Occurrence of Mixed-Mode Oscillations in a Dusty Plasma
Résumé
Nonlinear instabilities can appear in laboratory plasmas containing dust particles. They are easily observed during experiments and their analysis reveals mixed-mode oscillations (MMOs). In this presentation, experimental results and preliminary analyses are presented. Dusty (or complex in analogy with complex fluids) plasmas are partly ionized gases containing dust particles. These solid bodies acquire an electric charge that strongly perturbs the surrounding plasma. Dusty plasmas are thus multi-component systems with similarities with colloidal suspensions or granular media. They are encountered in many environments such as astrophysics, industrial processes and thermonuclear fusion. A dust-free region (void) is often observed in the plasma center, resulting from the balance of two forces of opposite directions. Self-excited oscillations of the void size can appear due to a break in this equilibrium. This "heartbeat" instability (due to its apparent similarity with a beating heart) can stop by its own through the occurrence of more and more failed contractions similar to MMOs. MMOs consist of an alternation of small and large (spikes) amplitude oscillations often considered as subthreshold oscillations and relaxation mechanisms. They exist in many fields such as chemistry (Belousov-Zhabotinskii reaction) and natural sciences (Hodgkin-Huxley model of neuronal activity). MMOs are intensively studied with dynamical system theories (canards, subcritical Hopf-homoclinic bifurcation ...).
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