Observations of a structure-forming instability in a dc-glow-discharge dusty plasma

Abstract

By adjusting the anode current and axial magnetic strength of a dc-glow-discharge dusty plasma, we have found plasma and dust conditions conducive to dusty plasma structurization, similar to the one discussed theoretically by Morfill and Tsytovich [Plasma Phys. Rep. 26, 682 (2000)]. The structurization instability leads to the formation of a pattern where the dust suspension transforms into alternating stationary regions of high and low dust densities. We have measured the dependence of the wavelength of the nonpropagating dust density structures on neutral pressure and plasma density and discussed the results in terms of the dispersion relation obtained by D'Angelo [Phys. Plasmas 5, 3155 (1998)] for an ionization and ion-drag instability. The observations are also considered in light of a recent theoretical prediction by Khrapak et al. [Phys. Rev. Lett. 102, 245004 (2009)] that under certain conditions the effects of the polarization force on dust particles can cause dust acoustic waves to stop propagating, resulting in the formation of aperiodic, stationary dust density structures.

Excitation of dust density waves in weak electric fields

“…This finding could be linked to the plasma structurization instability recently observed in a dc-glow discharge in the field of $1.8 V/cm. 12 Stronger fields increase the role of the ion drag force and can even change the direction of the dust flow. In the considered parameter regime, the fields of $3 À 4 V/cm do not lead to any cut-offs, bit result in a pronounced maximum of the dispersion curves giving the wave frequencies higher than the dust plasma frequency in the domain of large wavenumbers ( Figs.…”

“…12 We show that the discharge electric fields of the order of a few V/cm might cause significant equilibrium drifts of ion and dust components and thus affect the dispersion of the dust density perturbations. Inclusion of the particle drift into wave studies allows us to explain wave frequencies significantly higher than the dust plasma frequency, as observed in many experiments.…”

“…[13][14][15][16][17] Moreover, in this formalism, a zero frequency mode naturally appears, which might explain an aperiodic instability of the dust density perturbations observed recently in a dc discharge. 12 Our theoretical model is based on the fluid (hydrodynamic) approach, which is a good approximation for the description of low-frequency dust density modes. 11 To illustrate our findings, we take typical plasma parameters measured during a series of wave experiments performed at the University of Iowa and Auburn University and reported in Ref.…”

Dust Self‐Organized Structures II. Solutions of Master Equations for Small Diffusion

“…The distributions of structure parameters with the distance from the center can be scanned in the whole range (17) and gives the answer for sufficiently condition for equilibrium and possible change of topology of the structures with increasing n(0). Crucial is the requirement for the value of Havnes parameter P which should be positive inside the structure.…”

“…Formation of structures of the type investigated for large n(0) have been recently observed in laboratory experiments [17]. For detailed not only qualitative comparison of numerical results with observation it is desirable to have more numerical results using the future numerical programs mentioned partially in the next section.…”