Observation of simultaneous cohorent oscillations in discharge current and probe floating potential in coaxial DC glow discharges

Hysteresis effects in the I-V characteristics of DC glow discharges have been a subject of considerable interest in different system configurations [1-4]. Mostly these effects are observed in the presence of a third (auxiliary anode) electrode and have been attributed to formation of structures at this electrode. Also, nonlinear oscillations observed in either the auxiliary anode current or the floating potential of a Langmuir probe (LP) were attributed to dynamic changes in the structures. Recently, however, observations of floating potential oscillations without the use of auxiliary electrodes were reported in coaxial electrode geometry [4]. This paper reports nonlinear oscillations observed simultaneously in both, the floating potential of an LP and the discharge current in coaxial electrode geometry (without auxiliary electrodes), over a wide range of discharge parameters. In addition, the two sets of oscillations were found to have identical wave shapes and phasing, no matter what the nature of the oscillations. The latter feature is particularly notable since the current oscillations represent global effects, while the floating potential oscillations represent local effects. Typically, the oscillations are in the kHz range, with plasma densities ≈ 10⁹ cm^-3 and electron temperatures, ≈ 3 eV. Analysis of the experimental data using nonlinear dynamical tools will be presented, along with related hysteresis and negative differential resistance observations in the I-V characteristics of the discharge.