A plasma flame, whose cross-section is rectangular, can be produced by a particular type of a nozzle. It is composed of a two-stage entrance constrictor of circular cross-section and an exit constrictor of rectangular cross-section.
The arc voltage of the newly developed nozzle is less than that of the ordinary cylindrical one, and thus the effluent volume of a plasma is decreased. However, the stability can be improved conspicuously, because the magnitudes of axial and radial fluctuations of a plasma flame by the system is reduced to half that of the conventional one.