摘要:

The breakdown strength of rutile crystals has been measured ∥ and ⊥ to the optic axis. The dc breakdown is a thermal process occurring at a power level of 2 kw/cm3for the particular sample size and test cell used here, with field strengths of 20 kv/cm ∥ to the axis and 120 kv/cm ⊥. Impulse measurements at 1‐&mgr;sec rise time required special techniques of sample and electrode preparation in order to prevent field distortion and surface breakdown. Breakdown strengths of 570 kv/cm ⊥ and 690 kv/cm ∥ to the optic axis were measured.

ISSN:0021-8979    

DOI:10.1063/1.1736163

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Electron bunching in the multipacting mechanism of low‐pressure high‐frequency discharge, also known as the secondary electron resonance mechanism, is analyzed by an extension of simple multipacting theory. The bunching range is assumed to be that range in the electrical phase angle &phgr; within which secondary electrons emitted from one electrode can successfully traverse the interelectrode gap in ½ cycle and arrive at the opposite electrode with energy equal to or greater than emission energy. At the lower voltage limit of multipacting, the ½‐cycle bunching range is shown to be −90° ≤ &phgr; ≤ +90°; at the upper voltage limit, the range is narrowed to −90° ≤ &phgr; ≤ −40°. Typical examples of multipacting bunching, including higher‐order modes, are illustrated with graphical trajectories. The effects of secondary emission characteristics on bunching are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1736164

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Plane constant‐pressure shock waves were used to initiate wedge‐shaped pressings of PETN (pentaerythritol tetranitrate). The shocks entered the PETN from brass or Lucite plates. Shock pressures in the plates and depths at which the PETN was initiated were measured with a streak camera. It was found that a 50‐kbar shock in the brass was barely sufficient to initiate granular PETN pressed to a density of 1.0 g/cm3. This corresponded to a derived pressure of about 2½ kbar in the PETN pressing. It was further shown that the interstitial gas had no effect on the depth of initiation.

ISSN:0021-8979    

DOI:10.1063/1.1736165

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Dislocations in thin platelets of aluminum nitride grown from the vapor phase appear to be of two types. Some are dissociated into partials of the Shockley type; others are undissociated. A model is given for both types. The stacking fault associated with the dissociated dislocations consists of one lamella of the sphalerite structure. The stacking fault energy is deduced from the width of the ribbons and from the shape of the extended nodes; its value is &ggr; ≈ 4 ergs/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1736166

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Current‐voltage characteristics of hot electrons are analyzed for negative resistance regions. Electrons in a homogeneous semiconductor are assumed to interact only with acoustical phonons and charged centers of heavy mass. These charged centers could be ionized impurities or heavy holes with a negligible contribution to the current. A distribution function which ignores electron‐electron collision almost certainly does not lead to negative resistance. A postulated Maxwellian distribution may lead to a current discontinuity, but does not lead to a stable region of negative resistance, contrary to previous conclusions. For any physical distribution it is shown that the average electron energy increases monotonically with field strength. These results also apply to situations in gaseous discharge where hot electrons are scattered by neutral molecules and ions.

ISSN:0021-8979    

DOI:10.1063/1.1736167

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The coupling between transverse waves on a ``no‐space‐charge'' beam model via an rf pump field is investigated. It is found that the pump field should be two‐dimensional in order to couple only two waves together. For high‐frequency pumping only waves of same polarization can couple together, for low‐frequency pumping only two waves of opposite polarization can couple together. For high‐frequency pumping no ``spilling'' of higher‐order noise frequencies will occur. For low‐frequency pumping no ``spilling'' will occur if the pump field is purely circularly polarized. Except for cyclotron‐cyclotron wave coupling the pump wave will always be in synchronism with a beam wave and thus interact actively or passively with the beam. The effect of this coupling is investigated.

ISSN:0021-8979    

DOI:10.1063/1.1736168

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The self‐diffusion of alkali ions in alkali silicate glasses is discussed in terms of the formation, migration, and ultimate annihilation of defects. These defects exhibit a combination of the properties exhibited by Frenkel defects in alkali halides and Bjerrum defects in ice, and are treatable by many of the analytical techniques which are applicable to defects in crystalline solids. By utilizing the defect concept, relationships between self‐diffusion, ac and dc conductivity, and orientational polarization are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1736169

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The dislocation relaxation of MgO and Al2O3crystals was studied by means of anelastic measurements. The experimental data are analyzed according to the theory of Seeger, Donth, and Pfaff. It is shown that the ratio of Peierls force to shear modulus is about 2×10−5for MgO and possibly also for Al2O3. Comparison of the dislocation relaxation phenomena of oxides and metals indicates, rather surprisingly, that the ratio of Peierls force to shear modulus in oxides is about an order of magnitude smaller than that in fcc metals.

ISSN:0021-8979    

DOI:10.1063/1.1736170

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The partial pressure of cesium over the cesium antimonides whose compositions were Cs2.95Sb, Cs3.00Sb, and Cs3.25Sb was measured at various temperatures ranging from room temperature to about 180°C. The experimental tube consists of a spherical glass envelope and an ion gauge. The sample was prepared on the inner surface of the spherical envelope. The partial pressure of the cesium dissociated thermally from cesium antimonides was measured by Langmuir's positive ion method. The composition of the samples was determined by comparing their electrical resistivities and thermal activation energies associated with electrical conductivity with those of the cesium antimonides, which had a known composition. The preparation of the sample and the measuring method of the partial pressure of cesium are described precisely. The partial pressure of cesium over cesium antimonides was measured as a function of the absolute temperature, and the results showed that it was represented by the equation log10p(mm Hg) =A — B/T, whereAandBare constants. In the case of Cs3.00Sb, the values ofAandBwere 9.040 and 6300 deg, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1736171

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Passive coupling of the electron cyclotron and synchronous waves in quadrupolar pump fields is examined. It is shown that sinusoidal energy exchange occurs when the quadrupole field is pumped so that the effective or Doppler‐shifted pump frequency as observed by the drifting beam equals the electron cyclotron frequency. One fast and one slow wave are coupled when the pump frequency is greater than either of the beam wave frequencies, while two fast or two slow waves are coupled when the pump frequency is less than at least one of the beam wave frequencies. Experimental results confirming these predictions are presented and possible applications are discussed. In addition, it is shown that active coupling of two synchronous waves occurs when the effective pump frequency is zero.

ISSN:0021-8979    

DOI:10.1063/1.1736172

出版商:AIP    

年代:1961

数据来源: AIP