Simulation of the nonlinear dynamics of grid sheath oscillations in double plasma devices

The oscillation of ion bunches around a strongly negative grid in a double plasma device is studied with one-dimensional particle-in-cell simulation. The system exhibits feedback amplified virtual anode oscillations in the target chamber. The undriven system is shown to perform relaxation processes which can be described by the van der Pol equation for high nonlinearity. The periodically driven system exhibits nonlinear phenomena like mode locking and periodic pulling, which are in quantitative agreement with theoretical predictions for the driven van der Pol oscillator. For large driver amplitudes period doubling and weak chaos are found. (C) 1997 American Institute of Physics.