摘要:

An approximation technique previously developed for straight elastic surface wave guides utilizing thin films is extended and applied to curved guides with large radius‐to‐guide‐width ratios. The dispersion curves for the circular guides are obtained by employing approximate bound modes in place of the actual wave functions, which are not fully bound. This procedure is quite accurate for the determination of dispersion curves in the propagation range of interest. Nevertheless, since the actual wave functions are not fully bound, some radiation is always present in a curved guide. This radiation loss accompanying the approximate bound modes is evaluated. A critical radius‐to‐guide‐width ratio, beyond which a calculation cannot be performed by the method employed, is defined, and it is shown that the radiation attenuation becomes prohibitively large even before this limiting ratio is reached. The problem of the lowest symmetric guided elastic surface wave in a straight guide incident on a curved guide in the shape of a quarter‐circle is treated and the transmitted and reflected waves are determined, including in the calculation only the two lowest modes in each region and the radiation attenuation associated with each mode.

ISSN:0021-8979    

DOI:10.1063/1.1662518

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have developed a technique for measuring the electron‐beam distribution function as it evolves in phase space. Data illustrating the successful use of this technique are presented. Transit time and other effects which can cause errors using this technique are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662519

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An electromagnetic wave propagating obliquely to a counterstreaming plasma is shown to be unstable for all directions of the stream. The stream direction normal to the wave vector is a singular case for which the growth rate increases from zero as the wave number is increased and asymptotically approaches a maximum value for very large wave numbers. For all other directions unstable waves exist for wave numbers below a critical value and the growth rate increases from zero as the wave number is increased, reaches a maximum value, and then decreases to zero at the critical wave number. The maximum growth rate is found to be the same for all stream directions other than very close to the normal to the wave vector. The dependence of the growth rate on the stream direction with respect to the wave vector and the validity of the quasistatic approximation in predicting the nature of this instability are also examined.

ISSN:0021-8979    

DOI:10.1063/1.1662520

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Quantitative predictions are made of the spreading and attenuation of a single forward‐propagating wave packet on a random, dissipative, and dispersive transmission line modeled by a generalized telegraphist's equation with slowly varying random coefficients.

ISSN:0021-8979    

DOI:10.1063/1.1662521

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Possible nonlinearities of the secondary emission process are examined by a difference technique that compensates for other nonlinearities. At a current of 0.3 &mgr;A any intrinsic nonlinearity is found to be less than 1 part in 1000.

ISSN:0021-8979    

DOI:10.1063/1.1662522

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The statistical distributions of break‐arc durations have been examined as functions of arc current and number of operations under both ``clean'' and contaminated conditions. Exponential distributions were found for arcs between clean palladium electrodes operating below 0.9 A. At higher currents a Gaussian‐ (normal) type distribution was observed. Under highly contaminated conditions the Gaussian distribution was observed at all current levels examined. These distributions have been discussed in terms of the ``ionic‐burst'' mechanism and thermionic emission. A model for the so‐called activation or arc‐duration enhancement of arcs is presented.

ISSN:0021-8979    

DOI:10.1063/1.1662523

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Atomic beams of In and A1 were ionized on a heated Ir surface in a good vacuum. Curves of ion current density versus reciprocal surface temperature are plotted with atomic reservoir temperature as parameter, yielding also desorption energies of 4 to 5 eV. Ion current densities from [inverted lazy s] 10−9to 10−6A/cm2were measured in the temperature range from [inverted lazy s] 1400 to above 2000°K. The calculated ionization efficiency for the system In on Ir is about 40% taking into account excited atomic states.

ISSN:0021-8979    

DOI:10.1063/1.1662524

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A study of the quasistatic hybrid mode in high‐electron‐mobility semiconductor plasmas subject to perpendicular static electric and magnetic fields shows that when carrier‐heating effects are fully taken into account an entirely new mode arises as a result of the carrier heating. This mode has properties suitable for readily generating the two‐stream instability and the interaction of this mode with hole‐cyclotron harmonics is much stronger than that of any unheated mode.

ISSN:0021-8979    

DOI:10.1063/1.1662525

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A realistic model of a point‐cathode electron source is analyzed in this paper, and its electron optical properties are discussed. Both cathode and anode are modeled as equipotential surfaces of a sphere on orthogonal cone (SOC). The model predicts that the radius of the apparent electron source produced by this diode may be as small as 2–3 nm for field emitters and as small as 4–6 nm for strong‐field Schottky emitters. This source is found to be a virtual image of the emitting area of the cathode. The image position and magnification are determined for different representative cathode shapes, and quantitative results are also presented on geometric aberrations, effects arising from the initial energies of emission, and on source current and current density. An optimum cathode apex radius for smallest source sizes is predicted to be about 200 nm for field emission and about 700 nm for Schottky emission. These results are compared with those from the often used, but less accurate, sphere model.

ISSN:0021-8979    

DOI:10.1063/1.1662526

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The behavior of a single‐mesh pulse‐forming network for driving flashlamps in both steady and nonsteady time response regimes is discussed. The resistance of the flashlamp is modeled as dependent only on the stored energy in the flashlamp dischargeEp. This energy in turn depends only on the electrical energy input and a characteristic decay time &tgr;d. It is shown that this formulation applies for any input pulse width and allows analysis of the case where the desired input pulse is shorter than &tgr;d. Numerical solutions are presented for a wide range of parameters and critical damping parameters are presented for response conditions ranging from steady to very nonsteady. Finally, a procedure for obtaining these parameters experimentally is presented so that the previously developed solutions can be applied to specific situtations of interest.

ISSN:0021-8979    

DOI:10.1063/1.1662527

出版商:AIP    

年代:1973

数据来源: AIP