Chaotic Oscillations of Vertically Aligned Microrods in a Plasma Sheath

Experimental studies with one single dust rod and small assemblies of two and three vertically aligned dust rods levitated in the plasma sheath above the driven electrode are presented. The particle dynamics is studied at different gas pressures, from 90 to 250 mtorr, by varying continuously the input radio frequency (RF) power from 2 to 10 W. Oscillations of the levitated rods were observed in the experiments. In the case of the three-particle system, spontaneous rotation of the middle particle was induced. Its trajectory forms a chaotic attractor with the largest Lyapunov exponent positive. The attracting ion wakes are proposed as possible mechanisms for inducing the observed nonlinear oscillations.