Search

Your search keyword '"Balescu, Radu"' showing total 322 results
Start Over Author "Balescu, Radu"
322 results on '"Balescu, Radu"'

108. Plasmadynamics near a self-similar turbulent state

Author

Balescu, Radu and Balescu, Radu

Abstract

The transport properties of a turbulent plasma are investigated in the vicinity of a self-similar turbulent state (SSTS). This state plays the same role of reference as the local equilibrium for a collisional plasma. The stability of the SSTS against velocity gradients is proved. Under certain well-defined conditions a plasmadynamical regime is established, in which the initial conditions are forgotten and the macroscopic plasmadynamical quantities obey closed differential equations. The anomalous viscosity arising in this regime is investigated in detail. This quantity is time-dependent (a feature impressed by the self-similar character of the reference state). A number of additional typically turbulent terms appear in the equation of motion :they arise from interference between flow and collisions or magnetic field. © 1981, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1981

109. Instability and saturation of drift-convective modes in an inhomogeneous plasma

Author

Balescu, Radu, Shukla, Padma Kant, Bessenrodt, H., Spatschek, Karl Heinz, Balescu, Radu, Shukla, Padma Kant, Bessenrodt, H., and Spatschek, Karl Heinz

Abstract

It is found that the inclusion of the electron inertia effect (parallel to an external magnetic field) can provide a linear coupling between the electrostatic drift and the convective modes in a non-uniform plasma. This coupling leads to new branches of rapidly growing modes, which are calculated in the kinetic as well as in the hydrodynamic regimes. To study the saturation of the linear unstable modes, we account for the mode coupling and derive a set of model nonlinear fluid equations. A perturbation technique is employed to obtain a nonlinear evolution equation. In the steady state, the latter yields the saturated electric potential. It is argued that the enhanced low-frequency fluctuations can cause anomalous particle transport in a magnetoplasma. © 1987, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1987

110. Kinetic equation, spin hydrodynamics and collisional depolarization rate in a spin-polarized plasma

Author

Balescu, Radu, Zhang, Weiyan, Balescu, Radu, and Zhang, Weiyan

Abstract

On the basis of our previous work, a rigorous kinetic equation for a spin-polarized plasma is derived in the weak-coupling quasi-classical limit. The macroscopic polarization vector is defined in a unified form for spin-5 and spin-1 particles. Using the kinetic equation, an equation for the macroscopic polarization density is derived in the form of a ‘spin-hydrodynamical equation'. The depolarization rate for the spin-orbit interaction and the spin-spin interaction is estimated. Some difficulties for the spin-spin interaction are displayed and discussed. © 1988, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1988

111. Anomalous Transport Coefficients in a Magnetized Turbulent Plasma

Author

Xiaoming, Qiu, Balescu, Radu, Xiaoming, Qiu, and Balescu, Radu

Abstract

In this paper we generalize the formalism developed by Balescu and Paiva-Veretennicoff, valid for any kind of weak turbulence, for the determination of all the transport coefficients of an unmagnetized turbulent plasma, to the case of a magnetized one, and suggest a technique to avoid finding the inverse of the turbulent collision operator. The implicit plasmadynamical equations of a two-fluid plasma are presented by means of plasmadynamical variables. The anomalous transport coefficients appear in their natural places in these equations. It is shown that the necessary number of transport coefficients for describing macroscopically the magnetized turbulent plasma does not exceed the number for the unmagnetized one. The typical turbulent and gyromotion terms, representing dissipative effects peculiar to the magnetized system, which contribute to the frequency-dependent transport coefficients are clearly exhibited. © 1982, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1982

112. Self-similar state of a weakly turbulent plasma

Author

Balescu, Radu and Balescu, Radu

Abstract

The models of Vekshtein, Ryutov & Sagdeev (VRS), describing a marginally stable turbulent plasma sustaining an electric current, are shown to be incomplete by their neglect of the equations determining the spectral densities of the driving modes. An exhaustive study of these models, including a detailed determination of the frequencies, spectral densities and turbulent energy densities, shows that, strictly speaking, there exists no self-similar turbulent state (SSTS). However, an approximate SSTS can be constructed, based on the finding that the tail of the spectral densities behaves self-similarly. © 1980, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1980

113. Heating of electrons and ions by inverse bremsstrahltmg absorption: A self-similar state of the plasma

Author

Balescu, Radu and Balescu, Radu

Abstract

It is shown that, under the influence of a monochromatic HF electric field (laser beam), both the electrons and the ions in a high-Z plasma reach a homogeneous and isotropic self-similar state (SSS) in which the distribution functions are of the factorized form: F^w.t) = naWaZ(t) a(v)>v — w/Wa(t), a ~ e, i, where WJf) is a scaling velocity, the square of which is proportional to the effective temperature. Whereas the SSS for the electrons was known from previous work, with it is shown here that the corresponding ion SSS exists and is characterized by a simple Maxwellian, ocexp(— y2). The discussion of the thermal velocities Wa(t), which are obtained in analytical form, provides a transparent physical insight into the heating mechanism of the plasma by inverse bremsstrahlung absorption. © 1982, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1982

115. Anomalous transport coefficients in a turbulent plasma

Author

Balescu, Radu, Paiva-Veretennicoff, Irina, Balescu, Radu, and Paiva-Veretennicoff, Irina

Abstract

A general self-consistent framework is developed for the calculation of transport coefficients in a collisionless, weakly turbulent plasma. These coefficients characterize the response to a perturbation away from a quasi-steady turbulent state, which is assumed to exist as a result of the stabilization of the linear instabilities. It is shown that a purely hydrodynamical description does not exist for plasmas: the macroscopic picture must include non-conserved quantities, which lead to the plasmadynamical (or ‘two-fluid’) picture of the system. The number of independent transport coefficients, necessary for the macroscopic characterization of the plasma, is correspondingly increased as compared with a two-component mixture of two ordinary fluids. The typical turbulent contributions to the transport coefficients are clearly exhibited. © 1978, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1978

117. Kinetic Equations for Plasmas Subjected to a Strong Time-Dependent External Field. Part 4. Dynamics of Stochastic Correlations

Author

Balescu, Radu and Balescu, Radu

Abstract

In close analogy with part 1, the dynamics of stochastic correlations is used to reformulate the preceding treatment of turbulent equations. The result is an exact and closed equation for an average function, involving only asymptotic stochastic correlations, and no initial fluctuation. This stochastic kinetic equation is valid for all initial conditions, and the corresponding function is a significant particular projection on an independent subspace R(t). © 1975, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1975

118. Thermal conductivity in a laser-created plasma heated by inverse bremsstrahlung absorption

Author

Balescu, Radu and Balescu, Radu

Abstract

The heat conductivity of a laser-created plasma heated by inverse bremsstrahlung absorption is investigated in the vicinity of a self-similar state (SSS), taken as reference state. Under certain conditions, the slowly varying macroscopic quantities obey true, local hydrodynamical equations and a well-defined, positive, heat conductivity exists. The latter is strongly time-dependent through the unperturbed temperature. Its value, compared to the classical heat conductivity at the same temperature, shows a reduction of about 20 %. It is shown that, for high intensities and/or long wavelengths, the linear heat conduction theory necessarily breaks down, even if the temperature gradient is very small. © 1982, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1982

119. Kinetic Equations for Plasmas Subjected to a Strong Time-Dependent External Field. Part 3. Stochastic Equations for Plasma Turbulence

Author

Balescu, Radu and Balescu, Radu

Abstract

The kinetic equation obtained in parts 1 and 2 is treated stochastically: the external field is stochastic, with an average and a fluctuating part. The turbulence of the system is described by the induced fluctuations in the plasma, and a general equation is derived for the average distribution function. As a particular case, the stochastic Vlasov equation is treated explicitly, and compared with the descriptions of Dupree, Weinstock and Benford & Thomson. © 1975, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1975

121. The zero-mode instability: A new parametric decay instability of a plasma in an external field

Author

Balescu, Radu and Balescu, Radu

Abstract

The parametric resonances involving the coupling of an external harmonic electric field to the plasmadynamical (PD) modes are studied. Particular attention is devoted to the resonant triplets involving purely dissipative PD modes of zero frequency. It is shown that a new type of instability exists in this class of processes. © 1976, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1976

122. Kinetic theory of binary correlations in turbulent plasmas

Author

Misguich, Jacques, Balescu, Radu, Misguich, Jacques, and Balescu, Radu

Abstract

The two-particle correlations in a turbulent plasma are analyzed on a quite general basis by using the modern methods of non-equilibrium statistical mechanics. It is shown that the binary correlations can be split (in a time invariant way) into a part which decays quickly by ballistic motion, and a long-living part: ’the natural correlations’. The latter are continuously regenerated from the one-particle distribution function by the internal interactions, even in the absence of true collisions. The general theory can be made operational by using approximation schemes, among which the ‘RQL2’ method, which generalizes the renormalized quasi-linear approximation, leads to results comparable to, but more general than, those developed by previous authors. The explicit relation of the long-living enhanced correlations to the concept of ’ clumps ’ will be developed in a forthcoming paper. © 1978, Cambridge University Press. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1978

134. Binary correlations in ionized gases

Author

Balescu, Radu, Taylor, H.S., Balescu, Radu, and Taylor, H.S.

Abstract

SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1961

135. Sur la theorie moleculaire du mouvement brownien

Author

Prigogine, Ilya, Balescu, Radu, Prigogine, Ilya, and Balescu, Radu

Abstract

It is well known that the usual theory of brownian motion has a strictly phenomenological character. The equilibrium distribution is postulated but not derived, as is also the special stochastic process which permits the system to reach equilibrium. Thanks to a recent paper by one of us and R. Brout it is possible to go much further for a class of dynamical systems called “weakly coupled” systems. If for systems of this kind spatial homogeneity is assumed the evolution is described by a partial differential equation of the first order in time and of the second order in the action variables of the system. However, owing to the large number of independent variables, it is not easy to discuss in detail the solution of such an equation. For this reason special situations corresponding to the evolution of a single degree of freedom out of equilibrium are studied in detail in this paper. For such systems it is then possible to derive a theory of brownian motion starting from first principles. Two cases are studied in detail: weakly coupled oscillators like in slightly anharmonic solids or in radiation theory and gases interacting through weak long range forces (i.e. gravitational or electrostatic). In the first case it is possible to solve completely the problem while the results obtained in the second are not so exhaustive. It is shown that the approach to equilibrium is governed by non-gaussian markoffian processes. In the second example the well known results obtained by Chandrasekhar on dynamical friction are easily obtained by our method., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1957

Catalog

Books, media, physical & digital resources
See catalog results