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[en] A theory of the current sheath dynamics for a plasma focus including finite thickness effects is briefly communicated. Inner radial magnetic fields related to the filamentary structure are shown to be necessary for the sheath stability. The theory allows for analytic solutions in the stationary coaxial stage giving the slope and velocity of the sheath. (author)
[en] Energy distributions of nitrogen atoms (N) in a hollow-cathode planar sputtering magnetron were obtained by use of optical emission spectroscopy. A characteristic line, N I 8216.3 Aa, well separated from molecular nitrogen emission bands, was identified. Jansson's nonlinear spectral deconvolution method, refined by minimization of χw2, was used to obtain the optimal deconvolved spectra. These showed nitrogen atom energies from 1 eV to beyond 500 eV. Based on comparisons with VFTRIM computer code results, it is proposed that the energetic N's are generated from N2+ ions after these ions are accelerated through the sheath and dissociatively reflect from the cathode. (c) 2000 The American Physical Society
[en] Research and development in plasmas and magnetospheric environments is reported. Topics discussed include: analysis and techniques of software development; data analysis and modeling; spacecraft sheath effects; laboratory plasma flow studies; instrument development
[en] A micromachined array of ion lenses was fabricated and used to characterize several plasma chemistries. Although present measurement tools, such as Langmuir Probes, can provide insight into potentials present in laboratory plasmas, as well as useful density measurements, they also significantly change the characteristics of plasma around the probe. This unfortunate quality renders them unsuitable as a production diagnostics tool, and hinders their effectiveness as a laboratory instrument. The micromachined array of 2.5 million ion lenses provides a non-intrusive view of ion energy, current, and potential on plasma boundaries. Preliminary tests in argon and CF4 plasmas using the GEC Reference Cell are discussed. Comparisons are made to a simple computer model and future changes to the measurement tool are suggested
[en] In complex plasmas together with single particle behavior the study of collective phenomena in large assemblies is an important development. We analyze the interaction among particles in plasma in several cases, starting from clusters consisting of a few particles up to large assemblies. In some cases the formation of the self-built electric field at the edge of the cluster and the screening of an external electric field by the dust cloud are predicted. In the case of small clusters the formation of double layers at the edge of a cluster is considered. The dimension of the cluster plays a role. The competition for charge is crucial in explaining agglomeration of mesoscopic particles. Larger particles, of the size of a Debye length, agglomerate mainly because of the ion 'shadow' force, a small scale aspect of the self-built field. Experiments with an expansion of dust clusters in an external plasma sheath seem to prove the existence of the self-built electric field at the edge of the cloud and the screening of external sheath fields. Other experiments, such as formation of bubbles, lanes, electrorheological properties and 2D dislocations in crystals, enlarge the investigations on collective effects and show their importance in complex plasmas.
[en] In order to overcome the communication blackout problem suffered by hypersonic vehicles, a matching approach has been proposed for the first time in this paper. It utilizes a double-positive (DPS) material layer surrounding a hypersonic vehicle antenna to match with the plasma sheath enclosing the vehicle. Analytical analysis and numerical results indicate a resonance between the matched layer and the plasma sheath will be formed to mitigate the blackout problem in some conditions. The calculated results present a perfect radiated performance of the antenna, when the match is exactly built between these two layers. The effects of the parameters of the plasma sheath have been researched by numerical methods. Based on these results, the proposed approach is easier to realize and more flexible to the varying radiated conditions in hypersonic flight comparing with other methods
[en] The existence of two types of vortex modes in nonuniform unmagnetized dusty plasmas is theoretically predicted. Both the linear and nonlinear properties of the standard dust vortex and dust surface vortex mode are discussed. The vortex modes can appear in nonuniform plasma sheaths and in Saturn's rings
[en] The magnitude and structure of the ion wakefield potential below a single negatively charged dust particle levitated in the plasma sheath region were measured using a test particle. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy collisions between different mass particles in a well-defined electrostatic potential that constrained the dynamics of the collisions to one dimension. As the vertical spacing between the particles increased, the peak attractive force decreased and the width of the potential increased. For the largest vertical separations measured in this study, the lower particle does not form a vertical pair with the upper particle but rather has an equilibrium position offset from the bottom of the parabolic potential confining well.