Plasma sheath region near a boundary with positive ion backscattering

AbstractThe plasma sheath dynamics adjacent to the cathode in the presence of electrons, ions, and doubly ionized ions have been simulated in this work. The aim of the present investigation is, therefore, to study the effect of the doubly ionized ions on the characteristics of the plasma sheath dynamics such as potential distribution, sheath length, and ions dose and velocity near the surface (cathode). It was shown that the presence of the doubly ionized ions can increase the normalized potential of all positions in sheath region, sheath length, and ion/doubly ionized ions density ratio on the target. Obtained results may be helpful for analyzing the practical results of the surface operations such as ion implantation and plasma polymerization, etc.

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The positive ion temperature effect in magnetized electronegative plasma sheath with two species of positive ions

Physics of Plasmas ◽

10.1063/1.4759460 ◽

2012 ◽

Vol 19 (10) ◽

pp. 102108 ◽

Cited By ~ 10

Author(s):

A. K. Shaw ◽

S. Kar ◽

K. S. Goswami

Keyword(s):

Temperature Effect ◽

Plasma Sheath ◽

Ion Temperature ◽

Electronegative Plasma ◽

Positive Ions ◽

Positive Ion

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Temporal Ion Velocity Variation with Obliqueness in Magnetized Plasma Sheath

Journal of Nepal Physical Society ◽

10.3126/jnphyssoc.v7i2.38634 ◽

2021 ◽

Vol 7 (2) ◽

pp. 138-143

Author(s):

B. R. Adhikari ◽

R. Khanal

Keyword(s):

Magnetic Field ◽

Plasma Sheath ◽

Magnetized Plasma ◽

Velocity Variation ◽

Physical Parameters ◽

Sheath Region ◽

Narrow Region ◽

Force Equation ◽

Ion Velocity ◽

External Oblique Magnetic Field

A narrow region having sharp gradients in physical parameters is formed whenever plasma comes into contact with a material wall. In this work, the temporal velocity variation of ions in such a sheath has been studied in the presence of an external oblique magnetic field. The Lorentz force equation has been solved for the given boundary conditions using Runge-Kutta method. In order to satisfy the Bohm criterion, ions enter the sheath region with ion acoustic velocity. It is observed that all components of the velocity waves are damped in plasma in the time scale of one second. The computed oscillatory part of ion velocity match with the equation of the damped harmonic oscillator. Thus obtained damping constants as well as the frequency of all three components are nearly equal for obliqueness less than 600 after which they are distinctly different. This is due to the fact that the magnetic field becomes almost parallel to the wall. In earlier studies, only the final velocity profiles are reported and hence this study is useful in understanding how the ion velocities evolve in time as they move from sheath entrance towards the wall.

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Plasma Sheath Modeling in the Presence of Collisions

Fluids Engineering ◽

10.1115/imece2002-39352 ◽

2002 ◽

Author(s):

Subrata Roy ◽

Jonathan Poggie ◽

Datta V. Gaitonde

Keyword(s):

Experimental Data ◽

Electric Propulsion ◽

High Speed ◽

Noble Gas ◽

Plasma Sheath ◽

Third Order ◽

Plasma Dynamic ◽

Sheath Region ◽

Multiple Ionization ◽

Near Future

The present work develops a finite element discretized one-dimensional formulation for plasma-sheath dynamics, using multi-fluid equations. The applications include dc and rf sheath inside a glow discharge tube and a partially ionized plasma sheath inside a electric propulsion thruster channel. Based on the experimental data for multiple ionization of a noble gas, a third order polynomial has been used as a fit to describe ionization processes. Such a polynomial has been used to self-consistently calculate the rate of ionization in the plasma dynamic equations. The electron and ion number densities of the numerical solution decrease in the plasma-sheath region as expected. The ion velocity, sheath potential and electron temperature profiles also exhibit the expected behavior. The computed sheath potential compares well with the available experimental data. The model needs to be generalized in the near future for potential application to the high-speed air vehicles.

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The operation of Langmuir probes in electro-negative plasmas

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1959.0140 ◽

1959 ◽

Vol 252 (1268) ◽

pp. 102-119 ◽

Cited By ~ 105

Keyword(s):

Negative Ions ◽

Ion Current ◽

Langmuir Probes ◽

Negative Probe ◽

Ion Energy ◽

Ion Energy Distribution ◽

Sheath Region ◽

Sheath Edge ◽

Positive Ions ◽

Positive Ion

A criterion that must be satisfied by the positive-ion energy distribution at the edge of a sheath surrounding a negative probe is derived for the case when negative ions are present. This criterion is then used to derive the potential outside the sheath region surrounding a spherical probe immersed in an electro-negative plasma. It is found that the potential falls to low values when the ratio of negative ions to electrons exceeds 2. Under these circumstances the positive-ion current collected is the random current across the sheath edge. If, however, the ratio is much less than 2 then the collection of positive ions proceeds as for an electro-positive gas.

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Tungsten and Molybdenum Surfaces Exposed to Warm Deuterium Ion Plasma with Q-Nonextensive Distribution of Electrons

Journal of Nepal Physical Society ◽

10.3126/jnphyssoc.v6i1.30517 ◽

2020 ◽

Vol 6 (1) ◽

pp. 50-58

Author(s):

S. Basnet ◽

R. Khanal

Keyword(s):

Magnetic Field ◽

Impact Energy ◽

Target Surface ◽

Plasma Sheath ◽

Magnetized Plasma ◽

Sheath Region ◽

Two Fluids ◽

Positive Ions ◽

Nonextensive Distribution ◽

The Impact

This work is concerned with the effect of non-Maxwellian electrons and obliqueness of magnetic field on magnetized plasma sheath characteristics, in which plasma interacts with tungsten (W) and molybdenum (Mo) surfaces via non-neutral plasma sheath using two fluids model. It is assumed that the singly charged positive ions are treated as warm fluid whereas the electrons obey q-nonextensive distribution. It is found that the q-nonextensive distributed electrons and the temperature of ions affect the entrance velocity of positive ions, which is a key parameter in the plasma sheath formation. Also, the nonextensive parameter q affects the distribution of ions and electrons in the sheath region and their distributions explicitly related with the electrostatic potential variation. The parallel and perpendicular components of ions velocity are affected by the obliqueness of magnetic field. As the nonextensivity of electrons increases, the gradient in electric potential increases towards the wall and hence the impact energy also increases. The obliqueness of magnetic field and impact energy of ions is a key factor that determines the physical sputtering rate, particle reflection and absorption from the target surface. Furthermore, the probability of particle reflection coefficient from the W-surface is higher than that of Mo-surface.

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Numerical analysis of monoenergetic electrons energy effect on dynamic potential profile of plasma sheath

Journal of Plasma Physics ◽

10.1017/s0022377812001183 ◽

2013 ◽

Vol 79 (5) ◽

pp. 509-512 ◽

Cited By ~ 1

Author(s):

M. SHARIFIAN

Keyword(s):

Numerical Analysis ◽

Potential Distribution ◽

Plasma Sheath ◽

Cathode Potential ◽

Energy Effect ◽

Fast Electrons ◽

Sheath Region ◽

Dynamic Potential ◽

The Finite Difference Method ◽

Slow Electrons

AbstractThe dynamic behavior of the electric potential distribution of a plasma sheath region in the presence of monoenergetic electrons with two different values of energy, larger (fast electrons) and smaller (slow electrons) than the cathode potential energy, is examined numerically by the finite difference method. Exploring and comparing the plots of numerical computation results shows that the time evolution of the non-monotonic potential distribution heavily depends on the energy of monoenergetic electrons.

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