Nonlinear dynamics of a concentric double-grid cathode discharge

A transparent-cathode discharge, obtained by negatively biasing two concentric metallic grid spheres with axi-symmetrically aligned orifices was investigated by non-linear dynamic methods. The ignition of the self-sustaining discharge leads to the formation of complex plasma space charge structures. Tangent luminous semi-spherical formations (i.e. plasma bubble, plasma fireball-like structures) appear inside, in between and around the inner and outer grid. The overall dynamics of the discharges’ static current-voltage ( I-V ) characteristic contain sudden jumps and drops of the current correlated with the assembly and disassembly of the specific plasma formations. The increase and decrease, respectively, of the applied bias in absolute values on the two grids, reveals strong hysteresis effect and pronounced oscillatory behavior.