摘要:

We report experiments on methods to raise the proportion of multiply charged ions for high‐flux‐ion extraction from vacuum‐arc plasma sources. Beams of doubly and triply charged ions have application to induction linacs for heavy‐ion fusion. We confirmed that the arc cathode material strongly influenced the ion‐charge‐state proportions. We believe the electrostatic potential of the plasma streaming from the arc played a major role in the transport of multiply charged ions. Reduction of electron losses from the plasma increased the observed fluxes of doubly charged ions. We inhibited electron loss and enhanced the flux of multiply charge ions by applying a bias voltage to the plasma source and by adding an axial magnetic field. We also investigated a method to increase the proportion of multiply charged ions by time‐of‐flight separation following rapid switching of the expanding plasma. We developed a new arc‐source geometry for the experiments. The source had a hollow anode and an axial magnetic field to anchor the position of emission spots on the cathode.

ISSN:0021-8979    

DOI:10.1063/1.345379

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Operation of a new type of high‐power electron diode, the bidirectional voltage‐dividing (BVD) diode, has been demonstrated on a 1‐MV, 2.5‐MA, 20‐ns accelerator. This diode consists of a forward‐ and an inverse‐triaxial diode in series. The diode impedance and electron flow pattern agreed reasonably well with particle‐in‐cell code calculations. The radiation spectrum was measured using two different diagnostics, a differential absorption spectrometer and the time‐projection Compton spectrometer. Operating at a voltage of 850–1000 kV, the BVD diode produced a bremsstrahlung spectrum similar to that produced by a standard diode operating at 350–500 kV.

ISSN:0021-8979    

DOI:10.1063/1.345382

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Finite element analysis is used to calculate the shape of blisters formed in bilayer optical storage media due to the buildup of thermal stresses during laser writing. It is shown that practically usable blisters may be expected to form in a time period of about 15 ns. Such a thermal stress delamination process may also precede melting in conventional pit formation processes.

ISSN:0021-8979    

DOI:10.1063/1.345356

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This article deals with the determination of the effective (apparent) diffusivity from the topological characteristics of microscopically inhomogeneous materials. The porous medium is modeled as a three‐dimensional network of interconnected pores by means of the Voronoi–Delaunay tesselation. The calculation procedure is based on an improved version of the effective medium theory and the smooth field approximation. We investigate the case where the pores in the effective network are transformed to pores of a uniform cross‐sectional area, and the case where the pore conductances are all replaced by an effective one. The results are compared with the numerical network solution. It is shown that the effective cross‐section area approach reproduces the ‘‘exact’’ calculated transport coefficient with an error of less than 9%, whereas the effective uniform conductance approach fails considerably, displaying an error of 62%.

ISSN:0021-8979    

DOI:10.1063/1.345357

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper considers particle and power balances to estimate the bulk plasma potential of a hot‐filament discharge plasma produced in a multidipole plasma device. The bulk plasma potential dependence on positive dc bias applied to an anode is analyzed, and the predicted characteristics of the plasma potential are compared to the experiment. It is shown that the plasma potential can be more positive or more negative than the anode bias potential. When the potential is more negative, a steady‐state potential dip in front of an anode is observed using emissive probes with the zero‐emission inflection point method. Conditions for the potential dip formation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345358

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Studies on spatial and temporal behavior of the emission spectrum of excimer‐laser‐produced copper plasma in vacuum and in the presence of argon and neon gas are reported. Intensity of spectral lines increases in presence of background gas. Intensity of spontaneously emitted Cu itransition 4p 2P3/2‐4s2 2D5/2at 510.5 nm shows a strong dependence on pressure of neon gas.

ISSN:0021-8979    

DOI:10.1063/1.345359

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A one‐dimensional continuum model of glow discharge, which contains three charged particle species of electrons, positive and negative ions, is numerically solved. The model consists of three continuity equations of each particle species and electron temperature equation with Poisson’s equation. The charged particle formation mechanisms of the ionization and the attachment which depend on the electron energy are included in the model. A numerical algorithm based on the finite difference method on nonuniform staggered grids is developed and the results are obtained on a relatively small workstation computer. General behaviors of particle movements are similar to the previous works, but the reaction rates reveal somewhat different features.

ISSN:0021-8979    

DOI:10.1063/1.345360

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Depth profiles of ion‐implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe have been measured by use of the19F(p,&agr;&ggr;)16O resonance nuclear reaction at 872.1 keV with width &Ggr;=4.2 keV. In order to obtain the true range distribution of implanted fluorine from the experimental excitation yield curve, a convolution calculation method is presented, from which the range distribution parameters such as the average projected rangeRP, the projected range straggling &Dgr;RPand the skewness of the projected range distribution SK were obtained. These experimental range parameters were compared with those obtained by a theoretical calculation and by use of thetrim89 program, and shows that for all the materials studied here the experimentalRPvalues agree with the theoretical and thetrimvalues very well but the experimental range straggling &Dgr;RPare larger than those obtained by the theoretical calculation and thetrim89. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.

ISSN:0021-8979    

DOI:10.1063/1.345361

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A microphysically based material model for the dynamic inelastic response of a brittle material is developed. The progressive loss of strength as well as the post‐failure response of a granular material with friction are included. Crack instability conditions (an inelastic surface in stress space) and inelastic strains are obtained by considering the response of individual microcracks to an applied stress field. The assumptions of material isotropy and an exponential distribution for the crack radius are invoked to provide a tractable formulation. The constitutive model requires a minimal number of physical parameters, is compatible with a previously developed ductile fracture model [J. Appl. Phys.64, 6699 (1988)] that utilizes inelastic surfaces, and can be formulated as an efficient, robust numerical algorithm for use in three‐dimensional computer codes. The material model is implemented into a Lagrangian computer formulation for the demonstration of material response to dynamic loading conditions. Comparisons with one‐dimensional, uniaxial impact experiments are provided.

ISSN:0021-8979    

DOI:10.1063/1.346090

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The feasibility of determining the fourth‐order elastic moduli by means of measurements of the acoustic second‐harmonic generation in stressed crystals is explored. It is shown that the changes to be expected under hydrostatic pressure in the ratio of the second‐harmonic amplitude squared to the fundamental amplitudeA2/A21are of the order of 20%–30% per GPa, which should be easily measurable.

ISSN:0021-8979    

DOI:10.1063/1.345362

出版商:AIP    

年代:1990

数据来源: AIP