Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Tsankov, Tsanko Vaskov; Czarnetzki, Uwe

doi:10.1088/1361-6595/aa5f45

Cited by 29 publications

(68 citation statements)

References 57 publications

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“…The effect of the ion to electron temperature ratio was studied in previous works [4,22,24,26,28]. The INCEC mean free path is recognized as an important parameter to discriminate between the ABR and the OML behavior in recent theoretical works [29][30][31][32]. This article shows an experimentally observed transition from the ABR to the OML behavior as a function of the INCEC mean free path, λ + , to the Debye length, λ D , ratio Λ = λ + /λ D [26,28].…”

Section: Introductionmentioning

confidence: 85%

Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

et al. 2020

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This paper presents an experimentally observed transition from the validity of the radial theories to the validity of the orbital theories that model the ion current collected by a cylindrical Langmuir probe immersed in low-pressure, low-temperature helium plasma when it is negatively biased with respect to the plasma potential, as a function of the positive ion-neutral collision mean free path to the Debye length ratio Λ=λ+/λD. The study has been also conducted on argon and neon plasmas, which allows a comparison based on the mass of the ions, although no transition has been observed for these gases. As the radial or orbital behavior of the ions is essential to establish the validity of the different sheath theories, a theoretical analysis of such a transition not only as a function of the parameters Λ and β=T+/Te, T+ and Te being the positive ion and electron temperature, respectively, but also as a function of the ion mass is provided. This study allows us to recognize the importance of the mass of the ion as the parameter that explains the transition in helium plasmas. Motivated by these theoretical arguments, a novel set of measurements has been performed to study the relationship between the Λ and β parameters in the transition that demonstrate that the effect of the ion mean free path cannot be completely ignored and also that its influence on the ion current collected by the probe is less important than the effect of the ion temperature.

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Section: Introductionmentioning

confidence: 85%

Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

et al. 2020

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“…It is also defined as the point outside of which charge neutrality breaks down, so here we take ne = ni = n0 and φ = 0 at sheath edge. Regarding ion distribution function 𝑓 𝑖 in plasma sheath, it is possible to solve it from kinetic equation [40] , while for simplification one can assume zero ion temperature and treat all ions as monoenergetic particles. Considering energy conservation and flux conservation of ions in plasma sheath, there should be Eq.…”

Section: ⅲ Theoretical Analysesmentioning

confidence: 99%

Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

Zhang¹,

Sun²,

Volčokas³

et al. 2021

Plasma Sources Sci. Technol.

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The influence of charge trap states in the dielectric boundary material on capacitively coupled radio-frequency (RF) plasma discharge is investigated with theory and particle-in-cell/Monte Carlo collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion-induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within the solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electron trap density, and charge trapping through Auger neutralization and de-excitation. Theoretical analysis is carried out to reveal the effects of trap states on sheath solution, stability, plasma density and temperature, particle and power balance, etc. The theoretical work is supported by simulation results, showing the reduction of the mean RF sheath potential as charging-dependent emission coefficient increases. As the gas pressure increases, a shift of the maximum ionization rate from the bulk plasma center to the plasma-sheath interface is observed, which is also influenced by the trap states of the electrode material where the shift happens at a lower pressure with traps considered. In addition, charge traps are proven to be helpful for creating asymmetric plasma discharges with geometrically symmetric structures; such an effect is more pronounced in γ-mode discharges.

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“…A selfconsistent description of the electric response, indicated by a selfconsistent embedding of the electric double layer between two quasi-neutral, field-free regions, could thus be realized without taking collisions into account. The absence of collisions can be at most justified on the plasma side, where electrons are strongly depleted and hence nearly collisionless, and ions are only subject to ion-neutral collisions which however have to be considered only in particular situations [236][237][238] or when a very precise description of the plasma sheath is required [239]. Hence, on the plasma side ignoring or including collisions is essentially a question of how accurate one wants to describe the plasma sheath.…”

Section: A Integrated Modeling Of the Electric Double Layermentioning

confidence: 99%

Towards an integrated modeling of the plasma-solid interface

Bönitz

Filinov

Abraham

et al. 2019

Front. Chem. Sci. Eng.

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Solids facing a plasma are a common situation in many astrophysical systems and laboratory setups. Moreover, many plasma technology applications rely on the control of the plasma-surface interaction, i.e. of the particle, momentum and energy fluxes across the plasma-solid interface. However, presently often a fundamental understanding of them is missing, so most technological applications are being developed via trial and error. The reason is that the physical processes at the interface of a low-temperature plasma and a solid are extremely complex, involving a large number of elementary processes in the plasma, in the solid as well as fluxes across the interface. An accurate theoretical treatment of these processes is very difficult due to the vastly different system properties on both sides of the interface: quantum versus classical behavior of electrons in the solid and plasma, respectively; as well as the dramatically differing electron densities, length and time scales. Moreover, often the system is far from equilibrium. In the majority of plasma simulations surface processes are either neglected or treated via phenomenological parameters such as sticking coefficients, sputter rates or secondary electron emission coefficients. However, those parameters are known only in some cases and with very limited accuracy. Similarly, while surface physics simulations have often studied the impact of single ions or neutrals, so far, the influence of a plasma medium and correlations between successive impacts have not been taken into account. Such an approach, necessarily neglects the mutual influences between plasma and solid surface and cannot have predictive power.In this paper we discuss in some detail the physical processes a the plasma-solid interface which brings us to the necessity of coupled plasma-solid simulations. We briefly summarize relevant theoretical methods from solid state and surface physics that are suitable to contribute to such an approach and identify four methods. The first are mesoscopic simulations such as kinetic Monte Carlo (KMC) and molecular dynamics (MD) that are able to treat complex processes on large scales but neglect electronic effects. The second are quantum kinetic methods based on the quantum Boltzmann equation that give access to a more accurate treatment of surface processes using simplifying models for the solid. The third approach are ab initio simulations of surface process that are based on density functional theory (DFT) and time-dependent DFT. The fourths are nonequilibrium Green functions that able to treat correlation effects in the material and at the interface. The price for the increased quality is a dramatic increase of computational effort and a restriction to short time and length scales. We conclude that, presently, none of the four methods is capable of providing a complete picture of the processes at the interface. Instead, each of them provides complementary information, and we discuss possible combinations. PACS numbers:

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Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Cited by 29 publications

References 57 publications

Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

Towards an integrated modeling of the plasma-solid interface

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