Measurement of electron density in a microdischarge-integrated device operated in nitrogen at atmospheric pressure using a millimetre-wave transmission method

We have diagnosed the electron density in nitrogen plasma generated in a device composed of coaxial-hollow microdielectric-barrier discharges using a millimetre-wave transmission method. At atmospheric pressure the generated plasma occupied almost the entire hollow-electrode space, and the electron density was estimated as 1012–1013 cm−3. This value is in good agreement with theoretical prediction in a simple particle-balance model. We also studied the effect of small admixtures of H2O and O2 into nitrogen discharges at atmospheric pressure. In the case of H2O addition, the measured electron density was lower than that in pure nitrogen, in particular at high reduced electric fields, due to the increase in the loss processes of electrons. In the case of O2 addition, the electron density decreased with an increase in O2 concentration due to the additional loss process through the formation of negative ions.