An approach to line-shaped nitrogen plasma production at atmospheric pressure by slot-excited microwave discharge

Abstract

For large-area surface treatment processing at atmospheric pressure, a one-dimensional line-shaped plasma source using molecular gas discharge excited by a 2.45 GHz microwave was investigated. From the results of three-dimensional microwave simulation, a flat waveguide is proposed to increase the power density for the enhancement of the electric field inside the slot and easy breakdown and sustainment without markedly increasing the input power. A pure N2 plasma of submeter length was produced by a travelling wave of CW microwave power using the flat waveguide with a narrow-gap slot of 30 cm length incorporated into the loop waveguide system to suppress standing waves. The plasma length was increased by increasing the input microwave power from 1.0 to 2.5 kW and its maximum was about 14 cm. The medium gas temperature of 1100 K was measured from the rotational temperature of the N2 second positive band evaluated by optical emission spectroscopy.