Abstract:
A discharge plasma is created by simultaneously biasing two concentric spherical grids with
axisymmetric orifices. In this geometry, space charge structures in the form of multiple
quasi-spherical luminous plasma bodies appear simultaneously inside and around the
cathodes. The plasma formations are highly interdependent supplying each other with the
particle flow and current closure necessary for the maintenance of the discharge. To diagnose
these structures, space-resolved cold Langmuir probe measurements and optical emission
spectroscopy investigations were performed in the axial direction allowing for the mapping of
the axial profiles of plasma potential, electron temperature and density, ion density and optical
emission. The existence of an accelerating double layer in the vicinity of the holes has been
confirmed here, and in previous research (Teodorescu-Soare C T et al 2016 Phys. Scr. 91
034002; Schrittwieser R W et al 2017 Phys. Scr. 92 044001; Teodorescu-Soare C T et al 2019
Int. J. Mass Spectrom. 436 83). Besides the assessment of the relationship between discharge
conditions and plasma parameters in the novel cathode system, the importance of a multiple
concentric cathode discharge configuration is revealed for deposition applications.
