Investigation of fireball assisted double layer produced in a DC discharge plasma

A stable fireball is produced in front of a positively biased metal disc inside a filamentary dc discharge argon plasma. The measurement of the axial potential profile from the bulk plasma to the fireball shows a monotonic potential change near the boundary between the fireball and bulk plasma indicating the formation of a double layer (DL). The fireball -assisted DL is identified as weak DL with normalized potential phi(D) similar to 3 and thickness in the range of 20-35 lambda(D) which varies with the plate bias. The measured electron energy distribution functions (EEDFs) show two distinct electron distributions within the fireball where one is background Maxwellian electrons, and the other is higher energetic electron group accelerated by the DL potential. In the bulk, however, electrons follow a single Maxwellian distribution. The cross flow of electrons and ions through the DL has been established to explain the existence of the steady state DL.