Experimental phase synchronization of chaos in a plasma discharge

We demonstrate, for the first time, experimental phase synchronization in a chaotic plasma discharge. The nonlinear light and current discharge oscillations lock up in frequency with an external, low amplitude, periodic pacing signal, while their amplitude remains chaotic. Real-time observation of phase synchronization is made possible through a real-time sampling procedure, and the regions of synchronized/desynchronized states are presented. A set of equations is suggested to model the real plasma circuit.An experimental plasma system is driven with an information signal from a CD-player. With the plasma in the periodic regime, optical detection of the light emitted by the discharge allows the information signal to be heard from a loudspeaker. That does not happen when the plasma is chaotic, in which case we hear a noise-like hiss, typical of chaos. Modulation is observed in the periodic driven plasma, but it is not obvious when the plasma is chaotic. This procedure may be used as an encryption technique.Experimental phase synchronization of chaos is demonstrated for two different coupled oscillators: a plasma discharge and the Chua electronic circuit. Phase slips of 2pi are observed in the phase difference of the two oscillators, depending on the coupling strength. A power law indicates that an unstable-stable pair bifurcation crisis is responsible for the synchronization-desynchronization transition