摘要:

Computer calculations have been made of the propagation of the shock from an explosion at the origin of a spherically symmetric, exponential, ideal‐gas atmosphere. A generalization of Sachs scaling has been devised which allows a very convenient systematization of the pressure‐distance curves, and which shows that, for a suitable normalization, these curves are straight lines throughout a significant range of yield, distance, and degree of atmospheric inhomogeneity. This technique is also used to investigate the validity of modified Sachs scaling, an approximate method of generating pressure‐distance curves for an inhomogeneous atmosphere from the known results for a homogeneous atmosphere. It is found that modified Sachs scaling yields results which deviate from the hydrodynamic code calculations by at most 20% in the weak shock regime. This result is essentially independent of yield. Some comments are made on the applicability of these methods to the problem of shocks from explosions in horizontally stratified, real‐gas atmospheres.

ISSN:0031-9171    

DOI:10.1063/1.1692129

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A series of numerical computations has been carried out to obtain an accurate solution to the flow resulting from a detonating charge in contact with metal plates of various thicknesses in order to (i) determine the validity of the classical model for the detonation structure of condensed phase explosives, (ii) determine any effect of the complex wave interactions of the reflected waves within the reaction zone on the measured free‐surface velocities of the shocked metal, and (iii) remove the anomaly of the previously observed “decay” zone. The present investigation leads to a new interpretation of free‐surface velocity measurements for thin plates, which supports the classical theory of the detonation wave structure for condensed media and results in experimental values of the Chapman‐Jouguet parameters which are in consistent agreement with both the “theoretically” predicted Chapman‐Jouguet values and the directly measured (by the electromagnetic method) Chapman‐Jouguet values.

ISSN:0031-9171    

DOI:10.1063/1.1692130

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Experiments have been conducted on normal ionizing shock waves produced in a coaxial electromagnetic shock tube. Steady shock velocities were measured as a function of initial gas pressure, drive current, and applied axial magnetic field. The speeds agreed well with theoretical values. Measurements were made of the switch‐on magnetic field, the upstream transverse electric field, and the density ratio across the front. The data all show that trans‐Alfve´nic shocks(uA l f1< us≲ 3uA l f1)exhibit Chapman‐Jouguet behavior, with current flow in the shock front, and no separation of shock and drive currents. In contrast, super‐Alfve´nic shocks(us≳ 3uA l f1)appear to be gas dynamic in nature. Spectroscopic measurements and shock‐reflection studies demonstrated the presence of a nonluminous front and shock‐heated gas preceding the luminous drive current.

ISSN:0031-9171    

DOI:10.1063/1.1692131

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Separation of the electron density transition from the current sheet and the luminous peak has been observed with ionizing waves in an electromagnetic shock tube. Upon reflection of the shock, coalescing waves and macroscopic turbulence are seen.

ISSN:0031-9171    

DOI:10.1063/1.1692132

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The effect of collisions on harmonic generation in an ionized gas slab through which an electromagnetic wave is passing is considered. The gas is assumed to be slightly ionized with electron‐neutral molecule collisions dominating. An approximate distribution function is assumed which contains five undetermined parameters. Boltzmann's transport equation is used to obtain the appropriate kinetic equations governing the behavior of these parameters. The kinetic equations are coupled to Maxwell's equations and a Fourier solution in time is used. The ionized gas slab is stratified into a series of individually homogeneous laminae and the equations are solved. The first harmonic transmitted and third harmonic generated power are calculated and plotted versus input power for several collision cross sections.

ISSN:0031-9171    

DOI:10.1063/1.1692134

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The dispersion relation for circularly polarized electromagnetic waves in a warm two‐component plasma subject to parallel static electric and magnetic fields has been derived from the linearized coupled Boltzmann‐Maxwell equations with the collision frequency assumed to be independent of the particle velocity. The effect of a weak longitudinal electrostatic field,E0, on the propagation characteristic of the right‐ and left‐hand circularly polarized waves in an isothermal electron‐proton plasma is examined in detail and illustrated numerically for a conveniently chosen set of the system parameters. For the right‐hand polarized wave the electrostatic field effect is found to be significant for a wave with frequency &ohgr; in the vicinity of the electron cyclotron frequency&ohgr;z≡ (eB0/m). For example, for a given &ohgr; and &dgr; ≡(eE0/mc&ohgr;) > 0an increase in &dgr;, or inE0, leads to the increase or decrease of the attenuation constant &agr;, of the wave according to whetherY ≡ (&ohgr;z/&ohgr;) < 1 or Y > 1. Moreover, forY = 1.10, when &dgr; < 0 (i.e., whenE0and the wave vectorkare oppositely directed) &agr; increases with |&dgr;|. On the other hand, when &dgr; > 0 an increase in |&dgr;| causes &agr; to decrease and for a sufficiently large value of &dgr;, &agr; may become negative so that the wave may experience a spatial growth.

ISSN:0031-9171    

DOI:10.1063/1.1692135

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Numerical experiments on a one‐dimensional electron plasma were used to obtain an insight into nonlinear plasma phenomena. Three experiments were carried out. The first dealt with the damping of a large‐amplitude wave which is found to be much stronger than that predicted by linear theory. A rough theory for the damping is presented. The second experiment examined mode‐mode coupling. Quantitative agreement was found with theory after precautions were taken to avoid other effects, in particular, “trapped” particles. A rough theory for “trapping” is given. The third experiment examined the weak turbulence produced by a small bump in the tail of the distribution function, and present theory appears inadequate to describe this behavior. After initial growth, the unstable modes fluctuate on a time scale of10&ohgr;p−1. The bump in the tail of the velocity distribution flattens out in a short time(20&ohgr;p−1), and then evolves into a hot Gaussian tail which coexists with the main plasma for a long time(≳ 1000 &ohgr;p−1). Particles in the tail have been observed with four times the initial average energy of the beam electron. A discussion of the physical effects which appear to be involved in this experiment is given, and estimates of their importance for three‐dimensional plasmas are presented.

ISSN:0031-9171    

DOI:10.1063/1.1692136

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A mixed hydromagnetic‐electrostatic instability is found propagating perpendicular to the aligned magnetic field and electron streaming in a collisionless plasma. It is found that the growth rate may be comparable to that of the two‐stream instability, and there are cases where ions are heated more than electrons. The finite temperature case is considered and thermal damping of the instability is demonstrated.

ISSN:0031-9171    

DOI:10.1063/1.1692137

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A photoabsorption technique in the vacuum uv region is used to measure the density of atomic hydrogen in a decaying, highly ionized hydrogen plasma as a function of time and position. The plasma is formed in a metal cylinder with a strong axial magnetic field by a powerful pulsed cross‐field discharge that takes the form of an axially propagating ionization front. It is found that during the discharge a fraction of the gas is driven to the boundaries forming a layer of increased neutral density which later relaxes back into the plasma by diffusion. In the interior, the plasma is initially highly ionized and the atom density builds up as the ion density decreases. The rate is consistent with predictions based on the collisional‐radiative recombination model.

ISSN:0031-9171    

DOI:10.1063/1.1692138

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Following a discussion of existing probe theories for a collisional plasma, a new theory is given for ion collection by a spherical probe in a collisional plasma which goes over to the collisionless theory of Allenet al. at low pressures and the continuum theory of Su and Lam at high pressures. Numerical results are given in a form suitable for interpretation of experimental data. Experimental probe studies in the positive column (1 cm diameter) of a He discharge in the pressure range 0.05‐0.4 Torr are described and the use of the electron and ion saturation methods for determining plasma concentration compared with one another and with a microwave cavity perturbation method. The limitations of the theories and experimental methods are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692139

出版商:AIP    

年代:1968

数据来源: AIP