Formation of a boundary-free dust cluster in a low-pressure gas-discharge plasma.

An attraction between negatively charged micron-sized plastic particles was observed in the bulk of a low-pressure gas-discharge plasma under microgravity conditions. This attraction had led to the formation of a boundary-free dust cluster, containing one big central particle with a radius of about 6 microm and about 30 1 microm-sized particles situated on a sphere with a radius of 190 microm and with the big particle in the center. The stability of this boundary-free dust cluster was possible due to its confinement by the plasma flux on the central dust particle.

Measurement of the interaction force among particles in three-dimensional plasma clusters.

The interaction forces between particles have been studied in a 3D plasma cluster under weak external confinement. A suitable combination of dc and rf applied to a small electrode provided gravity compensation, uniform over dimensions much larger than the cluster itself. The forces acting on the particles could be reconstructed due to unique three-dimensional diagnostics, which allow us to obtain coordinates and velocities of all the particles simultaneously.

Diagnostics of the electronegative plasma sheath at low pressures using microparticles.

Levitated particles are a new powerful diagnostic of the midplasma sheath region. They can reveal features undetectable either to plasma or to surface measurements. The equilibrium position of microparticles suspended in an oxygen plasma sheath, together with a model of the levitation force and Langmuir probe measurements, gives evidence of secondary electropositive plasmas in the already established plasma sheath, in the range of parameters where the modified Bohm criterion breaks down into multiple solutions.

Electrostatic modes in collisional complex plasmas under microgravity conditions.

A linear dispersion relation in a highly collisional complex plasma, including ion drift, was derived in the light of recent PKE-Nefedov wave experiment performed under microgravity conditions onboard the International Space Station. Two modifications of dust density waves with wave frequencies larger than the dust-neutral collision frequency were obtained. The relevance to the space observations was analyzed and a comparison of theory and observations was made for two different complex plasma domains formed by small and large microparticles.

Rodlike particles in gas discharge plasmas: theoretical model.

Recently, complex plasmas with strongly asymmetric (rodlike) particles were investigated experimentally in rf and dc discharges [V. I. Molotkov et al.