Shota Nunomura

Effects of Ion Flow by E×B Drift on Dust Particle Behavior in Magnetized Cylindrical Electron Cyclotron Resonance Plasmas

Interactions between poloidal ion flow associated with E×B drift and dust particles have been investigated in magnetized cylindrical electron cyclotron resonance plasmas, in which radial electric field is controlled by a biased ring-shaped electrode. The dust particles are spun out and removed from the plasma due to poloidal ion drag force, even when the inward electric force on the dust particles is larger than the gravitational force. This indicates the possibility of using a new method to remove the dust particles from the processing plasma. On the other hand, in order to sustain the dust particles in the plasma, the effects of this poloidal ion flow should be substantially reduced by the friction between the dust particles and neutral gas.

Fabrication of Nanoparticle Composite Porous Films Having Ultralow Dielectric Constant

Nanoparticle composite porous films having a dielectric constant of er=1.7–3.5 have been deposited using plasma chemical vapor deposition. Nanoparticles as nano-building blocks and radicals as adhesives are generated in plasmas, and nanoparticles are deposited together with radicals on substrates to form porous films. Nano-sized pores are dispersed in the films and their dielectric constants are controlled by the concentrations of pores, i.e., their porosities. The method is applicable to depositing nanoparticle composite porous films for other applications.

Dynamic behaviors of dust particles in the plasma–sheath boundary

A variety of dynamic behaviors in dusty plasmas is expected under the experimental condition of weak friction with gas molecules. The device “KAGEROU” provides such an environment for dynamic collective phenomena. Self-excited dust oscillations in Coulomb crystals have been observed at low values of plasma density and gas pressure. An instability mechanism was identified to be delayed charging in an inhomogeneous equilibrium dust charge in the sheath. The theoretical growth rate was formulated in relation to the destabilization of a transverse dust lattice wave (T-DLW), which was found to be very sensitive to the presence of a small amount of hot electrons which produces a substantial positive equilibrium charge gradient ∇Qd-eq around the equilibrium position of dust particles in the plasma–sheath boundary. The first experimental observation of a correlated self-excited vertical oscillations in a one-dimensional dust chain indicates a destabilization of T-DLW. The experimental condition is very consistent...

Observation of the Structure and its Formation Process of a New Volumetric Coulomb Cloud Composed of Different Multiple Dust Layers

A three-dimensional funnel-shaped dust cloud composed of multiple layers with different sized dust particles has been clearly observed in a new configuration of DC glow discharge. The Coulomb crystal-like cloud seems to be supported against gravity by the electric field in the thick sheath above the mesh cathode, in which the heavier layer of dust cloud seems to push the sheath to have a greater electrostatic force. The structural formation process of such a new volumetric Coulomb cloud was observed by a video imaging technique with laser light scattered by moving dust particles. They seem to be transported from the far outside, attach to the lateral surface of the funnel, and build up. The cloud is observed to expand radially outward on the horizontal layer.

Observation of Transverse Dust Lattice Wave Excited by Unstable Vertical Oscillations of Dust Particles in an Ion Sheath with Low Gas Pressure.

A self-excited transverse wave propagating along a one-dimensional dust chain, which is levitated around the plasma-sheath boundary, has been clearly observed in the plasma with a low gas pressure using a high-speed intensified charge-coupled device (ICCD) camera. The vertically polarized transverse wave was found to be excited due to the positional dust instability. The frequency and wavelength obtained from the experimental observations have been found to satisfy the dispersion relationship theoretically predicted for the transverse dust lattice wave.