摘要:

We present here anN‐pole circuit analysis of a network of parallel plane grids immersed in an isotropic hot‐electron plasma. The associated self‐ and trans‐impedances are expressed in terms of the discrete spectrum of electrostatic waves. Voltage‐transfer ratios and transconductances between pairs of grid assemblies are calculated to study the feasibility of this scheme for launching and detecting Landau waves. Results show that widths of about 5 Debye lengths are optimum for modulator and detector gaps and that close‐range transmission between gaps is predominantly due to the fundamental exponentially damped Landau wave.

ISSN:0021-8979    

DOI:10.1063/1.1709268

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

We report here measurements of dispersion and damping of plane electrostatic waves having phase velocities between 1.5 and 3 times electron thermal speed 3×107cm/sec. These waves were excited and detected at frequencies &ohgr;p<&ohgr;<2.5&ohgr;pusing gridded rf probes within an isotropic, quiescent, and collision‐free sodium plasma at thermal equilibrium. As plasma electron density (1×107to 2×108cm−3) and rf (30 to 180 MHz) are varied, the measured wavelengths and spatial damping rates were scaled to Debye length using independent Langmuir probe data. Full agreement is then found between the experimental results and the fundamental solution of Landau's dispersion relation.

ISSN:0021-8979    

DOI:10.1063/1.1709269

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In many applications of silicon epitaxial layers grown on silicon substrates it is necessary to oxidize the substrate and then remove the oxide prior to epitaxial deposition. This oxidation step is found to produce a greatly increased density of stacking faults in the deposit. This anomalous increase in stacking faults can be eliminated if the back (undeposited) substrate surface is treated either to abrasive processes such as lapping and scribing or to a boron‐gettering process prior to oxidation. Both types of treatment are likewise found to eliminate saucer‐like pits observed in oxidized slices after structural etching. The incidence of these pits is closely correlated with the incidence of stacking faults in the grown layer. It is concluded that the pits represent precipitates of fast‐diffusing impurities and are probable nucleation sites for stacking faults.

ISSN:0021-8979    

DOI:10.1063/1.1709270

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A general theory concerning the properties of magnetic materials having a nonuniform saturation magnetization is developed. In this theory, the local saturation magnetization and the local exchange interaction are assumed to vary in an arbitrary manner throughout the sample. It is further assumed that a dc magnetic field is applied which is sufficiently large to magnetize the sample substantially to saturation. The general theory is then specialized for a calculation of the static magnetization, assuming that the host material contains inclusions of a material with a different saturation magnetization. If all inclusions are fairly large, the effect of the exchange interaction becomes negligible and a result previously derived by Ne´el is obtained. The inclusion of exchange reduces the deviation of the magnetization from its saturation value, particularly at low values of the internal field. If exchange is neglected, this deviation becomes infinitely large at zero internal field. If exchange is included, however, the deviation remains finite. The theory is, therefore (for suitable materials), still approximately valid at remanence.

ISSN:0021-8979    

DOI:10.1063/1.1709271

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A theory of the longitudinal susceptibility (response to an rf field applied parallel to the dc field) of magnetic materials with a nonuniform saturation magnetization is described. According to this theory the imaginary part of the longitudinal susceptibility, &khgr;″, considered as a function of dc magnetic field, should show a maximum when the internal magnetic field is approximately equal to (&ohgr;/&ggr;)‐&pgr;⟨M0⟩, where &ohgr; is the frequency, &ggr; the gyromagnetic ratio, and ⟨M0⟩ the average saturation magnetization. The height of the absorption peak is calculated to be proportional to the degree of inhomogeneity (mean square deviation of the local saturation magnetization from its average) and approximately inversely proportional to the square of the frequency. The width of the absorption peak is approximately 2&pgr;⟨M0⟩. If the nonuniformity of the saturation magnetization is due to the presence of pores or nonmagnetic inclusions, the absorption at low dc fields (near remanence) is found to be proportional to the total cross‐sectional area of the inclusions (rather than their volume). Thus many small inclusions have a stronger effect than few large ones of the same total volume. The real part of the susceptibility is negative on the low‐field side, positive on the highfield side of the absorption peak. In most of the calculations, the effect of the inhomogeneity‐induced scattering of spin waves has been neglected. This scattering is shown to be substantially equivalent to an additional damping of the spin waves, which is strongly frequency and field dependent.

ISSN:0021-8979    

DOI:10.1063/1.1709272

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Relaxation‐averaging formulas are derived for magnetic‐induction problems involving axially symmetric fields with sinusoidal or pulsed time dependence in media which may be linear or nonlinear, homogeneous or inhomogeneous. Solutions have been obtained from a high‐speed digital computer for time‐harmonic fields in linear, inhomogeneous media. From these solutions, the electromagnetic forces are calculated and compared with experimental measurements. It is found that the computed and measured values agree quite well and that most of the discrepancy can be explained by the fact that the permeability of the ferrite used in the measurements was different from that assumed in the calculations.

ISSN:0021-8979    

DOI:10.1063/1.1709273

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of the electrical conductivity of polyethylene film containing absorbed iodine are described and discussed. The influence of temperature, film thickness, iodine concentration, and voltage is examined. It is believed that carriers arise from a charge transfer between polymer molecules and the iodine. The results suggest that space charge is important.

ISSN:0021-8979    

DOI:10.1063/1.1709274

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

With applied dc electric fields in excess of 1.2 kV/mil, the current in iodine‐doped polyethylene is found to be no longer invariant with time, but to exhibit continuous oscillations superimposed upon a large background current. These oscillations appear at a well‐defined threshold field, which is found to be independent of temperature, but to depend on the concentration of iodine in the film. The frequency of the oscillations is very temperature dependent, having an activation energy of almost the same value as the conductivity. Increase of iodine concentration increases the frequency, but the frequency decreases with increase of field strength. The frequency is also found to be inversely proportional to film thickness. Transient response characteristics suggest that the formation of space‐charge regions may be important. The experimental results are compared with the theory of recombination waves in dielectrics, which considers the propagation of low‐field domains through the sample.

ISSN:0021-8979    

DOI:10.1063/1.1709275

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The results of an experimental study of the absorption properties of Cs as present in Cs‐Ar low‐pressure discharges under various discharge conditions are presented. The total Cs concentration at zero discharge current was varied between 1.5 and 15×1012cm−3. Absorption was measured in the 4555‐Å and 8521‐Å lines of Cs from which the stationary concentration of Cs (62S1/2) could be derived. Special attention was paid to determine the Cs concentration as the discharge changed from a low‐burning voltage mode to a high‐burning voltage mode. The pronounced variations of the discharge properties were found to be accompanied by rather drastic changes of the Cs concentration for which variations of a factor of ten or more were found.

ISSN:0021-8979    

DOI:10.1063/1.1709276

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A nonquasistatic treatment is established in order to study wave propagation along beam‐plasma systems in the presence of a dc magnetic field. Solutions to the dispersion equations are given for two cases: The column completely fills a cylindrical waveguide, or it is in an infinite dielectric (vacuum). The results are compared qualitatively to those already obtained by various authors for the same conditions by a quasistatic analysis.

ISSN:0021-8979    

DOI:10.1063/1.1709277

出版商:AIP    

年代:1967

数据来源: AIP