摘要:

Velocity modulation of a one‐dimensional electron beam is treated relativistically, starting from the collisionless Boltzmann equation and using first‐order perturbation theory. A general expression for the perturbation current densityj1is applied first to a mono‐energetic unperturbed beam. Compared to the non‐relativistic case, the magnitude ofj1is reduced by the factor (1−u2/c2)3/4, whereuis the unperturbed beam velocity andcthe velocity of light. The distance between the maxima ofj1is increased by the inverse of the same factor. Relativistic effects decrease the efficiency of modulation &eegr;, which is defined as the energy carried by the electric field generated by the perturbations, divided by the energy flux in the unperturbed beam. For an unperturbed beam with a rectangular velocity distribution of narrow widthwand a fixed mean velocityum, the results are independent ofwto first order. Expressions forj1and &eegr; are also found for an unperturbed beam with a rectangularmomentumdistribution of arbitrary width. When this width is small and increasing asumis fixed,j1increases in second order if the beam is highly relativistic or if its plasma frequency is larger than the frequency of modulation, while it decreases otherwise. Under either condition &eegr; decreases in second order.

ISSN:0021-8979    

DOI:10.1063/1.1713106

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The predictions of the Archard diffusion model for electron trajectory within a specimen are compared with experimental data. The predicted distributions in depth of primary x‐ray emissions are calculated. The applicability of the model to the absorption corrections in electron microanalysis is discussed in light of these calculations.

ISSN:0021-8979    

DOI:10.1063/1.1713107

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Only a few experimental techniques permit the determination of inhomogenities in the electron density of a plasma, and even these lose their usefulness near the walls of the plasma container. A microwave surface wave technique using the container boundary as a propagating surface is described. Under the assumption that the plasma is azimuthally symmetric and axially uniform, perturbation relations for the microwave field permit an integral transform to convert phase shifts into radial electron density. This technique applied to a 2‐Torr neon rf‐generated plasma in coaxial geometry indicates an electron density near the inner wall as having a square‐law distance dependence. This is not in accord with the well‐known theoretical models of diffusion‐limited plasmas, but can be explained qualitatively.

ISSN:0021-8979    

DOI:10.1063/1.1713108

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The electron ionization coefficient &agr;/p0(cm×Torr)−1has been measured over anE/p0(volts/cm×Torr) range from 20 to 100 in deuterium subjected to various purification procedures. The results obtained lie slightly below those previously reported by Rose; however, the agreement is within the combined experimental error. Comparison is also made with the measurements of the ionization frequency &ngr;i/p(sec×Torr)−1of Cottingham and Buchsbaum. The present results, at a givenE/p0value, lie above their data. The discrepancy between the ac and dc results is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713109

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Single crystals of In2O3were grown by a flux technique that is described in detail. The temperature dependence of the electrical conductivity was measured down to 4.2°K; an anomaly in the conductivity is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713110

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Some plasmas contain condensed species as liquid or solid particles which may be hot enough to emit electrons thermionically into the plasma. The charge and voltage distributions in the vicinity of the particle are determined from the Poisson—Boltzmann equation and from a plasma sheath theory that is modified to account for thermionic emission. There is a critical temperatureT0at which the sheath changes from an ion sheath to an electron sheath. At temperatures greater thanT0an electron cloud is injected into the plasma, but it is confined near the particle surface within a distance less than the Debye shielding distance. Some typical voltage and charge density profiles are given for a rocket exhaust plasma.

ISSN:0021-8979    

DOI:10.1063/1.1713111

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The image quality obtained with neon as an imaging gas was studied. Neon can give stable images of non‐refractory metals because its ionization field is lower than the evaporation field of these metals. Field evaporation occurs in helium and in neon at slightly lower fields than in vacuum when the incoming nonionized gas molecules which have both thermal and dipole attraction energy collide with the surface atoms. Localized field evaporation leads to dynamic end forms of the emitter tip which are characteristic for vacuum, neon, and helium. The ion image obtained with helium containing a few percent neon has a reduced contrast and shows more details around the low‐field areas. Field evaporation in this mixed gas produces surface vacancies inside closed net planes. These effects indicate that adsorbed neon atoms act as intermediate collision partners to allow a more efficient transfer of the energy from the light helium atom to the heavy metal atom.

ISSN:0021-8979    

DOI:10.1063/1.1713112

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A dc probe was placed behind a small slit in the collector electrode in each of several cesium‐vapor thermionic diodes. These systems were used to study the velocity distribution of the small fraction of the emitted electrons which passed through the collector slit. This technique overcomes several of the inherent disadvantages in the use of the dc Langmuir probe in cesium vapor. The error due to momentum defocusing in the collector slit is calculated with the presence of a plasma in the emitter—collector interspace. The probe log‐current vs voltage curves could be accurately fitted to a Maxwell—Boltzmann velocity distribution over several cycles in log‐current. In this manner, effective temperatures were defined as a measure of the randomness of the velocity component normal to the collector surface. No fully randomized, high‐temperature electron group was detected in the unignited mode of these diodes. The effective electron temperature in the unignited mode became increasingly larger than the emitter temperature as the latter temperature was increased, but the departure was always less than 25%. The effective electron temperature increased rapidly with diode current as the ignited mode was entered and rose to be 470% higher than the emitter temperature.

ISSN:0021-8979    

DOI:10.1063/1.1713113

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A set of general equations describing the time‐dependent behavior of a laser is derived. The derivation is based on a density matrix description of a homogeneously broadened laser transition and a semiclassical treatment of the radiation field, consisting of an arbitrary number of modes. The resulting equations resemble ordinary rate and energy conservation equations but contain additional interference terms which, in general, couple all of the modes. The strength of this coupling depends on the inhomogeneity of the population inversion as well as on the mode frequencies. The energy conservation equations imply that absorption and stimulated emission in such a system can apply, strictly speaking, only collectively to the system of modes as a whole. In addition, the threshold inversion is affected by mode coupling. Stability analysis carried out in the two‐mode case indicates that a spatial inhomogeneity in the pumping rate is required for undamped oscillations. It is also concluded that coupling of off‐axis modes is more likely to lead to undamped spiking than coupling of axial modes.

ISSN:0021-8979    

DOI:10.1063/1.1713114

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The thermionic work function of aluminum electrodes with anodized aluminum oxide coatings of 30 and 2000 Å was determined for each electrode from the contact potential difference of each electrode with a well outgassed and aged polycrystalline tungsten wire emitter. In vacuum, the thermionic work function of the 30‐Å coated electrode was 4.3±0.1 eV, relative to a polycrystalline tungsten work function of 4.6 eV and a tungsten emission constant of 120 A/cm2· °K2. In cesium vapor at reservoir temperatures up to 70°C, the 30‐Å coated electrode had a minimum observed work function of 1.4±0.1 eV relative to the same tungsten reference electrode. The resistance of the 2000‐Å film coated collector electrode was too large to allow accurate determination of the work function of this electrode. In both vacuum and cesium vapor, however, there was an indication that the work function of the 2000‐Å coated electrode was a few tenths of an electron volt lower than that for the 30‐Å coated electrode. It is suggested that similar but perhaps less stable oxide‐coated electrodes could occur naturally on the collector of a thermionic energy converter due to oxidation of the collector surface or buildup on the collector surface of outgassing products from the emitter.Auxillary experiments were performed on the secondary‐electron emission from these oxide‐coated electrodes. No lingering secondary electron emission current corresponding to a Malter effect was observed. The true secondary yield from the 2000‐Å coated electrode was 3 in vacuum and 7 in cesium vapor for a primary electron energy of 150 eV. The secondary yield for the 30‐Å coated electrode was similar in cesium vapor but was not studied in vacuum.

ISSN:0021-8979    

DOI:10.1063/1.1713115

出版商:AIP    

年代:1964

数据来源: AIP