Effect of surface produced negative ions on near wall sheath

Shah, Sejal; Bandyopadhyay, M.

doi:10.1088/0741-3335/51/3/035015

Cited by 10 publications

(12 citation statements)

References 32 publications

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“…The electronegative gases such as oxygen, chlorine, and fluorocarbons are used extensively in the industry and laboratory for material processing, Langmuir probe diagnostics, and plasma sheath lenses with focusing effects on the charged particle beams. The presence of the negative ions can change the main structure of the plasma sheath transition region where for some ranges of plasma parameters, the multilayers form which separate the two distinct regions of ion-ion core and ion-electron priority [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Edge of magnetized electronegative plasma ion source in the presence of collisional adiabatic thermal positive ions

Yasserian

Aslaninejad

2019

J Theor Appl Phys

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This paper develops a theoretical model for formation of multilayers in the magnetized electronegative plasma at the edge of plasma ion source. The impacts of positive ion temperature and collisions are studied and quantified by obtaining the structure of the plasma sheath. By adding the negative ions into the discharge, the solutions of Poisson's equation become oscillatory. A finite temperature for the positive ions and also the collisions results in a change in the behavior of such oscillatory solutions. Here, it is assumed that the collision frequency depends on the positive ions velocity and thermal positive ions flow is adiabatic. The spatial distribution of the species density, electric potential, and positive ion velocity is calculated for different values of positive ion temperature and negative ion concentration for two limiting cases where the collision frequency either is constant or depends linearly on velocity. In addition, the influence of the plasma parameters such as negative ion density and temperature and positive ion temperature is investigated on the space charge and positive ion flux as well as parameter space region. It is also shown that the presence of the negative ion into the plasma ion source influences the extracted positive ion flux and increases the positive ions intensity.keywords Magnetized electronegative plasma · Adiabatic thermal positive ions · Presheath-Sheath · Parameter space region * Kiomars Yasserian

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Section: Introductionmentioning

confidence: 99%

Edge of magnetized electronegative plasma ion source in the presence of collisional adiabatic thermal positive ions

Yasserian

Aslaninejad

2019

J Theor Appl Phys

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“…Therefore, the characteristic length of pre-sheath in this case is l = 0.57(c s /Z). [48,53] This indicates that the geometric length l is less than the ionization length (c s /Z). However, when the negative ion emission is considered, l increases to 0.85 (c s /Z) with J n , which is approximately close to one ionization length.…”

Section: F I G U R Ementioning

confidence: 99%

“…The behaviour of sheath/pre‐sheath during emission of negative ions from the surface has been considered in some recent studies . These studies are primarily motivated from the perspective of efficient negative hydrogen ion H − production from the low‐work‐function caesiated surfaces introduced in the plasma .…”

Section: Introductionmentioning

confidence: 99%

“…Wünderlich et al developed a 1d3v particle‐in‐cell (PIC) code to investigate the sheath behaviour near the plasma grid in a H − negative ion source . Shah et al treated the negative ion production from the surface as a fraction of the positive ions impinging on the electrode surface; however, the scope of the above study is limited as the negative ion yield by energetic neutral bombardment is dominant in comparison to the positive ions . In a recent theoretical work, McAdams et al have addressed this problem by considering the negative ions emission from an electrode surface as an independent parameter .…”

Section: Introductionmentioning

confidence: 99%

“…[41][42][43][44] The behaviour of sheath/pre-sheath during emission of negative ions from the surface has been considered in some recent studies. [45][46][47][48][49] These studies are primarily motivated from the perspective of efficient negative hydrogen ion H − production from the low-work-function caesiated surfaces introduced in the plasma. [50,51] Wünderlich et al developed a 1d3v particle-in-cell (PIC) code to investigate the sheath behaviour near the plasma grid in a H − negative ion source.…”

Section: Introductionmentioning

confidence: 99%

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Positive ion speed at the plasma–sheath boundary of a negative ion‐emitting electrode

Pandey

Karkari

2020

Contributions to Plasma Physics

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One‐dimensional fluid model for a planar sheath in front of a negative ion‐emitting electrode surface immersed in a collision‐less, non‐magnetized, electronegative plasma is presented. It was found that the positive ion speed at the plasma–sheath boundary (PSB) increases linearly with negative ion emission from the electrode but attains a saturation value as soon as a virtual cathode is formed near the electrode surface. The effect of negative ion emission on the pre‐sheath region shows that the potential drop increases across the pre‐sheath in accordance with the rise in positive ion speed at the PSB. The sheath width obtained using the present model shows a similar trend as the Child‐Langmuir law, but its magnitude is found to be consistently higher compared with a non‐emitting electrode. A plausible explanation has been given to explain these effects.

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Plasma sheath with multi‐species of positive ions and surface produced negative ions

Samanta

Moulick

Bhuyan

et al. 2023

Contrib. Plasma Phys

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The structure of a plasma sheath has been investigated in front of a caesium‐coated metallic plate, using a simple theoretical model. Along with the electrons, the plasma is composed of multi‐species of positive ions, and surface and volume produced negative ions. While the volume produced negative ions are common in many plasma processing chambers, the surface produced negative ions are of critical importance, especially to the Neutral Beam Injection (NBI) systems. The surface negative ions are produced via the coated metallic plate. With a single species of positive ion, the Bohm criterion, which determines the sheath edge potential, is multi‐valued for a specific range of electronegativity (). The width of the multi‐valued region has been reported to increase with the surface production yield (). Calculations are done for hydrogen plasma with a slight admixture of a second gas such as argon. Besides discussing the differences brought in by the mere presence of a second ion, the paper highlights the importance of the positive ion current density in determining the Bohm criterion. In addition, the effect of three species of positive ions in the surface production process has been discussed.

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Effect of surface produced negative ions on near wall sheath

Cited by 10 publications

References 32 publications

Edge of magnetized electronegative plasma ion source in the presence of collisional adiabatic thermal positive ions

Edge of magnetized electronegative plasma ion source in the presence of collisional adiabatic thermal positive ions

Positive ion speed at the plasma–sheath boundary of a negative ion‐emitting electrode

Plasma sheath with multi‐species of positive ions and surface produced negative ions

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