摘要:

A method has been developed to determine the maximum emission depth of true secondary electrons &lgr;. The method is based on observing the retarding potential characteristics as a function of film thickness of a specimen which was deposited on a substrate. With this method values of &lgr; for DC‐705, DC‐704, and Octoil‐S (diffusion pump oils) were determined to be about 30, 40, and 70 Å, respectively. No clear dependence of the &lgr; on primary‐electron energy was found for 200–1500 eV. These &lgr; values well agree those obtained by means of &dgr;‐&eegr; analysis. This fact gives an experimental evidence for the validity of &dgr;‐&eegr; analysis in which a film thickness where a break occurs on a &dgr;‐&eegr; curve is assumed to correspond to &lgr;.

ISSN:0021-8979    

DOI:10.1063/1.1658546

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Current partitioning at a tungsten cathode in a 1‐atm argon plasma is studied experimentally. Both ions and electrons are found to contribute to the cathode current in this case. The ion current is supplied by the plasma whereas the electron current is controlled by the thermoinic emission laws. The work function of the emitter is reduced due to the presence of an ion space‐charge field in a manner described by the Schottky effect.

ISSN:0021-8979    

DOI:10.1063/1.1658547

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The temporal behavior of the temperature, the electron density and the thermal conductivity of the restrike channel of a thin exploding wire were studied, using the electrical conductivity of the restrike channel, which was determined by simultaneous measurements of the current through the channel, the voltage drop cross the channel and the channel radius assuming that the current distribution within the channel was homogeneous. In this study, in which the channel plasma was assumed to be fully and singly ionized, the Spitzer equations for the electrical and thermal conductivity of a fully ionized plasma and a modified pinch relation for the restrike channel were used. The results show:(a) that the electrical conductivity reaches its maximum before the current maximum on the ledge observed on the voltage oscillograms;(b) that the temperature and thermal conductivity reach their maxima at the conductivity maximum;(c) that the electron density reaches its maximum after the conductivity maximum and near the current maximum;(d) that the maximum values of the electrical conductivity, the temperature, the electron density and the thermal conductivity increase when the energy‐input rate to the channel increases;(e) that the validity of the assumptions made is in general confirmed.For restrikes initiated at the exterior of the 13‐cm‐long 0.005‐cm‐diam constantan wires, the maximum values of the temperature and the electron density were found at 5 kV to the about 2×104°K and 1023electrons/m3respectively, and at 23 kV to be about 4×104°K and 1025electrons/m3, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1658548

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Breakdown phenomena and the low‐voltage xenon arc have been studied in xenon‐filled thermionic diodes. These measurements were made at gas pressures ranging from 1 Torr to atmospheric pressure and with diodes having interelectrode spacings of 0.05, 0.1, and 0.75 cm. Most of the results were obtained on tubes with a unipotential thoriated‐tungsten cathode operating at approximately 1700°C. The results showed that breakdown in xenon leading to the low‐voltage arc can occur at voltages even lower than the first excitation potential of xenon. No minimum spacing effect was observed; the low‐voltage arc occurred for interelectrode spacings down to 0.05 cm. At 0.05‐cm spacing and a cathode temperature of 1700°C, the low‐voltage xenon arc could be induced over the pressure range 1–500 Torr. Under some conditions of pressure and spacing the low‐voltage xenon arc could be sustained at voltages as low as 1–2 V.

ISSN:0021-8979    

DOI:10.1063/1.1658549

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experiments have been performed in which mechanical radiation pressure, generated by a megahertz sound field in helium II, successfully supported a metal sphere three dimensionally. Because the field's forces are spherically symmetrical and stable, and because the isothermal environment provided by the quantum coherence properties of helium II eliminates convection currents, only extremely small stray torques act on the suspended mass. It is demonstrated that stray torques less than 10−7dyn cm were present on the early test model, consistent with the theoretical predictions. Also presented is the predicted performance, based upon these results, of a more refined superfluid gyroscope which demonstrates the feasibility of observing general relativistic gyroscopic motion with a gyroscope rigidly connected to the earth. A proposed experiment to discriminate between Einstein's theory and competing theories of gravitation by measuring the spin‐spin interaction between a gyroscope and the spinning earth is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658550

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Absorption of high‐power CO2laser radiation on a block of quartz is considered. The SiO2(quartz) is vaporized and heated and absorption of the incident laser radiation is computed. If the gas is not ionized, the laser energy heats it sufficiently to make it transparent.

ISSN:0021-8979    

DOI:10.1063/1.1658551

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The current density and the magnetic field strength are calculated in a type‐I superconductor which has the form of a long cylinder with a sinusoidal surface contour. London's and Maxwell's equations are solved with a straightforward perturbation calculation. The amplitude of a protrusion &Dgr; is assumed to be small compared with the penetration depth &lgr;. The results show a sizable variation of current and field near the surface when &Dgr;/&lgr; and &lgr;/L(L=wavelength of protrusion) are both ≥0.1.

ISSN:0021-8979    

DOI:10.1063/1.1658552

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Magnetization measurements are reported on twisted multistrand NbTi superconducting composites. Data for copper matrix composites when fitted to the theoretical predictions give reasonable values for the matrix resistivity. Data for a CuNi matrix composite and data on the rate of decay of the magnetization at small twist rates do not agree with simple theory. An explanation based on the presence of an untwisted core removes the disagreement. Finally, the data are plotted to show a linear dependence of magnetization on filament diameter over the range 0.00036–0.015 in.

ISSN:0021-8979    

DOI:10.1063/1.1658553

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The observation of harmonics and subharmonics of the Josephson oscillation is shown to be in agreement with a rather simple model of the junction. The generation of harmonics provides an explanation of induced steps in the current‐voltage characteristic which occur at submultiples of the usual induced step voltages. The subharmonic oscillation is seen to be a relaxation‐like process which can be easily understood in terms of a mechanical analog.

ISSN:0021-8979    

DOI:10.1063/1.1658554

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

By fitting the Ne´el theory of ferrimagnetism to previously reported magnetic moment‐temperature data for several{Y3}[RxFe2−x](QyFe3−y)O12compositions, whereRandQrepresent diamagnetic octahedral and tetrahedral substitutions, i.e., Sc3+, In3+, Ga3+, and Al3+, the molecular field coefficients were determined to have the following linear relations with the levels of substitution:Ndd=−30.4(1−043x),Naa=−65.0(1−042y),Nad=97.0(1−0.125x−0.127y) mole/cm3,forx≤0.70 andy≤1.95. Since both intrasublattice coefficients are affected only by substitutions in the opposite sublattice, a strong similarity to Geller's random canting concepts is apparent. Below the antiferromagnetic transitions it is demonstrated that a clear correlation exists between the decrease in sublattice moment from canting and the reduction in magnitude of the molecular field constant. For both sublattices, the antiferromagnetic transition occurs whenNdd,Naa∼−20 mole/cm3. This observation lends further credence to the notion that canting sets in immediately upon substitution. To demonstrate the applicability of the above results, magnetic moment‐temperature curves are computed for compositions of {Y3} [Mgx2+Fe2−x] (Six4+Fe3−x) O12and are shown to compare very favorably with experiment, thus providing a method for predicting the behavior of a wide variety of substituted garnet compositions.

ISSN:0021-8979    

DOI:10.1063/1.1658555

出版商:AIP    

年代:1970

数据来源: AIP