Transition from the C3-dominated discharge to the sooting plasma

Mass spectrometry and photoemission spectroscopy of a graphite hollow cathode source identify the parameters of the transition from the C(3) dominated discharge to the sooting plasma. The transition is a function of the shape and profile of a special cusp magnetic field which is a function of radius and azimuth angle, the geometry of the source, the discharge current, and pressure. Characteristic atomic and molecular emission lines and bands in the C(3) discharge transform into broad bands emitted by the excited soot. We identify four prominent emission bands between 300 to 400 nm to be the hallmark of the sooting plasma.