摘要:

For a pure electron plasma in a sufficiently strong magnetic field, there is a many‐electron adiabatic invariant which constrains the collisional dynamics. For the case of a uniform magnetic field, the adiabatic invariant is the total kinetic energy associated with the electron velocity components that are perpendicular to the magnetic field (i.e., ∑j mv2j⊥ /2). Were the adiabatic invariant an exact constant of the motion, no exchange of energy would be possible between the parallel and the perpendicular degrees of freedom, and the plasma could acquire and maintain two different temperatures,T∥andT⊥. However, an adiabatic invariant is not strictly conserved. In the present case, each collision produces an exponentially small exchange of energy between the parallel and the perpendicular degrees of freedom, and these act cumulatively in such a way thatT∥andT⊥relax to a common value. This paper provides a calculation of the equipartition rate.

ISSN:0031-9171    

DOI:10.1063/1.865322

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The interaction between the two components of a relativistic binary gas is investigated. Starting from the relativistic Boltzmann equation, general expressions for the rate of energy exchange, the relaxation time, and the coefficient of bulk viscosity are obtained. As a particular example, the formalism is applied to the study of a gas at very high temperatures,T<∼6×109 °K, assuming that the energy exchange between matter and radiation is caused by Compton scattering; relativistic effects are fully taken into account.

ISSN:0031-9171    

DOI:10.1063/1.865323

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Conventional mode conversion theory in inhomogeneous plasmas starts with a local dispersion relation, which serves as a base for constructing a differential equation describing the waves in nearly degenerate plasma regions, where the mode conversion can take place. It will be shown, however, that the usual geometric optics perturbation scheme, which in the zero order leads to the aforementioned dispersion relation, predicts either rapid variations of the local wave vector and amplitude of the wave, or large first‐order corrections to the amplitude in nearly degenerate plasma regions. A novel, general, renormalized perturbation scheme will be suggested in order to remove this singular behavior. The new method is formulated in terms of the conventional, general plasma dielectric tensor and yields two coupled, energy‐conserving differential equations describing the mode conversion. Simple asymptotic solutions of these equations exist if the mode coupling is localized and weak. The method is applied to the classical problem of transformation of the extraordinary mode propagating in a cold magnetized plasma at small angles to the magnetic field. Generalization of the method to the case of an unreduced, multicomponent wave propagation problem is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865324

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An axially symmetrical spatial plasma echo is obtained theoretically by using the Vlasov–Poisson equation system. Several features of the echo are studied by making use of this echo solution. Common linear relations between exciter grid separationland the position of echo‐amplitude maximumleare shown, and an influence oflon the amplitude is also obtained. The radial extent of the echo and the effects of the magnetic field and the plasma temperature on the echo are discussed. Most importantly, the existence of the fine structure of the echo, such as the appearance of a side lobe (besides the main lobe) in the amplitude curve and the presence of a phase gap on the interferometric phase trace were demonstrated by their appearance in this experiment. Good agreement is obtained between theory and the experimental results concerning the side lobes and the phase gaps.

ISSN:0031-9171    

DOI:10.1063/1.865325

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Magnetic flux tubes (slabs or cylinders) are of considerable physical interest because of their occurrence in the sun’s atmosphere. The propagation of weakly nonlinear, long‐wavelength (weakly dispersive), sound waves in both a magnetic slab and a magnetic cylinder is discussed. The slab geometry leads to the Benjamin–Ono equation, viz., ∂v/∂t+cT(∂v/∂z) +&bgr;v(∂v/∂z) +(&agr;/&pgr;)(∂2/∂z2) ×∫&slash;∞−∞[v(s,t)ds/(s−z)]=0, and the cylindrical geometry yields its allied form, viz., ∂v/∂t+cT(∂v/∂z)+&bgr;v(∂v/∂z) +&agr;’(∂3/∂z3)∫∞−∞{v(s,t)ds/ [&lgr;2+(s−z)2]1/2}=0, an equation known also to arise in waves on concentrated vortices in fluids. The magnetic flux tube thus provides a simple illustration of these two equations, hitherto only considered in separate physical systems.

ISSN:0031-9171    

DOI:10.1063/1.865418

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The trapped electron instability, like other types of drift waves, may appear as a single mode in many linear plasma devices. Recognizing the significant variation of density gradient over the mode localization region, a nonlocal linear analysis in slab model yields eigenfunctions for Weber‐like equations. Using three‐wave, nonresonant, two‐dimensional mode coupling based on these Weber‐like eigenfunctions, two mode‐coupling equations for the fundamental and higher‐order radial harmonics are derived. The solution of these coupled equations yields the nonlinear saturation level of the unstable mode. Mode coupling to the damped higher‐order radial modes is the principal physical saturation mechanism of the unstable fundamental mode.

ISSN:0031-9171    

DOI:10.1063/1.865326

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A study is made of the linear stability of finite‐thickness, anisotropic compressible shear layersv=zˆvz(x), with a parallel uniform magnetic field,B=zˆB0. The stability of such sheared flows, described by the double adiabatic equations of Chew, Goldberger, and Low [Proc. R. Soc. London Ser.  A  236, 112 (1956)], and involving the nonlocal coupling of the firehose and mirror modes caused by the velocity shear, is relevant in a number of astrophysical, geophysical, and space plasma configurations. The scalar perturbation quantities have the form  f (x) exp[i(kzz−&ohgr;t)]. The dimensionless variables characterizing a shear layer with a given velocity profile, assumed to be a linear profile in the present work, are the sonic Mach number,M ≡ (2vzm/S⊥), the ratio of the magnetic field energy density to the perpendicular thermal energy density,q2 ≡ (vA/S⊥)2, and the anisotropy parameter,r2 ≡ (S∥/S⊥)2. Here,vz(x=±∞)=±vzm,S∥, andS⊥are the sound speeds parallel and perpendicular to the magnetic field, andvAis the Alfve´n speed. The dimensionless variable characterizing the perturbation is the wavenumberB ≡ kzL, whereLis the shear layer thickness. It is shown that the resonance of the sound and firehose modes drives unstable standing and traveling waves for a shear layer having a vortex sheet profile [wherevz(x) is a step function]. For the vortex sheet, the unstable standing wave modes first appear atM=2(3)1/2rforr>(1+q2)1/2/2, and the unstable traveling wave modes first appear atM=0 forr<((1+q2)1/2/2). Numerical methods are used to generate values of &ohgr;rand &ohgr;i>0 (corresponding to unstable wave motion) for the ‘‘linear’’ shear layer in the (B, M) plane for various values ofqandr.The coverage of the (B, M) plane is forB≤5,M≤10, and for discrete values ofq≤0.5 andr≤2. Two regimes of instability are found to occur in the (B, M) plane with the structure of the unstable modes of the ‘‘linear’’ layer being very different from that for the anisotropic vortex sheet. The unstable modes are standing waves with &ohgr;r=0, and traveling waves with &ohgr;r≠0.

ISSN:0031-9171    

DOI:10.1063/1.865327

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An analytical study is presented of the interaction between a fast Alfve´n wave having a frequency larger than the ion‐cyclotron frequency, and low frequency density fluctuations. When appropriatek, &ohgr; matching conditions are satisfied, the interaction results in a beat current that acts as anin‐situantenna, exciting ion Bernstein modes resonantly. Since such modes have relatively small damping for large parallel phase velocities, their excitation can significantly enhance the damping of fast waves having smallk∥, particularly in those regions of the plasma where the temperature is relatively low. The interaction with coherent, as well as with broad band density fluctuations is investigated, and the role of plasma nonuniformities is examined. Specific features of relevance to ion‐cyclotron range of frequency heating of tokamak plasmas are considered.

ISSN:0031-9171    

DOI:10.1063/1.865328

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A statistical theory is developed for magnetohydrodynamic turbulent shear flows in the presence of both mean velocity and magnetic gradients. In the case of magnetic Prandtl number unity, the correlations between fluctuating velocity and magnetic fields, which play a crucially important role in the equations for the mean velocity and magnetic fields, are calculated with the aid of the two‐scale, direct‐interaction approximation. The electromotive force expressing the effect of turbulent fields in the equation for mean magnetic field is found from the results. Particularly, the electromotive force related linearly to the mean magnetic field is shown to originate from the statistical inhomogeneity of fluctuating fields, which is sustained by the mean field gradients.

ISSN:0031-9171    

DOI:10.1063/1.865329

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

It is shown that in general the stability of a hot‐electron‐stabilized symmetric tandem mirror is the same as the stability of its barrier‐plug cell alone, plus an additional limitation on the center‐cell length such that the center‐cell Alfve´n frequency is higher than the average barrier‐plugE×Bdrift and the hot‐electron precession frequency. The stability of the hot‐electron barrier‐plug cell is studied extensively.

ISSN:0031-9171    

DOI:10.1063/1.865330

出版商:AIP    

年代:1985

数据来源: AIP