On-off intermittency at the onset of the ion-acoustic instability in a laboratory plasma

The ion-ion beam instability is experimentally studied just above threshold in a laboratory double-plasma device. Intermittent bursts of unstable wave s are recorded in the target plasma and the distribution of the recurrence times of the bursts is estimated. At the onset of instability, the measurem ents are in agreement with the expected evolution deduced from a theoretica l model that combines the normal form of a supercritical Hopf-Andronov bifu rcation and the parametric noisy deviations from threshold typical of on-of f intermittency. In both the experiment and the model, the distribution of the recurrence times of the bursts decays as an inverse power law and the e volution of the mean laminar length when the control parameter is increased beyond threshold exhibits a power law of exponent -1.