共查询到20条相似文献,搜索用时 31 毫秒
1.
We provide a theory of dynamo (alpha effect) and momentum transport in three-dimensional magnetohydrodynamics. For the first time, we show that the alpha effect is reduced by the shear even in the absence of magnetic field. The alpha effect is further suppressed by magnetic fields well below equipartition (with the large-scale flow) with different scalings depending on the relative strength of shear and magnetic field. The turbulent viscosity is also found to be significantly reduced by shear and magnetic fields, with positive value. These results suggest a crucial effect of shear and magnetic field on dynamo quenching and momentum transport reduction, with important implications for laboratory and astrophysical plasmas, in particular, for the dynamics of the Sun. 相似文献
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The nonlinear dynamics of microtearing modes in standard tokamak plasmas are investigated by means of ab initio gyrokinetic simulations. The saturation levels of the magnetic field fluctuations can be understood in the framework of a balance between (small poloidal wave number) linear drive and small-scale dissipation. The resulting heat transport is dominated by the electron magnetic component, and the transport levels are found to be experimentally relevant. Microtearing modes thus constitute another candidate for explaining turbulent transport in such toroidal systems. 相似文献
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Using direct numerical simulations of a hybrid Vlasov-Maxwell model, kinetic processes are investigated in a two-dimensional turbulent plasma. In the turbulent regime, kinetic effects manifest through a deformation of the ion distribution function. These patterns of non-Maxwellian features are concentrated in space nearby regions of strong magnetic activity: the distribution function is modulated by the magnetic topology, and can elongate along or across the local magnetic field. These results open a new path on the study of kinetic processes such as heating, particle acceleration, and temperature anisotropy, commonly observed in astrophysical and laboratory plasmas. 相似文献
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The dynamo equations are solved numerically with a helical forcing corresponding to the Roberts flow. In the fully turbulent regime the flow behaves as a Roberts flow on long time scales, plus turbulent fluctuations at short time scales. The dynamo onset is controlled by the long time scales of the flow, in agreement with the former Karlsruhe experimental results. The dynamo mechanism is governed by a generalized α effect, which includes both the usual α effect and turbulent diffusion, plus all higher order effects. Beyond the onset we find that this generalized α effect scales as O(Rm(-1)), suggesting the takeover of small-scale dynamo action. This is confirmed by simulations in which dynamo occurs even if the large-scale field is artificially suppressed. 相似文献
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S. V. Bulanov T. Zh. Esirkepov D. Habs F. Pegoraro T. Tajima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):483-507
The paper is devoted to the prospects of using the laser radiation
interaction with plasmas in the laboratory relativistic astrophysics
context. We discuss the dimensionless parameters characterizing the
processes in the laser and astrophysical plasmas and emphisize a similarity
between the laser and astrophysical plasmas in the ultrarelativistic energy
limit. In particular, we address basic mechanisms of the charged particle
acceleration, the collisionless shock wave and magnetic reconnection and
vortex dynamics properties relevant to the problem of ultrarelativistic
particle acceleration. 相似文献
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The spin-orbit coupling effects on the velocity space electromagnetic instabilities have been analytically studied. In this order, first, a suitable form of the kinetic theory is introduced and then, results are investigated for real ICF and astrophysical plasmas. For the ICF plasmas, Low intensity magnetic field can not provide a suitable field for effectiveness of the particle’s spin, while transmission to astrophysical subjects is different. For astrophysical applications, the spin-orbit coupling effects can lead to addition free energy so that, it can overcoming the non relativistic effects and leads to increasing the instability growth rate. 相似文献
10.
Nonlinear fluid simulations are developed by us to investigate the properties of fully developed two-dimensional (2D) electron fluid turbulence in a very dense Fermi (quantum) plasma. We find that a 2D quantum electron plasma exhibits dual cascades, in which the electron number density cascades towards smaller turbulent scales, while the electrostatic potential forms larger scale eddies. The characteristic turbulent spectrum associated with the nonlinear electron plasma oscillations (EPO) is determined critically by a ratio of the energy density of the EPOs and the electron kinetic energy density of quantum plasmas. The turbulent transport corresponding to the large-scale potential distribution is predominant in comparison with the small-scale electron number density variation, a result that is consistent with the classical diffusion theory. 相似文献
11.
XIE Bai-Song 《理论物理通讯》2006,46(3):561-562
Two new solutions for non-constant-α force-free magnetic field are found analytically. Implications of the results to astrophysical solar plasmas as well tokamak plasmas are discussed. 相似文献
12.
本文用解析方法表示了高比压环流器的平衡位形,进而计算了局部理想磁流体判据,并着重讨论了低q运行的可能性。结果发现存在一大类具有这些特性的环流器平衡位形,有的位形其中心约束区域有很高的稳定性余度。对p′(ψ)剖面不同的位形以及不同位移函数的位形的稳定性做比较,发现大的位移及平坦的p′(ψ)剖面有更好的稳定性。
关键词: 相似文献
13.
Flux tubes confined in tokamaks are observed to erupt explosively in some plasma disruptions and edge localized modes. Similar eruptions occur in astrophysical plasmas, for example, in solar flares and magnetospheric substorms. A single unifying nonlinear evolution equation describing such behavior in both astrophysical and tokamak plasmas is derived. This theory predicts that flux tubes rise explosively, narrow, and twist to pass through overlying magnetic field lines without reconnection. 相似文献
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The phase-relationship between large-scale motions and small-scale fluctuations in a non-equilibrium turbulent boundary layer was investigated. A zero-pressure-gradient flat plate turbulent boundary layer was perturbed by a short array of two-dimensional roughness elements, both statically, and under dynamic actuation. Within the compound, dynamic perturbation, the forcing generated a synthetic very-large-scale motion (VLSM) within the flow. The flow was decomposed by phase-locking the flow measurements to the roughness forcing, and the phase-relationship between the synthetic VLSM and remaining fluctuating scales was explored by correlation techniques. The general relationship between large- and small-scale motions in the perturbed flow, without phase-locking, was also examined. The synthetic large scale cohered with smaller scales in the flow via a phase-relationship that is similar to that of natural large scales in an unperturbed flow, but with a much stronger organizing effect. Cospectral techniques were employed to describe the physical implications of the perturbation on the relative orientation of large- and small-scale structures in the flow. The correlation and cospectral techniques provide tools for designing more efficient control strategies that can indirectly control small-scale motions via the large scales. 相似文献
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XIE Bai-Song 《理论物理通讯》2006,46(4):735-738
Some new approaches for nonlinear force-free magnetic field are presented and new exact solutions are found analytically. Examples are given and some implications of results to astrophysical solar plasmas as well as tokamak or/and spheromak plasmas are discussed. 相似文献
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J. S. Sarff A. F. Almagri J. K. Anderson B. E. Chapman D. Craig C -S. Chiang N. A. Crocker D. J. Den Hartog G. Fiksel A. K. Hansen S. C. Prager 《Czechoslovak Journal of Physics》2000,50(12):1471-1476
Edge biasing in MST plasmas decreases electrostatic turbulent particle transport and increases the global particle confinement
time. New Langmuir probe measurements in the edge identify decreased electric field fluctuations and increased anti-correlation
of density and potential fluctuations to be responsible. Fast loss of momentum in the core of MST during sawtooth crash events
can be explained as a result of nonlinear magnetic torques which allow viscous coupling over relatively distant regions of
the plasma. Flow modifications resulting from biasing, plus other experiments, help reveal the nonlinear nature of this process,
most directly measured by the triple product bispectral correlation between the nonlinearly interacting modes.
Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000. 相似文献
17.
Nagashima Y Hoshino K Ejiri A Shinohara K Takase Y Tsuzuki K Uehara K Kawashima H Ogawa H Ido T Kusama Y Miura Y 《Physical review letters》2005,95(9):095002
Two types of electrostatic modes with small-poloidal wave numbers (approximately 1 and 10-15 kHz) are observed in the edge region of Ohmically heated plasmas in the JFT-2M tokamak. The envelope of the higher frequency coherent mode is modulated at the frequency of the lower frequency mode. A bispectral analysis revealed that a significant nonlinear coupling among the two types of fluctuations and the broadband background turbulent potential fluctuations occurs inside the last closed magnetic flux surface, suggesting that a nonlinear process such as the parametric-modulational instability is involved. 相似文献
18.
Two-point OH time-series measurements using a high-speed, laser-induced fluorescence system have been performed in a turbulent
nonpremixed jet flame to obtain both radial and axial space–time correlations. Turbulent OH structures in such flames are
found to undergo convection both axially and radially, but OH convection does not satisfy the ‘frozen-turbulence’ hypothesis
owing to various turbulent interactions and chemical reactions. While axial OH convection occurs at approximately the local
mean bulk velocity, radial convection is largely compromised by strong turbulent mixing along the same direction. The hydroxyl
integral length scale can be interpreted as the typical dimension of a convective OH structure, which is axially elongated
and becomes more isotropic in the post-flame region. The hydroxyl integral time scale can be interpreted as approximately
the ratio of an axial integral length scale to a corresponding local mean flow velocity. In general, macroscale fluctuations
of OH are dominated by large-scale turbulence, with little contribution from small-scale turbulence and OH chemistry. 相似文献
19.
We investigate the inverse scattering problem for statistically homogeneous, isotropic random media under conditions of strong fluctuations of optical wavefields. We present a method for determining the spectral density of the dielectric constant fluctuations in such media from scattering of partially coherent light. The method may find applications to a wide class of turbulent media such as the turbulent atmosphere and certain turbulent plasmas where backscattering and depolarization effects are negligible. 相似文献