Heartbeat instability as auto-oscillation between dim and bright void regimes

TL;DR

This study explores the heartbeat instability in RF complex plasma, revealing how laser control influences void regimes and identifying the transition mechanism between dim and bright states based on electric field effects.

Contribution

It provides new insights into the control and underlying physics of heartbeat instability, highlighting the role of laser modulation and electric field-driven void transitions.

Findings

Laser stabilization of microparticle suspension

Resonant laser modulation induces void contraction

Void transition from dim to bright regime explained by electric field heating

Abstract

We investigated the self-excited as well as optogalvanically stimulated heartbeat instability in RF discharge complex plasma. Three video cameras measured the motion of the microparticles, the plasma emission, and the laser-induced fluorescence simultaneously. Comprehensive studies of the optogalvanic control of the heartbeat instability revealed that the microparticle suspension can be stabilized by a continuous laser, whereas a modulated laser beam induces the void contraction either transiently or resonantly. The resonance occurred when the laser modulation frequency coincided with the frequency of small breathing oscillations of the microparticle suspension, which are known to be a prerequisite to the heartbeat instability. Based on the experimental results we suggest that the void contraction during the instability is caused by an abrupt void transition from the dim to the bright regime [Pikalev et al., Plasma Sources Sci. Technol. 30, 035014 (2021)]. In the bright regime, a time-averaged electric field at the void boundary heats the electrons causing bright plasma emission inside the void. The dim void has much lower electric field at the boundary and exhibits therefore no emission feature associated with it.