摘要:

A dark‐field oscillatory spark microphotography technique has been developed to study with tracers the structure of the gas boundary layer in the shock tube. By using these particles as tracers, velocity profiles of the boundary layer both in laminar and turbulent regions are measured and the velocity fluctuations observed. The time and space resolution of this technique is high. Laminar velocity profiles show a significant deviation from theoretical expectations. The turbulent average velocity profiles have the usual 1/7th power variation with distance from the wall in the top 90% of the layer. The velocity of the flow within a few microns from the wall is sometimes much greater than the value predicted by Mirels assuming zero velocity at the wall. A possibility of slip flow in the shock tube is discussed. This technique allows measurements to be made as close to the wall as the size of the particle's diffraction pattern, which is about 1 &mgr;.

ISSN:0031-9171    

DOI:10.1063/1.1724502

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The one‐dimensional initial‐value problem of a monatomic single component gas is considered. Using the linearized Boltzmann equation the dispersion relation is studied. In addition to the usual gas‐dynamic sound waves, one finds an infinity of decaying propagating waves. The phenomenon exhibits itself as a sequence of epochs, the last state of which is hydrodynamic. With reference to the same problem, macroscopic equations such as Euler, Navier‐Stokes, Burnett, moments equations, etc., are considered. In addition, the recently considered ``kinetic models'' of Grosset al.are applied to the problem. These various formulations are critically analyzed and compared with each other and with the Boltzmann analysis. Lastly, several modifications are offered which remedy some of the shortcomings which appear in the approximate theories.

ISSN:0031-9171    

DOI:10.1063/1.1724496

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A new approach is devised for the study of thermodynamic systems composed of particles interacting with Coulomb forces, specifically applied to solutions of strong electrolytes (composed of ions of equal size). A method is constructed for the evaluation of the average number density as a function of position about an ion expressed as a series of terms dependent on the average potential about the ion. The problem is formulated in such a manner that averages of quantities are found by the method of steepest descents. The electrolyte equation is found in first approximation to be similar to the nonlinearized Debye‐Hu¨ckel equation, containing, however, terms referring to the ion size. When the ionic fractional volume is much less than one this equation becomes the nonlinearized Debye‐Hu¨ckel equation. In the limit of small concentrations it is also shown that the equation governing the electrolyte is precisely the nonlinearized Debye‐Hu¨ckel equation. The electrolyte equation is briefly discussed in higher‐order approximations.

ISSN:0031-9171    

DOI:10.1063/1.1724503

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An expansion of a formally rigorous integral solution of the Boltzmann equation in powers of the electric field andm/Mis used to demonstrate the correct expression for the conductivity of a spatially homogeneous slightly ionized gas. The conditions under which the isotropic part of the electron distribution function reduces to the Margenau distribution are determined. A discussion of the physical reasons for the possibility of negative conductivity is given.

ISSN:0031-9171    

DOI:10.1063/1.1724504

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A generalization of the phenomenological description of ambipolar diffusion of a plasma is made to include the effects of a weak impressed magnetic field. The assumptions of congruence of the flow vectors (div &Ggr;+= div &Ggr;−) for ions and electrons and of proportionality [n−grad (n+) =n+grad (n−)] on the signed charge densities are utilized as in the existing theory of ambipolar diffusion; however, because of the rotational effects of the magnetic field, and additional assumption is made on the curls of &Ggr;±. This assumption is curl &Ggr;+= curl &Ggr;−. The resulting diffusion is found to be a combination of electronic and ionic diffusion, and the components of the ambipolar diffusion tensor are calculated for a unidirectional magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1724505

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A presentation of transport coefficients in a fully ionized plasma in terms of effective collision, gyration, and oscillation frequencies is given. It has the virtue of reducing the task of presenting the data to the tabulation of certain dimensionless functions of restricted variation. Moreover the quantities involved are directly related to the reciprocals of the coefficients usually considered, for instance to the resistivity rather than the conductivity.

ISSN:0031-9171    

DOI:10.1063/1.1724506

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

In thermally anisotropic plasmas or sheet pinches, the zero‐order counterstreaming or directed streaming of like particles gives rise to instability modes that correspond essentially to the formation of local first‐order pinches within the plasma. The marginal stability criteria for all such modes can be interpreted in terms of Bennett's pinch condition. The range of examples discussed includes Weibel's thermally anisotropic hot‐electron plasma instability in null field, which is generalized for hot ions and finite magnetic field, and which is applied to interpenetrating neutral plasma streams, to a spherical electrostatic plasma‐containment scheme, and to the Astron thermonuclear experiment. The familiar ``mirror instability'' is shown to be another example of a ``pinch''‐type mode. Sheet pinches with or without longitudinal magnetic field are generally unstable against tearing into subsidiary linear pinches.

ISSN:0031-9171    

DOI:10.1063/1.1724507

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A gyrotropic plasma withT∥/T⊥≡ &ggr; < 1, whereT⊥andT∥are the transverse and longitudinal temperatures, is shown to be unstable to a perturbation in the form of a transverse wave with a wave vectorksuch thatk2<k02= {&ohgr;c2(1−&ggr;)2+ &ohgr;p2(1−&ggr;)/&ggr;}/c2, &ohgr;cand &ohgr;pare the gyro and plasma frequencies. ForT∥>T⊥such an instability arises only if &ohgr;c2/&ohgr;p2> 1/&ggr;(&ggr;−1) and then only fork2<k02. However, in the latter case, the phase velocity of the instability exceedscand the growth rate must be made to vanish because of relativistic considerations. No such instability arises for complete isotropyT⊥=T∥.

ISSN:0031-9171    

DOI:10.1063/1.1724508

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

In a plasma the ionization energy is decreased due to the presence of the microfield. In the past several attempts have been made to calculate this effect. These calculations, which use statistical and thermodynamical procedures, give different results. They produce either a ``polarization term'' or a ``lattice term'' or both of them. Moreover there are quantitative discrepancies. The lowering of the ionization energy is here derived by a statistical method, which is physically conceivable. The results cover a wide density range below and above the so‐called critical density. The new results are compared with the results of all earlier calculations and reveal the cause of their discrepancies.

ISSN:0031-9171    

DOI:10.1063/1.1724509

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

By application of the concept of collective description to a fully ionized gas, Vlasov's equation follows from Liouville's theorem. We want to investigate to what extent the statistical collective procedure describes correctly the behavior of the single system under consideration. Therefore a criterion for the validity of the collective approach is deduced by comparison of the Vlasov equation with the exact individual description. The result is exemplified by an application to Landau's theory of damping of plasma oscillations.

ISSN:0031-9171    

DOI:10.1063/1.1724510

出版商:AIP    

年代:1963

数据来源: AIP