Observation of multi-shell structure of dusty cloud by the TAPD method in plasmas under microgravity condition

Paper number

IAC-05-A2.3.03

Author

Dr. Satoru Iizuka, Tohoku University, Japan

Coauthor

Mr. Wataru Suzukawa, Tohoku University, Japan

Year

2005

Abstract

Dusty plasma has been known to form Coulomb crystals in strongly coupled state since dust particles in plasmas are strongly charged up to provide the condition that the Coulomb energy of dusts well surpass their thermal energy. On the earth, however, the mass of dust cannot be neglected, so the dusts are forced to move downward into plasma sheath with strong electric field, where upward electric force can be balanced with the gravity. Therefore, the crystal structure is strongly modified by the electric field. In order to reduce such gravity effect for ideal Coulomb crystal formation the experiments under microgravity condition had been proposed. However, it became a problem that a void was included in the dust cloud. The void was formed by ion drag forces, which push the dusts from plasma center to plasma periphery, depending on the plasma density. Therefore, it has been a subject how the dust particles can be sustained in the plasma center in the presence of the ion drag force.
    In this paper we propose a technique for the formation of dust cloud without a void inside in the plasma center region under microgravity condition. Here, we newly propose a time-averaged particle driving (TAPD) method. The method contains very simple time-varying forces acting on the dusty particles, i.e., electrostatic force and ion drag force caused by additional point electrodes. Because of the large mass the dust particles feel only average force varying in time. Here, two small point electrodes are introduced between parallel RF electrodes of 10 cm in diameter. When we apply positive voltage alternatively to both RF electrodes, the dusty particles are transported toward a middle position between the both point electrodes. This driving force can maintain the dust cloud in the plasma center region even when ion drag force is strong enough for excluding the dusts from the plasma center.
        The microgravity experiment has been carried out by a parabolic flight of aircraft. After reaching the microgravity dust particles of 10 micron meters are injected between the RF electrodes. We have observed for the first time a generation of dust cloud between the RF electrodes without forming a void inside. From a careful observation the dust cloud forms a multi-shell structure like an onion. Therefore, this TAPD method is quite useful for the formation of dusty cloud in the plasma center under microgravity condition.
    In conclusion, we have observed for the first time a multi-shell structure of dust cloud by introducing a TAPD method in the microgravity experiments.

Abstract document

IAC-05-A2.3.03.pdf

Manuscript document

IAC-05-A2.3.03.pdf (🔒 authorized access only).

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