摘要:

The surface flow pattern of decaying turbulence generated by a vertical bar grid in a towing tank has been studied. The velocities and positions of about 2×104Al aluminum filing tracers following the surface motion have been measured and statistically analyzed. From ten photo series, each of 10 mesh width span and 40 mesh widths long, 2000 surface eddies were identified and studied. The flow field is decomposed into ‘‘closed’’ rotating flow structures (the surface eddies) and ‘‘open’’ flow structures (rivers) of predominantly translational motion. There are also relatively stagnant areas that grow in number and size with time. Immediately behind the grid the average energy densities of the surface eddieseeand the riverserare about equal buteedecays at a greater rate thaner. The eddy size distribution gradually shifts to larger eddies and an increasing fraction of the fluctuating kinetic energy is transferred into the rivers. In the collision‐dominated equilibrium region, the eddy and the river energy distributions can be described by Boltzmann‐type functions. These distributions may then be characterized by ‘‘temperature’’ &thgr;eand &thgr;rfor eddies and rivers. These temperatures decay steadily throughout the observation period, but remain approximately equal to each other. The relationship between the surface flow dynamics and the subsurface and bulk turbulent grid‐flow is examined.

ISSN:0031-9171    

DOI:10.1063/1.865532

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The Lie group invariance properties of the one‐dimensional radiation hydrodynamic equations with the equilibrium diffusion approximation, a local thermodynamical equilibrium assumption, and an arbitrary material equation of state are derived. These properties are used systematically to generate similarity solutions of these equations for a given form of the equation of state. A comprehensive list of allowed similarity solutions for a perfect gas is presented. Several special cases that have been found previously by other authors appear in the list. Many other cases not reported previously are also presented. An example numerical solution is given for a piston‐driven shock with a thermal precursor.

ISSN:0031-9171    

DOI:10.1063/1.865533

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The thermal equilibrium electric field fluctuation energy of the gyrokinetic model of magnetized plasma is computed and found to be smaller than the well‐known result ⟨&dgr;E⋅&dgr;E⟩(k)/8&pgr;= 1/2T/[1+(k&lgr;D)2] valid for arbitrarily magnetized plasmas. It is shown that, in a certain sense, the equilibrium electric field energy is minimum in the gyrokinetic regime.

ISSN:0031-9171    

DOI:10.1063/1.865534

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The linear and the nonlinear radial propagation of drift wave energy in an inhomogeneous plasma is studied numerically based on model equations of Hasegawa–Mima for the collisionless case and of Hasegawa–Wakatani–Taniuti–Kaw for the collisional case. In the linear regime the drift wave energy spreads out symmetrically along the direction of inhomogeneity with a finite group velocity. In the nonlinear regime for the collisionless case the radially located drift wave energy is found to propagate in the radial direction. However, the direction of propagation depends on the initial parameters of the pulse. In the collisional case the energy is found to propagate in the direction of decreasing resistivity. These results provide qualitative insights into the phenomenon of drift wave turbulence observed in tokamak plasmas.

ISSN:0031-9171    

DOI:10.1063/1.865535

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Direct numerical simulations of two‐dimensional magnetohydrodynamic (MHD) flows propagating in a mean uniform magnetic field, with correlated velocity and magnetic fields are discussed. A high correlation inhibits the amount of excitation transferred to small scales, showing steeper spectral slopes at very high correlation, as in previous closure calculations. The growth of the correlation coefficient between kinetic and magnetic fields is attributed to the nondefinite positiveness of the cross correlation, which reverses its sign at small scales, because of nonlinear interactions between large and small scales in the MHD equations.

ISSN:0031-9171    

DOI:10.1063/1.865536

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this paper a hybrid particle–fluid simulation code is used to examine the large‐scale (&lgr;∼c/&ohgr;pi) low‐frequency (&ohgr;∼&ohgr;ci) formation and evolution of a collisonless shock in two dimensions where the shock is caused by a plasma slug of finite thickness traveling perpendicular to the ambient magnetic field in the presence of a uniform background plasma. During the evolution of the shock structure, background ions are energized in the perpendicular direction and then isotropized. The isotropization process is associated with the presence of large‐amplitude, primarily electromagnetic, waves propagating parallel to the ambient magnetic field that are created by the self‐consistent plasma interaction. High Mach number shocks are found to be inherently two‐dimensional objects.

ISSN:0031-9171    

DOI:10.1063/1.865537

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In a homogeneous plasma with no external fields, an equation of evolution for the space‐averaged distribution f¯ (v,t) is derived without making use of the Markovian approximation. The Vlasov equation is integrated for a limited, albeit arbitrary, time interval along analytical particle orbits. Orbit failure is avoided by considering a sequence of initial value problems. A Markovian limit is identified, in which quasilinear, resonance broadening, and mode coupling theories are recovered. Under non‐Markovian conditions, the quasilinear wave–particle resonance is broadened at orderE2.

ISSN:0031-9171    

DOI:10.1063/1.865538

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A method for finding integrable Hamiltonian systems with one and a half degrees of freedom is introduced and applied to the problem of finding vacuum magnetic fields with rotational transform and a dense set of toroidal flux surfaces. In this method, the fixed points of the return map must be located, and the values of the corresponding residues calculated. The residues, being indicators of stochasticity, are systematically reduced by variation of the parameters of the system. Application of this method to the problem of finding integrable magnetic fields shows that it is practical, and it yields substantial improvement of the configuration. In particular, this method can result in an increase of the simple equilibrium‐&bgr; estimate, &igr;2&egr;, by a factor of 2 or more.

ISSN:0031-9171    

DOI:10.1063/1.865539

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A relativistic theory for a nonlinear magnetosonic wave propagating perpendicularly to a magnetic field is developed. On the basis of a relativistic two‐fluid cold plasma model, the structure of a stationary magnetosonic wave is studied. Relativistic effects become important for the parameter regime &ohgr;ce/&ohgr;pe≳1, because the fluid electron velocity perpendicular to a magnetic field and parallel to the wave front takes values close to the speed of light for such plasma parameters. It is found that there exists a stationary solitary wave solution even in the relativistic model. Some properties of the solitary wave, such as the soliton width, are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865540

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A set of nonlinear mode coupling equations, describing the interaction of large amplitude electron‐cyclotron waves with low‐frequency electrostatic as well as electromagnetic fluctuations, is presented. Accounting for the contributions of the ponderomotive force and relativistic electron mass variation nonlinearities, a general dispersion relation has been obtained for the parametric processes. Modulation and filamentation instabilities are investigated.

ISSN:0031-9171    

DOI:10.1063/1.865541

出版商:AIP    

年代:1986

数据来源: AIP