Heartbeat Instability Research Articles

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

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)PSTEEU0963-025210.1088/1361-6595/abe0a2]. 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.

Physical aspects of dust–plasma interactions

AbstractLow‐pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle‐forming plasmas, where the dust‐induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle‐resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state‐of‐the‐art understanding of such complicated, discharge‐type‐specific phenomena as dust‐induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.

Turbulence in an Auto-Oscillating Complex Plasma

We present an experiment on the development of turbulence in a microparticle cloud in a low-temperature plasma laboratory onboard the International Space Station. First, the complex plasma cloud was stabilized with an alternating electric field. Once the stabilization was switched OFF, a so-called heartbeat instability developed in which the microparticles are oscillating radially. We show that the kinetic energy spectra develop a double cascade once the cloud becomes unstable. A double cascade has been predicted by Kraichnan and Leith for forced 2-D turbulence, but has only seldomly been observed in experiments. We also show that the reduced rates of energy and enstrophy transfer can be used to infer the excitation wavenumber $k_{\text {exc}}$ , in good agreement with $k_{\text {exc}}$ obtained from the energy spectrum.

Instability onset and scaling laws of an auto-oscillating turbulent flow in a complex plasma.

We study a complex plasma under microgravity conditions that is first stabilized with an oscillating electric field. Once the stabilization is stopped, the so-called heartbeat instability develops. We study how the kinetic energy spectrum changes during and after the onset of the instability and compare with the double cascade predicted by Kraichnan and Leith for two-dimensional turbulence. The onset of the instability manifests clearly in the ratio of the reduced rates of cascade of energy and enstrophy and in the power-law exponents of the energy spectra.

Density waves at the interface of a binary complex plasma

Density waves were studied in a phase-separated binary complex plasma under microgravity conditions. For the big particles, waves were self-excited by the two-stream instability, while for small particles, they were excited by heartbeat instability with the presence of reversed propagating pulses of a different frequency. By studying the dynamics of wave crests at the interface, we recognize a “collision zone” and a “merger zone” before and after the interface, respectively. The results provide a generic picture of wave-wave interaction at the interface between two “mediums”.

Wave turbulence observed in an auto-oscillating complex (dusty) plasma

We study a complex plasma under microgravity conditions that is auto-oscillating due to a heartbeat instability and contains quasi-solitary wave ridges —oscillons. We demonstrate that this system can serve as a nearly ideal model system to mimic weak Kolmogorov-Zakharov–type wave turbulence. The slopes of the structure functions agree reasonably well with power laws assuming extended self-similarity. The energy spectrum displays multiple cascades, which we attribute to the influence of friction, the heartbeat instability and a modulational instability.

On the heterogeneous character of the heartbeat instability in complex (dusty) plasmas

A hypothesis on the physical mechanism generating the heartbeat instability in complex (dusty) plasmas is presented. It is suggested that the instability occurs due to the periodically repeated critical transformation on the boundary between the microparticle-free area (void) and the complex plasma. The critical transformation is supposed to be analogous to the formation of the sheath in the vicinity of an electrode. The origin of the transformation is the loss of the electrons and ions on microparticles surrounding the void. We have shown that this hypothesis is consistent with the experimentally measured stability parameter range, with the evolution of the plasma glow intensity and microparticle dynamics during the instability, as well as with the observed excitation of the heartbeat instability by an intensity-modulated laser beam (inducing the modulation of plasma density).

Threshold Phenomena in a Throbbing Complex Plasma

In complex plasmas, the trapped dust particle cloud is often characterized by a central dust-free region ("void"). The void induces a spatial inhomogeneity of the dust particle distribution and is at the origin of many intricate unstable phenomena. One type of this kind of behavior is the so-called heartbeat instability consisting of successive contractions and expansions of the void. This instability is characterized by a strong nonlinear dynamics which can reveal the occurrence of incomplete sequences corresponding to failed contractions. Experimental results based on high-speed imaging are presented for the first time and underline this threshold effect in both the dust cloud motion and the evolution of the plasma light emission.

Special issue on applications and advances in problem frames

Special issue on applications and advances in problem frames

Self-excited void instability in dusty plasmas: plasma and dust cloud dynamics during the heartbeat instability

When a three-dimensional dust cloud is present in a plasma, a dust-free region, called a void, is usually obtained in the plasma centre. Under certain conditions, this region exhibits a self-excited unstable behaviour consisting of successive contractions and expansions of its size. In this paper, this low frequency instability (few Hz), called a ‘heartbeat’, is characterised by various diagnostics. Electrical and optical measurements both correlated with high speed imaging brought to the fore the main features of this instability. Forces involved in the void existence are an inward electrostatic force and an outward ion drag one. The force balance ensures an open void but this equilibrium can be disturbed, leading to the observed instabilities. As these forces are strongly dependent on local ionisation conditions, correlations between physical processes in the plasma volume and the dust cloud motion are investigated through experimental results.

Experimental investigations of void dynamics in a dusty discharge

The first electrical and spectroscopic characterizations of an instability, usually called the “heartbeat” instability, occurring in a laboratory dusty plasma are reported. The heartbeat instability consists of successive contractions and expansions of the central dust free region observed in a dense cloud of dust particles. This cloud is formed in a radio-frequency plasma by sputtering polymer material deposited on the electrodes. The evolution of the discharge current reveals the relatively complex shape of the instability and allows one to measure its evolution as a function of gas pressure and radio-frequency power.