摘要:

The problem of representing electromagnetic fields in an electron plasma subjected to large and rapid electron‐density variations due to transient ionization processes is considered. The inherently nonlinear character of this problem, which arises in the Maxwell‐Euler equations through the electron transport term ▿· (nV), is retained under the assumption that temporal variations of the electron densitynare of first order in magnitude while spatial variations innare of second order. That is, we asume V·▿n≪n▿·V and consequently, ▿· (nV)≃n▿·V, where V is the induced velocity field. With the aid of vector and scalar potentials, it is shown that, in this case, the set of ten coupled Maxwell‐Euler equations describing a cold, isotropic, lossy, electron plasma with current and ionization sources can be reduced to a set of five integro‐differential equations which are effectively decoupled. A method of solving these equations based on perturbation techniques is sketched for the case where the initial electron density is zero.

ISSN:0021-8979    

DOI:10.1063/1.1658713

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Calculations have been made of the collective field emission and thermally enhanced emission from a multiplicity of emitters in order to simulate the properties of large‐area electrodes in vacuum subjected to high voltages. The individual emitters were assumed to be noninteracting. In one set of calculations, the individual emitters comprising the groups were characterized by randomly selected values of &bgr;, work function, and projection height lying between the limits of 50 and 200, 4.4 to 5.0 eV, and 0.5×10−4and 10−3cm respectively. In other computations values of work function and projection height were fixed at 4.5 eV and 5×10−4cm respectively and values of &bgr; determined from an assumed normal distribution with a central value of 100. It is the intent of this work to show the behavior of these collections of emitters in detail. Although the collective emission from these groups yielded an apparently straight‐line Fowler‐Nordheim plot, computed values of effective &bgr; and effective emitting area varied noticably with field. At low field the effective &bgr; is closely similar to the maximum value of &bgr; in any given collection of emitters. As the field is increased, the effective &bgr; declines while effective emitting area increases. The change in effective &bgr; over an average field ranging from 100 to 500 kV/cm is typically 5%–10%.

ISSN:0021-8979    

DOI:10.1063/1.1658714

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Ion‐chamber measurements of the photoionization produced by point‐to‐plane corona discharges in air, oxygen, and nitrogen (commerical grade) over a pressure range of 0.1 to 18 Torr are reported in this paper. The results are expressed in a generalized form that reduces the data for each gas to a single curve relating photoionization to pressure (p) times distance (R) from the discharge. The range ofRpvalues is between 1 and 550 cm Torr. Absorption coefficients are compared to those reported by other investigators by plotting absorption coefficient/pressure vsRp. In air and oxygen the values fall along a common curve. These results indicate that relating the ion‐chamber currents toRpin the manner described in this paper may provide a useful basis for calculating the photoionization produced by discharges in these gases.

ISSN:0021-8979    

DOI:10.1063/1.1658715

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Retarding potential and cylindrical electrostatic analyzer experiments have determined the equivalent voltage loss needed to electrostatically spray positively charged droplets of glycerol doped with sodium iodide. The cylindrical analyzer was also used as a mass spectrometer to identify in‐flight evaporation processes. Evaporation from discrete multimolecular droplets containing one sodium ion in conjunction with low numbers of glycerol molecules was identified. The kinetics of this process made it possible to assign an energy loss of 400±200 V for the spraying process.

ISSN:0021-8979    

DOI:10.1063/1.1658716

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The basic mechanism by which dust particles are charged through impact was studied. Redistribution of charges during impact was described in terms of the dynamics of the impacting bodies, and the properties of the materials of the contacting surfaces. An electrostatic probe theory was developed and applied to three cases: single particles, clouds of particles, and turbulent suspensions. Experiments were performed with pulverized coal dust suspended in air, a principal area of application of the electrostatic probes utilizing impact charging. Results showed that the electrostatic probe provides an accurate means for monitoring the flow rate of particles in a dusty suspension.

ISSN:0021-8979    

DOI:10.1063/1.1658717

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The first approximation analysis for deriving activation energy spectra from relaxation data, originally derived for linear distributed relaxation processes, is shown to be valid as well for nonlinear distributed processes. The analysis is also applied to nonlinear, undistributed processes and found to indicate a spectrum of activation energies with a maximum at the characteristic energy of the single process. The characteristics of spectra resulting from nonlinearities are considered, and a procedure for evaluating the possible physical significance of derived activation energy spectra is considered.

ISSN:0021-8979    

DOI:10.1063/1.1658718

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The thermal conductivity of three amorphous polymers has been measured between 0.4° and 4°K. The thermal conductivity of all samples has a similar temperature dependence, nearly temperature independent near 4°K and decreasing with an increasing power of the temperature as the temperature decreases. At the lowest temperatures the thermal conductivity is proportional to the three‐halves power of the temperature. Above 1.2°K the data can be explained by resonant scattering; however, below 1.2°K, the data are not explained by existing theories. Between 2° and 4.2°K, the heat capacity is calculated from thermal diffusivity measurements. The data obey aT3law but the magnitude is about 100% higher than that calculated from sound velocity measurements indicating an excess specific heat.

ISSN:0021-8979    

DOI:10.1063/1.1658719

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In this paper we present a theory to explain the observed lens effect produced by a photocurrent in Cds. An applied dc voltage causes local heating due to the presence of a localized photocurrent produced by a focused laser beam. The local heating causes an increase in the index of refraction and hence focusing. The theory predicts that the magnification should be linear in the power dissipated by the photocurrent and these predictions fall very near the measured values of magnification for different values of photoconductance, with no fitted parameters. In order to explain the threshold effect observed in some Cds samples the change in the index of refraction with temperature of Cds is measured over a temperature range of 20°–350° and is found to bedN/dT=1.5×10−4(°C)−1.

ISSN:0021-8979    

DOI:10.1063/1.1658720

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The paper discusses the use of internal second‐harmonic generation as a means of lengthening the pulses of Q‐switched lasers. The second‐harmonic generator acts as both a nonlinear power‐dependent loss and as an output coupler for the laser. The lengthening arises if the coupling to the second harmonic is greater than that necessary to maximize the peak second‐harmonic power. It is shown that a pulse‐lengthening factor of about 100 should be obtainable.

ISSN:0021-8979    

DOI:10.1063/1.1658721

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The interaction of high‐intensity laser beams with metals has been analyzed on the basis of detailed quantitative measurements of the energy balance. The interaction of normal (not Q‐switched) pulses with energies ranging from 1 to 30 J from a Nd‐doped glass laser with metals having a variety of thermal and optical properties was studied. The time‐dependent radiation reflectance of the metals, measured during the laser pulse, is found to account for most of the incident power in the initial stages of the interaction. As time progresses, much of the incident power is absorbed. It was found that the greatest part of the absorbed radiation energy is used to remove material in the liquid and vapor phases. Due to a large heat of vaporization for most metals, the amount of energy required to remove a given mass is strongly dependent on the relative amounts removed in the liquid and vapor phases. To determine this ratio, the total mass of material and the mass of molten material were measured.

ISSN:0021-8979    

DOI:10.1063/1.1658722

出版商:AIP    

年代:1970

数据来源: AIP