摘要:

The diffuse scattering and intensities of Bragg peaks from single crystals of Cu77Au23and Cu78Au22have been studied for various degrees of long‐range order. The results indicate that the excess Cu atoms, replacing Au in Cu3Au1distribute themselves at random for the maximum degree of long‐range order. The maximum values of the order parameter indicate that the Cu sublattice is completely filled. For order less than the maximum, the results can be explained in terms of a large number of small ordered regions antiphase to the matrix; these regions are primarily two dimensional and vary in composition from point to point in the alloy. These are more Cu rich than similar regions in Cu3Au. Evidence is presented that the difference in atomic sizes of the species varies with degree of order. It is also shown that the scattering due to differences in atomic size and thermal vibrations and that due to local order can be separated completely at one temperature by symmetry operations, as suggested by Borie and Sparks.

ISSN:0021-8979    

DOI:10.1063/1.1657375

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Clear, transparent (0.5–5.0 &mgr;), solution‐grown, single crystals of negative uniaxial LiIO3show no optically induced damage and remain stable in the temperature range 20°–256°C. The crystals are of point group 6 and are optically active and pyroelectric. We have measured the linear electrooptic coefficients in the visible and the optical activity in the infrared. For &lgr;1=1.0845 &mgr; phase‐matched second harmonic generation (PMSHG) occurred at &thgr;m=28.9° and this angle changed by less than 0.3° in the range 20–256°C. PMSHG was employed to determine the single domain quality of the crystals and to measure |d31(LiIO3)/d36(KDP) |=11. At 1.06 &mgr; we have measured the coherence lengths and the ratio of the nonlinear coefficients |d33/d31|=0.8.

ISSN:0021-8979    

DOI:10.1063/1.1657376

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The general problem of microwave breakdown of a gas subjected to a nonuniform field over a semi‐infinite spatial region is treated. This problem is particularly applicable to high‐power‐handling antennas radiating into free space or into a plasma gas, in which case there is no outer surface for the electrons to diffuse to. Basically, solutions to the electron continuity equation determine an eigenvalue spectrum which governs the breakdown criteria. When the domain is finite, the spectrum must be discrete. This case has been previously treated. For the infinite domain, we demonstrate that for a realistic form of the net ionization rate, a continuous spectrum arises along with a bounded discrete spectrum which, when it exists, dominates the breakdown criteria. Two specific examples are included and the results are applied to breakdown predictions of a rectangular slot. A variational calculation is also treated.

ISSN:0021-8979    

DOI:10.1063/1.1657377

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurements of hydrogen‐plasma resistivity were made under conditions where the dominant loss mechanism was electron‐neutral collisions. Three‐inch‐diameter tubes with electrode spacings ranging from 2–22 in. were used. Measurements were made at 15 and 22 kA, 56‐&mgr;sec pulse duration, and pressures of 0.5, 1.0, and 5.0 Torr. Electron‐density and temperature measurements were obtained from Stark‐broadening and line‐intensity‐ratio techniques. The predicted resistivity was calculated from electron‐proton and electron‐neutral collisions and compared with the absolute resistivity calculated from the voltage‐current measurements. The gas‐temperature rise was determined from the resistance difference obtained from the two calculations. The energy expended in gas heating was determined to be 2.4%–4.2% of the input energy.

ISSN:0021-8979    

DOI:10.1063/1.1657378

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A linear analysis is given of the interaction of a homogeneous, monoenergetic cylindrical electron beam, of radiusa, with a homogeneous, cold plasma for two cases: (A) the plasma is unbounded and (B) the plasma is bounded by a conductor at radiusb(>a). The quasistatic approximation is compared with an exact treatment, and conditions for the validity of the former are stated. A stability analysis according to the method of Derfler and Briggs is carried out in terms of the mapping of &ohgr; into the complexkplane. It is shown that the system is always absolutely unstable and the dependence of the stability analysis on the system parameters is discussed. The absolute instability is, however, always sufficiently weak that in practice the stabilizing effect of collisions is sufficient to quench it, leaving a convective instability. The properties of the amplifying waves resulting from collisional stabilization are discussed for parameter values appropriate to the experimental conditions described in Pt. II.

ISSN:0021-8979    

DOI:10.1063/1.1657379

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurements were made on a beam‐plasma system under particularly simple and well‐defined conditions. The system could be operated at will in three distinct regimes, namely, (i) a quiescent steady‐state regime, (ii) a linear growth regime, and (iii) a nonlinear regime. The steady state is shown to agree with a static theory for a beam‐generated plasma. Measurements of spatially growing waves in the linear regime are described and compared with the theory discussed in Pt. I. Reasonable agreement is found when the effects of finite beam radius and collisions are taken into account, but it is indicated that the effect of radial inhomogeneity is also important. Some preliminary measurements on the nonlinear regime are reported and discussed in terms of the available nonlinear and quasilinear theories. The latter are judged too idealized to account for the nonlinear behavior of real beam‐plasma systems and suggestions are made concerning those respects in which they need generalizing.

ISSN:0021-8979    

DOI:10.1063/1.1657380

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

This paper concerns propagation of surface waves along a plasma column, and their amplification by interaction with an electron beam penetrating the plasma. First, surface wave propagation is analyzed for stationary and drifting plasmas. In addition to undamped propagation, the dispersion relation describes infinite sets of modes which can be categorized as evanescent and damped propagating waves. Next, it is shown how surface waves can be driven unstable by an electron beam. When the beam partially fills the plasma, interaction may occur not only with surface waves but also with plasma oscillations. A detailed stability analysis for the case of beam filling the plasma shows that the system may be either convectively or absolutely unstable, depending on the beam parameters. These findings are compared with the predictions of weak coupled mode theory, which are demonstrated to be misleading. Experiments aimed at measuring surface wave amplification, and checking the theory, are described. The propagation observed is interpreted as a beating between a weakly growing and a damped surface wave. The maximum growth corresponded to an electronic gain of 2 dB/cm at 470 MHz. The paper concludes with a brief discussion of the applicability of the results to development of a practical beam/plasma microwave amplifier.

ISSN:0021-8979    

DOI:10.1063/1.1657381

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A mathematical model was developed to predict radial and axial temperature profiles in an induction‐coupled plasma torch. The model employed temperature dependent physical properties and included radiation heat loss. Temperature fields based on the model were calculated for an atmospheric pressure argon plasma. Computed radial temperature profiles were in agreement with experimental profiles reported in the literature. The gas flow rate and flow pattern in the torch did not greatly affect the radial temperature profiles in the hottest region of the torch under ordinary operating conditions, also in agreement with experiment. A one‐dimensional analysis was developed which predicted these hot‐spot profiles accurately. The plasma model was also found to accurately predict distribution of energy losses from the plasma. Based on the equilibrium current density and temperature profiles provided by the model, the question of the existence of local thermodynamic equilibrium was re‐examined. It was concluded that equilibrium is closely approached in the high‐temperature central portion of the plasma, in agreement with previous investigators; however, nonequilibrium conditions can exist in the region of high temperature gradient at the plasma edge.

ISSN:0021-8979    

DOI:10.1063/1.1657382

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The spontaneous emission from hollow‐cathode discharges in flowing nitrogen is investigated spectroscopically. The vibrational energy distributions in theC3&Pgr;ustate of N2and theB2&Sgr;u+state of N2+are studied as a function of discharge current, magnetic‐field strength, and gas flow. The rotational energy distributions in these electronic states of N2have also been determined. The effective rotational and vibrational excitation temperatures are found to be low,TR≈2000°K andTV≈10 000°K respectively. The electronic excitation of N+, the dominant emitting atomic species, is found to correspond to much higher temperatures,Texc=35 000°K.

ISSN:0021-8979    

DOI:10.1063/1.1657383

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In crossed electric and magnetic dc fields, gyrating electrons are subject to alternate acceleration and deceleration by the electric field. This speed modulation occurs with the gyrofrequency and periodically changes the colliding electron's velocity relative to the background neutral particles. Thus these orbiting electrons see the collision cross‐sectional area, associated with target neutral particles, as if it were varying with the gyrofrequency. In very weakly ionized gases, this effect of time‐varying collision probability can cause deviated random walk of guiding centers in the direction of the electric field applied perpendicular to the dc magnetic field. It is proposed and argued that the conventional Chapman‐Cowling type formula giving the Pedersen mobility need be reexamined in the light of this new effect. Results of computer simulation indicate that the value of the Pedersen mobility of electrons differs considerably from that given by the conventional formula.

ISSN:0021-8979    

DOI:10.1063/1.1657384

出版商:AIP    

年代:1969

数据来源: AIP