摘要:

Using a four‐moment method of the kinetic theory of gases, an analytical expression is derived for the problem of vapor condensation on and evaporation from spherical liquid droplets when the droplet is not in equilibrium with its surrounding vapor in temperature and pressure. Unlike the linearized theories, the result for the mass flux to or from the droplet surface is obtained for a general case of finite temperature and pressure differences between the droplet and its vapor. It is believed, therefore, that the present nonlinear theory should be more realistic in predicting the rate of vapor condensation or evaporation phenomena of a droplet.

ISSN:0021-8979    

DOI:10.1063/1.325122

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The trajectories of an intense relativistic electron beam propagating between a toroidal plasma column and a conducting vacuum wall are calculated theoretically and verified experimentally. Three classes of trajectories are observed, including a set of banana‐type orbits. The significance of these trajectories on the ability of the beam to transfer energy to the plasma is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325123

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The present work is concerned with a one‐dimensional dynamic simulation, incorporting a self‐consistent treatment of space‐charge effects, of the buildup and decay of ac discharges in a high‐ (≳100 Torr) pressure mixture of Ne+0.1&percent; Ar confined to a narrow gap (∼10−2cm) between insulator (MgO) covered metal electrodes. Numerical modeling has been done of the dynamics of successive avalanches triggered by the electric‐field‐dependent secondary emission of electrons at the cathode due to ionic species, metastables, and photons. The basic continuity equations of the problem deal with the following collisional phenomena in the gas volume: (i) electron impact excitation and ionization of neon atoms, (ii) collisional ionization involving excited neon states, (iii) two‐body and three‐body collisional processes involving energy transfer, and (iv) absorption and reemission of imprisoned resonant radiation. The computed results show a satisfactory agreement with measured parameters on a single cell of a specially constructed ’’one‐dimensional’’ ac plasma panel whose electrode linewidths were made an order of magnitude larger than the gas gap. Neon ions were found to play a dominant role in the secondary electron emission from the MgO surfaces, while photoemission was negligible. The theoretical and experimental results were fitted to yield a value of 0.45 for the intrinsic secondary‐emission coefficient of MgO surfaces caused by the arrival of neon ions under vacuum conditions. Finally, sample results are presented for the spatial and temporal profiles of the electric field, charged particle concentrations, and the volume density of various excited species of the host gas.

ISSN:0021-8979    

DOI:10.1063/1.325124

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have studied the spatial distribution of arcing as a function of electrode spacing and preionization pattern in CO2laser discharge mixtures, using circular electrodes which allowed a gap of up to 10 cm and a discharge volume of ∼3 liters. We utilized both cathode‐field enhancement with uniform preionization and apertured preionization with uniform field to define the discharge boundaries. In both cases, we found a threshold value of cathode‐field enhancement below which arcing was uniform and confined to the discharge region and above which arcing became highly nonuniform, with arcs localized to the high‐field region.

ISSN:0021-8979    

DOI:10.1063/1.325125

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A theory of the hollow cathode arc is given which explains the physical mechanisms of operation of these discharges. The following basic phenomena are studied: the gas flow inside the cathode; the formation of the internal plasma column by ionization of the neutral gas by the primary electrons emitted by the cathode, which are accelerated in the cathode sheath; the transport of the ions towards the cathode wall; the transport of current and of kinetic energy towards the exit of the cathode, by the Maxwellian electrons of the plasma; and, finally, the thermal equilibrium of the cathode wall. This theory gives the axial variation of the gas pressure and wall temperature, the electron temperature, the mean number of excitations and of ionizations produced per primary electron, and the radial and the axial variation of the plasma density and plasma potential. The field‐enhanced thermionic effect constitutes the basic emission mechanism of the cathode, the wall being heated mainly by ion bombardment. Theoretical results for discharges in argon with a tantalum cathode are in excellent agreement with all the available experimental results.

ISSN:0021-8979    

DOI:10.1063/1.325126

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In this paper we have studied the problem of self‐focusing of a Gaussian laser beam in a collisionless magnetoplasma when the direction of wave propagation is at right angles to the magnetic field. The nonlinearity arises through the ponderomotive force and subsequent redistribution of plasma along the magnetic field. It is seen that as the magnetic field increases the extent of self‐focusing increases. The isointensity surfaces of a three‐dimensional beam are elliptical. In the case of a plane‐uniform laser beam it is seen that it is unstable for small‐scale fluctuations, and the growth rate of instability increases very rapidly with magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.325134

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The ESR‐induced changes in the dc resistance, &Dgr;&rgr;/&rgr;‖ESR, of P‐ion‐implanted silicon have been observed for the first time. The transfer of absorbed Zeeman energy at liquid‐He temperature has been investigated. The &Dgr;&rgr;/&rgr;‖ESRsignals observed were a narrow line with agvalue of 1.9988 for light‐dose implantation and a new broad line with a little largergvalue for heavy‐dose implantation. The line shape of these &Dgr;&rgr;/&rgr;‖ESRsignals was Lorentzian as well as the ESR signal, but the linewidth &Dgr;H1/2of the broad &Dgr;&rgr;/&rgr;‖ESRsignal was about 10 times as broad as the ESR linewidth. It is suggested that the anomalously broad line of &Dgr;&rgr;/&rgr;‖ESRoriginates from the transfer of the Zeeman energy absorbed by the localized donor electrons at the tail regions with low donor concentration (5×1017<ND≲1.5×1018P/cm3) to the layer with intermediate donor concentration (1.5×1018<ND≲3.7×1018P/cm3) where the resistance changes take place. This transfer is caused by the existence of the peak regions with high donor concentration (ND≳2×1019P/cm3) which act as Zeeman energy absorbers.

ISSN:0021-8979    

DOI:10.1063/1.325081

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

High‐resolution electron microscopy of a commerical ZnO‐based varistor reveals that the Bi‐rich intergranular phase is found at all three‐ and four‐grain junctions and that the majority of the ZnO grains are not surrounded by an oxide‐barrier film as previously believed.

ISSN:0021-8979    

DOI:10.1063/1.325135

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A series of molten Al‐rich wires between 10 and 500 &mgr; wide were translated through thin (100) and (111) silicon wafers in a thermal gradient to produce verticalp‐njunctions, which are sufficiently narrow to be considered for some integrated‐circuit applications. Thermal gradients were generated by heating the silicon wafers with either a scanning electron beam in vacuum or a hot tungsten filament in various atmospheres. The migration rate rapidly increased with the wafer temperature in agreement with calculations of the temperature gradient through the wafer. A reduction in the magnitude of the gradient near the colder wafer surface was explained by radiative‐heat transport through the semitransparent silicon wafer. The width of the resulting doped region was finer in (100) wafers than in (111) wafers, because the shape of the liquid wire was narrower for the (100) orientation. A relationship between the linewidth, wafer temperature, and Al film geometry was derived to predict the linewidths from 30 to 140 &mgr; in (100) wafers.

ISSN:0021-8979    

DOI:10.1063/1.325082

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have observed the temperature stability of the amorphous structure in many transition‐metal‐alloy systems (Nb‐Mo, Ta‐W, Nb‐Zr, Mo‐Ru, W‐Re, Mo‐Rh, Ta‐Re, Zr‐Mo, Ta‐Ir, and Zr‐Ru) prepared by electron‐beam evaporation onto liquid‐helium‐cooled substrates. Past observations which established criteria for the formation of amorphous metallic alloys were largely limited to close‐packed elements. In this paper, which includes a large number of bcc elements, we find that the crystalline‐state immiscibiltiy of the elements is a stronger factor in determining the stability, as well as the ease of formation of the amporhous structure, than is the difference in atomic size of the constituent elements.

ISSN:0021-8979    

DOI:10.1063/1.325083

出版商:AIP    

年代:1978

数据来源: AIP