Striations in a Low-Pressure RF-Driven Argon Plasma

Mulders, Hans; Brok, W.J.M.; Stoffels, WW Winfred

doi:10.1109/tps.2008.927094

Cited by 18 publications

(17 citation statements)

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“…Plasma stratification in molecular gases remains poorly understood.Standing striations have been also observed in radiofrequency (RF) discharges [5]. In Capacitively Coupled Plasma (CCP) created between two wires wrapped around a long dielectric tube, standing striations were observed in Argon over a certain range of frequencies and gas pressures [6,7]. Their wavelength is proportional to the tube radius and decreases with increasing gas pressure.…”

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Plasma stratification in radio-frequency discharges in argon gas

Kolobov¹,

Arslanbekov²,

Levko³

et al. 2020

J. Phys. D: Appl. Phys.

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We conducted experimental studies and computer simulations of standing striations in capacitive coupled plasma in Argon gas. Standing striations were observed at frequencies 3.6, 8.4 and 19.0 MHz, in a pressure range 0.05-10 Torr, tube radius R=1.1 cm, for a certain range of discharge currents (plasma densities). Numerical simulations revealed similar nature of standing striations in CCP and moving striations in DC discharges under similar discharge conditions. Comparison of computer simulations with experimental observations helped clarify the nature of these striations. The non-linear dependence of the ionization rate on electron density is shown to be the main underlying mechanism of the stratification phenomena. DOI:XXXPlasma stratification often occurs in laboratory devices and has been observed in space plasmas [1]. The most studied are striations in direct current (DC) glow discharges [2]. Moving striations are usually observed in noble gases, while standing striations are typical for molecular gases. The nature of moving striations (also called ionization waves) in noble gases is relatively well understood [3,4]. Plasma stratification in molecular gases remains poorly understood.Standing striations have been also observed in radiofrequency (RF) discharges [5]. In Capacitively Coupled Plasma (CCP) created between two wires wrapped around a long dielectric tube, standing striations were observed in Argon over a certain range of frequencies and gas pressures [6,7]. Their wavelength is proportional to the tube radius and decreases with increasing gas pressure. The wavelength varies discontinuously with changing the interelectrode distance in such a way that an integer number of standing waves always forms between the electrodes. The wavelength weakly depends on driving frequency in the range from 3 MHz to 60 MHz. Although discussions of surface-wave and kinetic effects can be found in the literature, no satisfactory explanations of these striations have been proposed so far. Standing striations have been also observed in Inductively Coupled Plasma (ICP) for certain geometries and discharge conditions [8,9].Striations appeared also in Particle-in-Cell (PIC) simulations of plasmas in different gases and gas mixtures [10,11,12]. Plasma stratification, as an example of selforganization at the kinetic level, remains a great challenge for the plasma science and physics of gas discharges [13].Previously, standing striations in argon CCP have been observed in a range of frequencies 3-80 MHz and gas pressure 2 Torr, in a tube with radius R=1.25 cm [7]. By changing the driving frequency and the distance L between the electrodes, the researchers were able to change the number of striations. However, the number of striations per unit length remained constant at different interelectrode distances. For driving frequencies of 70, 29,6, 4.2, and 3.7 MHz, they observed 8,9,10,11,and 12 striations at L=30 cm. Light emission oscillated at the second harmonic of the applied voltage. The nature of the striations remained unclear...

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“…Instantaneous distributions of the electric field (a) and power dissipation (b) calculated according to Eq (7)…”

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confidence: 99%

Plasma stratification in radio-frequency discharges in argon gas

Kolobov¹,

Arslanbekov²,

Levko³

et al. 2020

J. Phys. D: Appl. Phys.

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“…In fact, most rf striations have been found in narrow discharge spaces. 2,3,6) This may be related to the critical condition expressed as " ) Ã for dc striations. In the case of rf striations, Ã may also be the reference length of the discharge space.…”

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“…With E rf ðtÞ in eq. (1), the electric field Eðt; Þ at an azimuthal position z ¼ can be described as 6) Eðt;…”

Section: Modelingmentioning

confidence: 99%

“…5) Although the aforementioned work has been of immense value, few simulations of striations in rf discharges appear in the literature. 6,7) Mulders et al 6) simulated striations in an rf discharge observed in a tube. Their method was deterministic in that they assumed density profiles for electrons and ions to obtain an electric field that compared well with the measured one.…”

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Particle-in-Cell/Monte Carlo Collision Simulations of Striations in Inductively Coupled Plasmas

Denpoh¹

2012

Jpn. J. Appl. Phys.

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Striations in inductively coupled plasmas (ICPs) appear as a series of cocoons beneath a coil through which a source current is driven. In this study, we have simulated striations in ICPs using the particle-in-cell/Monte Carlo collision method. The simulated effects of pressure on striation characteristics are in good agreement with experimental observations. It is found that the discharge structure and electron heating mechanism of striated ICPs are markedly different from those of normal ICPs. In particular, electron heating occurs once in one rf cycle in striated ICPs but twice in normal ICPs. Electron heating in striated ICPs may be ascribed to a strong self-excited electric field induced by the oscillating motion of the electron density at approximately the ion density, resulting in a high electron temperature. Furthermore, the relationship between the spatial period of the striation and the discharge space is put forward as a generation criterion for striations in rf discharges. Striations tend to occur when the region of plasma generation due to ionization is adjacent to walls where plasma is lost. #

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