摘要:

It is demonstrated through a time‐dependent particle simulation that an extended sheath forms spontaneously when a nonneutral plasma reflects from a potential barrier. An analytical description shows that extended sheaths develop when the flow velocity is smaller than the Gould‐Trivelpiece speed, hence a generalization of the Bohm‐condition to nonneutral systems is obtained. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47888

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We demonstrate non‐evasive methods for observing ion and ion cloud oscillation frequencies in a quadrupole ion trap. These trap resonances are measured for small clouds using a photon correlation technique. For large clouds the rotation frequency can be detected with the help of an additional pulsed probe laser. We show applications of the photon correlation method such as estimating the dynamic properties of a combined trap and detecting ion crystals. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47889

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experimental techniques for charging, trapping, and observing macroscopic particles (dust) are described. Particles with a sufficiently large charge‐to‐mass ratio (4×10−3C/kg) are created by using hollow glass microspheres about 50 &mgr;m in diameter charged to a potential of −30 volts by electrons from a filament. The charge spheres drop by gravity into a Kingdom trap and are trapped in near‐circular orbits by a rising potential. A spherical version of the trap with a Keplerian potential is also used. Illumination from a halogen lamp is sufficient for videotapes to be made of particle dynamics. Phenomena observed in the Kingdom trap include libration due to a resonant perturbation and the resonant coupling of two adjacent orbiters. Precession due to gravity is observed in the spherical trap. Confinement times in the Kingdom trap approach an hour. Briefly discussed are the use of charged liquid droplets, a planar trap based upon the ponderomotive force and the collective phenomena of a non‐neutral plasma in a Kingdom trap. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47890

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Cyclotron modes varying as exp(il&thgr;), withl=1, 2 and 3, have been observed in an unneutralized Mg ion plasma. Thel=1 mode is observed to be down‐shifted from the corresponding cyclotron frequency, while thel≥2 modes are found to be up‐shifted. Good agreement is found between the observed down‐shifts of thel=1 modes of Mg+and Mg++and the predictions of a multi‐species cold plasma theory. The down‐shifts depend on the composition and size of the plasma, and the relative abundance of each ion can thus be determined. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47891

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A summary of numerical simulations and some new experimental results and some new experimental results on cold one‐component plasmas, confined by external forces is presented. A system of 20,000 ions in isotropic confinement with a constant harmonic force had been explored by the molecular dynamics calculation. The simulation shows a dimensional phase transition and oscillations of an ion cloud which has been observed experimentally. (AIP) ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.47892

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Several numerical tools for modeling non‐neutral plasmas have been developed at Brigham Young University, including codes for computing equilibria, for simulating plasmas, and for computing mode frequencies with numerical eigenvalue methods. Our hope is that these programs will allow us to make careful comparisons between theory and experiment and allow us also to investigate the differences between various plasma models. This talk will summarize this work and give examples of physical applications. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47894

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe some recent experiments that use a new Penning trap to trap and laser‐cool more than 105Be+ions. In this wrok the Coulomb coupling parameter was estimated to by typically greter than 100 and in some cases greater than 300. Shell structure was difficult to observe in the ion fluorescence from these large clouds. An initial Bragg scattering experiment to obtain information on the ion correlations is described. We also briefly review our work on the electrostatic modes of a Penning trap plasma including the use fo the modes to diagnose the shape and density of a cryogenic electron plasma. Some applications of laser‐cooled plasmas in Penning traps, such as atomic clocks, are discussed. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47896

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Brillouin‐density pure ion plasmas have been generated in a quadrupole Penning tray by electron‐beam ionization of a low‐pressure gas. Large, spheroidal, steady‐state plasmas are produced that extend to one of the trap electrodes. With the density fixed at the Brillouin limit by the high ion production rate, the electrode potentials determine the plasma shape. The frequencies of azimuthally propagating cyclotron and diocotron modes are found to vary significantly with the plasma aspect ratio. For oblate plasmas, we are able to test theoretical predictions of a simple fluid model, and the frequencies are in good agreement. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47897

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

As plasmas with extremely reduced dimensionality, properties of one‐dimensional classical plasmas are analyzed in the domain of strong coupling. These plasmas may be realized in Penning traps with sufficiently strong confinement and also in semiconductor quantum wires under appropriate conditions. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47898

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A novel framework for the description of thermodynamic and correlation properties in a dense one‐component plasma (OCP) is presented in a representation based on an ensemble of Coulomb clusters. The properties of spherical and nonspherical Coulomb clusters with number of particlesNin the ground state as well as in a thermally excited state are investigated forN=2–13 by computer simulations. It is shown that a Coulomb cluster with a magic‐number structure, such as an octahedron atN=6 and an icosahedron atN=12, is conspicuously stable even near to the melting temperature of a bulk OCP. Thermodynamic states of the OCP in such a Coulomb‐cluster model are obtained by minimizing the model free energy with respect to fractional population of the clusters with different sizes. In light of such a cluster‐model description, we investigate the issues of cluster formation and possible local order in a dense Coulomb matter. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47899

出版商:AIP    

年代:1995

数据来源: AIP