摘要:

The characteristics of the nonadiabatic transverse (E&thgr;,Bz) pinch are studied for configurations in which the discharge tube, current coils, and condenser form an integral structure, allowing very high voltage gradients (105to 106v/cm). The dynamics of the first pinch contraction are analyzed using the Garwin‐Rosenbluth model of an infinitely conducting, collisionless plasma, and expressions are derived for the parameter values corresponding to maximum energy transfer to the gas for given energy per particle. Theoretical curves of pinch radius, current, and plasma kinetic energy as functions of time for typical cases are shown, and the relative merits of this transverse pinch and the more common longitudinal (Ez,B&thgr;) pinch are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1735055

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

When a plasma is of finite transverse cross section, space‐charge waves may propagate even in the absence of a drift motion or thermal velocities of the plasma. Some of the properties of these space charge waves have been investigated by regarding the plasma as a dielectric and solving the resulting field equations. The effect of a steady axial magnetic field is considered, but motion of heavy ions and electron temperature effects are neglected. Waves are found to exist at frequencies low compared with the plasma frequency as well as waves with oppositely directed phase and group velocities (backward waves).Many of the features of these waves have been verified experimentally by measuring phase velocity and attenuation of waves along the positive column of a low pressure mercury arc in an axial magnetic field. Measurements of electron density have been made using these waves and the results are compared with those obtained by other methods. An interesting feature of these measurements, of value in plasma diagnostics, is that they can be made with frequencies which are small compared with the plasma frequency.

ISSN:0021-8979    

DOI:10.1063/1.1735056

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The presence of polymorphic phase transitions, apparently unique among high polymers, enhances interest in polytetrafluoroethylene, while its potentialities for cryogenic applications make low temperature data particularly valuable. Compression measurements have been made on samples of Teflon at various temperatures between 75°K and 380°K and at pressures up to 21 000 atmos. The phase diagram found for the region above the ice point is in qualitative agreement with previously published results, with a possible additional transition appearing above room temperature at pressures of over 11 000 atmos. Time effects and a large pressure hysteresis make the transition parameters quite ambiguous, and the hysteresis becomes so broad at low temperatures that the phase diagram cannot be extended below the ice point. An apparent negative thermal expansion indicated by the isothermal compression measurements is shown to result from an incomplete high pressure transition. From an engineering standpoint, the measurements indicate that a Teflon gasket loaded to 3000 atmos at room temperature should maintain a seal at any lower temperature.

ISSN:0021-8979    

DOI:10.1063/1.1735057

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Plastic deformation of InSb by uniaxial compression was found to produce decreases in both the electron mobility and magnetoresistance, but to have no effect on the Hall coefficient. Analyses of the temperature dependence of the conductivity mobility and the weak‐field magnetoresistance, in terms of mixed scattering by acoustic lattice vibrations and ionized impurities, suggest that the principal effect of this mode of deformation is the creation of ionized vacancies and interstitials in approximately equal densities. The analysis permits an estimate of the density of point defects, which can then be related to the total energy expended during deformation. Reference is made to the effects of plastic bending of InSb where the carrier concentration is affected. This behavior is similar to results on silicon and germanium which have been analyzed in terms of the Shockley‐Read trapping model.

ISSN:0021-8979    

DOI:10.1063/1.1735058

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The amount of 90° reorientation during poling was determined from mechanical strains measured during the poling process. With tetragonal lead titanate zirconate 53% of the possible 90° reorientation occurred during poling, but this figure dropped to 44% upon removal of the poling field. With barium titanate the figures are only 17% and 12%, respectively. Comparison of the polarization of poled polycrystalline barium titanate with that for single crystals indicates that 180° reorientation is virtually perfect. Application of very high compressive stress parallel to the polar axis causes 90° switching of nearly all aligned domains, and, therefore, removes virtually all polarization. Curves of released charge as function of mechanical strain are nearly linear, but curves of released charge as function of stress are strongly nonlinear. Application of high compressive stress perpendicular to the polar axis also causes 90° domain reorientation and a reduction in the total polarization of the ceramic. This domain reorientation may be interpreted as a shift of the polar axes of some domains into a position more closely corresponding to the plane of cross expansion, and typically the total electric moment is reduced by less than 10%. High electric stress causes 180° as well as 90° domain reorientation. With prepoled specimens dc fields in the same direction as the poling field cause 90° switching, while reverse dc fields cause both 90° and 180° reorientation, with the latter predominating.

ISSN:0021-8979    

DOI:10.1063/1.1735059

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

At low currents in the prebreakdown region of broad area diffused siliconp‐njunctions in which the breakdown is by an avalanche mechanism, only a few light‐emitting microplasmas are present. These appear in succession as the current is increased and the appearance of each spot is accompanied by its own set of characteristic microplasma current pulses. It is found also that effectively all the emitted light arises at these microplasmas and that they carry, essentially, all of the breakdown current. The light intensity of an individual microplasma is roughly proportional to the current flowing through it.

ISSN:0021-8979    

DOI:10.1063/1.1735060

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Retrograde motion of mercury arc spots when in a groove in the cathode above the level of mercury was compared with motion of spots at the junction of mercury and the molybdenum cathode. A rapid rise in retrograde velocity occurs at about 10 000 oe for junction motion but at less than 5000 oe for groove motion. Spectra show more multiply charged ions for groove than for junction motion for the same magnetic field strength. The velocity for groove motion always exceeds the velocity for junction motion, and it increases markedly with a reduction in mercury vapor pressure. For groove motion increasing current causes the retrograde velocity to pass through a maximum. Observations are described by the mechanism proposed by St. John and Winans.

ISSN:0021-8979    

DOI:10.1063/1.1735061

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

By making use of an emitter region shorted by a metallic contact to an adjacent base region, a new form ofp‐n‐p‐nswitch is obtained. Several new structures are described, including a symmetrical (or ac) switch. Typical experimental results on switches which breakdown in the range from 25 to 40 v are presented.

ISSN:0021-8979    

DOI:10.1063/1.1735062

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Grain‐boundary and lattice diffusion of zinc vapor into copper at 550°C were measured with the electron‐probe microanalyzer and the results were used to calculate the diffusion coefficients. The lattice diffusion coefficientDLincreases from 5×10−13to 3×10−11over the concentration range from 2 to 27.5 atomic percent zinc. Over the same concentration range, the grain boundary diffusion coefficientDBchanges from 1×10−7to 7×10−6. The ratio of grain boundary diffiusion coefficient to lattice diffusionDB/DLremains at approximately 106.

ISSN:0021-8979    

DOI:10.1063/1.1735063

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

This paper is devoted to a study of helical fields, that is fields which are invariant under screw motions of space which move a certain helix into itself.Simple, analytic, helically invariant solutions of the Laplace equation are given and combined to describe the electrostatic field of a charged helix, and of the magnetic field of a helical electric current. A flux function &psgr; is introduced for solenoidal helical vector fields, and differential equations resembling Cauchy‐Riemann equations are derived for the potential function &phgr; and the flux function &psgr;. Certain graphical flux plotting methods are outlined and illustrated, and network analogies are suggested for solving these fields.

ISSN:0021-8979    

DOI:10.1063/1.1735064

出版商:AIP    

年代:1959

数据来源: AIP