Mass spectrometry with ion sources operating at atmospheric pressure

The streamer and return stroke concepts in positive corona breakdown are reviewed, and examined critically for the case of short (<5 cm) gaps in ambient air. It is shown that return strokes normally should not be observed, but that return streamers may occur in longer or highly overvolted streamer channels. A new physical picture is presented of the secondary streamer, as one or several high field domains formed by Douglas‐Hamilton–Mani‐type attachment instability of the residual channel created by the passage of the primary streamer. In this way, both the erratic origin and development of the secondary streamer in air are easily explained, as well as the fact that spark breakdown follows if and when the secondary streamer fills the complete residual channel length. Further, it follows that the secondary streamer is not the cause of breakdown, but only a secondary side effect.

The residual streamer channel: Return strokes and secondary streamers

Electrohydrodynamic atomization: A two-decade effort to produce and process micro-/nanoparticulate materials.

https://www3.nd.edu/~sst/teaching/AME60637/reading/2004_JE_Adamiak_Atten_point_plane_simulation.pdf

Simulation of corona discharge in point–plane configuration

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of `saw-toothed' current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive `shells' of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

https://iopscience.iop.org/article/10.1088/0022-3727/30/22/008/pdf

The theory of positive glow corona

Unipolar space‐charge distribution ρ(t) drifting with constant ion mobility μ in gas under time and space dependent electric fields will evolve according to the unipolar charge drift formula [1/ρ(t)]−[1/ρ(t0)] = (μ/e0)(t−t0), neglecting diffusion effects. This general formula is especially useful as a starting point for approximate treatment of space‐charge effects, both in ion drift and diffusion experiments, and in electrical coronas. A first simple derivation of an equivalent of the Warburg cos5ϑ current‐density distribution for point‐to‐plane coronas is given, together with a formula for the maximum possible unipolar ion current (the unipolar saturation current) Is ≊2μe0 V2/d, for a given corona voltage V and point‐to‐plane distance d. It is demonstrated that corona currents in excess of this limit always involve free electron or bipolar conduction phenomena, like streamers.

R. S. Sigmond

Papers

Simple approximate treatment of unipolar space‐charge‐dominated coronas: The Warburg law and the saturation current