An Experimental Approach To Period Doubling Bifurcation In Plasmas

A direct current (dc) driven semiconductor-gas discharge system is designed to study nonlinear behavior and period doubling features experimentally. Numerical analysis and theoretical studies show that the period doubling is expected in the discharge
¹
. The plasma is generated between two planar electrodes separated by a narrow gap: cathode is undoped Gallium Arsenide (GaAs) and anode is an IndiumTin Oxide (ITO) coated glass electrode. The GaAs is extensively studied in solid-state physics
²
, since it is a promising material with the properties of high carrier mobility, wide band sensitivity and large absorption coefficient. In this experimental setup, GaAs is preferred since it can be operated without the requirements of cyrocooling and remains in a linear regime. The plasma is obtained in 1mm gap using nitrogen gas at partial atmospheric pressure. Fluctuations observed in the discharge are investigated using plasma current (I), voltage (V) and optical emission from the plasma. These data sets are collected as long time series data, and are acquired numerous times under a parametric scan of applied voltage. At lower applied voltage, single frequency oscillations are present in the measured fluctuations. By increasing the applied voltage, first harmonic frequency generation takes place and the fundamental frequency shifts towards higher frequency values. By increasing the voltage at even higher values, a period doubling is observed in the fluctuations. Harmonics of the fundamental frequency and their sub-harmonic oscillations appear in the discharge. We are currently observing 10 kHz to 100 kHz fluctuation measurements indicating that the system is nonlinear in nature. Manifestation of the period doubling in the discharge is studied in detail.