摘要:

Stored microwave energy has been released using a high‐intensity electron beam switch. Experiments using this switch have produced energy compression at room temperature and pulses as short as several nanoseconds. Here we discuss the experimental results and the underlying theory.

ISSN:0021-8979    

DOI:10.1063/1.328143

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The values of charge on individual particles exiting three different laboratory precipitators have been measured in an experimental apparatus containing a Millikan cell. Measurements were obtained for dioctylphthalate (DOP) droplets and fly ash particles at temperatures from 23 to 343 °C. At comparable voltages and currents for positive and negative coronas, the data show that the ratio of the values of negative‐to‐positive charge for radii in the range 0.6–1.3 &mgr;m increases from about 1 to 2 as the temperature increases from 37 to 343 °C. The predictions of a mathematical model of electrostatic precipitation which employs an ionic charging theory show good agreement with all the positive charging data, but show good agreement with the negative charging data only at temperatures below 37 °C. The differences in the measurements and the model predictions are consistent with the postulation of free electron charging at elevated temperatures in negative corona.

ISSN:0021-8979    

DOI:10.1063/1.328144

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Excited‐state densities in the interelectrode plasma produced by a 1.2‐kA‐peak‐current 0.65‐ms HAFW discharge between Al butt electrodes, 12 mm in diameter spaced 4.4 mm apart and located in a vacuum ambient, were determined by measurement of the absolute line intensities. Densities divided by degeneracies at midplane near peak current for the Al I 3s2 4s2S, Al II 3p2 1D, and Al III 4p 2pstates were 8×1014, 2×1016, and 3×1016m−3, respectively. Densities in Al II and Al III states studied could be described by distribution temperatures of 1.1 and 1.2 eV, respectively. As a function of distance from the cathode, Al I and Al II densities declined from their maximum near the cathode, with the Al I density rising slightly near the anode, while Al III states generally rose from minimum values near the cathode, reaching maximums after midplane. As a function of time, Al III densities reached a maximum near current maximum, and then decayed rapidly, while Al II densities reached their maximum about 0.2 ms after peak current, and Al I reached its maximum only near the tail end of the current pulse.

ISSN:0021-8979    

DOI:10.1063/1.328145

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A model is formulated to calculate excited‐state densities in a multicathode‐spot (MCS) vacuum arc. The model is composed of two components: (1) a semiempirical model for the emission of ions from the cathode surface and subsequent plasma flow and (2) a theoretical model for inelastic collisions, including excitation and ionization, and radiation in the interelectrode plasma. After consideration of characteristic times prevalent in MCS arcs, the model is reduced to a set ofP‐1 simultaneous linear equations and one differential equation for each ionic species considered, wherePis the number of states considered for that species, where the independent variable is time in the frame of the flowing plasma, or equivalently distance from the cathode, and where the dependent variables are the populations of the various states. The model was used to determine the electron temperature in a MCS Al arc by leaving the electron temperature as a free parameter and choosing the value giving the best agreement with experimentally determined excited‐state populations. For a 107‐A m−2arc an electron temperature of 6 eV was determined. It was further concluded that inelastic collisions dominate elastic collisions as an electron energy loss mechanism in this plasma.

ISSN:0021-8979    

DOI:10.1063/1.328146

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

High‐speed photographs of a decreasing‐current vacuum arc are used to examine the luminous zone area of cathode spots. The luminous zone was observed because it provides an upper limit to the area of the spot and because it provides for relative comparisons to other published data. The photographs are used to obtain experimental values for relative total emitting area, spot area, and spot current as a function of time for decreasing current. These data were taken both for periods when a spot extinguished and when it did not. The data were obtained from a series of high‐speed photographs with exposure times as short as 2.5 &mgr;s. The electrode orientation was such that a direct line of sight was used.

ISSN:0021-8979    

DOI:10.1063/1.328147

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Grain boundaries in bulk polycrystalline InP wafers are preferentially attacked by a 5 HCl:3 HNO3:4 HF etch. Canyons with depths greater than 10 &mgr;m and widths approximately 1 &mgr;m are the most common form of attack. Although the etch has no effect on simple twin boundaries, preferential attack occurs at interfaces formed by multiple twinning events.

ISSN:0021-8979    

DOI:10.1063/1.328148

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Preexisting oxidation stacking faults in silicon are expected to shrink when annealed in inert ambients. We have found that they sometimes exhibited a strange behavior of first shrinking and then expanding, though eventually shrinking again until disappearance. This phenomenon was not observed in silicon substrates with bare surfaces, or in oxygen‐free substrates. It was traced to the combined effect of oxygen precipitation and the action of certain surface coverings, silicon nitride films in particular. In a model to explain this phenomenon, the precipitation of bulk oxygen would generate excess silicon self‐interstitials which, when allowed to build up to some supersaturation, would feed the growth of the stacking faults. A bare surface would readily assimilate the excess self‐interstitials by means of surface regrowth, thus suppressing a supersaturation. Information concerning the supersaturation of self‐interstitials and the kinetics of surface regrowth, previously unavailable, has been obtained from this work.

ISSN:0021-8979    

DOI:10.1063/1.328149

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Thermal‐neutron transmutation doping of silicon produces phosphorus donors by the nuclear reaction30Si(n,&ggr;)31Si →31P+&bgr;−. Nearly exact compensation of residual impurities in float‐zone silicon is possible with careful monitoring of the neutron fluence. To achieve this goal, an understanding of the dependence on neutron fluence of the various room‐temperature semiconductor electrical parameters is required. An analysis of the fluence dependence of resistivity, Hall coefficient, mobility, and carrier concentration is presented.

ISSN:0021-8979    

DOI:10.1063/1.328150

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The resistivity inhomogeneity in neutron transmutation doped (NTD) silicon is a function of both the initial inhomogeneity before transmutation doping and the final compensation ratio after transmutation doping which, in turn, is a function of the irradiation thermal‐neutron fluence. Calculations of this inhomogeneity &Dgr;&rgr;/? as a function of compensation ratio are presented. These calculations are then compared to experimental data obtained by probe measurements of NTD silicon compensated to resistivities as high as 100 000 &OHgr; cm. Calculations are also presented which yield the maximum possible mean resistivity which can be obtained, given an initial &Dgr;&rgr;/?, before fluctuation‐induced mixed typing occurs.

ISSN:0021-8979    

DOI:10.1063/1.328151

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The initial pinning rate of dislocations, as computed from changes in Young’s modulus, was measured in high‐purity polycrystalline copper during electron and neutron irradiations. For the same sample, flux and temperature dependencies of the pinning rate were studied for irradiations by 14.1‐MeV neutrons and 1.0‐ and 0.5‐MeV electrons. For a temperature of 330 K, the initial pinning rate depended on the flux to the 0.89±0.2 power in contradiction of simple kinetics. Additionally, to duplicate a given pinning rate due to a 14.1‐MeV neutron flux between 1011and 1012m−2 s−1, a 0.5‐MeV electron flux of 21.7±0.7 or a 1‐MeV electron flux of 2.2±0.1 times the neutron flux was necessary. Temperature dependence studies from 310 to 390 K showed the same dependence for neutron and electron irradiations. The difference in migration energies in the lattice and along the dislocations was found to be 0.18±0.02 eV over this temperature range. The copper sample exhibited the Simpson‐Sosin peaking of the decrement during all irradiations. The above observations lead us to conclude that the same defect, the interstitial, is responsible for pinning during both electron and neutron irradiation.

ISSN:0021-8979    

DOI:10.1063/1.328152

出版商:AIP    

年代:1980

数据来源: AIP