摘要:

The interaction between dust and plasma leads to a variety of physical and dynamical consequences for both the dust and the plasma. One important consequence for the plasma is the effect on its charge state. While dust could act as a sink for the plasma by providing a recombination site for the electrons and ions, it could also act as a source of electrons in numerous ways. Here we discuss this latter problem. In particular we consider the role of photoelectric emission and thermionic emission from dust in enhancing the electron density in several environments, in each case considering both a cosmic one and a terrestrial one. With regard to photoelectric emission we briefly review some of our earlier work pertaining to interstellar molecular clouds and Coulomb crystals. With regard to thermionic emission, we present preliminary results of ongoing work pertaining to hydrocarbon combustion flames and dusty circumstellar shells around carbon rich red giant stars. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56670

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Observational evidence of electrical forces acting significantly on small solids is present for both the modern solar system in Saturn’s rings (1) and the ancient solar system in chondritic meteorites (2). It is likely that grain-grain coagulation rates are affected by the distribution of charges on small grains. Plasma particle impacts and photoelectric effects can provide the charges. It appears that some charging is inevitable and that plasma grain interactions need to be evaluated to determine the size of the effect on coagulation rates. We apply the results of our previous charging work (3, 4, 5) to models of the protoplanetary nebula. It is expected that the protoplanetary nebula is weakly ionized (6) except in certain instances and locations such as: solar flares in the interior, ultraviolet radiation at the outer boundary, and during enhanced luminosity of the star. Since the grains we study are non-conducting and show strong dipole moments in flowing plasma, we modify the geometric cross sections to include the effects of flowing plasma on non-conducting grains with plasma mediated shielding. This paper provides results showing how plasma flow affects the processes involved in charging the grains—total charge and charge distribution. We calculate the modifications to the cross sections and subsequent changes in the coagulation rates. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56659

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Dust grains in plasma carry a substantial negative charge and are subject to strong repulsion. As a result, grains are typically assumed to be stable against growth by agglomeration. However, the instantaneous particle charge undergoes fluctuations whose magnitude and duration can be substantial. These fluctuations arise from the stochastic nature of particle-ion and particle-electron collisions and obey Gaussian statistics with parameters that are functions of the particle size and of the properties of the plasma species. Excursions of the charge from the mean value alters the particle behavior and results in interactions that could be stronger, or weaker than average. Here we calculate the rate of particle agglomeration taking into account the statistical distribution of the particle charge. We find that effect of fluctuations is to always increase the rate of agglomeration. Because of this enhancement the agglomeration rate of small particles is significantly higher than what would be obtained in the absence of fluctuations and can be comparable to the agglomeration rate for uncharged particles of the same size. The agglomeration rate of larger particles is enhanced significantly, but the overall collision rate remains too low. Under these conditions, growth by agglomeration is fueled by small particles and is predicted to result in narrow size distributions. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56682

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electrostatic traps have been used to confine negatively charged dust particles to orbits about a central electrode in vacuum. The particles are glass microballoons about 50 microns in diameter charged to a potential of about −20 volts. The central electrode, at a potential of about +8 kV, is either a 6-mm diameter rod or a 12-mm diameter sphere. Particle orbits decay gradually until the particles strike the central electrode. Experiments with gas pressures from10−4to10−7&hthinsp;Torrindicate that the confinement is limited by molecular drag. The longest confinement times are about 6 hours. At lower pressures, there may be dissipation caused by the motion of image charges in the walls of the traps. This is being investigated by varying the placement of the walls and by resistively loading the walls. Resistive dissipation may account for the orbits becoming circular more rapidly than predicted by molecular drag alone. As many as seven particles have been trapped simultaneously and collisions and resonances between particles have been observed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56683

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Fine particle plasmas were produced by irradiation of UV light on aluminum fine particles generated by using boat method. Fine particle density was obtained by observing the attenuation and scattered intensity of He-Ne laser light. Fine particle plasma beam has streamed into the static electric fields and static magnetic fields. Plasma beam separated into two beams after pass through the fields. We could estimate the charges of particles by using its separation and trajectory. We are now try making simulations of planetary rings. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56684

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

If we assume that the interaction potential of a dust particle in a plasma is of a Yukawa type, then we can determine the particle charge and the screening length from its trajectory during central collisions. We present a theoretical approach taking into account, that the particles are horizontally confined and that friction may influence the trajectories. In addition we show former results (1) based on this theory in the limit of negligible friction and confinement forces. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56685

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The Fisk Plasma Source (FPS) is a new experimental plasma device that produces low electron temperature(Te<10&hthinsp;eV)plasmas using DC glow discharge or thermionically emitting filaments. The FPS device is being used to study the global confinement of charged micron-sized particles within a plasma. This paper reports on observations of the vertical confinement of dust particles in the FPS device as a function of anode and cathode bias voltages. Comparisons are made between the confinement of the dust particles and changes in the plasma parameters. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56689

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An overview of a new analytic model of the macroscopic particle kinetic temperature in dusty plasmas is presented. The model is based on a Langevin analysis of the single particle equation of motion and includes electrostatic heating effects. Electrostatic heating of the particles is thought to be necessary to explain anomalously high particle kinetic temperatures observed in recent laboratory dusty plasma experiments. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56686

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A laboratory investigation has been developed to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. The intent is to investigate under what conditions particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam. Primary emphasis in this report is on secondary emission of electrons. Preliminary results are presented. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56687

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The status of collective processes in dusty is summarized. The effects of dust-neutral and dust-dust interactions, dust charge fluctuations, and magnetic fields on low-frequency electrostatic wave spectra are discussed. Some powerful mechanisms for exciting dusty plasma waves are presented. The importance of dust-acoustic wave induced wake-potential for charged dust attraction is illustrated. The relevance of our investigation to laboratory plasmas has been pointed out. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56688

出版商:AIP    

年代:1998

数据来源: AIP