摘要:

Thermal transpiration in a cylindrical tube is studied by using the Bhatnagar‐Gross‐Krook model and methods previously used by Ferziger and Cercignani and Sernagiotto in solving the Poiseuille flow problem. It appears that recent results of Sone and Yamamoto are in slight error. Finally, in analogy with the recent work of Mason and co‐workers on the dusty gas model, a relation forftr, the translational Eucken factor, is developed.

ISSN:0031-9171    

DOI:10.1063/1.1692346

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The linearized Boltzmann equation for the hard‐sphere gas is analyzed by comparing the eigenvalues of its relaxation rate with those of the corresponding foreign gas equation. An analysis of the latter, carried out by reduction to a second‐order differential equation, exists elsewhere. It is shown for the angular indices 0 and 1 that the Boltzmann equation has an infinite set of eigenvalues each of which is smaller than the corresponding eigenvalue of the foreign gas equation. The basic theorem is also valid for the angular index 2. However, as the properties of the foreign gas equation have not yet been established for this case, only tentative conclusions can be drawn. The two equations share the same continuous spectrum; it covers all values larger than a positive minimum. The discrete series found are asymptotic to the minimum.

ISSN:0031-9171    

DOI:10.1063/1.1692347

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The problem for the laminar free convection from a horizontal isothermal infinite strip facing downward is studied by the momentum‐integral method within the boundary‐layer approximations when a vertical magnetic field is imposed on the plate. The solutions are presented in an integral form for the case when the induced magnetic field is negligible. The detailed calculations for Pr = 0.025 and 1 are compared with those of the nonmagnetic case. It is found that the boundary‐layer thickness increases and the Nusselt number decreases with the increase of the magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1692348

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It has been found analytically that an aligned electric current increases the drag of a sphere moving in an incompressible fluid if the sphere is less conducting than the fluid, and decreases the drag if it is more conducting.

ISSN:0031-9171    

DOI:10.1063/1.1692349

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The neutral particle flux in a plasma wind tunnel has been measured using a BeCu detector and has been found to be less than 1% of the ion density making it very unlikely that neutrals play an important role in the dissipation processes in the collision‐free flow.

ISSN:0031-9171    

DOI:10.1063/1.1692350

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The quantum‐mechanical convergent kinetic equation of Gould and DeWitt is used for the calculation of static transport coefficients through first order in the plasma parameter for a fully ionized, nondengenerate, two‐component plasma near thermal equilibrium. The equation is solved with the standard Chapman‐Enskog procedure using a three‐term Sonine polynomial expansion. Since close collisions and dynamic screening effects are treated correctly, the results contain both logarithmic (dominant) and nonlogarithmic (subdominant) terms evaluated exactly to first order in the plasma parameter. Since close collisions are treated quantum mechanically the transport coefficients obtained are valid for a wide range of temperatures. For the case where only one Sonine polynomial is used in the evaluation of the electrical conductivity, the result obtained here reduces to that of Kivelson and DuBois in the high‐temperature limit(kT ≫ Ry)and to that of Gould and DeWitt in the low‐temperature, classical limit(kT ≪ Ry). Using more than one Sonine polynomial in the expansion of the distribution function, we obtain for the electrical conductivity&sgr;(&khgr;) = c(&khgr;)&sgr;(1), where&khgr;is the number of terms in the Sonine expansion and&sgr;(1)is the result for one term. In the limit where the Coulomb logarithm is large,c(3) = 1.95andc(∞) = 1.973, so that our results are accurate to 1 or 2% for a wide range of temperatures (includingkT ∼ Ry).

ISSN:0031-9171    

DOI:10.1063/1.1692351

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The influence of small dc axial magnetic fields upon the stability of the focused plasma column is shown in the light of soft x rays. The material damage to the center electrode and the intense x‐ray emission at the electrode face as a result of electron bombardment is considerably reduced. Although the final heating of the ions and electrons is inhibited as expected due to a trapped magnetic field, the spatial stability of the focused column offers a greater possibility for scaling to higher energies.

ISSN:0031-9171    

DOI:10.1063/1.1692352

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurements have been made of the longitudinal pressure gradient in dc discharges in helium, neon, and argon. Studies have been conducted at current densities∼ 1 A/cm2, over a pressure range of approximately two orders of magnitude with an accuracy of± 5&mgr;. Present results when compared at high pressures with calculations based on theory indicate good agreement with Leiby and Oskam's theory by comparison with previous theories of the effect. The studies also indicate an anomalous behavior of the gradient at higher discharge currents in neon and argon.

ISSN:0031-9171    

DOI:10.1063/1.1692353

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electrostatic probe theory for a slightly ionized, collision‐dominated plasma is extended, in the sense of problem formulation, to allow for the presence of a uniform magnetic field. Provided that the Debye length is very much smaller than a probe dimension, ion and electron currents to the probe saturate, respectively, at large negative and positive probe bias with respect to the plasma potential. It is shown that it is not necessary to go through a lengthy asymptotic analysis to compute the saturation currents. Ion and electron saturation currents to ellipsoids of revolution inclined at an arbitrary angle to the magnetic field are given in compact form in terms of common elliptic functions.

ISSN:0031-9171    

DOI:10.1063/1.1692354

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An intense collimated light beam of frequency&ohgr;tincident on a quiescent plasma with plasma frequency&ohgr;pe ≪ &ohgr;tcan couple with electron plasma waves, to enhance their level well above the equilibrium value. As a consequence, the spectrum of the scattered light “reddens,” and a part of the beam energy is transferred to the plasma. For a bandwidth&Dgr;&ohgr; < &ohgr;peof the beam, two basic regimes are important: one where the enhanced fluctuations travel at large angles to the light beam and which is the equivalent at high intensities of the equilibrium collective scattering, and a second, where electromagnetic and plasma waves have phase velocity nearly parallel and of the same order which seems suited for an important absorption of the light. Competing processes such as instability of the scattered light, and decay of plasma waves into ion‐acoustic waves, become important in certain ranges of the beam and plasma parameters. All the mentioned processes are investigated in detail in the framework of lowest‐order mode coupling using a corrected random‐phase approximation. The results indicate that nonlinearly enhanced scattering should be detectable for a beam of laser light passing through a laser‐produced plasma, whereas it seems doubtful that the considered mechanism can produce an appreciable anomalous absorption.

ISSN:0031-9171    

DOI:10.1063/1.1692355

出版商:AIP    

年代:1969

数据来源: AIP