摘要:

The developing velocities of the positive and negative corona streamers on insulating plates have been measured by using the dust figure technique at low pressure in air. By applying nanosecond time pulses from 10‐ to 50‐nsec duration to a needle point where the insulating plate is sandwiched in between the needle and plate electrodes, the diameters of the recorded dincharge pattern against the pulse duration in a pressure range of 150 to 760 Torr were obtained. The maximum velocities of the developing corona streamers which were measured at a voltage of 13.0 kV were 3.0×108cm/sec in the positive case and 2.5×108cm/sec in the negative case for a pressure of 150 Torr. Moreover, when a time pulse of 10 nsec was applied to the needle point at a pressure of less than 250 Torr, the velocity of the positive streamer seemed to reach a limiting value for a given voltage, while the negative increased proportionately to the inverse of the pressure. The resulting polarity effect suggests that when the nanosecond pulse voltage is applied, the field distortion due to the accumulation of the positive ions produced by electron‐collision ionization is one of the most important phenomena for the positive streamer developing at low pressure.

ISSN:0021-8979    

DOI:10.1063/1.325753

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The Townsend primary (&agr;) and secondary (&ggr;) coefficients and Paschen curves for neon, krypton, and their mixtures are reported. The primary coefficient was determined by measuring the variation in the luminous flux in a self‐sustained Townsend discharge between two parallel‐plate nickel electrodes spaced 21.5 mm apart. The values for the reduced primary coefficient &agr;/p0for Ne and Kr are about 10–20% lower than the published values obtained by the classical method of Townsend. The &agr;/p0values for Ne agree with results of previous work using the same luminous‐flux method. The ionization efficiency function &eegr; (&eegr;=&agr;/E, whereEis the electric field) for a Ne‐Kr gas mixture has a maximum value (0.0040 V−1) for Ne admixed with 0.1% Kr.

ISSN:0021-8979    

DOI:10.1063/1.325754

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The heterogeneous reaction of F atoms with SiO2(thermal oxide) has been measured using a discharge‐flow tube technique. The reaction probability for F atoms is &egr;F= (1.63±0.15) ×10−2 exp(−0.163 eV/kT) for 250<T<365 K.

ISSN:0021-8979    

DOI:10.1063/1.325755

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

This paper presents an investigation of the growth of a Guassian ripple on a uniform‐plane electromagnetic wave front in plasmas. The redistribution of electron density in a plasma because of nonuniform intensity distribution along an electromagnetic wave front gives rise to a nonlinear dependence of the effective dielectric constant on the intensity. The redistribution in collisionless plasmas takes place because of ponderomotive force; this is also true in collisional plasmas for periods less than the energy relaxation time &tgr;&egr;. The redistribution in collisional plasmas for periods greater than the energy relaxation time &tgr;&egr;is on account of the nonuniform heating of electrons along the wave front. This nonlinearity in the effective dielectric constant makes a ripple of a given radius to self‐focus, when the initial power of the ripple (P) is between two critical powers (Pcr1<P<Pcr2). WhenP≳Pcr2orP<Pcr1, respectively, oscillatory and monotonic defocusing of the ripple occurs. For powersPlying betweenPcr1<P<Pcr2, oscillatory self‐focusing of the ripple takes place. The critical power for self‐focusing of the ripple and the nature of self‐focusing is highly dependent on the power of the main beam, the phase difference between the electric vector of the ripple and main beam, and the absorption. The analysis is also valid for a weakly inhomogeneous plasma within the WKB approximation.

ISSN:0021-8979    

DOI:10.1063/1.325756

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Deposition occurs onto a cathode from an oxide plasma generated inside a hollow oxide anode by the mechanism called the electrolysis of plasma. The temperature of the cathode is usually over 2000 °C during deposition. Deposits attain fairly large crystalline sizes (about 0.3 mm) in spite of their high deposition rates. And besides, some unusual crystals are formed. For the deposition from ZrO2, HfO2, and ThO2plasmas, the deposition rate, growth rate, and the current efficiency increase with the plasma current (0.4–8 A) and with feeding O2gas into the plasmas. On the other hand, heating a cathode externally or feeding Ar gas into them leads to the reduction of those rates, the current efficiency, and yield. The maximum growth rate from the ThO2plasma is 8.4 &mgr;m/sec. Yields exceed 90% in general. Mass‐spectrometric analyses showed that the main depositing ion species is ZrO+for the deposition from the ZrO2plasma. Deposits obtained are usually black oxides, whose O/M(M=Zr, Hf, and Th) ratios are 1.95, 1.95, and 1.64, respectively. The deposits from ZrO2, HfO2, and ThO2plasmas are monoclinic ZrO2with precipitates of metallic &agr;‐Zr, monoclinic HfO2with a small amount of unknown hexagonal crystals (whose lattice parameters area=3.17 andc=5.02 A˚), and a mixture of fcc ThO2and Th, respectively. When O2gas is fed into those plasmas, transparent oxide crystals of stoichiometric composition are formed. The deposits from a CeO2plasma are the black oxides whose O/Ce ratios are 1.53 on the average. Contrary to the phase diagram of the Ce‐O system, they show x‐ray structures of fcc crystals whose lattice parameter varies from 5.506 to 5.411 A˚.

ISSN:0021-8979    

DOI:10.1063/1.325757

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Results of an experimental and analytical study of a Blumlein‐type transverse fast discharge operating with He and Xe are presented. An electro‐optical voltage probe was used to measure the discharge voltage. The measured voltages were in good agreement with the computed voltages. The analytical model was used to predict the dependence of the discharge efficiency for producing metastables and ions on the important plasma and external circuit parameters. In He the ion efficiency is greater than the metastable efficiency, whereas in Xe the opposite is true. Much larger ion efficiencies (&eegr;+∼0.12) occur in He than in Xe, whereas much larger metastable efficiencies (&eegr;+∼0.20) occur in Xe than in He. The large dissociative recombination rate of Xe compared to He accounts for the differences in performance between Xe and He.

ISSN:0021-8979    

DOI:10.1063/1.325758

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Microwave‐radiation bursts at &lgr;∼1 cm are observed when a rotating relativistic electron beam interacts with a plasma. The power level exceeds 1 MW, and the radiation pulse lasts as long as the electron beam pulse for beams up to 1 &mgr;sec long. The results are consistent with a model of coherent curvature radiation from electrons bunched due to a two‐stream instability. Other mechanisms are ruled out by observations of harmonic splittings and the power spectrum.

ISSN:0021-8979    

DOI:10.1063/1.325759

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The electric potential produced by the strain field surrounding a dislocation in a piezoelectric crystal was calculated by the ’’exact’’ plane‐strain method. The results are in close agreement with those of the earliest approximate calculation. A major discrepancy between previous calculations has been traced to a sign error in the exact formulation. The most recent approximate calculation is shown to be incorrect in principle.

ISSN:0021-8979    

DOI:10.1063/1.325760

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Chromium can assume three different charge states in semi‐insulating GaAs :Cr. An EPR‐optical method is described which allows the Cr concentration in each of these states to be quantitatively determined. Typical results are given for a number of Cr‐doped GaAs samples.

ISSN:0021-8979    

DOI:10.1063/1.325761

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Experimental results are presented which show how the electron drag on mobile dislocations varies with temperature, applied strain rate, and magnetic field. In both copper and aluminum the same functional dependence of the change in stress with magnetic field is observed, that is, the change in stress varies with the square of the field, and is independent of temperature and applied strain rate, for a given change in field. These results are compared with various models of electron dislocation drag, for the case where the dislocations move as underdamped oscillators. The observations are qualitatively consistent with the dislocations moving as underdamped oscillators, for the temperature range studied.

ISSN:0021-8979    

DOI:10.1063/1.325762

出版商:AIP    

年代:1979

数据来源: AIP