Nonlinear resonances of particles in a dusty plasma sheath.

Vertical oscillations of microparticles trapped in the sheath of a capacitive rf discharge have been excited showing a strongly nonlinear resonance. The nonlinear oscillations are analyzed in terms of an anharmonic fourth-order potential energy curve. It is demonstrated that the observed nonlinearities can be related to a position dependent charge of the microspheres, whereas the electric field is found to be as nearly linearly increasing. The experimental results on the position dependent charging and electric field structure are compared to a numerical model.