共查询到20条相似文献,搜索用时 359 毫秒
1.
M. A. Pedrosa C. Hidalgo E. Calderon A. Alonso R. O. Orozco J. L. De Pablos TJ-II team P. Balan 《Czechoslovak Journal of Physics》2005,55(12):1579-1587
The influence of plasma density and edge gradients in the development of perpendicular sheared flow has been investigated
in the plasma edge region of the TJ-II stellarator. It has been experimentally observed that the generation of spontaneous
perpendicular sheared flow (i.e. the naturally occurring shear layer) requires a minimum plasma density or gradient. It has
been found that there is a coupling between the onset of sheared flow development and an increase in the level of plasma edge
turbulence; once sheared flow is fully developed the level of fluctuations and turbulent transport slightly decreases whereas
edge gradients and plasma density increase. The resulting shearing rate is close to the one required to trigger a transition
to improved confinement regimes with reduction of edge turbulence, showing that spontaneous sheared flows and fluctuations
keep themselves near marginal stability.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
2.
We investigate the turbulence modulation by particles in a turbulent two-phase channel flow via an analysis of turbulence anisotropy-invariants. The fluid turbulence is calculated by a large eddy simulation with a point-force two-way coupling model and particles are tracked by the Lagrangian trajectory method. The channel turbulence follows the two-component turbulence state within the viscous sub-layer region and outside the region the turbulence tends to follow the right curve of the anisotropy-invariant.... 相似文献
3.
Reversed rotation of limit cycle oscillation and dynamics of low-intermediate-high confinement transition
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The dynamics of the confinement transition from L mode to H mode(LH) is investigated in detail theoretically via the extended three-wave coupling model describing the interaction of turbulence and zonal flow(ZF) for the first time.Thereinto, turbulence is divided into a positive-frequency(PF) wave and a negative-frequency(NF) one, and the gradient of pressure is added as the auxiliary energy for the system. The LH confinement transition is observed for a sufficiently high input energy. Moreover, it is found that the rotation direction of the limit cycle oscillation(LCO) of PF wave and pressure gradient is reversed during the transition. The mechanism is illustrated by exploring the wave phases. The results presented here provide a new insight into the analysis of the LH transition, which is helpful for the experiments on the fusion devices. 相似文献
4.
评述和分析了磁约束核聚变理论研究、数值模拟和实验研究等方面最近几年共同关心的一个重要问题——寻找托卡马克等离子体湍流中的带状剪切流(zonal flows)。简要介绍了作者最近对电阻性-重力模湍流中的带状剪切流的研究结果。 Progress of the research on the zonal flows in tokamak plasma turbulence is surveyed, especially it is reviewed that the zonal flows observed in the experiments and numerical simulations on atmosphere turbulence and ocean turbulence and the discovery of H-mode in tokamak experiments how lead the researchers in magnetic confinement fusion community to find out the existence of the zonal flow in tokamak plasma turbulence and subsequently give the experimental verification of its existence. Finally, the results of our research on zonal flow generation and evolution in resistive-g mode turbulence are presented in brief. 相似文献
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A nonlinear wave coupling algorithm and its programing and application in plasma turbulences
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The fully developed turbulence can be regarded as a nonlinear system, with wave coupling inside, which causes the nonlinear energy to transfer, and drives the turbulence to develop further or be suppressed. Spectral analysis is one of the most effective methods to study turbulence system. In order to apply it to the study of the nonlinear wave coupling process of edge plasma turbulence, an efficient algorithm based on spectral analysis technology is proposed to solve the nonlinear wave coupling equation. The algorithm is based on a mandatory temporal static condition with the nonideal spectra separated from the ideal spectra. The realization idea and programing flow are given. According to the characteristics of plasma turbulence, the simulation data are constructed and used to verify the algorithm and its implementation program. The simulation results and experimental results show the accuracy of the algorithm and the corresponding program, which can play a great role in the studying the energy transfer in edge plasma turbulences. As an application, the energy cascade analysis of typical edge plasma turbulence is carried out by using the results of a case calculation. Consequently, a physical picture of the energy transfer in a kind of fully developed turbulence is constructed, which confirms that the energy transfer in this turbulent system develops from lower-frequency region to higher-frequency region and from linear growing wave to damping wave. 相似文献
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M. Takeuchi T. Imanishi D. Ushijima K. Kawashima K. Fujiwara 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We have investigated field-induced features of optical transitions in asymmetric double-well superlattices (ADW-SLs) with and without barrier sequence modulation by low-temperature photocurrent (PC) spectroscopy. The difference between the heavy-hole confinement energies in the wide and narrow wells results in two types of Stark-ladder transitions, so that four ±1st-order spatially indirect transitions are expected to exist in the ADW-SL. The oscillator strength of these indirect transitions is affected by the strength and the direction of coupling between the wide and narrow wells. The introduction of the barrier sequence modulation into the ADW-SL realizes the control of these coupling mechanisms. This technique is a new method to modulate the oscillator strength of the indirect Stark-ladder transitions. 相似文献
9.
From our recent theory based on the generation of shear flow and field in finite beta plasmas, the criterion for bifurcation from low to high confinement mode yields a critical parameter proportional to T(e)/square root (L(n)), where T(e) is the electron temperature and L(n) is the density scale length. The predicted threshold shows very good agreement with edge measurements on discharges undergoing low-to-high transitions in DIII-D. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter. The theory also provides an explanation for pellet injection H modes in DIII-D, thereby unifying unconnected methods for accomplishing the transition. 相似文献
10.
Conway GD Angioni C Ryter F Sauter P Vicente J;ASDEX Upgrade Team 《Physical review letters》2011,106(6):065001
A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear. 相似文献
11.
We report experimental evidence of transitions from limit cycle oscillations through a phase turbulent regime to space-time defect turbulence in a spatially (quasi-)one-dimensional electrochemical system with nonlocal coupling. The transitions are characterized in terms of the defect density, the Karhunen-Loève decomposition dimension, and a measure of the degree of spatial correlation in the data. Furthermore, these quantities give the first experimental confirmation that the spatial coupling range in electrochemical systems indeed depends on the distance between the working and the counterelectrode. 相似文献
12.
Wilhelm H Baenitz M Schmidt M Rössler UK Leonov AA Bogdanov AN 《Physical review letters》2011,107(12):127203
We report on detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at T(C)=278.2(3) K. Precursor phenomena display a complex succession of temperature-driven crossovers and phase transitions in the vicinity of T(C). The A-phase region, present below T(C) and fields H<0.5 kOe, is split in several pockets. The complexity of the magnetic phase diagram is theoretically explained by the confinement of solitonic kinklike or Skyrmionic units that develop an attractive and oscillatory intersoliton coupling owing to the longitudinal inhomogeneity of the magnetization. 相似文献
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Xu Y Weynants RR Jachmich S Van Schoor M Vergote M Peleman P Jakubowski MW Mitri M Reiser D Unterberg B Finken KH;TEXTOR Team 《Physical review letters》2006,97(16):165003
Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the Er x B flow. In the laminar region, the turbulence is found to react to an observed reduced flow shear. 相似文献
15.
C. A. de Sousa 《Zeitschrift fur Physik C Particles and Fields》1989,44(3):503-508
Giving up the restriction ε/p=const, we show that equations of state with ε?3p=Δ>0 will be driven to the inflationary solution with ε=?p after sufficiently long times. Subsequently, we show that confinement transitions may provide such an equation of state due to a change of degrees of freedom. Depending on the energy scale of the confinement transition inflation may occur during confinement. Numerical results for quark and subquark confinement are given. For QCD-confinement the transition time is too short, compared to the energy density, for a significant deviation of the scale factor to occur. 相似文献
16.
Gurjav Ganbold 《Physics of Particles and Nuclei》2012,43(1):79-105
We study the behavior of the QCD effective coupling α
s
in the low-energy region by exploiting the conventional meson spectrum within a relativistic quantum-field model based on
analytical confinement of quarks and gluons. The spectra of quark-antiquark and two-gluon bound states are defined by using
a master equation similar to the ladder Bethe-Salpeter equation. A new, independent and specific infrared-finite behavior
of QCD coupling is found below energy scale ∼1 GeV. Particularly, an infrared-fixed point is extracted at α
s
(0) ≅ 0.757 for confinement scale Λ = 345 MeV. We provide a new analytic estimate of the lowest-state glueball mass. As applications,
we also estimate masses of some intermediate and heavy mesons as well as the weak-decay constants of light mesons. By introducing
only a minimal set of parameters (the quark masses m
f
and Λ) we obtain results in reasonable agreement with recent experimental data in a wide range of energy scale ∼0.1–10 GeV.
We demonstrate that global properties of some low-energy phenomena may be explained reasonably in the framework of a simple
relativistic quantum-field model if one guesses correct symmetry structure of the quark-gluon interaction in the confinement
region and uses simple forms of propagators in the hadronisation regime. The model may serve a reasonable framework to describe
simultaneously different sectors in low-energy particle physics. 相似文献
17.
A. Boughamoura H. Belmabrouk S. Ben Nasrallah L. Le Penven 《ARI - An International Journal for Physical and Engineering Sciences》2001,52(1):14-22
This paper is concerned with the simulation of a turbulent flow submitted to a cyclic one-dimensional compression and expansion between two parallel flat pistons moving with opposite velocities in the direction of their perpendicular axis. The turbulence model used is the second-order model developed at a low Reynolds number by Craft and Launder. Numerical results show that the turbulent field may be considered as homogeneous in an extended part of the domain. The confinement effect appears mainly in the vicinity of the moving walls while the central region is especially influenced by the compression effect. The evolution of the heat flux, transferred from the fluid through the moving walls, tends to a zero limit cycle in the turbulent flow and to a non-zero limit cycle in the laminar flow. The disappearance of the turbulent energy is not predicted by the k-l model. 相似文献
18.
Barnes M Parra FI Highcock EG Schekochihin AA Cowley SC Roach CM 《Physical review letters》2011,106(17):175004
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E×B shear value for plasma confinement. Local maxima in the momentum fluxes are observed, implying the possibility of bifurcations in the E×B shear. The critical temperature gradient for the onset of turbulence increases with flow shear at low flow shears; at higher flow shears, the dependence of heat flux on temperature gradient becomes less stiff. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity. 相似文献
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A scale for two-dimensional β-plane magnetohydrodynamic turbulence is proposed that characterizes an upper bound of the energy containing interval similar to a classical Rhines scale for neutral fluid turbulence on a -plane. It is found that only unsteady zonal flows with complex temporal dynamics are formed in two-dimensional magnetohydrodynamic turbulence on the -plane. It is shown that flow nonstationarity is due to the appearance of isotropic magnetic islands caused by the Lorentz force in the system. The characteristic dimensions of a flow are in agreement with the proposed scale. 相似文献