The floating potential of a Langmuir probe in a high-pressure plasma

Abstract

The floating potential (ie the potential assumed by a probe when the net current collected by it is zero) of a spherical electrostatic (Langmuir) probe in a collision-dominated plasma is investigated. The plasma is considered to be either static or flowing at subsonic velocities. The experimentally realistic situation is also considered where the probe is cold compared with the bulk plasma. The two extreme probe temperature conditions are discussed: that in which the electrons remain at their uncooled temperature, characteristic of the bulk plasma; and that in which they cool to the temperature of the neutrals near the probe. It is concluded that only in the case when the electrons cool and the sheath is thin does the floating potential vary appreciably from its value obtained in the absence of thermal gradients and thermoelectric effects. Experimental results are presented which support the concept that, for the opposite of the above condition (ie uncooled electrons, thick sheath), the floating potential is unaffected. In addition, the data have also been analysed in a manner suggested by Lam to yield an accurate value for the electron temperature.

Potentiometric Detection of Model Bioaerosol Particles

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The transport dynamics of tens of micrometer-sized water droplets in RF atmospheric pressure glow discharges

“…While the droplet here is positioned at the lower edge of the plasma instead of being immersed in the center of the plasma, the asymmetric charging is still seen. The droplet potential and the charge on the surface of the droplet immersed in the plasma can also be estimated from the electron and ion fluxes to the surface of the droplet by analytical models [36,37,[53][54][55]. These models require knowledge of the electron temperature and density in the bulk plasma which was taken from the continuum emission measurements (see table 2).…”

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“…Within this sheath at floating potential electroneutrality is violated and electrons are repelled so n e À { n M 1. The cations are not significantly affected by this electric field because u M 1 { u e À. Clements and Smy 35 derived an expression relating the floating potential with the imbalance electron concentration in the bulk plasma and adjacent to the electrode. In their approach the pressure gradient was equated with the electric force per unit volume on the electrons.…”