摘要:

Early breakdown effects have been measured in relatively high‐pressure thermionic diodes under given conditions of pressure and anode spacing. Apparent breakdown conditions are obtained at anode voltages considerably lower than the ionization potential of the gas. Measurements on xenon‐ and mercury‐filled thermionic diodes, under space‐charge conditions of operation, are presented which show that this breakdown voltage seems to be associated with the first excited state of the gas. Experimentally, early ignition occurs in diodes with a fixed cathode‐anode spacing in a limited pressure range only. A theoretical explanation for this behavior is based on the model that, in the limited pressure range, electrons traversing the cathode‐anode space can pick up almost all the energy of the applied voltage.In addition, data are presented showing that early breakdown in an inert gas‐filled diode can occur at voltages much lower than the first excited state. This has been accomplished in thermionic diodes exposed to the radiation of a nuclear reactor. A qualitative explanation for this behavior is proposed.

ISSN:0021-8979    

DOI:10.1063/1.1713296

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The capacitance contribution from the space charge and associated potential distribution in the metal electrodes of a parallel‐plane capacitor has been estimated by a classical, electrostatic calculation. The electron density is assumed to be given by the absolute zero temperature, Fermi‐Dirac distribution function. The first integration of Poisson's equation and application of the boundary conditions for the electric field at the metal‐dielectric interfaces result in two nonlinear, algebraic equations (one for each electrode) for the potential distribution as a function of the dielectric thickness and applied voltage. These equations were solved numerically. The results show that for reasonable electric fields in the dielectric (<108V/cm) the lumped‐series capacitance of the electrodes is practically constant and independent of applied voltage and dielectric thickness, in good, qualitative agreement with previously reported experimental results. The total capacitance is the series combination of the capacitances of the dielectric and the electrodes. The electrodes are effectively a capacitor with a thickness 2.3L, whereLis a length characteristic of the metal. This electrode series capacitance for metals such as gold is of the order of 1 &mgr;F/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1713297

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Direct current measurements have been made of film currents in and emission currents from thin‐film sandwiches consisting of beryllium, thermally formed beryllium oxide, and overlayers of silver, barium or a combination of the two.Silver covered oxide films formed at low temperature yield regular film current characteristics but no electron emission. With high oxidizing temperatures, electron emission can be obtained but the films are subject to frequent breakdown. An intermediate temperature range yields more reproducible film currents and, in many cases, small but steady electron emission. A discontinuous forming process generally precedes the electron emission.Films with barium overlayers break down and heal repeatedly, accompanied by very irregular emission at film voltages considerably below those for silver covered films. Brief exposure of a silver overlayer to barium vapor induces marked changes. Initially, the film current is irregular as it is for barium alone, but as the current increases the characteristic reverts to that for silver without barium. Electron emission is more frequently obtained in this way, though it occurs in the same voltage range as without barium.The film‐current curve shapes indicate that the current is carried mainly by electrons passing over a voltage‐dependent barrier (Schottky effect), but cooling the samples has no effect on these curves, probably because of localized heating.A tentative model is proposed to account for the particular observations reported here. Work function differences, the porosity of the thin silver films, and cracks or grain boundaries in the oxide layer combine to produce highly localized currents, heating, and structural changes consistent with measurements and observed emission patterns.

ISSN:0021-8979    

DOI:10.1063/1.1713299

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Quantitative measurements of the energy dependence of the extinction distance and transmissive power for electron waves in crystals have been carried out photographically and electrically with 100‐kV and 300‐kV electron microscopes. The observations show that the relativistic correction for the mass of the electron must not be disregarded in the dynamical theory of electron diffraction for either the elastic or inelastic scattering. The energy dependence of the visibility of thickness extinction contour fringes and the resolutions of the images of thick films are also discussed. Some of the features observed in electron micrographs of thin metallic films taken at 250–300 kV are illustrated.

ISSN:0021-8979    

DOI:10.1063/1.1713300

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Microwave reflection is considered for nonuniform plasmas with an exponential electron distribution that approaches an equilibrium value far downstream. Several approximate formulas for the reflection coefficient and phase‐shift angle and the graphical results of some numerical calculations are presented. Comparison of the results with those for ``ramped'' electron distributions shows an interesting point; when piecewise linear segments are used to represent a continuous electron distribution, the wave interactions may affect the reflection and transmission of electromagnetic waves.

ISSN:0021-8979    

DOI:10.1063/1.1713301

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An integrating sphere was adapted to measurement of external efficiencies of GaAs injection lasers. External efficiencies rise rather sharply with current once the laser threshold is reached, attaining ultimate values of about 35% at 77°K for the more efficient diodes, as high as 60% at 20°K. On the basis of a highly simplified model, the observed external efficiencies indicate junction efficiencies near unity.

ISSN:0021-8979    

DOI:10.1063/1.1713302

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The limiting value of the current density in a beam compressed by an arbitrarily large magnetic field has been derived from Liouville's theorem and the adiabatic invariance theorem. For sufficiently large compression ratios the limiting values are (1+eV/kt), as a result expected from the Langmuir‐Pierce expression. Some of the effects due to the use of a finite magnetic field have been examined with particular reference to the current density obtainable at the planes where cathode images are formed. The transit time scatter imposes an upper limit on the maximum compression ratio for which these cathode images can be utilized.

ISSN:0021-8979    

DOI:10.1063/1.1713303

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The oscillations in low‐pressure plasma thermionic energy converters are ion acoustic oscillations that may be explained on the basis of an electron beam‐plasma interaction. A low‐energy beam is formed by the acceleration of electrons through an ion sheath at the emitting surface. The ion acoustic oscillations are observed as expected when the ordered beam velocity is greater than the phase velocity of the wave and less than the plasma electron thermal velocity. Their frequency isf=&lgr;−1(&ggr;ekTe/mi)12where the emitter to collector spacing is a multiple of the half‐wavelength. Langmuir probes indicate high effective electron temperatures, and the agreement between calculated and measured frequencies is good if &ggr;e=3 is used, whether or not the electron‐electron collision frequency is higher than the frequency of the observed oscillations.

ISSN:0021-8979    

DOI:10.1063/1.1713304

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Equations are presented which give the intensity (photons/electron steradian) ofKcharacteristic x radiation produced by pure elements under electron bombardment at normal incidence. For values of &phgr; (the angle between the x‐ray beam and the specimen surface) between 0° and 90° the equations may be summarized:&ngr;K=(&dgr;&ohgr;/4&pgr;)NK,NK=WRf(&khgr;)NQ¯xK+NKf,wherevKis the number ofKquanta per incident electron radiated into solid angle &dgr;&ohgr; at takeoff angle &phgr;,Wis the fluorescence yield factor,Ris a correction for loss of ionization due to electron back scattering,f(&khgr;) is Castaing's absorption correction function,Nis the number of atoms per unit volume,Q¯is an average over electron energy of the cross section forKshell ionization,xKis the electron path length at which the energy of the electron drops to that necessary forKshell ionization, andNKfis the contribution due to secondaryKshell ionization by high energy continuous x radiation. It is concluded that the predictions of this theory are in general in good agreement with available experimental data; further, that this theory shows certain advantages over those of Archard (1960) and of Green and Cosslett (1961). Values off(&khgr;) are calculated and compared with the experimental work of Castaing and the calculations of Archard and Mulvey.

ISSN:0021-8979    

DOI:10.1063/1.1713305

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The limiting current density that can be achieved with thermal velocities in the source emission is calculated by phase‐space ellipse transformations. The results check those of Pierce, and are applicable to a wider range of problems. Simple lens systems can realize the ellipse transformations which give the limiting density. Under certain conditions the maximum current density is obtained between the object plane and the image plane, a situation analogous to the ``waist'' formation in a beam transport system used with particle accelerators.

ISSN:0021-8979    

DOI:10.1063/1.1713306

出版商:AIP    

年代:1964

数据来源: AIP