Abstract:The Instability Enhanced Friction theory [Baalrud et al., Phys. Rev. Lett. 103, 205002 (2009)] is extended to account for the influence of neutral pressure in predicting the flow speed of each ion species at the sheath edge of plasmas containing two ion species. Particle-in-cell simulations show that the theory accurately predicts both the neutral pressure cutoff of ion-ion two-stream instabilities and the ion flow speeds at the sheath edge as pressure is varied over several orders of magnitude. The simulation… Show more
“…Experiments revealed good agreement with the predictions of the extended theory [150]. The extended model has also been shown to agree well with PIC simulations [98]. An example is shown in figure 14, which shows the speed of He and Xe ions in a mixture as a function of the neutral pressure.…”
Section: Plasma With Multiple Ion Speciessupporting
confidence: 63%
“…At sufficiently high neutral pressure, one would expect that ionneutral collisions cause the ion-ion two-stream instability to damp, which will alter the predicted threshold condition (∆V c ). Recent work has extended the above analysis to account for ion-neutral collisions by including a BGK collision model in the linear dielectric function [98,150]. Experiments revealed good agreement with the predictions of the extended theory [150].…”
Section: Plasma With Multiple Ion Speciesmentioning
confidence: 99%
“…If any combination causes instability, it leads to an enhanced friction force between each species. This model has also been tested using PIC simulations [95,98,147]. The first simulations appeared to contradict the model because the ion speeds were observed to enter the ion sheath with their individual sound speeds [147], even though the prediction for ∆V c of an early analytic model predicted instability [92].…”
Section: Plasma With Multiple Ion Speciesmentioning
Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.
“…Experiments revealed good agreement with the predictions of the extended theory [150]. The extended model has also been shown to agree well with PIC simulations [98]. An example is shown in figure 14, which shows the speed of He and Xe ions in a mixture as a function of the neutral pressure.…”
Section: Plasma With Multiple Ion Speciessupporting
confidence: 63%
“…At sufficiently high neutral pressure, one would expect that ionneutral collisions cause the ion-ion two-stream instability to damp, which will alter the predicted threshold condition (∆V c ). Recent work has extended the above analysis to account for ion-neutral collisions by including a BGK collision model in the linear dielectric function [98,150]. Experiments revealed good agreement with the predictions of the extended theory [150].…”
Section: Plasma With Multiple Ion Speciesmentioning
confidence: 99%
“…If any combination causes instability, it leads to an enhanced friction force between each species. This model has also been tested using PIC simulations [95,98,147]. The first simulations appeared to contradict the model because the ion speeds were observed to enter the ion sheath with their individual sound speeds [147], even though the prediction for ∆V c of an early analytic model predicted instability [92].…”
Section: Plasma With Multiple Ion Speciesmentioning
Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.
“…At the plasma edge 60 mm, neutral particle is richer than core and its effect should be strong. Thus, another candidates of identity of the low freuquency modes could be related neutral pressure gradient from edge to core 30 , 31 , 39 . Figure 5 Radial profile of power spectrum density of normalized density fluctuations.…”
High-spatial resolution observation of high-wavenumber broadband turbulence is achieved by controlling the magnetic field to be relatively low and measuring with a azimuthally arranged multi-channel Langmuir array in a basic laboratory plasma. The observed turbulence consists of narrowband low-frequency fluctuations and broadband high-frequency turbulent fluctuations. The low-frequency fluctuations have a frequency of about 0.7 times the ion cyclotron frequency and a spatial scale of 1/10 of the ion inertial scale. In comparison, high-frequency fluctuations have a higher frequency than the ion cyclotron frequency and spatial scales of 1/10–1/40 of the ion inertial scale. Two-dimensional correlation analysis evaluates the spatial and temporal correlation lengths and reveals that the high-wavenumber broadband fluctuations have turbulent characteristics. The measurements give us further understanding of small scale turbulence in space and fusion plasmas.
“…Therefore, studies on ion acoustic waves [33,34] and a generalized Bohm criterion [35][36][37] depicted this mixture as a simple example for a multi-ion discharge. Recent studies by Kim et al [38] and Adrian et al [39] contributed to those discussions using or referring to Ar/Xe plasmas.…”
An argon-xenon (Ar/Xe) plasma is used as a model system for complex plasmas. Based on this system, symmetric low-pressure capacitively coupled radiofrequency discharges are examined utilizing Particle-In-Cell/Monte Carlo Collisions (PIC/MCC) simulations. In addition to the simulation, an analytical energy balance model fed with the simulation data is applied to analyze the findings further. This work focuses on investigating the ion dynamics in a plasma with two ion species and a gas mixture as background. By varying the gas composition and driving voltage of the single-frequency discharge, fundamental mechanics of the discharge, such as the evolution of the plasma density and the energy dispersion, are discussed. Thereby, close attention is paid to these measures' influence on the ion energy distribution functions at the electrode surfaces. The results show that both the gas composition and the driving voltage can significantly impact the ion dynamics. The mixing ratio of argon to xenon allows for shifting the distribution function for one ion species from collisionless to collision dominated. The mixing ratio serves as a control parameter for the ion flux and the impingement energy of ions at the surfaces. Additionally, a synergy effect between the ionization of argon and the ionization of xenon is found and discussed.
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