摘要:

Measurements of thermoelectric power, resistivity, and the temperature coefficient of resistance have been made on annealed silver films. The values obtained for the energy dependence of the mean free path of conduction electrons, [(∂ ln&lgr;/∂ lnW)]W=WF, and the Fermi surface area, [(∂ lnA/∂ lnW)]W=WF, were 1.29 and −2.45, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1662151

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The electrical breakdown characteristics of long spark gaps have been modified by laser‐induced ionization. The mean velocity of −500‐kV streamers is increased by an order of magnitude, to[inverted lazy s]3×108 cm/sec, and discharge columns are guided over a straight path in air and other atmospheres, by a 1.06 &mgr; optical beam focused to[inverted lazy s]10 11 W/cm2.Time‐resolved studies of the experimental phenomena, together with theoretical models for the evolution of laser‐induced ionization, indicate that a continuous low‐level ionization, rather than the occasional optical breakdown beads along the beam path, is responsible for the observed effects. Analysis of the discharge data and direct measurement of the ionization generated by laser radiation focused to subbreakdown intensities both confirm that positive and negative ion pair densities in the range 1010−1011/cm3are responsible for directing and increasing the streamer velocities; photodetachment of electrons by the luminous streamer tip enhances the streamer propagation. Our model can also be used to interpret previously reported optical influence on electrical breakdown.

ISSN:0021-8979    

DOI:10.1063/1.1662152

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Results are presented of an experimental study of the relative concentration of ions in the positive column of small‐diameter noble‐gas discharges. The ratio of the molecular ion concentration to the atomic ion concentration has been measured as a function of discharge pressure and current for dc discharges in argon, krypton, and xenon. Discharge pressures and currents were varied from 0.1 to 10 Torr and 15 to 40 mA. A simple theoretical model of the positive column was developed and the pressure dependence of the ion concentration ratio was calculated. By parametrically fitting the predicted ion ratio equation to the experimental data, estimates of several reaction rate coefficients could be derived. Where possible, the ion ratio data and the derived rate coefficients have been compared to previously published data.

ISSN:0021-8979    

DOI:10.1063/1.1662153

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper reports on an experimental investigation of the spatial variation in electron density in a cylindrical inertial‐electrostatic plasma confinement device. A microwave cavity operating at 4 and 8 mm employing both longitudinal and transverse modes and a laser heterodyne system operating at 3.39&mgr; were used to investigate the charge structure. The microwave data showed a nonlinear increase in electron density as a function of center electrode current, implying trapping for ion injection. The laser heterodyne data showed a distinct oscillatory form of electron density as a function of radius for both electron and ion injection, with densities of 8×1011electrons/cm3and variations in maxima to minima exceeding 30% of the average density.

ISSN:0021-8979    

DOI:10.1063/1.1662154

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The application of low‐energy molecular‐beam techniques to the analysis of the neutral (metastable and ground‐state) particles emitted by a thermal plasma is described. The technique is illustrated with the use of an apparatus that contains a rotating slotted‐disk velocity analyzer and an inhomogeneous‐field deflecting magnet. The beam source is a hot‐cathode low‐voltage continuous discharge in a rare gas. With this apparatus the Lande´gfactor was found to be 1.51 ± 0.01 for Ne3P2and 1.50 ± 0.02 for Ar3P2, in accord with theory. In addition, measurement of the velocity distributions of the two Ne metastable atoms (3P0and3P2) demonstrated that they could be characterized by Maxwell‐Boltzmann distribution functions with different temperatures for the two states.

ISSN:0021-8979    

DOI:10.1063/1.1662155

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The power‐law and constant‐loss theories of secondary electron emission have been modified to include the effects of secondary scattering within the solid. For power‐law exponent values of 1.35, 1.66, and 2.00, the scattering effects reduced penetration depths at maximum yield by almost a factor of 2 and decreased the maximum yields by about 70% in each case. Reduced yield curves were also computed for the different cases and the results indicate that scattering has only a small effect on the shape of the curves. Where reduced yield curves are involved, it may be concluded that the simpler theories could be sufficiently accurate in many cases. It is also shown that the exponent value of 1.35 provides reasonable agreement with experiment for lower primary energies, while 1.66 is more suitable at higher energies, in general accord with the energy ranges employed in the electron transmission measurements from which the above exponent values were originally determined.

ISSN:0021-8979    

DOI:10.1063/1.1662156

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The current collection characteristics of a moving cylindrical Langmuir probe are evaluated for a range of probe speeds and potentials which are applicable to earth and planetary measurements. The current expressions derived include the cases of the general accelerated current, sheath area limited current, orbital motion limited current, and retarded current. For the orbital motion limited current, a simple algebric expression is obtained which includes and generalizes the Mott‐Smith and Langmuir expressions for both a stationary probe and a rapidly moving probe. For a rapidly moving probe, a single formula adequately represents both the accelerated and the retarded current.

ISSN:0021-8979    

DOI:10.1063/1.1662157

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Electrical conduction in polymers under a relatively low applied electric field is considered to be ionic and is affected strongly by the structural factors of the polymers. The following equation for the electrical conductivity &sgr; was derived in which free volumeVf, jump energyEj, and ionic dissociation energyWwere taken into consideration:&sgr;=&sgr;0exp− [&ggr; Vi*/Vf+(Ej+W/2&egr;)(kT)−1], where &sgr;ois a constant, &ggr; the numerical factor to correct the overlap of free volume,Vi*the critical volume required for transport of an ion, &egr; the dielectric constant,kBoltzmann's constant, andTthe absolute temperature. This equation describes well the conduction phenomena in polymethylmethacrylate, polystyrene, and an unsaturated polyester. Relationships between electrical conduction and free volume are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662158

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The hydrostatic properties of the materials methanol, isopropyl alcohol, water, sodium chloride, silver chloride, and the binary mixtures pentane‐isopentane and methanol‐ethanol have been determined in the diamond‐anvil pressure cell up to 180 kbar by line‐broadening and line‐shift measurements of the sharpR1ruby fluorescence line. A liquid mixture 4 : 1 by volume of methanol : ethanol remains hydrostatic to almost 100 kbar at room temperature. This mixture exceeds the hydrostatic limit of the previous generally accepted fluid, 1 : 1 pentane : isopentane which has a hydrostatic limit of about 70 kbar. Silver chloride and water (ice VII) are better than sodium chloride as pressure‐transmitting media, but do not even qualitatively approach hydrostatic conditions much above 70 kbar. The stress sensitivity level of the ruby limits the extent to which slight deviations from hydrostatic conditions can be determined in solid systems and suggests the qualitative nature of the method in characterization of quasihydrostatic states. The equilibrium freezing pressure of methanol at 24°C was redetermined to be 35.8±0.8 kbar.

ISSN:0021-8979    

DOI:10.1063/1.1662159

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Two light waves with different directions of propagation derived from a pulsed Nd:YAG laser are superimposed in an absorbing sample and generate an interference field. Due to absorption, a spatially periodic temperature distribution occurs, producing a spatial modulation of the refractive index which can be considered a thermal phase grating. The light of an argon laser simultaneously incident on the sample is diffracted by the thermal grating. When excitation is over, the decay time of the diffracted light is measured. From this decay time the thermal diffusivity of the sample is determined. Measurements on colored methanol and glycerin as well as on ruby compare favorably with the results of other authors. The possibility of exciting and detecting temperature waves (second sound) in solids by the method of light‐induced gratings is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662160

出版商:AIP    

年代:1973

数据来源: AIP