Experimental study of the nonlinear dynamics of a harmonically forced double layer

A plasma double layer is created by an anode grid in the target chamber of the double plasma device. When the separation grid of the double plasma dev ice is floating, very coherent plasma oscillations, triggered by the unstab le double layer, are observed. The oscillations have a frequency close to 1 kHz and very high amplitude. The amplitude and frequency of these oscillat ions depend on the anode bias and on the discharge Voltage of the plasma so urce. The anode characteristics exhibit hysteresis. When plasma oscillation s are coupled to the external oscillator, by modulating the floating potent ial of the separation grid, synchronization and periodic pulling are observ ed. When external oscillations are tuned to the second, third or fourth har monics, period doubling bifurcations are observed, when the external amplit ude is increased. At synchronization with the third and fourth harmonics, o scillations become chaotic after the first period doubling bifurcation. The correlation dimension of the underlying attractor is found to be fractal b etween 2.3 and 2.8, with a positive largest Lyapunov exponent.