Nonlinear mode behavior and mode coupling for strongly coupled pair system with nonreciprocal interaction*

Complex plasmas (micron­sized particles immersed in ionized gas) have interesting properties in that they can self­organize into various structural states. A key component of the formation and stability of the structures observed in laboratory experiments is the interaction between the charged dust particles and the flowing ions in the plasma sheath. In this experiment the non­linear characteristics of the particle interaction force, as mediated by the ion flow, was investigated using a strongly coupled dust particle pair aligned along the direction of the ion flow confined within a glass box placed on the lower electrode of a GEC rf cell. The modes of this coupled system in the vertical direction were analyzed employing amplitude­frequency response under external excitation. The resulting high frequency mode (i.e., the breathing mode) shows an obvious spring­hardening response indicating that strongly nonlinear forces are responsible for this oscillation mode, while the low frequency mode(i.e., the sloshing mode) shows weak nonlinear behavior with only a slight spring­softening response observed.