Electrostatic charging of acoustically suspended dust grains by ultraviolet radiation and by plasma
An experimental apparatus was developed for the study of dust grain charging by photoemission and by immersion in plasma. The technique used to do this involved acoustically suspending the dust grains against gravity while they are exposed to the charging influences. The apparatus consisted of a terminated acoustic plane-wave tube coupled to an assembly of microwave equipment for use in the plasma charging studies. The origin of the acoustic force used to levitate the dust grains is a nonlinear dependence of fluid drag on an object with the flow velocity past the object. The effectiveness of the resulting force for the levitation of dust grains against gravity was inversely proportional to both grain radius and grain density. Grains of various materials including metals and silica with diameters ranging from 5 to 90[mu]m were readily levitated in krypton gas at 100 torr. These dust grain parameters and background gas conditions were standard for all of the grain charging. The interaction between a high intensity traveling acoustic wave with a highly collisional microwave producted plasma was investigated. The dominant effect of the acoustic wave on the plasma occurred in the plasma production rate. The resulting audio frequency plasma density fluctuations then propagated away from the production region in both directions as the plasma diffused out from this region against the background gas. In the dust grain charging studies, the steady state charge acquired by the grains was set by a condition on the electrostatic potential of the grains. This was true in both the photoemission charging experiments and the plasma charging studies. All of the grain charge measurements were made by observing the electrophoresis of the grains through the background gas in an externally applied electric field. The mobility of spherical grains varies proportionally with the ratio q/r. The mobility was independent of radius observed in the experiments.
- Research Organization:
- California Univ., San Diego, CA (United States)
- OSTI ID:
- 7161758
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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