摘要:

This paper surveys experimental results concerned with secondary electron emission of surfaces bombarded by primary electrons with respect to scanning electron microscopy. The energy distribution, the angular distribution, and the yield of secondary electrons from metals and insulators are reviewed as well as the escape depth of the secondary electrons and the contribution of the backscattered electrons to the secondary electron yield. The different detectors for secondary electrons in the scanning electron microscope are described. The contrast mechanisms in the scanning electron microscope, material, topography, voltage, magnetic, and crystallographic orientation contrast based on secondary electron emission, as well as the lateral resolution, depending among other things on the spatial distribution of the emitted secondary electrons, are discussed.

ISSN:0021-8979    

DOI:10.1063/1.332840

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Results are presented for elastic wave scattering from irregular voids embedded in Ti alloy by the diffusion bonding process. The defects examined are: two overlapping spherical voids of unequal radii, two overlapping voids consisting of a sphere and a prolate spheroid, and a spherical void with an encircling crack. Representative plots are given for the raw waveforms, magnitude of the deconvolved Fourier transform, and in some cases the time impulse response function. The data are compared to and analyzed in terms of two current theoretical approaches. While good quantitative agreement was observed over certain ranges, the comparisons point to definite (in some cases not unexpected) limitations in either the pertaining theory or experiment or both. The results are discussed with an eye toward applications to nondestructive evaluation.

ISSN:0021-8979    

DOI:10.1063/1.331943

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A single‐beam Doppler interferometer is described, whereby light scattered by the diffuse target at slightly different directions interfere, producing a differential Doppler frequency which is much smaller than the Doppler shift of either beam. Due to the diffuse nature of the light scattered by the target, the conditions for alignment of the interferometer must include the effects of speckle decorrelation caused by both longitudinal and tilting motions of the target. Error sources, both systematic and random, are discussed. Ways to minimize the systematic error stemming from uncertainty in the actual direction of the motion, are discussed. The interference signals are processed digitally to minimize the effect of random errors, which can be reduced typically to 8% for the acceleration period and to a negligible degree for the constant velocity phase of the motion. A special exploding‐foil accelerator was constructed to test the new measurement scheme. Experimental results show repeatable measurements of velocity profiles up to about 0.4 mm/&mgr;s.

ISSN:0021-8979    

DOI:10.1063/1.331944

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Experimental results from previous studies on manganin and ytterbium piezoresistance gauges are analyzed. The gauge stresses and strains for the analysis were approximated from geometrical considerations as suggested in the earlier studies. The results of our analysis lead to conclusions that are significantly different from the previous work. The reasons for these differences are discussed and the requirements for a more rigorous analysis are outlined.

ISSN:0021-8979    

DOI:10.1063/1.331945

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Useful applications of charging phenomena occuring during scanning electron microscopy (SEM) of conductor‐insulator composites have been investigated. Unlike the charging of insulating particles in conventional SEM techniques, the local field effect in a conductive composite enhances the relative secondary electron emission in the isolated conductive grains. This ‘‘reverse’’ charging characteristic was utilized for the mapping of dispersion, orientation and segregation characterization in conductor‐insulator composite systems. The charging phenomenon directly reflects the relative electrical continuity of the conductive filler particles in the insulating matrix. The photographic display of the conductive filler arrangement in the composite using this charging phenomenon is termed a SEM charging micrograph. Carbon black/polyvinyl chloride composites with both spherical and chain‐like carbon blacks were used in this study. The structural aspects of such composites as revealed by charge display techniques were found to be directly correlatable with the electrical properties of the composites. This technique is applicable to composites with both small (100 A˚) and large (over 10 &mgr;) fillers.

ISSN:0021-8979    

DOI:10.1063/1.331946

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Neutralization of the positive ion space charge between the grids of a positively charged‐ion accelerator by injecting negative charges into this region has been studied theoretically. The current density of a beam of charged particles being accelerated between two parallel plate electrodes can be increased substantially by this injection. Multiple beams of oppositely charged particles can be used to produce the most substantial increases in the current density of the primary beam. The current density of this beam increases monotomically with the number of optimally selected, injected particle beams being used. There is an optimum injected particle current density and energy associated with each beam that yields the maximum extracted beam current density for a given number of injection stages. The total required injected particle current density, regardless of the number of stages used, is of the order of the ion current density times the square root of the extracted ion‐to‐injected particle mass ratio.

ISSN:0021-8979    

DOI:10.1063/1.331947

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A comprehensive model is presented to describe the physics of positive ion sources used to generate hydrogen isotope neutral beams for the heating of confined plasma in magnetic fusion energy programs. The model considers 11 important atomic and molecular reactions. A set of particle balance equations, together with those for the primary and secondary electrons in the sources, are solved simultaneously. Taking as input the source geometry, gas inlet flow rate, arc current and voltage, as well as the wall recombination coefficient and the measured temperatures of neutral atoms and molecules, the model gives as output the following information: the ion current densities available for extraction, primary electron density and energy distribution, and secondary electron density and temperature. These calculated results are compared with data of several Lawrence Berkeley Laboratory ion sources, both conventional and magnetic bucket types. Exploratory calculations are made for sources of different proposed designs with the aim of improving the source performance.

ISSN:0021-8979    

DOI:10.1063/1.331948

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

X‐ray spectroscopy was performed in the 12–15‐A˚ region, recordingL‐series lines from selected laser‐irradiated transition metals. Line coincidences and near coincidences were identified between Cr, Mn, Fe, and NiLspectra, and F viiiand F ixK‐shell lines. Wavelengths were determined to accuracies of 1–3 mA˚ and will be utilized in selecting potential pumping candidates in future x‐ray lasing schemes. High‐resolution x‐ray spectra were collected under controlled illumination and target conditions, using 1.05‐ and 0.527‐&mgr;m laser excitation with the KMS CHROMA laser. Laser intensity varied from 1.2–2.5×1014W/cm2in 200‐ps pulses. Three groups of x‐ray spectra were collected with highly dispersive x‐ray crystals at wave bands centered at 12.643, 13.781, and 14.458 A˚, corresponding to H‐ and He‐like lines from fluorine. Two specially designed flat crystal spectrographs employing camera shutters were used with pairs of beryl and thallium acid phthalate (TAP) crystals. The spectra from potential lasant and pump candidates could be recorded on the same spectrogram to aid in identifying x‐ray line coincidences. In cases where wavelengths were measured in both the 1.05‐ and 0.527‐&mgr;m laser work, agreement within 1–3 mA˚ was obtained for theL‐series x‐ray lines. Within this accuracy range, some fiveL‐series x‐ray lines, mostly 2p‐3dtransitions from the metals Cr, Mn, and Ni, had wavelength values coincident withK‐series lines in fluorine.

ISSN:0021-8979    

DOI:10.1063/1.331949

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Recent studies of attachment in pure HCl and HCl–N2mixtures are analyzed by Monte Carlo simulations. The drift velocity and attachment coefficients are calculated as a function of field strength and relative concentration of HCl. Cross sections for momentum transfer, vibrational excitation, and attachment are derived.

ISSN:0021-8979    

DOI:10.1063/1.331950

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We describe two diagnostic methods for measuring the velocity components of mildly relativistic, high current electron beams. The first involves a measurement of the radial electrostatic potential and of the beam current and yields the time resolved, spatially averaged axial beam velocityv∥. The second requires a measurement of the beam cyclotron wavelength in the guiding magnetic field and yields a spatially averaged product &ggr;v∥, where &ggr;=(1−v2⊥/c2−v2⊥/c2)−1/2andv⊥is the transverse beam velocity. By combining the two techniques we obtainv∥andv⊥for a 0.4–1.2 MV electron beam carrying a current of 1–2 kA.

ISSN:0021-8979    

DOI:10.1063/1.331929

出版商:AIP    

年代:1983

数据来源: AIP