摘要:

Microwave diagnosis showed that the early afterglow of an oxygen plasma was controlled by ambipolar diffusion and by recombination (&agr;r), depending upon pressure (from 0.15–4.0 mm Hg), at elevated gas temperatures (up to 900°K). AtTgas=300°K attachment also seemed to be important for higher pressures (p>0.65 mm Hg). For low plasma excitation energy the measurements yielded &agr;r=2.1×10−7cm3sec−1atTgas=300°K, dropping gradually to 1.4×10−7cm3sec−1at 894°K. The plasma excitation energy had a marked effect on the apparent recombination and attachment rates which tend to indicate that vibrationally excited ions and molecules do affect these rates as has been suggested previously.

ISSN:0021-8979    

DOI:10.1063/1.1713922

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An experimental method for separating collective effects from collision dominated phenomena in plasmas consists of probing the plasma at a frequency between the collision and plasma frequencies that govern the rates of the individual and collective processes. This method is applied to the measurement of anomalous resistance by utilizing a re‐entrant cavity to expose a quiescent plasma to the strong electric fields at this intermediate frequency, thus provoking anomalous resistance. The resistive loading of the cavity is then observed as a function of power level or field strength, giving evidence of an anomalous resistance above power levels which initiate the two‐stream instability.

ISSN:0021-8979    

DOI:10.1063/1.1713923

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The self‐consistent field approach is used to obtain integral equations for the modes in symmetric and nonsymmetric resonators with arbitrary numbers of mirrors. The resonator fields are considered as TEM clockwise and counterclockwise traveling waves which for passive resonators are uncoupled and which independently satisfy the necessary boundary conditions on reflection from the resonator mirrors. An arbitrarily polarized field is resolved into two linearly polarized components which can be treated separately and identically. The component perpendicular to the plane of the resonator is considered and integral equations are obtained for the spatial distribution of resonator modes just after reflection from any mirror in both the symmetric and nonsymmetric resonators. The integral equation for the symmetricN‐mirror resonator is investigated in detail. Because of the astigmatic focusing of the reflectors there is no situation corresponding to the confocal resonator, however, a ``pseudoconfocal'' resonator with nonspherical mirrors is discussed. The integral equation for the resonator with arbitrary mirror spacing is solved in the limit of infinite Fresnel numbers and the resonator field is described in terms of Hermite‐Gaussian functions. The mirror spacing must satisfy the condition 0≤l/bcos&agr;≤2. A general resonance condition is obtained and the results of numerical computations of diffraction losses are presented for three‐ and four‐mirror resonators. For minimum diffraction loss the ratio of mirror spacing to mirror curvature is not constant but varies from mode to mode and the amount of variation differs with the number of mirrors.

ISSN:0021-8979    

DOI:10.1063/1.1713924

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The conditions for maximized peak power extraction from a giant pulse laser are examined. In order to formulate an appropriate mathematical framework relating the various significant magnitudes, some simplifying assumptions and approximations have been used. The critical coupling conditions and the value of the resulting optimum peak power as a function of a characteristic loss factor have been determined. A distinction is made between maximum peak power and maximum energetic yield since the conditions for the achievement of both are slightly different.

ISSN:0021-8979    

DOI:10.1063/1.1713925

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The specific heats of Ge, Si, and Ge‐Si alloys were determined in the temperature range 300° to 1000°K, by a novel temperature‐modulation technique. The specific heat at constant pressurecpexceeds appreciably the Dulong‐Petit valuecDPat high temperature. Above the Debye temperature &thgr;Dthe divergence can be represented bycp/cDP=0.95+&agr;T/&thgr;DwhereTis the absolute temperature and &agr;=0.081 is a coefficient independent of alloy composition. This result is in disagreement with the current theory of the anharmonic contribution to the specific heat at high temperatures, which predicts &agr;=0.016 for Ge, and &agr;=0.030 for Si.

ISSN:0021-8979    

DOI:10.1063/1.1713926

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Tin films were deposited from the vapor at various substrate temperatures and their superconducting properties determined as a function of film structure. Magnetic hysteresis in the superconducting state to normal state phase transition of these films increased with increasing grain size. Hysteresis could be attributed solely to supercooling only in the smaller‐grained films deposited at low substrate temperatures. For the larger‐grained films, superheating was also observed. The hysteresis observed experimentally was in agreement with the predictions of the Ginzburg‐Landau theory of superconductivity.

ISSN:0021-8979    

DOI:10.1063/1.1713927

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A cesium vapor diode was operated both before and after cesium fluoride was introduced into the interelectrode space. The electrodes were plane parallel, had a cross‐sectional area of 2 cm2, and were made of molybdenum having a polycrystalline surface. The interelectrode spacing was varied from 0.01 to 10 mm. The cesium fluoride vapor additive caused an increase in the optimized output power density. For a given emitter temperature this enhancement increased with spacing until the spacing reached about 0.89 mm, after which it became uniform. The enhancement decreased with an increase in emitter temperature. The increase averaged about 20% for a combination of these cases. When all parameters were held constant except the cesium fluoride reservoir temperature, an increase in the additive vapor pressure caused the enhancement to decrease. The optimum collector temperatures decreased up to 2% after the cesium fluoride addition. The optimum cesium vapor pressures were decreased by about 15°K after the CsF addition.

ISSN:0021-8979    

DOI:10.1063/1.1713928

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Magnetic data from measurements at moderate to high magnetic fields in the temperature range 1.4° to 300°K, lattice constants, and preparative data are reported for the systems {Gd3}[ScxFe2−x](Fe3)O12, {Gd2Y}[ScxFe2−x](Fe3)O12, {Gd3−xCax}[Fe2] (Fe3−xSix)O12, {Gd3−xCax} Fe5−xGexO12, {Gd3}Fe5−xAlxO12, {Gd3}[MgxFe2−x] (Fe3−xSix)O12, and for the three garnets {Gd2Ca}[ZrFe](Fe3)O12, {Gd0.6Y2.4}[ScFe](Fe3)O12, and {GdCa2}[Zr2](Fe3)O12.The following model for the general features of the 0°K magnetic structures of the substituted gadolinium iron garnets is proposed. At 0°K, gadolinium iron garnet itself is an ideal Ne´el ferrimagnet. The moments of the octahedral Fe3+ions and of the dodecahedral Gd3+ions are strictly antiparallel to the moments of the tetrahedral Fe3+ions. Replacement of some of the octahedral Fe3+ions by nonmagnetic ions such as Sc3+ions as in {Gd3}[ScxFe2−x](Fe3)O12causes random canting of the tetrahedral Fe3+ions. Because the strong interactions of the Gd3+ion moments are with those of the tetrahedral Fe3+ion moments, this leads also to random canting of the Gd3+ion moments thereby reducing the contribution of the dodecahedral sublattice to the net spontaneous moment of the garnet. Replacement of the tetrahedral Fe3+by nonmagnetic ions as in {Gd3−xCax}[Fe2] (Fe3−xSix)O12causes random canting of the octahedral Fe3+ion moments, but this is not expected to affect the alignment of the Gd3+ion moments. Such substitution appears to have the effect of removing from contribution to the net moment, those Gd3+ions which are not linked through oxygen atoms to at least one tetrahedral Fe3+ion.A comparison of the results on the systems {Gd3}[ScxFe2−x](Fe3)O12and {Gd2Y}[ScxFe2−x](Fe3)O12indicates that at or very near 0°K, the interaction in the dodecahedral sublattice appears to have a ferromagnetic component. Also the garnet {GdCa2}[Zr2](Fe3)O12appears to be a weak ferromagnet.

ISSN:0021-8979    

DOI:10.1063/1.1713929

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Single‐crystal films of Ni&sngbnd;Fe prepared by vapor deposition onto (100) planes of heated rocksalt substrates exhibit high‐speed and quasistatic magnetization switching behavior which is characteristic of biaxial elements and is not found in uniaxial or isotropic films. The biaxial critical curve for coherent‐rotational switching can be combined with partial switching and labyrinth‐switching concepts, adapted from observations in uniaxial films, to provide a semiquantitative explanation for observations in single‐crystal films. Direct verification of switching models here inferred from electronic measurements, and limited Bitter studies, will require Lorentz microscopy or detailed Bitter studies of walls formed during the switching process.

ISSN:0021-8979    

DOI:10.1063/1.1713853

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The heat capacity of glycerol glass was measured between 1.5° and 4°K. Below 2°K the heat capacity is in excess of that expected from theoretical considerations for an isotropic solid. The use of glycerol as a heat exchange medium is discussed and described.

ISSN:0021-8979    

DOI:10.1063/1.1713854

出版商:AIP    

年代:1965

数据来源: AIP