.D.; Li, G.X.
1994-04-01
The low frequency E x B turbulence driven by the shear in the mass flow velocity parallel to the magnetic field is studied using the fluid theory in a slab configuration with magnetic shear. Ion temperature gradient effects are taken into account. The eigenfunctions of the linear instability are asymmetric about the mode rational surfaces. Quasilinear Reynolds stress induced by such asymmetric fluctuations produces momentum and energy transport across the magnetic field. Analytic formulas for the parallel and perpendicular Reynolds stress, viscosity and energy transport coefficients are given. Experimental observations of the parallel and poloidal plasma flows on TEXT-U are presented and compared with the theoretical models
Momentum and scalar transport at the turbulent/non-turbulent interface of a jet
DEFF Research Database (Denmark)
Westerweel, J.; Fukushima, C.; Pedersen, Jakob Martin
2009-01-01
and well-defined bounding interface between the turbulent and non-turbulent regions of flow. The jet carries a fluorescent dye measured with planar laser-induced fluorescence (LIF), and the surface discontinuity in the scalar concentration is identified as the fluctuating turbulent jet interface. Thence...... velocity and mean scalar and a tendency towards a singularity in mean vorticity. These actual or asymptotic discontinuities are consistent with the conditional mean momentum and scalar transport equations integrated across the interface. Measurements of the fluxes of turbulent kinetic energy and enstrophy...
Energetics of turbulent transport processes in tokamaks
International Nuclear Information System (INIS)
Haas, F.A.; Thyagaraja, A.
1987-01-01
The effect of electromagnetic turbulence on electrons and ions under Tokamak conditions is considered using a kinetic description. Taking the magnetic fluctuation spectrum as given, the density fluctuation spectrum is self-consistently calculated taking account of quasi-neutrality. The calculation is valid for arbitrary collisionality and appropriate to low frequencies typical of experiment. In addition to the usual enhancement of the radial electron energy transport, it is found that the turbulent fluctuations can heat the plasma at rates comparable to ordinary ohmic heating under well-defined conditions. Interestingly, electromagnetic turbulence appears to imply only an insignificant correction to the toroidal resistance of the plasma as estimated from Spitzer resistivity. The scalings of anomalous transport, fluctuations and heating with temperature and plasma volume are investigated. The assumption that the magnetic fluctuation spectrum of the turbulence is invariant under a wide range of conditions is shown to result in interesting consequences for JET-like plasmas. (author)
Turbulent transport in 2D collisionless guide field reconnection
Muñoz, P. A.; Büchner, J.; Kilian, P.
2017-02-01
Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic
Mean-field theory of differential rotation in density stratified turbulent convection
Rogachevskii, I.
2018-04-01
A mean-field theory of differential rotation in a density stratified turbulent convection has been developed. This theory is based on the combined effects of the turbulent heat flux and anisotropy of turbulent convection on the Reynolds stress. A coupled system of dynamical budget equations consisting in the equations for the Reynolds stress, the entropy fluctuations and the turbulent heat flux has been solved. To close the system of these equations, the spectral approach, which is valid for large Reynolds and Péclet numbers, has been applied. The adopted model of the background turbulent convection takes into account an increase of the turbulence anisotropy and a decrease of the turbulent correlation time with the rotation rate. This theory yields the radial profile of the differential rotation which is in agreement with that for the solar differential rotation.
Bao, Jian; Lau, Calvin; Kuley, Animesh; Lin, Zhihong; Fulton, Daniel; Tajima, Toshiki; Tri Alpha Energy, Inc. Team
2017-10-01
Collisional and turbulent transport in a field reversed configuration (FRC) is studied in global particle simulation by using GTC (gyrokinetic toroidal code). The global FRC geometry is incorporated in GTC by using a field-aligned mesh in cylindrical coordinates, which enables global simulation coupling core and scrape-off layer (SOL) across the separatrix. Furthermore, fully kinetic ions are implemented in GTC to treat magnetic-null point in FRC core. Both global simulation coupling core and SOL regions and independent SOL region simulation have been carried out to study turbulence. In this work, the ``logical sheath boundary condition'' is implemented to study parallel transport in the SOL. This method helps to relax time and spatial steps without resolving electron plasma frequency and Debye length, which enables turbulent transports simulation with sheath effects. We will study collisional and turbulent SOL parallel transport with mirror geometry and sheath boundary condition in C2-W divertor.
The Kolmogorov-Obukhov Statistical Theory of Turbulence
Birnir, Björn
2013-08-01
In 1941 Kolmogorov and Obukhov postulated the existence of a statistical theory of turbulence, which allows the computation of statistical quantities that can be simulated and measured in a turbulent system. These are quantities such as the moments, the structure functions and the probability density functions (PDFs) of the turbulent velocity field. In this paper we will outline how to construct this statistical theory from the stochastic Navier-Stokes equation. The additive noise in the stochastic Navier-Stokes equation is generic noise given by the central limit theorem and the large deviation principle. The multiplicative noise consists of jumps multiplying the velocity, modeling jumps in the velocity gradient. We first estimate the structure functions of turbulence and establish the Kolmogorov-Obukhov 1962 scaling hypothesis with the She-Leveque intermittency corrections. Then we compute the invariant measure of turbulence, writing the stochastic Navier-Stokes equation as an infinite-dimensional Ito process, and solving the linear Kolmogorov-Hopf functional differential equation for the invariant measure. Finally we project the invariant measure onto the PDF. The PDFs turn out to be the normalized inverse Gaussian (NIG) distributions of Barndorff-Nilsen, and compare well with PDFs from simulations and experiments.
Gyrokinetic simulations of turbulent transport: size scaling and chaotic behaviour
International Nuclear Information System (INIS)
Villard, L; Brunner, S; Casati, A; Aghdam, S Khosh; Lapillonne, X; McMillan, B F; Bottino, A; Dannert, T; Goerler, T; Hatzky, R; Jenko, F; Merz, F; Chowdhury, J; Ganesh, R; Garbet, X; Grandgirard, V; Latu, G; Sarazin, Y; Idomura, Y; Jolliet, S
2010-01-01
Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper presents some of the main recent advances in gyrokinetic theory and computing of turbulence. Solving 5D gyrokinetic equations for each species requires state-of-the-art high performance computing techniques involving massively parallel computers and parallel scalable algorithms. The various numerical schemes that have been explored until now, Lagrangian, Eulerian and semi-Lagrangian, each have their advantages and drawbacks. A past controversy regarding the finite size effect (finite ρ * ) in ITG turbulence has now been resolved. It has triggered an intensive benchmarking effort and careful examination of the convergence properties of the different numerical approaches. Now, both Eulerian and Lagrangian global codes are shown to agree and to converge to the flux-tube result in the ρ * → 0 limit. It is found, however, that an appropriate treatment of geometrical terms is necessary: inconsistent approximations that are sometimes used can lead to important discrepancies. Turbulent processes are characterized by a chaotic behaviour, often accompanied by bursts and avalanches. Performing ensemble averages of statistically independent simulations, starting from different initial conditions, is presented as a way to assess the intrinsic variability of turbulent fluxes and obtain reliable estimates of the standard deviation. Further developments concerning non-adiabatic electron dynamics around mode-rational surfaces and electromagnetic effects are discussed.
Turbulent Flow and Sand Dune Dynamics: Identifying Controls on Aeolian Sediment Transport
Weaver, C. M.; Wiggs, G.
2007-12-01
Sediment transport models are founded on cubic power relationships between the transport rate and time averaged flow parameters. These models have achieved limited success and recent aeolian and fluvial research has focused on the modelling and measurement of sediment transport by temporally varying flow conditions. Studies have recognised turbulence as a driving force in sediment transport and have highlighted the importance of coherent flow structures in sediment transport systems. However, the exact mechanisms are still unclear. Furthermore, research in the fluvial environment has identified the significance of turbulent structures for bedform morphology and spacing. However, equivalent research in the aeolian domain is absent. This paper reports the findings of research carried out to characterise the importance of turbulent flow parameters in aeolian sediment transport and determine how turbulent energy and turbulent structures change in response to dune morphology. The relative importance of mean and turbulent wind parameters on aeolian sediment flux was examined in the Skeleton Coast, Namibia. Measurements of wind velocity (using sonic anemometers) and sand transport (using grain impact sensors) at a sampling frequency of 10 Hz were made across a flat surface and along transects on a 9 m high barchan dune. Mean wind parameters and mass sand flux were measured using cup anemometers and wedge-shaped sand traps respectively. Vertical profile data from the sonic anemometers were used to compute turbulence and turbulent stress (Reynolds stress; instantaneous horizontal and vertical fluctuations; coherent flow structures) and their relationship with respect to sand transport and evolving dune morphology. On the flat surface time-averaged parameters generally fail to characterise sand transport dynamics, particularly as the averaging interval is reduced. However, horizontal wind speed correlates well with sand transport even with short averaging times. Quadrant
Turbulence spectra, transport, and E × B flows in helical plasmas
International Nuclear Information System (INIS)
Watanabe, T.-H.; Nunami, M.; Sugama, H.; Satake, S.; Matsuoka, S.; Ishizawa, A.; Tanaka, K.; Maeyama, Shinya
2012-11-01
Gyrokinetic simulation of ion temperature gradient turbulence and zonal flows for helical plasmas has been validated against the Large Helical Device experiments with high ion temperature, where a reduced modeling of ion heat transport is also considered. It is confirmed by the entropy transfer analysis that the turbulence spectrum elongated in the radial wavenumber space is associated with successive interactions with zonal flows. A novel multi-scale simulation for turbulence and zonal flows in poloidally-rotating helical plasmas has demonstrated strong zonal flow generation by turbulence, which implies that turbulent transport processes in non-axisymmetric systems are coupled to neoclassical transport through the macroscopic E × B flows determined by the ambipolarty condition for neoclassical particle fluxes. (author)
Statistical theory of plasmas turbulence
International Nuclear Information System (INIS)
Kim, Eun-jin; Anderson, Johan
2009-01-01
We present a statistical theory of intermittency in plasma turbulence based on short-lived coherent structures (instantons). In general, the probability density functions (PDFs) of the flux R are shown to have an exponential scaling P(R) ∝ exp (-cR s ) in the tails. In ion-temperature-gradient turbulence, the exponent takes the value s=3/2 for momentum flux and s=3 for zonal flow formation. The value of s follows from the order of the highest nonlinear interaction term and the moments for which the PDFs are computed. The constant c depends on the spatial profile of the coherent structure and other physical parameters in the model. Our theory provides a powerful mechanism for ubiquitous exponential scalings of PDFs, often observed in various tokamaks. Implications of the results, in particular, on structure formation are further discussed. (author)
A group-kinetic theory of turbulent collective collisions
International Nuclear Information System (INIS)
Tchen, C.M.; Misguich, J.H.
1983-05-01
The main objective is the derivation of the kinetic equation of turbulence which has a memory in the turbulent collision integral. We consider the basic pair-interaction, and the interaction between a fluctuation and the organized cluster of other fluctuations in the collection systems, called the multiple interaction. By a group-scaling procedure, a fluctuation is decomposed into three groups to represent the three coupled transport processes of evolution, transport coefficient, and relaxation. The kinetic equation of the scaled singlet distribution is capable of investigating the spectrum of turbulence without the need of the knowledge of the pair distribution. The exact propagator describes the detailed trajectory in the phase space, and is fundamental to the Lagrangian-Eulerian transformation. We calculate the propagator and its scaled groups by means of a probability of retrograde transition. Thus our derivation of the kinetic equation of the distribution involves a parallel development of the kinetic equations of the propagator and the transition probability. In this way, we can avoid the assumptions of independence and normality. Our result shows that the multiple interaction contributes to a shielding and an enchancement of the collision in weak turbulence and strong turbulence, respectively. The weak turbulence is dominated by the wave resonance, and the strong turbulence is dominated by the diffusion
BOOK REVIEW: Plasma and Fluid Turbulence: Theory and Modelling
Yoshizawa, A.; Itoh, S. I.; Itoh, K.
2003-03-01
extensive description of dynamo theory in Magnetohydrodynamic turbulence. This area has applications both in geophysics and plasma confinement by magnetic fields. The most well known example being the reversed field pinch. This part is fundamental in several respects and the principle of relaxation of the turbulence to quasi stationary states that can be predicted theoretically is very elegant. The problem of rotation of magnetized plasmas and its importance for obtaining internal transport barriers is also treated here. This part is entirely described by the one-fluid magnetohydrodynamic (MHD) equations. The next part deals with plasma turbulence. It starts from the Braginskii collisional fluid equations. These are then reduced for typical cases of quasi two dimensional plasma turbulence where the magnetic perturbations can be described by a vector potential which is parallel to the unperturbed magnetic field. Also a couple of well known sets of nonlinear electrostatic systems for drift waves are presented as well as a gyro-averaged kinetic description for inhomogeneous plasmas. Then, several low frequency eigenmodes in magnetized plasmas are described and finally the quasilinear theory of transport is presented. The following part deals with strongly nonlinear phenomena in inhomogeneous plasma turbulence. Here, concepts of importance for confinement such as convective cells, zonal flows and streamers are presented. As a natural continuation, renormalization and scale invariance methods for strongly nonlinear plasmas are given. Also non-Markovian properties are discussed. This is natural since turbulence in inhomogeneous plasmas typically has a rather large real eigenfrequency leading to memory of the wave phase. The next part deals with plasma turbulence driven by inhomogeneities. This is followed by a new part on flows where the flows this time are generated by the turbulence which is driven by plasma inhomogeneities. In particular flows driven by such instabilities can
New Theories on Boundary Layer Transition and Turbulence Formation
Directory of Open Access Journals (Sweden)
Chaoqun Liu
2012-01-01
Full Text Available This paper is a short review of our recent DNS work on physics of late boundary layer transition and turbulence. Based on our DNS observation, we propose a new theory on boundary layer transition, which has five steps, that is, receptivity, linear instability, large vortex structure formation, small length scale generation, loss of symmetry and randomization to turbulence. For turbulence generation and sustenance, the classical theory, described with Richardson's energy cascade and Kolmogorov length scale, is not observed by our DNS. We proposed a new theory on turbulence generation that all small length scales are generated by “shear layer instability” through multiple level ejections and sweeps and consequent multiple level positive and negative spikes, but not by “vortex breakdown.” We believe “shear layer instability” is the “mother of turbulence.” The energy transferring from large vortices to small vortices is carried out by multiple level sweeps, but does not follow Kolmogorov's theory that large vortices pass energy to small ones through vortex stretch and breakdown. The loss of symmetry starts from the second level ring cycle in the middle of the flow field and spreads to the bottom of the boundary layer and then the whole flow field.
Energy Technology Data Exchange (ETDEWEB)
Dubuit, N
2006-10-15
This work deals with the transport of impurities in magnetically confined thermonuclear plasmas. The accumulation of impurities in the core of the plasma would imply dramatic losses of energy that may lead to the extinction of the plasma. On the opposite, the injection of impurities in the plasma edge is considered as an efficient means to extract heat without damaging the first wall. The balance between these 2 contradictory constraints requires an accurate knowledge of the impurity transport inside the plasma. The effect of turbulence, the main transport mechanism for impurities is therefore a major issue. In this work, the complete formula of a turbulent flow of impurities for a given fluctuation spectrum has been inferred. The origin and features of the main accumulation processes have been identified. The main effect comes from the compressibility of the electrical shift speed in a plane perpendicular to the magnetic field. This compressibility appears to be linked to the curvature of the magnetic field. A less important effect is a thermal-diffusion process that is inversely proportional to the number of charges and then disappears for most type of impurities except the lightest. This effect implies an impurity flux proportional to the temperature gradient and its direction can change according to the average speed of fluctuations. A new version of the turbulence code TRB has been developed. This new version allows the constraints of the turbulence not by the gradients but by the flux which is more realistic. The importance of the processes described above has been confirmed by a comparison between calculation and experimental data from Tore-supra and the Jet tokamak. The prevailing role of the curvature of the magnetic field in the transport impurity is highlighted. (A.C.)
Radially sheared azimuthal flows and turbulent transport in a cylindrical helicon plasma device
International Nuclear Information System (INIS)
Tynan, G R; Burin, M J; Holland, C; Antar, G; Diamond, P H
2004-01-01
A radially sheared azimuthal flow is observed in a cylindrical helicon plasma device. The shear flow is roughly azimuthally symmetric and contains both time-stationary and slowly varying components. The turbulent radial particle flux is found to peak near the density gradient maximum and vanishes at the shear layer location. The shape of the radial plasma potential profile associated with the azimuthal E x B flow is predicted accurately by theory. The existence of the mean shear flow in a plasma with finite flow damping from ion-neutral collisions and no external momentum input implies the existence of radial angular momentum transport from the turbulent Reynolds-stress
Turbulent and neoclassical toroidal momentum transport in tokamak plasmas
International Nuclear Information System (INIS)
Abiteboul, J.
2012-10-01
The goal of magnetic confinement devices such as tokamaks is to produce energy from nuclear fusion reactions in plasmas at low densities and high temperatures. Experimentally, toroidal flows have been found to significantly improve the energy confinement, and therefore the performance of the machine. As extrinsic momentum sources will be limited in future fusion devices such as ITER, an understanding of the physics of toroidal momentum transport and the generation of intrinsic toroidal rotation in tokamaks would be an important step in order to predict the rotation profile in experiments. Among the mechanisms expected to contribute to the generation of toroidal rotation is the transport of momentum by electrostatic turbulence, which governs heat transport in tokamaks. Due to the low collisionality of the plasma, kinetic modeling is mandatory for the study of tokamak turbulence. In principle, this implies the modeling of a six-dimensional distribution function representing the density of particles in position and velocity phase-space, which can be reduced to five dimensions when considering only frequencies below the particle cyclotron frequency. This approximation, relevant for the study of turbulence in tokamaks, leads to the so-called gyrokinetic model and brings the computational cost of the model within the presently available numerical resources. In this work, we study the transport of toroidal momentum in tokamaks in the framework of the gyrokinetic model. First, we show that this reduced model is indeed capable of accurately modeling momentum transport by deriving a local conservation equation of toroidal momentum, and verifying it numerically with the gyrokinetic code GYSELA. Secondly, we show how electrostatic turbulence can break the axisymmetry and generate toroidal rotation, while a strong link between turbulent heat and momentum transport is identified, as both exhibit the same large-scale avalanche-like events. The dynamics of turbulent transport are
Turbulent transport of energetic ions
International Nuclear Information System (INIS)
Dannert, Tilman; Hauff, Thilo; Jenko, Frank; Guenter, Sibylle
2006-01-01
Approaching ITER operation, the issue of anomalous transport of fast particles becomes more and more important. This is partly because the ITER heating and current drive system relies heavily on neutral beam injection. Moreover burning plasmas are heated by fast fusion α particles.Fusion α particles are characterised by a fixed energy and an isotropic velocity distribution. Therefore they have gyroradii one magnitude larger than the thermal ions. The dependency of the particle diffusion of α test particles on the Kubo number K = VExBτc/λc (VExB mean E x B velocity, τc, λc correlation time and length of the turbulent potential) is presented. For different turbulent regimes, different dependency of the diffusion on the gyroradius is found. For large Kubo numbers, the transport is found to remain constant for gyroradii up to the correlation length of the potential, whereas it is drastically reduced in the small Kubo number regime.In the second part, a model for beam ions injected along the equilibrium magnetic field is described. The beam ions are treated gyrokinetically in a self-consistent way with the equilibrium distribution function taken as a shifted Maxwellian. The implications of such a model for the Vlasov equation, the field equations, and the calculation of moments and fluxes are discussed. Linear and nonlinear results, obtained with the gyrokinetic flux tube code GENE show the existence of a new instability driven by fast beam ions. The instability has a maximum growth rate at perpendicular wave numbers of kyρs ∼ 0.15 and depends mainly on the beam velocity and the density gradient of the beam ions. This instability leads to a replacement of bulk ion particle transport by fast ion particle transport, connected to a strongly enhanced heat flux. In the presence of this instability, the turbulent particle and heat transport is dominated by fast ions
Time dependent plasma viscosity and relation between neoclassical transport and turbulent transport
International Nuclear Information System (INIS)
Shaing, K.C.
2005-01-01
Time dependent plasma viscosities for asymmetric toroidal plasmas in various collisionality regimes are calculated. It is known that in the symmetric limit the time dependent plasma viscosities accurately describe plasma flow damping rate. Thus, time dependent plasma viscosities are important in modeling the radial electric field of the zonal flow. From the momentum balance equation, it is shown that, at the steady state, the balance of the viscosity force and the momentum source determines the radial electric field of the zonal flow. Thus, for a fixed source, the smaller the viscous force is, the larger the value of the radial electric field is, which in turn suppresses the turbulence fluctuations more and improves turbulence transport. However, the smaller the viscous force also implies the smaller the neoclassical transport fluxes based on the neoclassical flux-force relationship. We thus show that when neoclassical transport fluxes are improved so are the turbulent fluxes in toroidal plasmas. (author)
Energy Technology Data Exchange (ETDEWEB)
Zentgraf, Florian; Baum, Elias; Dreizler, Andreas [Fachgebiet Reaktive Strömungen und Messtechnik (RSM), Center of Smart Interfaces (CSI), Technische Universität Darmstadt, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Böhm, Benjamin [Fachgebiet Energie und Kraftwerkstechnik (EKT), Technische Universität Darmstadt, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Peterson, Brian, E-mail: brian.peterson@ed.ac.uk [Department of Mechanical Engineering, School of Engineering, Institute for Energy Systems, University of Edinburgh, The King’s Buildings, Mayfield Road, Edinburgh EH9 3JL, Scotland (United Kingdom)
2016-04-15
Planar particle image velocimetry (PIV) and tomographic PIV (TPIV) measurements are utilized to analyze turbulent statistical theory quantities and the instantaneous turbulence within a single-cylinder optical engine. Measurements are performed during the intake and mid-compression stroke at 800 and 1500 RPM. TPIV facilitates the evaluation of spatially resolved Reynolds stress tensor (RST) distributions, anisotropic Reynolds stress invariants, and instantaneous turbulent vortical structures. The RST analysis describes distributions of individual velocity fluctuation components that arise from unsteady turbulent flow behavior as well as cycle-to-cycle variability (CCV). A conditional analysis, for which instantaneous PIV images are sampled by their tumble center location, reveals that CCV and turbulence have similar contributions to RST distributions at the mean tumble center, but turbulence is dominant in regions peripheral to the tumble center. Analysis of the anisotropic Reynolds stress invariants reveals the spatial distribution of axisymmetric expansion, axisymmetric contraction, and 3D isotropy within the cylinder. Findings indicate that the mid-compression flow exhibits a higher tendency toward 3D isotropy than the intake flow. A novel post-processing algorithm is utilized to classify the geometry of instantaneous turbulent vortical structures and evaluate their frequency of occurrence within the cylinder. Findings are coupled with statistical theory quantities to provide a comprehensive understanding of the distribution of turbulent velocity components, the distribution of anisotropic states of turbulence, and compare the turbulent vortical flow distribution that is theoretically expected to what is experimentally observed. The analyses reveal requisites of important turbulent flow quantities and discern their sensitivity to the local flow topography and engine operation.
Turbulence and transport in a magnetized argon plasma
International Nuclear Information System (INIS)
Pots, B.F.M.
1979-01-01
An experimental study on turbulence and transport in the highly ionized argon plasma of a hollow cathode discharge is described. In order to determine the plasma parameters three standard diagnostics have been used, whilst two diagnostics have been developed to study the plasma turbulence. (Auth.)
Turbulent diffusion of chemically reacting flows: Theory and numerical simulations.
Elperin, T; Kleeorin, N; Liberman, M; Lipatnikov, A N; Rogachevskii, I; Yu, R
2017-11-01
The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)PLEEE81539-375510.1103/PhysRevE.90.053001] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damköhler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.
Turbulent transport across invariant canonical flux surfaces
International Nuclear Information System (INIS)
Hollenberg, J.B.; Callen, J.D.
1994-07-01
Net transport due to a combination of Coulomb collisions and turbulence effects in a plasma is investigated using a fluid moment description that allows for kinetic and nonlinear effects via closure relations. The model considered allows for ''ideal'' turbulent fluctuations that distort but preserve the topology of species-dependent canonical flux surfaces ψ number-sign,s triple-bond ∫ dF · B number-sign,s triple-bond ∇ x [A + (m s /q s )u s ] in which u s is the flow velocity of the fluid species. Equations for the net transport relative to these surfaces due to ''nonideal'' dissipative processes are found for the total number of particles and total entropy enclosed by a moving canonical flux surface. The corresponding particle transport flux is calculated using a toroidal axisymmetry approximation of the ideal surfaces. The resulting Lagrangian transport flux includes classical, neoclassical-like, and anomalous contributions and shows for the first time how these various contributions should be summed to obtain the total particle transport flux
Theory of resistivity-gradient-driven turbulence
International Nuclear Information System (INIS)
Garcia, L.; Carreras, B.A.; Diamond, P.H.; Callen, J.D.
1984-10-01
A theory of the nonlinear evolution and saturation of resistivity-driven turbulence, which evolves from linear rippling instabilities, is presented. The nonlinear saturation mechanism is identified both analytically and numerically. Saturation occurs when the turbulent diffusion of the resistivity is large enough so that dissipation due to parallel electron thermal conduction balances the nonlinearly modified resistivity gradient driving term. The levels of potential, resistivity, and density fluctuations at saturation are calculated. A combination of computational modeling and analytic treatment is used in this investigation
Breakdown of Onsager symmetry in neoclassical transport theory
International Nuclear Information System (INIS)
Molvig, K.; Bernstein, I.B.
1982-01-01
Neoclassical transport theory is developed in a Lagrangian rather than the usual Eulerian formulation.. It is shown that an underlying asymmetry exists in the neoclassical pinch and bootstrap effects and demonstrate the physical basis of the Onsager symmetry relationship in the pinch-bootstrap duality. A simple model calculation shows that low frequency turbulence can destroy the bootstrap current at levels, ephi-circumflex/Tsub(c) approximately 10 -2 , too low to affect the Ware pinch. (author)
Transport due to ion temperature gradient mode vortex turbulence
International Nuclear Information System (INIS)
Pavlenko, V.P.; Weiland, J.
1991-01-01
The ion energy transport due to an ensemble of nonlinear vortices is calculated in the test particle approximation for a strongly turbulent plasma. A diffusion coefficient proportional to the root of the stationary turbulence level is obtained. (au)
Density effects on tokamak edge turbulence and transport with magnetic X-points
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Nevins, W.M.; Rognlien, T.D.; Ryutov, D.D.; Umansky, M.V.; Pearlstein, L.D.; Bulmer, R.H.; Russell, D.A.; Myra, J.R.; D'Ippolito, D.A.; Greenwald, M.; Snyder, P.B.; Mahdavi, M.A.
2005-01-01
Results are presented from the 3D electromagnetic turbulence code BOUT, the 2D transport code UEDGE, and theoretical analysis of boundary turbulence and transport in a real divertor-plasma geometry and its relationship to the density limit. Key results include: (1) a transition of the boundary turbulence from resistive X-point to resistive-ballooning as a critical plasma density is exceeded; (2) formation of an X-point MARFE in 2D UEDGE transport simulations for increasing outboard radial transport as found by BOUT for increasing density; (3) identification of convective transport by localized plasma 'blobs' in the SOL at high density during neutral fueling, and decorrelation of turbulence between the midplane and the divertor leg due to strong X-point magnetic shear; (4) a new divertor-leg instability driven at high plasma beta by a radial tilt of the divertor plate. (author)
Turbulent transport in the MST reversed-field pinch
International Nuclear Information System (INIS)
Rempel, T.D.; Almagri, A.F.; Assadi, S.; Den Hartog, D.J.; Hokin, S.A.; Prager, S.C.; Sarff, J.S.; Shen, W.; Sidikman, K.L.; Spragins, C.W.; Sprott, J.C.; Stoneking, M.R.; Zita, E.J.
1991-11-01
Measurements of edge turbulence and the associated transport are ongoing in the Madison Symmetric Torus (R = 1.5 m, a = 0.52 m) reversed-field pinch using magnetic and electrostatic probes. Magnetic fluctuations are dominated by m = 1 and n ∼ 2R/a tearing modes. Particle losses induced by magnetic field fluctuations have been found to be ambipolar ( parallel B r > = O). Electrostatic fluctuations are broadband and turbulent, with mode widths δm ∼ 3--7 and δn ∼70--150. Particle, parallel current, and energy transport arising from coherent motion with the fluctuating ExB drift has been measured. Particle transport via this channel is comparable to the total particle loss from MST. Energy transport (from phi >/B o ) due to electrostatic fluctuations is relatively small, and parallel current transport (from parallel E chi >/B o ) may be small as well
Weak turbulence theory of Langmuir waves: A reconsideration of validity of quasilinear theory
International Nuclear Information System (INIS)
Liang, Y.M.; Diamond, P.H.
1991-01-01
The weak turbulence theory of Langmuir waves in a one-dimensional, one-species plasma is discussed. Analytical calculations using the theory of two-point correlation functions show that in the weak turbulence regime τ ac much-lt min[τ tr , γ k -1 ], the nonlinear enhancement of the mode growth rate relative to the linear Landau mode growth rate γ k L is rather weak, and quasilinear theory is reproduced at the lowest order. Hence this work also proves the validity of the quasilinear theory. Here τ ac ∼ (kΔv ph ) -1 is the phase-mixing time or the auto-correlation time, and τ tr ∼ (k 2 D ql ) -1/3 is the particle decorrelation time or the turbulence trapping time. In particular, the lowest order nonlinear correction to γ k L in the regime τ ac much-lt τ tr much-lt γ k -1 is proportional to (1/ω k τ tr )γ k L . Both corrections are additive, not multiplicative, and are of higher order in the weak turbulence expansion. The smallness of the corrections is due to the fact that the only mechanism for the relaxation of the plasma distribution function in a one-dimensional, one-species plasma is momentum exchange between waves and particles, which is exactly the interaction considered in the quasilinear theory. No like-like particle momentum exchange is allowed due to momentum conservation constraints. Similar calculations are also done for the traveling wave tube, which can be used to test this theory experimentally, especially for the case of bump-on-tail instability. A comparison of theoretical predictions with experimental results is presented. 3 refs
Turbulence and anomalous transport in toroidal plasmas
International Nuclear Information System (INIS)
Nordman, H.
1989-01-01
In present-day Tokamak fusion machines, instabilities and turbulence driven by temperature gradients can have a considerable impact on the confinement qualities. This thesis is mainly devoted to analyzing the nonlinear evolution of these instabilities and the associated turbulent transport. A combined analytical and numerical study of the ion temperature gradient driven turbulence is presented. An analytical expression for the ion thermal conductivity is derived and found to be in good agreement with the simulation results. The scaling properties of chi i are investigated and compared with experimental results. The transport due to the simultaneous presence of a trapped electron mode and an ion temperature gradient mode is analysed. It is found that the coupling of the modes can give rise to inward diffusive fluxes of both particles and energy. The tendency of the system to equilibrate density and temperature scale lengths is compared with recent experimental trends. The nonlinear behaviour of the instabilities is also studied in the context of low dimensional dynamical systems. Here, the relation between the fully nonlinear fluid models and the low dimensional models is discussed. The influence of a high frequency RF-field on the ion temperature gradient driven mode is investigated analytically. The consequences for mode stability and transport are considered. 23 refs
Turbulence and anomalous transport in toroidal plasmas
Energy Technology Data Exchange (ETDEWEB)
Nordman, H
1990-12-31
In present-day Tokamak fusion machines, instabilities and turbulence driven by temperature gradients can have a considerable impact on the confinement qualities. This thesis is mainly devoted to analyzing the nonlinear evolution of these instabilities and the associated turbulent transport. A combined analytical and numerical study of the ion temperature gradient driven turbulence is presented. An analytical expression for the ion thermal conductivity is derived and found to be in good agreement with the simulation results. The scaling properties of chi{sub i} are investigated and compared with experimental results. The transport due to the simultaneous presence of a trapped electron mode and an ion temperature gradient mode is analysed. It is found that the coupling of the modes can give rise to inward diffusive fluxes of both particles and energy. The tendency of the system to equilibrate density and temperature scale lengths is compared with recent experimental trends. The nonlinear behaviour of the instabilities is also studied in the context of low dimensional dynamical systems. Here, the relation between the fully nonlinear fluid models and the low dimensional models is discussed. The influence of a high frequency RF-field on the ion temperature gradient driven mode is investigated analytically. The consequences for mode stability and transport are considered. 23 refs.
Compressibility and rotation effects on transport suppression in magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Yoshizawa, A.
1996-01-01
Compressibility and rotation effects on turbulent transports in magnetohydrodynamic (MHD) flows under arbitrary mean field are investigated using a Markovianized two-scale statistical approach. Some new aspects of MHD turbulence are pointed out in close relation to plasma compressibility. Special attention is paid to the turbulent electromotive force, which plays a central role in the generation of magnetic and velocity fluctuations. In addition to plasma rotation, the interaction between compressibility and magnetic fields is shown to bring a few factors suppressing MHD fluctuations and, eventually, density and temperature transports, even in the presence of steep mean density and temperature gradients. This finding is discussed in the context of the turbulence-suppression mechanism in the tokamak close-quote s high-confinement modes. copyright 1996 American Institute of Physics
A reduced model for ion temperature gradient turbulent transport in helical plasmas
International Nuclear Information System (INIS)
Nunami, M.; Watanabe, T.-H.; Sugama, H.
2013-07-01
A novel reduced model for ion temperature gradient (ITG) turbulent transport in helical plasmas is presented. The model enables one to predict nonlinear gyrokinetic simulation results from linear gyrokinetic analyses. It is shown from nonlinear gyrokinetic simulations of the ITG turbulence in helical plasmas that the transport coefficient can be expressed as a function of the turbulent fluctuation level and the averaged zonal flow amplitude. Then, the reduced model for the turbulent ion heat diffusivity is derived by representing the nonlinear turbulent fluctuations and zonal flow amplitude in terms of the linear growth rate of the ITG instability and the linear response of the zonal flow potentials. It is confirmed that the reduced transport model results are in good agreement with those from nonlinear gyrokinetic simulations for high ion temperature plasmas in the Large Helical Device. (author)
Characterization of intermittency of impurity turbulent transport in tokamak edge plasmas
International Nuclear Information System (INIS)
Futatani, S.; Benkadda, S.; Nakamura, Y.; Kondo, K.
2008-01-01
The statistical properties of impurity transport of a tokamak edge plasma embedded in a dissipative drift-wave turbulence are investigated using structure function analysis. The impurities are considered as a passive scalar advected by the plasma flow. Two cases of impurity advection are studied and compared: A decaying impurities case (given by a diffusion-advection equation) and a driven case (forced by a mean scalar gradient). The use of extended self-similarity enables us to show that the relative scaling exponent of structure functions of impurity density and vorticity exhibit similar multifractal scaling in the decaying case and follows the She-Leveque model. However, this property is invalidated for the impurity driven advection case. For both cases, potential fluctuations are self-similar and exhibit a monofractal scaling in agreement with Kolmogorov-Kraichnan theory for two-dimensional turbulence. These results obtained with a passive scalar model agree also with test-particle simulations.
Numerical and Theoretical Studies of Turbulence and Transport with E x B Shear Flows
International Nuclear Information System (INIS)
Krommes, J.A.; Chance, M.S.; Hahm, T.S.; Lin, Z.
1999-01-01
This paper reports: (1) substantial transport reduction by turbulence-driven E x B flows observed in 3D nonlinear gyrokinetic simulations of microturbulence in magnetically-confined toroidal plasmas; (2) analytical derivation of the effective shearing rate for the time-dependent E x B flow; (3) interpretation of experimental data using linear gyrokinetic microinstability rotation models of E x B shear; and (4) other developments in gyrokinetic theory and simulation
On the Eulerian-Lagrangian Transform in the Statistical Theory of Turbulence
DEFF Research Database (Denmark)
Wandel, C. F:; Kofoed-Hansen, O.
1962-01-01
"Fundamental Problems in Turbulence" Conference Paper (see Abstr. 1962A024007). Two important types of probing of a turbulent velocity field droarr/dtoarr = voarr (voarr constant) and the Lagrangian probing defined by droarr/dtoarr = roarr (roarr t). Explicit expressions are derived for the trans......"Fundamental Problems in Turbulence" Conference Paper (see Abstr. 1962A024007). Two important types of probing of a turbulent velocity field droarr/dtoarr = voarr (voarr constant) and the Lagrangian probing defined by droarr/dtoarr = roarr (roarr t). Explicit expressions are derived...... for the transformation of autocorrelations and power spectra obtained by Eulerian and Lagrangian probing in the case of fully developed isotropic and homogeneous turbulence. The derivations are based on a statistical representation of the turbulent velocity field using the results of the equilibrium theory of turbulence....... The Taylor (1921) hypothesis is verified in the limit of high probing velocities. The Hay-Pasquill (1960) conjecture relating the Lagrangian and Eulerian power spectra results as an approximation to the transformation equations. Application of the results to the theory of turbulent diffusion is indicated....
Turbulence optimisation in stellarator experiments
Energy Technology Data Exchange (ETDEWEB)
Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)
2015-05-01
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.
Coarse Grained Transport Model for Neutrals in Turbulent SOL Plasmas
Energy Technology Data Exchange (ETDEWEB)
Marandet, Y.; Mekkaoui, A.; Genesio, P.; Rosato, J.; Capes, H.; Godbert-Mouret, L.; Koubiti, M.; Stamm, R., E-mail: yannick.marandet@univ-amu.fr [PIIM, CNRS/Aix-Marseille University, Marseille (France); Reiter, D.; Boerner, P. [IEK4, FZJ, Juelich (Germany)
2012-09-15
Full text: Edge plasmas of magnetic fusion devices exhibit strong intermittent turbulence, which governs perpendicular transport of particles and heat. Turbulent fluxes result from the coarse graining procedure used to derive the transport equation, which entails time averaging of the underlying equations governing the turbulent evolution of the electron and ion fluids. In previous works, we have pointed out that this averaging is not carried out on the Boltzmann equation that describes the transport of neutral particles (atoms, molecules) in current edge code suites (such as SOLPS). Since fluctuations in the far SOL are of order unity, calculating the transport of neutral particles, hence the source terms in plasma fluid equations, in the average plasma background might lead to misleading results. In particular, retaining the effects of fluctuations could affect the estimation of the importance of main chamber recycling, hence first wall sputtering by charge exchange atoms, as well as main chamber impurity contamination and transport. In this contribution, we obtain an exact coarse-grained equation for the average neutral density, assuming that density fluctuations are described by multivariate Gamma statistics. This equation is a scattering free Boltzmann equation, where the ionization rate has been renormalized to account for fluctuations. The coarse grained transport model for neutrals has been implemented in the EIRENE code, and applications in 2D geometry with ITER relevant plasma parameters are presented. Our results open the way for the implementation of the effects of turbulent fluctuations on the transport of neutral particles in coupled plasma/neutral edge codes like B2-EIRENE. (author)
Self-consistency constraints on turbulent magnetic transport and relaxation in collisionless plasma
International Nuclear Information System (INIS)
Terry, P.W.; Diamond, P.H.; Hahm, T.S.
1985-10-01
Novel constraints on collisionless relaxation and transport in drift-Alfven turbulence are reported. These constraints arise due to the consideration of mode coupling and incoherent fluctuations and the proper application of self-consistency conditions. The result that electrostatic fluctuations alone regulate transport in drift-Alfven turbulence follows directly. Quasilinear transport predictions are discussed in light of these constraints
Non-diffusive transport in 3-D pressure driven plasma turbulence
International Nuclear Information System (INIS)
Del-Castillo-Negrete, D.; Carreras, B.A.; Lynch, V.
2005-01-01
Numerical evidence of non-diffusive transport in 3-dimensional, resistive, pressure-gradient-driven plasma turbulence is presented. It is shown that the probability density function (pdf) of tracers is strongly non-Gaussian and exhibits algebraic decaying tails. To describe these results, a transport model using fractional derivative operators in proposed. The model incorporates in a unified way non-locality (i.e., non-Fickian transport), memory effects (i.e., non-Markovian transport), and non-diffusive scaling features known to be present in fusion plasmas. There is quantitative agreement between the model and the turbulent transport numerical calculations. In particular, the model reproduces the shape and space-time scaling of the pdf, and the super-diffusive scaling of the moments. (author)
Magnetic turbulence and anomalous transport
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.
1990-01-01
The self consistency conditions for magnetic turbulence are reviewed. The main features of magnetic topology involving stochastic flux lines are summarized. Two driving sources are considered: thermal effects which require large scale residual islands and electron diamagnetism which involves fluctuation scales smaller than the ion Larmor radius and a β p threshold of order one. Stability criteria and transport coefficients are given
Energy Technology Data Exchange (ETDEWEB)
B. A. Kashiwa; W. B. VanderHeyden
2000-12-01
A formalism for developing multiphase turbulence models is introduced by analogy to the phenomenological method used for single-phase turbulence. A sample model developed using the formalism is given in detail. The procedure begins with ensemble averaging of the exact conservation equations, with closure accomplished by using a combination of analytical and experimental results from the literature. The resulting model is applicable to a wide range of common multiphase flows including gas-solid, liquid-solid and gas-liquid (bubbly) flows. The model is positioned for ready extension to three-phase turbulence, or for use in two-phase turbulence in which one phase is accounted for in multiple size classes, representing polydispersivity. The formalism is expected to suggest directions toward a more fundamentally based theory, similar to the way that early work in single-phase turbulence has led to the spectral theory. The approach is unique in that a portion of the total energy decay rate is ascribed to each phase, as is dictated by the exact averaged equations, and results in a transport equation for energy decay rate associated with each phase. What follows is a straightforward definition of a turbulent viscosity for each phase, and accounts for the effect of exchange of fluctuational energy among phases on the turbulent shear viscosity. The model also accounts for the effect of slip momentum transfer among the phases on the production of turbulence kinetic energy and on the tensor character of the Reynolds stress. Collisional effects, when appropriate, are included by superposition. The model reduces to a standard form in limit of a single, pure material, and is expected to do a credible job of describing multiphase turbulent flows in a wide variety of regimes using a single set of coefficients.
Electromagnetic Transport From Microtearing Mode Turbulence
International Nuclear Information System (INIS)
Guttenfelder, W.; Candy, J.; Kaye, S.M.; Nevins, W.M.; Wang, E.; Bell, R.E.; Hammett, G.W.; LeBlanc, B.P.; Mikkelsen, D.R.; Yuh, H.
2011-01-01
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.
Plasma Soliton Turbulence and Statistical Mechanics
International Nuclear Information System (INIS)
Treumann, R.A.; Pottelette, R.
1999-01-01
Collisionless kinetic plasma turbulence is described approximately in terms of a superposition of non-interacting solitary waves. We discuss the relevance of such a description under astrophysical conditions. Several types of solitary waves may be of interest in this relation as generators of turbulence and turbulent transport. A consistent theory of turbulence can be given only in a few particular cases when the description can be reduced to the Korteweg-de Vries equation or some other simple equation like the Kadomtsev-Petviashvili equation. It turns out that the soliton turbulence is usually energetically harder than the ordinary weakly turbulent plasma description. This implies that interaction of particles with such kinds of turbulence can lead to stronger acceleration than in ordinary turbulence. However, the description in our model is only classical and non-relativistic. Transport in solitary turbulence is most important for drift wave turbulence. Such waves form solitary drift wave vortices which may provide cross-field transport. A more general discussion is given on transport. In a model of Levy flight trapping of particles in solitons (or solitary turbulence) one finds that the residence time of particles in the region of turbulence may be described by a generalized Lorentzian probability distribution. It is shown that under collisionless equilibrium conditions far away from thermal equilibrium such distributions are natural equilibrium distributions. A consistent thermodynamic description of such media can be given in terms of a generalized Lorentzian statistical mechanics and thermodynamics. (author)
Turbulence and transport characteristics of a barrier in a toroidal plasma
International Nuclear Information System (INIS)
Fujisawa, A; Shimizu, A; Nakano, H; Ohsima, S; Itoh, K; Iguchi, H; Yoshimura, Y; Minami, T; Nagaoka, K; Takahashi, C; Kojima, M; Nishimura, S; Isobe, M; Suzuki, C; Akiyama, T; Nagashima, Y; Ida, K; Toi, K; Ido, T; Itoh, S-I; Matsuoka, K; Okamura, S; Diamond, P H
2006-01-01
Turbulence and zonal flow at a transport barrier are studied with twin heavy ion beam probes in a toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e.g. spectra of both density and potential fluctuations, the coherence and the phase between them and the dispersion relation. Particle transport estimated from the fundamental characteristics is found to clearly rise with their intermittent activities after the barrier is broken down. Time-dependent analysis reveals that the intermittency of turbulence is correlated with the evolution of the stationary zonal flow
Turbulence and transport characteristics of a barrier in a toroidal plasma
International Nuclear Information System (INIS)
Fujisawa, A.; Shimizu, A.; Nakano, H.
2005-10-01
Turbulence and zonal flow at a transport barrier are studied with twin heavy ion beam probes in a toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e.g., spectra of both density and potential fluctuations, coherence and phase between them, and the dispersion relation. Particle transport estimated from the fundamental characteristics is found to clearly rise with their intermittent activities after the barrier is broken down. The time-dependent analysis reveals that intermittency of turbulence is correlated with evolution of stationary zonal flow. (author)
International Nuclear Information System (INIS)
Gilmore, Mark Allen
2017-01-01
Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, instability driving mechanisms (such as gradients), plasma flows, and flow shear. Though many of the detailed physics of the interrelationship between turbulence, transport, drive mechanisms, and flow remain unclear, there have been many demonstrations that transport and/or turbulence can be suppressed or reduced via manipulations of plasma flow profiles. This is well known in magnetic fusion plasmas [e.g., high confinement mode (H-mode) and internal transport barriers (ITB's)], and has also been demonstrated in laboratory plasmas. However, it may be that the levels of particle transport obtained in such cases [e.g. H-mode, ITB's] are actually lower than is desirable for a practical fusion device. Ideally, one would be able to actively feedback control the turbulent transport, via manipulation of the flow profiles. The purpose of this research was to investigate the feasibility of using both advanced model-based control algorithms, as well as non-model-based algorithms, to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles. The University of New Mexico was responsible for the experimental portion of the project, while our collaborators at the University of Montana provided plasma transport modeling, and collaborators at Lehigh University developed and explored control methods.
Energy Technology Data Exchange (ETDEWEB)
Gilmore, Mark Allen [Univ. of New Mexico, Albuquerque, NM (United States)
2017-02-05
Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, instability driving mechanisms (such as gradients), plasma flows, and flow shear. Though many of the detailed physics of the interrelationship between turbulence, transport, drive mechanisms, and flow remain unclear, there have been many demonstrations that transport and/or turbulence can be suppressed or reduced via manipulations of plasma flow profiles. This is well known in magnetic fusion plasmas [e.g., high confinement mode (H-mode) and internal transport barriers (ITB’s)], and has also been demonstrated in laboratory plasmas. However, it may be that the levels of particle transport obtained in such cases [e.g. H-mode, ITB’s] are actually lower than is desirable for a practical fusion device. Ideally, one would be able to actively feedback control the turbulent transport, via manipulation of the flow profiles. The purpose of this research was to investigate the feasibility of using both advanced model-based control algorithms, as well as non-model-based algorithms, to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles. The University of New Mexico was responsible for the experimental portion of the project, while our collaborators at the University of Montana provided plasma transport modeling, and collaborators at Lehigh University developed and explored control methods.
Tokamak fluidlike equations, with applications to turbulence and transport in H mode discharges
International Nuclear Information System (INIS)
Kim, Y.B.; Biglari, H.; Carreras, B.A.; Diamond, P.H.; Groebner, R.J.; Kwon, O.J.; Spong, D.A.; Callen, J.D.; Chang, Z.; Hollenberg, J.B.; Sundaram, A.K.; Terry, P.W.; Wang, J.F.
1990-01-01
Significant progress has been made in developing tokamak fluidlike equations which are valid in all collisionality regimes in toroidal devices, and their applications to turbulence and transport in tokamaks. The areas highlighted in this paper include: the rigorous derivation of tokamak fluidlike equations via a generalized Chapman-Enskog procedure in various collisionality regimes and on various time scales; their application to collisionless and collisional drift wave models in a sheared slab geometry; applications to neoclassical drift wave turbulence; i.e. neoclassical ion-temperature-gradient-driven turbulence and neoclassical electron-drift-wave turbulence; applications to neoclassical bootstrap-current-driven turbulence; numerical simulation of nonlinear bootstrap-current-driven turbulence and tearing mode turbulence; transport in Hot-Ion H mode discharges. 20 refs., 3 figs
Morphing continuum theory for turbulence: Theory, computation, and visualization
Chen, James
2017-10-01
A high order morphing continuum theory (MCT) is introduced to model highly compressible turbulence. The theory is formulated under the rigorous framework of rational continuum mechanics. A set of linear constitutive equations and balance laws are deduced and presented from the Coleman-Noll procedure and Onsager's reciprocal relations. The governing equations are then arranged in conservation form and solved through the finite volume method with a second-order Lax-Friedrichs scheme for shock preservation. A numerical example of transonic flow over a three-dimensional bump is presented using MCT and the finite volume method. The comparison shows that MCT-based direct numerical simulation (DNS) provides a better prediction than Navier-Stokes (NS)-based DNS with less than 10% of the mesh number when compared with experiments. A MCT-based and frame-indifferent Q criterion is also derived to show the coherent eddy structure of the downstream turbulence in the numerical example. It should be emphasized that unlike the NS-based Q criterion, the MCT-based Q criterion is objective without the limitation of Galilean invariance.
International Nuclear Information System (INIS)
Zhnag, Y.Z.; Mahajan, S.M.
1994-01-01
On basis of equal-time correlation theory (a non-perturbative approach) inviscid power laws of 2D isotropic plasma turbulences with one Lagrangian inviscid constant of motion are unambiguously solved by determining the dynamical characteristics. Two distinct types of induced transport according to the divergence of the inverse correlation length in the inviscid limit are revealed. This analysis also suggests a physically reasonable closure. The self-consistent system (a set of integral equations) for plasma filaments is investigated in detail, and is found to be a nonlinear differential eigenvalue problem for diffusion coefficient D, whereon the Dyson-like (integral) equation plays a role of boundary condition. This new type of transport is non-Bohm-like, and is very much like the quasilinear formula even in the strong turbulence regime. Physically, it arises from synchronization of shrinking squared correlation length with decorrelation time, for which the ''mixing-length'' breaks down. The shrinkage of correlation length is a characteristic pertaining to the new type of turbulence; its relationship with the turbulence observed in supershot regime on TFTR is commented on. (author). 12 refs, 2 figs
Theory of HF induced turbulence in the ionosphere: Status and challenges
Dubois, D. F.
In the past five years the combination of new theoretical concepts and computer simulations along with dramatically improved observational diagnostics appear to have led to a detailed, quantitative, understanding of the properties of the Langmuir turbulence induced in the unpreconditioned ionosphere at Arecibo during the first tens of milliseconds following the turn-on of the HF heater. This is the only observational regime in which the initial ionospheric conditions are known to a high level of confidence. The so called strong Langmuir turbulence (SLT) theory predicts observed features in this early time heating which are completely at odds with the prediction of the traditional weak turbulence approximation. The understanding of the observed signatures for times greater than say 30-50 ms following the onset of heating at Arecibo is still incomplete. The same is apparently true for the observations at Tromso where the unique predictions of SLT theory are not so clearly observed. Density irregularities, induced by heating at Arecibo and perhaps present in the ambient ionosphere at Tromso, appear to control the properties of the turbulence. The proper description of the coexistence of Langmuir turbulence with various density irregularities and accounting for the turbulent modification of the electron velocity distribution are challenges for the theory. In this paper the author reviews, starting from the Vlasov-Poisson equations, the fundamental basis of the reduced models used to describe SLT and suggest improvements to the standard model including a new local quasi linear theory for the treatment of hot electron acceleration and transit time damping or burnout of collapsing Langmuir cavitons.
Characterisation of temperature gradient driven turbulence and transport
International Nuclear Information System (INIS)
Ottaviani, M.A.
2002-01-01
We report on extensive numerical studies aimed at characterising various aspects of temperature gradient driven turbulence. We specifically discuss results from 3D fluid models of ETG and of ITG turbulence, and results from a 2D+2D gyrokinetic model of trapped ion turbulence. Global transport exhibits gyro-Bohm scaling in both the ETG and the ITG model. The conductivity of the ETG model decreases weakly with beta. The heat transport is due to the EXB advection, the effect of the magnetic flutter is negligible. However the transport level is much lower than experimentally observed. In both 3D models the correlation lengths scale with the gyroradius, but they are typically a factor 10 larger. Vortices are elongated but their aspect ratio is independent of the gyroradius. Their radial size is limited by LD. The trapped ion model gives larger vortices due to the absence of LD from passing ions. Avalanches are observed in all the models, the weakest occurring in the ITG system. Their range increases with gyroradius, but more weakly than linearly. Finally, ZFs can limit the range of the avalanches, which explains why avalanches are weaker in the ITG model which is more sensitive to ZFs. (author)
Toward the Theory of Turbulence in Magnetized Plasmas
International Nuclear Information System (INIS)
Boldyrev, Stanislav
2013-01-01
The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a 'condensate', that is, concentration of magnetic and kinetic energy at small kllel)). A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model
Resolving the mystery of transport within internal transport barriers
Energy Technology Data Exchange (ETDEWEB)
Staebler, G. M.; Belli, E. A.; Candy, J.; Waltz, R. E.; Greenfield, C. M.; Lao, L. L.; Smith, S. P. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Kinsey, J. E. [CompX, P.O. Box 2672, Del Mar, California 92014-5672 (United States); Grierson, B. A. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Chrystal, C. [University of California-San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States)
2014-05-15
The Trapped Gyro-Landau Fluid (TGLF) quasi-linear model [G. M. Staebler, et al., Phys. Plasmas 12, 102508 (2005)], which is calibrated to nonlinear gyrokinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures, and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges. This is a strong validation of gyrokinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. The mystery of transport inside the ITB is that momentum and particle transport is far above the predicted neoclassical levels in apparent contradiction with the expectation from the theory of suppression of turbulence by E×B velocity shear. The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E×B velocity shear and to improvements to TGLF that allow momentum transport from gyrokinetic turbulence to be faithfully modeled.
ION ACOUSTIC TURBULENCE, ANOMALOUS TRANSPORT, AND SYSTEM DYNAMICS IN HALL EFFECT THRUSTERS
2017-06-30
NUMBER (Include area code) 30 June 2017 Briefing Charts 26 May 2017 - 30 June 2017 ION ACOUSTIC TURBULENCE, ANOMALOUS TRANSPORT, AND SYSTEM DYNAMICS ...Robert Martin N/A ION ACOUSTIC TURBULENCE, ANOMALOUS TRANSPORT, AND SYSTEM DYNAMICS IN HALL EFFECT THRUSTERS Robert Martin1, Jonathan Tran2 1AIR FORCE...Approved for Public Release; Distribution is Unlimited. PA# 17394 1 / 13 OUTLINE 1 INTRODUCTION 2 TRANSPORT 3 DYNAMIC SYSTEM 4 SUMMARY AND CONCLUSION
Fractional Transport in Strongly Turbulent Plasmas
Isliker, Heinz; Vlahos, Loukas; Constantinescu, Dana
2017-07-01
We analyze statistically the energization of particles in a large scale environment of strong turbulence that is fragmented into a large number of distributed current filaments. The turbulent environment is generated through strongly perturbed, 3D, resistive magnetohydrodynamics simulations, and it emerges naturally from the nonlinear evolution, without a specific reconnection geometry being set up. Based on test-particle simulations, we estimate the transport coefficients in energy space for use in the classical Fokker-Planck (FP) equation, and we show that the latter fails to reproduce the simulation results. The reason is that transport in energy space is highly anomalous (strange), the particles perform Levy flights, and the energy distributions show extended power-law tails. Newly then, we motivate the use and derive the specific form of a fractional transport equation (FTE), we determine its parameters and the order of the fractional derivatives from the simulation data, and we show that the FTE is able to reproduce the high energy part of the simulation data very well. The procedure for determining the FTE parameters also makes clear that it is the analysis of the simulation data that allows us to make the decision whether a classical FP equation or a FTE is appropriate.
Anomalous transport in turbulent plasmas and continuous time random walks
International Nuclear Information System (INIS)
Balescu, R.
1995-01-01
The possibility of a model of anomalous transport problems in a turbulent plasma by a purely stochastic process is investigated. The theory of continuous time random walks (CTRW's) is briefly reviewed. It is shown that a particular class, called the standard long tail CTRW's is of special interest for the description of subdiffusive transport. Its evolution is described by a non-Markovian diffusion equation that is constructed in such a way as to yield exact values for all the moments of the density profile. The concept of a CTRW model is compared to an exact solution of a simple test problem: transport of charged particles in a fluctuating magnetic field in the limit of infinite perpendicular correlation length. Although the well-known behavior of the mean square displacement proportional to t 1/2 is easily recovered, the exact density profile cannot be modeled by a CTRW. However, the quasilinear approximation of the kinetic equation has the form of a non-Markovian diffusion equation and can thus be generated by a CTRW
Gyrokinetic theory for particle and energy transport in fusion plasmas
Falessi, Matteo Valerio; Zonca, Fulvio
2018-03-01
A set of equations is derived describing the macroscopic transport of particles and energy in a thermonuclear plasma on the energy confinement time. The equations thus derived allow studying collisional and turbulent transport self-consistently, retaining the effect of magnetic field geometry without postulating any scale separation between the reference state and fluctuations. Previously, assuming scale separation, transport equations have been derived from kinetic equations by means of multiple-scale perturbation analysis and spatio-temporal averaging. In this work, the evolution equations for the moments of the distribution function are obtained following the standard approach; meanwhile, gyrokinetic theory has been used to explicitly express the fluctuation induced fluxes. In this way, equations for the transport of particles and energy up to the transport time scale can be derived using standard first order gyrokinetics.
Pressure gradient turbulent transport and collisionless reconnection
International Nuclear Information System (INIS)
Connor, J.W.
1993-01-01
The scale invariance technique is employed to discuss pressure gradient driven turbulent transport when an Ohm's law with electron inertia, rather than resistivity, is relevant. An expression for thermal diffusivity which has many features appropriate to L-mode transport in tokamaks, is seen to have greater generality than indicated by their particular calculation. The results of applying the technique to a more appropriate collisionless Ohm's law are discussed. (Author)
Bob Dewar and turbulence theory: lessons in creativity and courage
International Nuclear Information System (INIS)
Krommes, John A
2012-01-01
Some of the contributions that Bob Dewar made to plasma turbulence theory are recounted and put into historical perspective. Some remarks are made on the transition to turbulence and bifurcation analysis of models for the low-high confinement transition in tokamaks. However, the focus of the paper is on renormalized oscillation-center theory, to which Dewar made pioneering, creative and courageous contributions. The relationship of that approach to the formalism of Martin, Siggia, and Rose is discussed briefly. (personal reflection)
Comparison of simulations and theory of low-frequency plasma turbulence
Energy Technology Data Exchange (ETDEWEB)
LoDestro, L L; Cohen, B I; Cohen, R H; Dimits, A M; Matsuda, Y; Nevins, W M; Newcomb, W A; Williams, T J; Koniges, A E; Dannevik, W P; Crotinger, J A; Amala, P A.K. [Lawrence Livermore National Lab., CA (USA); Sydora, R D; Dawson, J M; Ma, S; Decyk, V K [California Univ., Los Angeles, CA (USA). Dept. of Physics; Lee, W W; Hahm, T S [Princeton Univ., NJ (USA). Plasma Physics Lab.; Naitou, H
1990-08-15
We use a combination of computational and analytic methods to study low-frequency turbulence and turbulent transport in a strongly magnetized plasma. We describe two major computational efforts, one based on gyrokinetic-particle simulation and the second on numerical solution of closure approximations to fluid equations. These codes are used to study instabilities on the drift timescale, and to assess the validity of qualitative predictions of energy-transport scalings based on dimensional analysis and on analytic versions of closure approximations. 27 refs., 2 figs.
Verma, Siddhartha; Blanquart, Guillaume; P. K. Yeung Collaboration
2011-11-01
Accurate simulation of high Schmidt number scalar transport in turbulent flows is essential to studying pollutant dispersion, weather, and several oceanic phenomena. Batchelor's theory governs scalar transport in such flows, but requires further validation at high Schmidt and high Reynolds numbers. To this end, we use a new approach with the velocity field fully resolved, but the scalar field only partially resolved. The grid used is fine enough to resolve scales up to the viscous-convective subrange where the decaying slope of the scalar spectrum becomes constant. This places the cutoff wavenumber between the Kolmogorov scale and the Batchelor scale. The subgrid scale terms, which affect transport at the supergrid scales, are modeled under the assumption that velocity fluctuations are negligible beyond this cutoff wavenumber. To ascertain the validity of this technique, we performed a-priori testing on existing DNS data. This Velocity-Resolved LES (VR-LES) technique significantly reduces the computational cost of turbulent simulations of high Schmidt number scalars, and yet provides valuable information of the scalar spectrum in the viscous-convective subrange.
Momentum transport in gyrokinetic turbulence
Energy Technology Data Exchange (ETDEWEB)
Buchholz, Rico
2016-07-01
In this thesis, the gyrokinetic-Vlasov code GKW is used to study turbulent transport, with a focus on radial transport of toroidal momentum. To support the studies on turbulent transport an eigenvalue solver has been implemented into GKW. This allows to find, not only the most unstable mode, but also subdominant modes. Furthermore it is possible to follow the modes in parameter scans. Furthermore, two fundamental mechanisms that can generate an intrinsic rotation have been investigated: profile shearing and the velocity nonlinearity. The study of toroidal momentum transport in a tokamak due to profile shearing reveals that the momentum flux can not be accurately described by the gradient in the turbulent intensity. Consequently, a description using the profile variation is used. A linear model has been developed that is able to reproduce the variations in the momentum flux as the profiles of density and temperature vary, reasonably well. It uses, not only the gradient length of density and temperature profile, but also their derivative, i.e. the second derivative of the logarithm of the temperature and the density profile. It is shown that both first as well as second derivatives contribute to the generation of a momentum flux. A difference between the linear and nonlinear simulations has been found with respect to the behaviour of the momentum flux. In linear simulations the momentum flux is independent of the normalized Larmor radius ρ{sub *}, whereas it is linear in ρ{sub *} for nonlinear simulations, provided ρ{sub *} is small enough (≤4.10{sup -3}). Nonlinear simulations reveal that the profile shearing can generate an intrinsic rotation comparable to that of current experiments. Under reactor conditions, however, the intrinsic rotation from the profile shearing is expected to be small due to the small normalized Larmor radius ρ{sub *}
Remarks on transport theories of interplanetary fluctuations
International Nuclear Information System (INIS)
Ye Zhou; Matthaeus, W.H.
1990-01-01
The structure of approximate transport theories for the radial behavior of interplanetary fluctuations is reconsidered. The emphasis is on theories derived under the assumption of scale separation; i.e., the correlation length of the fluctuations is much less than the scale of large inhomogeneities. In these cases the zero-wavelength limit provides a first approximation to the spectral evolution equations for the radial dependence of interplanetary fluctuation spectra. The goal here is to investigate the structure of a recently presented (Zhou and Matthaeus, 1989) transport theory, in which coupling of inward- and outward-type fluctuations appears in the leading order, an effect the authors call mixing. In linear theory, mixing-type couplings of inward-type and outward-type waves are formally a nonresonant effect. However, leading order mixing terms do not vanish at zero wavelength for fluctuations that vary nearly perpendicular to the local magnetic field, or when the mean magnetic field is weak. Leading order mixing terms also survive when the dispersion relation fails and there is a nonunique relationship between frequency and wave number. The former case corresponds to nearly two-dimensional structures; these are included, for example, in isotropic models of turbulence. The latter instance occurs when wave-wave couplings are sufficiently strong. Thus there are a variety of situations in which leading order mixing effects are expected to be present
Turbulence, transport and confinement: from tokamaks to star magnetism
International Nuclear Information System (INIS)
Strugarek, Antoine
2012-01-01
This thesis is part of the general study of self-organization in hot and magnetized plasmas. We focus our work on two specific objects: stars and tokamaks. We use first principle numerical simulations to study turbulence, transport and confinement in these plasmas. The first part of this thesis introduces the main characteristics of stellar and tokamak plasmas. The reasons for studying them together are properly detailed. The second part is focused on stellar aspects. We study the interactions between the 3D turbulent motions in the solar convection zone with an internal magnetic field in the tachocline (the transition region between the instable and stable zones in the Sun). The tachocline is a very thin layer (less than five percent of the solar radius) that acts as a transport barrier of angular momentum. We show that such an internal magnetic field is not likely to explain the observed thickness of the tachocline and we give some insights on how to find alternative mechanisms to constrain it. We also explore the effect of the environment of star on its structure. We develop a methodology to study the influence of stellar wind and of the magnetic coupling of a star with its orbiting planets. We use the same methodology to analyse the magnetic interaction between a stellar wind and a planetary magnetosphere that acts as a transport barrier of matter. Then, the third part is dedicated to fusion oriented research. We present a numerical investigation on the experimental mechanisms that lead to the development of transport barriers in the plasma. These barriers are particularly important for the design of high performance fusion devices. The creation of transport barriers is obtained in turbulent first principle simulations for the very first time. The collaboration between the two scientific teams lead to the results presented in the fourth part of this thesis. An original spectral method is developed to analyse the saturation of stellar convective dynamos and of
Turbulence induced radial transport of toroidal momentum in boundary plasma of EAST tokamak
International Nuclear Information System (INIS)
Zhao, N.; Yan, N.; Xu, G. S.; Wang, H. Q.; Wang, L.; Ding, S. Y.; Chen, R.; Chen, L.; Zhang, W.; Hu, G. H.; Shao, L. M.; Wang, Z. X.
2016-01-01
Turbulence induced toroidal momentum transport in boundary plasma is investigated in H-mode discharge using Langmuir-Mach probes on EAST. The Reynolds stress is found to drive an inward toroidal momentum transport, while the outflow of particles convects the toroidal momentum outwards in the edge plasma. The Reynolds stress driven momentum transport dominates over the passive momentum transport carried by particle flux, which potentially provides a momentum source for the edge plasma. The outflow of particles delivers a momentum flux into the scrape-off layer (SOL) region, contributing as a momentum source for the SOL flows. At the L-H transitions, the outward momentum transport suddenly decreases due to the suppression of edge turbulence and associated particle transport. The SOL flows start to decelerate as plasma entering into H-mode. The contributions from turbulent Reynolds stress and particle transport for the toroidal momentum transport are identified. These results shed lights on the understanding of edge plasma accelerating at L-H transitions.
A nonlinear theory of cosmic ray pitch angle diffusion in homogeneous magnetostatic turbulence
International Nuclear Information System (INIS)
Goldstein, M.L.
1975-04-01
A plasma strong turbulence, weak coupling theory is applied to the problem of cosmic ray pitch angle scattering in magnetostatic turbulence. The theory used is a rigorous generalization of Weinstock's resonance-broadening theory and contains no ad hoc approximations. A detailed calculation is presented for a model of slab turbulence with an exponential correlation function. The results agree well with numerical simulations. The rigidity dependence of the pitch angle scattering coefficient differs from that found by previous researchers. The differences result from an inadequate treatment of particle trajectories near 90 0 pitch angle in earlier work
Self-organized criticality revisited: non-local transport by turbulent amplification
DEFF Research Database (Denmark)
Milovanov, Alexander V.; Rasmussen, Jens Juul
2015-01-01
We revise the applications of self-organized criticality (SOC) as a paradigmatic model for tokamak plasma turbulence. The work, presented here, is built around the idea that some systems do not develop a pure critical state associable with SOC, since their dynamical evolution involves as a compet......We revise the applications of self-organized criticality (SOC) as a paradigmatic model for tokamak plasma turbulence. The work, presented here, is built around the idea that some systems do not develop a pure critical state associable with SOC, since their dynamical evolution involves...... as a competing key factor an inverse cascade of the energy in reciprocal space. Then relaxation of slowly increasing stresses will give rise to intermittent bursts of transport in real space and outstanding transport events beyond the range of applicability of the 'conventional' SOC. Also, we are concerned...... with the causes and origins of non-local transport in magnetized plasma, and show that this type of transport occurs naturally in self-consistent strong turbulence via a complexity coupling to the inverse cascade. We expect these coupling phenomena to occur in the parameter range of strong nonlinearity and time...
Sand Transport under Highly Turbulent Airflow on a Beach Surface
Baas, A. C. W.; Jackson, D. W. T.; Cooper, J. A. G.; Lynch, K.; Delgado-Fernandez, I.; Beyers, J. H. M.
2012-04-01
The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune ('against' the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u', v', w'). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that shear velocity
Turbulence and intermittent transport at the boundary of magnetized plasmas
DEFF Research Database (Denmark)
Garcia, O.E.; Naulin, V.; Nielsen, A.H.
2005-01-01
Numerical fluid simulations of interchange turbulence for geometry and parameters relevant to the boundary region of magnetically confined plasmas are shown to result in intermittent transport qualitatively similar to recent experimental measurements. The two-dimensional simulation domain features...... a forcing region with spatially localized sources of particles and heat outside which losses due to the motion along open magnetic-field lines dominate, corresponding to the edge region and the scrape-off layer, respectively. Turbulent states reveal intermittent eruptions of hot plasma from the edge region...... fluctuation wave forms and transport statistics are also in a good agreement with those derived from the experiments. Associated with the turbulence bursts are relaxation oscillations in the particle and heat confinements as well as in the kinetic energy of the sheared poloidal flows. The formation of blob...
Statistical description of turbulent transport for flux driven toroidal plasmas
Anderson, J.; Imadera, K.; Kishimoto, Y.; Li, J. Q.; Nordman, H.
2017-06-01
A novel methodology to analyze non-Gaussian probability distribution functions (PDFs) of intermittent turbulent transport in global full-f gyrokinetic simulations is presented. In this work, the auto-regressive integrated moving average (ARIMA) model is applied to time series data of intermittent turbulent heat transport to separate noise and oscillatory trends, allowing for the extraction of non-Gaussian features of the PDFs. It was shown that non-Gaussian tails of the PDFs from first principles based gyrokinetic simulations agree with an analytical estimation based on a two fluid model.
Statistical properties of turbulent transport and fluctuations in tokamak and stellarator devices
Energy Technology Data Exchange (ETDEWEB)
Hidalgo, C; Pedrosa, M A; Milligen, B Van; Sanchez, E; Balbin, R; Garcia-Cortes, I [Euratom-CIEMAT Association, Madrid (Spain); Bleuel, J; Giannone, L.; Niedermeyer, H [Euratom-IPP Association, Garching (Germany)
1997-05-01
The statistical properties of fluctuations and turbulent transport have been studied in the plasma boundary region of stellarator (TJ-IU, W7-AS) and tokamak (TJ-I) devices. The local flux probability distribution function shows the bursty character of the flux and presents a systematic change as a function of the radial location. There exist large amplitude transport bursts that account for a significant part of the total flux. There is a strong similarity between the statistical properties of the turbulent fluxes in different devices. The value of the radial coherence associated with fluctuations and turbulent transport is strongly intermittent. This result emphasizes the importance of measurements with time resolution in understanding the interplay between the edge and the core regions in the plasma. For measurements in the plasma edge region of the TJ-IU torsatron, the turbulent flux does not, in general, show a larger radial coherence than the one associated with the fluctuations. (author). 14 refs, 6 figs.
Rogue waves, rational solitons and wave turbulence theory
International Nuclear Information System (INIS)
Kibler, Bertrand; Hammani, Kamal; Michel, Claire; Finot, Christophe; Picozzi, Antonio
2011-01-01
Considering a simple one-dimensional nonlinear Schroedinger optical model, we study the existence of rogue wave events in the highly incoherent state of the system and compare them with the recently identified hierarchy of rational soliton solutions. We show that rogue waves can emerge in the genuine turbulent regime and that their coherent deterministic description provided by the rational soliton solutions is compatible with an accurate statistical description of the random wave provided by the wave turbulence theory. Furthermore, the simulations reveal that even in the weakly nonlinear regime, the nonlinearity can play a key role in the emergence of an individual rogue wave event in a turbulent environment. -- Highlights: → Rogue wave events are studied in the highly incoherent regime of interaction. → We show that rogue waves can emerge in the genuine turbulent regime. → Their coherent deterministic description is provided by the rational solutions. → It coexists with a statistical description provided of the random wave. → The nonlinearity plays a key role even in a turbulent environment.
Fast Propagation in Fluid Transport Models with Evolution of Turbulence Saturation
International Nuclear Information System (INIS)
Lopez-Bruna, D.
2012-01-01
This report compiles and extends two works on models that reproduce the experimental facts of non local transport and pulse propagation in magnetically confined fusion plasmas. The works are based on fluid transport models, originally designed to explain the formation of edge or internal transport barriers, that include fast evolution equations for the particle and heat fluxes. The heating of the plasma core in response to a sudden edge cooling or the propagation of turbulent fronts around transport barriers are a consequence of the competing roles of linear drive and non-linear reduction of the turbulent fluxes. Possibilities to use the models to interpret TJ-II plasmas are discussed. (Author) 62 refs.
Fast Propagation in Fluid Transport Models with Evolution of Turbulence Saturation
Energy Technology Data Exchange (ETDEWEB)
Lopez-Bruna, D.
2012-07-01
This report compiles and extends two works on models that reproduce the experimental facts of non local transport and pulse propagation in magnetically confined fusion plasmas. The works are based on fluid transport models, originally designed to explain the formation of edge or internal transport barriers, that include fast evolution equations for the particle and heat fluxes. The heating of the plasma core in response to a sudden edge cooling or the propagation of turbulent fronts around transport barriers are a consequence of the competing roles of linear drive and non-linear reduction of the turbulent fluxes. Possibilities to use the models to interpret TJ-II plasmas are discussed. (Author) 62 refs.
Radiative heat transfer in turbulent combustion systems theory and applications
Modest, Michael F
2016-01-01
This introduction reviews why combustion and radiation are important, as well as the technical challenges posed by radiation. Emphasis is on interactions among turbulence, chemistry and radiation (turbulence-chemistry-radiation interactions – TCRI) in Reynolds-averaged and large-eddy simulations. Subsequent chapters cover: chemically reacting turbulent flows; radiation properties, Reynolds transport equation (RTE) solution methods, and TCRI; radiation effects in laminar flames; TCRI in turbulent flames; and high-pressure combustion systems. This Brief presents integrated approach that includes radiation at the outset, rather than as an afterthought. It stands as the most recent developments in physical modeling, numerical algorithms, and applications collected in one monograph.
Turbulent transport and shear at the E x B velocity in wall plasma of the TF-2 tokamak
International Nuclear Information System (INIS)
Budaev, V.P.
1999-01-01
Turbulence of near-the-wall plasma and potentialities of affecting the turbulence and periphery transport of the TF-2 tokamak by inducing radial electric fields and ergodization of periphery magnetic structure have been investigated, the results are presented. Essential role of the E x B velocity shear in suppression of the turbulence and turbulent transport in periphery has been pointed out. Decrease in transport losses stemming from effect of radial electric fields is brought about suppression of turbulence amplitude, decrease in correlations and decrease in the width of the wave numbers spectrum. Profiles of plasma density, electron temperature, turbulence level, electric fields over entire periphery of discharge change as a result. Ergodization of magnetic structure also results in the change of properties of periphery turbulence and turbulent transport [ru
Renormalized plasma turbulence theory: A quasiparticle picture
International Nuclear Information System (INIS)
DuBois, D.F.
1981-01-01
A general renormalized statistical theory of Vlasov turbulence is given which proceeds directly from the Vlasov equation and does not assume prior knowledge of sophisticated field-theoretic techniques. Quasiparticles are the linear excitations of the turbulent system away from its instantaneous mean (ensemble-averaged) state or background; the properties of this background state ''dress'' or renormalize the quasiparticle responses. It is shown that all two-point responses (including the dielectric) and all two-point correlation functions can be completely described by the mean distribution function and three fundamental quantities. Two of these are the quasiparticle responses: the propagator and the potential source: which measure, respectively, the separate responses of the mean distribution function and the mean electrostatic potential to functional changes in an external phase-space source added to Vlasov's equation. The third quantity is the two-point correlation function of the incoherent part of the phase-space density which acts as a self-consistent source of quasiparticle and potential fluctuations. This theory explicitly takes into account the self-consistent nature of the electrostatic-field fluctuations which introduces new effects not found in the usual ''test-particle'' theories. Explicit equations for the fundamental quantities are derived in the direct interaction approximation. Special attention is paid to the two-point correlations and the relation to theories of phase-space granulation
Energy Technology Data Exchange (ETDEWEB)
Rahbarnia, Kian; Brown, Benjamin P.; Clark, Mike M.; Kaplan, Elliot J.; Nornberg, Mark D.; Rasmus, Alex M.; Taylor, Nicholas Zane; Forest, Cary B. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave, Madison, WI 53706 (United States); Jenko, Frank; Limone, Angelo [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, D-85748 Garching (Germany); Pinton, Jean-Francois; Plihon, Nicolas; Verhille, Gautier, E-mail: kian.rahbarnia@ipp.mpg.de [Laboratoire de Physique de l' Ecole Normale Superieure de Lyon, CNRS and Universite de Lyon, F-69364 Lyon (France)
2012-11-10
For the first time, we have directly measured the transport of a vector magnetic field by isotropic turbulence in a high Reynolds number liquid metal flow. In analogy with direct measurements of the turbulent Reynolds stress (turbulent viscosity) that governs momentum transport, we have measured the turbulent electromotive force (emf) by simultaneously measuring three components of velocity and magnetic fields, and computed the correlations that lead to mean-field current generation. Furthermore, we show that this turbulent emf tends to oppose and cancel out the local current, acting to increase the effective resistivity of the medium, i.e., it acts as an enhanced magnetic diffusivity. This has important implications for turbulent transport in astrophysical objects, particularly in dynamos and accretion disks.
International Nuclear Information System (INIS)
Rahbarnia, Kian; Brown, Benjamin P.; Clark, Mike M.; Kaplan, Elliot J.; Nornberg, Mark D.; Rasmus, Alex M.; Taylor, Nicholas Zane; Forest, Cary B.; Jenko, Frank; Limone, Angelo; Pinton, Jean-François; Plihon, Nicolas; Verhille, Gautier
2012-01-01
For the first time, we have directly measured the transport of a vector magnetic field by isotropic turbulence in a high Reynolds number liquid metal flow. In analogy with direct measurements of the turbulent Reynolds stress (turbulent viscosity) that governs momentum transport, we have measured the turbulent electromotive force (emf) by simultaneously measuring three components of velocity and magnetic fields, and computed the correlations that lead to mean-field current generation. Furthermore, we show that this turbulent emf tends to oppose and cancel out the local current, acting to increase the effective resistivity of the medium, i.e., it acts as an enhanced magnetic diffusivity. This has important implications for turbulent transport in astrophysical objects, particularly in dynamos and accretion disks.
Energy Technology Data Exchange (ETDEWEB)
Boughanem, H.
1998-03-24
The assumption of gradient transport for the mean reaction progress variable has a limited domain of validity in premixed turbulent combustion. The existence of two turbulent transport regimes, gradient and counter-gradient, is demonstrated in the present work using Direct Numerical Simulations (DNS) of plane flame configurations. The DNS data base describes the influence of the heat release factor, of the turbulence-to-flame velocity ratio, and of an external pressure gradient. The simulations reveal a strong correlation between the regime of turbulent transport and the turbulent flame speed and turbulent flame thickness. These effects re not well described by current turbulent combustion models. A conditional approach `fresh gases / burnt gases` is proposed to overcome these difficulties. Furthermore, he development of flame instabilities in turbulent configurations is also observed in the simulations. A criterion is derived that determines the domain of occurrence of these instabilities (Darrieus- Landau instabilities, Rayleigh- Taylor instabilities, thermo-diffusive instabilities). This criterion suggests that the domain of occurrence of flame instabilities is not limited to small Reynolds numbers. (author) 98 refs.
Self-consistent gyrokinetic modeling of neoclassical and turbulent impurity transport
Estève, D.; Sarazin, Y.; Garbet, X.; Grandgirard, V.; Breton, S.; Donnel, P.; Asahi, Y.; Bourdelle, C.; Dif-Pradalier, G.; Ehrlacher, C.; Emeriau, C.; Ghendrih, Ph.; Gillot, C.; Latu, G.; Passeron, C.
2018-03-01
Trace impurity transport is studied with the flux-driven gyrokinetic GYSELA code (Grandgirard et al 2016 Comput. Phys. Commun. 207 35). A reduced and linearized multi-species collision operator has been recently implemented, so that both neoclassical and turbulent transport channels can be treated self-consistently on an equal footing. In the Pfirsch-Schlüter regime that is probably relevant for tungsten, the standard expression for the neoclassical impurity flux is shown to be recovered from gyrokinetics with the employed collision operator. Purely neoclassical simulations of deuterium plasma with trace impurities of helium, carbon and tungsten lead to impurity diffusion coefficients, inward pinch velocities due to density peaking, and thermo-diffusion terms which quantitatively agree with neoclassical predictions and NEO simulations (Belli et al 2012 Plasma Phys. Control. Fusion 54 015015). The thermal screening factor appears to be less than predicted analytically in the Pfirsch-Schlüter regime, which can be detrimental to fusion performance. Finally, self-consistent nonlinear simulations have revealed that the tungsten impurity flux is not the sum of turbulent and neoclassical fluxes computed separately, as is usually assumed. The synergy partly results from the turbulence-driven in-out poloidal asymmetry of tungsten density. This result suggests the need for self-consistent simulations of impurity transport, i.e. including both turbulence and neoclassical physics, in view of quantitative predictions for ITER.
Electromagnetic weak turbulence theory revisited
Energy Technology Data Exchange (ETDEWEB)
Yoon, P. H. [IPST, University of Maryland, College Park, Maryland 20742 (United States); Ziebell, L. F. [Instituto de Fisica, UFRGS, Porto Alegre, RS (Brazil); Gaelzer, R.; Pavan, J. [Instituto de Fisica e Matematica, UFPel, Pelotas, RS (Brazil)
2012-10-15
The statistical mechanical reformulation of weak turbulence theory for unmagnetized plasmas including fully electromagnetic effects was carried out by Yoon [Phys. Plasmas 13, 022302 (2006)]. However, the wave kinetic equation for the transverse wave ignores the nonlinear three-wave interaction that involves two transverse waves and a Langmuir wave, the incoherent analogue of the so-called Raman scattering process, which may account for the third and higher-harmonic plasma emissions. The present paper extends the previous formalism by including such a term.
Information Theory and Plasma Turbulence
International Nuclear Information System (INIS)
Dendy, R. O.
2009-01-01
Information theory, applied directly to measured signals, yields new perspectives on, and quantitative knowledge of, the physics of strongly nonlinear and turbulent phenomena in plasmas. It represents a new and productive element of the topical research programmes that use modern techniques to characterise strongly nonlinear signals from plasmas, and that address global plasma behaviour from a complex systems perspective. We here review some pioneering studies of mutual information in solar wind and magnetospheric plasmas, using techniques tested on standard complex systems.
Turbulence Spreading into Linearly Stable Zone and Transport Scaling
International Nuclear Information System (INIS)
Hahm, T.S.; Diamond, P.H.; Lin, Z.; Itoh, K.; Itoh, S.-I.
2003-01-01
We study the simplest problem of turbulence spreading corresponding to the spatio-temporal propagation of a patch of turbulence from a region where it is locally excited to a region of weaker excitation, or even local damping. A single model equation for the local turbulence intensity I(x, t) includes the effects of local linear growth and damping, spatially local nonlinear coupling to dissipation and spatial scattering of turbulence energy induced by nonlinear coupling. In the absence of dissipation, the front propagation into the linearly stable zone occurs with the property of rapid progression at small t, followed by slower subdiffusive progression at late times. The turbulence radial spreading into the linearly stable zone reduces the turbulent intensity in the linearly unstable zone, and introduces an additional dependence on the rho* is always equal to rho i/a to the turbulent intensity and the transport scaling. These are in broad, semi-quantitative agreements with a number of global gyrokinetic simulation results with zonal flows and without zonal flows. The front propagation stops when the radial flux of fluctuation energy from the linearly unstable region is balanced by local dissipation in the linearly stable region
Energy Technology Data Exchange (ETDEWEB)
T.S. Hahm; Z. Lin; P.H. Diamond; G. Rewoldt; W.X. Wang; S. Ethier; O. Gurcan; W.W. Lee; W.M. Tang
2004-12-21
An integrated program of gyrokinetic particle simulation and theory has been developed to investigate several outstanding issues in both turbulence and neoclassical physics. Gyrokinetic particle simulations of toroidal ion temperature gradient (ITG) turbulence spreading using the GTC code and its related dynamical model have been extended to the case with radially increasing ion temperature gradient, to study the inward spreading of edge turbulence toward the core. Due to turbulence spreading from the edge, the turbulence intensity in the core region is significantly enhanced over the value obtained from simulations of the core region only. Even when the core gradient is within the Dimits shift regime (i.e., self-generated zonal flows reduce the transport to a negligible value), a significant level of turbulence and transport is observed in the core due to spreading from the edge. The scaling of the turbulent front propagation speed is closer to the prediction from our nonlinear diffusion model than one based on linear toroidal coupling. A calculation of ion poloidal rotation in the presence of sharp density and toroidal angular rotation frequency gradients from the GTC-Neo particle simulation code shows that the results are significantly different from the conventional neoclassical theory predictions. An energy conserving set of a fully electromagnetic nonlinear gyrokinetic Vlasov equation and Maxwell's equations, which is applicable to edge turbulence, is being derived via the phase-space action variational Lie perturbation method. Our generalized ordering takes the ion poloidal gyroradius to be on the order of the radial electric field gradient length.
International Nuclear Information System (INIS)
Hahm, T.S.; Lin, Z.; Diamond, P.H.; Gurcan, O.; Rewoldt, G.; Wang, W.X.; Ethier, S.; Lee, W.W.; Lewandowski, J.L.V.; Tang, W.M.
2005-01-01
An integrated program of gyrokinetic particle simulation and theory has been developed to investigate several outstanding issues in both turbulence and neoclassical physics. Gyrokinetic particle simulations of toroidal ion temperature gradient (ITG) turbulence spreading using the GTC code and its related dynamical model have been extended to the case with radially increasing ion temperature gradient, to study the inward spreading of edge turbulence toward the core. Due to turbulence spreading from the edge, the turbulence intensity in the core region is significantly enhanced over the value obtained from simulations of the core region only. Even when the core gradient is within the Dimits shift regime (i.e., self-generated zonal flows reduce the transport to a negligible value), a significant level of turbulence and transport is observed in the core due to spreading from the edge. The scaling of the turbulent front propagation speed is closer to the prediction from our nonlinear diffusion model than one based on linear toroidal coupling. A calculation of ion poloidal rotation in the presence of sharp density and toroidal angular rotation frequency gradients from the GTC-Neo particle simulation code shows that the results are significantly different from the conventional neoclassical theory predictions. An energy conserving set of a fully electromagnetic nonlinear gyrokinetic Vlasov equation and Maxwell's equations, which is applicable to edge turbulence, is being derived via the phase-space action variational Lie perturbation method. Our generalized ordering takes the ion poloidal gyroradius to be on the order of the radial electric field gradient length. (author)
Mongiovì, Maria Stella; Jou, David; Sciacca, Michele
2018-01-01
This review paper puts together some results concerning non equilibrium thermodynamics and heat transport properties of superfluid He II. A one-fluid extended model of superfluid helium, which considers heat flux as an additional independent variable, is presented, its microscopic bases are analyzed, and compared with the well known two-fluid model. In laminar situations, the fundamental fields are density, velocity, absolute temperature, and heat flux. Such a theory is able to describe the thermomechanical phenomena, the propagation of two sounds in liquid helium, and of fourth sound in superleak. It also leads in a natural way to a two-fluid model on purely macroscopical grounds and allows a small amount of entropy associated with the superfluid component. Other important features of liquid He II arise in rotating situations and in superfluid turbulence, both characterized by the presence of quantized vortices (thin vortex lines whose circulation is restricted by a quantum condition). Such vortices have a deep influence on the transport properties of superfluid helium, as they increase very much its thermal resistance. Thus, heat flux influences the vortices which, in turn, modify the heat flux. The dynamics of vortex lines is the central topic in turbulent superfluid helium. The model is generalized to take into account the vortices in different cases of physical interest: rotating superfluids, counterflow superfluid turbulence, combined counterflow and rotation, and mass flow in addition to heat flow. To do this, the averaged vortex line density per unit volume L, is introduced and its dynamical equations are considered. Linear and non-linear evolution equations for L are written for homogeneous and inhomogeneous, isotropic and anisotropic situations. Several physical experiments are analyzed and the influence of vortices on the effective thermal conductivity of turbulent superfluid helium is found. Transitions from laminar to turbulent flows, from diffusive to
Turbulence measurements in fusion plasmas
International Nuclear Information System (INIS)
Conway, G D
2008-01-01
Turbulence measurements in magnetically confined toroidal plasmas have a long history and relevance due to the detrimental role of turbulence induced transport on particle, energy, impurity and momentum confinement. The turbulence-the microscopic random fluctuations in particle density, temperature, potential and magnetic field-is generally driven by radial gradients in the plasma density and temperature. The correlation between the turbulence properties and global confinement, via enhanced diffusion, convection and direct conduction, is now well documented. Theory, together with recent measurements, also indicates that non-linear interactions within the turbulence generate large scale zonal flows and geodesic oscillations, which can feed back onto the turbulence and equilibrium profiles creating a complex interdependence. An overview of the current status and understanding of plasma turbulence measurements in the closed flux surface region of magnetic confinement fusion devices is presented, highlighting some recent developments and outstanding problems.
Nonlinear closure relations theory for transport processes in nonequilibrium systems
International Nuclear Information System (INIS)
Sonnino, Giorgio
2009-01-01
A decade ago, a macroscopic theory for closure relations has been proposed for systems out of Onsager's region. This theory is referred to as the thermodynamic field theory (TFT). The aim of this work was to determine the nonlinear flux-force relations that respect the thermodynamic theorems for systems far from equilibrium. We propose a formulation of the TFT where one of the basic restrictions, namely, the closed-form solution for the skew-symmetric piece of the transport coefficients, has been removed. In addition, the general covariance principle is replaced by the De Donder-Prigogine thermodynamic covariance principle (TCP). The introduction of TCP requires the application of an appropriate mathematical formalism, which is referred to as the entropy-covariant formalism. By geometrical arguments, we prove the validity of the Glansdorff-Prigogine universal criterion of evolution. A new set of closure equations determining the nonlinear corrections to the linear ('Onsager') transport coefficients is also derived. The geometry of the thermodynamic space is non-Riemannian. However, it tends to be Riemannian for high values of the entropy production. In this limit, we recover the transport equations found by the old theory. Applications of our approach to transport in magnetically confined plasmas, materials submitted to temperature, and electric potential gradients or to unimolecular triangular chemical reactions can be found at references cited herein. Transport processes in tokamak plasmas are of particular interest. In this case, even in the absence of turbulence, the state of the plasma remains close to (but, it is not in) a state of local equilibrium. This prevents the transport relations from being linear.
Transport by negative eddy viscosity in soliton turbulence
Tchen, C. M.
1986-01-01
The forced Schrodinger equation is used to describe the microhydrodynamical state of strong soliton turbulence. The Schrodinger equation is transformed into a master equation and is decomposed into a macrogroup, a microgroup, and a submicrogroup, representative of the three transport processes of spectral evolution, transport property, and relaxation. The kinetic equation for the macrodistribution is derived and reverted to the continuum by the method of moments in order to find the equation of spectral evolution. The spectral flow is found to be governed by three types of transport, which are discussed.
International Nuclear Information System (INIS)
Mynick, H.E.
1989-05-01
The transport equations arising from the ''generalized Balescu- Lenard'' (gBL) collision operator are obtained, and some of their properties examined. The equations contain neoclassical and turbulent transport as two special cases, having the same structure. The resultant theory offers potential explanation for a number of results not well understood, including the anomalous pinch, observed ratios of Q/ΓT on TFTR, and numerical reproduction of ASDEX profiles by a model for turbulent transport invoked without derivation, but by analogy to neoclassical theory. The general equations are specialized to consideration of a number of particular transport mechanisms of interest. 10 refs
Turbulent flow structures and aeolian sediment transport over a barchan sand dune
Wiggs, G. F. S.; Weaver, C. M.
2012-03-01
The turbulent structure of airflow over a barchan sand dune is determined using quadrant analysis of wind velocity data derived from sonic anemometers. Results indicate an increased frequency of ejection and sweep events in the toe region of the dune, characteristic of the turbulent bursting process. In contrast, at the crest there was a significant increase in the occurrence of outward interactions. Combined with high frequency saltation data our analyses show that turbulent structures characterised by a positive streamwise fluctuating velocity (+u‧ sweeps at the toe and outward interactions at the crest) have a dominant influence on sand transport on the dune, together accounting for up to 83% and 95% of transporting events at the toe and crest respectively.
Turbulent Diffusion of the Geomagnetic Field and Dynamo Theories
Filippi, Enrico
2016-01-01
The thesis deals with the Dynamo Theories of the Earth’s Magnetic Field and mainly deepens the turbulence phenomena in the fluid Earth’s core. Indeed, we think that these phenomena are very important to understand the recent decay of the geomagnetic field. The thesis concerns also the dynamics of the outer core and some very rapid changes of the geomagnetic field observed in the Earth’s surface and some aspects regarding the (likely) isotropic turbulence in the Magnetohydrodynamics. These top...
Evidence for strange kinetics in Hasegawa-Mima turbulent transport
International Nuclear Information System (INIS)
Annibaldi, S.V.; Drury, L.O'C.; Manfredi, G.; Dendy, R.O.
2000-01-01
We have studied the transport of test particle ensembles moving in turbulent electrostatic fields governed by the Hasegawa-Mima (HM) equation. As a result of the interplay of the linear dispersive term and the nonlinear term in the HM equation, 'strange kinetics' emerge: the poloidal particle transport undergoes a qualitative transition from diffusive, through supradiffusive, to ballistic. (author). Letter-to-the-editor
Dynamic method to study turbulence and turbulence transport
International Nuclear Information System (INIS)
Inagaki, S.; Itoh, S.-I.; Kasuya, N.; Sasaki, M.; Fujisawa, A.; Ida, K.; Itoh, K.; Tokuzawa, T.; Tamura, N.; Kubo, S.; Shimozuma, T.; Tanaka, K.; Tsuchiya, H.; Nagayama, Y.; Yamada, H.; Komori, A.; Kobayashi, T.; Kosuga, Y.; Kamiya, Kensaku
2014-10-01
Here we developed research methods of plasma turbulence transport associated with the non-local features. The ECH modulation experiment and the higher harmonic analysis of the heat wave indicated: (1) propagation of the change of T e at the time of switch-off/on of ECH power is about 5 times faster than that of perturbation itself, (2) propagation of the higher (7th) harmonic of the T e perturbation is 5 times faster than prediction by the diffusive model. New bi-spectral analysis of fluctuations demonstrated a non-linear coupling of micro-fluctuations at different radial locations. These results are beneficial for control of plasma dynamics in future fusion reactors. (author)
Towards CFD modeling of turbulent pipeline material transportation
Shahirpour, Amir; Herzog, Nicoleta; Egbers, Cristoph
2013-04-01
Safe and financially efficient pipeline transportation of carbon dioxide is a critical issue in the developing field of the CCS Technology. In this part of the process, carbon dioxide is transported via pipes with diameter of 1.5 m and entry pressure of 150 bar, with Reynolds number of 107 and viscosity of 8×10(-5) Pa.s as dense fluid [1]. Presence of large and small scale structures in the pipeline, high Reynolds numbers at which CO2 should be transferred, and 3 dimensional turbulence caused by local geometrical modifications, increase the importance of simulation of turbulent material transport through the individual components of the CO2 chain process. In this study, incompressible turbulent channel flow and pipe flow have been modeled using OpenFoam, an open source CFD software. In the first step, simulation of a turbulent channel flow has been considered using LES for shear Reynolds number of 395. A simple geometry has been chosen with cyclic fluid inlet and outlet boundary conditions to simulate a fully developed flow. The mesh is gradually refined towards the wall to provide values close enough to the wall for the wall coordinate (y+). Grid resolution study has been conducted for One-Equation model. The accuracy of the results is analyzed with respect to the grid smoothness in order to reach an optimized resolution for carrying out the next simulations. Furthermore, three LES models, One-Equation, Smagorinsky and Dynamic Smagorinsky are applied for the grid resolution of (60 × 100 × 80) in (x, y, z) directions. The results are then validated with reference to the DNS carried out by Moser et al.[2] for the similar geometry using logarithmic velocity profile (U+) and Reynolds stress tensor components. In the second step the similar flow is modeled using Reynolds averaged method. Several RANS models, like K-epsilon and Launder-Reece-Rodi are applied and validated against DNS and LES results in a similar fashion. In the most recent step, it has been intended
Kim, J.; Simon, T. W.
1987-01-01
The effects of streamwise convex curvature, recovery, and freestream turbulence intensity on the turbulent transport of heat and momentum in a mature boundary layer are studied using a specially designed three-wire hot-wire probe. Increased freestream turbulence is found to increase the profiles throughout the boundary layer on the flat developing wall. Curvature effects were found to dominate turbulence intensity effects for the present cases considered. For the higher TI (turbulence intensity) case, negative values of the turbulent Prandtl number are found in the outer half of the boundary layer, indicating a breakdown in Reynolds analogy.
External intermittency prediction using AMR solutions of RANS turbulence and transported PDF models
Olivieri, D. A.; Fairweather, M.; Falle, S. A. E. G.
2011-12-01
External intermittency in turbulent round jets is predicted using a Reynolds-averaged Navier-Stokes modelling approach coupled to solutions of the transported probability density function (pdf) equation for scalar variables. Solutions to the descriptive equations are obtained using a finite-volume method, combined with an adaptive mesh refinement algorithm, applied in both physical and compositional space. This method contrasts with conventional approaches to solving the transported pdf equation which generally employ Monte Carlo techniques. Intermittency-modified eddy viscosity and second-moment turbulence closures are used to accommodate the effects of intermittency on the flow field, with the influence of intermittency also included, through modifications to the mixing model, in the transported pdf equation. Predictions of the overall model are compared with experimental data on the velocity and scalar fields in a round jet, as well as against measurements of intermittency profiles and scalar pdfs in a number of flows, with good agreement obtained. For the cases considered, predictions based on the second-moment turbulence closure are clearly superior, although both turbulence models give realistic predictions of the bimodal scalar pdfs observed experimentally.
Plasma turbulence. Structure formation, selection rule, dynamic response and dynamics transport
International Nuclear Information System (INIS)
Ito, Sanae I.
2010-01-01
The five-year project of Grant-in-Aid for Specially Promoted Research entitled general research on the structure formation and selection rule in plasma turbulence had brought many outcomes. Based on these outcomes, the Grant-in-Aid for Scientific Research (S) program entitled general research on dynamic response and dynamic transport in plasma turbulence has started. In the present paper, the state-of-the-art of the research activities on the structure formation, selection rule and dynamics in plasma turbulence are reviewed with reference to outcomes of these projects. (author)
Renormalized perturbation theory: Vlasov-Poisson System, weak turbulence limit and gyrokinetics
International Nuclear Information System (INIS)
Zhang, Y.Z.; Mahajan, S.M.
1987-10-01
The Self-consistency of the renormalized perturbation theory is demonstrated by applying it to the Vlasov-Poisson System and showing that the theory has the correct weak turbulence limit. Energy conservation is proved to arbitrary high order for the electrostatic drift waves. The theory is applied to derive renormalized equations for a low-β gyrokinetic system. Comparison of our theory with other current theories is presented. 22 refs
Impurity and trace tritium transport in tokamak edge turbulence
DEFF Research Database (Denmark)
Naulin, V.
2005-01-01
The turbulent transport of impurity or minority species, as for example tritium, is investigated in drift-Alfven edge turbulence. The full effects of perpendicular and parallel convection are kept for the impurity species. The impurity density develops a granular structure with steep gradients...... and locally exceeds its initial values due to the compressibility of the flow. An approximate decomposition of the impurity flux into a diffusive part and an effective convective part (characterized by a pinch velocity) is performed and a net inward pinch effect is recovered. The pinch velocity is explained...
Low-Z impurity transport in DIII-D - observations and implications
International Nuclear Information System (INIS)
Wade, M.R.; Houlberg, W.A.; Baylor, L.R.; West, W.P.; Baker, D.R.
2001-01-01
Impurity transport studies on DIII-D have revealed transport phenomena that are qualitatively consistent with that expected from turbulence transport theory in some cases and neoclassical transport theory in other cases. The transport model proposed here, which assumes that the total impurity transport is a linear sum of turbulence-driven transport and neoclassical transport, is shown to reproduce many of these observed features. This transport model is then applied to burn condition calculations, revealing that profile effects associated with neoclassical transport have a large effect on the maximum allowable impurity fraction in machines based on achieving neoclassical transport levels
Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars
Warnecke, J.; Rheinhardt, M.; Tuomisto, S.; Käpylä, P. J.; Käpylä, M. J.; Brandenburg, A.
2018-01-01
Aims: We investigate dynamo action in global compressible solar-like convective dynamos in the framework of mean-field theory. Methods: We simulate a solar-type star in a wedge-shaped spherical shell, where the interplay between convection and rotation self-consistently drives a large-scale dynamo. To analyze the dynamo mechanism we apply the test-field method for azimuthally (φ) averaged fields to determine the 27 turbulent transport coefficients of the electromotive force, of which six are related to the α tensor. This method has previously been used either in simulations in Cartesian coordinates or in the geodynamo context and is applied here for the first time to fully compressible simulations of solar-like dynamos. Results: We find that the φφ-component of the α tensor does not follow the profile expected from that of kinetic helicity. The turbulent pumping velocities significantly alter the effective mean flows acting on the magnetic field and therefore challenge the flux transport dynamo concept. All coefficients are significantly affected by dynamically important magnetic fields. Quenching as well as enhancement are being observed. This leads to a modulation of the coefficients with the activity cycle. The temporal variations are found to be comparable to the time-averaged values and seem to be responsible for a nonlinear feedback on the magnetic field generation. Furthermore, we quantify the validity of the Parker-Yoshimura rule for the equatorward propagation of the mean magnetic field in the present case.
The role of the Kubo number in two-component turbulence
International Nuclear Information System (INIS)
Qin, G.; Shalchi, A.
2013-01-01
We explore the random walk of magnetic field lines in two-component turbulence by using computer simulations. It is often assumed that the two-component model provides a good approximation for solar wind turbulence. We explore the dependence of the field line diffusion coefficient on the Kubo number which is a fundamental and characteristic quantity in the theory of turbulence. We show that there are two transport regimes. One is the well-known quasilinear regime in which the diffusion coefficient is proportional to the Kubo number squared, and the second one is a nonlinear regime in which the diffusion coefficient is directly proportional to the Kubo number. The so-called percolative transport regime which is often discussed in the literature cannot be found. The numerical results obtained in the present paper confirm analytical theories for random walking field lines developed in the past
Nature of turbulent transport across sheared zonal flows: insights from gyrokinetic simulations
International Nuclear Information System (INIS)
Sanchez, R; Newman, D E; Leboeuf, J-N; Decyk, V K
2011-01-01
The traditional view regarding the reduction of turbulence-induced transport across a stable sheared flow invokes a reduction of the characteristic length scale in the direction perpendicular to the flow as a result of the shearing and stretching of eddies caused by the differential pull exerted in the direction of the flow. A reduced effective transport coefficient then suffices to capture the reduction, that can then be readily incorporated into a transport model. However, recent evidence from gyrokinetic simulations of the toroidal ion-temperature-gradient mode suggests that the dynamics of turbulent transport across sheared flows changes in a more fundamental manner, and that the use of reduced effective transport coefficients fails to capture the full dynamics that may exhibit both subdiffusion and non-Gaussian statistics. In this contribution, after briefly reviewing these results, we propose some candidates for the physical mechanisms responsible for endowing transport with such non-diffusive characteristics, backing these proposals with new numerical gyrokinetic data.
Electromotive force in strongly compressible magnetohydrodynamic turbulence
Yokoi, N.
2017-12-01
Variable density fluid turbulence is ubiquitous in geo-fluids, not to mention in astrophysics. Depending on the source of density variation, variable density fluid turbulence may be divided into two categories: the weak compressible (entropy mode) turbulence for slow flow and the strong compressible (acoustic mode) turbulence for fast flow. In the strong compressible turbulence, the pressure fluctuation induces a strong density fluctuation ρ ', which is represented by the density variance ( denotes the ensemble average). The turbulent effect on the large-scale magnetic-field B induction is represented by the turbulent electromotive force (EMF) (u': velocity fluctuation, b': magnetic-field fluctuation). In the usual treatment in the dynamo theory, the expression for the EMF has been obtained in the framework of incompressible or weak compressible turbulence, where only the variation of the mean density , if any, is taken into account. We see from the equation of the density fluctuation ρ', the density variance is generated by the large mean density variation ∂ coupled with the turbulent mass flux . This means that in the region where the mean density steeply changes, the density variance effect becomes relevant for the magnetic field evolution. This situation is typically the case for phenomena associated with shocks and compositional discontinuities. With the aid of the analytical theory of inhomogeneous compressible magnetohydrodynamic (MHD) turbulence, the expression for the turbulent electromotive force is investigated. It is shown that, among others, an obliqueness (misalignment) between the mean density gradient ∂ and the mean magnetic field B may contribute to the EMF as ≈χ B×∂ with the turbulent transport coefficient χ proportional to the density variance (χ ). This density variance effect is expected to strongly affect the EMF near the interface, and changes the transport properties of turbulence. In the case of an interface under the MHD slow
Transport of solar electrons in the turbulent interplanetary magnetic field
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Ablaßmayer, J.; Tautz, R. C., E-mail: robert.c.tautz@gmail.com [Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin (Germany); Dresing, N., E-mail: dresing@physik.uni-kiel.de [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Leibnizstraße 11, D-24118 Kiel (Germany)
2016-01-15
The turbulent transport of solar energetic electrons in the interplanetary magnetic field is investigated by means of a test-particle Monte-Carlo simulation. The magnetic fields are modeled as a combination of the Parker field and a turbulent component. In combination with the direct calculation of diffusion coefficients via the mean-square displacements, this approach allows one to analyze the effect of the initial ballistic transport phase. In that sense, the model complements the main other approach in which a transport equation is solved. The major advancement is that, by recording the flux of particles arriving at virtual detectors, intensity and anisotropy-time profiles can be obtained. Observational indications for a longitudinal asymmetry can thus be explained by tracing the diffusive spread of the particle distribution. The approach may be of future help for the systematic interpretation of observations for instance by the solar terrestrial relations observatory (STEREO) and advanced composition explorer (ACE) spacecrafts.
Impact of phenomenological theory of turbulence on pragmatic approach to fluvial hydraulics
Ali, Sk Zeeshan; Dey, Subhasish
2018-04-01
The phenomenological theory of turbulence (PTT) remains a long-standing and fascinating theory in turbulence research. In this review article, we highlight the state-of-the-science of the impact of the PTT on the pragmatic approach to fluvial hydraulics, explored over recent decades, discussing the salient and the subtle roles that the turbulence plays in governing many physical processes. To acquire a theoretical explanation of this pragmatic approach necessitates an intuitive thought that can bring together the background mechanisms of all the physical processes under one law—a thought that is capable of finding their inextricable links with the turbulent energy spectrum. We begin here with emphasizing the spectral and the co-spectral origin of the well-recognized laws of the wall, the resistance equation, and the turbulence intensities by portraying the typical momentum transfer mechanism of eddies in a turbulent flow. Next, we focus on the scaling laws of key fluvial processes derived from the perspective of the PTT, enlightening their physical insight and ability to judge how far the so-called empirical formulas can be used with confidence. The PTT has been able to disclose the origin of several primeval empirical formulas that have been used over many years without having any theoretical clarification and confirmation. Finally, we make an effort to describe some unsolved issues to be resolved as a future scope of research.
Zonal flow dynamics and control of turbulent transport in stellarators.
Xanthopoulos, P; Mischchenko, A; Helander, P; Sugama, H; Watanabe, T-H
2011-12-09
The relation between magnetic geometry and the level of ion-temperature-gradient (ITG) driven turbulence in stellarators is explored through gyrokinetic theory and direct linear and nonlinear simulations. It is found that the ITG radial heat flux is sensitive to details of the magnetic configuration that can be understood in terms of the linear behavior of zonal flows. The results throw light on the question of how the optimization of neoclassical confinement is related to the reduction of turbulence.
''Turbulent Equipartition'' Theory of Toroidal Momentum Pinch
International Nuclear Information System (INIS)
Hahm, T.S.; Diamond, P.H.; Gurcan, O.D.; Rewaldt, G.
2008-01-01
The mode-independent part of magnetic curvature driven turbulent convective (TuroCo) pinch of the angular momentum density (Hahm et al., Phys. Plasmas 14,072302 (2007)) which was originally derived from the gyrokinetic equation, can be interpreted in terms of the turbulent equipartition (TEP) theory. It is shown that the previous results can be obtained from the local conservation of 'magnetically weighted angular momentum density', nm i U # parallel# R/B 2 , and its homogenization due to turbulent flows. It is also demonstrated that the magnetic curvature modification of the parallel acceleration in the nonlinear gyrokinetic equation in the laboratory frame, which was shown to be responsible for the TEP part of the TurCo pinch of angular momentum density in the previous work, is closely related to the Coriolis drift coupling to the perturbed electric field. In addition, the origin of the diffusive flux in the rotating frame is highlighted. Finally, it is illustrated that there should be a difference in scalings between the momentum pinch originated from inherently toroidal effects and that coming from other mechanisms which exist in a simpler geometry.
Turbulent transport regimes and the scrape-off layer heat flux width
Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.
2015-04-01
Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks and for seeking possible mitigation schemes. In this paper, we present a qualitative and conceptual framework for understanding various regimes of edge/SOL turbulence and the role of turbulent transport as the mechanism for establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. We find a heat flux width scaling with major radius R that is generally positive, consistent with the previous findings [Connor et al., Nucl. Fusion 39, 169 (1999)]. The possible relationship of turbulence mechanisms to the neoclassical orbit width or heuristic drift mechanism in core energy confinement regimes known as low (L) mode and high (H) mode is considered, together with implications for the future experiments.
Turbulent transport regimes and the scrape-off layer heat flux width
International Nuclear Information System (INIS)
Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.
2015-01-01
Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks and for seeking possible mitigation schemes. In this paper, we present a qualitative and conceptual framework for understanding various regimes of edge/SOL turbulence and the role of turbulent transport as the mechanism for establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. We find a heat flux width scaling with major radius R that is generally positive, consistent with the previous findings [Connor et al., Nucl. Fusion 39, 169 (1999)]. The possible relationship of turbulence mechanisms to the neoclassical orbit width or heuristic drift mechanism in core energy confinement regimes known as low (L) mode and high (H) mode is considered, together with implications for the future experiments
Tokamak electron heat transport by direct numerical simulation of small scale turbulence
International Nuclear Information System (INIS)
Labit, B.
2002-10-01
In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure β or the normalized Larmor radius, ρ * . The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters β and ρ * . The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve. From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values. The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkama's formula. On the other hand, the crucial role of the
International Nuclear Information System (INIS)
Kleva, R.G.
1980-01-01
The first part of this work is concerned with test particle transport in a stochastic magnetic field. In the absence of collisions, the test particle self-diffusion coefficient is given by D = D/sub m/ V (in the zero gyroradius limit), where D/sub m/ is the magnetic diffusion coefficient due to a given spectrum of magnetic fluctuations and V is the particle velocity along a field line. The effect of collisions, either classical or turbulent, on this result is considered. The second part of this work is concerned with the evolution of the collisionless tearing mode in the presence of a stochastic magnetic field. A statistical closure approximation, obtained from the DIA by neglecting a mode-coupling term, is used to derive a nonlinear dispersion relation. For L 0 < L/sub K/ the dominant nonlinear effect is shown to be a turbulent broadening of the perturbed current layer. Saturation occurs when the perturbed current layer broadens to the point where Δ' = 0, where Δ' is the jump in the logarithmic derivative of the vector potential across the perturbed current layer
Theory of 'strong' turbulence - Application to the ion acoustic instability
International Nuclear Information System (INIS)
Abdel-Gawad, Hamdy Ibrahim
1984-01-01
In this thesis, we apply the techniques recently developed in the theory of turbulence to study the evolution of the current-driven ion acoustic instability. We present a method allow to describe analytically and with a self-coherent manner the dynamic of the deformation of the distribution function of particles in the same time as the evolution of the turbulent energy. We have also discerned the saturation mechanisms of the instability as well as their domain of validity. (author) [fr
The 'generalized Balescu-Lenard' transport equations
International Nuclear Information System (INIS)
Mynick, H.E.
1990-01-01
The transport equations arising from the 'generalized Balescu-Lenard' collision operator are obtained and some of their properties examined. The equations contain neoclassical and turbulent transport as two special cases having the same structure. The resultant theory offers a possible explanation for a number of results not well understood, including the anomalous pinch, observed ratios of Q/ΓT on TFTR, and numerical reproduction of ASDEX profiles by a model for turbulent transport invoked without derivation, but by analogy with neoclassical theory. The general equations are specialized to consideration of a number of particular transport mechanisms of interest. (author). Letter-to-the-editor. 10 refs
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
Theory of ion-temperature-gradient-driven turbulence in tokamaks
International Nuclear Information System (INIS)
Lee, G.S.; Diamond, P.H.
1986-01-01
An analytic theory of ion-temperature-gradient-driven turbulence in tokamaks is presented. Energy-conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion-temperature-gradient-driven turbulence. Corrections to mixing-length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity chi/sub i/ = 0.4[(π/2)ln(1 + eta/sub i/)] 2 [(1 + eta/sub i/)/tau] 2 rho/sub s/ 2 c/sub s//L/sub s/ is derived and is found to be consistent with experimentally-deduced thermal diffusivities. The associated electron thermal diffusivity and particle and heat-pinch velocities are also calculated. The effect of impurity gradients on saturated ion-temperature-gradient-driven turbulence is discussed and a related explanation of density profile steepening during Z-mode operation is proposed. 35 refs., 4 figs
Energy Technology Data Exchange (ETDEWEB)
Caldas, Ibere L.; Heller, M.V.A.P.; Brasilio, Z.A. [Sao Paulo Univ., SP, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. In this work we summarize the results from experiments on electrostatic and magnetic fluctuations in tokamak plasmas. Spectral analyses show that these fluctuations are turbulent, having a broad spectrum of wavectors and a broad spectrum of frequencies at each wavector. The electrostatic turbulence induces unexpected anomalous particle transport that deteriorates the plasma confinement. The relationship of these fluctuations to the current state of plasma theory is still unclear. Furthermore, we describe also attempts to control this plasma turbulence with external magnetic perturbations that create chaotic magnetic configurations. Accordingly, the magnetic field lines may become chaotic and then induce a Lagrangian diffusion. Moreover, to discuss nonlinear coupling and intermittency, we present results obtained by using numerical techniques as bi spectral and wavelet analyses. (author)
International Nuclear Information System (INIS)
Dey, Prasanta K.; Zikanov, Oleg
2012-01-01
Highlights: ► Turbulent passive scalar transport in an MHD flow in a channel is studied using DNS. ► Magnetic fields of wall-normal, spanwise, and streamwise orientations are considered. ► Magnetic fields suppress turbulent transport and modifies scalar distribution. ► The effect is particularly strong at wall-normal and spanwise magnetic fields. ► Decrease of Nusselt number is approximated by a linear function of magnetic interaction parameter. - Abstract: DNS of turbulent flow and passive scalar transport in a channel are conducted for the situation when the fluid is electrically conducting (for example, a liquid metal) and the flow is affected by an imposed magnetic field. The cases of wall-normal, spanwise, and streamwise orientation of the magnetic field are considered. As main results, we find that the magnetic fields, especially those in the wall-normal and spanwise directions, significantly reduce the turbulent scalar transport and modify the properties of the scalar distribution.
Low frequency turbulence, particle and heat transport in the Wisconsin levitated octupole
International Nuclear Information System (INIS)
Garner, H.R.
1982-01-01
Low frequency turbulence in the drift frequency range and its relation to the observed particle transport in the Wisconsin Levitated Octupole has been studied with a microwave scattering apparatus. The experimental parameters were T/sub e/ approx. T/sub i/ 13 cm -3 , 200 G < B/sub p-average/ < 1.25 kG. The effect of shear on the transport was studied by the addition of a small toroidal field. By matching experimentally measured density profiles to those given by numerical solutions of the transport equations, diffusion coefficients were obtained. Time dependent density fluctuation spectra were measured with an 8 mm microwave scattering diagnostic to correlate the drift wave portion of the spectrum with the observed diffusion. The density fluctuation spectrum of low frequency (1 kHz < ω < 6 MHz) turbulence was measured for several values of perpendicular wavenumber, k/sub perpendicular to/. Electron heat transport was studied by fitting experimentally measured electron temperature profiles to those predicted by numerical solutions of electron energy transport equation
Ion transport in turbulent edge plasmas
International Nuclear Information System (INIS)
Helander, P.; Massachusetts Inst. of Tech., Cambridge, MA; Hazeltine, R.D.; Catto, P.J.
1996-02-01
Edge plasmas, such as the tokamak scrape-off layer, exist as a consequence of a balance between cross-field diffusion and parallel losses. The former is usually anomalous, and is widely thought to be driven by strong electrostatic turbulence. It is shown that the anomalous diffusion affects the parallel ion transport by giving rise to a new type of thermal force between different ion species. This force is parallel to the magnetic field, but arises entirely because of perpendicular gradients, and could be important for impurity retention in the tokamak divertor. (author)
Sandpile dynamics as a paradigm for turbulent transport
International Nuclear Information System (INIS)
Newman, D.E.; Carreras, B.A.; Diamond, P.H.
1995-01-01
To shed some light on the apparent discrepancies between most theoretical models of turbulent transport and experimental observations of the transport in magnetically confined plasmas, a model for transport has been developed based on the concept of self-organized criticality (SOC). This model seeks to describe the dynamics of the transport without relying on the underlying local fluctuation mechanisms. Computations based on a cellular automata model have found that SOC systems maintain average profiles that are linearly stable (submarginal) and yet are able to sustain active transport dynamics in contrast to naive marginal stability arguments. It is also found that the dominant scales in the transport dynamics in the absence of sheared flow are system scales rather than the underlying local fluctuation scales. However, the addition of sheared flow into the dynamics leads to a large reduction of the system-scale transport events and a commensurate increase in the fluctuation-scale transport events needed to maintain the constant flux. The dynamics of these models and the potential ramifications for transport studies are discussed
Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks
International Nuclear Information System (INIS)
Parra, Felix I.; Barnes, Michael; Peeters, Arthur G.
2011-01-01
Two symmetries of the local nonlinear δf gyrokinetic system of equations in tokamaks in the high flow regime are presented. The turbulent transport of toroidal angular momentum changes sign under an up-down reflection of the tokamak and a sign change of both the rotation and the rotation shear. Thus, the turbulent transport of toroidal angular momentum must vanish for up-down symmetric tokamaks in the absence of both rotation and rotation shear. This has important implications for the modeling of spontaneous rotation.
Epps, Brenden; Cushman-Roisin, Benoit
2017-11-01
Fluid turbulence is an outstanding unsolved problem in classical physics, despite 120+ years of sustained effort. Given this history, we assert that a new mathematical framework is needed to make a transformative breakthrough. This talk offers one such framework, based upon kinetic theory tied to the statistics of turbulent transport. Starting from the Boltzmann equation and ``Lévy α-stable distributions'', we derive a turbulence model that expresses the turbulent stresses in the form of a fractional derivative, where the fractional order is tied to the transport behavior of the flow. Initial results are presented herein, for the cases of Couette-Poiseuille flow and 2D boundary layers. Among other results, our model is able to reproduce the logarithmic Law of the Wall in shear turbulence.
Renormalization group approach in the turbulence theory
International Nuclear Information System (INIS)
Adzhemyan, L.Ts.; Vasil'ev, A.N.; Pis'mak, Yu.M.
1983-01-01
In the framework of the renormalization groUp approach in the turbulence theory sUggested in another paper, the problem of renormalization and evaluation of critical dimensions of composite operators is discussed. Renormalization of a system of operators of canonical dimension equal to 4, including the operator F=phiΔphi (where phi is the velocity field), is considered. It is shown that the critical dimension Δsub(F)=0. The appendice includes the brief proofs of two theorems: 1) the theorem on the equivalence between the arbitrary stochastic problem and quantum field theory; 2) the theorem which determines the reduction of Green functions of the stochastic problem to the hypersurface of coinciding times
Rigorous upper bounds for transport due to passive advection by inhomogeneous turbulence
International Nuclear Information System (INIS)
Krommes, J.A.; Smith, R.A.
1987-05-01
A variational procedure, due originally to Howard and explored by Busse and others for self-consistent turbulence problems, is employed to determine rigorous upper bounds for the advection of a passive scalar through an inhomogeneous turbulent slab with arbitrary generalized Reynolds number R and Kubo number K. In the basic version of the method, the steady-state energy balance is used as a constraint; the resulting bound, though rigorous, is independent of K. A pedagogical reference model (one dimension, K = ∞) is described in detail; the bound compares favorably with the exact solution. The direct-interaction approximation is also worked out for this model; it is somewhat more accurate than the bound, but requires considerably more labor to solve. For the basic bound, a general formalism is presented for several dimensions, finite correlation length, and reasonably general boundary conditions. Part of the general method, in which a Green's function technique is employed, applies to self-consistent as well as to passive problems, and thereby generalizes previous results in the fluid literature. The formalism is extended for the first time to include time-dependent constraints, and a bound is deduced which explicitly depends on K and has the correct physical scalings in all regimes of R and K. Two applications from the theory of turbulent plasmas ae described: flux in velocity space, and test particle transport in stochastic magnetic fields. For the velocity space problem the simplest bound reproduces Dupree's original scaling for the strong turbulence diffusion coefficient. For the case of stochastic magnetic fields, the scaling of the bounds is described for the magnetic diffusion coefficient as well as for the particle diffusion coefficient in the so-called collisionless, fluid, and double-streaming regimes
Coherent structures and transport in drift wave plasma turbulence
Energy Technology Data Exchange (ETDEWEB)
Bang Korsholm, S.
2011-12-15
Fusion energy research aims at developing fusion power plants providing safe and clean energy with abundant fuels. Plasma turbulence induced transport of energy and particles is a performance limiting factor for fusion devices. Hence the understanding of plasma turbulence is important for optimization. The present work is a part of the puzzle to understand the basic physics of transport induced by drift wave turbulence in the edge region of a plasma. The basis for the study is the Hasegawa-Wakatani model. Simulation results for 3D periodic and nonperiodic geometries are presented. The Hasegawa-Wakatani model is further expanded to include ion temperature effects. Another expansion of the model is derived from the Braginskii electron temperature equation. The result is a self-consistent set of equations describing the dynamical evolution of the drift wave fluctuations of the electron density, electron temperature and the potential in the presence of density and temperature gradients. 3D simulation results of the models are presented. Finally, the construction and first results from the MAST fluctuation reflectometer is described. The results demonstrate how L- to H-mode transitions as well as edge-localized-modes can be detected by the relatively simple diagnostic system. The present Risoe report is a slightly updated version of my original PhD report which was submitted in April 2002 and defended in August 2002. (Author)
Coherent structures and transport in drift wave plasma turbulence
International Nuclear Information System (INIS)
Bang Korsholm, S.
2011-12-01
Fusion energy research aims at developing fusion power plants providing safe and clean energy with abundant fuels. Plasma turbulence induced transport of energy and particles is a performance limiting factor for fusion devices. Hence the understanding of plasma turbulence is important for optimization. The present work is a part of the puzzle to understand the basic physics of transport induced by drift wave turbulence in the edge region of a plasma. The basis for the study is the Hasegawa-Wakatani model. Simulation results for 3D periodic and nonperiodic geometries are presented. The Hasegawa-Wakatani model is further expanded to include ion temperature effects. Another expansion of the model is derived from the Braginskii electron temperature equation. The result is a self-consistent set of equations describing the dynamical evolution of the drift wave fluctuations of the electron density, electron temperature and the potential in the presence of density and temperature gradients. 3D simulation results of the models are presented. Finally, the construction and first results from the MAST fluctuation reflectometer is described. The results demonstrate how L- to H-mode transitions as well as edge-localized-modes can be detected by the relatively simple diagnostic system. The present Risoe report is a slightly updated version of my original PhD report which was submitted in April 2002 and defended in August 2002. (Author)
Energy Technology Data Exchange (ETDEWEB)
Labit, B
2002-10-01
In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure {beta} or the normalized Larmor radius, {rho}{sub *}. The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters {beta} and {rho}{sub *}. The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve. From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values. The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkama's formula. On the other hand
Suppression of turbulent resistivity in turbulent Couette flow
Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe
2015-07-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
Energy Technology Data Exchange (ETDEWEB)
Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
International Nuclear Information System (INIS)
Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.
2015-01-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations
Edge turbulence and transport: Text and ATF modeling
International Nuclear Information System (INIS)
Ritz, C.P.; Rhodes, T.L.; Lin, H.; Rowan, W.L.; Bengtson, R.; Wootton, A.J.; Diamond, P.H.; Ware, A.S.; Thayer, D.R.
1990-01-01
We present experimental results on edge turbulence and transport from the tokamak TEXT and the torsatron ATF. The measured electrostatic fluctuations can explain the edge transport of particles and energy. Certain drive (radiation) and stabilizing (velocity shear) terms are suggested by the results. The experimental fluctuation levels and spectral widths can be reproduced by considering the nonlinear evolution of the reduced MHD equations, incorporating a thermal drive from line radiation. In the tokamak limit (with toroidal electric field) the model corresponds to the resistivity gradient mode, while in the currentless torsatron or stellarator limit it corresponds to a thermally driven drift wave
Modelling of transport phenomena
International Nuclear Information System (INIS)
Itoh, Kimitaka; Itoh, Sanae; Fukuyama, Atsushi.
1993-09-01
In this review article, we discuss key features of the transport phenomena and theoretical modelling to understand them. Experimental observations have revealed the nature of anomalous transport, i.e., the enhancement of the transport coefficients by the gradients of the plasma profiles, the pinch phenomena, the radial profile of the anomalous transport coefficients, the variation of the transport among the Bohm diffusion, Pseudo-classical confinement, L-mode and variety of improved confinement modes, and the sudden jumps such as L-H transition. Starting from the formalism of the transport matrix, the modelling based on the low frequency instabilities are reviewed. Theoretical results in the range of drift wave frequency are examined. Problems in theories based on the quasilinear and mixing-length estimates lead to the renewal of the turbulence theory, and the physics picture of the self-sustained turbulence is discussed. The theory of transport using the fluid equation of plasma is developed, showing that the new approach is very promising in explaining abovementioned characteristics of anomalous transport in both L-mode and improved confinement plasmas. The interference of the fluxes is the key to construct the physics basis of the bifurcation theory for the L-H transition. The present status of theories on the mechanisms of improved confinement is discussed. Modelling on the nonlocal nature of transport is briefly discussed. Finally, the impact of the anomalous transport on disruptive phenomena is also described. (author) 95 refs
Edge gradient and safety factor effects on electrostatic turbulent transport in tokamaks
International Nuclear Information System (INIS)
Tan, Ing Hwie.
1992-05-01
Electrostatic turbulence and transport measurements are performed on the Tokapole-II tokamak at the University of Wisconsin-Madison, as the safety-factor and the edge equilibrium gradients and varied substantially. Tokapole-II is a poloidal divertor tokamak capable of operating at a wide range of safety factors due to its unique magnetic limiter configuration. It also has retractable material limiters in a large scrape-off region, which permits the study of edge boundary conditions like density and temperature gradients. The turbulence is independent of safety factor, but strongly sensitive to the local density gradient, which itself depends upon the limiter configuration. When a material limiter is inserted in a high discharge, the density gradient is increased locally together with a local increase of the turbulence. On the other hand, limiter insertion in low discharges did not increase the density gradient as much and the turbulence properties are unchanged with respect to the magnetic limiter case. It is conducted then, that electrostatic turbulence is caused by the density gradient. Although the electrostatic fluctuation driven transport is enhanced in the large density gradient case, it is in all cases to small to explain the observed energy confinement times. To explore instabilities with small wavelengths, a 0.5 mm diameter shperical Langmuir probe was constructed, and its power compared with the power measured by larger cylindrical probes
Papapostolou, Vassilios
2017-09-11
Enstrophy is an intrinsic feature of turbulent flows, and its transport properties are essential for the understanding of premixed flame-turbulence interaction. The interrelation between the enstrophy transport and flow topologies, which can be assigned to eight categories based on the three invariants of the velocity-gradient tensor, has been analysed here. The enstrophy transport conditional on flow topologies in turbulent premixed flames has been analysed using a Direct Numerical Simulation database representing the corrugated flamelets (CF), thin reaction zones (TRZ) and broken reaction zones (BRZ) combustion regimes. The flame in the CF regime exhibits considerable flame-generated enstrophy, and the dilatation rate and baroclinic torque contributions to the enstrophy transport act as leading order sink and source terms, respectively. Consequently, flow topologies associated with positive dilatation rate values, contribute significantly to the enstrophy transport in the CF regime. By contrast, enstrophy decreases from the unburned to the burned gas side for the cases representing the TRZ and BRZ regimes, with diminishing influences of dilatation rate and baroclinic torque. The enstrophy transport in the TRZ and BRZ regimes is governed by the vortex-stretching and viscous dissipation contributions, similar to non-reacting flows, and topologies existing for all values of dilatation rate remain significant contributors.
International Nuclear Information System (INIS)
Ayala, Orlando; Rosa, Bogdan; Wang Lianping
2008-01-01
The effect of air turbulence on the geometric collision kernel of cloud droplets can be predicted if the effects of air turbulence on two kinematic pair statistics can be modeled. The first is the average radial relative velocity and the second is the radial distribution function (RDF). A survey of the literature shows that no theory is available for predicting the radial relative velocity of finite-inertia sedimenting droplets in a turbulent flow. In this paper, a theory for the radial relative velocity is developed, using a statistical approach assuming that gravitational sedimentation dominates the relative motion of droplets before collision. In the weak-inertia limit, the theory reveals a new term making a positive contribution to the radial relative velocity resulting from a coupling between sedimentation and air turbulence on the motion of finite-inertia droplets. The theory is compared to the direct numerical simulations (DNS) results in part 1, showing a reasonable agreement with the DNS data for bidisperse cloud droplets. For droplets larger than 30 μm in radius, a nonlinear drag (NLD) can also be included in the theory in terms of an effective inertial response time and an effective terminal velocity. In addition, an empirical model is developed to quantify the RDF. This, together with the theory for radial relative velocity, provides a parameterization for the turbulent geometric collision kernel. Using this integrated model, we find that turbulence could triple the geometric collision kernel, relative to the stagnant air case, for a droplet pair of 10 and 20 μm sedimenting through a cumulus cloud at R λ =2x10 4 and ε=600 cm 2 s -3 . For the self-collisions of 20 μm droplets, the collision kernel depends sensitively on the flow dissipation rate
Parker, Jeffrey B.; LoDestro, Lynda L.; Told, Daniel; Merlo, Gabriele; Ricketson, Lee F.; Campos, Alejandro; Jenko, Frank; Hittinger, Jeffrey A. F.
2018-05-01
The vast separation dividing the characteristic times of energy confinement and turbulence in the core of toroidal plasmas makes first-principles prediction on long timescales extremely challenging. Here we report the demonstration of a multiple-timescale method that enables coupling global gyrokinetic simulations with a transport solver to calculate the evolution of the self-consistent temperature profile. This method, which exhibits resiliency to the intrinsic fluctuations arising in turbulence simulations, holds potential for integrating nonlocal gyrokinetic turbulence simulations into predictive, whole-device models.
Turbulent edge transport in the Princeton Beta Experiment-Modified high confinement mode
Tynan, G. R.; Schmitz, L.; Blush, L.; Boedo, J. A.; Conn, R. W.; Doerner, R.; Lehmer, R.; Moyer, R.; Kugel, H.; Bell, R.; Kaye, S.; Okabayashi, M.; Sesnic, S.; Sun, Y.
1994-10-01
The first probe measurements of edge turbulence and transport in a neutral beam induced high confinement mode (H-mode) are reported. A strong negative radial electric field is directly observed in H-mode. A transient suppression of normalized ion saturation and floating potential fluctuation levels occurs at the low confinement mode to high confinement mode (L-H) transition, followed by a recovery to near low mode (L-mode) levels. The average poloidal wave number and the poloidal wave-number spectral width are decreased, and the correlation between fluctuating density and potential is reduced. A large-amplitude coherent oscillation, localized to the strong radial electric field region, is observed in H-mode but does not cause transport. In H-mode the effective turbulent diffusion coefficient is reduced by an order of magnitude inside the last closed flux surface and in the scrape-off layer. The results are compared with a heuristic model of turbulence suppression by velocity-shear stabilization.
Turbulent lubrication theory considering the surface roughness effects, 2
International Nuclear Information System (INIS)
Hashimoto, Hiromu; Wada, Sanae; Kobayashi, Toshinobu.
1990-01-01
This second paper describes an application of the generalized turbulent lubrication theory considering the surface roughness effects, which is developed in the previous paper, to the finite-width journal bearings. In the numerical analysis, the nonlinear equations for the modified turbulence coefficients are simplified to save a computation time within a satisfactory accuracy under the assumption that the shear flow is superior to the pressure flow in the turbulent lubrication films. The numerical results of pressure distribution, Sommerfeld number, attitude angle, friction coefficient and flow rate for the Reynolds number of Re=2000, 5000 and 10000 are indicated in graphic form for various values of relative roughness, and the effects of surface roughness on these static performance characteristics are discussed. Moreover, the eccentricity ratio and attitude angle of the journal bearings with homogeneous rough surface are obtained experimentally for a wide range of Sommerfeld number, and the experimental results are compared with theoretical results. (author)
Thermally driven convective cells and tokamak edge turbulence
International Nuclear Information System (INIS)
Thayer, D.R.; Diamond, P.H.
1987-07-01
A unified theory for the dynamics of thermally driven convective cell turbulence is presented. The cells are excited by the combined effects of radiative cooling and resistivity gradient drive. The model also includes impurity dynamics. Parallel thermal and impurity flows enhanced by turbulent radial duffusion regulate and saturate overlapping cells, even in regimes dominated by thermal instability. Transport coefficients and fluctuation levels characteristic of the saturated turbulence are calculated. It is found that the impurity radiation increases transport coefficients for high density plasmas, while the parallel conduction damping, elevated by radial diffusion, in turn quenches the thermal instability. The enhancement due to radiative cooling provides a resolution to the dilemma of explaining the experimental observation that potential fluctuations exceed density fluctuations in the edge plasma (e PHI/T/sub e/ > n/n 0 )
Asymptotic expansion and statistical description of turbulent systems
International Nuclear Information System (INIS)
Hagan, W.K. III.
1986-01-01
A new approach to studying turbulent systems is presented in which an asymptotic expansion of the general dynamical equations is performed prior to the application of statistical methods for describing the evolution of the system. This approach has been applied to two specific systems: anomalous drift wave turbulence in plasmas and homogeneous, isotropic turbulence in fluids. For the plasma case, the time and length scales of the turbulent state result in the asymptotic expansion of the Vlasov/Poisson equations taking the form of nonlinear gyrokinetic theory. Questions regarding this theory and modern Hamiltonian perturbation methods are discussed and resolved. A new alternative Hamiltonian method is described. The Eulerian Direct Interaction Approximation (EDIA) is slightly reformulated and applied to the equations of nonlinear gyrokinetic theory. Using a similarity transformation technique, expressions for the thermal diffusivity are derived from the EDIA equations for various geometries, including a tokamak. In particular, the unique result for generalized geometry may be of use in evaluating fusion reactor designs and theories of anomalous thermal transport in tokamaks. Finally, a new and useful property of the EDIA is pointed out. For the fluid case, an asymptotic expansion is applied to the Navier-Stokes equation and the results lead to the speculation that such an approach may resolve the problem of predicting the Kolmogorov inertial range energy spectrum for homogeneous, isotropic turbulence. 45 refs., 3 figs
The gyro-radius scaling of ion thermal transport from global numerical simulations of ITG turbulence
International Nuclear Information System (INIS)
Ottaviani, M.; Manfredi, G.
1998-12-01
A three-dimensional, fluid code is used to study the scaling of ion thermal transport caused by Ion-Temperature-Gradient-Driven (ITG) turbulence. The code includes toroidal effects and is capable of simulating the whole torus. It is found that both close to the ITG threshold and well above threshold, the thermal transport and the turbulence structures exhibit a gyro-Bohm scaling, at least for plasmas with moderate poloidal flow. (author)
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.C.; Komoshvili, K.
2002-01-01
Turbulent transport of heat and particles is the principle obstacle confronting controlled fusion today. Thus, we investigate quantitatively the suppression of turbulence and formation of transport barriers in spherical tokamaks by sheared electric fields generated by externally driven radio-frequency (RF) waves, in the frequency range o)A n o] < o)ci (e)A and o)ci are the Alfven and ion cyclotron frequencies). This investigation consists of the solution of the full-wave equation for a spherical tokamak in the presence of externally driven fast waves and the evaluation of the power dissipation by the mode-converted Alfven waves. This in turn, provides a radial flow shear responsible for the suppression of plasma turbulence. Thus, a strongly non-linear equation for the radial sheared electric field is solved, the turbulent transport suppression rate is evaluated and compared with the ion temperature gradient (ITG) instability increment. For illustration, the case of START-like device (Sykes 2000) is treated. Thus, (i) the exact D-shape cross-section is considered; (ii) additional kinetic (including Landau damping) and particle trapping effects are added to the resistive two-fluid dielectric tensor operator; (iii) a finite extension antenna located on the low-field-side of the plasma is considered; (iv) a rigorous 2.5 finite elements numerical code (Sewell 1993) is used; and (v) the turbulence and transport barrier generated as a result of wave-plasma interaction is evaluated
Stochastic models of edge turbulent transport in the thermonuclear reactors
International Nuclear Information System (INIS)
Volchenkov, Dima
2005-01-01
Two-dimensional stochastic model of turbulent transport in the scrape-off layer (SOL) of thermonuclear reactors is considered. Convective instability arisen in the system with respect to perturbations reveals itself in the strong outward bursts of particle density propagating ballistically across the SOL. The criterion of stability for the fluctuations of particle density is formulated. A possibility to stabilize the system depends upon the certain type of plasma waves interactions and the certain scenario of turbulence. A bias of limiter surface would provide a fairly good insulation of chamber walls excepting for the resonant cases. Pdf of the particle flux for the large magnitudes of flux events is modeled with a simple discrete time toy model of I-dimensional random walks concluding at the boundary. The spectra of wandering times feature the pdf of particle flux in the model and qualitatively reproduce the experimental statistics of transport events
Parker, Jeffrey; Lodestro, Lynda; Told, Daniel; Merlo, Gabriele; Ricketson, Lee; Campos, Alejandro; Jenko, Frank; Hittinger, Jeffrey
2017-10-01
Predictive whole-device simulation models will play an increasingly important role in ensuring the success of fusion experiments and accelerating the development of fusion energy. In the core of tokamak plasmas, a separation of timescales between turbulence and transport makes a single direct simulation of both processes computationally expensive. We present the first demonstration of a multiple-timescale method coupling global gyrokinetic simulations with a transport solver to calculate the self-consistent, steady-state temperature profile. Initial results are highly encouraging, with the coupling method appearing robust to the difficult problem of turbulent fluctuations. The method holds potential for integrating first-principles turbulence simulations into whole-device models and advancing the understanding of global plasma behavior. Work supported by US DOE under Contract DE-AC52-07NA27344 and the Exascale Computing Project (17-SC-20-SC).
Transported PDF Modeling of Nonpremixed Turbulent CO/H-2/N-2 Jet Flames
Energy Technology Data Exchange (ETDEWEB)
Zhao, xinyu; Haworth, D. C.; Huckaby, E. David
2012-01-01
Turbulent CO/H{sub 2}/N{sub 2} (“syngas”) flames are simulated using a transported composition probability density function (PDF) method. A consistent hybrid Lagrangian particle/Eulerian mesh algorithm is used to solve the modeled PDF transport equation. The model includes standard k–ϵ turbulence, gradient transport for scalars, and Euclidean minimum spanning tree (EMST) mixing. Sensitivities of model results to variations in the turbulence model, the treatment of radiation heat transfer, the choice of chemical mechanism, and the PDF mixing model are explored. A baseline model reproduces the measured mean and rms temperature, major species, and minor species profiles reasonably well, and captures the scaling that is observed in the experiments. Both our results and the literature suggest that further improvements can be realized with adjustments in the turbulence model, the radiation heat transfer model, and the chemical mechanism. Although radiation effects are relatively small in these flames, consideration of radiation is important for accurate NO prediction. Chemical mechanisms that have been developed specifically for fuels with high concentrations of CO and H{sub 2} perform better than a methane mechanism that was not designed for this purpose. It is important to account explicitly for turbulence–chemistry interactions, although the details of the mixing model do not make a large difference in the results, within reasonable limits.
Turbulence and sediment transport over sand dunes and ripples
Bennis, A.; Le Bot, S.; lafite, R.; Bonneton, P.; Ardhuin, F.
2013-12-01
Several bedforms are present near to the surfzone of natural beaches. Dunes and ripples are frequently observed. Understanding the turbulence over these forms is essential for the sediment transport. The turbulent flow and the suspended sand particles interact with each other. At the moment, the modelling strategy for turbulence is still a challenge. According to the spatial scales, some different methods to model the turbulence are employed, in particular the RANS (Reynolds Averaged Navier-Stokes) and the LES (Large Eddy Simulation). A hybrid method combining both RANS and LES is set up here. We have adapted this method, initially developed for atmospheric flow, to the oceanic flow. This new method is implemented inside the 3D hydrodynamic model, MARS 3D, which is forced by waves. LES is currently the best way to simulate turbulent flow but its higher cost prevents it from being used for large scale applications. So, here we use RANS near the bottom while LES is set elsewhere. It allows us minimize the computational cost and ensure a better accuracy of the results than with a fully RANS model. In the case of megaripples, the validation step was performed with two sets of field data (Sandy Duck'97 and Forsoms'13) but also with the data from Dune2D model which uses only RANS for turbulence. The main findings are: a) the vertical profiles of the velocity are similar throughout the data b) the turbulent kinetic energy, which was underestimated by Dune2D, is in line with the observations c) the concentration of the suspended sediment is simulated with a better accuracy than with Dune2D but this remains lower than the observations.
Self-consistent gyrokinetic modeling of neoclassical and turbulent impurity transport
Estève , D. ,; Sarazin , Y.; Garbet , X.; Grandgirard , V.; Breton , S. ,; Donnel , P. ,; Asahi , Y. ,; Bourdelle , C.; Dif-Pradalier , G; Ehrlacher , C.; Emeriau , C.; Ghendrih , Ph; Gillot , C.; Latu , G.; Passeron , C.
2018-01-01
International audience; Trace impurity transport is studied with the flux-driven gyrokinetic GYSELA code [V. Grandgirard et al., Comp. Phys. Commun. 207, 35 (2016)]. A reduced and linearized multi-species collision operator has been recently implemented, so that both neoclassical and turbulent transport channels can be treated self-consistently on an equal footing. In the Pfirsch-Schlüter regime likely relevant for tungsten, the standard expression of the neoclassical impurity flux is shown t...
Two-point theory of current-driven ion-cyclotron turbulence
International Nuclear Information System (INIS)
Chiueh, T.; Diamond, P.H.
1985-02-01
An analytical theory of current-driven ion-cyclotron turbulenc which treats incoherent phase space density granulations (clumps) is presented. In contrast to previous investigations, attention is focused on the physically relevant regime of weak collective dissipation, where waves and clumps coexist. The threshold current for nonlinear instability is calculated, and is found to deviate from the linear threshold. A necessary condition for the existence of stationary wave-clump turbulence is derived, and shown to be analogous to the test particle model fluctuation-dissipation theorem result. The structure of three dimensional magnetized clumps is characterized. It is proposed that instability is saturated by collective dissipation due to ion-wave scattering. For this wave-clump turbulence regime, it is found that the fluctuation level (e psi/T/sub e/)/sub rms/ less than or equal to 0.1, and that the modification of anomalous resistivity to levels predicted by conventional nonlinear wave theories is moderate. It is also shown that, in marked contrast to the quasilinear prediction, ion heating significantly exceeds electron heating
Physics of transport in tokamaks
Energy Technology Data Exchange (ETDEWEB)
Garbet, X [Assoc. EURATOM-CEA, CEA/DSM/DRFC CEA-Cadarache, 13108 Saint Paul lez Durance (France); Mantica, P [Istituto di Fisica del Plasma EURATOM-ENEA/CNR, via Cozzi 53, 20125 Milan (Italy); Angioni, C [MPI fuer Plasmaphysik, EURATOM-Assoz., D-8046 Garching (Germany)] [and others
2004-12-01
This paper is an overview of recent results relating to turbulent particle and heat transport, and to the triggering of internal transport barriers (ITBs). The dependence of the turbulent particle pinch velocity on plasma parameters has been clarified and compared with experiment. Magnetic shear and collisionality are found to play a central role. Analysis of heat transport has made progress along two directions: dimensionless scaling laws, which are found to agree with the prediction for electrostatic turbulence, and analysis of modulation experiments, which provide a stringent test of transport models. Finally the formation of ITBs has been addressed by analysing electron transport barriers. It is confirmed that negative magnetic shear, combined with the Shafranov shift, is a robust stabilizing mechanism. However, some well established features of internal barriers are not explained by theory.
International Nuclear Information System (INIS)
Horton, W.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates
Poloidal profiles and transport during turbulent heating
International Nuclear Information System (INIS)
Mascheroni, P.L.
1977-01-01
The current penetration stage of a turbulently heated tokamak is modeled. The basic formulae are written in slab geometry since the dominant anomalous transport has a characteristic frequency much larger than the bounce frequency. Thus, the basic framework is provided by the Maxwell and fluid equations, with classical and anomalous transport. Quasi-neutrality is used. It is shown that the anomalous collision frequency dominates the anomalous viscosity and thermal conductivity, and that the convective wave transport can be neglected. For these numerical estimates, the leading term in the quasi-linear series is used. During the current penetration stage the distribution function for the particles will depart from a single Maxwellian type. Hence, the first objective was to numerically compare calculated poloidal magnetic field profiles with measured, published poloidal profiles. The poloidal magnetic field has been calculated using a code which handles the anomalous collision frequency self-consistently. The agreement is good, and it is concluded that the current penetration stage can be satisfactorily described by this model
Ranjan, R.; Menon, S.
2018-04-01
The two-level simulation (TLS) method evolves both the large-and the small-scale fields in a two-scale approach and has shown good predictive capabilities in both isotropic and wall-bounded high Reynolds number (Re) turbulent flows in the past. Sensitivity and ability of this modelling approach to predict fundamental features (such as backscatter, counter-gradient turbulent transport, small-scale vorticity, etc.) seen in high Re turbulent flows is assessed here by using two direct numerical simulation (DNS) datasets corresponding to a forced isotropic turbulence at Taylor's microscale-based Reynolds number Reλ ≈ 433 and a fully developed turbulent flow in a periodic channel at friction Reynolds number Reτ ≈ 1000. It is shown that TLS captures the dynamics of local co-/counter-gradient transport and backscatter at the requisite scales of interest. These observations are further confirmed through a posteriori investigation of the flow in a periodic channel at Reτ = 2000. The results reveal that the TLS method can capture both the large- and the small-scale flow physics in a consistent manner, and at a reduced overall cost when compared to the estimated DNS or wall-resolved LES cost.
Boundary-layer turbulence as a kangaroo process
Dekker, H.; Leeuw, G. de; Maassen van den Brink, A.
1995-01-01
A nonlocal mixing-length theory of turbulence transport by finite size eddies is developed by means of a novel evaluation of the Reynolds stress. The analysis involves the contruct of a sample path space and a stochastic closure hypothesis. The simplifying property of exhange (strong eddies) is
The dynamics of marginality and self-organized criticality as a paradigm for turbulent transport
International Nuclear Information System (INIS)
Newman, D.E.; Carreras, B.A.; Diamond, P.H.; Hahm, T.S.
1995-01-01
A general paradigm, based on the concept of self-organized criticality (SOC), for turbulent transport in magnetically confined plasmas has been recently suggested as an explanation for some of the apparent discrepancies between most theoretical models of turbulent transport and experimental observations of the transport in magnetically confined plasmas. This model describes the dynamics of the transport without relying on the underlying local fluctuation mechanisms. Computations based on a cellular automata realization of such a model have found that noise driven SOC systems can maintain average profiles that are linearly stable (submarginal) and yet are able to sustain active transport dynamics. It is also found that the dominant scales in the transport dynamics in the absence of sheared flow are system scales rather than the underlying local fluctuation scales. The addition of sheared flow into the dynamics leads to a large reduction of the system-scale transport events and a commensurate increase in the fluctuation-scale transport events needed to maintain the constant flux. The dynamics of these models and the potential ramifications for transport studies are discussed
Nonlinear turbulence theory and simulation of Buneman instability
International Nuclear Information System (INIS)
Yoon, P. H.; Umeda, T.
2010-01-01
In the present paper, the weak turbulence theory for reactive instabilities, formulated in a companion paper [P. H. Yoon, Phys. Plasmas 17, 112316 (2010)], is applied to the strong electron-ion two-stream (or Buneman) instability. The self-consistent theory involves quasilinear velocity space diffusion equation for the particles and nonlinear wave kinetic equation that includes quasilinear (or induced emission) term as well as nonlinear wave-particle interaction term (or a term that represents an induced scattering off ions). We have also performed one-dimensional electrostatic Vlasov simulation in order to benchmark the theoretical analysis. Under the assumption of self-similar drifting Gaussian distribution function for the electrons it is shown that the current reduction and the accompanying electron heating as well as electric field turbulence generation can be discussed in a self-consistent manner. Upon comparison with the Vlasov simulation result it is found that quasilinear wave kinetic equation alone is insufficient to account for the final saturation amplitude. Upon including the nonlinear scattering term in the wave kinetic equation, however, we find that a qualitative agreement with the simulation is recovered. From this, we conclude that the combined quasilinear particle diffusion plus induced emission and scattering (off ions) processes adequately account for the nonlinear development of the Buneman instability.
Asymptotic theory for Brownian semi-stationary processes with application to turbulence
DEFF Research Database (Denmark)
Corcuera, José Manuel; Hedevang, Emil; Pakkanen, Mikko S.
2013-01-01
This paper presents some asymptotic results for statistics of Brownian semi-stationary (BSS) processes. More precisely, we consider power variations of BSS processes, which are based on high frequency (possibly higher order) differences of the BSS model. We review the limit theory discussed......, which allow to obtain a valid central limit theorem for the critical region. Finally, we apply our statistical theory to turbulence data....
Instability, Turbulence, and Enhanced Transport in Collisionless Black-Hole Accretion Flows
Kunz, Matthew
Many astrophysical plasmas are so hot and diffuse that the collisional mean free path is larger than the system size. Perhaps the best examples of such systems are lowluminosity accretion flows onto black holes such as Sgr A* at the center of our own Galaxy, or M87 in the Virgo cluster. To date, theoretical models of these accretion flows are based on magnetohydrodynamics (MHD), a collisional fluid theory, sometimes (but rarely) extended with non-MHD features such as anisotropic (i.e. magnetic-field-aligned) viscosity and thermal conduction. While these extensions have been recognized as crucial, they require ad hoc assumptions about the role of microscopic kinetic instabilities (namely, firehose and mirror) in regulating the transport properties. These assumptions strongly affect the outcome of the calculations, and yet they have never been tested using more fundamental (i.e. kinetic) models. This proposal outlines a comprehensive first-principles study of the plasma physics of collisionless accretion flows using both analytic and state-of-the-art numerical models. The latter will utilize a new hybrid-kinetic particle-in-cell code, Pegasus, developed by the PI and Co-I specifically to study this problem. A comprehensive kinetic study of the 3D saturation of the magnetorotational instability in a collisionless plasma will be performed, in order to understand the interplay between turbulence, transport, and Larmor-scale kinetic instabilities such as firehose and mirror. Whether such instabilities alter the macroscopic saturated state, for example by limiting the transport of angular momentum by anisotropic pressure, will be addressed. Using these results, an appropriate "fluid" closure will be developed that can capture the multi-scale effects of plasma kinetics on magnetorotational turbulence, for use by the astrophysics community in building evolutionary models of accretion disks. The PI has already successfully performed the first three-dimensional kinetic
Effect of air turbulence on gas transport in soil; comparison of approaches
Pourbakhtiar, Alireza; Papadikis, Konstantinos; Poulsen, Tjalfe; Bridge, Jonathan; Wilkinson, Stephen
2017-04-01
Greenhouse gases are playing the key role in global warming. Soil is a source of greenhouse gases such as methane (CH4). Radon (Rn) which is a radioactive gas can emit form subsurface into the atmosphere and leads to health concerns in urban areas. Temperature, humidity, air pressure and vegetation of soil can affect gas emissions inside soil (Oertel et al., 2016). It's shown in many cases that wind induced fluctuations is an important factor in transport of gas through soil and other porous media. An example is: landfill gas emissions (Poulsen et al., 2001). We applied an experimental equipment for measuring controlled air turbulence on gas transport in soil in relation to the depth of sample. Two approaches for measurement of effect of wind turbulence on gas transport were applied and compared. Experiments were carried out with diffusion of CO2 and air as tracer gases with average vertical wind speeds of 0 to 0.83 m s-1. In approach A, Six different sample thicknesses from 5 to 30 cm were selected and total of 4 different wind conditions with different speed and fluctuations were applied. In approach B, a sample with constant depth was used. Five oxygen sensors were places inside sample at different depths. Total of 111 experiments were carried out. Gas transport is described by advection-dispersion equation. Gas transport is quantified as a dispersion coefficient. Oxygen breakthrough curves as a function of distance to the surface of the sample exposed to wind were derived numerically with an explicit forward time, central space finite-difference based model to evaluate gas transport. We showed that wind turbulence-induced fluctuations is an important factor in gas transport that can increase gas transport with average of 45 times more than molecular diffusion under zero wind condition. Comparison of two strategies for experiments, indicated that, constant deep samples (Approach B) are more reliable for measurement of gas transport under influence of wind
A turbulent transport network model in MULTIFLUX coupled with TOUGH2
International Nuclear Information System (INIS)
Danko, G.; Bahrami, D.; Birkholzer, J.T.
2011-01-01
A new numerical method is described for the fully iterated, conjugate solution of two discrete submodels, involving (a) a transport network model for heat, moisture, and airflows in a high-permeability, air-filled cavity; and (b) a variably saturated fractured porous medium. The transport network submodel is an integrated-parameter, computational fluid dynamics solver, describing the thermal-hydrologic transport processes in the flow channel system of the cavity with laminar or turbulent flow and convective heat and mass transport, using MULTIFLUX. The porous medium submodel, using TOUGH2, is a solver for the heat and mass transport in the fractured rock mass. The new model solution extends the application fields of TOUGH2 by integrating it with turbulent flow and transport in a discrete flow network system. We present demonstrational results for a nuclear waste repository application at Yucca Mountain with the most realistic model assumptions and input parameters including the geometrical layout of the nuclear spent fuel and waste with variable heat load for the individual containers. The MULTIFLUX and TOUGH2 model elements are fully iterated, applying a programmed reprocessing of the Numerical Transport Code Functionalization model-element in an automated Outside Balance Iteration loop. The natural, convective airflow field and the heat and mass transport in a representative emplacement drift during postclosure are explicitly solved in the new model. The results demonstrate that the direction and magnitude of the air circulation patterns and all transport modes are strongly affected by the heat and moisture transport processes in the surrounding rock, justifying the need for a coupled, fully iterated model solution such as the one presented in the paper.
Turbulent Scalar Transport Model Validation for High Speed Propulsive Flows, Phase I
National Aeronautics and Space Administration — This effort entails the validation of a RANS turbulent scalar transport model (SFM) for high speed propulsive flows, using new experimental data sets and...
Directory of Open Access Journals (Sweden)
G. Forget
2015-10-01
Full Text Available Although estimation of turbulent transport parameters using inverse methods is not new, there is little evaluation of the method in the literature. Here, it is shown that extended observation of the broad-scale hydrography by Argo provides a path to improved estimates of regional turbulent transport rates. Results from a 20-year ocean state estimate produced with the ECCO v4 (Estimating the Circulation and Climate of the Ocean, version 4 non-linear inverse modeling framework provide supporting evidence. Turbulent transport parameter maps are estimated under the constraints of fitting the extensive collection of Argo profiles collected through 2011. The adjusted parameters dramatically reduce misfits to in situ profiles as compared with earlier ECCO solutions. They also yield a clear reduction in the model drift away from observations over multi-century-long simulations, both for assimilated variables (temperature and salinity and independent variables (biogeochemical tracers. Despite the minimal constraints imposed specifically on the estimated parameters, their geography is physically plausible and exhibits close connections with the upper-ocean stratification as observed by Argo. The estimated parameter adjustments furthermore have first-order impacts on upper-ocean stratification and mixed layer depths over 20 years. These results identify the constraint of fitting Argo profiles as an effective observational basis for regional turbulent transport rate inversions. Uncertainties and further improvements of the method are discussed.
Energy Technology Data Exchange (ETDEWEB)
Gammon, M.; Shalchi, A., E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)
2017-10-01
In several astrophysical applications one needs analytical forms of cosmic-ray diffusion parameters. Some examples are studies of diffusive shock acceleration and solar modulation. In the current article we explore perpendicular diffusion based on the unified nonlinear transport theory. While we focused on magnetostatic turbulence in Paper I, we included the effect of dynamical turbulence in Paper II of the series. In the latter paper we assumed that the temporal correlation time does not depend on the wavenumber. More realistic models have been proposed in the past, such as the so-called damping model of dynamical turbulence. In the present paper we derive analytical forms for the perpendicular diffusion coefficient of energetic particles in two-component turbulence for this type of time-dependent turbulence. We present new formulas for the perpendicular diffusion coefficient and we derive a condition for which the magnetostatic result is recovered.
A comprehensive spectral theory of zonal-mode dynamics in trapped electron mode turbulence
International Nuclear Information System (INIS)
Terry, P.W.; Gatto, R.; Baver, D.A.; Fernandez, E.
2005-01-01
A comprehensive, self-consistent theory for spectral dynamics in trapped electron mode (TEM) turbulence offers critical new understanding and insights into zonal-mode physics. This theory shows that 1) zonal mode structure, anisotropy, excitation, and temporal behavior arise at and from the interface of nonlinear advection and linear wave properties; 2) waves induce a marked spectral energy-transfer anisotropy that preferentially drives zonal modes relative to non zonal modes; 3) triplet correlations involving density (as opposed to those involving only flow) mediate the dominant energy transfer at long wavelengths; 4) energy transfer becomes inverse in the presence of wave anisotropy, where otherwise it is forward; 5) zonal-mode excitation is accompanied by excitation of a spectrum of damped eigenmodes, making zonal modes nonlinearly damped; and 6) the combination of anisotropic transfer to zonal modes and their nonlinear damping make this the dominant saturation mechanism for TEM turbulence. This accounts for the reduction of turbulence level by zonal modes, not zonal-flow ExB shearing. (author)
Ballistic propagation of turbulence front in tokamak edge plasmas
International Nuclear Information System (INIS)
Sugita, Satoru; Itoh, Kimitaka; Itoh, Sanae-I; Yagi, Masatoshi; Fuhr, Guillaume; Beyer, Peter; Benkadda, Sadruddin
2012-01-01
The flux-driven nonlinear simulation of resistive ballooning mode turbulence with tokamak edge geometry is performed to study the non-steady component in the edge turbulence. The large-scale and dynamical events in transport are investigated in a situation where the mean flow is suppressed. Two types of dynamics are observed. One is the radial propagation of the pulse of pressure gradient, the other is the appearance/disappearance of radially elongated global structure of turbulent heat flux. The ballistic propagation is observed in the pulse of pressure gradient, which is associated with the front of turbulent heat flux. We focus on this ballistic propagation phenomenon. Both of the bump of pressure gradient and the front of heat flux propagate inward and outward direction. It is confirmed that the strong fluctuation propagates with the pulse front. It is observed that the number of pulses going outward is close to those going inward. This ballistic phenomenon does not contradict to the turbulence spreading theory. Statistical characteristics of the ballistic propagation of pulses are evaluated and compared with scaling laws which is given by the turbulence spreading theory. It is found that they give qualitatively good agreement. (paper)
Renormalization Group Theory of Bolgiano Scaling in Boussinesq Turbulence
Rubinstein, Robert
1994-01-01
Bolgiano scaling in Boussinesq turbulence is analyzed using the Yakhot-Orszag renormalization group. For this purpose, an isotropic model is introduced. Scaling exponents are calculated by forcing the temperature equation so that the temperature variance flux is constant in the inertial range. Universal amplitudes associated with the scaling laws are computed by expanding about a logarithmic theory. Connections between this formalism and the direct interaction approximation are discussed. It is suggested that the Yakhot-Orszag theory yields a lowest order approximate solution of a regularized direct interaction approximation which can be corrected by a simple iterative procedure.
Lectures on neutron transport theory
International Nuclear Information System (INIS)
Benoist, P.
1986-02-01
This note is divided in two parts. In the first one the basis of transport theory, that is, the principal forms of the transport equation and the resulting theorems, are presented. The second part is particularly devoted to the applications of integral transport theory to reactor lattice problems [fr
RANS-based simulation of turbulent wave boundary layer and sheet-flow sediment transport processes
DEFF Research Database (Denmark)
Fuhrman, David R.; Schløer, Signe; Sterner, Johanna
2013-01-01
A numerical model coupling the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equationswith two-equation k−ω turbulence closure is presented and used to simulate a variety of turbulent wave boundary layer processes. The hydrodynamic model is additionally coupled...... with bed and suspended load descriptions, the latter based on an unsteady turbulent-diffusion equation, for simulation of sheet-flow sediment transport processes. In addition to standard features common within such RANS-based approaches, the present model includes: (1) hindered settling velocities at high...
DETAILED FIT OF 'CRITICAL BALANCE' THEORY TO SOLAR WIND TURBULENCE MEASUREMENTS
International Nuclear Information System (INIS)
Forman, Miriam A.; Wicks, Robert T.; Horbury, Timothy S.
2011-01-01
We derive the reduced spectrum of turbulent magnetic fluctuations at different frequencies f which would be observed by a single spacecraft in the solar wind when the magnetic field was at an angle θ B to the solar wind flow, if the wavevector spectrum in the solar wind frame were in anisotropic 'critical balance' (CB) as proposed by Goldreich and Sridhar in 1995 (GS95). The anisotropic power spectrum in the inertial range, P(f, θ B ), is scaled onto one curve with f- 5/3 behavior at θ B near 90 0 and f -2 behavior at small θ B . The transition between the two limiting spectra depends on the form of the GS95 wavevector spectrum and the CB scaling parameter L. Using wavelet analysis of Ulysses magnetic field data in three 30-day periods in the high-latitude solar wind in 1995, we verify that the scaling of power with angle and frequency is qualitatively consistent with GS95 theory. However, the scale length L required to fit the observed P(f, θ B ) to the original CB theory is rather less than the scale predicted by that theory for the solar wind. Part, possibly all, of this discrepancy is removed when the GS95 theory modified for imbalanced turbulence is used.
Fluid simulations of ∇Te-driven turbulence and transport in boundary plasmas
International Nuclear Information System (INIS)
Xu, X.Q.
1992-01-01
It is clear that the edge plasma plays a crucial role in global tokamak confinement. This paper is a report on simulations of a new drift wave type instability driven by the electron temperature gradient in tokamak scrapeoff-layers (SOL). A 2d fluid code has been developed in order to explore the anomalous transport in the boundary plasmas. The simulation consists of a set of fluid equations for the vorticity ∇ perpendicular 2 φ, the electron density n c and the temperature T c in a shearless plasma slab confined by a uniform, straight magnetic field B z with two divertor (or limiter) plates intercepting the magnetic field. The model has two regions separated by a magnetic separatrix: in the edge region inside the separatrix, the model is periodic along the magnetic field while in the SOL region outside the separatrix, the magnetic field is taken to be of finite length with model boundary conditions at diverter plates. The simulation results show that the observed linear instability agrees well with theory, and that a saturated state of turbulence is reached. In saturated turbulence, clear evidence of the expected long-wavelength mode penetration into the edge is seen, an inverse cascade of wave energy is observed. The simulation results also show that amplitudes of potential and the electron temperature fluctuations are somewhat above and the heat flux are somewhat below those of the simplest mixing-length estimates, and furthermore the large-scale radial structures of fluctuation quantities indicate that the cross-field transport is not diffusive. After saturation, the electron density and temperature profiles are flattened. A self-consistent simulation to determine the microturbulent SOL electron temperature profile has been done, the results of which reasonably agree with the experimental measurements
Energy Transfer and Dual Cascade in Kinetic Magnetized Plasma Turbulence
International Nuclear Information System (INIS)
Plunk, G. G.; Tatsuno, T.
2011-01-01
The question of how nonlinear interactions redistribute the energy of fluctuations across available degrees of freedom is of fundamental importance in the study of turbulence and transport in magnetized weakly collisional plasmas, ranging from space settings to fusion devices. In this Letter, we present a theory for the dual cascade found in such plasmas, which predicts a range of new behavior that distinguishes this cascade from that of neutral fluid turbulence. These phenomena are explained in terms of the constrained nature of spectral transfer in nonlinear gyrokinetics. Accompanying this theory are the first observations of these phenomena, obtained via direct numerical simulations using the gyrokinetic code AstroGK. The basic mechanisms that are found provide a framework for understanding the turbulent energy transfer that couples scales both locally and nonlocally.
Energy Transfer and Dual Cascade in Kinetic Magnetized Plasma Turbulence
Plunk, G. G.; Tatsuno, T.
2011-04-01
The question of how nonlinear interactions redistribute the energy of fluctuations across available degrees of freedom is of fundamental importance in the study of turbulence and transport in magnetized weakly collisional plasmas, ranging from space settings to fusion devices. In this Letter, we present a theory for the dual cascade found in such plasmas, which predicts a range of new behavior that distinguishes this cascade from that of neutral fluid turbulence. These phenomena are explained in terms of the constrained nature of spectral transfer in nonlinear gyrokinetics. Accompanying this theory are the first observations of these phenomena, obtained via direct numerical simulations using the gyrokinetic code AstroGK. The basic mechanisms that are found provide a framework for understanding the turbulent energy transfer that couples scales both locally and nonlocally.
Energy Technology Data Exchange (ETDEWEB)
Merci, Bart [Department of Flow, Heat and Combustion Mechanics, Ghent University-UGent, Ghent (Belgium); Roekaerts, Dirk [Department of Multi-Scale Physics, Delft University of Technology, Delft (Netherlands); Naud, Bertrand [CIEMAT, Madrid (Spain); Pope, Stephen B. [Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY (United States)
2006-07-15
Numerical simulation results are presented for turbulent jet diffusion flames with various levels of turbulence-chemistry interaction, stabilized behind a bluff body (Sydney Flames HM1-3). Interaction between turbulence and combustion is modeled with the transported joint-scalar PDF approach. The mass density function transport equation is solved in a Lagrangian manner. A second-moment-closure turbulence model is applied to obtain accurate mean flow and turbulent mixing fields. The behavior of two micromixing models is discussed: the Euclidean minimum spanning tree model and the modified Curl coalescence dispersion model. The impact of the micromixing model choice on the results in physical space is small, although some influence becomes visible as the amount of local extinction increases. Scatter plots and profiles of conditional means and variances of thermochemical quantities, conditioned on the mixture fraction, are discussed both within and downstream of the recirculation region. A distinction is made between local extinction and incomplete combustion, based on the CO species mass fraction. The differences in qualitative behavior between the micromixing models are explained and quantitative comparison to experimental data is made. (author)
Transport and turbulence in TORE SUPRA ohmic discharges
International Nuclear Information System (INIS)
Garbet, X.; Payan, J.; Laviron, C.; Devynck, P.; Saha, S.K.; Capes, H.; Chen, X.P.; Coulon, J.P.; Gil, C.; Harris, G.; Hutter, T.; Pecquet, A.L.
1992-01-01
The mechanisms underlying the energy confinement behaviour in ohmic tokamak discharges are not yet understood. It is well known that the confinement time increases with the average density and saturates above a critical value of the density, but several explanations exist for this saturation. The present study is an analysis of a set of ohmic discharges in Tore Supra with I p =1.6 MA, B=4 T, R=2.35 m and a=0.78 m, where the average density was increased from 0.9 to 4.2 10 19 m -3 . For these plasma parameters, the energy confinement time given by magnetic measurements saturates for e > ≥ 2.5 10 19 m -3 . It is emphasized here that the onset of ionic turbulence is unlikely in Tore Supra. This conclusion relies on a transport analysis and turbulence measurements by CO 2 laser scattering, whose results are presented in this paper
DEFF Research Database (Denmark)
Li, Jinzhao; Qi, Meilan; Fuhrman, David R.
2018-01-01
-normal distribution for uniform channel-open flows. The comparisons of sediment transport rates where turbulent fluctuations in the bed shear stress are, or are not, taken into account show that the sediment transport rates calculated by the mean bed shear stress are under-predicted. Furthermore, a new sediment......This study concerns the flow and associated sediment transport in front of a cylinder in steady currents. The study comprises (i) flow characteristics induced by the turbulent horseshoe vortex (THV), (ii) bed shear stress within the THV region, and (iii) predicted sediment transport rates...
International Nuclear Information System (INIS)
Lin, Z; Rewoldt, G; Ethier, S; Hahm, T S; Lee, W W; Lewandowski, J L V; Nishimura, Y; Wang, W X
2005-01-01
Recent progress in gyrokinetic particle-in-cell simulations of turbulent plasmas using the gyrokinetic toroidal code (GTC) is surveyed. In particular, recent results for electron temperature gradient (ETG) modes and their resulting transport are presented. Also, turbulence spreading, and the effects of the parallel nonlinearity, are described. The GTC code has also been generalized for non-circular plasma cross-section, and initial results are presented. In addition, two distinct methods of generalizing the GTC code to be electromagnetic are described, along with preliminary results. Finally, a related code, GTC-Neo, for calculating neoclassical fluxes, electric fields, and velocities, are described
Stochastic transport models for mixing in variable-density turbulence
Bakosi, J.; Ristorcelli, J. R.
2011-11-01
In variable-density (VD) turbulent mixing, where very-different- density materials coexist, the density fluctuations can be an order of magnitude larger than their mean. Density fluctuations are non-negligible in the inertia terms of the Navier-Stokes equation which has both quadratic and cubic nonlinearities. Very different mixing rates of different materials give rise to large differential accelerations and some fundamentally new physics that is not seen in constant-density turbulence. In VD flows material mixing is active in a sense far stronger than that applied in the Boussinesq approximation of buoyantly-driven flows: the mass fraction fluctuations are coupled to each other and to the fluid momentum. Statistical modeling of VD mixing requires accounting for basic constraints that are not important in the small-density-fluctuation passive-scalar-mixing approximation: the unit-sum of mass fractions, bounded sample space, and the highly skewed nature of the probability densities become essential. We derive a transport equation for the joint probability of mass fractions, equivalent to a system of stochastic differential equations, that is consistent with VD mixing in multi-component turbulence and consistently reduces to passive scalar mixing in constant-density flows.
Applications of Turbulence Models for Transport of Dissolved Pollutants and Particles
DEFF Research Database (Denmark)
Petersen, Ole
The present report concerns itself with numerical models of turbulent transport and mixing, with emphasis on the description of the mixing processes which occur in recipients and tanks. Consequently a part of the report is dedicated to a discussion of flows where differences in density play...
Stochastic catastrophe theory and instabilities in plasma turbulence
International Nuclear Information System (INIS)
Rajkovic, Milan; Skoric, Milos
2009-01-01
Full text: A Langevin equation (LE) describing evolution of turbulence amplitude in plasma is analyzed from the aspect of stochastic catastrophe theory (SCT) so that turbulent plasma is considered as a stochastic gradient system. According to SCT the dynamics of the system is completely determined by the stochastic potential function and the maximum likelihood estimates of stable and unstable equilibria are associated with the modes and anti-modes, respectively, of the system's stationary probability density function. First order phase transitions occur at degenerate equilibrium points and the potential function at these points may be represented in a generic way. Since the diffusion function of plasma LE is not constant the probability density function (pdf) is not a reliable estimator of the number of stable states. We show that the generalized pdf represented as the product of the stationary pdf and the diffusion function is a reliable estimator of the stable states and that it can be evaluated from the zero mean crossing analysis of plasma turbulence signal. Stochastic bifurcations, and particularly the sudden (catastrophic) ones, are recognized from the pdf's obtained by the zero crossing analysis and we illustrate the applications of SCT in plasma turbulence on data obtained from the MAST (Mega Ampere Spherical Tokamak) for low (L), high (H) and unstable dithering (L/H) confinement regimes. The relationship of the transformation invariant zero-crossing function and SCT is shown to provide important information about the nature of edge localized modes (ELMs) and L-H transition. Finally we show that ELMs occur as a result of catastrophic (hard) bifurcations ruling out the self-organized criticality scenario for their origin. (author)
Fluid simulations of ∇Te-driven turbulence and transport in boundary plasmas
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.
1993-01-01
This paper is a report on simulations of a new drift wave type instability driven by the electron temperature gradient in tokamak scrapeoff-layers (SOL). A 2D(x,y) fluid code has been developed in order to explore the anomalous transport in the boundary plasmas. The simulation consists of a set of fluid equations (in the electrostatic limit) for the vorticity ∇ perpendicular 2 φ, the electron density n e and the temperature T e in a shearless plasma slab confined by a uniform, straight magnetic field B z with two diverter (or limiter) plates intercepting the magnetic field. The model has two regions separated by a magnetic separatrix: in the edge region inside the separatrix, the model is periodic along the magnetic field while in the SOL region outside the separatrix, the magnetic field is taken to be of finite length with model (logical sheath) boundary conditions at diverter (or limiter) plates. The simulation results show that the observed linear instability agrees well with theory, and that a saturated state of turbulence is reached. In saturated turbulence, clear evidence of the expected long-wavelength mode penetration into the edge is seen, an inverse cascade of wave energy (toward both long wavelengths and low frequencies) is observed. The simulation results also show that amplitudes of potential and the electron temperature fluctuations are somewhat above and the heat flux are somewhat below those of the simplest mixing-length estimates. The results from the self-consistent simulations to determine the microturbulent SOL electron temperature profile agree reasonably with the experimental measurements. The effects on the mode of neutral gas collisions at the divertor sheath and comparisons with the ionization driven turbulence are discussed
International Nuclear Information System (INIS)
Kaw, P.K.; Singh, R.; Weiland, J.G.
2001-01-01
Analytical investigations of several linear and nonlinear features of ETG turbulence are reported. The linear theory includes effects such as finite beta induced electromagnetic shielding, coupling to electron magnetohydrodynamic modes like whistlers etc. It is argued that nonlinearly, turbulence and transport are dominated by radially extended modes called 'streamers'. A nonlinear mechanism generating streamers based on a modulational instability theory of the ETG turbulence is also presented. The saturation levels of the streamers using a Kelvin Helmholtz secondary instability mechanism are calculated and levels of the electron thermal transport due to streamers are estimated. (author)
Energy Technology Data Exchange (ETDEWEB)
Futtersack, R., E-mail: romain.futtersack@cea.fr [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Universite Paul Sabatier Toulouse, LAPLACE, 118 Route de Narbonne, F-31062 Toulouse Cedex 9 (France); Tamain, P. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Hagelaar, G. [Universite Paul Sabatier Toulouse, LAPLACE, 118 Route de Narbonne, F-31062 Toulouse Cedex 9 (France); Ghendrih, Ph.; Simonin, A. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
2013-07-15
We investigate the impact of both parallel and transverse boundary conditions on the current and charge transport in open field line systems using the TOKAM2D code, which solves a minimal model for interchange turbulence. Various limit test cases are discussed and analyzed. In the parallel direction, the sheath conductivity is found to play an essential role in the stabilization of large-scale potential structures, leading to the formation of transport channel or transport barrier respectively for an insulating end wall or a wall with an enhanced sheath conductivity. On another hand, the addition of transverse boundary conditions intrinsically changes the transport characteristics, influencing both radial profiles and probability density functions. It underlines that in some cases a detailed description of the plasma-wall interaction process is required to get a proper description of the current loop pattern that determines electrostatic turbulent transport.
Edge transport and fluctuation induced turbulence characteristics in early SST-1 plasma
Energy Technology Data Exchange (ETDEWEB)
Kakati, B., E-mail: bharat.kakati@ipr.res.in; Pradhan, S., E-mail: pradhan@ipr.res.in; Dhongde, J.; Semwal, P.; Yohan, K.; Banaudha, M.
2017-02-15
Highlights: • Anomalous particle transport during the high MHD activity at SST-1. • Electrostatic turbulence is modulated by MHD activity at SST-1 tokamak. • Edge floating potential fluctuations shows poloidal long-range cross correlation. - Abstract: Plasma edge transport characteristics are known to be heavily influenced by the edge fluctuation induced turbulences. These characteristics play a critical role towards the confinement of plasma column in a Tokamak. The edge magnetic fluctuations and its subsequent effect on electrostatic fluctuations have been experimentally investigated for the first time at the edge of the SST-1 plasma column. This paper reports the correlations that exist and is experimentally been observed between the edge densities and floating potential fluctuations with the magnetic fluctuations. The edge density and floating potential fluctuations have been measured with the help of poloidally separated Langmuir probes, whereas the magnetic fluctuations have been measured with poloidally spaced Mirnov coils. Increase in magnetic fluctuations associated with enhanced MHD activities has been found to increase the floating potential and ion saturation current. These observations indicate electrostatic turbulence getting influenced with the MHD activities and reveal the edge anomalous particle transport during SST-1 tokamak discharge. Large-scale coherent structures have been observed in the floating potential fluctuations, indicating long-distance cross correlation in the poloidal directions. From bispectral analysis, a strong nonlinear coupling among the floating potential fluctuations is observed in the low-frequency range about 0–15 kHz.
International Nuclear Information System (INIS)
Misguich, J.H.
1978-09-01
The physical meaning of perturbed trajectories in turbulent fields is analysed. Special care is devoted to the asymptotic description of average trajectories for long time intervals, as occuring in many recent plasma turbulence theories. Equivalence is proved between asymptotic average trajectories described as well (i) by the propagators V(t,t-tau) for retrodiction and Wsub(J)(t,t+tau) for prediction, and (ii) by the long time secular behavior of the solution of the equations of motion. This confirms the equivalence between perturbed orbit theories and renormalized theories, including non-Markovian contributions
Directory of Open Access Journals (Sweden)
Florian Ries
2017-08-01
Full Text Available In the present paper, thermal transport and entropy production mechanisms in a turbulent round jet of compressed nitrogen at supercritical thermodynamic conditions are investigated using a direct numerical simulation. First, thermal transport and its contribution to the mixture formation along with the anisotropy of heat fluxes and temperature scales are examined. Secondly, the entropy production rates during thermofluid processes evolving in the supercritical flow are investigated in order to identify the causes of irreversibilities and to display advantageous locations of handling along with the process regimes favorable to mixing. Thereby, it turned out that (1 the jet disintegration process consists of four main stages under supercritical conditions (potential core, separation, pseudo-boiling, turbulent mixing, (2 causes of irreversibilities are primarily due to heat transport and thermodynamic effects rather than turbulence dynamics and (3 heat fluxes and temperature scales appear anisotropic even at the smallest scales, which implies that anisotropic thermal diffusivity models might be appropriate in the context of both Reynolds-averaged Navier–Stokes (RANS and large eddy simulation (LES approaches while numerically modeling supercritical fluid flows.
Directory of Open Access Journals (Sweden)
Cheng-Hung Chen
2014-12-01
Full Text Available This study aimed to engage in an empirical investigation on school leaders’ comprehensive perspectives of adopting both turbulence theory and multi-frame leadership model on change and leadership within school settings. Applying the qualitative case study approach, workshops and focus group interviews were held involving five directors and three principals from different elementary schools, who graduated from the master program in school administration where the researcher serves, to discuss and reflect upon the cross match of two theories as they may be applied to change and leadership. Accordingly, both theories’ practical application encompassed three advantages: “both theories interactively match with each other,” “both theories correspond to the authentic context of school leadership and change,” and “the matching matrix of both theories could serve as school leaders’ decision check list;” meanwhile, there were two issues that needed to be noticed and examined, including “the differentiation, definition and measurement of turbulence levels,” and “the subjective identification of turbulence levels.” This study concluded by proposing practical implications of applying theory into practice of school leadership and change.
Ion and impurity transport in turbulent, anisotropic magnetic fields
International Nuclear Information System (INIS)
Negrea, M; Petrisor, I; Isliker, H; Vogiannou, A; Vlahos, L; Weyssow, B
2011-01-01
We investigate ion and impurity transport in turbulent, possibly anisotropic, magnetic fields. The turbulent magnetic field is modeled as a correlated stochastic field, with Gaussian distribution function and prescribed spatial auto-correlation function, superimposed onto a strong background field. The (running) diffusion coefficients of ions are determined in the three-dimensional environment, using two alternative methods, the semi-analytical decorrelation trajectory (DCT) method, and test-particle simulations. In a first step, the results of the test-particle simulations are compared with and used to validate the results obtained from the DCT method. For this purpose, a drift approximation was made in slab geometry, and relatively good qualitative agreement between the DCT method and the test-particle simulations was found. In a second step, the ion species He, Be, Ne and W, all assumed to be fully ionized, are considered under ITER-like conditions, and the scaling of their diffusivities is determined with respect to varying levels of turbulence (varying Kubo number), varying degrees of anisotropy of the turbulent structures and atomic number. In a third step, the test-particle simulations are repeated without drift approximation, directly using the Lorentz force, first in slab geometry, in order to assess the finite Larmor radius effects, and second in toroidal geometry, to account for the geometric effects. It is found that both effects are important, most prominently the effects due to toroidal geometry and the diffusivities are overestimated in slab geometry by an order of magnitude.
Ion and impurity transport in turbulent, anisotropic magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Negrea, M; Petrisor, I [Department of Physics, Association Euratom-MEdC, Romania, University of Craiova, A.I. Cuza str. 13, Craiova (Romania); Isliker, H; Vogiannou, A; Vlahos, L [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Thessaloniki, Association Euratom-Hellenic Republic, 541 24 Thessaloniki (Greece); Weyssow, B [Physique Statistique-Plasmas, Association Euratom-Etat Belge, Universite Libre de Bruxelles, Campus Plaine, Bd. du Triomphe, 1050 Bruxelles (Belgium)
2011-08-15
We investigate ion and impurity transport in turbulent, possibly anisotropic, magnetic fields. The turbulent magnetic field is modeled as a correlated stochastic field, with Gaussian distribution function and prescribed spatial auto-correlation function, superimposed onto a strong background field. The (running) diffusion coefficients of ions are determined in the three-dimensional environment, using two alternative methods, the semi-analytical decorrelation trajectory (DCT) method, and test-particle simulations. In a first step, the results of the test-particle simulations are compared with and used to validate the results obtained from the DCT method. For this purpose, a drift approximation was made in slab geometry, and relatively good qualitative agreement between the DCT method and the test-particle simulations was found. In a second step, the ion species He, Be, Ne and W, all assumed to be fully ionized, are considered under ITER-like conditions, and the scaling of their diffusivities is determined with respect to varying levels of turbulence (varying Kubo number), varying degrees of anisotropy of the turbulent structures and atomic number. In a third step, the test-particle simulations are repeated without drift approximation, directly using the Lorentz force, first in slab geometry, in order to assess the finite Larmor radius effects, and second in toroidal geometry, to account for the geometric effects. It is found that both effects are important, most prominently the effects due to toroidal geometry and the diffusivities are overestimated in slab geometry by an order of magnitude.
Ion and impurity transport in turbulent, anisotropic magnetic fields
Negrea, M.; Petrisor, I.; Isliker, H.; Vogiannou, A.; Vlahos, L.; Weyssow, B.
2011-08-01
We investigate ion and impurity transport in turbulent, possibly anisotropic, magnetic fields. The turbulent magnetic field is modeled as a correlated stochastic field, with Gaussian distribution function and prescribed spatial auto-correlation function, superimposed onto a strong background field. The (running) diffusion coefficients of ions are determined in the three-dimensional environment, using two alternative methods, the semi-analytical decorrelation trajectory (DCT) method, and test-particle simulations. In a first step, the results of the test-particle simulations are compared with and used to validate the results obtained from the DCT method. For this purpose, a drift approximation was made in slab geometry, and relatively good qualitative agreement between the DCT method and the test-particle simulations was found. In a second step, the ion species He, Be, Ne and W, all assumed to be fully ionized, are considered under ITER-like conditions, and the scaling of their diffusivities is determined with respect to varying levels of turbulence (varying Kubo number), varying degrees of anisotropy of the turbulent structures and atomic number. In a third step, the test-particle simulations are repeated without drift approximation, directly using the Lorentz force, first in slab geometry, in order to assess the finite Larmor radius effects, and second in toroidal geometry, to account for the geometric effects. It is found that both effects are important, most prominently the effects due to toroidal geometry and the diffusivities are overestimated in slab geometry by an order of magnitude.
Verification of Gyrokinetic Particle of Turbulent Simulation of Device Size Scaling Transport
Institute of Scientific and Technical Information of China (English)
LIN Zhihong; S. ETHIER; T. S. HAHM; W. M. TANG
2012-01-01
Verification and historical perspective are presented on the gyrokinetic particle simulations that discovered the device size scaling of turbulent transport and indentified the geometry model as the source of the long-standing disagreement between gyrokinetic particle and continuum simulations.
Nonlocal stochastic mixing-length theory and the velocity profile in the turbulent boundary layer
Dekker, H.; Leeuw, G. de; Maassen van den Brink, A.
1995-01-01
Turbulence mixing by finite size eddies will be treated by means of a novel formulation of nonlocal K-theory, involving sample paths and a stochastic closure hypothesis, which implies a well defined recipe for the calculation of sampling and transition rates. The connection with the general theory
Theory of Vortex Crystal Formation in Two-Dimensional Turbulence
Jin, D. Z.
1999-11-01
The free relaxation of inviscid, incompressible 2D turbulence is often dominated by strong vortices (coherent patches of intense vorticity) that move chaotically and merge. However, recent experiments(K.S. Fine et al., Phys. Rev. Lett. 75), 3277 (1995). with pure electron plasmas have found that freely relaxing turbulent flows with a single sign of vorticity can spontaneously form ``vortex crystals'' -- symmetric, stable arrays of strong vortices that are immersed in a low vorticity background. In this talk we discuss how these complex equilibria can form from 2D turbulence. First, we formulate a statistical theory of the vortex crystals. We show that vortex crystals are well described as ``regional'' maximum fluid entropy (RMFE) states, which are equilibrium states reached through ergodic mixing of the background by the strong vortices.(D.Z. Jin and D.H.E. Dubin, Phys. Rev. Lett. 80), 4434 (1998). Given the dynamically conserved quantities as well as the number and the vorticity distributions of the strong vortices, the theory predicts the positions of the strong vortices and the coarse-grained vorticity distribution of the background. These predictions agree well with the observed vortex crystals. Second, we examine the formation process of the vortex crystals in more detail. In the RMFE theory, the vortex crystal equilibrium can only be predicted if the number Nc of the strong vortices in the final state is given. Here, we estimate Nc from the characteristics of the early turbulent flow. The estimate relies on the idea that vortex crystals form because the chaotic motions of the strong vortices are ``cooled'' due to mixing of the background by the vortices. When the rate of cooling is faster than the rate of pairwise mergers, the vortices fall into a crystal pattern before they can merge. We estimate the merger rate from the observed power law decay of the number of strong vortices in the early stages of the flow, and the cooling rate from the rate of mixing of
Statistical analyses of local transport coefficients in Ohmic ASDEX discharges
International Nuclear Information System (INIS)
Simmet, E.; Stroth, U.; Wagner, F.; Fahrbach, H.U.; Herrmann, W.; Kardaun, O.J.W.F.; Mayer, H.M.
1991-01-01
Tokamak energy transport is still an unsolved problem. Many theoretical models have been developed, which try to explain the anomalous high energy-transport coefficients. Up to now these models have been applied to global plasma parameters. A comparison of transport coefficients with global confinement time is only conclusive if the transport is dominated by one process across the plasma diameter. This, however, is not the case in most Ohmic confinement regimes, where at least three different transport mechanisms play an important role. Sawtooth activity leads to an increase in energy transport in the plasma centre. In the intermediate region turbulent transport is expected. Candidates here are drift waves and resistive fluid turbulences. At the edge, ballooning modes or rippling modes could dominate the transport. For the intermediate region, one can deduce theoretical scaling laws for τ E from turbulent theories. Predicted scalings reproduce the experimentally found density dependence of τ E in the linear Ohmic confinement regime (LOC) and the saturated regime (SOC), but they do not show the correct dependence on the isotope mass. The relevance of these transport theories can only be tested in comparing them to experimental local transport coefficients. To this purpose we have performed transport calculations on more than a hundred Ohmic ASDEX discharges. By Principal Component Analysis we determine the dimensionless components which dominate the transport coefficients and we compare the results to the predictions of various theories. (author) 6 refs., 2 figs., 1 tab
MHD turbulent dynamo in astrophysics: Theory and numerical simulation
Chou, Hongsong
2001-10-01
This thesis treats the physics of dynamo effects through theoretical modeling of magnetohydrodynamic (MHD) systems and direct numerical simulations of MHD turbulence. After a brief introduction to astrophysical dynamo research in Chapter 1, the following issues in developing dynamic models of dynamo theory are addressed: In Chapter 2, nonlinearity that arises from the back reaction of magnetic field on velocity field is considered in a new model for the dynamo α-effect. The dependence of α-coefficient on magnetic Reynolds number, kinetic Reynolds number, magnetic Prandtl number and statistical properties of MHD turbulence is studied. In Chapter 3, the time-dependence of magnetic helicity dynamics and its influence on dynamo effects are studied with a theoretical model and 3D direct numerical simulations. The applicability of and the connection between different dynamo models are also discussed. In Chapter 4, processes of magnetic field amplification by turbulence are numerically simulated with a 3D Fourier spectral method. The initial seed magnetic field can be a large-scale field, a small-scale magnetic impulse, and a combination of these two. Other issues, such as dynamo processes due to helical Alfvénic waves and the implication and validity of the Zeldovich relation, are also addressed in Appendix B and Chapters 4 & 5, respectively. Main conclusions and future work are presented in Chapter 5. Applications of these studies are intended for astrophysical magnetic field generation through turbulent dynamo processes, especially when nonlinearity plays central role. In studying the physics of MHD turbulent dynamo processes, the following tools are developed: (1)A double Fourier transform in both space and time for the linearized MHD equations (Chapter 2 and Appendices A & B). (2)A Fourier spectral numerical method for direct simulation of 3D incompressible MHD equations (Appendix C).
Energy Technology Data Exchange (ETDEWEB)
Lefeuvre, N; Djenidi, L [University of Newcastle, NSW Australia (Australia); Tardu, S, E-mail: nathan.lefeuvre@uon.edu.au [Laboratoire des Ecoulements Geophysiques et Industriels (LEGI), Grenoble (France)
2011-12-22
A numerical simulation is undertaken to investigate the transport of momentum and a passive scalar in a localised turbulence in a channel with a contraction. The simulation is carried out using a hybrid method which combines the lattice Boltzmann method (LBM, for the velocity field) and the energy equation (for the temperature field). The localised turbulence is generated through pulsed jets issued in the Poiseuille flow developing in the channel at a Reynolds number of about 1000. The aim of the study is twofold : i) determine effect of the contraction on the localised turbulence, and ii) study how the passive scalar behaves in such contracted localised turbulence. The contraction increase the averaged vorticity in the channel flow, which is accompanied by an increase in the averaged kinetic energy. The contraction also tends to reduce the Reynolds stresses. These results are similar those obtained in turbulent pipe flow with an axisymmetric contraction and in a turbulent boundary layer subjected to a favourable pressure gradient. However, it is found that the heat transport in the normal to the wall direction is more dramatically affected (reduced) than that in the direction of the flow.
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Transition in multiple-scale-lengths turbulence in plasmas
Energy Technology Data Exchange (ETDEWEB)
Itoh, S.-I.; Yagi, M.; Kawasaki, M.; Kitazawa, A. [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Itoh, K. [National Inst. for Fusion Science, Toki, Gifu (Japan)
2002-02-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Statistical nonlinear interactions between semi-micro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. The thermal fluctuation of the scale length of {lambda}{sub D} is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power-laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three-classes of modes is also developed. A new catastrophe of turbulent sates is obtained. (author)
Transition in multiple-scale-lengths turbulence in plasmas
International Nuclear Information System (INIS)
Itoh, S.-I.; Yagi, M.; Kawasaki, M.; Kitazawa, A.
2002-02-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Statistical nonlinear interactions between semi-micro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. The thermal fluctuation of the scale length of λ D is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power-laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three-classes of modes is also developed. A new catastrophe of turbulent sates is obtained. (author)
Classical dissipation and transport in plasmas
International Nuclear Information System (INIS)
Hinton, F.L.
1989-01-01
This paper reviews the subject of classical and neoclassical transport. The paper is organized into four main parts, dealing with plasma kinetic theory, classical transport, neoclassical transport, and the present state of the subject. The results of the neoclassical theory of transport are still being used to give the lower limit on the transport rates in tokamaks, which would apply if instabilities and turbulence could be suppressed. So far, only the ion thermal conductivity and the current density have been found experimentally to agree with this theory, and only under special conditions. The electron thermal conductivity has been found experimentally to be much larger than the neoclassical prediction
Spectral Cascade-Transport Turbulence Model Development for Two-Phase Flows
Brown, Cameron Scott
Turbulence modeling remains a challenging problem in nuclear reactor applications, particularly for the turbulent multiphase flow conditions in nuclear reactor subchannels. Understanding the fundamental physics of turbulent multiphase flows is crucial for the improvement and further development of multiphase flow models used in reactor operation and safety calculations. Reactor calculations with Reynolds-averaged Navier-Stokes (RANS) approach continue to become viable tools for reactor analysis. The on-going increase in available computational resources allows for turbulence models that are more complex than the traditional two-equation models to become practical choices for nuclear reactor computational fluid dynamic (CFD) and multiphase computational fluid dynamic (M-CFD) simulations. Similarly, increased computational capabilities continue to allow for higher Reynolds numbers and more complex geometries to be evaluated using direct numerical simulation (DNS), thus providing more validation and verification data for turbulence model development. Spectral turbulence models are a promising approach to M-CFD simulations. These models resolve mean flow parameters as well as the turbulent kinetic energy spectrum, reproducing more physical details of the turbulence than traditional two-equation type models. Previously, work performed by other researchers on a spectral cascade-transport model has shown that the model behaves well for single and bubbly twophase decay of isotropic turbulence, single and two-phase uniform shear flow, and single-phase flow in a channel without resolving the near-wall boundary layer for relatively low Reynolds number. Spectral models are great candidates for multiphase RANS modeling since bubble source terms can be modeled as contributions to specific turbulence scales. This work focuses on the improvement and further development of the spectral cascadetransport model (SCTM) to become a three-dimensional (3D) turbulence model for use in M
International Nuclear Information System (INIS)
Kim, Eun-jin; Diamond, P.H.; Malkov, M.
2003-01-01
Two examples of non-perturbative models of intermittency in drift-wave (DW) turbulence are presented. The first is a calculation of the probability distribution function (PDF) of ion heat flux due to structures in ion temperature gradient turbulence. The instanton calculus predicts the PDF to be a stretched exponential. The second is a derivation of a bi-variate Burgers equation for the evolution of the DW population density in the presence of radially extended streamer flows. The PDF of fluctuation intensity avalanches is determined. The relation of this to turbulence spreading, observed in simulations, is discussed. (author)
Weak turbulence theory for the Gross-Pitaevskii equation
International Nuclear Information System (INIS)
Nazarenko, S.; West, R.; Lvov, Y.
2001-01-01
The goal of this paper is to use the ideas developed for the NLSE to derive a weak turbulence theory for a large set of random waves described by the Gross-Pitaevskii equation. An interesting picture emerges even from a naive application of the results already obtained for the NLSE case. Imagine an arbitrary initial excitation; a superposition of modes with energies somewhere in the middle of the potential well. Because of the nonlinear interaction (''collisions'') there is a redistribution of energy E and particles N among the modes. (orig.)
Suppression of turbulent transport in NSTX internal transport barriers
Yuh, Howard
2008-11-01
Electron transport will be important for ITER where fusion alphas and high-energy beam ions will primarily heat electrons. In the NSTX, internal transport barriers (ITBs) are observed in reversed (negative) shear discharges where diffusivities for electron and ion thermal channels and momentum are reduced. While neutral beam heating can produce ITBs in both electron and ion channels, High Harmonic Fast Wave (HHFW) heating can produce electron thermal ITBs under reversed magnetic shear conditions without momentum input. Interestingly, the location of the electron ITB does not necessarily match that of the ion ITB: the electron ITB correlates well with the minimum in the magnetic shear determined by Motional Stark Effect (MSE) [1] constrained equilibria, whereas the ion ITB better correlates with the maximum ExB shearing rate. Measured electron temperature gradients can exceed critical linear thresholds for ETG instability calculated by linear gyrokinetic codes in the ITB confinement region. The high-k microwave scattering diagnostic [2] shows reduced local density fluctuations at wavenumbers characteristic of electron turbulence for discharges with strongly negative magnetic shear versus weakly negative or positive magnetic shear. Fluctuation reductions are found to be spatially and temporally correlated with the local magnetic shear. These results are consistent with non-linear gyrokinetic simulations predictions showing the reduction of electron transport in negative magnetic shear conditions despite being linearly unstable [3]. Electron transport improvement via negative magnetic shear rather than ExB shear highlights the importance of current profile control in ITER and future devices. [1] F.M. Levinton, H. Yuh et al., PoP 14, 056119 [2] D.R. Smith, E. Mazzucato et al., RSI 75, 3840 [3] Jenko, F. and Dorland, W., PRL 89 225001
Lee, Dorothy B; Faget, Maxime A
1956-01-01
A modified method of Van Driest's flat-plate theory for turbulent boundary layer has been found to simplify the calculation of local skin-friction coefficients which, in turn, have made it possible to obtain through Reynolds analogy theoretical turbulent heat-transfer coefficients in the form of Stanton number. A general formula is given and charts are presented from which the modified method can be solved for Mach numbers 1.0 to 12.0, temperature ratios 0.2 to 6.0, and Reynolds numbers 0.2 times 10 to the 6th power to 200 times 10 to the 6th power.
International Nuclear Information System (INIS)
Jayaraju, S.T.; Sathiah, P.; Roelofs, F.; Dehbi, A.
2015-01-01
Highlights: • Near-wall modeling uncertainties in the RANS particle transport and deposition are addressed in a turbulent duct flow. • Discrete Random Walk (DRW) model and Continuous Random Walk (CRW) model performances are tested. • Several near-wall anisotropic model accuracy is assessed. • Numerous sensitivity studies are performed to recommend a robust, well-validated near-wall model for accurate particle deposition predictions. - Abstract: Dust accumulation in the primary system of a (V)HTR is identified as one of the foremost concerns during a potential accident. Several numerical efforts have focused on the use of RANS methodology to better understand the complex phenomena of fluid–particle interaction at various flow conditions. In the present work, several uncertainties relating to the near-wall modeling of particle transport and deposition are addressed for the RANS approach. The validation analyses are performed in a fully developed turbulent duct flow setup. A standard k − ε turbulence model with enhanced wall treatment is used for modeling the turbulence. For the Lagrangian phase, the performance of a continuous random walk (CRW) model and a discrete random walk (DRW) model for the particle transport and deposition are assessed. For wall bounded flows, it is generally seen that accounting for near wall anisotropy is important to accurately predict particle deposition. The various near-wall correlations available in the literature are either derived from the DNS data or from the experimental data. A thorough investigation into various near-wall correlations and their applicability for accurate particle deposition predictions are assessed. The main outcome of the present work is a well validated turbulence model with optimal near-wall modeling which provides realistic particle deposition predictions
On the dynamics of turbulent transport near marginal stability
International Nuclear Information System (INIS)
Diamond, P.H.; Hahm, T.S.
1995-03-01
A general methodology for describing the dynamics of transport near marginal stability is formulated. Marginal stability is a special case of the more general phenomenon of self-organized criticality. Simple, one field models of the dynamics of tokamak plasma self-organized criticality have been constructed, and include relevant features such as sheared mean flow and transport bifurcations. In such models, slow mode (i.e. large scale, low frequency transport events) correlation times determine the behavior of transport dynamics near marginal stability. To illustrate this, impulse response scaling exponents (z) and turbulent diffusivities (D) have been calculated for the minimal (Burgers) and sheared flow models. For the minimal model, z = 1 (indicating ballastic propagation) and D ∼(S 0 2 ) 1/3 , where S 0 2 is the noise strength. With an identically structured noise spectrum and flow with shearing rate exceeding the ambient decorrelation rate for the largest scale transport events, diffusion is recovered with z = 2 and D ∼ (S 0 2 ) 3/5 . This indicates a qualitative change in the dynamics, as well as a reduction in losses. These results are consistent with recent findings from ρ scaling scans. Several tokamak transport experiments are suggested
Stochastic field-line wandering in magnetic turbulence with shear. I. Quasi-linear theory
Energy Technology Data Exchange (ETDEWEB)
Shalchi, A. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Negrea, M.; Petrisor, I. [Department of Physics, University of Craiova, Association Euratom-MEdC, 13A.I.Cuza Str, 200585 Craiova (Romania)
2016-07-15
We investigate the random walk of magnetic field lines in magnetic turbulence with shear. In the first part of the series, we develop a quasi-linear theory in order to compute the diffusion coefficient of magnetic field lines. We derive general formulas for the diffusion coefficients in the different directions of space. We like to emphasize that we expect that quasi-linear theory is only valid if the so-called Kubo number is small. We consider two turbulence models as examples, namely, a noisy slab model as well as a Gaussian decorrelation model. For both models we compute the field line diffusion coefficients and we show how they depend on the aforementioned Kubo number as well as a shear parameter. It is demonstrated that the shear effect reduces all field line diffusion coefficients.
Stochastic field-line wandering in magnetic turbulence with shear. I. Quasi-linear theory
International Nuclear Information System (INIS)
Shalchi, A.; Negrea, M.; Petrisor, I.
2016-01-01
We investigate the random walk of magnetic field lines in magnetic turbulence with shear. In the first part of the series, we develop a quasi-linear theory in order to compute the diffusion coefficient of magnetic field lines. We derive general formulas for the diffusion coefficients in the different directions of space. We like to emphasize that we expect that quasi-linear theory is only valid if the so-called Kubo number is small. We consider two turbulence models as examples, namely, a noisy slab model as well as a Gaussian decorrelation model. For both models we compute the field line diffusion coefficients and we show how they depend on the aforementioned Kubo number as well as a shear parameter. It is demonstrated that the shear effect reduces all field line diffusion coefficients.
Monte Carlo simulation of the turbulent transport of airborne contaminants
International Nuclear Information System (INIS)
Watson, C.W.; Barr, S.
1975-09-01
A generalized, three-dimensional Monte Carlo model and computer code (SPOOR) are described for simulating atmospheric transport and dispersal of small pollutant clouds. A cloud is represented by a large number of particles that we track by statistically sampling simulated wind and turbulence fields. These fields are based on generalized wind data for large-scale flow and turbulent energy spectra for the micro- and mesoscales. The large-scale field can be input from a climatological data base, or by means of real-time analyses, or from a separate, subjectively defined data base. We introduce the micro- and mesoscale wind fluctuations through a power spectral density, to include effects from a broad spectrum of turbulent-energy scales. The role of turbulence is simulated in both meander and dispersal. Complex flow fields and time-dependent diffusion rates are accounted for naturally, and shear effects are simulated automatically in the ensemble of particle trajectories. An important adjunct has been the development of computer-graphics displays. These include two- and three-dimensional (perspective) snapshots and color motion pictures of particle ensembles, plus running displays of differential and integral cloud characteristics. The model's versatility makes it a valuable atmospheric research tool that we can adapt easily into broader, multicomponent systems-analysis codes. Removal, transformation, dry or wet deposition, and resuspension of contaminant particles can be readily included
Theories of transporting processes of Cu in Jiaozhou Bay
Yang, Dongfang; Su, Chunhua; Zhu, Sixi; Wu, Yunjie; Zhou, Wei
2018-02-01
Many marine bays have been polluted along with the rapid development of industry and population size, and understanding the transporting progresses of pollutants is essential to pollution control. In order to better understanding the transporting progresses of pollutants in marine, this paper carried on a comprehensive research of the theories of transporting processes of Cu in Jiaozhou Bay. Results showed that the transporting processes of Cu in this bay could be summarized into seven key theories including homogeneous theory, environmental dynamic theory, horizontal loss theory, source to waters transporting theory, sedimentation transporting theory, migration trend theory and vertical transporting theory, respectively. These theories helpful to better understand the migration progress of pollutants in marine bay.
Energy Technology Data Exchange (ETDEWEB)
Leconte, M.
2008-11-15
The H confinement regime is set when the heating power reaches a threshold value P{sub c} and is linked to the formation of a transport barrier in the edge region of the plasma. Such a barrier is characterized by a high pressure gradient and is submitted to ELM (edge localized mode) instabilities. ELM instabilities trigger violent quasi-periodical ejections of matter and heat that induce quasi-periodical relaxations of the transport barrier called relaxation oscillations. In this work we studied the interaction between sheared flows and turbulence in fusion plasmas. In particular, we studied the complex dynamics of a transport barrier and we show through a simulation that resonant magnetic perturbations could control relaxation oscillations without a significant loss of confinement
Homogeneous turbulence dynamics
Sagaut, Pierre
2018-01-01
This book provides state-of-the-art results and theories in homogeneous turbulence, including anisotropy and compressibility effects with extension to quantum turbulence, magneto-hydodynamic turbulence and turbulence in non-newtonian fluids. Each chapter is devoted to a given type of interaction (strain, rotation, shear, etc.), and presents and compares experimental data, numerical results, analysis of the Reynolds stress budget equations and advanced multipoint spectral theories. The role of both linear and non-linear mechanisms is emphasized. The link between the statistical properties and the dynamics of coherent structures is also addressed. Despite its restriction to homogeneous turbulence, the book is of interest to all people working in turbulence, since the basic physical mechanisms which are present in all turbulent flows are explained. The reader will find a unified presentation of the results and a clear presentation of existing controversies. Special attention is given to bridge the results obta...
Effect of turbulent collisions on diffusion in stationary plasma turbulence
International Nuclear Information System (INIS)
Xia, H.; Ishihara, O.
1990-01-01
Recently the velocity diffusion process was studied by the generalized Langevin equation derived by the projection operator method. The further study shows that the retarded frictional function plays an important role in suppressing particle diffusion in the velocity space in stronger turbulence as much as the resonance broadening effect. The retarded frictional effect, produced by the effective collisions due to the plasma turbulence is assumed to be a Gaussian, but non-Markovian and non-wide-sense stationary process. The relations between the proposed formulation and the extended resonance broadening theory is discussed. The authors also carry out test particle numerical experiment for Langmuir turbulence to test the theories. In a stronger turbulence a deviation of the diffusion rate from the one predicted by both the quasilinear and the extended resonance theories has been observed and is explained qualitatively by the present formulation
Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung
2012-11-01
In this work we clarify the role of Markstein diffusivity on turbulent flame speed and it's scaling, from analysis and experimental measurements on constant-pressure expanding flames propagating in near isotropic turbulence. For all C0-C4 hydrocarbon-air mixtures presented in this work and recently published C8 data from Leeds, the normalized turbulent flame speed data of individual mixtures approximately follows the recent theoretical and experimental ReT, f 0 . 5 scaling, where the average radius is the length scale and thermal diffusivity is the transport property. We observe that for a constant ReT, f 0 . 5 , the normalized turbulent flame speed decreases with increasing Mk. This could be explained by considering Markstein diffusivity as the large wavenumber, flame surface fluctuation dissipation mechanism. As originally suggested by the theory, replacing thermal diffusivity with Markstein diffusivity in the turbulence Reynolds number definition above, the present and Leeds dataset could be scaled by the new ReT, f 0 . 5 irrespective of the fuel considered, equivalence ratio, pressure and turbulence intensity for positive Mk flames. This work was supported by the Combustion Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under Award Number DE-SC0001198 and by the Air Force Office of Scientific Research.
Turbulence, transport, and zonal flows in the Madison symmetric torus reversed-field pinch
Williams, Z. R.; Pueschel, M. J.; Terry, P. W.; Hauff, T.
2017-12-01
The robustness and the effect of zonal flows in trapped electron mode (TEM) turbulence and Ion Temperature Gradient (ITG) turbulence in the reversed-field pinch (RFP) are investigated from numerical solutions of the gyrokinetic equations with and without magnetic external perturbations introduced to model tearing modes. For simulations without external magnetic field perturbations, zonal flows produce a much larger reduction of transport for the density-gradient-driven TEM turbulence than they do for the ITG turbulence. Zonal flows are studied in detail to understand the nature of their strong excitation in the RFP and to gain insight into the key differences between the TEM- and ITG-driven regimes. The zonal flow residuals are significantly larger in the RFP than in tokamak geometry due to the low safety factor. Collisionality is seen to play a significant role in the TEM zonal flow regulation through the different responses of the linear growth rate and the size of the Dimits shift to collisionality, while affecting the ITG only minimally. A secondary instability analysis reveals that the TEM turbulence drives zonal flows at a rate that is twice that of the ITG turbulence. In addition to interfering with zonal flows, the magnetic perturbations are found to obviate an energy scaling relation for fast particles.
Suppression of Phase Mixing in Drift-Kinetic Plasma Turbulence
Parker, J. T.; Dellar, P. J.; Schekochihin, A. A.; Highcock, E. G.
2017-12-01
The solar wind and interstellar medium are examples of strongly magnetised, weakly collisional, astrophysical plasmas. Their turbulent fluctuations are strongly anisotropic, with small amplitudes, and frequencies much lower than the Larmor frequency. This regime is described by gyrokinetic theory, a reduced five-dimensional kinetic system describing averages over Larmor orbits. A turbulent plasma may transfer free energy, a measure of fluctuation amplitudes, from injection at large scales, typically by an instability, to dissipation at small physical scales like a turbulent fluid. Alternatively, a turbulent plasma may form fine scale structures in velocity space via phase-mixing, the mechanism that leads to Landau damping in linear plasma theory. Macroscopic plasma properties like heat and momentum transport are affected by both mechanisms. While each is understood in isolation, their interaction is not. We study this interaction using a Hankel-Hermite velocity space representation of gyrokinetic theory. The Hankel transform interacts neatly with the Bessel functions that arise from averaging over Larmor orbits, so the perpendicular velocity space is decoupled for linearized problems. The Hermite transform expresses phase mixing as nearest-neighbor coupling between parallel velocity space scales represented by Hermite mode numbers. We use this representation to study transfer mechanisms in drift-kinetic plasma turbulence, the long wavelength limit of gyrokinetic theory. We show that phase space is divided into two regions, with one transfer mechanism dominating in each. Most energy is contained in the region where the fluid-like nonlinear cascade dominates. Moreover, in that region the nonlinear cascade interferes with phase mixing by exciting an "anti phase mixing" transfer of free energy from small to large velocity space scales. This cancels out the usual phase mixing, and renders the overall behavior fluid-like. These results profoundly change our understanding
International Nuclear Information System (INIS)
Birkenmeier, Gregor
2012-01-01
For more than 60 years, fusion scientists try to confine a plasma by means of external magnetic fields in order to achieve appropriately high densities and temperatures for the ignition of nuclear fusion. Despite of great progress in the design of confinement concepts, which are considered for the confinement of burning plasmas in the near future, theoretical plasma physics promises further confinement improvements using novel magnetic field geometries. Therefor, the key is the minimization of turbulent transport by choosing appropiate magnetic field geometries, which necessitates a fundamental understanding of the influence of magnetic field geometry on plasma turbulence. There are several theoretical works on turbulent plasma dynamics in three-dimensional geometries, but only a few experimental studies for validation of the theoretical results exist. Hence, the present work aims at providing experimental data for comparison with theory and to gain insights into the interplay between drift-wave turbulence and magnetic field geometry. By means of two multi-probe arrays, local density and potential fluctuations are measured in low-temperature plasmas at 128 positions on a single flux surface of the stellarator TJ-K with high temporal resolution. Using methods of statistical timeseries analysis structure sizes and dynamic properties of the drift-wave turbulence in TJ-K are determined. Thereby, it is shown that the size of turbulent structures perpendicular to the magnetic field is reduced in regions of high absolute local magnetic shear. In addition, a poloidal displacement with respect to the magnetic field lines and a complex propagation pattern of parallelly extended turbulent structures is found. Also, poloidal profiles of turbulent transport are calculated from the probe data. The maximum transport is found to be poloidally localized in a region of negative normal curvature (unfavourable curvature). In addition, the results point to an influence of geodesic
International Nuclear Information System (INIS)
Holland, C.; Kim, E.J.; Champeaux, S.; Gurcan, O.; Rosenbluth, M.N.; Diamond, P.H.; Tynan, G.R.; Nevins, W.; Candy, J.
2003-01-01
Understanding the physics of shear flow and structure formation in plasmas is a central problem for the advancement of magnetic fusion because of the roles such flows are believed to play in regulating turbulence and transport levels. In this paper, we report on integrated experimental, computational, and theoretical studies of sheared zonal flows and radially extended convective cells, with the aim of assessing the results of theory experiment and theory-simulation comparisons. In particular, simulations are used as test beds for verifying analytical predictions and demonstrating the suitability of techniques such as bispectral analysis for isolating nonlinear couplings in data. Based on intriguing initial results suggesting increased levels of nonlinear coupling occur during L-H transitions, we have undertaken a comprehensive study of bispectral quantities in fluid and gyrokinetic simulations, and compared these results with theoretical expectations. Topics of study include locality and directionality of energy transfer, amplitude scaling, and parameter dependences. Techniques for inferring nonlinear coupling coefficients from data are discussed, and initial results from experimental data are presented. Future experimental studies are motivated. We also present work investigating the role of structures in transport. Analysis of simulation data indicates that the turbulent heat flux can be represented as an ensemble of 'heat pulses' of varying sizes, with a power law distribution. The slope of the power law is shown to determine global transport scaling (i.e. Bohm or gyro-Bohm). Theoretical work studying the dynamics of the largest cells (termed 'streamers') is presented, as well as results from ongoing analysis studying connections between heat pulse distribution and bispectral quantities. (author)
Problems of linear electron (polaron) transport theory in semiconductors
Klinger, M I
1979-01-01
Problems of Linear Electron (Polaron) Transport Theory in Semiconductors summarizes and discusses the development of areas in electron transport theory in semiconductors, with emphasis on the fundamental aspects of the theory and the essential physical nature of the transport processes. The book is organized into three parts. Part I focuses on some general topics in the theory of transport phenomena: the general dynamical theory of linear transport in dissipative systems (Kubo formulae) and the phenomenological theory. Part II deals with the theory of polaron transport in a crystalline semicon
Universal Probability Distribution Function for Bursty Transport in Plasma Turbulence
International Nuclear Information System (INIS)
Sandberg, I.; Benkadda, S.; Garbet, X.; Ropokis, G.; Hizanidis, K.; Castillo-Negrete, D. del
2009-01-01
Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density fluctuations observed in plasma edge of several magnetic confinement devices and the remarkable scaling between their skewness S and kurtosis K. Similar statistical characteristics of variabilities have been also observed in other physical systems that are characterized by convection such as the x-ray fluctuations emitted by the Cygnus X-1 accretion disc plasmas and the sea surface temperature fluctuations.
Turbulence and abnormal transport in tokamak plasmas
International Nuclear Information System (INIS)
Garbet, X.
1988-09-01
Microinstabilities in linear and nonlinear tokamak plasmas were studied. A variational method based on the existence of a system of angular variables and action for the charged particles in the magnetic configuration of a tokamak is described. The corresponding functional, extremal in relation to the fluctuating electromagnetic field, is calculated analytically, taking into account the effects of the toroidal geometry. A numerical code, TORRID, was derived from these principles and the main instabilities, especially ion instabilities and microtearing, were studied linearly. Nonlinear methods were also applied to microtearing. Quasi-linear transport coefficients are derived from a principle of minimum entropy production. Thermal ionic conductivity and viscosity are calculated for an ionic turbulence [fr
Bray, Richard S.; Larsen, William E.
1965-01-01
An investigation of several factors which may contribute to the problem of piloting jet transport aircraft in heavy turbulence was conducted by using a piloted simulator that included the most significant airplane response and cockpit vibrations induced by rough air. Results indicated that the primary fuselage structural frequency contributed significantly to a distracting cockpit environment, and there was obtained evidence of severely reduced instrument flight proficiency during simulated maneuvering flight in heavy turbulence. It is concluded that the addition of similar rough-air response capabilities to training simulators would be of value in pilot indoctrination in turbulent-flight procedures.
Structure formation in turbulent plasmas - test of nonlinear processes in plasma experiments
International Nuclear Information System (INIS)
Itoh, S.-I.; Yagi, Masatoshi; Inagaki, Shigeru
2009-01-01
Full text: Recent developments in plasma physics, either in the fusion research in a new era of ITER, or in space and in astro-physics, the world-wide and focused research has been developed on the subject of structural formation in turbulent plasma being associated with electro-magnetic field formation. Keys for the progress were a change of the physics view from the 'linear, local and deterministic' picture to the description based on 'nonlinear instability, nonlocal interaction and probabilistic excitation' for the turbulent state, and the integration of the theory-simulation-experiment. In this presentation, we first briefly summarize the theory of microscopic turbulence and mesoscale fluctuations and selection rules. In addition, the statistical formation of large-scale structure/deformation by turbulence is addressed. Then, the experimental measurements of the mesoscale structures (e.g., zonal flows, zonal fields, streamer and transport interface) and of the nonlinear interactions among them in turbulent plasmas are reported. Confirmations by, and new challenges from, the experiments are overviewed. Work supported by the Grant-in-Aid for Specially-Promoted Research (16002005). (author)
Numerical assessment of the ion turbulent thermal transport scaling laws
International Nuclear Information System (INIS)
Ottaviani, M.; Manfredi, G.
2001-01-01
Numerical simulations of ion temperature gradient (ITG) driven turbulence were carried out to investigate the parametric dependence of the ion thermal transport on the reduced gyroradius and on the local safety factor. Whereas the simulations show a clear proportionality of the conductivity to the gyroradius, the dependence on the safety factor cannot be represented as a simple power law like the one exhibited by the empirical scaling laws. (author)
DEFF Research Database (Denmark)
Chougule, Abhijit S.; Mann, Jakob; Kelly, Mark C.
2017-01-01
A spectral tensor model is presented for turbulent fluctuations of wind velocity components and temperature, assuming uniform vertical gradients in mean temperature and mean wind speed. The model is built upon rapid distortion theory (RDT) following studies by Mann and by Hanazaki and Hunt, using...... the eddy lifetime parameterization of Mann to make the model stationary. The buoyant spectral tensor model is driven via five parameters: the viscous dissipation rate epsilon, length scale of energy-containing eddies L, a turbulence anisotropy parameter Gamma, gradient Richardson number (Ri) representing...
Directory of Open Access Journals (Sweden)
S. Yahaya
2009-05-01
Full Text Available This paper deals with the characteristics of the atmospheric turbulent flow in the vicinity of the ground, and particularly with the profile of the horizontal wind variance. The study is based on experimental measurements performed with fast cup anemometers located near the ground at 5 different levels (from 0.25 to 4 m and sampled at 1 Hz. The experiment was carried over two agricultural plots with various tillage treatments in a fallow semiarid area (Central Aragon, Spain. The results of this study reveal that near the ground surface and under moderate wind, the horizontal wind variance logarithmically increases with height, in direct relationship with the friction velocity and the roughness length scale. A theoretical development has allowed us to link this behaviour to the modeling of the turbulent kinetic energy (TKE transport through the eddy diffusivity. Thus, the study proposes a formulation of the similarity universal function of the horizontal wind variance. Besides, the formulation offers a new method for the determination of the friction velocity and the roughness length scale and can be used for the evaluation of the TKE transport rate.
A structure-based model for the transport of passive scalars in homogeneous turbulent flows
International Nuclear Information System (INIS)
Panagiotou, C.F.; Kassinos, S.C.
2016-01-01
Highlights: • The Interacting Particle Representation Model (IPRM) is extended for passive scalar transport. • We develop a structure-based set of scale equations for the scalar field and couple them to the IPRM. • The complete model is evaluated for several cases of homogeneous deformation with good results. • We outline steps for coupling the new scalar scales to the Algebraic Structure-Based Model (ASBM). - Abstract: A structure-based model has been constructed, for the first time, for the study of passive scalar transport in turbulent flows. The scalar variance and the large-scale scalar gradient variance are proposed as the two turbulence scales needed for closure of the scalar equations in the framework of the Interacting Particle Representation Model (IPRM). The scalar dissipation rate is modeled in terms of the scalar variance and the large-scale enstrophy of the velocity field. Model parameters are defined by matching the decay rates in freely isotropic turbulence. The model is validated for a large number of cases of deformation in both fixed and rotating frames, showing encouraging results. The model shows good agreement with DNS results for the case of pure shear flow in the presence of either transverse or streamwise mean scalar gradient, while it correctly predicts the presence of direct cascade for the passive scalar variance in two dimensional isotropic turbulence.
Numerical Test of Different Approximations Used in the Transport Theory of Energetic Particles
Qin, G.; Shalchi, A.
2016-05-01
Recently developed theories for perpendicular diffusion work remarkably well. The diffusion coefficients they provide agree with test-particle simulations performed for different turbulence setups ranging from slab and slab-like models to two-dimensional and noisy reduced MHD turbulence. However, such theories are still based on different analytical approximations. In the current paper we use a test-particle code to explore the different approximations used in diffusion theory. We benchmark different guiding center approximations, simplifications of higher-order correlations, and the Taylor-Green-Kubo formula. We demonstrate that guiding center approximations work very well as long as the particle's unperturbed Larmor radius is smaller than the perpendicular correlation length of the turbulence. Furthermore, the Taylor-Green-Kubo formula and the definition of perpendicular diffusion coefficients via mean square displacements provide the same results. The only approximation that was used in the past in nonlinear diffusion theory that fails is to replace fourth-order correlations by a product of two second-order correlation functions. In more advanced nonlinear theories, however, this type of approximation is no longer used. Therefore, we confirm the validity of modern diffusion theories as a result of the work presented in the current paper.
Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models
Rodriguez-Fernandez, P.; White, A. E.; Howard, N. T.; Grierson, B. A.; Staebler, G. M.; Rice, J. E.; Yuan, X.; Cao, N. M.; Creely, A. J.; Greenwald, M. J.; Hubbard, A. E.; Hughes, J. W.; Irby, J. H.; Sciortino, F.
2018-02-01
A long-standing enigma in plasma transport has been resolved by modeling of cold-pulse experiments conducted on the Alcator C-Mod tokamak. Controlled edge cooling of fusion plasmas triggers core electron heating on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas.
Numerical and theoretical investigations of resistive drift wave turbulence
International Nuclear Information System (INIS)
Sunn Pedersen, T.
1995-07-01
With regard to the development of thermonuclear fusion utilizing a plasma confined in a magnetic field, anomalous transport is a major problem and is considered to be caused by electrostatic drift wave turbulence. A simplified quasi-two-dimensional slab model of resistive drift wave turbulence is investigated numerically and theoretically. The model (Hasegawa and Wakatani), consists of two nonlinear partial differential equations for the density perturbation n and the electrostatic potential perturbation φ. It includes the effect of a background density gradient perpendicular to the magnetic field and a generalized Ohm's law for the electrons in the direction parallel to the magnetic field. It may be used to model the basic features of electrostatic turbulence and the associated transport in an edge plasma. Model equations are derived and some important properties of the system are discussed. It is described how the Fourier spectral method is applied to the Hasegawa-Wakatani equations, how the time integration is developed to ensure accurate and fast simulations in a large parameter regime, and how the accuracy of the code is checked. Numerical diagnostics are developed to verify and extend the results in publications concerning quasi-stationary turbulent states and to give an overview of the properties of the quasi-stationary turbulent state. The use of analysis tools, not previously applied to the Hasegawa-Wakatani system, and the results obtained are described. Fluid particles are tracked to obtain Lagrangian statistics for the turbulence. A new theoretical analysis of relative dispersion leads to a decomposition criterion for the particles. The significance of this is investigated numerically and characteristic time scales for particles are determined for a range of parameter values. It is indicated that the turbulent state can be characterized in the context of nonlinear dynamics and chaos theory as an attractor with a large basin of attraction. The basic
The Influence of Turbulent Coherent Structure on Suspended Sediment Transport
Huang, S. H.; Tsai, C.
2017-12-01
The anomalous diffusion of turbulent sedimentation has received more and more attention in recent years. With the advent of new instruments and technologies, researchers have found that sediment behavior may deviate from Fickian assumptions when particles are heavier. In particle-laden flow, bursting phenomena affects instantaneous local concentrations, and seems to carry suspended particles for a longer distance. Instead of the pure diffusion process in an analogy to Brownian motion, Levy flight which allows particles to move in response to bursting phenomena is suspected to be more suitable for describing particle movement in turbulence. And the fractional differential equation is a potential candidate to improve the concentration profile. However, stochastic modeling (the Differential Chapmen-Kolmogorov Equation) also provides an alternative mathematical framework to describe system transits between different states through diffusion/the jump processes. Within this framework, the stochastic particle tracking model linked with advection diffusion equation is a powerful tool to simulate particle locations in the flow field. By including the jump process to this model, a more comprehensive description for suspended sediment transport can be provided with a better physical insight. This study also shows the adaptability and expandability of the stochastic particle tracking model for suspended sediment transport modeling.
International Nuclear Information System (INIS)
Mukhopadhyay, Banibrata; Saha, Kanak
2011-01-01
The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle. Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity. Hence, any viscosity in such systems must be due to turbulence, arguably governed by magnetorotational instability, especially when temperature T > or approx. 10 5 . However, such disks around quiescent cataclysmic variables, protoplanetary and star-forming disks, and the outer regions of disks in active galactic nuclei are practically neutral in charge because of their low temperature, and thus are not expected to be coupled with magnetic fields enough to generate any transport due to the magnetorotational instability. This flow is similar to plane Couette flow including the Coriolis force, at least locally. What drives their turbulence and then transport, when such flows do not exhibit any unstable mode under linear hydrodynamic perturbation? We demonstrate that the three-dimensional secondary disturbance to the primarily perturbed flow that triggers elliptical instability may generate significant turbulent viscosity in the range 0.0001 ∼ t ∼< 0.1, which can explain transport in accretion flows.
International Nuclear Information System (INIS)
Hahm, T.S.
1990-12-01
Ion temperature gradient turbulence based transport models have difficulties reconciling the recent DIII-D H-mode results where the density profile is flat, but χ e > χ i in the core region. In this work, a nonlinear theory is developed for recently discovered ion temperature gradient trapped electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for L Ti /R approx-lt κ θ ρ s approx-lt (L Ti /R) 1/4 . They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave-particle-wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity. 17 refs., 3 figs
International Nuclear Information System (INIS)
Colin-Bellot, Clothilde
2015-01-01
The possibility to produce power by using magnetically confined fusion is a scientific and technological challenge. The perspective of ITER conveys strong signals to intensify modeling effort on magnetized fusion plasmas. The success of the fusion operation is conditioned by the quality of plasma confinement in the core of the reactor and by the control of plasma exhaust on the wall. Both phenomena are related to turbulent cross-field transport that is at the heart of the notion of magnetic confinement studies, particle and heat losses. The study of edge phenomena is therefore complicated by a particularly complex magnetic geometry.This calls for an improvement of our capacity to develop numerical tools able to reproduce turbulent transport properties reliable to predict particle and energy fluxes on the plasma facing components. This thesis introduces the TOKAM3X fluid model to simulate edge plasma turbulence. A special focus is made on the code Verification and the Validation. It is a necessary step before using a code as a predictive tool. Then new insights on physical properties of the edge plasma turbulence are explored. In particular, the poloidal asymmetries induced by turbulence and observed experimentally in the Low-Field-Side of the devices are investigated in details. Great care is dedicated to the reproduction of the MISTRAL base case which consists in changing the magnetic configuration and observing the impact on parallel flows in the poloidal plane. The simulations recover experimental measurements and provide new insights on the effect of the plasma-wall contact position location on the turbulent features, which were not accessible in experiments. (author) [fr
Energy Technology Data Exchange (ETDEWEB)
Schuster, Eugenio
2014-05-02
The strong coupling between the different physical variables involved in the plasma transport phenomenon and the high complexity of its dynamics call for a model-based, multivariable approach to profile control where those predictive models could be exploited. The overall objective of this project has been to extend the existing body of work by investigating numerically and experimentally active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport can be monitored by an array of electrostatic probes, and Ex B flow profiles can be controlled via a set of biased concentric ring electrodes that terminate the plasma column. The goals of the proposed research have been threefold: i- to develop a predictive code to simulate plasma transport in the linear HELCAT (HELicon-CAThode) plasma device at the University of New Mexico (UNM), where the experimental component of the proposed research has been carried out; ii- to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles, iii- to investigate the fundamental nonlinear dynamics of turbulence and transport physics. Lehigh University (LU), including Prof. Eugenio Schuster and one full-time graduate student, has been primarily responsible for control-oriented modeling and model-based control design. Undergraduate students have also participated in this project through the National Science Foundation Research Experience for Undergraduate (REU) program. The main goal of the LU Plasma Control Group has been to study the feasibility of controlling turbulence-driven transport by shaping the radial poloidal flow profile (i.e., by controlling flow shear) via biased concentric ring electrodes.
Collection of problems in transport theory
International Nuclear Information System (INIS)
Kaper, H.G.
1975-01-01
Problems presented are: (1) definition of transport operators; (2) relation between the integro-differential and integral form of the transport equation; (3) asymptotic behavior of the scalar density near curved boundaries and interfaces; (4) singularities at a corner; (5) regularity of the solution of the transport equation; (7) transport equations on a manifold; (8) numerical analysis; (9) cubature; (10) point spectrum of the transport operator; (11) convergence of the multigroup approximation; (12) convergence of discrete ordinates approximations; (13) the finite double-norm property; (14) convergence of discrete ordinates approximation. The presentation of the problems is intended to direct attention to gaps in the existing knowledge of transport theory and to stimulate research into new areas of transport theory
Turbulence modelling; Modelisation de la turbulence isotherme
Energy Technology Data Exchange (ETDEWEB)
Laurence, D. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-{epsilon} two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the `standard` (R{sub ij}-{epsilon}) Reynolds tensions transport model and introduces more recent models called `feasible`. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author). 37 refs.
Electromagnetic transport components and sheared flows in drift-Alfven turbulence
DEFF Research Database (Denmark)
Naulin, V.
2003-01-01
Results from three-dimensional numerical simulations of drift-Alfven turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma beta we ob...... with a folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution. (C) 2003 American Institute of Physics....... related to magnetic flutter is proposed. The characteristics of the ExB flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well...
Transport perturbation theory in nuclear reactor analysis
International Nuclear Information System (INIS)
Nishigori, Takeo; Takeda, Toshikazu; Selvi, S.
1985-01-01
Perturbation theory is formulated on the basis of transport theory to obtain a formula for the reactivity changes due to possible variations of cross sections. Useful applications to cell homogenization are presented for the whole core calculation in transport and in diffusion theories. (author)
Kinetic theory and transport phenomena
Soto, Rodrigo
2016-01-01
This textbook presents kinetic theory, which is a systematic approach to describing nonequilibrium systems. The text is balanced between the fundamental concepts of kinetic theory (irreversibility, transport processes, separation of time scales, conservations, coarse graining, distribution functions, etc.) and the results and predictions of the theory, where the relevant properties of different systems are computed. The book is organised in thematic chapters where different paradigmatic systems are studied. The specific features of these systems are described, building and analysing the appropriate kinetic equations. Specifically, the book considers the classical transport of charges, the dynamics of classical gases, Brownian motion, plasmas, and self-gravitating systems, quantum gases, the electronic transport in solids and, finally, semiconductors. Besides these systems that are studied in detail, concepts are applied to some modern examples including the quark–gluon plasma, the motion of bacterial suspen...
Hackerott, João A.; Bakhoday Paskyabi, Mostafa; Reuder, Joachim; de Oliveira, Amauri P.; Kral, Stephan T.; Marques Filho, Edson P.; Mesquita, Michel dos Santos; de Camargo, Ricardo
2017-11-01
We discuss scalar similarities and dissimilarities based on analysis of the dissipation terms in the variance budget equations, considering the turbulent kinetic energy and the variances of temperature, specific humidity and specific CO_2 content. For this purpose, 124 high-frequency sampled segments are selected from the Boundary Layer Late Afternoon and Sunset Turbulence experiment. The consequences of dissipation similarity in the variance transport are also discussed and quantified. The results show that, for the convective atmospheric surface layer, the non-dimensional dissipation terms can be expressed in the framework of Monin-Obukhov similarity theory and are independent of whether the variable is temperature or moisture. The scalar similarity in the dissipation term implies that the characteristic scales of the atmospheric surface layer can be estimated from the respective rate of variance dissipation, the characteristic scale of temperature, and the dissipation rate of temperature variance.
Kleeorin, N.
2018-06-01
We discuss a mean-field theory of the generation of large-scale vorticity in a rotating density stratified developed turbulence with inhomogeneous kinetic helicity. We show that the large-scale non-uniform flow is produced due to either a combined action of a density stratified rotating turbulence and uniform kinetic helicity or a combined effect of a rotating incompressible turbulence and inhomogeneous kinetic helicity. These effects result in the formation of a large-scale shear, and in turn its interaction with the small-scale turbulence causes an excitation of the large-scale instability (known as a vorticity dynamo) due to a combined effect of the large-scale shear and Reynolds stress-induced generation of the mean vorticity. The latter is due to the effect of large-scale shear on the Reynolds stress. A fast rotation suppresses this large-scale instability.
International Nuclear Information System (INIS)
Scott, B.; Jenko, F.; Peeters, A.G.; Teo, A.C.Y.
1999-01-01
(1) Computations of turbulence from the electromagnetic gyro fluid model are performed in a flux surface geometry representing the actual MHD equilibrium of the ASDEX Upgrade edge flux surfaces. The transition to ideal ballooning seen in simple geometries as the plasma beta rises is suppressed, leaving the transport at quantitatively realistic levels. Computations for core parameters at half-radius geometry show significant contribution due to the finite beta electron dynamics, possibly removing the standard ITG threshold. (2) Strong inward vorticity transport in edge turbulence, resulting from ion diamagnetic flows, may lead to a build up of mean ExB vorticity fast enough to cause an H-mode transition. (3) Friction of mean ion flows against neutrals involves both toroidal and poloidal flow components, leading to a finite radial current due to a given ExB profile even with zero poloidal rotation. (author)
International Nuclear Information System (INIS)
Scott, B.; Jenko, F.; Peeters, A.; Teo, A.C-Y.
2001-01-01
(1) Computations of turbulence from the electromagnetic gyrofluid model are performed in a flux surface geometry representing the actual MHD equilibrium of the ASDEX Upgrade edge flux surfaces. The transition to ideal ballooning seen in simple geometries as the plasma beta rises is suppressed, leaving the transport at quantitatively realistic levels. Computations for core parameters at half-radius geometry show significant contribution due to the finite beta electron dynamics, possibly removing the standard ITG threshold. (2) Strong inward vorticity transport in edge turbulence, resulting from ion diamagnetic flows, may lead to a build up of mean ExB vorticity fast enough to cause an H-mode transition. (3) Friction of mean ion flows against neutrals involves both toroidal and poloidal flow components, leading to a finite radial current due to a given ExB profile even with zero poloidal rotation. (author)
Lee, Z. S.; Baas, A. C.; Jackson, D.; Cooper, J. A.; Lynch, K.; Delgado-Fernandez, I.; Beyers, M.
2010-12-01
Recent studies have suggested the significant role of boundary layer turbulence and coherent flow structures on sand transport by wind over beaches and desert dunes. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated a move beyond the basic monitoring of shear velocities and bulk sediment transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a small-scale point-location field study of boundary layer turbulence and shear stresses conducted under obliquely onshore winds over a beach at Magilligan Strand, Northern Ireland. High-frequency (25 Hz) 3D wind vector measurements were collected at five different heights between 0.13 and 1.67 metres above the bed using sonic anemometry for durations of several hours, and the associated sand transport response was measured using an array of Safires. The wind data are used to investigate the vertical structure of Reynolds shear stresses and burst-sweep event characteristics, as well as a comparison with the standard logarithmic (law-of-the-wall) wind profile. The study explores the identification and selection of a characteristic event duration based on integral time-scales as well as spectral analysis, and includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u’, v’, w’). Results show how the contributions to shear stress and the average pitch of bursts and sweeps changes as a function of height above the bed, indicating the transformation of top-down turbulent eddies as they travel toward the surface. A comparison between the turbulence data and the synchronous sand transport events, meanwhile, reveals the potential effects of enhanced saltation layer roughness feedback on eddies close to the bed.
Hong, R.; Li, J. C.; Hajjar, R.; Chakraborty Thakur, S.; Diamond, P. H.; Tynan, G. R.
2018-05-01
Detailed measurements of intrinsic axial flow generation parallel to the magnetic field in the controlled shear decorrelation experiment linear plasma device with no axial momentum input are presented and compared to theory. The results show a causal link from the density gradient to drift-wave turbulence with broken spectral symmetry and development of the axial mean parallel flow. As the density gradient steepens, the axial and azimuthal Reynolds stresses increase and radially sheared azimuthal and axial mean flows develop. A turbulent axial momentum balance analysis shows that the axial Reynolds stress drives the radially sheared axial mean flow. The turbulent drive (Reynolds power) for the azimuthal flow is an order of magnitude greater than that for axial flow, suggesting that the turbulence fluctuation levels are set by azimuthal flow shear regulation. The direct energy exchange between axial and azimuthal mean flows is shown to be insignificant. Therefore, the axial flow is parasitic to the turbulence-zonal flow system and is driven primarily by the axial turbulent stress generated by that system. The non-diffusive, residual part of the axial Reynolds stress is found to be proportional to the density gradient and is formed due to dynamical asymmetry in the drift-wave turbulence.
Fluid model of the magnetic presheath in a turbulent plasma
International Nuclear Information System (INIS)
Stanojevic, M; Duhovnik, J; Jelic, N; Kendl, A; Kuhn, S
2005-01-01
A fluid model of the magnetic presheath in a turbulent boundary plasma is presented. Turbulent transport corrections of the classical three-dimensional fluid transport equations, which can be used to study magnetic presheaths in various geometries, are derived by means of the ensemble averaging procedure from the statistical theory of plasma turbulence. Then, the magnetic presheath in front of an infinite plane surface is analysed in detail. The linearized planar magnetic presheath equations are applied to the plasma-presheath-magnetic-presheath boundary (i.e. the magnetic presheath edge), whereas the original non-linear planar magnetic presheath equations are used for the entire magnetic presheath, allowing for various sets of experimentally relevant free model parameters to be applied. Important new results of this study are, among others, new expressions for the fluid Bohm criterion at the Debye sheath edge and for the ion flux density perpendicular to the wall. These new results, which exhibit corrections due to the turbulent charged particle transport, can qualitatively explain the fact that whenever the angle between the magnetic field and the wall is very small (i.e. several degrees) or zero, electric currents, measured by Langmuir probes in the boundary regions of nuclear fusion devices and in various low-temperature plasmas, are anomalously enhanced in comparison with those expected or predicted by other theoretical models
International Nuclear Information System (INIS)
Burrell, K.H.
1996-11-01
One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization
Formation, growth, and transport of soot in a three-dimensional turbulent non-premixed jet flame
Attili, Antonio; Bisetti, Fabrizio; Mü eller, Michael E.; Pitsch, Heinz G.
2014-01-01
The formation, growth, and transport of soot is investigated via large scale numerical simulation in a three-dimensional turbulent non-premixed n-heptane/air jet flame at a jet Reynolds number of 15,000. For the first time, a detailed chemical mechanism, which includes the soot precursor naphthalene and a high-order method of moments are employed in a three-dimensional simulation of a turbulent sooting flame. The results are used to discuss the interaction of turbulence, chemistry, and the formation of soot. Compared to temperature and other species controlled by oxidation chemistry, naphthalene is found to be affected more significantly by the scalar dissipation rate. While the mixture fraction and temperature fields show fairly smooth spatial and temporal variations, the sensitivity of naphthalene to turbulent mixing causes large inhomogeneities in the precursor fields, which in turn generate even stronger intermittency in the soot fields. A strong correlation is apparent between soot number density and the concentration of naphthalene. On the contrary, while soot mass fraction is usually large where naphthalene is present, pockets of fluid with large soot mass are also frequent in regions with very low naphthalene mass fraction values. From the analysis of Lagrangian statistics, it is shown that soot nucleates and grows mainly in a layer close to the flame and spreads on the rich side of the flame due to the fluctuating mixing field, resulting in more than half of the total soot mass being located at mixture fractions larger than 0.6. Only a small fraction of soot is transported towards the flame and is completely oxidized in the vicinity of the stoichiometric surface. These results show the leading order effects of turbulent mixing in controlling the dynamics of soot in turbulent flames. Finally, given the difficulties in obtaining quantitative data in experiments of turbulent sooting flames, this simulation provides valuable data to guide the development of
Formation, growth, and transport of soot in a three-dimensional turbulent non-premixed jet flame
Attili, Antonio
2014-07-01
The formation, growth, and transport of soot is investigated via large scale numerical simulation in a three-dimensional turbulent non-premixed n-heptane/air jet flame at a jet Reynolds number of 15,000. For the first time, a detailed chemical mechanism, which includes the soot precursor naphthalene and a high-order method of moments are employed in a three-dimensional simulation of a turbulent sooting flame. The results are used to discuss the interaction of turbulence, chemistry, and the formation of soot. Compared to temperature and other species controlled by oxidation chemistry, naphthalene is found to be affected more significantly by the scalar dissipation rate. While the mixture fraction and temperature fields show fairly smooth spatial and temporal variations, the sensitivity of naphthalene to turbulent mixing causes large inhomogeneities in the precursor fields, which in turn generate even stronger intermittency in the soot fields. A strong correlation is apparent between soot number density and the concentration of naphthalene. On the contrary, while soot mass fraction is usually large where naphthalene is present, pockets of fluid with large soot mass are also frequent in regions with very low naphthalene mass fraction values. From the analysis of Lagrangian statistics, it is shown that soot nucleates and grows mainly in a layer close to the flame and spreads on the rich side of the flame due to the fluctuating mixing field, resulting in more than half of the total soot mass being located at mixture fractions larger than 0.6. Only a small fraction of soot is transported towards the flame and is completely oxidized in the vicinity of the stoichiometric surface. These results show the leading order effects of turbulent mixing in controlling the dynamics of soot in turbulent flames. Finally, given the difficulties in obtaining quantitative data in experiments of turbulent sooting flames, this simulation provides valuable data to guide the development of
Energy Technology Data Exchange (ETDEWEB)
Goldbaum, Nathan J. [National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801 (United States); Krumholz, Mark R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2601 (Australia); Forbes, John C., E-mail: ngoldbau@illinois.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
2016-08-10
Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 and leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.
International Nuclear Information System (INIS)
Arnold, R.C.
1977-06-01
The formalism of Martin, Siggia and Rose is utilized to write a functional-integral representation for generating functionals in plasma transport theory, following Nakayama and Dawson. Parallel treatments of Navier-Stokes turbulence (attempted by Rosen) and of critical dynamics, by Kawasaki, are compared to illustrate the application of common field-theory techniques, such as the effective action. Quasi-classical methods for functional integrals are discussed
Fundamental Statistical Descriptions of Plasma Turbulence in Magnetic Fields
Energy Technology Data Exchange (ETDEWEB)
John A. Krommes
2001-02-16
A pedagogical review of the historical development and current status (as of early 2000) of systematic statistical theories of plasma turbulence is undertaken. Emphasis is on conceptual foundations and methodology, not practical applications. Particular attention is paid to equations and formalism appropriate to strongly magnetized, fully ionized plasmas. Extensive reference to the literature on neutral-fluid turbulence is made, but the unique properties and problems of plasmas are emphasized throughout. Discussions are given of quasilinear theory, weak-turbulence theory, resonance-broadening theory, and the clump algorithm. Those are developed independently, then shown to be special cases of the direct-interaction approximation (DIA), which provides a central focus for the article. Various methods of renormalized perturbation theory are described, then unified with the aid of the generating-functional formalism of Martin, Siggia, and Rose. A general expression for the renormalized dielectric function is deduced and discussed in detail. Modern approaches such as decimation and PDF methods are described. Derivations of DIA-based Markovian closures are discussed. The eddy-damped quasinormal Markovian closure is shown to be nonrealizable in the presence of waves, and a new realizable Markovian closure is presented. The test-field model and a realizable modification thereof are also summarized. Numerical solutions of various closures for some plasma-physics paradigms are reviewed. The variational approach to bounds on transport is developed. Miscellaneous topics include Onsager symmetries for turbulence, the interpretation of entropy balances for both kinetic and fluid descriptions, self-organized criticality, statistical interactions between disparate scales, and the roles of both mean and random shear. Appendices are provided on Fourier transform conventions, dimensional and scaling analysis, the derivations of nonlinear gyrokinetic and gyrofluid equations
Fundamental Statistical Descriptions of Plasma Turbulence in Magnetic Fields
International Nuclear Information System (INIS)
Krommes, John A.
2001-01-01
A pedagogical review of the historical development and current status (as of early 2000) of systematic statistical theories of plasma turbulence is undertaken. Emphasis is on conceptual foundations and methodology, not practical applications. Particular attention is paid to equations and formalism appropriate to strongly magnetized, fully ionized plasmas. Extensive reference to the literature on neutral-fluid turbulence is made, but the unique properties and problems of plasmas are emphasized throughout. Discussions are given of quasilinear theory, weak-turbulence theory, resonance-broadening theory, and the clump algorithm. Those are developed independently, then shown to be special cases of the direct-interaction approximation (DIA), which provides a central focus for the article. Various methods of renormalized perturbation theory are described, then unified with the aid of the generating-functional formalism of Martin, Siggia, and Rose. A general expression for the renormalized dielectric function is deduced and discussed in detail. Modern approaches such as decimation and PDF methods are described. Derivations of DIA-based Markovian closures are discussed. The eddy-damped quasinormal Markovian closure is shown to be nonrealizable in the presence of waves, and a new realizable Markovian closure is presented. The test-field model and a realizable modification thereof are also summarized. Numerical solutions of various closures for some plasma-physics paradigms are reviewed. The variational approach to bounds on transport is developed. Miscellaneous topics include Onsager symmetries for turbulence, the interpretation of entropy balances for both kinetic and fluid descriptions, self-organized criticality, statistical interactions between disparate scales, and the roles of both mean and random shear. Appendices are provided on Fourier transform conventions, dimensional and scaling analysis, the derivations of nonlinear gyrokinetic and gyrofluid equations
Multi-group neutron transport theory
International Nuclear Information System (INIS)
Zelazny, R.; Kuszell, A.
1962-01-01
Multi-group neutron transport theory. In the paper the general theory of the application of the K. M. Case method to N-group neutron transport theory in plane geometry is given. The eigenfunctions (distributions) for the system of Boltzmann equations have been derived and the completeness theorem has been proved. By means of general solution two examples important for reactor and shielding calculations are given: the solution of a critical and albedo problem for a slab. In both cases the system of singular integral equations for expansion coefficients into a full set of eigenfunction distributions has been reduced to the system of Fredholm-type integral equations. Some results can be applied also to some spherical problems. (author) [fr
The Theory of Nearly Incompressible Magnetohydrodynamic Turbulence: Homogeneous Description
Zank, G. P.; Adhikari, L.; Hunana, P.; Shiota, D.; Bruno, R.; Telloni, D.; Avinash, K.
2017-09-01
The theory of nearly incompressible magnetohydrodynamics (NI MHD) was developed to understand the apparent incompressibility of the solar wind and other plasma environments, particularly the relationship of density fluctuations to incompressible manifestations of turbulence in the solar wind and interstellar medium. Of interest was the identification of distinct leading-order incompressible descriptions for plasma beta β ≫ 1 and β ∼ 1 or ≪ 1 environments. In the first case, the “dimensionality” of the MHD description is 3D whereas for the latter two, there is a collapse of dimensionality in that the leading-order incompressible MHD description is 2D in a plane orthogonal to the large-scale or mean magnetic field. Despite the success of NI MHD in describing fluctuations in a low-frequency plasma environment such as the solar wind, a basic turbulence description has not been developed. Here, we rewrite the NI MHD system in terms of Elsässer variables. We discuss the distinction that emerges between the three cases. However, we focus on the β ∼ 1 or ≪ 1 regimes since these are appropriate to the solar wind and solar corona. In both cases, the leading-order turbulence model describes 2D turbulence and the higher-order description corresponds to slab turbulence, which forms a minority component. The Elsäasser β ∼ 1 or ≪ 1 formulation exhibits the nonlinear couplings between 2D and slab components very clearly, and shows that slab fluctuations respond in a passive scalar sense to the turbulently evolving majority 2D component fluctuations. The coupling of 2D and slab fluctuations through the β ∼ 1 or ≪ 1 NI MHD description leads to a very natural emergence of the “Goldreich-Sridhar” critical balance scaling parameter, although now with a different interpretation. Specifically, the critical balance parameter shows that the energy flux in wave number space is a consequence of the intensity of Alfvén wave sweeping versus passive scalar
Relativistic transport theory for cosmic-rays
International Nuclear Information System (INIS)
Webb, G.M.
1985-01-01
Various aspects of the transport of cosmic-rays in a relativistically moving magnetized plasma supporting a spectrum of hydromagnetic waves that scatter the cosmic-rays are presented. A local Lorentz frame moving with the waves or turbulence scattering the cosmic-rays is used to specify the individual particle momentum. The comoving frame is in general a noninertial frame in which the observer's volume element is expanding and shearing, geometric energy change terms appear in the cosmic-ray transport equation which consist of the relativistic generalization of the adiabatic deceleration term and a further term involving the acceleration vector of the scatterers. A relativistic version of the pitch angle evolution equation, including the effects of adiabatic focussing, pitch angle scattering, and energy changes is presented
Final Report for Grant DE-FG03-99ER54551. [Turbulent plasma transport
International Nuclear Information System (INIS)
David Newman
2003-01-01
The approach to treating plasma transport based on the paradigm of self-organized criticality (SOC) is largely due to the success of this paradigm as an explanation for some of the discrepancies between theoretical predictions of turbulent transport and the experimental observations. Characteristics of SOC systems are that they maintain average profiles that are linearly stable and yet are able to sustain active transport dynamics (as often observed in experiment). The dominant transport scales in SOC systems are not the underlying local fluctuation scales but are the scales of the system (again as often observed). Finally, in the presence of sheared flow, the transport can exhibit a large reduction in system sized transport. This reduction is accompanied by an increase in fluctuation (bursty) events needed to maintain the constant flux, this too is something that has been observed
Transport theory of dissipative heavy-ion collisions
International Nuclear Information System (INIS)
Norenberg, W.
1979-01-01
The lectures present the formulation of a transport theory, the derivation of a practicable transport equation (Fokker-Planck equation) and the evaluation of transport coefficients for dissipative (or deeply inelastic) heavy-ion collisions. The applicability of the theoretical concept is tested with remarkable success in the analyses of various experimental information (mass transfer, angular-momentum dissipation and energy loss). Some critical remarks on the present situation of transport theories are added. Future developments are outlined. (author)
Transport theory of dissipative heavy-ion collisions
International Nuclear Information System (INIS)
Noerenberg, W.
1979-03-01
The lectures present the formulation of a transport theory, the derivation of a practicable transport equation (Fokker-Planck equation) and the evaluation of transport coefficients for dissipative (or deeply inelastic) heavyion collisions. The applicability of the theoretical concept is tested with remarkable success in the analyses of various experimental informations (mass transfer, angular-momentum dissipation and energy loss). Some critical remarks on the present situation of transport theories are added. Future developments are outlined. (orig.) [de
SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Energy Technology Data Exchange (ETDEWEB)
Lin, Zhihong [Univ. of California, Irvine, CA (United States)
2013-12-18
During the first year of the SciDAC gyrokinetic particle simulation (GPS) project, the GPS team (Zhihong Lin, Liu Chen, Yasutaro Nishimura, and Igor Holod) at the University of California, Irvine (UCI) studied the tokamak electron transport driven by electron temperature gradient (ETG) turbulence, and by trapped electron mode (TEM) turbulence and ion temperature gradient (ITG) turbulence with kinetic electron effects, extended our studies of ITG turbulence spreading to core-edge coupling. We have developed and optimized an elliptic solver using finite element method (FEM), which enables the implementation of advanced kinetic electron models (split-weight scheme and hybrid model) in the SciDAC GPS production code GTC. The GTC code has been ported and optimized on both scalar and vector parallel computer architectures, and is being transformed into objected-oriented style to facilitate collaborative code development. During this period, the UCI team members presented 11 invited talks at major national and international conferences, published 22 papers in peer-reviewed journals and 10 papers in conference proceedings. The UCI hosted the annual SciDAC Workshop on Plasma Turbulence sponsored by the GPS Center, 2005-2007. The workshop was attended by about fifties US and foreign researchers and financially sponsored several gradual students from MIT, Princeton University, Germany, Switzerland, and Finland. A new SciDAC postdoc, Igor Holod, has arrived at UCI to initiate global particle simulation of magnetohydrodynamics turbulence driven by energetic particle modes. The PI, Z. Lin, has been promoted to the Associate Professor with tenure at UCI.
On the theory of turbulent flame velocity
Bychkov, Vitaly; Akkerman, Vyacheslav; Petchenko, Arkady
2012-01-01
The renormalization ideas of self-similar dynamics of a strongly turbulent flame front are applied to the case of a flame with realistically large thermal expansion of the burning matter. In that case a flame front is corrugated both by external turbulence and the intrinsic flame instability. The analytical formulas for the velocity of flame propagation are obtained. It is demonstrated that the flame instability is of principal importance when the integral turbulent length scale is much large...
Physics of transport in Tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Asp, E.; Bourdelle, C.; Hoang, T.; Imbeaux, F.; Joffrin, E.; Litaudon, X.; Angioni, C.; Manini, A.; Peeter, A.; Ryter, F.; Baranov, Y.; Cordey, G.; McDonald, D.C.; Parail, V.; Valovic, M.; Thyagaraja, A.; Voitsekhovitch, I.; Budny, R.; Kirneva, N.; Hogeweij, D.; Nordman, H.; Weilland, J.; Tala, T.; Weisen, H.; Zabolotsky, A.
2004-01-01
This paper is an overview of recent results related to turbulent particle and heat transport, and triggering of Internal Transport Barriers. Particle transport is characterised by a pinch velocity that is found to be larger than the value predicted by theory of collisional transport (Ware pinch) in L-mode plasmas. Also it increases with magnetic shear. In H-mode, density peaking decreases with collisionality. Pinch velocity reaches the Ware value for large collision frequencies. Heat transport has made progress along two directions: dimensionless scaling laws and analysis of modulation experiments. Dimensionless scaling law of thermal confinement agrees with the prediction for electrostatic turbulence. Dependence with collisionality remains to be understood. Heat modulation experiments have been investigated in several devices using a critical gradient model, micro-stability analysis and predictive modelling. Thresholds and stiffness are correctly reproduced by stability analysis and modelling with Weiland model. Analysis with a critical gradient model leads to a large variability of stiffness. Finally the question of triggering Internal Transport Barriers has been addressed by analysing electron transport barriers. It is confirmed that negative magnetic shear combined with Shafranov shift is a robust stabilizing mechanism. However, some well established features of internal barriers are hardly explained by theory, in particular the role of low order rational values of the minimum safety factor, and the existence of multiple barriers. (authors)
Steady State Turbulent Transport in Magnetic Fusion Plasmas
International Nuclear Information System (INIS)
Lee, W.W.; Ethier, S.; Kolesnikov, R.; Wang, W.X.; Tang, W.M.
2007-01-01
For more than a decade, the study of microturbulence, driven by ion temperature gradient (ITG) drift instabilities in tokamak devices, has been an active area of research in magnetic fusion science for both experimentalists and theorists alike. One of the important impetus for this avenue of research was the discovery of the radial streamers associated the ITG modes in the early nineties using a Particle-In-Cell (PIC) code. Since then, ITG simulations based on the codes with increasing realism have become possible with the dramatic increase in computing power. The notable examples were the demonstration of the importance of nonlinearly generated zonal flows in regulating ion thermal transport and the transition from Bohm to GyroBoham scaling with increased device size. In this paper, we will describe another interesting nonlinear physical process associated with the parallel acceleration of the ions, that is found to play an important role for the steady state turbulent transport. Its discovery is again through the use of the modern massively parallel supercomputers
Particle Acceleration and Fractional Transport in Turbulent Reconnection
Isliker, Heinz; Pisokas, Theophilos; Vlahos, Loukas; Anastasiadis, Anastasios
2017-11-01
We consider a large-scale environment of turbulent reconnection that is fragmented into a number of randomly distributed unstable current sheets (UCSs), and we statistically analyze the acceleration of particles within this environment. We address two important cases of acceleration mechanisms when particles interact with the UCS: (a) electric field acceleration and (b) acceleration by reflection at contracting islands. Electrons and ions are accelerated very efficiently, attaining an energy distribution of power-law shape with an index 1-2, depending on the acceleration mechanism. The transport coefficients in energy space are estimated from test-particle simulation data, and we show that the classical Fokker-Planck (FP) equation fails to reproduce the simulation results when the transport coefficients are inserted into it and it is solved numerically. The cause for this failure is that the particles perform Levy flights in energy space, while the distributions of the energy increments exhibit power-law tails. We then use the fractional transport equation (FTE) derived by Isliker et al., whose parameters and the order of the fractional derivatives are inferred from the simulation data, and solving the FTE numerically, we show that the FTE successfully reproduces the kinetic energy distribution of the test particles. We discuss in detail the analysis of the simulation data and the criteria that allow one to judge the appropriateness of either an FTE or a classical FP equation as a transport model.
Particle Acceleration and Fractional Transport in Turbulent Reconnection
Energy Technology Data Exchange (ETDEWEB)
Isliker, Heinz; Pisokas, Theophilos; Vlahos, Loukas [Department of Physics, Aristotle University of Thessaloniki, GR-52124 Thessaloniki (Greece); Anastasiadis, Anastasios [Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236 Penteli (Greece)
2017-11-01
We consider a large-scale environment of turbulent reconnection that is fragmented into a number of randomly distributed unstable current sheets (UCSs), and we statistically analyze the acceleration of particles within this environment. We address two important cases of acceleration mechanisms when particles interact with the UCS: (a) electric field acceleration and (b) acceleration by reflection at contracting islands. Electrons and ions are accelerated very efficiently, attaining an energy distribution of power-law shape with an index 1–2, depending on the acceleration mechanism. The transport coefficients in energy space are estimated from test-particle simulation data, and we show that the classical Fokker–Planck (FP) equation fails to reproduce the simulation results when the transport coefficients are inserted into it and it is solved numerically. The cause for this failure is that the particles perform Levy flights in energy space, while the distributions of the energy increments exhibit power-law tails. We then use the fractional transport equation (FTE) derived by Isliker et al., whose parameters and the order of the fractional derivatives are inferred from the simulation data, and solving the FTE numerically, we show that the FTE successfully reproduces the kinetic energy distribution of the test particles. We discuss in detail the analysis of the simulation data and the criteria that allow one to judge the appropriateness of either an FTE or a classical FP equation as a transport model.
Final technical report on studies of plasma transport
International Nuclear Information System (INIS)
O'Neil, T.M.; Driscoll, C.F.; Malmberg, J.H.
1997-01-01
This document gives an overview of the scientific results obtained under the DOE grant, and references the journal articles which give more complete descriptions of the various topics. Recently, the research has been focused on 2-dimensional vortices and turbulence: experiments using a new camera-diagnosed electron plasma apparatus have given surprising results which both clarify and challenge theories. Here, the crossfield E x B flow of the electron plasma is directly analogous to the 2-d flow of an ideal fluid such as water, and may also give insight into more complicated poloidal flows exhibited in toroidal plasmas. The shear-flow instabilities, turbulence, and vortices can be accurately observed, and the free relaxation of this turbulence has been characterized. The physical processes underlying the complicated turbulent evolution can also be studied in more controlled near-linear regimes. The original experimental focus of this program was on radial particle transport from applied external field asymmetries. Here, this research program clearly identified the importance of the collective response of the plasma, giving smaller fields from shielding, or enhanced fields from resonant modes. Experiments and theory work have also elucidated the flow of a plasma along the magnetic field. Finally, some theory was pursued for direct application to fusion plasmas, and to gravitating gas clouds in astrophysics. This program was highly successful in clarifying basic plasma transport processes
Turbulence and abnormal transport in tokamak plasmas
International Nuclear Information System (INIS)
Garbet, X.
1988-06-01
The objective of this thesis is the study of plasma microinstabilities in linear and nonlinear tokamak regime. After a brief review of experimental results the theoretical tools used in this study are presented. A variational method founded on the existence of angular variables system and on action for charged particles in tokamak configurations is detailed. The correspondent functional extreme with regard to fluctuating electromagnetic field, is calculated analytically with taking into account the toroidal geometry. A numerical code, TORRID, has been constructed on this principle and the main instabilities, particularly ionic instabilities and microtearing, has been linearly studied. The most simple non linear methods are rewieved and applied at the microtearing instabilities. The quasilinear transport coefficients are deducted of an entropy minimum production principle. The ionic thermic conductivity and the viscosity are calculated for an ionic turbulence [fr
Turbulent transport across an interface between dry and humid air in a stratified environment
Gallana, Luca; de Santi, Francesca; di Savino, Silvio; Iovieno, Michele; Ricchiardone, Renzo; Tordella, Daniela
2014-11-01
The transport of energy and water vapor across a thin layer which separates two decaying isotropic turbulent flows with different kinetic energy and humidity is considered. The interface is placed in a shearless stratified environment in temporal decay. This system reproduces a few aspects of small scale turbulent transport across a dry air/moist air interface in an atmospheric like context. In our incompressible DNS at Reλ = 250 , Boussinesq's approximation is used for momentum and energy transport while the vapor is modeled as a passive scalar (Kumar, Schumacher & Shaw 2014). We investigated different stratification levels with an initial Fr between 0.8 and 8 in presence of a kinetic energy ratio equal to 7. As the buoyancy term becomes of the same order of the inertial ones, a spatial redistribution of kinetic energy, dissipation and vapor concentration is observed. This eventually leads to the onset of a well of kinetic energy in the low energy side of the mixing layer which blocks the entrainment of dry air. Results are discussed and compared with laboratory and numerical experiments. A posteriori estimates of the eventual compression/expansion of fluid particles inside the interfacial mixing layer are given (Nance & Durran 1994).
International Nuclear Information System (INIS)
Stefanovic, D.
1975-09-01
The research work of this contract was oriented towards the study of different methods in neutron transport theory. Authors studied analytical solution of the neutron slowing down transport equation and extension of this solution to include the energy dependence of the anisotropy of neutron scattering. Numerical solution of the fast and resonance transport equation for the case of mixture of scatterers including inelastic effects were also reviewed. They improved the existing formalism for treating the scattering of neutrons on water molecules; Identifying modal analysis as the Galerkin method, general conditions for modal technique applications have been investigated. Inverse problems in transport theory were considered. They obtained the evaluation of an advanced level distribution function, made improvement of the standard formalism for treating the inelastic scattering and development of a cluster nuclear model for this evaluation. Authors studied the neutron transport treatment in space energy groups for criticality calculation of a reactor core, and development of the Monte Carlo sampling scheme from the neutron transport equation
Energy Technology Data Exchange (ETDEWEB)
Cannon, Bradford E. [Physics Department, Florida State University, Tallahassee, FL 32306 (United States); Smith, Charles W.; Isenberg, Philip A.; Vasquez, Bernard J.; Joyce, Colin J. [Physics Department and Space Science Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824 (United States); Murphy, Neil [Jet Propulsion Laboratory, Mail Stop 180-600, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Nuno, Raquel G., E-mail: bc13h@my.fsu.edu, E-mail: Charles.Smith@unh.edu, E-mail: Phil.Isenberg@unh.edu, E-mail: Bernie.Vasquez@unh.edu, E-mail: cjl46@wildcats.unh.edu, E-mail: Neil.Murphy@jpl.nasa.gov, E-mail: raquel.nuno@asu.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States)
2014-06-01
The low-frequency magnetic waves that arise from the isotropization of newborn interstellar pickup ions (PUIs) are reasonably well described by linear and quasi-linear kinetic theory in so far as those theories predict the wave frequency and polarization in the spacecraft frame. Those theories fail to describe the scarce observability of the waves. Quasilinear theory predicts that the wave power should accumulate over long periods of time as the relatively weak kinetic instability slowly adds power to the observed spectrum. At the same time it has been argued that the same wave energy must serve as a secondary source of thermal ion heating in the outer heliosphere once the initial turbulence is depleted. To the extent that turbulent transport of the wave energy acts against the spectrally confined accumulation of wave energy, turbulence should be a limiting factor in observability. We argue that turbulence does limit the observability of the waves and we use turbulence theory to predict the observed wave energy. We compare this prediction against a database of 502 wave observations attributed to newborn interstellar PUIs observed by the Ulysses spacecraft.
International Nuclear Information System (INIS)
Cannon, Bradford E.; Smith, Charles W.; Isenberg, Philip A.; Vasquez, Bernard J.; Joyce, Colin J.; Murphy, Neil; Nuno, Raquel G.
2014-01-01
The low-frequency magnetic waves that arise from the isotropization of newborn interstellar pickup ions (PUIs) are reasonably well described by linear and quasi-linear kinetic theory in so far as those theories predict the wave frequency and polarization in the spacecraft frame. Those theories fail to describe the scarce observability of the waves. Quasilinear theory predicts that the wave power should accumulate over long periods of time as the relatively weak kinetic instability slowly adds power to the observed spectrum. At the same time it has been argued that the same wave energy must serve as a secondary source of thermal ion heating in the outer heliosphere once the initial turbulence is depleted. To the extent that turbulent transport of the wave energy acts against the spectrally confined accumulation of wave energy, turbulence should be a limiting factor in observability. We argue that turbulence does limit the observability of the waves and we use turbulence theory to predict the observed wave energy. We compare this prediction against a database of 502 wave observations attributed to newborn interstellar PUIs observed by the Ulysses spacecraft.
Anomalous energy exchange in the gBL and quasilinear theories
International Nuclear Information System (INIS)
Mynick, H.E.
1992-02-01
The rate of turbulence-induced energy exchange W o between species is computed in the framework of the quasilinear and gBL transport theories, and the relationship between these two theories, and the relationship between these two similar theories is thereby elucidated. For both theories, general formal expressions for W o are developed, and then applied to the trapped electron mode for illustration. The general expressions for W o in the two theories are formally closely related, but can yield predictions of very different magnitude in concrete applications. The fact that quasilinear theory is not valid for saturated steady-state turbulence gives rise to certain peculiarities in its predictions for this normal experimental situation, such as permitting energy to flow from the cooler to the hotter species, even in the limit of thermal equilibrium, where real-space gradients vanish. The gBL theory may be viewed as a modification of quasilinear theory to be valid for steady-state turbulence, keeping extra terms due to the self-consistent back reaction of particles on the fluctuations, which are just such as to eliminate these peculiarities
Dissipation range turbulent cascades in plasmas
International Nuclear Information System (INIS)
Terry, P. W.; Almagri, A. F.; Forest, C. B.; Nornberg, M. D.; Rahbarnia, K.; Sarff, J. S.; Fiksel, G.; Hatch, D. R.; Jenko, F.; Prager, S. C.; Ren, Y.
2012-01-01
Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
Furno, I.; Fasoli, A.; Avino, F.; Bovet, A.; Gustafson, K.; Iraji, D.; Labit, B.; Loizu, J.; Ricci, P.; Theiler, C.
2012-04-01
TORPEX is a toroidal device located at the CRPP-EPFL in Lausanne. In TORPEX, a vertical magnetic field superposed on a toroidal field creates helicoidal field lines with both ends terminating on the torus vessel. The turbulence driven by magnetic curvature and plasma gradients causes plasma transport in the radial direction while at the same time plasma is progressively lost along the field lines. The relatively simple magnetic geometry and diagnostic access of the TORPEX configuration facilitate the experimental study of low frequency instabilities and related turbulent transport, and make an accurate comparison between simulations and experiments possible. We first present a detailed investigation of electrostatic interchange turbulence, associated structures and their effect on plasma using high-resolution diagnostics of plasma parameters and wave fields throughout the whole device cross-section, fluid models and numerical simulations. Interchange modes nonlinearly develop blobs, radially propagating filaments of enhanced plasma pressure. Blob velocities and sizes are obtained from probe measurements using pattern recognition and are described by an analytical expression that includes ion polarization currents, parallel sheath currents and ion-neutral collisions. Then, we describe recent advances of a non-perturbative Li 6+ miniaturized ion source and a detector for the investigation of the interaction between supra thermal ions and interchange-driven turbulence. We present first measurements of the spatial and energy space distribution of the fast ion beam in different plasma scenarios, in which the plasma turbulence is fully characterized. The experiments are interpreted using two-dimensional fluid simulations describing the low-frequency interchange turbulence, taking into account the plasma source and plasma losses at the torus vessel. By treating fast ions as test particles, we integrate their equations of motion in the simulated electromagnetic fields, and
Inverse scattering problem in turbulent magnetic fluctuations
Directory of Open Access Journals (Sweden)
R. A. Treumann
2016-08-01
Full Text Available We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand–Levitan–Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes
Mathematical foundations of transport theory
International Nuclear Information System (INIS)
Ershov, Yu.I.; Shikhov, S.B.
1985-01-01
Foundations of mathematical transport theory are presented. Definitions and theorems of functional analysis are given. Linear kinetic equation of neutron transport in multiplication media is derived. A model of neutron interaction with nuclei of medium determining completely the coefficient properties in transport equation is described. Non-stationary problems regarding and without regard of d=e layed neutrons are analyzed. Results of solving Cauchy problem are discussed
Gyrokinetic simulations of ETG Turbulence*
Nevins, William
2005-10-01
Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence [1,2] produced different results despite similar plasma parameters. Ref.[1] differs from Ref.[2] in that [1] eliminates magnetically trapped particles ( r/R=0 ), while [2] retains magnetically trapped particles ( r/R 0.18 ). Differences between [1] and [2] have been attributed to insufficient phase-space resolution and novel physics associated with toroidicity and/or global simulations[2]. We have reproduced the results reported in [2] using a flux-tube, particle-in-cell (PIC) code, PG3EQ[3], thereby eliminating global effects as the cause of the discrepancy. We observe late-time decay of ETG turbulence and the steady-state heat transport in agreement with [2], and show this results from discrete particle noise. Discrete particle noise is a numerical artifact, so both the PG3EQ simulations reported here and those reported in Ref.[2] have little to say about steady-state ETG turbulence and the associated anomalous electron heat transport. Our attempts to benchmark PIC and continuum[4] codes at the plasma parameters used in Ref.[2] produced very large, intermittent transport. We will present an alternate benchmark point for ETG turbulence, where several codes reproduce the same transport levels. Parameter scans about this new benchmark point will be used to investigate the parameter dependence of ETG transport and to elucidate saturation mechanisms proposed in Refs.[1,2] and elsewhere[5-7].*In collaboration with A. Dimits (LLNL), J. Candy, C. Estrada-Mila (GA), W. Dorland (U of MD), F. Jenko, T. Dannert (Max-Planck Institut), and G. Hammett (PPPL). Work at LLNL performed for US DOE under Contract W7405-ENG-48.[1] F. Jenko and W. Dorland, PRL 89, 225001 (2002).[2] Z. Lin et al, 2004 Sherwood Mtg.; 2004 TTF Mtg.; Fusion Energy 2004 (IAEA, Vienna, 2005); Bull. Am. Phys. Soc. (November, 2004); 2005 TTF Mtg.; 2005 Sherwood Mtg.; Z. Lin, et al, Phys. Plasmas 12, 056125 (2005). [3] A.M. Dimits
Particle Settling in Low Energy Turbulence
Allen, Rachel; MacVean, Lissa; Tse, Ian; Mazzaro, Laura; Stacey, Mark; Variano, Evan
2014-11-01
Particle settling velocities can be altered by turbulence. In turbulence, dense particles may get trapped in convergent flow regions, and falling particles may be swept towards the downward side of turbulent eddies, resulting in enhanced settling velocities. The degree of velocity enhancement may depend on the Stokes number, the Rouse number, and the turbulent Reynolds number. In a homogeneous, isotropic turbulence tank, we tested the effects of particle size and type, suspended sediment concentration, and level of turbulence on the settling velocities of particles typically found in muddy estuaries. Two Acoustic Doppler Velocimeters (ADVs), separated vertically, measured turbulent velocities and suspended sediment concentrations, which yield condition dependent settling velocities, via ∂/á C ñ ∂ t = -∂/∂ z (ws á C ñ + á w ' C ' ñ) . These results are pertinent to fine sediment transport in estuaries, where high concentrations of suspended material are transported and impacted by low energy turbulence.
Directory of Open Access Journals (Sweden)
Li-ren Yu
2012-03-01
Full Text Available This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters. Three depth-averaged two-equation turbulence closure models, k˜−ε˜,k˜−w˜, and k˜−ω˜ , were used to close the non-simplified quasi-three dimensional hydrodynamic fundamental governing equations. The discretized equations were solved with the advanced multi-grid iterative method using non-orthogonal body-fitted coarse and fine grids with collocated variable arrangement. Except for steady flow computation, the processes of contaminant inpouring and plume development at the beginning of discharge, caused by a side-discharge of a tributary, have also been numerically investigated. The three depth-averaged two-equation closure models are all suitable for modeling strong mixing turbulence. The newly established turbulence models such as the k˜−ω˜ model, with a higher order of magnitude of the turbulence parameter, provide a possibility for improving computational precision.
Peterson, Jayson Luc
2011-10-01
Observations in the National Spherical Torus Experiment (NSTX) have found electron temperature gradients that greatly exceed the linear threshold for the onset for electron temperature gradient-driven (ETG) turbulence. These discharges, deemed electron internal transport barriers (e-ITBs), coincide with a reversal in the shear of the magnetic field and with a reduction in electron-scale density fluctuations, qualitatively consistent with earlier gyrokinetic predictions. To investigate this phenomenon further, we numerically model electron turbulence in NSTX reversed-shear plasmas using the gyrokinetic turbulence code GYRO. These first-of-a-kind nonlinear gyrokinetic simulations of NSTX e-ITBs confirm that reversing the magnetic shear can allow the plasma to reach electron temperature gradients well beyond the critical gradient for the linear onset of instability. This effect is very strong, with the nonlinear threshold for significant transport approaching three times the linear critical gradient in some cases, in contrast with moderate shear cases, which can drive significant ETG turbulence at much lower gradients. In addition to the experimental implications of this upshifted nonlinear critical gradient, we explore the behavior of ETG turbulence during reversed shear discharges. This work is supported by the SciDAC Center for the Study of Plasma Microturbulence, DOE Contract DE-AC02-09CH11466, and used the resources of NCCS at ORNL and NERSC at LBNL. M. Ono et al., Nucl. Fusion 40, 557 (2000).
Benchmarks with diffusion theory and transport theory
International Nuclear Information System (INIS)
Cunha Menezes Filho, A. da; Souza, A.L. de.
1984-01-01
The multiplication factor and some spectral indices for five critical assemblies (ZPR-6-7, ZPR-3-11, GODIVA, BIG-TEN and FLATTOP) are calculated by Diffusion and Transport Theory, with group constants generated by MC 2 (for diffusion calculations) and by NJOY (for transport calculations). The discrepancies encountered in the ZPR-6-7 spectra, can be tracked to the large differences in the elastic cross section for Iron, calculated by MC 2 and NJOY. (Author) [pt
One possible method of mathematical modeling of turbulent transport processes in plasma
International Nuclear Information System (INIS)
Skvortsova, Nina N.; Batanov, German M.; Petrov, Alexander E.; Pshenichnikov, Anton A.; Sarksyan, Karen A.; Kharchev, Nikolay K.; Bening, Vladimir E.; Korolev, Victor Yu.
2003-01-01
It is proposed to use the mathematical modeling of the increments of fluctuating plasma variables to analyzing the probability characteristics of turbulent transport processes in plasma. It is shown that, in plasma of the L-2M stellarator and the TAU-1 linear device, the increments of the process of local fluctuating particle flux are stochastic in nature and their distribution is a scale mixture of Gaussians. (author)
Theory of pseudo-classical confinement and transmutation to L-mode
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Yagi, M.; Fukuyama, A.; Azumi, M.
1993-05-01
Theory of the self-sustained turbulence is developed for resistive plasma in toroidal devices. Pseudo-classical confinement is obtained in the low temperature limit. As temperature increases, the current-diffusivity prevails upon resistivity, and the turbulence nature changes so as to recover the L-mode transport. Comparison with experimental observation on this transition is made. Hartmann number is also given. (author)
A mixed SOC-turbulence model for nonlocal transport and Lévy-fractional Fokker–Planck equation
DEFF Research Database (Denmark)
Juul Rasmussen, Jens; Milovanov, Alexander V.
2014-01-01
The phenomena of nonlocal transport in magnetically confined plasma are theoretically analyzed. A hybrid model is proposed, which brings together the notion of inverse energy cascade, typical of drift-wave- and two-dimensional fluid turbulence, and the ideas of avalanching behavior, associable...
Statistical properties of transport in plasma turbulence
DEFF Research Database (Denmark)
Naulin, V.; Garcia, O.E.; Nielsen, A.H.
2004-01-01
The statistical properties of the particle flux in different types of plasma turbulence models are numerically investigated using probability distribution functions (PDFs). The physics included in the models range from two-dimensional drift wave turbulence to three-dimensional MHD dynamics...
Directory of Open Access Journals (Sweden)
Roger Bruce Mason
2013-11-01
Full Text Available This article proposes that the external environment influences the choice of distribution tactics. Since businesses and markets are complex adaptive systems, using complexity theory to understand such environments is necessary, but it has not been widely researched. A qualitative case method using in-depth interviews investigated four successful, versus less successful, companies in turbulent versus stable environments. The results tentatively confirmed that the more successful company, in a turbulent market, sees distribution activities as less important than other aspects of the marketing mix, but uses them to stabilise customer relationships and to maintain distribution processes. These findings can benefit marketers by emphasising a new way to consider place activities. How marketers can be assisted, and suggestions for further research, are provided.
Nakano, Takeshi
The aim of this paper is to interpret Charles Horton Cooley's "Theory of Transportation", situating it in his interactionist sociology of communication and social process. Cooley defines transportation as a spatial and physical form of communication. He also develops a interactionist theory of valuation and articulates that value as an end of action is shaped an d transformed by communication and interaction. These insights suggest that transportation as a form of communication will change and develop economic society through transforming personal desires and values so as to change behaviours. Cooley's theory implies that an interactionist approach is useful for understanding the subjective side of phenomena of transportation.
Dynamics of phytoplankton blooms in turbulent vortex cells
DEFF Research Database (Denmark)
Lindemann, Christian; Visser, Andre; Mariani, Patrizio
2017-01-01
the effects of turbulent transport on the phytoplankton population growth and its spatial structure in a vertical two-dimensional vortex flow field. In particular, we focus on how turbulent flow velocities and sinking influence phytoplankton growth and biomass aggregation. Our results indicate that conditions...... can be maintained with increasing turbulent flow velocities, allowing the apparently counter-intuitive persistence of fast sinking phytoplankton populations in highly turbulent and deep mixed layers. These dynamics demonstrate the role of considering advective transport within a turbulent vortex...
Statistical Mechanics of Turbulent Flows
International Nuclear Information System (INIS)
Cambon, C
2004-01-01
This is a handbook for a computational approach to reacting flows, including background material on statistical mechanics. In this sense, the title is somewhat misleading with respect to other books dedicated to the statistical theory of turbulence (e.g. Monin and Yaglom). In the present book, emphasis is placed on modelling (engineering closures) for computational fluid dynamics. The probabilistic (pdf) approach is applied to the local scalar field, motivated first by the nonlinearity of chemical source terms which appear in the transport equations of reacting species. The probabilistic and stochastic approaches are also used for the velocity field and particle position; nevertheless they are essentially limited to Lagrangian models for a local vector, with only single-point statistics, as for the scalar. Accordingly, conventional techniques, such as single-point closures for RANS (Reynolds-averaged Navier-Stokes) and subgrid-scale models for LES (large-eddy simulations), are described and in some cases reformulated using underlying Langevin models and filtered pdfs. Even if the theoretical approach to turbulence is not discussed in general, the essentials of probabilistic and stochastic-processes methods are described, with a useful reminder concerning statistics at the molecular level. The book comprises 7 chapters. Chapter 1 briefly states the goals and contents, with a very clear synoptic scheme on page 2. Chapter 2 presents definitions and examples of pdfs and related statistical moments. Chapter 3 deals with stochastic processes, pdf transport equations, from Kramer-Moyal to Fokker-Planck (for Markov processes), and moments equations. Stochastic differential equations are introduced and their relationship to pdfs described. This chapter ends with a discussion of stochastic modelling. The equations of fluid mechanics and thermodynamics are addressed in chapter 4. Classical conservation equations (mass, velocity, internal energy) are derived from their
Nonlinear wave collapse and strong turbulence
International Nuclear Information System (INIS)
Robinson, P.A.
1997-01-01
The theory and applications of wave self-focusing, collapse, and strongly nonlinear wave turbulence are reviewed. In the last decade, the theory of these phenomena and experimental realizations have progressed rapidly. Various nonlinear wave systems are discussed, but the simplest case of collapse and strong turbulence of Langmuir waves in an unmagnetized plasma is primarily used in explaining the theory and illustrating the main ideas. First, an overview of the basic physics of linear waves and nonlinear wave-wave interactions is given from an introductory perspective. Wave-wave processes are then considered in more detail. Next, an introductory overview of the physics of wave collapse and strong turbulence is provided, followed by a more detailed theoretical treatment. Later sections cover numerical simulations of Langmuir collapse and strong turbulence and experimental applications to space, ionospheric, and laboratory plasmas, including laser-plasma and beam-plasma interactions. Generalizations to self-focusing, collapse, and strong turbulence of waves in other systems are also discussed, including nonlinear optics, solid-state systems, magnetized auroral and astrophysical plasmas, and deep-water waves. The review ends with a summary of the main ideas of wave collapse and strong-turbulence theory, a collection of open questions in the field, and a brief discussion of possible future research directions. copyright 1997 The American Physical Society
Measurement and theory of turbulence in RR Lyrae
International Nuclear Information System (INIS)
Benz, W.; Stellingwerf, R.F.
1985-01-01
CORAVEL observations of time-dependent turbulence in RR Lyrae are presented. Variation in the width of the mean velocity correlation function implies turbulent velocities that peak at 10 to 15 km/sec for a brief interval of phase near minimum radius. Comparison with a nonlinear pulsation model shows that these amplitudes of the turbulent velocity are expected near the hydrogen ionization zone, again only near minimum radius
Turbulence theories and modelling of fluids and plasmas
Energy Technology Data Exchange (ETDEWEB)
Yoshizawa, Akira; Yokoi, Nobumitsu [Institute of Industrial Science, Univ. of Tokyo, Tokyo (Japan); Itoh, Sanae-I. [Research Institute for Applied Mechanics, Kyushu Univ., Kasuga, Fukuoka (Japan); Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)
2001-04-01
Theoretical and heuristic modelling methods are reviewed for studying turbulence phenomena of fluids and plasmas. Emphasis is put on understanding of effects on turbulent characteristics due to inhomogeneities of field and plasma parameters. The similarity and dissimilarity between the methods for fluids and plasmas are sought in order to shed light on the properties that are shared or not by fluid and plasma turbulence. (author)
Perturbation theory and importance functions in integral transport formulations
International Nuclear Information System (INIS)
Greenspan, E.
1976-01-01
Perturbation theory expressions for the static reactivity derived from the flux, collision density, birth-rate density, and fission-neutron density formulations of integral transport theory, and from the integro-differential formulation, are intercompared. The physical meaning and relation of the adjoint functions corresponding to each of the five formulations are established. It is found that the first-order approximation of the perturbation expressions depends on the transport theory formulation and on the adjoint function used. The approximations of the integro-differential formulation corresponding to different first-order approximations of the integral transport theory formulations are identified. It is found that the accuracy of all first-order approximations of the integral transport formulations examined is superior to the accuracy of first-order integro-differential perturbation theory
Interchange turbulence model for the edge plasma in SOLEDGE2D-EIRENE
Energy Technology Data Exchange (ETDEWEB)
Bufferand, H.; Marandet, Y. [Aix-Marseille Universite, CNRS, PIIM, Marseille (France); Ciraolo, G.; Ghendrih, P.; Bucalossi, J.; Fedorczak, N.; Gunn, J.; Tamain, P. [CEA, IRFM, Saint-Paul-Lez-Durance (France); Colin, C.; Galassi, D.; Leybros, R.; Serre, E. [Aix-Marseille Universite, CNRS, M2P2, Marseille (France)
2016-08-15
Cross-field transport in edge tokamak plasmas is known to be dominated by turbulent transport. A dedicated effort has been made to simulate this turbulent transport from first principle models but the numerical cost to run these simulations on the ITER scale remains prohibitive. Edge plasma transport study relies mostly nowadays on so-called transport codes where the turbulent transport is taken into account using effective ad-hoc diffusion coefficients. In this contribution, we propose to introduce a transport equation for the turbulence intensity in SOLEDGE2D-EIRENE to describe the interchange turbulence properties. Going beyond the empirical diffusive model, this system automatically generates profiles for the turbulent transport and hence reduces the number of degrees of freedom for edge plasma transport codes. We draw inspiration from the k-epsilon model widely used in the neutral fluid community. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Nearly incompressible MHD turbulence in the solar wind
International Nuclear Information System (INIS)
Matthaeus, W.H.; Zhou, Y.
1989-01-01
Observational studies indicate that solar wind plasma and magnetic field fluctuations may be meaningfully viewed as an example of magnetohydrodynamic turbulence. This paper presents a brief summary of some relevant results of turbulence theory and reviews a turbulence style description of 'typical' solar wind conditions. Recent results, particularly those regarding the radial evolution of inertial range cross helicity, support the viewpoint that interplanetary turbulence is active and evolving with heliocentric distance. A number of observed properties can be understood by appeal to incompressible turbulence mechanisms. This connection may be understood by appeal to incompressible turbulence mechanisms. This connection may be understood in terms of theories of pseudosound density fluctuations and nearly incompressible magnetohydrodynamics, which are also reviewed here. Finally, we summarize a recent two-scale dynamical theory of the radial and temporal evolution of the turbulence, which may provide an additional framework for understanding the observations. (author). 49 refs
Turbulent transport reduction by E x B velocity shear during edge plasma biasing in tokamaks
Energy Technology Data Exchange (ETDEWEB)
Van Oost, G. [Dept. of Applied Physics, Ghent Univ., Ghent (Belgium); Adamek, J.; Antoni, V.; Balan, P.; Boedo, J.A.; Devynck, P.; Duran, I.; Eliseev, L.; Gunn, J.P.; Hron, M.; Ionita, C.; Jachmich, S.; Kirnev, G.S.; Martines, E.; Melnikov, A.; Peleman, P.; Schrittwieser, R.; Silva, C.; Stoeckel, J.; Tendler, M.; Varandas, C.; Van Schoor, M.; Vershkov, V.; Weynants, R.R.
2004-07-01
Experiments in the tokamaks TEXTOR, CASTOR, T-10 and ISTTOK have provided new and complementary evidence on the physics of the universal mechanism of E x B velocity shear stabilization of turbulence, concomitant transport barrier formation and radial conductivity by using various edge biasing techniques. (orig.)
Transport and turbulence in a magnetized argon plasma
International Nuclear Information System (INIS)
Vogels, J.M.M.J.
1984-01-01
Three aspects of the longitudinal motion of ionized and neutral particles in a hollow cathode arc are investigated. The longitudinal plasma momentum balance of the column has been investigated, we have studied the momentum balance in relation to turbulence and we have investigated the source properties of the cathode. The study of the plasma momentum balance contains two aspects: (1) to collect experimental data on ion drift velocities and temperatures with Fabry-Perot interferometry, on electron densities and temperatures with Thomson scattering or optical spectroscopy and on neutral densities with a collisional radiative model combined with the ion energy balance; (2) to check the (classical) theory of the momentum balance with these data. The coupling between these aspects has been investigated and found to be in good agreement. (Auth.)
Energy Technology Data Exchange (ETDEWEB)
Liu, Chun-Ho [The Hong Kong Polytechnic University, Kowloon (Hong Kong). Department of Building and Real Estate; Leung, Dennis Y.C. [The University of Hong Kong (Hong Kong). Department of Mechanical Engineering
2006-11-15
This study employs a direct numerical simulation (DNS) technique to study the flow, turbulence structure, and passive scalar plume transport behind line sources in an unstably stratified open channel flow. The scalar transport behaviors for five emission heights (z{sub s}=0, 0.25H, 0.5H, 0.75H, and H, where H is the channel height) at a Reynolds number of 3000, a Prandtl number and a Schmidt number of 0.72, and a Richardson number of -0.2 are investigated. The vertically meandering mean plume heights and dispersion coefficients calculated by the current DNS model agree well with laboratory results and field measurements in literature. It is found that the plume meandering is due to the movement of the positive and negative vertical turbulent scalar fluxes above and below the mean plume heights, respectively. These findings help explaining the plume meandering mechanism in the unstably stratified atmospheric boundary layer. (author)
Three points of view in transport theory
International Nuclear Information System (INIS)
Ruben, Panta Pazos; Tilio de Vilhena, M.
2001-01-01
A lot of efforts in Transport Theory is used to develop numerical methods or hybrid numerical-analytical techniques. We present in this work three points of view about transport problems. First the C0 semigroup approach, in which the free transport operator ψ → μ ∇ generates an strongly continuous semigroup. The operators operator ψ → σt and operator ψ → ∫ ∇ k(x,μ,μ' ψ(x,μ') dμ' are bounded operators, and by perturbation the transport operator ψ → μ ∇ ψ + σt ψ - K ψ also generates an strongly continuous semigroup. To prove the convergence of the approximations of a numerical methods to the exact solution we use the approximation theorem of C0 semi-groups in canonical form. In other way, the discrete schemes theory is employed in searching the rate of convergence of numerical techniques in transport theory. For 1D dependent of time transport problem and two-dimensional steady state problem we summarize some estimates, incorporating different boundary conditions. Finally we give a survey about the dynamical behavior of the SN approximations. In order to give a unified approach, some results illustrates the equivalence of the three points of views for the case of the steady-state transport problem for slab geometry. (author)
Dynamic structure in self-sustained turbulence
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Yagi, M.; Fukuyama, A.
1995-06-01
Dynamical equation for the self-sustained and pressure-driven turbulence in toroidal plasmas is derived. The growth rate of the dressed-test mode, which belongs to the subcritical turbulence, is obtained as a function of the turbulent transport coefficient. In the limit of the low fluctuation level, the mode has the feature of the nonlinear instability and shows the explosive growth. The growth rate vanishes when the driven transport reaches to the stationarily-turbulent level. The stationary solution is thermodynamically stable. The characteristic time, by which the stationary and self-sustained turbulence is established, scales with the ion-sound transit time and is accelerated by the bad magnetic curvature. Influences of the pressure gradient as well as the radial electric field inhomogeneity are quantified. (author)
Scalar transport across the turbulent/non-turbulent interface in jets: Schmidt number effects
Silva, Tiago S.; B. da Silva, Carlos; Idmec Team
2016-11-01
The dynamics of a passive scalar field near a turbulent/non-turbulent interface (TNTI) is analysed through direct numerical simulations (DNS) of turbulent planar jets, with Reynolds numbers ranging from 142 <= Reλ <= 246 , and Schmidt numbers from 0 . 07 <= Sc <= 7 . The steepness of the scalar gradient, as observed from conditional profiles near the TNTI, increases with the Schmidt number. Conditional scalar gradient budgets show that for low and moderate Schmidt numbers a diffusive superlayer emerges at the TNTI, where the scalar gradient diffusion dominates, while the production is negligible. For low Schmidt numbers the growth of the turbulent front is commanded by the molecular diffusion, whereas the scalar gradient convection is negligible. The authors acknowledge the Laboratory for Advanced Computing at University of Coimbra for providing HPC, computing, consulting resources that have contributed to the research results reported within this paper. URL http://www.lca.uc.pt.
Why turbulence sustains in supercritically stratified free atmosphere?
Zilitinkevich, Sergej
2016-04-01
It is widely believed that in very stable stratifications, at Richardson numbers (Ri) exceeding critical value Ric ˜ 0.25 turbulence decays and flow becomes laminar. This is so at low Reynolds numbers (Re), e.g., in lab experiments; but this is not true in very-high-Re geophysical flows. Free atmosphere and deep ocean are turbulent in spite of strongly supercritical stratifications: 1 role of negative buoyancy flux, Fb > 0, in turbulence energetics was treated in terms of the turbulent kinetic energy (TKE) budget equation and understood as just consumption of TKE by the buoyancy forces. This has led to the conclusion that sufficiently strong static stability causes the negative buoyancy flux sufficiently strong to exceed the TKE generation rate and thus to kill turbulence. However, considering TKE equation together with budget equation for turbulent potential energy (TPE proportional to the squared buoyancy fluctuations) shows that the role of Fb in turbulence energetics is nothing but conversion of TKE into TPE (Fb just quantifies the rate of this conversion); so that Fb does not affect total turbulent energy (TTE = TKE + TPE). Moreover, as follows from the buoyancy-flux budget equation, TPE generates positive (directed upward) buoyancy flux irrespective of the sign of the buoyancy gradient. Indeed, the warmer fluid particles (with positive buoyancy fluctuation) rise up, whereas the cooler particles sink down, so that both contribute to the positive buoyancy flux opposing to the usual, negative flux generated by mean buoyancy gradient. In this context, strengthening the negative buoyancy flux leads to decreasing TKE and increasing TPE. The latter enhances the counter-gradient share of the total flux, thus reduces |Fb| and, eventually, increases TKE. The above negative feedback was disregarded in the conventional concept of down-gradient turbulent transport. This mechanism imposes a limit on the maximal (independent of the buoyancy gradient) value of |Fb| and thus
Magnetohydrodynamic turbulence revisited
International Nuclear Information System (INIS)
Goldreich, P.; Sridhar, S.
1997-01-01
In 1965, Kraichnan proposed that MHD turbulence occurs as a result of collisions between oppositely directed Alfvacute en wave packets. Recent work has generated some controversy over the nature of nonlinear couplings between colliding Alfvacute en waves. We find that the resolution to much of the confusion lies in the existence of a new type of turbulence, intermediate turbulence, in which the cascade of energy in the inertial range exhibits properties intermediate between those of weak and strong turbulent cascades. Some properties of intermediate MHD turbulence are the following: (1) in common with weak turbulent cascades, wave packets belonging to the inertial range are long-lived; (2) however, components of the strain tensor are so large that, similar to the situation in strong turbulence, perturbation theory is not applicable; (3) the breakdown of perturbation theory results from the divergence of neighboring field lines due to wave packets whose perturbations in velocity and magnetic fields are localized, but whose perturbations in displacement are not; (4) three-wave interactions dominate individual collisions between wave packets, but interactions of all orders n≥3 make comparable contributions to the intermediate turbulent energy cascade; (5) successive collisions are correlated since wave packets are distorted as they follow diverging field lines; (6) in common with the weak MHD cascade, there is no parallel cascade of energy, and the cascade to small perpendicular scales strengthens as it reaches higher wavenumbers; (7) for an appropriate weak excitation, there is a natural progression from a weak, through an intermediate, to a strong cascade. copyright 1997 The American Astronomical Society
Ristorcelli, J. R.
1995-01-01
The mathematical consequences of a few simple scaling assumptions about the effects of compressibility are explored using a simple singular perturbation idea and the methods of statistical fluid mechanics. Representations for the pressure-dilation and dilatational dissipation covariances appearing in single-point moment closures for compressible turbulence are obtained. While the results are expressed in the context of a second-order statistical closure they provide some interesting and very clear physical metaphors for the effects of compressibility that have not been seen using more traditional linear stability methods. In the limit of homogeneous turbulence with quasi-normal large-scales the expressions derived are - in the low turbulent Mach number limit - asymptotically exact. The expressions obtained are functions of the rate of change of the turbulence energy, its correlation length scale, and the relative time scale of the cascade rate. The expressions for the dilatational covariances contain constants which have a precise and definite physical significance; they are related to various integrals of the longitudinal velocity correlation. The pressure-dilation covariance is found to be a nonequilibrium phenomena related to the time rate of change of the internal energy and the kinetic energy of the turbulence. Also of interest is the fact that the representation for the dilatational dissipation in turbulence, with or without shear, features a dependence on the Reynolds number. This article is a documentation of an analytical investigation of the implications of a pseudo-sound theory for the effects of compressibility.
Theory of neoclassical resistivity-gradient-driven turbulence
International Nuclear Information System (INIS)
Kwon, O.J.; Diamond, P.H.; Hahm, T.S.
1988-12-01
It is shown that rippling instabilities can tap the density gradient expansion free energy source through the density dependence of the neoclassical resistivity. Linear analyses show that the region where neoclassical rippling modes are significantly excited extends from the edge of the plasma to the region where ν/sub *e/ ≤ 1. Since these modes are non-dispersive, diamagnetic effects are negligible in comparison to the nonlinear decorrelation rate at saturation. Thus, the relevant regime is the 'strong turbulence' regime. The turbulent radial diffusivities of the temperature and the density are obtained as eigenvalues of the renormalized eigenmode equations at steady state. The density gradient acts to enhance the level of turbulence, compared to that driven by the temperature gradient alone. The saturated turbulent state is characterized by: current decoupling, the breakdown of Boltzmann relation, a radial mode scale of density fluctuations exceeding that of temperature fluctuations, implying that density diffusivity exceeds temperature diffusivity, and that density fluctuation levels exceed temperature fluctuation levels. Magnetic fluctuation levels are negligible. 29 refs., 1 fig
Research on new methods in transport theory
International Nuclear Information System (INIS)
Stefanovicj, D.
1975-01-01
Neutron transport theory is the basis for development of reactor theory and reactor calculational methods. It has to be acknowledged that recent applications of these disciplines have influenced considerably the development of power reactor concepts and technology. However, these achievements were implemented in a rather heuristic way, since the satisfaction of design demands were of utmost importance. Often this kind of approach turns out to be very restrictive and not even adequate for rather typical reactor applications. Many aspects and techniques of reactor theory and calculations ought to be reevaluated and/or reformulated on the more sound physical and mathematical foundations. At the same time, new reactor concepts and operational demands give rise to more sophisticated and complex design requirements. These new requirements can be met only by the development of new design techniques, which in the case of reactor neutronic calculation lead directly to the advanced transport theory methods. In addition, the rapid development of computer technology opens new opportunities for applications of advanced transport theory in practical calculations
Wall roughness induces asymptotic ultimate turbulence
Zhu, Xiaojue; Verschoof, Ruben Adriaan; Bakhuis, Dennis; Huisman, Sander Gerard; Verzicco, Roberto; Sun, Chao; Lohse, Detlef
2018-01-01
Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by
Potential-vorticity inversion and the wave-turbulence jigsaw: some recent clarifications
Directory of Open Access Journals (Sweden)
M. E. McIntyre
2008-06-01
Full Text Available Two key ideas stand out as crucial to understanding atmosphere-ocean dynamics, and the dynamics of other planets including the gas giants. The first key idea is the invertibility principle for potential vorticity (PV. Without it, one can hardly give a coherent account of even so important and elementary a process as Rossby-wave propagation, going beyond the simplest textbook cases. Still less can one fully understand nonlinear processes like the self-sharpening or narrowing of jets – the once-mysterious "negative viscosity" phenomenon. The second key idea, also crucial to understanding jets, might be summarized in the phrase "there is no such thing as turbulence without waves", meaning Rossby waves especially. Without this idea one cannot begin to make sense of, for instance, momentum budgets and eddy momentum transports in complex large-scale flows. Like the invertibility principle the idea has long been recognized, or at least adumbrated. However, it is worth articulating explicitly if only because it can be forgotten when, in the usual way, we speak of "turbulence" and "turbulence theory" as if they were autonomous concepts. In many cases of interest, such as the well-studied terrestrial stratosphere, reality is more accurately described as a highly inhomogeneous "wave-turbulence jigsaw puzzle" in which wavelike and turbulent regions fit together and crucially affect each other's evolution. This modifies, for instance, formulae for the Rhines scale interpreted as indicating the comparable importance of wavelike and turbulent dynamics. Also, weakly inhomogeneous turbulence theory is altogether inapplicable. For instance there is no scale separation. Eddy scales are not much smaller than the sizes of the individual turbulent regions in the jigsaw. Here I review some recent progress in clarifying these ideas and their implications.
International Nuclear Information System (INIS)
Banerjee, Tirtha; De Roo, Frederik; Mauder, Matthias
2017-01-01
Parameterizations of biosphere-atmosphere interaction processes in climate models and other hydrological applications require characterization of turbulent transport of momentum and scalars between vegetation canopies and the atmosphere, which is often modeled using a turbulent analogy to molecular diffusion processes. However, simple flux-gradient approaches (K-theory) fail for canopy turbulence. One cause is turbulent transport by large coherent eddies at the canopy scale, which can be linked to sweep-ejection events, and bear signatures of non-local organized eddy motions. K-theory, that parameterizes the turbulent flux or stress proportional to the local concentration or velocity gradient, fails to account for these non-local organized motions. The connection to sweep-ejection cycles and the local turbulent flux can be traced back to the turbulence triple moment (C ′ W ′ W ′ )-bar. In this work, we use large-eddy simulation to investigate the diagnostic connection between the failure of K-theory and sweep-ejection motions. Analyzed schemes are quadrant analysis (QA) and a complete and incomplete cumulant expansion (CEM and ICEM) method. The latter approaches introduce a turbulence timescale in the modeling. Furthermore, we find that the momentum flux needs a different formulation for the turbulence timescale than the sensible heat flux. In conclusion, accounting for buoyancy in stratified conditions is also deemed to be important in addition to accounting for non-local events to predict the correct momentum or scalar fluxes.
Three points of view in transport theory
Energy Technology Data Exchange (ETDEWEB)
Ruben, Panta Pazos [Faculdade de Matematica, PUCRS, Porto Alegre, RS (Brazil); Tilio de Vilhena, M. [Instituto de Matematica, UFRGS, Porto Alegre, RS (Brazil)
2001-07-01
A lot of efforts in Transport Theory is used to develop numerical methods or hybrid numerical-analytical techniques. We present in this work three points of view about transport problems. First the C0 semigroup approach, in which the free transport operator {psi} {yields} {mu} {nabla} generates an strongly continuous semigroup. The operators operator {psi} {yields} {sigma}t and operator {psi} {yields} {integral} {nabla} k(x,{mu},{mu}') {psi}(x,{mu}') d{mu}' are bounded operators, and by perturbation the transport operator {psi} {yields} {mu} {nabla} {psi} + {sigma}t {psi} - K {psi} also generates an strongly continuous semigroup. To prove the convergence of the approximations of a numerical methods to the exact solution we use the approximation theorem of C0 semi-groups in canonical form. In other way, the discrete schemes theory is employed in searching the rate of convergence of numerical techniques in transport theory. For 1D dependent of time transport problem and two-dimensional steady state problem we summarize some estimates, incorporating different boundary conditions. Finally we give a survey about the dynamical behavior of the SN approximations. In order to give a unified approach, some results illustrates the equivalence of the three points of views for the case of the steady-state transport problem for slab geometry. (author)
Mathematical foundations of transport theory
International Nuclear Information System (INIS)
Ershov, Yu.I.; Shikhov, S.B.
1985-01-01
Main items of application of the operator equations analyzing method in transport theory problems are considered. The mathematical theory of a reactor critical state is presented. Theorems of existence of positive solutions of non-linear non-stationary equations taking into account the temperature and xenon feedbacks are proved. Conditions for stability and asymptotic stability of steady-state regimes for different distributed models of a nuclear reactor are obtained on the basis of the modern operator perturbation theory, certain problems on control using an absorber are considered
Schertzer, D.; Falgarone, E.
appropriate editorial structure, in particular a large number of editors covering a wide range of methodologies, expertises and schools. At least two of its sections (Scaling and Multifractals, Turbulence and Diffusion) were directly related to the topics of the workshop, in any case contributors were invited to choose their editor freely. 2 Goals of the Workshop The objective of this meeting was to enhance the confrontation between turbulence theories and empirical data from geophysics and astrophysics fluids with very high Reynolds numbers. The importance of these data seems to have often been underestimated for the evaluation of theories of fully developed turbulence, presumably due to the fact that turbulence does not appear as pure as in laboratory experiments. However, they have the great advantage of giving access not only to very high Reynolds numbers (e.g. 1012 for atmospheric data), but also to very large data sets. It was intended to: (i) provide an overview of the diversity of potentially available data, as well as the necessary theoretical and statistical developments for a better use of these data (e.g. treatment of anisotropy, role of processes which induce other nonlinearities such as thermal instability, effect of magnetic field and compressibility ... ), (ii) evaluate the means of discriminating between different theories (e.g. multifractal intermittency models) or to better appreciate the relevance of different notions (e.g. Self-Organized Criticality) or phenomenology (e.g. filaments, structures), (iii) emphasise the different obstacles, such as the ubiquity of catastrophic events, which could be overcome in the various concerned disciplines, thanks to theoretical advances achieved. 3 Outlines of the Workshop During the two days of the workshop, the series of presentations covered many manifestations of turbulence in geophysics, including: oceans, troposphere, stratosphere, very high atmosphere, solar wind, giant planets, interstellar clouds... up to the
Directory of Open Access Journals (Sweden)
D. Schertzer
1996-01-01
. It had an appropriate editorial structure, in particular a large number of editors covering a wide range of methodologies, expertises and schools. At least two of its sections (Scaling and Multifractals, Turbulence and Diffusion were directly related to the topics of the workshop, in any case contributors were invited to choose their editor freely. 2 Goals of the Workshop The objective of this meeting was to enhance the confrontation between turbulence theories and empirical data from geophysics and astrophysics fluids with very high Reynolds numbers. The importance of these data seems to have often been underestimated for the evaluation of theories of fully developed turbulence, presumably due to the fact that turbulence does not appear as pure as in laboratory experiments. However, they have the great advantage of giving access not only to very high Reynolds numbers (e.g. 1012 for atmospheric data, but also to very large data sets. It was intended to: (i provide an overview of the diversity of potentially available data, as well as the necessary theoretical and statistical developments for a better use of these data (e.g. treatment of anisotropy, role of processes which induce other nonlinearities such as thermal instability, effect of magnetic field and compressibility ... , (ii evaluate the means of discriminating between different theories (e.g. multifractal intermittency models or to better appreciate the relevance of different notions (e.g. Self-Organized Criticality or phenomenology (e.g. filaments, structures, (iii emphasise the different obstacles, such as the ubiquity of catastrophic events, which could be overcome in the various concerned disciplines, thanks to theoretical advances achieved. 3 Outlines of the Workshop During the two days of the workshop, the series of presentations covered many manifestations of turbulence in geophysics, including: oceans, troposphere, stratosphere, very high atmosphere, solar wind, giant planets, interstellar clouds
International Nuclear Information System (INIS)
Krommes, J.A.
2000-01-01
Recent results and future challenges in the systematic analytical description of plasma turbulence are described. First, the importance of statistical realizability is stressed, and the development and successes of the Realizable Markovian Closure are briefly reviewed. Next, submarginal turbulence (linearly stable but nonlinearly self-sustained fluctuations) is considered and the relevance of nonlinear instability in neutral-fluid shear flows to submarginal turbulence in magnetized plasmas is discussed. For the Hasegawa-Wakatani equations, a self-consistency loop that leads to steady-state vortex regeneration in the presence of dissipation is demonstrated and a partial unification of recent work of Drake (for plasmas) and of Waleffe (for neutral fluids) is given. Brief remarks are made on the difficulties facing a quantitatively accurate statistical description of submarginal turbulence. Finally, possible connections between intermittency, submarginal turbulence, and self-organized criticality (SOC) are considered and outstanding questions are identified
Exact Theory of Compressible Fluid Turbulence
Drivas, Theodore; Eyink, Gregory
2017-11-01
We obtain exact results for compressible turbulence with any equation of state, using coarse-graining/filtering. We find two mechanisms of turbulent kinetic energy dissipation: scale-local energy cascade and ``pressure-work defect'', or pressure-work at viscous scales exceeding that in the inertial-range. Planar shocks in an ideal gas dissipate all kinetic energy by pressure-work defect, but the effect is omitted by standard LES modeling of pressure-dilatation. We also obtain a novel inverse cascade of thermodynamic entropy, injected by microscopic entropy production, cascaded upscale, and removed by large-scale cooling. This nonlinear process is missed by the Kovasznay linear mode decomposition, treating entropy as a passive scalar. For small Mach number we recover the incompressible ``negentropy cascade'' predicted by Obukhov. We derive exact Kolmogorov 4/5th-type laws for energy and entropy cascades, constraining scaling exponents of velocity, density, and internal energy to sub-Kolmogorov values. Although precise exponents and detailed physics are Mach-dependent, our exact results hold at all Mach numbers. Flow realizations at infinite Reynolds are ``dissipative weak solutions'' of compressible Euler equations, similarly as Onsager proposed for incompressible turbulence.
Turbulent equipartitions in two dimensional drift convection
International Nuclear Information System (INIS)
Isichenko, M.B.; Yankov, V.V.
1995-01-01
Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
Particle transport methods for LWR dosimetry developed by the Penn State transport theory group
International Nuclear Information System (INIS)
Haghighat, A.; Petrovic, B.
1997-01-01
This paper reviews advanced particle transport theory methods developed by the Penn State Transport Theory Group (PSTTG) over the past several years. These methods have been developed in response to increasing needs for accuracy of results and for three-dimensional modeling of nuclear systems
Heat Transport Enhancement of Turbulent Thermal Convection by Inserted Channels
Xia, Ke-Qing; Zhang, Lu
2017-11-01
We report an experimental study on the heat transport properties of turbulent Rayleigh Benard Convection (RBC) in a rectangular cell with two types of 3D-printed structures inserted inside. The first one splits the original rectangular cell into 60 identical sub cells whose aspect ratio is 1:1:10 (length, width, height). The second one splits the cell into 30 sub cells, each with a 1:2:10 aspect ratio and a baffle in the center. We find that for large Rayleigh numbers (Ra), the Nusselt numbers (Nu) of both structures increase compared with that of the empty rectangular cell. An enhancement in Nu as much as 20% is found for the second type of insertion at Rayleigh number 2 ×109 . Moreover, the Nu-Ra scaling shows a transition with both geometries. The particle image velocimetry (PIV) measurement within a single sub unit indicates that the transition may be related to the laminar to turbulent transition in flow field. Direct numerical simulations (DNS) confirm the experimental results. Our results demonstrate the potential in using insertions to enhance passive heat transfer. This work was supported by the Research Grants Council (RGC) of HKSAR (Nos. CUHK404513 and CUHK14301115).
Multiscaling Dynamics of Impurity Transport in Drift-Wave Turbulence
International Nuclear Information System (INIS)
Futatani, S.; Benkadda, S.; Nakamura, Y.; Kondo, K.
2008-01-01
Intermittency effects and the associated multiscaling spectrum of exponents are investigated for impurities advection in tokamak edge plasmas. The two-dimensional Hasagawa-Wakatani model of resistive drift-wave turbulence is used as a paradigm to describe edge tokamak turbulence. Impurities are considered as a passive scalar advected by the plasma turbulent flow. The use of the extended self-similarity technique shows that the structure function relative scaling exponent of impurity density and vorticity follows the She-Leveque model. This confirms the intermittent character of the impurities advection in the turbulent plasma flow and suggests that impurities are advected by vorticity filaments
Analysis of zonal flow bifurcations in 3D drift wave turbulence simulations
International Nuclear Information System (INIS)
Kammel, Andreas
2012-01-01
The main issue of experimental magnetic fusion devices lies with their inherently high turbulent transport, preventing long-term plasma confinement. A deeper understanding of the underlying transport processes is therefore desirable, especially in the high-gradient tokamak edge which marks the location of the drift wave regime as well as the outer boundary of the still badly understood high confinement mode. One of the most promising plasma features possibly connected to a complete bifurcation theory for the transition to this H-mode is found in large-scale phenomena capable of regulating radial transport through vortex shearing - i.e. zonal flows, linearly stable large-scale poloidal vector E x vector B-modes based on radial flux surface averages of the potential gradient generated through turbulent self-organization. Despite their relevance, few detailed turbulence studies of drift wave-based zonal flows have been undertaken, and none of them have explicitly targeted bifurcations - or, within a resistive sheared-slab environment, observed zonal flows at all. In this work, both analytical means and the two-fluid code NLET are used to analyze a reduced set of Hasegawa-Wakatani equations, describing a sheared collisional drift wave system without curvature. The characteristics of the drift waves themselves, as well as those of the drift wave-based zonal flows and their retroaction on the drift wave turbulence are examined. The single dimensionless parameter ρ s proposed in previous analytical models is examined numerically and shown to divide the drift wave scale into two transport regimes, the behavioral characteristics of which agree perfectly with theoretical expectations. This transport transition correlates with a transition from pure drift wave turbulence at low ρ s into the high-ρ s zonal flow regime. The associated threshold has been more clearly identified by tracing it back to a tipping of the ratio between a newly proposed frequency gradient length at
Aspects of turbulence in nonlinear systems. Year one final report, February 1-October 31, 1985
International Nuclear Information System (INIS)
Frieman, E.A.; Hagan, W.K.
1985-07-01
Gyrokinetic theory was developed from a pragmatic point of view. Since our interest in gyrokinetic theory is to ultimately shed some light on drift wave turbulence and anomalous transport, we have tried from the outset to incorporate into our theory some of the characteristics of these phenomena as measured in experiments. This approach has led to a theory in which two time and two space scales naturally emerge. We were also led to express the full nonlinear distribution function as an equilibrium part and pertubation part, with the equilibrium being driven by the higher order interactions of the rapid fluctuations
Navier-Stokes equations and turbulence
Foias, C; Manley, Oscar; Rosa, Ricardo M S; Temam, R
2001-01-01
This book presents the mathematical theory of turbulence to engineers and physicists, and the physical theory of turbulence to mathematicians. The mathematical technicalities are kept to a minimum within the book, enabling the language to be at a level understood by a broad audience. Each chapter is accompanied by appendices giving full details of the mathematical proofs and subtleties. This unique presentation should ensure a volume of interest to mathematicians, engineers, and physicists.
On the theory of weak turbulence for the nonlinear Schrödinger equation
Escobedo, M
2015-01-01
The authors study the Cauchy problem for a kinetic equation arising in the weak turbulence theory for the cubic nonlinear Schrödinger equation. They define suitable concepts of weak and mild solutions and prove local and global well posedness results. Several qualitative properties of the solutions, including long time asymptotics, blow up results and condensation in finite time are obtained. The authors also prove the existence of a family of solutions that exhibit pulsating behavior.
Cascade of circulations in fluid turbulence.
Eyink, Gregory L
2006-12-01
Kelvin's theorem on conservation of circulations is an essential ingredient of Taylor's theory of turbulent energy dissipation by the process of vortex-line stretching. In previous work, we have proposed a nonlinear mechanism for the breakdown of Kelvin's theorem in ideal turbulence at infinite Reynolds number. We develop here a detailed physical theory of this cascade of circulations. Our analysis is based upon an effective equation for large-scale coarse-grained velocity, which contains a turbulent-induced vortex force that can violate Kelvin's theorem. We show that singularities of sufficient strength, which are observed to exist in turbulent flow, can lead to nonvanishing dissipation of circulation for an arbitrarily small coarse-graining length in the effective equations. This result is an analog for circulation of Onsager's theorem on energy dissipation for singular Euler solutions. The physical mechanism of the breakdown of Kelvin's theorem is diffusion of lines of large-scale vorticity out of the advected loop. This phenomenon can be viewed as a classical analog of the Josephson-Anderson phase-slip phenomenon in superfluids due to quantized vortex lines. We show that the circulation cascade is local in scale and use this locality to develop concrete expressions for the turbulent vortex force by a multiscale gradient expansion. We discuss implications for Taylor's theory of turbulent dissipation and we point out some related cascade phenomena, in particular for magnetic flux in magnetohydrodynamic turbulence.
International Nuclear Information System (INIS)
Mika, J.
1975-09-01
Originally the work was oriented towards two main topics: a) difference and integral methods in neutron transport theory. Two computers were used for numerical calculations GIER and CYBER-72. During the first year the main effort was shifted towards basic theoretical investigations. At the first step the ANIS code was adopted and later modified to check various finite difference approaches against each other. Then the general finite element method and the singular perturbation method were developed. The analysis of singularities of the one-dimensional neutron transport equation in spherical geometry has been done and presented. Later the same analysis for the case of cylindrical symmetry has been carried out. The second and the third year programme included the following topics: 1) finite difference methods in stationary neutron transport theory; 2)mathematical fundamentals of approximate methods for solving the transport equation; 3) singular perturbation method for the time-dependent transport equation; 4) investigation of various iterative procedures in reactor calculations. This investigation will help to better understanding of the mathematical basis for existing and developed numerical methods resulting in more effective algorithms for reactor computer codes
Can one extract source radii from transport theories?
International Nuclear Information System (INIS)
Aichelin, J.
1996-01-01
To known the space time evolution of a heavy ion reaction is of great interest especially in cases where the measured spectra do not allow to ascertain the underlying reaction mechanism. In recent times it became popular to believe that the comparison of Hanbury-Brown Twiss correlation functions obtained from classical or semiclassical transport theories, like Boltzmann Uehling Uhlenbeck (BUU), Quantum Molecular Dynamics (QMD), VENUS or ARC, with experiments may provide this insight. It is the purpose of this article to show that this is not the case. None of these transport theories provides a reliable time evolution of those quantities which are mandatory for a correct calculation of the correlation function. The reason for this failure is different for the different transport theories. (author)
Can one extract source radii from transport theories?
Energy Technology Data Exchange (ETDEWEB)
Aichelin, J.
1996-12-31
To known the space time evolution of a heavy ion reaction is of great interest especially in cases where the measured spectra do not allow to ascertain the underlying reaction mechanism. In recent times it became popular to believe that the comparison of Hanbury-Brown Twiss correlation functions obtained from classical or semiclassical transport theories, like Boltzmann Uehling Uhlenbeck (BUU), Quantum Molecular Dynamics (QMD), VENUS or ARC, with experiments may provide this insight. It is the purpose of this article to show that this is not the case. None of these transport theories provides a reliable time evolution of those quantities which are mandatory for a correct calculation of the correlation function. The reason for this failure is different for the different transport theories. (author).
Control of long range turbulent transport with biasing in the tokamak scrape-off-layer
International Nuclear Information System (INIS)
Figarella, C.F.; Ghendrih, Ph.; Sarazin, Y.; Attuel, G.; Benkadda, S.; Beyer, P.; Falchetto, G.; Fleurence, E.; Garbet, X.; Grandgirard, V.
2005-01-01
Cross-field transport in the SOL influences tokamak performance in particular regarding the divertor efficiency. Recent experiment evidence emphasizes non-exponential and/or flat SOL profiles that suggest a large perpendicular transport. A 2D fluid model based on the interchange instability to simulate the SOL turbulence was found to exhibits intermittent dynamics of the particle flux. We propose a control method that prevents long range transport events from reaching the far SOL: It consists in biasing the far SOL leading to a transport barrier which stops the propagation of these intermittent events. The best trade off is to localize the biased toroidal ring around the baffles. We show that such a control is achievable providing the strength of the barrier is strong enough. The investigation of the minimal biasing power required to achieve the control as well as its experimental estimate is performed
Control of long range turbulent transport with biasing in the tokamak scrape-off-layer
International Nuclear Information System (INIS)
Figarella, C.F.; Ghendrih, Ph.; Sarazin, Y.; Attuel, G.; Falchetto, G.; Fleurence, E.; Garbet, X.; Grandgirard, V.
2004-01-01
Cross field transport in the SOL (scrape-off-layer) influences tokamak performance in particular regarding the divertor efficiency. Recent experiment evidence emphasizes non-exponential and/or flat SOL profiles that suggest a large perpendicular transport. A 2-dimensional fluid model based on the interchange instability to simulate the SOL turbulence was found to exhibits intermittent dynamics of the particle flux. We propose a control method that prevents long range transport events from reaching the far SOL: It consists in biasing the far SOL leading to a transport barrier which stops the propagation of these intermittent events. The best trade off is to localize the biased toroidal ring around the baffles. We show that such a control is achievable providing the strength of the barrier is strong enough. The investigation of the minimal biasing power required to achieve the control as well as its experimental estimate is performed. (authors)
Anomalous diffusion, clustering, and pinch of impurities in plasma edge turbulence
DEFF Research Database (Denmark)
Priego, M.; Garcia, O.E.; Naulin, V.
2005-01-01
The turbulent transport of impurity particles in plasma edge turbulence is investigated. The impurities are modeled as a passive fluid advected by the electric and polarization drifts, while the ambient plasma turbulence is modeled using the two-dimensional Hasegawa-Wakatani paradigm for resistive...... drift-wave turbulence. The features of the turbulent transport of impurities are investigated by numerical simulations using a novel code that applies semi-Lagrangian pseudospectral schemes. The diffusive character of the turbulent transport of ideal impurities is demonstrated by relative...... orientation determined by the charge of the impurity particles. Second, a radial pinch scaling linearly with the mass-charge ratio of the impurities is discovered. Theoretical explanation for these observations is obtained by analysis of the model equations. (C) 2005 American Institute of Physics....
Feigenbaum scenario for turbulence and Cantorian E-infinity theory of high energy particle physics
International Nuclear Information System (INIS)
El Naschie, M.S.
2007-01-01
The work draws some fundamental connections between Feigenbaum's golden mean renormalization group and scenario for turbulence on the one side and high energy particle physics on the other side. The analysis which is based on the natural and obvious connections between the Fibonacci-like geometrical growth rate of ε (∞) spacetime and Feigenbaum's renormalization gives vital information to basic questions not only of quantum geometry, but also of quantum field theory
Theory-based scaling of the SOL width in circular limited tokamak plasmas
International Nuclear Information System (INIS)
Halpern, F.D.; Ricci, P.; Labit, B.; Furno, I.; Jolliet, S.; Loizu, J.; Mosetto, A.; Arnoux, G.; Silva, C.; Gunn, J.P.; Horacek, J.; Kočan, M.; LaBombard, B.
2013-01-01
A theory-based scaling for the characteristic length of a circular, limited tokamak scrape-off layer (SOL) is obtained by considering the balance between parallel losses and non-linearly saturated resistive ballooning mode turbulence driving anomalous perpendicular transport. The SOL size increases with plasma size, resistivity, and safety factor q. The scaling is verified against flux-driven non-linear turbulence simulations, which reveal good agreement within a wide range of dimensionless parameters, including parameters closely matching the TCV tokamak. An initial comparison of the theory against experimental data from several tokamaks also yields good agreement. (letter)
Turbulent transport stabilization by ICRH minority fast ions in low rotating JET ILW L-mode plasmas
Bonanomi, N.; Mantica, P.; Di Siena, A.; Delabie, E.; Giroud, C.; Johnson, T.; Lerche, E.; Menmuir, S.; Tsalas, M.; Van Eester, D.; Contributors, JET
2018-05-01
The first experimental demonstration that fast ion induced stabilization of thermal turbulent transport takes place also at low values of plasma toroidal rotation has been obtained in JET ILW (ITER-like wall) L-mode plasmas with high (3He)-D ICRH (ion cyclotron resonance heating) power. A reduction of the gyro-Bohm normalized ion heat flux and higher values of the normalized ion temperature gradient have been observed at high ICRH power and low NBI (neutral beam injection) power and plasma rotation. Gyrokinetic simulations indicate that ITG (ion temperature gradient) turbulence stabilization induced by the presence of high-energetic 3He ions is the key mechanism in order to explain the experimental observations. Two main mechanisms have been identified to be responsible for the turbulence stabilization: a linear electrostatic wave-fast particle resonance mechanism and a nonlinear electromagnetic mechanism. The dependence of the stabilization on the 3He distribution function has also been studied.
BOOK REVIEW: Statistical Mechanics of Turbulent Flows
Cambon, C.
2004-10-01
This is a handbook for a computational approach to reacting flows, including background material on statistical mechanics. In this sense, the title is somewhat misleading with respect to other books dedicated to the statistical theory of turbulence (e.g. Monin and Yaglom). In the present book, emphasis is placed on modelling (engineering closures) for computational fluid dynamics. The probabilistic (pdf) approach is applied to the local scalar field, motivated first by the nonlinearity of chemical source terms which appear in the transport equations of reacting species. The probabilistic and stochastic approaches are also used for the velocity field and particle position; nevertheless they are essentially limited to Lagrangian models for a local vector, with only single-point statistics, as for the scalar. Accordingly, conventional techniques, such as single-point closures for RANS (Reynolds-averaged Navier-Stokes) and subgrid-scale models for LES (large-eddy simulations), are described and in some cases reformulated using underlying Langevin models and filtered pdfs. Even if the theoretical approach to turbulence is not discussed in general, the essentials of probabilistic and stochastic-processes methods are described, with a useful reminder concerning statistics at the molecular level. The book comprises 7 chapters. Chapter 1 briefly states the goals and contents, with a very clear synoptic scheme on page 2. Chapter 2 presents definitions and examples of pdfs and related statistical moments. Chapter 3 deals with stochastic processes, pdf transport equations, from Kramer-Moyal to Fokker-Planck (for Markov processes), and moments equations. Stochastic differential equations are introduced and their relationship to pdfs described. This chapter ends with a discussion of stochastic modelling. The equations of fluid mechanics and thermodynamics are addressed in chapter 4. Classical conservation equations (mass, velocity, internal energy) are derived from their
Turbulence and the Li abundance in main sequence and giant stars
International Nuclear Information System (INIS)
Charbonneau, P.; Michaud, G.
1990-01-01
Calculations of Li burning via turbulent transport are conducted to determine the extent to which observed Li abundances in first ascent giants constrain the various turbulence parameterizations used to model the main-sequence surface Li abundance evolution. A full time-dependent solution to the transport equation is performed, including nuclear reaction terms and evolutionary effects. It is found that turbulence can lead to the extreme Li underabundances observed in giants of M67 and NGC 752. Consideration is given to the possibility of using observations of Li abundances to discriminate between turbulent particle transport and meridional circulation transport. Numerical solutions of the turbulent diffusion coefficient of Vauclair (1988) is used to model the Hyades Li abundance gap. The astrophysical implications of the results for main-sequence and giant stars are discussed. 36 refs
Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D
Energy Technology Data Exchange (ETDEWEB)
Chrystal, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Grierson, B. A.; Solomon, W. M.; Wang, W. X. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Rhodes, T. L.; Schmitz, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States); Mordijck, S. [College of William and Mary, P.O. Box 8795, Williamsburg, Virginia 23187-8795 (United States); Meneghini, O. [Oak Ridge Associated Universities, 1299 Bethel Valley Rd, Bldg SC-200, Oak Ridge, Tennessee 37830 (United States)
2014-07-15
Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E{sup →}×B{sup →} shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain.
Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D
International Nuclear Information System (INIS)
Chrystal, C.; Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de; Grierson, B. A.; Solomon, W. M.; Wang, W. X.; Rhodes, T. L.; Schmitz, L.; Mordijck, S.; Meneghini, O.
2014-01-01
Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E → ×B → shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain
Identification of zonal flows and their characteristics on transport barrier in CHS
International Nuclear Information System (INIS)
Fujisawa, A.; Shimizu, A.; Nakano, H.; Ohshima, S.; Iguchi, H.; Yoshimura, Y.; Minami, T.; Itoh, K.; Isobe, M.; Suzuki, C.; Nishimura, S.; Akiyama, T.; Nagaoka, K.; Takahashi, C.; Ida, K.; Toi, K.; Okamura, S.; Matsuoka, K.; Itoh, S.-I.; Diamond, P.H.
2005-01-01
Relation between turbulence and electric field has been one of the central issues related to the transport physics of toroidal plasmas. Recently, zonal flow, axi-symmetric band-like structure (m=n=0) with a finite radial wavelength, has just come up the third element responsible for the plasma transport. Theories and simulations have expected that the zonal flow should be a mechanism to control the saturation level of turbulence and the resultant transport. In CHS, dual heavy ion beam probes (HIBP) succeeded to prove the presence of the zonal flow and to show the dynamics and structure of the zonal flows. The experiment shows a long-distance correlation between radial electric field (or plasma flow) in low frequency range (< ∼1 kHz), together with radial structure of the zonal flow; characteristic radial length of ∼1.5 cm and life time of ∼1.5 ms. Different characteristics of the zonal flow and turbulence was found in states with and without a transport barrier; the zonal flow activity shrinks with an increase in turbulence level after the barrier breaks down. The recent HIBP experiments have just provided further insight into the system of zonal flow and turbulence. A wavelet analysis is performed on the fluctuation on the barrier position in the state with the transport barrier. The analysis reveals a causal relationship between the zonal flow evolution and turbulence level; the zonal flow is found to increase toward the mean flow direction as turbulence level decreases in the frequency range of 100-150kHz. The observation shows the presence of a nonlinear interaction between zonal flow and the turbulence, or a process of the zonal flow to affect the turbulence level. This paper presents surveys on zonal flow, particularly the recent experiments to demonstrate a causal relationship between zonal flow component and turbulence. Besides, other results obtained with a wavelet analysis are presented on the transport barrier; e.g., density and potential
Four-fluid description of turbulent plasma focus dynamics
International Nuclear Information System (INIS)
Hayd, A.; Maurer, M.; Meinke, P.; Kaeppeler, H.J.
1984-06-01
The dynamic phenomena in the compression, pinch and late phases of the plasma focus experiment POSEIDON in its operational mode at 60 kV, 280 kJ, were previously calculated from a two-fluid theory using the new hybrid code REDUCE/FORTRAN. Two important results were found: the neutron production already in the pinch phase for currents larger than 500 kA and filamentary structures on and around the pinch axis. In a continuation of this work, a four-fluid system of dynamical equations was formulated and programmed with the REDUCE/FORTRAN code. Besides macro-turbulence, the new four-fluid theory includes micro-instabilities and anomalous transport properties, as well as the runaway effect for electrons and ions. First results from calculations with this new theory are presented and are compared with previous calculations and with recent experimental observations. (orig.)
Scale separation closure and Alfven wave turbulence
International Nuclear Information System (INIS)
Chen, C.Y.; Mahajan, S.M.
1985-04-01
Based on the concept of scale separation between coherent response function and incoherent source for renormalized turbulence theories, a closure scheme is proposed. A model problem dealing with shear-Alfven wave turbulence is numerically solved; the solution explicitly shows expected turbulence features such as frequency shift from linear modes, band-broadening, and a power law dependence for the turbulence spectrum
Transport of light, trace impurities in Alcator C-Mod
Rowan, W. L.; Bespamyatnov, I. O.; Liao, K. T.; Horton, W.; Fu, X. R.; Hughes, J. W.
2012-10-01
Light impurity profiles for boron were measured in ITB, H-mode, L-mode, and I-mode discharges in Alcator C-Mod. Within this wide range of modes, the profiles varied from peaked to hollow to flat. Specifically, hollow profiles are often observed in H-mode, while ITBs produce strong peaking, and L-mode produces moderate peaking. I-mode discharges are characterized by flat impurity profiles. For the study reported here, the profiles were measured with charge exchange recombination spectroscopy. The dependences of Rv/D were sought on dimensionless quantities including ion density scale length, effective charge, collisionality, and temperature scale length. We find that neoclassical transport consistently underestimates the measured transport. The excess measured transport is assumed to be turbulent. The strongest dependence of Rv/D is with temperature scale length. In addition, the measured transport was compared with the prediction of an analytical theory of drift wave turbulence that identifies transport implications for drift waves driven by ion and impurity density gradients.
Neutron stochastic transport theory with delayed neutrons
International Nuclear Information System (INIS)
Munoz-Cobo, J.L.; Verdu, G.
1987-01-01
From the stochastic transport theory with delayed neutrons, the Boltzmann transport equation with delayed neutrons for the average flux emerges in a natural way without recourse to any approximation. From this theory a general expression is obtained for the Feynman Y-function when delayed neutrons are included. The single mode approximation for the particular case of a subcritical assembly is developed, and it is shown that Y-function reduces to the familiar expression quoted in many books, when delayed neutrons are not considered, and spatial and source effects are not included. (author)
Katul, G. G.; Palmroth, S.; Manzoni, S.; Oren, R.
2012-12-01
Global climate models predict decreases in leaf stomatal conductance (gs) and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at decadal time-scales. Thus, a theory explaining the differential sensitivity of stomata to changing atmospheric CO2 and other environmental conditions such as soil moisture at the ecosystem scale must be identified. Here, these responses are investigated using an optimality theory applied to stomatal conductance. An analytical model for gs is first proposed based on (a) Fickian mass transfer of CO2 and H2O through stomata; (b) a biochemical photosynthesis model that relates intercellular CO2 to net photosynthesis; and (c) a stomatal model based on optimization for maximizing carbon gains when water losses represent a cost. The optimization theory produced three gas exchange responses that are consistent with observations across a wide-range of species: (1) the sensitivity of gs to vapour pressure deficit (D) is similar to that obtained from a previous synthesis of more than 40 species, (2) the theory is consistent with the onset of an apparent 'feed-forward' mechanism in gs, and (3) the emergent non-linear relationship between the ratio of intercellular to atmospheric CO2 (ci/ca) and D agrees with the results available on this response. A simplified version of this leaf-scale approach recovers the linear relationship between stomatal conductance and leaf-photosynthesis employed in numerous climate models that currently use a variant on the 'Ball-Berry' or the 'Leuning' approaches provided the marginal water use efficiency increases linearly with atmospheric CO2. The model is then up-scaled to the canopy-level using novel theories about the structure of turbulence inside vegetation. This up-scaling proved to be effective in resolving the complex (and two-way) interactions between leaves and their immediate micro
Secondary instability in drift wave turbulence as a mechanism for avalanche and zonal flow formation
International Nuclear Information System (INIS)
Diamond, P.H.; Champeaux, S.; Malkov, M.
2001-01-01
We report on recent developments in the theory of secondary instability in drift-ITG turbulence. Specifically, we explore secondary instability as a mechanism for avalanche formation. A theory of radially extended streamer cell formation and self-regulation is presented. Aspects of streamer structure and dynamics are used to estimate the variance of the drift-wave induced flux. The relation between streamer cell structures and the avalanche concept is discussed, as are the implications of our results for transport modeling. (author)
Multifractal Modeling of Turbulent Mixing
Samiee, Mehdi; Zayernouri, Mohsen; Meerschaert, Mark M.
2017-11-01
Stochastic processes in random media are emerging as interesting tools for modeling anomalous transport phenomena. Applications include intermittent passive scalar transport with background noise in turbulent flows, which are observed in atmospheric boundary layers, turbulent mixing in reactive flows, and long-range dependent flow fields in disordered/fractal environments. In this work, we propose a nonlocal scalar transport equation involving the fractional Laplacian, where the corresponding fractional index is linked to the multifractal structure of the nonlinear passive scalar power spectrum. This work was supported by the AFOSR Young Investigator Program (YIP) award (FA9550-17-1-0150) and partially by MURI/ARO (W911NF-15-1-0562).
International Nuclear Information System (INIS)
Suluksna, Keerati; Juntasaro, Ekachai
2008-01-01
The γ-Re θ transition model of Menter et al. [Menter, F.R., Langtry, R.B., Volker, S., Huang, P.G., 2005. Transition modelling for general purpose CFD codes. ERCOFTAC International Symposium Engineering Turbulence Modelling and Measurements] is a highly generalized transport equation model in which it has been developed based on the concept of local variables compatible with modern CFD methods where the unstructured grid and the parallel computing technique are usually integrated in. To perform the prediction with this model, two essential parameters, F length which is used to control the length of the transition region and Re θc which is used to control the onset of the transition location, must be specified to close the model. At present, both parameters are proprietary and their formulations are unpublished. For the first time here, the relations for both parameters are formulated by means of numerical experiments and analysis under the assumption of Re θc = Re θt corresponding with the bypass transition behavior. Based on this analysis, the optimized values of the parameters are found and their relations can be constructed as follows: Re θc = 803.73(Tu ∞ , le + 0.6067) -1.027 and F length = 163 ln(Tu ∞ , le ) + 3.625. The performance of this transition model is assessed by testing with the experimental cases of T3AM, T3A, and T3B. Detailed comparisons with the predicted results by the transition models of Suzen and Huang [Suzen, Y.B., Huang, P.G., 2000. Modeling of flow transition using an intermittency transport equation. J. Fluids Eng. 122, 273-284] and Lodefier et al. [Lodefier, K., Merci, B., De Langhe, C., Dick, E., 2003. Transition modelling with the SST turbulence model and intermittency transport equation. ASME Turbo Expo, Atlanta, GA, USA, June 16-19], and also with the predicted results by the k-ε model of Launder and Sharma [Launder, B.E., Sharma, B., 1974. Application of the energy dissipation model of turbulence to the calculation of
Controlling Heat Transport and Flow Structures in Thermal Turbulence Using Ratchet Surfaces
Jiang, Hechuan; Zhu, Xiaojue; Mathai, Varghese; Verzicco, Roberto; Lohse, Detlef; Sun, Chao
2018-01-01
In this combined experimental and numerical study on thermally driven turbulence in a rectangular cell, the global heat transport and the coherent flow structures are controlled with an asymmetric ratchetlike roughness on the top and bottom plates. We show that, by means of symmetry breaking due to the presence of the ratchet structures on the conducting plates, the orientation of the large scale circulation roll (LSCR) can be locked to a preferred direction even when the cell is perfectly leveled out. By introducing a small tilt to the system, we show that the LSCR orientation can be tuned and controlled. The two different orientations of LSCR give two quite different heat transport efficiencies, indicating that heat transport is sensitive to the LSCR direction over the asymmetric roughness structure. Through a quantitative analysis of the dynamics of thermal plume emissions and the orientation of the LSCR over the asymmetric structure, we provide a physical explanation for these findings. The current work has important implications for passive and active flow control in engineering, biofluid dynamics, and geophysical flows.
Laptev, A. G.; Basharov, M. M.
2018-05-01
The problem of modeling turbulent transfer of finely dispersed particles in liquids has been considered. An approach is used where the transport of particles is represented in the form of a variety of the diffusion process with the coefficient of turbulent transfer to the wall. Differential equations of transfer are written for different cases, and a solution of the cell model is obtained for calculating the efficiency of separation in a channel. Based on the theory of turbulent transfer of particles and of the boundary layer model, an expression has been obtained for calculating the rate of turbulent deposition of finely dispersed particles. The application of this expression in determining the efficiency of physical coagulation of emulsions in different channels and on the surface of chaotic packings is shown.
International Nuclear Information System (INIS)
Eilek, J.A.
1989-01-01
Recent theories of magnetohydrodynamic turbulence are used to construct microphysical turbulence models, with emphasis on models of anisotropic turbulence. These models have been applied to the determination of the emergent polarization from a resolved uniform source. It is found that depolarization alone is not a unique measure of the turbulence, and that the turblence will also affect the total-intensity distributions. Fluctuations in the intensity image can thus be employed to measure turbulence strength. In the second part, it is demonstrated that a power-spectral analysis of the total and polarized intensity images can be used to obtain the power spectra of the synchrotron emission. 81 refs
Turbulence-Free Double-slit Interferometer
Smith, Thomas A.; Shih, Yanhua
2018-02-01
Optical turbulence can be detrimental for optical observations. For instance, atmospheric turbulence may reduce the visibility or completely blur out the interference produced by an interferometer in open air. However, a simple two-photon interference theory based on Einstein's granularity picture of light makes a turbulence-free interferometer possible; i.e., any refraction index, length, or phase variations along the optical paths of the interferometer do not have any effect on its interference. Applying this mechanism, the reported experiment demonstrates a two-photon double-slit interference that is insensitive to atmospheric turbulence. The turbulence-free mechanism and especially the turbulence-free interferometer would be helpful in optical observations that require high sensitivity and stability such as for gravitational-wave detection.
Destructive interference of TEM and ITG turbulence
International Nuclear Information System (INIS)
Merz, F.; Jenko, F.
2009-01-01
Full text: Turbulence driven by ion temperature gradient (ITG) modes and trapped electron modes (TEMs) is generally considered the key mechanism for anomalous transport in fusion devices on ion scales. But while pure ITG and, to a lesser extent, also pure TEM turbulence have been studied in detail over the last years, not much is presently known about nonlinear interactions between ITG modes and TEMs, which are often present simultaneously in experimentally relevant situations. This important issue is addressed by means of linear and nonlinear gyrokinetic simulations with the GENE code. To examine the properties of the (linear) TEM and ITG instabilities in the (realistic) transitional regime, the GENE code is run as eigenvalue solver, which allows for a systematic study of dominant and subdominant modes. Corresponding nonlinear initial value computations show that the particle transport of the turbulent system can be completely suppressed if the two driving instabilities are active simultaneously. The direct comparison of the linear modes and the corresponding turbulent system reveals a coexistence of the two microinstabilities in a transitional regime even at the same wave number. The consequences of this dual turbulence drive for transport modeling is discussed. (author)
Validation of the kinetic-turbulent-neoclassical theory for edge intrinsic rotation in DIII-D
Ashourvan, Arash; Grierson, B. A.; Battaglia, D. J.; Haskey, S. R.; Stoltzfus-Dueck, T.
2018-05-01
In a recent kinetic model of edge main-ion (deuterium) toroidal velocity, intrinsic rotation results from neoclassical orbits in an inhomogeneous turbulent field [T. Stoltzfus-Dueck, Phys. Rev. Lett. 108, 065002 (2012)]. This model predicts a value for the toroidal velocity that is co-current for a typical inboard X-point plasma at the core-edge boundary (ρ ˜ 0.9). Using this model, the velocity prediction is tested on the DIII-D tokamak for a database of L-mode and H-mode plasmas with nominally low neutral beam torque, including both signs of plasma current. Values for the flux-surface-averaged main-ion rotation velocity in the database are obtained from the impurity carbon rotation by analytically calculating the main-ion—impurity neoclassical offset. The deuterium rotation obtained in this manner has been validated by direct main-ion measurements for a limited number of cases. Key theoretical parameters of ion temperature and turbulent scale length are varied across a wide range in an experimental database of discharges. Using a characteristic electron temperature scale length as a proxy for a turbulent scale length, the predicted main-ion rotation velocity has a general agreement with the experimental measurements for neutral beam injection (NBI) powers in the range PNBI balanced—but high powered—NBI, the net injected torque through the edge can exceed 1 Nm in the counter-current direction. The theory model has been extended to compute the rotation degradation from this counter-current NBI torque by solving a reduced momentum evolution equation for the edge and found the revised velocity prediction to be in agreement with experiment. Using the theory modeled—and now tested—velocity to predict the bulk plasma rotation opens up a path to more confidently projecting the confinement and stability in ITER.
Kolmogorov Behavior of Near-Wall Turbulence and Its Application in Turbulence Modeling
Shih, Tsan-Hsing; Lumley, John L.
1992-01-01
The near-wall behavior of turbulence is re-examined in a way different from that proposed by Hanjalic and Launder and followers. It is shown that at a certain distance from the wall, all energetic large eddies will reduce to Kolmogorov eddies (the smallest eddies in turbulence). All the important wall parameters, such as friction velocity, viscous length scale, and mean strain rate at the wall, are characterized by Kolmogorov microscales. According to this Kolmogorov behavior of near-wall turbulence, the turbulence quantities, such as turbulent kinetic energy, dissipation rate, etc. at the location where the large eddies become Kolmogorov eddies, can be estimated by using both direct numerical simulation (DNS) data and asymptotic analysis of near-wall turbulence. This information will provide useful boundary conditions for the turbulent transport equations. As an example, the concept is incorporated in the standard k-epsilon model which is then applied to channel and boundary flows. Using appropriate boundary conditions (based on Kolmogorov behavior of near-wall turbulence), there is no need for any wall-modification to the k-epsilon equations (including model constants). Results compare very well with the DNS and experimental data.
Microinstabilities and turbulent transport in the reversed field pinch
Carmody, Daniel Richard
-analytic equilibrium, the adjusted circular model (ACM), is developed and implemented in the gyrokinetic code GENE to investigate representative PPCD discharges. The flexibility of the ACM enables it to be used for the high-theta PPCD discharges where the TBFM breaks down. The dominant linear instabilites for the discharges modeled here---ITG and the trapped electron mode (TEM)---are studied, as are their scaling properties in the PPCD regime. It is found that these instabilities are present outside of the reversal surface, where the driving gradients are strongest. Nonlinear simulations of the TEM turbulence are performed, the first such done for the RFP, and zonal flows are found to play an important role in the nonlinear saturation mechanism. These zonal flows lead to a large Dimits-like shift and suppressed transport. There is also evidence that residual global tearing mode fluctuations are a necessary part of modeling transport in the RFP, even in improved confinement PPCD discharges, and by modeling these residual fluctuations through the use of an externally imposed perpendicular magnetic field perturbation it is possible to bring simulated fluxes into agreement with experiment. Finally, the nature of the collisionless MTM, an instability seen to arise in some parameter regimes of the RFP, is investigated analytically using a fluid expansion in the drift-kinetic framework. Particular attention is paid to the role of magnetic drifts, and some evidence for their role in the collisionless instability is presented. Comparisons are made to gyrokinetic simulations and to earlier theory on the magnetic-curvature drift instability.
Baas, A. C.; Jackson, D.; Cooper, J. A.; Lynch, K.; Delgado-Fernandez, I.; Beyers, M.; Lee, Z. S.
2010-12-01
The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune (‘against’ the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u’, v’, w’). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that
Near bed suspended sediment flux by single turbulent events
Amirshahi, Seyed Mohammad; Kwoll, Eva; Winter, Christian
2018-01-01
The role of small scale single turbulent events in the vertical mixing of near bed suspended sediments was explored in a shallow shelf sea environment. High frequency velocity and suspended sediment concentration (SSC; calibrated from the backscatter intensity) were collected using an Acoustic Doppler Velocimeter (ADV). Using quadrant analysis, the despiked velocity time series was divided into turbulent events and small background fluctuations. Reynolds stress and Turbulent Kinetic Energy (TKE) calculated from all velocity samples, were compared to the same turbulent statistics calculated only from velocity samples classified as turbulent events (Reevents and TKEevents). The comparison showed that Reevents and TKEevents was increased 3 and 1.6 times, respectively, when small background fluctuations were removed and that the correlation with SSC for TKE could be improved through removal of the latter. The correlation between instantaneous vertical turbulent flux (w ‧) and SSC fluctuations (SSC ‧) exhibits a tidal pattern with the maximum correlation at peak ebb and flood currents, when strong turbulent events appear. Individual turbulent events were characterized by type, strength, duration and length. Cumulative vertical turbulent sediment fluxes and average SSC associated with individual turbulent events were calculated. Over the tidal cycle, ejections and sweeps were the most dominant events, transporting 50% and 36% of the cumulative vertical turbulent event sediment flux, respectively. Although the contribution of outward interactions to the vertical turbulent event sediment flux was low (11%), single outward interaction events were capable of inducing similar SSC ‧ as sweep events. The results suggest that on time scales of tens of minutes to hours, TKE may be appropriate to quantify turbulence in sediment transport studies, but that event characteristics, particular the upward turbulent flux need to be accounted for when considering sediment transport
Simulation Of Microtearing Turbulence In NSTX
International Nuclear Information System (INIS)
Guttenfelder, W.; Candy, J.; Kaye, S.M.; Nevins, W.M.; Wanag, E.; Zhang, J.; Bell, R.E.; Crocker, N.A.; Hammett, G.W.; LeBlanc, B.P.; Mikkelsen, D.R.; Ren, Y.; Yuh, H.
2012-01-01
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.
About the theory of congested transport streams
Valeriy GUK
2009-01-01
Talked about a theory, based on integrity of continuous motion of a transport stream. Placing of car and its speed is in a stream - second. Principle of application of the generalized methods of design and new descriptions of the states of transport streams opens up. Travelling and transport potentials are set, and also external capacity of the system a «transport stream» is an exergy, that allows to make differential equation and decide the applied tasks of organization of travelling motion....
Cazalbou, J.-B.; Chassaing, P.
2002-02-01
The behavior of Reynolds-stress-transport models at the free-stream edges of turbulent flows is investigated. Current turbulent-diffusion models are found to produce propagative (possibly weak) solutions of the same type as those reported earlier by Cazalbou, Spalart, and Bradshaw [Phys. Fluids 6, 1797 (1994)] for two-equation models. As in the latter study, an analysis is presented that provides qualitative information on the flow structure predicted near the edge if a condition on the values of the diffusion constants is satisfied. In this case, the solution appears to be fairly insensitive to the residual free-stream turbulence levels needed with conventional numerical methods. The main specific result is that, depending on the diffusion model, the propagative solution can force turbulence toward definite and rather extreme anisotropy states at the edge (one- or two-component limit). This is not the case with the model of Daly and Harlow [Phys. Fluids 13, 2634 (1970)]; it may be one of the reasons why this "old" scheme is still the most widely used, even in recent Reynolds-stress-transport models. In addition, the analysis helps us to interpret some difficulties encountered in computing even very simple flows with Lumley's pressure-diffusion model [Adv. Appl. Mech. 18, 123 (1978)]. A new realizability condition, according to which the diffusion model should not globally become "anti-diffusive," is introduced, and a recalibration of Lumley's model satisfying this condition is performed using information drawn from the analysis.
A formal derivation of the local energy transfer (LET) theory of homogeneous turbulence
McComb, W. D.; Yoffe, S. R.
2017-09-01
A statistical closure of the Navier-Stokes hierarchy which leads to equations for the two-point, two-time covariance of the velocity field for stationary, homogeneous isotropic turbulence is presented. It is a generalisation of the self-consistent field method due to Edwards (1964) for the stationary, single-time velocity covariance. The probability distribution functional P≤ft[\\mathbf{u},t\\right] is obtained, in the form of a series, from the Liouville equation by means of a perturbation expansion about a Gaussian distribution, which is chosen to give the exact two-point, two-time covariance. The triple moment is calculated in terms of an ensemble-averaged infinitesimal velocity-field propagator, and shown to yield the Edwards result as a special case. The use of a Gaussian zero-order distribution has been found to justify the introduction of a fluctuation-response relation, which is in accord with modern dynamical theories. In a sense this work completes the analogy drawn by Edwards between turbulence and Brownian motion. Originally Edwards had shown that the noise input was determined by the correlation of the velocity field with the externally applied stirring forces but was unable to determine the system response. Now we find that the system response is determined by the correlation of the velocity field with internal quasi-entropic forces. This analysis is valid to all orders of perturbation theory, and allows the recovery of the local energy transfer (LET) theory, which had previously been derived by more heuristical methods. The LET theory is known to be in good agreement with experimental results. It is also unique among two-point statistical closures in displaying an acceptable (i.e. non-Markovian) relationship between the transfer spectrum and the system response, in accordance with experimental results. As a result of the latter property, it is compatible with the Kolmogorov (K41) spectral phenomenology. In memory of Professor Sir Sam Edwards F
Gyrokinetic Simulation of Global Turbulent Transport Properties in Tokamak Experiments
Energy Technology Data Exchange (ETDEWEB)
Wang, W.X.; Lin, Z.; Tang, W.M.; Lee, W.W.; Ethier, S.; Lewandowski, J.L.V.; Rewoldt, G.; Hahm, T.S.; Manickam, J.
2006-01-01
A general geometry gyro-kinetic model for particle simulation of plasma turbulence in tokamak experiments is described. It incorporates the comprehensive influence of noncircular cross section, realistic plasma profiles, plasma rotation, neoclassical (equilibrium) electric fields, and Coulomb collisions. An interesting result of global turbulence development in a shaped tokamak plasma is presented with regard to nonlinear turbulence spreading into the linearly stable region. The mutual interaction between turbulence and zonal flows in collisionless plasmas is studied with a focus on identifying possible nonlinear saturation mechanisms for zonal flows. A bursting temporal behavior with a period longer than the geodesic acoustic oscillation period is observed even in a collisionless system. Our simulation results suggest that the zonal flows can drive turbulence. However, this process is too weak to be an effective zonal flow saturation mechanism.
Overview of edge turbulence and zonal flow studies on TEXTOR
International Nuclear Information System (INIS)
Xu, Y.; Kraemer-Flecken, A.; Reiser, D.
2008-01-01
In the TEXTOR tokamak, the edge turbulence properties and turbulence-associated zonal flows have been systematically investigated both experimentally and theoretically. The experimental results include the investigation of self-organized criticality (SOC) behavior, the intermittent blob transport and the geodesic acoustic mode (GAM) zonal flows. During the Dynamic Ergodic Divertor (DED) operation in TEXTOR, the impact of an ergodized plasma boundary on edge turbulence, turbulent transport and the fluctuation propagation has also been studied in detail. The results show substantial influence by the DED on edge turbulence. The theoretical simulations for TEXTOR parameters show characteristic features of the GAM flows and strong reduction of the blob transport by the DED at the plasma periphery. Moreover, the modelling reveals the importance of the Reynolds stress in driving mean (or zonal) flows at the plasma edge in the ohmic discharge phase in TEXTOR. (author)
Edge-core interaction of ITG turbulence in Tokamaks: Is the Tail Wagging the Dog?
Ku, S.; Chang, C. S.; Dif-Pradalier, G.; Diamond, P. H.
2010-11-01
A full-f XGC1 gyrokinetic simulation of ITG turbulence, together with the neoclassical dynamics without scale separation, has been performed for the whole-volume plasma in realistic diverted DIII-D geometry. The simulation revealed that the global structure of the turbulence and transport in tokamak plasmas results from a synergy between edge-driven inward propagation of turbulence intensity and the core-driven outward heat transport. The global ion confinement and the ion temperature gradient then self-organize quickly at turbulence propagation time scale. This synergy results in inward-outward pulse scattering leading to spontaneous production of strong internal shear layers in which the turbulent transport is almost suppressed over several radial correlation lengths. Co-existence of the edge turbulence source and the strong internal shear layer leads to radially increasing turbulence intensity and ion thermal transport profiles.
International Nuclear Information System (INIS)
Terry, P.W.; Diamond, P.H.
1986-01-01
We appreciate the interest of Krommes in our recent paper and welcome the opportunity to discuss his comments and other related issues. In our opinion, most of the objections hea has raised follow from a misunderstanding of the physics treated by clump and hole theory. In particular, throughout his critique Krommes attempts to extrapolate results and intuition of homogeneous Navier-Stokes turbulence (HN-ST) to the more complicated case of dissipative drift-wave turbulence (DD-WT). Since these two cases are so dissimilar with regard to their fundamental constituents, drive, characteristic scales and interaction mechanisms, extrapolations from one case to the other are unwarranted and misleading. Moreover, the hypotheses and results of clump and hole theories have fared well in several tests using laboratory and simulation data which is relevant to the theoretical models analyzed. 7 refs
1993-01-01
MINISTRY OF TOURISM , JERUSALEM, ISRAEL. Boundary-Layer Meteorology 62: x, 1993.I WELCOMING ADDRESS I want to welcome you to Israel, to sunny Eilat...turbulently mixing with other cells. Smm mnnm-, mmnml n n i nn mm l 30 ROLAND B. STULL Idealizations within classical local turbulence theory, such as
Transport processes in space physics and astrophysics
Zank, Gary P
2014-01-01
Transport Processes in Space Physics and Astrophysics' is aimed at graduate level students to provide the necessary mathematical and physics background to understand the transport of gases, charged particle gases, energetic charged particles, turbulence, and radiation in an astrophysical and space physics context. Subjects emphasized in the work include collisional and collisionless processes in gases (neutral or plasma), analogous processes in turbulence fields and radiation fields, and allows for a simplified treatment of the statistical description of the system. A systematic study that addresses the common tools at a graduate level allows students to progress to a point where they can begin their research in a variety of fields within space physics and astrophysics. This book is for graduate students who expect to complete their research in an area of plasma space physics or plasma astrophysics. By providing a broad synthesis in several areas of transport theory and modeling, the work also benefits resear...
International Nuclear Information System (INIS)
Gerhauser, H.
1980-02-01
Two superimposed miscible liquids are separated by a diffuse boundary layer providing a steady transition of density. If the heavy fluid is on top of the light one, Rayleigh-Taylor-instabilities develop and cause a rapid interchange and eventually an intermixing. This process can be subjected to dynamic stabilization by enforcing vertical oscillations upon the whole system. However, since only part of the unstable mode spectrum is completely stabilized, the remaining weakly unstable modes lead to turbulent transport processes through the boundary layer ('anomalous diffusion'), so that only a quasistationary equilibrium is achieved. In the present paper, previous experimental results on the dynamic stabilization of water superimposed by an aqueous ZnJ-solution are theoretically interpreted, and the observed spatial structure as well as the time development of the density profiles are explained. There exists an analogy between these phenomena and turbulent transport processes in tokamak discharges such as the sawtooth oscillations of internal disruptions. (orig.) [de
International Nuclear Information System (INIS)
Futatani, S.; Benkadda, S.; Del-Castillo-Negrete, D.
2009-01-01
The spatiotemporal multiscale dynamics of the turbulent transport of impurities is studied in the context of the collisional drift wave turbulence. Two turbulence regimes are considered: a quasihydrodynamic regime and a quasiadiabatic regime. The impurity is assumed to be a passive scalar advected by the corresponding ExB turbulent flow in the presence of diffusion. Two mixing scenarios are studied: a freely decaying case, and a forced case in which the scalar is forced by an externally imposed gradient. The results of the direct numerical simulations are analyzed using proper orthogonal decomposition (POD) techniques. The multiscale analysis is based on a space-time separable POD of the impurity field. The low rank spatial POD eigenfunctions capture the large scale coherent structures and the high rank eigenfunctions capture the small scale fluctuations. The temporal evolution at each scale is dictated by the corresponding temporal POD eigenfunctions. Contrary to the decaying case in which the POD spectrum decays fast, the spectrum in the forced case is relatively flat. The most striking difference between these two mixing scenarios is in the temporal dynamics of the small scale structures. In the decaying case the POD reveals the presence of 'bursty' dynamics in which successively small (high POD rank) scales are intermittently activated during the mixing process. On the other hand, in the forced simulations the temporal dynamics exhibits stationary fluctuations. Spatial intermittency or 'patchiness' in the mixing process characterizes the distribution of the passive tracer in the decaying quasihydrodynamic regime. In particular, in this case the probability distribution function of the low rank POD spatial reconstruction error is non-Gaussian. The spatiotemporal POD scales exhibit a diffusive-type scaling in the quasiadiabatic regime. However, this scaling seems to be absent in the quasihydrodynamic regime that shows no scaling (in the decaying case) or two
THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY
Energy Technology Data Exchange (ETDEWEB)
WONG,SK; CHAN,VS
2002-11-01
OAK B202 THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY. This article presents a comprehensive description of neoclassical transport theory in the banana regime for large aspect ratio flux surfaces of arbitrary shapes. The method of matched asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates discussion of the treatment of dynamical constraints. it is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard.
THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY
International Nuclear Information System (INIS)
WONG, S.K.; CHAN, V.S.
2002-01-01
OAK B202 THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY. This article presents a comprehensive description of neoclassical transport theory in the banana regime for large aspect ratio flux surfaces of arbitrary shapes. The method of matched asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates discussion of the treatment of dynamical constraints. it is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard
Koga, D; Chian, A C-L; Hada, T; Rempel, E L
2008-02-13
Magnetohydrodynamic (MHD) turbulence is commonly observed in the solar wind. Nonlinear interactions among MHD waves are likely to produce finite correlation of the wave phases. For discussions of various transport processes of energetic particles, it is fundamentally important to determine whether the wave phases are randomly distributed (as assumed in the quasi-linear theory) or have a finite coherence. Using a method based on the surrogate data technique, we analysed the GEOTAIL magnetic field data to evaluate the phase coherence in MHD turbulence in the Earth's foreshock region. The results demonstrate the existence of finite phase correlation, indicating that nonlinear wave-wave interactions are in progress.
Dissipative time-dependent quantum transport theory.
Zhang, Yu; Yam, Chi Yung; Chen, GuanHua
2013-04-28
A dissipative time-dependent quantum transport theory is developed to treat the transient current through molecular or nanoscopic devices in presence of electron-phonon interaction. The dissipation via phonon is taken into account by introducing a self-energy for the electron-phonon coupling in addition to the self-energy caused by the electrodes. Based on this, a numerical method is proposed. For practical implementation, the lowest order expansion is employed for the weak electron-phonon coupling case and the wide-band limit approximation is adopted for device and electrodes coupling. The corresponding hierarchical equation of motion is derived, which leads to an efficient and accurate time-dependent treatment of inelastic effect on transport for the weak electron-phonon interaction. The resulting method is applied to a one-level model system and a gold wire described by tight-binding model to demonstrate its validity and the importance of electron-phonon interaction for the quantum transport. As it is based on the effective single-electron model, the method can be readily extended to time-dependent density functional theory.
Anomalous diffusion and Levy random walk of magnetic field lines in three dimensional turbulence
International Nuclear Information System (INIS)
Zimbardo, G.; Veltri, P.; Basile, G.; Principato, S.
1995-01-01
The transport of magnetic field lines is studied numerically where three dimensional (3-D) magnetic fluctuations, with a power law spectrum, and periodic over the simulation box are superimposed on an average uniform magnetic field. The weak and the strong turbulence regime, δB∼B 0 , are investigated. In the weak turbulence case, magnetic flux tubes are separated from each other by percolating layers in which field lines undergo a chaotic motion. In this regime the field lines may exhibit Levy, rather than Gaussian, random walk, changing from Levy flights to trapped motion. The anomalous diffusion laws left-angle Δx 2 i right-angle ∝s α with α>1 and α<1, are obtained for a number of cases, and the non-Gaussian character of the field line random walk is pointed out by computing the kurtosis. Increasing the fluctuation level, and, therefore stochasticity, normal diffusion (α congruent 1) is recovered and the kurtoses reach their Gaussian value. However, the numerical results show that neither the quasi-linear theory nor the two dimensional percolation theory can be safely extrapolated to the considered 3-D strong turbulence regime. copyright 1995 American Institute of Physics
Role of secondary instability theory and parabolized stability equations in transition modeling
El-Hady, Nabil M.; Dinavahi, Surya P.; Chang, Chau-Lyan; Zang, Thomas A.
1993-01-01
In modeling the laminar-turbulent transition region, the designer depends largely on benchmark data from experiments and/or direct numerical simulations that are usually extremely expensive. An understanding of the evolution of the Reynolds stresses, turbulent kinetic energy, and quantifies in the transport equations like the dissipation and production is essential in the modeling process. The secondary instability theory and the parabolized stability equations method are used to calculate these quantities, which are then compared with corresponding quantities calculated from available direct numerical simulation data for the incompressible boundary-layer flow of laminar-turbulent transition conditions. The potential of the secondary instability theory and the parabolized stability equations approach in predicting these quantities is discussed; results indicate that inexpensive data that are useful for transition modeling in the early stages of the transition region can be provided by these tools.
Turbulence beneath finite amplitude water waves
Energy Technology Data Exchange (ETDEWEB)
Beya, J.F. [Universidad de Valparaiso, Escuela de Ingenieria Civil Oceanica, Facultad de Ingenieria, Valparaiso (Chile); The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Peirson, W.L. [The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Banner, M.L. [The University of New South Wales, School of Mathematics and Statistics, Sydney, NSW (Australia)
2012-05-15
Babanin and Haus (J Phys Oceanogr 39:2675-2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed a threshold wave parameter a {sup 2}{omega}/{nu} = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments. Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a {sup 2}{omega}/{nu} = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings of wave behaviour. (orig.)
Formation and collapse of internal transport barrier
International Nuclear Information System (INIS)
Fukuyama, A.; Itoh, K.; Itoh, S.I.; Yagi, M.
1999-01-01
A theoretical model of internal transport barrier (ITB) is developed. The transport model based on the self-sustained turbulence theory of the current-diffusive ballooning mode is extended to include the effects of ExB rotation shear. Delayed formation of ITB is observed in transport simulations. The influence of finite gyroradius is also discussed. Simulation of the current ramp-up experiment successfully described the radial profile of density, temperature and safety factor. A model of ITB collapse due to magnetic braiding is proposed. Sudden enhancement of transport triggered by overlapping of magnetic islands terminates ITB. The possibility of destabilizing global low-n modes is also discussed. (author)
Formation and collapse of internal transport barrier
International Nuclear Information System (INIS)
Fukuyama, A.; Itoh, K.; Itoh, S.-I.; Yagi, M.
2001-01-01
A theoretical model of internal transport barrier (ITB) is developed. The transport model based on the self-sustained turbulence theory of the current-diffusive ballooning mode is extended to include the effects of ExB rotation shear. Delayed formation of ITB is observed in transport simulations. The influence of finite gyroradius is also discussed. Simulation of the current ramp-up experiment successfully described the radial profile of density, temperature and safety factor. A model of ITB collapse due to magnetic braiding is proposed. Sudden enhancement of transport triggered by overlaping of magnetic islands terminates ITB. The possibility of destabilizing global low-n modes is also discussed. (author)
International Nuclear Information System (INIS)
Cottier, Pierre
2013-01-01
The magnetic confinement in tokamaks is for now the most advanced way towards energy production by nuclear fusion. Both theoretical and experimental studies showed that rotation generation can increase its performance by reducing the turbulent transport in tokamak plasmas. The rotation influence on the heat and particle fluxes is studied along with the angular momentum transport with the quasi-linear gyro-kinetic eigenvalue code QuaLiKiz. For this purpose, the QuaLiKiz code is modified in order to take the plasma rotation into account and compute the angular momentum flux. It is shown that QuaLiKiz framework is able to correctly predict the angular momentum flux including the E*B shear induced residual stress as well as the influence of rotation on the heat and particle fluxes. The major approximations of QuaLiKiz formalisms are reviewed, in particular the ballooning representation at its lowest order and the eigenfunctions calculated in the hydrodynamic limit. The construction of the quasi-linear fluxes is also reviewed in details and the quasi-linear angular momentum flux is derived. The different contributions to the turbulent momentum flux are studied and successfully compared both against non-linear gyro-kinetic simulations and experimental data. (author) [fr
High-electric-field quantum transport theory for semiconductor superlattices
International Nuclear Information System (INIS)
Nguyen Hong Shon; Nazareno, H.N.
1995-12-01
Based on the Baym-Kadanoff-Keldysh nonequilibrium Green's functions technique, a quantum transport theory for semiconductor superlattices under high-electric field is developed. This theory is capable of considering collisional broadening, intra-collisional field effects and band transport and hopping regimes simultaneously. Numerical calculations for narrow-miniband superlattices in high electric field, when the hopping regime dominates are in reasonable agreement with experimental results and show a significant deviation from the Boltzmann theory. A semiphenomenological formula for current density in hopping regime is proposed. (author). 60 refs, 4 figs
Some improved methods in neutron transport theory
Energy Technology Data Exchange (ETDEWEB)
Pop-Jordanov, J; Stefanovic, D; Kocic, A; Matausek, M; Bosevski, T [Boris Kidric Institute of Nuclear Sciences Vinca, Beograd (Yugoslavia)
1973-07-01
The methods described in this paper are: analytical approach to neutron spectra in case of energy dependent anisotropy of elastic scattering; Monte Carlo estimations of neutron absorption reaction rate during slowing down process; spherical harmonics treatment of space-angle-lethargy dependent slowing down transport equation; integral transport theory based on point-wise representation of variables.
Atmospheric turbulence and diffusion research
International Nuclear Information System (INIS)
Hosker, R.P. Jr.
1993-01-01
The Atmospheric Turbulence and Diffusion Division (well known in the atmospheric dispersion community as the Atmospheric Turbulence and Diffusion Laboratory, ATDL) is one of several field facilities of NOAAs Air Resources Laboratory, headquartered in Silver Spring, Maryland. The laboratory conducts research on matters of atmospheric diffusion and turbulent exchange, concerning air quality. ATDD focuses attention on the physics of the lower atmosphere, with special emphasis on the processes contributing to atmospheric transport, dispersion, deposition, and air-surface exchange, and on the development of predictive capabilities using the results of this research. Research is directed toward issues of national and global importance related to the missions of DOE, to DOE's Oak Ridge Field Office, and to NOAA. The program is divided into four major projects: plume transport and diffusion in the planetary boundary layer, complex topography, canopy micrometeorology, and air-surface exchange
Destabilizing turbulence in pipe flow
Kühnen, Jakob; Song, Baofang; Scarselli, Davide; Budanur, Nazmi Burak; Riedl, Michael; Willis, Ashley P.; Avila, Marc; Hof, Björn
2018-04-01
Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities1-3, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.
Controlling heat transport and flow structures in thermal turbulence using ratchet surfaces
Sun, Chao; Jiang, Hechuan; Zhu, Xiaojue; Mathai, Varghese; Verzicco, Roberto; Lohse, Detlef
2017-11-01
In this combined experimental and numerical study on thermally driven turbulence in a rectangular cell, the global heat transport and the coherent flow structures are controlled with an asymmetric ratchet-like roughness on the top and bottom plates. We show that, by means of symmetry breaking due to the presence of the ratchet structures on the conducting plates, the orientation of the Large Scale Circulation Roll (LSCR) can be locked to a preferred direction even when the cell is perfectly leveled out. By introducing a small tilt to the system, we show that the LSCR orientation can be tuned and controlled. The two different orientations of LSCR give two quite different heat transport efficiencies, indicating that heat transport is sensitive to the LSCR direction over the asymmetric roughness structure. Through analysis of the dynamics of thermal plume emissions and the orientation of the LSCR over the asymmetric structure, we provide a physical explanation for these findings. This work is financially supported by the Natural Science Foundation of China under Grant No. 11672156, the Dutch Foundation for Fundamental Research on Matter (FOM), the Dutch Technology Foundation (STW) and a VIDI Grant.
Current-driven turbulence in plasmas
International Nuclear Information System (INIS)
Kluiver, H. de.
1977-10-01
Research on plasma heating in linear and toroidal systems using current-driven turbulence is reviewed. The motivation for this research is presented. Relations between parameters describing the turbulent plasma state and macroscopic observables are given. Several linear and toroidal devices used in current-driven turbulence studies are described, followed by a discussion of special diagnostic methods used. Experimental results on the measurement of electron and ion heating, anomalous plasma conductivity and associated turbulent fluctuation spectra are reviewed. Theories on current-driven turbulence are discussed and compared with experiments. It is demonstrated from the experimental results that current-driven turbulence occurs not only for extreme values of the electric field but also for an experimentally much more accessible and wide range of parameters. This forms a basis for a discussion on possible future applications in fusion-oriented plasma research
Fully-kinetic Ion Simulation of Global Electrostatic Turbulent Transport in C-2U
Fulton, Daniel; Lau, Calvin; Bao, Jian; Lin, Zhihong; Tajima, Toshiki; TAE Team
2017-10-01
Understanding the nature of particle and energy transport in field-reversed configuration (FRC) plasmas is a crucial step towards an FRC-based fusion reactor. The C-2U device at Tri Alpha Energy (TAE) achieved macroscopically stable plasmas and electron energy confinement time which scaled favorably with electron temperature. This success led to experimental and theoretical investigation of turbulence in C-2U, including gyrokinetic ion simulations with the Gyrokinetic Toroidal Code (GTC). A primary objective of TAE's new C-2W device is to explore transport scaling in an extended parameter regime. In concert with the C-2W experimental campaign, numerical efforts have also been extended in A New Code (ANC) to use fully-kinetic (FK) ions and a Vlasov-Poisson field solver. Global FK ion simulations are presented. Future code development is also discussed.
Wall roughness induces asymptotic ultimate turbulence
Zhu, Xiaojue; Verschoof, Ruben A.; Bakhuis, Dennis; Huisman, Sander G.; Verzicco, Roberto; Sun, Chao; Lohse, Detlef
2018-04-01
Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by combining extensive experiments and numerical simulations, we examine the paradigmatic Taylor-Couette system, which describes the closed flow between two independently rotating coaxial cylinders. We show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents associated with wall-bounded turbulence. We reveal that if only one of the walls is rough, the bulk velocity is slaved to the rough side, due to the much stronger coupling to that wall by the detaching flow structures. If both walls are rough, the viscosity dependence is eliminated, giving rise to asymptotic ultimate turbulence—the upper limit of transport—the existence of which was predicted more than 50 years ago. In this limit, the scaling laws can be extrapolated to arbitrarily large Reynolds numbers.
Turbulent transport of toroidal angular momentum in low flow gyrokinetics
International Nuclear Information System (INIS)
Parra, Felix I; Catto, Peter J
2010-01-01
We derive a self-consistent equation for the turbulent transport of toroidal angular momentum in tokamaks in the low flow ordering that only requires solving gyrokinetic Fokker-Planck and quasineutrality equations correct to second order in an expansion on the gyroradius over scale length. We also show that according to our orderings the long wavelength toroidal rotation and the long wavelength radial electric field satisfy the neoclassical relation that gives the toroidal rotation as a function of the radial electric field and the radial gradients of pressure and temperature. Thus, the radial electric field can be solved for once the toroidal rotation is calculated from the transport of toroidal angular momentum. Unfortunately, even though this methodology only requires a gyrokinetic model correct to second order in gyroradius over scale length, current gyrokinetic simulations are only valid to first order. To overcome this difficulty, we exploit the smallish ratio B p /B, where B is the total magnetic field and B p is its poloidal component. When B p /B is small, the usual first order gyrokinetic equation provides solutions that are accurate enough to employ for our expression for the transport of toroidal angular momentum. We show that current δf and full f simulations only need small corrections to achieve this accuracy. Full f simulations, however, are still unable to determine the long wavelength, radial electric field from the quasineutrality equation.
Bi, Q.
2015-01-01
Sediment transport due to fluid motion is a crucial process in many environmental and engineered systems. Therefore, understanding sediment transport is critical for predicting sediment movements and evaluating the short and/or long-term influence to the surface water systems. Despite the importance of sediment transport, the fundamental aspects involved are far from being completely understood. At the core of the problem is the complex interaction between a turbulent flow field and sediment ...
Generalized perturbation theory using two-dimensional, discrete ordinates transport theory
International Nuclear Information System (INIS)
Childs, R.L.
1979-01-01
Perturbation theory for changes in linear and bilinear functionals of the forward and adjoint fluxes in a critical reactor has been implemented using two-dimensional discrete ordinates transport theory. The computer program DOT IV was modified to calculate the generalized functions Λ and Λ*. Demonstration calculations were performed for changes in a reaction-rate ratio and a reactivity worth caused by system perturbations. The perturbation theory predictions agreed with direct calculations to within about 2%. A method has been developed for calculating higher lambda eigenvalues and eigenfunctions using techniques similar to those developed for generalized functions. Demonstration calculations have been performed to obtain these eigenfunctions
Electron Temperature Fluctuation Measurements and Transport Model Validation at Alcator C-Mod
Energy Technology Data Exchange (ETDEWEB)
White, Anne [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2017-06-22
The tokamak is a type of toroidal device used to confine a fusion plasma using large magnetic fields. Tokamaks and stellarators the leading devices for confining plasmas for fusion, and the capability to predict performance in these magnetically confined plasmas is essential for developing a sustainable fusion energy source. The magnetic configuration of tokamaks and stellarators does not exist in Nature, yet, the fundamental processes governing transport in fusion plasmas are universal – turbulence and instabilities, driven by inhomogeneity and asymmetry in the plasma, conspire to transport heat and particles across magnetic field lines and can play critical roles in impurity confinement and generation of intrinsic rotation. Turbulence exists in all plasmas, and in neutral fluids as well. The study of turbulence is essential to developing a fundamental understanding of the nature of the fourth state of matter, plasmas. Experimental studies of turbulence in tokamaks date back to early scattering observations from the late 1970s. Since that time, great advances in turbulence diagnostics have been made, all of which have significantly enhanced our knowledge and understanding of turbulence in tokamaks. Through comparisons with advanced gyrokinetic theory and turbulent-transport models a great deal of evidence exists to implicate turbulent-driven transport as an important mechanism determining transport in all channels: heat, particle and momentum However, prediction and control of turbulent-driven transport remains elusive. Key to development of predictive transport models for magnetically confined fusion plasmas is validation of the nonlinear gyrokinetic transport model, which describes transport due to turbulence. Validation of gyrokinetic codes must include detailed and quantitative comparisons with measured turbulence characteristics, in addition to comparisons with inferred transport levels and equilibrium profiles. For this reason, advanced plasma diagnostics
Relation of astrophysical turbulence and magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Lazarian, A. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Eyink, Gregory L. [Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Vishniac, E. T. [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)
2012-01-15
Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.
Fundamentals of Turbulent and Multi-Phase Combustion
Kuo, Kenneth Kuan-yun
2012-01-01
Detailed coverage of advanced combustion topics from the author of Principles of Combustion, Second Edition Turbulence, turbulent combustion, and multiphase reacting flows have become major research topics in recent decades due to their application across diverse fields, including energy, environment, propulsion, transportation, industrial safety, and nanotechnology. Most of the knowledge accumulated from this research has never been published in book form-until now. Fundamentals of Turbulent and Multiphase Combustion presents up-to-date, integrated coverage of the fundamentals of turbulence
Dynamics of zonal flows and self-regulating drift-wave turbulence
International Nuclear Information System (INIS)
Diamond, P.H.; Fleischer, J.; Rosenbluth, M.N.; Hinton, F.L.; Malkov, M.; Smolyakov, A.
1999-01-01
We present a theory of zonal flow - drift wave dynamics. Zonal flows are generated by modulational instability of a drift wave spectrum, and are damped by collisions. Drift waves undergo random shearing-induced refraction, resulting in increased mean square radial wavenumber. Drift waves and zonal flows together form a simple dynamical system, which has a single stable fixed point. In this state, the fluctuation intensity and turbulent diffusivity are ultimately proportional to the collisional zonal flow damping. The implications of these results for transport models is discussed. (author)
Dynamics of zonal flows and self-regulating drift-wave turbulence
International Nuclear Information System (INIS)
Diamond, P.H.; Fleischer, J.; Rosenbluth, M.; Hinton, F.L.; Malkov, M.; Smolyakov, A.
2001-01-01
We present a theory of zonal flow - drift wave dynamics. Zonal flows are generated by modulational instability of a drift wave spectrum, and are damped by collisions. Drift waves undergo random shearing-induced refraction, resulting in increased mean square radial wavenumber. Drift waves and zonal flows together form a simple dynamical system, which has a single stable fixed point. In this state, the fluctuation intensity and turbulent diffusivity are ultimately proportional to the collisional zonal flow damping. The implications of these results for transport models is discussed. (author)
Kinetic simulations of neoclassical and anomalous transport processes in helical systems
International Nuclear Information System (INIS)
Sugama, Hideo; Watanabe, Tomohiko; Nunami, Masanori; Satake, Shinsuke; Matsuoka, Seikichi; Tanaka, Kenji
2012-01-01
Drift kinetic and gyrokinetic theories and simulations are powerful means for quantitative predictions of neoclassical and anomalous transport fluxes in helical systems such as the Large Helical Device (LHD). The δf Monte Carlo particle simulation code, FORTEC-3D, is used to predict radial profiles of the neoclassical particle and heat transport fluxes and the radial electric field in helical systems. The radial electric field profiles in the LHD plasmas are calculated from the ambipolarity condition for the neoclassical particle fluxes obtained by the global simulations using the FORTEC-3D code, in which effects of ion or electron finite orbit widths are included. Gyrokinetic Vlasov simulations using the GKV code verify the theoretical prediction that the neoclassical optimization of helical magnetic configuration enhances the zonal flow generation which leads to the reduction of the turbulent heat diffusivity χ i due to the ion temperature gradient (ITG) turbulence. Comparisons between results for the high ion temperature LHD experiment and the gyrokinetic simulations using the GKV-X code show that the χ i profile and the poloidal wave number spectrum of the density fluctuation obtained from the simulations are in reasonable agreements with the experimental results. It is predicted theoretically and confirmed by the linear GKV simulations that the E × B rotation due to the background radial electric field E r can enhance the zonal-flow response to a given source. Thus, in helical systems, the turbulent transport is linked to the neoclassical transport through E r which is determined from the ambipolar condition for neoclassical particle fluxes and influences the zonal flow generation leading to reduction of the turbulent transport. In order to investigate the E r effect on the regulation of the turbulent transport by the zonal flow generation, the flux-tube bundle model is proposed as a new method for multiscale gyrokinetic simulations. (author)
Inelastic transport theory for nanoscale systems
DEFF Research Database (Denmark)
Frederiksen, Thomas
2007-01-01
This thesis describes theoretical and numerical investigations of inelastic scat- tering and energy dissipation in electron transport through nanoscale sys- tems. A computational scheme, based on a combination of density functional theory (DFT) and nonequilibrium Green’s functions (NEGF), has been...
Robust flow stability: Theory, computations and experiments in near wall turbulence
Bobba, Kumar Manoj
Helmholtz established the field of hydrodynamic stability with his pioneering work in 1868. From then on, hydrodynamic stability became an important tool in understanding various fundamental fluid flow phenomena in engineering (mechanical, aeronautics, chemical, materials, civil, etc.) and science (astrophysics, geophysics, biophysics, etc.), and turbulence in particular. However, there are many discrepancies between classical hydrodynamic stability theory and experiments. In this thesis, the limitations of traditional hydrodynamic stability theory are shown and a framework for robust flow stability theory is formulated. A host of new techniques like gramians, singular values, operator norms, etc. are introduced to understand the role of various kinds of uncertainty. An interesting feature of this framework is the close interplay between theory and computations. It is shown that a subset of Navier-Stokes equations are globally, non-nonlinearly stable for all Reynolds number. Yet, invoking this new theory, it is shown that these equations produce structures (vortices and streaks) as seen in the experiments. The experiments are done in zero pressure gradient transiting boundary layer on a flat plate in free surface tunnel. Digital particle image velocimetry, and MEMS based laser Doppler velocimeter and shear stress sensors have been used to make quantitative measurements of the flow. Various theoretical and computational predictions are in excellent agreement with the experimental data. A closely related topic of modeling, simulation and complexity reduction of large mechanics problems with multiple spatial and temporal scales is also studied. A nice method that rigorously quantifies the important scales and automatically gives models of the problem to various levels of accuracy is introduced. Computations done using spectral methods are presented.
International Nuclear Information System (INIS)
1993-12-01
The long-range goal of the Numerical Tokamak Project (NTP) is the reliable prediction of tokamak performance using physics-based numerical tools describing tokamak physics. The NTP is accomplishing the development of the most advanced particle and extended fluid model's on massively parallel processing (MPP) environments as part of a multi-institutional, multi-disciplinary numerical study of tokamak core fluctuations. The NTP is a continuing focus of the Office of Fusion Energy's theory and computation program. Near-term HPCC work concentrates on developing a predictive numerical description of the core plasma transport in tokamaks driven by low-frequency collective fluctuations. This work addresses one of the greatest intellectual challenges to our understanding of the physics of tokamak performance and needs the most advanced computational resources to progress. We are conducting detailed comparisons of kinetic and fluid numerical models of tokamak turbulence. These comparisons are stimulating the improvement of each and the development of hybrid models which embody aspects of both. The combination of emerging massively parallel processing hardware and algorithmic improvements will result in an estimated 10**2--10**6 performance increase. Development of information processing and visualization tools is accelerating our comparison of computational models to one another, to experimental data, and to analytical theory, providing a bootstrap effect in our understanding of the target physics. The measure of success is the degree to which the experimentally observed scaling of fluctuation-driven transport may be predicted numerically. The NTP is advancing the HPCC Initiative through its state-of-the-art computational work. We are pushing the capability of high performance computing through our efforts which are strongly leveraged by OFE support
Turbulent regimes in the tokamak scrape-off layer
International Nuclear Information System (INIS)
Mosetto, A.
2014-01-01
The tokamak scrape-off layer (SOL) is the plasma region characterized by open field lines that start and end on the vessel walls. The plasma dynamics in the SOL plays a crucial role in determining the overall performance of a tokamak, since it controls the plasma-wall interactions, being responsible of exhausting the tokamak power, it regulates the overall plasma confinement, and it governs the plasma refueling and the removal of fusion ashes. Scrape-off layer physics is intrinsically non-linear and characterized by phenomena that occur on a wide range of spatio-temporal scales. Free energy sources drive a number of unstable modes that develop into turbulence and lead to transport of particles and heat across the magnetic field lines. Depending on the driving instability, different SOL turbulent regimes can be identified. As the SOL turbulent regimes determine the plasma confinement properties and the SOL width (and, consequently, the power flux on the vessel wall, for example), it is of crucial importance to understand which turbulent regimes are active in the SOL, under which conditions they develop, and which are the main properties of the associated turbulent transport. In the present thesis we define the SOL turbulent regimes, and we provide a framework to identify them, given the operational SOL parameters. Our study is based on the drift-reduced Braginskii equations and it is focused on a limited tokamak SOL configuration. We first describe the main SOL linear instabilities, such as the inertial and resistive branches of the drift waves, the resistive, inertial and ideal branches of the ballooning modes, and the ion temperature gradient mode. Then, we find the SOL turbulent regimes depending on the instability driving turbulent transport, assuming that turbulence saturates when the radial gradient associated to the pressure fluctuations is comparable to the equilibrium one. Our methodology for the turbulent regime identification is supported by the analysis
Pebble Accretion in Turbulent Protoplanetary Disks
Xu, Ziyan; Bai, Xue-Ning; Murray-Clay, Ruth A.
2017-09-01
It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the “Hill regime”), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time {τ }s˜ 0.1{--}1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to {τ }s˜ 0.01) can be modestly reduced by strong turbulence for low-mass cores.
Quantal foundation of the nucleon exchange transport theory
International Nuclear Information System (INIS)
Randrup, J.
1985-07-01
The central elements of the nucleon exchange transport theory are discussed within a fully quantal framework in order to elucidate the principal characteristics, validity and limitations of the theory. Special consideration is given to the mean rate of energy dissipation and the penetrability coefficient. (orig.)
Progress in wall turbulence 2 understanding and modelling
Jimenez, Javier; Marusic, Ivan
2016-01-01
This is the proceedings of the ERCOFTAC Workshop on Progress in Wall Turbulence: Understanding and Modelling, that was held in Lille, France from June 18 to 20, 2014. The workshop brought together world specialists of near wall turbulence and stimulated exchanges between them around up-to-date theories, experiments, simulations and numerical models. This book contains a coherent collection of recent results on near wall turbulence including theory, new experiments, DNS, and modeling with RANS, LES.The fact that both physical understanding and modeling by different approaches are addressed by the best specialists in a single workshop is original.
MEASUREMENTS AND COMPUTATIONS OF FUEL DROPLET TRANSPORT IN TURBULENT FLOWS
Energy Technology Data Exchange (ETDEWEB)
Joseph Katz and Omar Knio
2007-01-10
The objective of this project is to study the dynamics of fuel droplets in turbulent water flows. The results are essential for development of models capable of predicting the dispersion of slightly light/heavy droplets in isotropic turbulence. Since we presently do not have any experimental data on turbulent diffusion of droplets, existing mixing models have no physical foundations. Such fundamental knowledge is essential for understanding/modeling the environmental problems associated with water-fuel mixing, and/or industrial processes involving mixing of immiscible fluids. The project has had experimental and numerical components: 1. The experimental part of the project has had two components. The first involves measurements of the lift and drag forces acting on a droplet being entrained by a vortex. The experiments and data analysis associated with this phase are still in progress, and the facility, constructed specifically for this project is described in Section 3. In the second and main part, measurements of fuel droplet dispersion rates have been performed in a special facility with controlled isotropic turbulence. As discussed in detail in Section 2, quantifying and modeling the of droplet dispersion rate requires measurements of their three dimensional trajectories in turbulent flows. To obtain the required data, we have introduced a new technique - high-speed, digital Holographic Particle Image Velocimetry (HPIV). The technique, experimental setup and results are presented in Section 2. Further information is available in Gopalan et al. (2005, 2006). 2. The objectives of the numerical part are: (1) to develop a computational code that combines DNS of isotropic turbulence with Lagrangian tracking of particles based on integration of a dynamical equation of motion that accounts for pressure, added mass, lift and drag forces, (2) to perform extensive computations of both buoyant (bubbles) and slightly buoyant (droplets) particles in turbulence conditions
Plasma transport simulation modeling for helical confinement systems
International Nuclear Information System (INIS)
Yamazaki, K.; Amano, T.
1991-08-01
New empirical and theoretical transport models for helical confinement systems are developed based on the neoclassical transport theory including the effect of radial electric field and multi-helicity magnetic components, and the drift wave turbulence transport for electrostatic and electromagnetic modes, or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with CHS (Compact Helical System) experimental data, which indicates that the central transport coefficient of the ECH plasma agrees with the neoclassical axi-symmetric value and the transport outside the half radius is anomalous. On the other hand, the transport of NBI-heated plasmas is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these flat-density-profile discharges. For the detailed prediction of plasma parameters in LHD (Large Helical Device), 3-D(dimensional) equilibrium/1-D transport simulations including empirical or drift wave turbulence models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase of the global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to the half level of the present scaling, like so-called 'H-mode' of the tokamak discharge, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius is effective for improving plasma confinement and raising more than 50% of the fusion product by reducing this neoclassical asymmetric ion transport loss and increasing 10% in the plasma radius. (author)
Saturation of ion-acoustic turbulence
International Nuclear Information System (INIS)
Bychenkov, V.Yu.; Gradov, O.M.
1985-01-01
The time evolution of ion-acoustic turbulence is investigated taking into consideration both the scattering of electrons and the induced scattering of waves by the ions. The growth rate of the ion-acoustic turbulence is studied as the function of the wave number, including the long-wave ion sound excitations. It is shown that the relaxation of the ion-acoustic turbulence leads to the quasistationary noise distributions, which are the products of distributions according to the wave number and to the angle. The spectra conform to the stationary theory. (D.Gy.)
Kinetic theory of nonlinear transport phenomena in complex plasmas
International Nuclear Information System (INIS)
Mishra, S. K.; Sodha, M. S.
2013-01-01
In contrast to the prevalent use of the phenomenological theory of transport phenomena, a number of transport properties of complex plasmas have been evaluated by using appropriate expressions, available from the kinetic theory, which are based on Boltzmann's transfer equation; in particular, the energy dependence of the electron collision frequency has been taken into account. Following the recent trend, the number and energy balance of all the constituents of the complex plasma and the charge balance on the particles is accounted for; the Ohmic loss has also been included in the energy balance of the electrons. The charging kinetics for the complex plasma comprising of uniformly dispersed dust particles, characterized by (i) uniform size and (ii) the Mathis, Rumpl, and Nordsieck power law of size distribution has been developed. Using appropriate expressions for the transport parameters based on the kinetic theory, the system of equations has been solved to investigate the parametric dependence of the complex plasma transport properties on the applied electric field and other plasma parameters; the results are graphically illustrated.
SU-E-P-04: Transport Theory Learning Module in the Maple Environment
Energy Technology Data Exchange (ETDEWEB)
Both, J [University of Miami, Miller School of Medicine, Department of Radiation Oncology (United States)
2014-06-01
Purpose: The medical physics graduate program at the University of Miami is developing a computerized instructional module which provides an interactive mechanism for students to learn transport theory. While not essential in the medical physics curriculum, transport theory should be taught because the conceptual level of transport theory is fundamental, a substantial literature exists and ought to be accessible, and students should understand commercial software which solves the Boltzmann equation.But conventional teaching and learning of transport theory is challenging. Students may be under prepared to appreciate its methods, results, and relevance, and it is not substantially addressed in textbooks for the medical physicists. Other resources an instructor might reasonably use, while excellent, may be too briskly paced for beginning students. The purpose of this work is to render teaching of transport theory more tractable by making learning highly interactive. Methods: The module is being developed in the Maple mathematics environment by instructors and graduate students. It will refresh the students' knowledge of vector calculus and differential equations, and will develop users' intuition for phase space concepts. Scattering concepts will be developed with animated simulations using tunable parameters characterizing interactions, so that students may develop a “feel” for cross section. Transport equations for one and multiple types of radiation will be illustrated with phase space animations. Numerical methods of solution will be illustrated. Results: Attempts to teach rudiments of transport theory in radiation physics and dosimetry courses using conventional classroom techniques at the University of Miami have had small success, because classroom time is limited and the material has been hard for our students to appreciate intuitively. Conclusion: A joint effort of instructor and students to teach and learn transport theory by building an
SU-E-P-04: Transport Theory Learning Module in the Maple Environment
International Nuclear Information System (INIS)
Both, J
2014-01-01
Purpose: The medical physics graduate program at the University of Miami is developing a computerized instructional module which provides an interactive mechanism for students to learn transport theory. While not essential in the medical physics curriculum, transport theory should be taught because the conceptual level of transport theory is fundamental, a substantial literature exists and ought to be accessible, and students should understand commercial software which solves the Boltzmann equation.But conventional teaching and learning of transport theory is challenging. Students may be under prepared to appreciate its methods, results, and relevance, and it is not substantially addressed in textbooks for the medical physicists. Other resources an instructor might reasonably use, while excellent, may be too briskly paced for beginning students. The purpose of this work is to render teaching of transport theory more tractable by making learning highly interactive. Methods: The module is being developed in the Maple mathematics environment by instructors and graduate students. It will refresh the students' knowledge of vector calculus and differential equations, and will develop users' intuition for phase space concepts. Scattering concepts will be developed with animated simulations using tunable parameters characterizing interactions, so that students may develop a “feel” for cross section. Transport equations for one and multiple types of radiation will be illustrated with phase space animations. Numerical methods of solution will be illustrated. Results: Attempts to teach rudiments of transport theory in radiation physics and dosimetry courses using conventional classroom techniques at the University of Miami have had small success, because classroom time is limited and the material has been hard for our students to appreciate intuitively. Conclusion: A joint effort of instructor and students to teach and learn transport theory by building an interactive
Large-aspect-ratio limit of neoclassical transport theory
International Nuclear Information System (INIS)
Wong, S K.; Chan, V.S.
2003-01-01
This paper presents a comprehensive description of neoclassical transport theory in the banana regime for large-aspect-ratio flux surfaces of arbitrary shapes. The method of matched-asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates the discussion of the treatment of dynamical constraints. It is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard
Large-aspect-ratio limit of neoclassical transport theory.
Wong, S K; Chan, V S
2003-06-01
This paper presents a comprehensive description of neoclassical transport theory in the banana regime for large-aspect-ratio flux surfaces of arbitrary shapes. The method of matched-asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates the discussion of the treatment of dynamical constraints. It is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard.
Statistical Mechanics of Turbulent Dynamos
Shebalin, John V.
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random