Space Potential and Ion Energies in a Low Pressure Discharge Containing at least Two Negative Species

Ingram, Samantha; Braithwaite, Nicholas

doi:10.1557/proc-117-281

Cited by 8 publications

(5 citation statements)

References 7 publications

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“…As shown in figure 3(a), at this internal sheath the positive ion flux has not attained the required value and spatial space-charge oscillations result as discussed in [11]. These oscillations are the fluid model analogue of the single double-layer predicted from kinetic theory [17][18][19]. After a number of oscillations, the Bohm criterion is finally satisfied and a terminal sheath forms.…”

Section: Non-neutral Solutionsmentioning

confidence: 92%

“…they are not numerical artefacts). However, if kinetic ions are used [17], a single double-layer is formed [18,19]-kinetic ions born at rest (or suffering collisions) will fill the potential valleys that are allowed by the fluid model. Second, do the oscillations effect the flux?…”

Section: Non-neutral Solutionsmentioning

confidence: 99%

“…That is, since the flux is an integral of the positive ion source over the entire discharge, it is not effected by the presence (or absence) of space-charge oscillations when q 1. Although both the fluid and kinetic models [17] can be solved for the collisionless limit, it may prove simpler to extend the fluid model to moderately collisional regimes [5].…”

Section: Non-neutral Solutionsmentioning

confidence: 99%

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Positive ion flux from a low-pressure electronegative discharge

Sheridan

Chabert

Boswell

1999

Plasma Sources Sci. Technol.

117

166

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We compute the flux of positive ions exiting a low-pressure, planar, electronegative discharge as a function of the negative ion concentration and temperature. The positive ions are modelled as a cold, collisionless fluid, while both the electron and negative ion densities obey Boltzmann relations. For the plasma approximation, the plasma edge potential is double-valued when the negative ions are sufficiently cold. When strict charge neutrality is relaxed, spatial space-charge oscillations are observed at the edge of the plasma when the flux associated with the low (in absolute value) potential solution is less than that of the high potential solution. However, the flux is always well defined and varies continuously with the negative ion concentration. We demonstrate that the correct solution for the plasma approximation is that having the greater flux.

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Section: Non-neutral Solutionsmentioning

confidence: 92%

Section: Non-neutral Solutionsmentioning

confidence: 99%

Section: Non-neutral Solutionsmentioning

confidence: 99%

See 1 more Smart Citation

Positive ion flux from a low-pressure electronegative discharge

Sheridan

Chabert

Boswell

1999

Plasma Sources Sci. Technol.

117

166

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“…In such an ion rich plasma, a large change in the plasma is expected as a result of varying a small parameter (the electron density). For example, a sudden change in the sheath criterion and the hysteresis of the plasma-sheath boundary with the variation of the negative ion density is an interesting problem to be examined experimentally (Ingram and Braithwaite 1988). Another problem involves the scaling units, both in length and time (Emeleus 1986).…”

Section: Occurrence Of and Interest In Plasmas With Negative Ionsmentioning

confidence: 99%

Plasmas with negative ions-probe measurements and charge equilibrium

Amemiya

1990

J. Phys. D: Appl. Phys.

204

107

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Extensions of the electrostatic probe technique to situations with negative ions, both theoretical and experimental, are described. Charged particle distributions and the plasma-sheath boundary are discussed in relation to probe measurements. Plasmas with negative ions, their occurrence and interest, particularly situations where the negative ion density becomes comparable to or exceeds the electron density are described. Some data in negative ion containing plasmas are shown and discussed. ( a ) DC discharges O2 (Thompson 1961) 0.01-0.05 20 108 12, O2 (Emeleus and Coulter 1983) 0.1-10 3102 ? SF, (Ogle and Woolsey 1987) 0.1-10 400-700 107-109 SF6/Ar (Picard et a/ 1986) 0.2 10-103 109-1 010 l2 (Doucet 1970) =10-3 -103 109 O2 (Bacal and Doucet 1974) 10-3 >IO 108-109 SF, (Wong er a/ 1975) -10-5 >l03 109 CsCl (Goeler et a/ 1966) ? 10-100 10'~-10'2 Scavenge by SF6, WF,; CsCI, Csl, KCI, K1 (Sheehan and Rynn 1988) ? 20-1 04 109-1 010 ( f ) Diffusion plasma l2 (Amemiya 1988a) 10-2-10-' 103-104 109 (g) Lower ionosphere (D-layer) 0, 02, etc (Rose and Widdel

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“…Models describing electronegative discharges are of great practical importance due to the widespread use of such discharges in plasma processing. Most available theories consider either the limit of collisionless ion motion [1][2][3][4][5][6] or the opposing limit of fully-collisional (i.e. mobility-limited) motion [7,8].…”

Section: Introductionmentioning

confidence: 99%

Double layers in a modestly collisional electronegative discharge

Sheridan¹

1999

J. Phys. D: Appl. Phys.

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The effect of ion-neutral collisions on the structure and ion flux emanating from a steady-state, planar discharge with two negative components is investigated. The positive ion component is modelled as a cold fluid subject to constant-mobility collisions, while the electrons and negative ions obey Boltzmann relations. The model includes the collisionless limit. When the negative ions are sufficiently cold three types of discharge structures are found. For small negative ion concentrations or high collisionality, the discharge is `stratified', with an electronegative core and an electropositive edge. For the opposite conditions, the discharge is `uniform' with the negative ion density remaining significant at the edge of the plasma. Between these cases lies the special case of a double-layer-stratified discharge, where quasi-neutrality is violated at the edge of the electronegative core. Double-layer-stratified solutions are robust in that they persist for moderate collisionality. Numerical solutions for finite non-neutrality verify that the plasma flux varies continuously with collisionality, although the derivative of the flux with respect to collisionality is discontinuous when the discharge structure changes from uniform to stratified. Double-layer solutions are found when the flux predicted for the plasma approximation is double-valued and the flux associated with the smaller plasma edge potential is less than that associated with the larger edge potential. A comparison with numerical non-neutral solutions confirms that the flux is correctly predicted using the plasma approximation when the larger value of the flux is taken in the two-solution regime.

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Space Potential and Ion Energies in a Low Pressure Discharge Containing at least Two Negative Species

Cited by 8 publications

References 7 publications

Positive ion flux from a low-pressure electronegative discharge

Positive ion flux from a low-pressure electronegative discharge

Plasmas with negative ions-probe measurements and charge equilibrium

Double layers in a modestly collisional electronegative discharge

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