Filamentation of capacitively coupled plasmas in large magnetic fields

Abstract

Over the last decade, dusty plasma research has sought to explore the physics of magnetized dusty plasmas. Due to the small charge-to-mass ratio of micron-sized dust grains, magnetic fields of B ! 1 T are needed to magnetize these particles. A peculiar phenomenon that occurs in capacitively coupled, glow discharge dusty plasmas at high magnetic fields that are perpendicular to the electrodes is the formation of stationary or mobile filamentary structures that are aligned along the magnetic field. In experiments, these filaments are found to form at a low neutral gas pressure, low applied radio frequency power, and a high magnetic field. This paper reports on new simulations of capacitively coupled plasmas at a high magnetic field for a configuration with a powered metal electrode and a grounded electrode with a dielectric barrier. It is shown that for this configuration, it is possible to form filamentary structures that appear in the electron density, potential, and light emission, which have properties that scale qualitatively with experiments. For these conditions, the dielectric strength of the boundary is most strongly correlated with the formation of the filaments. Implications of these observations and how they could be used to motivate future experiments are discussed.

Variation of filamentation phenomenon in strongly magnetized plasma with various discharge parameters

“…[ 24–29 ] Formation of these self‐organized patterns in low‐pressure magnetized plasmas (filamentation phenomenon) has been observed for over two decades. [ 24–29 ] These patterns are extended in the discharge along the magnetic axis, channelling from one sheath region to another. So far, filamentation phenomenon has been reported to appear at very low pressure () plasmas that are exposed to strong magnetic fields ().…”

“…The image sums up 500 frames of 8 μm diameter dust particles suspended in an argon plasma at a pressure, p = 16.6 Pa (125 mTorr), a radio frequency (rf) input power, P RF = 1.6 W, at 13.56 MHz, and a magnetic field of B = 2.5 T. The image reveals the competition between the previously reported dust gridding phenomenon (i.e., the rectangular grid pattern formed by the dust particle motion, shown as white lines in the image) [21][22][23] and the light grey, spiral structures observed in the visible light glow of the plasma (i.e., filamentary structures). [24][25][26][27][28][29] Therefore, in order to understand the dynamics of the dust particles in strongly magnetized plasmas, it is essential that we understand the underlying plasma dynamics. This paper is motivated by these observations and focuses on furthering the understanding of this pattern formation in the background plasma at high magnetic fields.…”

“…Filamentary patterns are self-organized structures within a strongly magnetized plasma that differ from the rest of plasma in terms of parameters such as density, optical brightness, and electron temperature. [24][25][26][27][28][29] Formation of these self-organized patterns in low-pressure magnetized plasmas (filamentation phenomenon) has been observed for over two decades. [24][25][26][27][28][29] These patterns are extended in the discharge along the magnetic axis, channelling from one sheath region to another.…”

“…The formation and properties of the filamentary patterns in magnetized plasmas can be affected by various parameters such as neutral gas pressure, magnetic field, type of the discharge gas, electrodes conductivity, and the geometry of the plasma chamber. [25,27,29] Schwabe et al [25] experimentally investigated the variation of filamentation phenomenon with gas pressure and magnetic field strength and showed the strong dependence of the phenomenon on the ion Hall parameter (the ratio of the ions mean-free-path to their gyro-radius). The effect of the ion Hall parameter along with the impact of electrode conductivity and gas type on filamentation phenomenon was also identified in numerical simulations of the phenomenon by Menati et al [27,29] Despite all the efforts, introducing a comprehensive theoretical framework that successfully describes the formation mechanism of filamentary structures in strongly magnetized plasmas and their dependency on the aforementioned parameters is still an ongoing research study.…”

“…[30,31] In addition to that, due to the complicated nature of the filamentary structures, application of optical measurement methods such as laser induced fluorescence (LIF) is limited. [25][26][27][28][29] Therefore, numerical and theoretical investigation of the magnetized plasma remains one of the most effective ways of studying this phenomenon.…”