摘要:

A spectroscopic study was made of imploding shock waves in a hemispherical chamber filled with an O2‐H2‐He mixture at high pressure (∼10 atm). The waves were generated by reflecting an exploding detonation wave off the periphery of the chamber. The strong focusing of classical imploding shock waves was verified quantitatively, but the temperature of the shock‐heated gas near the origin of the chamber was found to be limited to rather low values (∼5000°K). The results generally agree well with calculations employing the artificial‐viscosity technique if it is assumed that the minimum shock radius near the origin is limited to the extent of the experimentally observed luminosity region.

ISSN:0031-9171    

DOI:10.1063/1.1693662

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

During unipolar (or ambipolar) injection of charge carriers into an insulating liquid, a liquid motion is generally observed. This motion, generated by the charge carriers, is thought to be responsible for the high carrier mobility which is about2×10−3 cm3 V−1 sec−1in nitrobenzene, i.e., an order of magnitude higher than the true mobility value(1.9×10−4 cm2 V−1 sec−1). Recent schlieren photographs strongly support the assumption that when the applied voltage is high enough, for nitrobenzene of the order103‐104V, the “self‐generated” motion is turbulent shortly after the voltage is applied. This turbulence invades the undisturbed fluid at practically constant velocity. Neglecting the true carrier mobility and making certain assumptions concerning the turbulent structure, the charge transport and consequently the entrainment can be described to a good approximation by a Lagrangian diffusion process and the charge distribution is governed by a diffusion equation. The latter remains valid during the steady state. The experimental results are found to be in very satisfactory agreement with the theoretical analysis. It is also shown that the turbulent energy is produced byE uq, producing kinetic as well as electric energy, the latter being negligible. The turbulence is very intense,u′≈102 cm sec−1, and its scale is only a fraction of the electrode distance. The corresponding turbulence Reynolds number is of the order ofRel≈6×102.

ISSN:0031-9171    

DOI:10.1063/1.1693663

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A simple model for an ion‐exosphere with an open magnetic field is set up. The ions move under the influence of (1) the gravitational field, (2) the monotonic decreasing static magnetic field, and (3) the electrostatic potential due to a small charge separation. Neglecting collisions and particle drift across the magnetic field lines the particles can be classified into four classes: ballistic, escaping, trapped, and incoming particles. For each class the number density, the particle flux, the momentum fluxes, and the energy flux are calculated as a function of the electrostatic potential. Finally, it is shown how this potential can easily be computed by considering two basic physical conditions: (1) the quasineutrality, and (2) the zero current condition.

ISSN:0031-9171    

DOI:10.1063/1.1693664

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The spatial distributions of the ion density and the space potential in the boundary layer at a conducting sphere of 2.5‐cm radius are measured with a small movable cylindrical probe. The measured density distributions are in good agreement with the theory of Lam in the collisionless case and with the diffusion model in the collision‐dominated limit. The existence of a near‐Boltzmann distribution of the electrons in the collisionless quasineutral layer is demonstrated by a plot of the logarithm of the ion density versus space potential. The electron temperature obtained from this plot, from the floating potential of the sphere, and from the characteristic of the small probe differ from each other by at most 12%. A new method to detect deviations from the Boltzmann distribution in the transitional layer is tested. The ion densities measured by using the sphere as a probe agree within 13% with those obtained with the small cylindrical probe in the collisionless case.

ISSN:0031-9171    

DOI:10.1063/1.1693665

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The problem of the electron velocity distribution for a plasma in a steady state is investigated. The principal deviation from Maxwellian results from inelastic collisions of electrons with atoms and ions wherein the excited level depopulates predominantly by radiating a photon. A simple analytic solution to the Boltzmann equation is obtained for the case where we are in the tail of the distribution (this allows simplification of the Fokker‐Planck Coulomb operator) and for the case where the inelastic cross section varies as 1/E, whereEis the kinetic energy of the incident electron. A generalization is made to the case where many atomic levels can be excited, if the cross section for each varies as 1/E. In applying the results to astrophysical plasmas it is found that the non‐Maxwellian corrections are always small. For example, the relative corrections to inelastic collision rates for the primordial hydrogen‐helium plasma are less than10−3. In gaseous nebulae the typical corrections are even smaller(about 10−6). For some cosmic x‐ray sources and for stellar coronae the corrections are also of this order(10−6).

ISSN:0031-9171    

DOI:10.1063/1.1693666

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements have been made on density, velocity, electron temperature, and ion temperature in streaming plasmas generated by allowing the high‐density, high‐temperature material formed by aQ‐switched laser pulse focused on a solid target to expand into vacuum. Langmuir probe and Lecher‐wire microwave systems for this application have been developed and their reliable operation has been verified. Typical conditions at distances 15‐50 cm from the target are found to be:Te≃1‐12 eV, ne = &Sgr;niZi≃1010‐1012/cm3, Ti < 10 eV, peak flow velocityU ≃ 10‐20 cm/&mgr;sec, the exact values depending on target materials, laser power, and position. Photoionization and charge exchange in a low‐density background gas have been observed.

ISSN:0031-9171    

DOI:10.1063/1.1693667

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Exact Riemann wave solutions to the magnetohydrodynamic equations for a compressible medium under the influence of a gravitational field are obtained. The method of solution consists of an application of Hamburger's subsidiary equations previously found useful in the analysis of such three‐dimensional waves in compressible hydrodynamics under gravity. The resultant magnetoacoustic waves cannot be classified as slow and fast modes, and their propagation characteristics are found to be quite different from those in a uniform medium. In particular, the phenomenon of large amplitude wave ducting is examined. Certain wave properties correspond exceedingly well with the observed fine structure of waves propagating away from solar flares.

ISSN:0031-9171    

DOI:10.1063/1.1693668

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A particularly dangerous mode of instability in confined plasmas is the trapped particle mode which is highly insensitive to magnetic shear and average favorable curvature. The study of the collisionless trapped particle mode is extended to include the effects of finite&bgr; = 8&pgr;nT / B2. It is found that the “magnetic well” dug by plasma diamagnetism is highly effective in stabilizing the collisionless trapped‐particle mode. It is found that for magnetohydrodynamically stable systems the collisionless trapped‐particle mode becomes stable when the diamagnetic well is sufficient to give all particles average favorable drift. It would appear from this result that, in general, the diamagnetic well should be an effective stabilizing agent against all nonflutelike microinstabilities.

ISSN:0031-9171    

DOI:10.1063/1.1693669

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A dynamic helium plasma, produced by a conicalz‐pinch gun, was used to study interactions with an inhomogeneous transverse magnetic field. Magnetic probe measurements show that up to a critical value of the fieldBcthe plasma penetrates the region occupied by the field by completely removing it. An increase in the plasma electron temperature and density is seen. For fields higher than the critical valueBc, plasma penetrates in the form of thin sheets oriented along the magnetic field lines. The observed effects are compatible with the available theory if resistive effects are taken into account.

ISSN:0031-9171    

DOI:10.1063/1.1693670

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

For an infinite cold plasma consisting of several species in relative motion a Hamiltonian is derived in terms of creation and annihilation operators for plasmons. From a quantum‐mechanical point of view the two‐stream instability may be described as the creation of pairs of plasmons, one with positive and the other with negative energy. The Hamiltonian derived includes both the linear and nonlinear interactions. In order to discuss the nonlinear instability a canonical (Bogolyubov) transformation is performed to diagonalize the linear part of the Hamiltonian. It is shown that the nonlinear interactions may cause the explosive instabilities, even though the plasma is stable for the linear instability.

ISSN:0031-9171    

DOI:10.1063/1.1693671

出版商:AIP    

年代:1971

数据来源: AIP