Ion and electron sheath characteristics in a low density and low temperature plasma

Borgohain, Binita; Bailung, Heremba

doi:10.1063/1.5006133

Cited by 7 publications

(5 citation statements)

References 24 publications

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“…Simulation results are consistent with equation (35), as shown in gure 19. Recent experiments by Borgohain and Bailung [169] have tested the sheath thickness and plasma potential pro les implied by these predictions, showing good agreement.…”

Section: Steady-state Propertiessupporting

confidence: 77%

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Baalrud

Scheiner

Yee

et al. 2020

Plasma Sources Sci. Technol.

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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.

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Section: Steady-state Propertiessupporting

confidence: 77%

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Baalrud

Scheiner

Yee

et al. 2020

Plasma Sources Sci. Technol.

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“…The electron sheaths are generally observed around Langmuir probe 9 , plasma contactor 10 , magnetically constricted electrode 11 etc. The electron sheath has been also characterised at low density and low temperature plasmas 12 . The transition of electron sheath and its different states like anode glow and anode spot has been studied in detail 8,13 .…”

Section: Introductionmentioning

confidence: 99%

Electron sheath evolution controlled by a magnetic field in modified hollow cathode glow discharge

et al. 2018

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The electron sheath formation in a DC magnetised plasma of modified hollow cathode source is studied. The discharge consists of two plane parallel cathodes and a small cubical anode placed off axis at the center. The argon plasma is produced and the properties of the plasma in response to the sheath formation near the anode are studied using electrical and optical diagnostics. In particular, the effect of pressure, magnetic field on discharge parameters such as discharge current, plasma potential, plasma density and electron temperature is studied. The discharge showed an onset of anode glow at a critical applied magnetic field indicating the formation of electron sheath and a double layer. The discharge current initially decreases; however it starts to rise again as the anode spot appears on the anode. The critical magnetic field at which anode glow formation takes place is dependent upon operating pressure and discharge voltage. The transition from ion sheath to electron sheath is investigated in detail by Langmuir probe and spectroscopy diagnostics. The plasma potential near the anode decreases during the transition from ion sheath to electron sheath. The plasma potential locks to the ionization potential of argon gas when anode spot is completely formed. A systematic study showed that during the transition, the electron temperature increases and plasma density decreases in the bulk plasma. The spectroscopy of the discharge showed presence of strong atomic and ionic lines of argon. The intensity of these spectral lines showed a dip during the transition between two sheaths. After the formation of the anode spot, oscillations of the order of 5-20 kHz are observed in the discharge current and floating potential due to the enhanced ionisation and excitation processes in the electron sheath. The reason of the electron sheath formation at particular magnetic field is attributed to the reduction of the electron flux reaching to the anode in the direction perpendicular to the magnetic field.

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“…In that case, the electron fluid cannot be modelled with a Boltzmann relation. Recent numerical and experimental works have reported electron inertial effects in electron sheaths and presheaths [17][18][19], plasma sheath instabilities [20], Langmuir probes [21], magnetized plasmas [22][23][24], and Hall thrusters instabilities [25]. Similarly, the effect of the ion temperature on the plasma-wall interaction has been studied experimentally [26] and analytically [27], showing small deviations from the classical theory as the ionto-electron temperature ratio increases.…”

Section: Introductionmentioning

confidence: 95%

Plasma-sheath transition in multi-fluid models with inertial terms under low pressure conditions: Comparison with the classical and kinetic theory

Laguna

Magin

Massot

et al. 2019

Plasma Sources Sci. Technol.

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We present high-order accuracy simulations of the plasma-sheath transition with an ion-electron multi-fluid model that considers the electron inertial terms and the ion pressure gradient. By means of a third-order accuracy time-dependent finite volume scheme, we solve the isothermal multi-fluid equations with realistic ion-to-electron mass ratios. We propose a numerical procedure and boundary conditions that retrieve a steady-state solution of a planar 1D floating sheath. The classical solution to this problem neglects the ion temperature since the model equations present a singularity for a finite ion temperature. The multi-fluid simulations provide a rigorous solution to the plasma-sheath transition without singularities. We compare our solution to the classical theory, finding perfect agreement when the ion-to-electron temperature tends to zero. We discuss the effect of the ion temperature, the electron inertia, and the elastic collisions with neutrals in low-pressure plasmas. Finally, relying on a kinetic approach, we derive analytical expressions for the electron macroscopic quantities inside a steady sheath that assumes a truncated Maxwellian electron velocity distribution function (EVDF) with a wall that collects the electron random flux. The derived analytical expressions are beyond the classical isothermal solution with Boltzmann electrons. The isothermal multi-fluid solution captures properly the first two moments of the EVDF inside the sheath. Our analytical expressions show the need for solving for higher-order moments to fully explain the electron physics inside the sheath, as opposite to the classical isothermal assumption. This work demonstrates that the multi-fluid simulations are able to capture the plasma-sheath transition under weakly collisional conditions with a solution that is consistent with the classical and the kinetic theory.

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Ion and electron sheath characteristics in a low density and low temperature plasma

Cited by 7 publications

References 24 publications

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Electron sheath evolution controlled by a magnetic field in modified hollow cathode glow discharge

Plasma-sheath transition in multi-fluid models with inertial terms under low pressure conditions: Comparison with the classical and kinetic theory

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