Daniel Soderstrom, Hana Barankova, Ladislav Bardos

On dimensions of atmospheric-pressure hollow cathodes

IEEE Transactions on Plasma Science 35 (2007) 522-526

The hollow cathode is known as a source of high-density plasmas. This property is due to the hollow-cathode effect (HCE), which can be explained by the oscillations of fast electrons between repelling potentials of opposing space-charge sheaths. At atmospheric pressure, one should be able to create an RCE by adjusting the dimension of the hollow cathode. Experiments show that the dimensions could be as large as 500 mu m, so that the sheath thickness may be on the order of 100 mu m. Theoretical models of the atmospheric-pressure sheaths based on the conventional Child-Langmuir approach give the sheath thicknesses on the order of 10 mu m, which contradicts the experiments. We introduce here a new model which takes into account three groups of electrons: slow, fast, and secondary. By adding a group of fast and secondary electrons, we show that the sheath thickness increases as compared with only slow electrons present.

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