抄録
We have observed a Coulomb crystal composed of the dust particles levitated in the plasma-sheath boundary region at a low gas pressure of less than 1.3Pa (10 mtorr). The dust particles form a crystal with the triangular structure above the electrode, making in one horizontal layer. The mean interparticle distance is about 500μm, and the Coulomb coupling parameter Γ is estimated to be about 500-1000. The vertical position of the Coulomb crystal can be controlled by changing the electron density ne and/or the biasing voltage Vb. A decrease in ne and/or an increase in Vb result in moving the Coulomb crystal upward. In this paper, we will show the detailed analysis on the levitating position of the Coulomb crystal, by taking account of the gravity and the electrostatic force acting the dust particle, which was estimated precisely based on the sheath theory.
