We report the first experimental observation of chaotic behavior and period doubling in a pulsed plasma discharge sensitive to initial and boundary conditions. The Feigenbaum constants have been measured experimentally in one of the observed chaotic discharge routes.PACS numbers: 52.25. Gj, 05.45.+b, 52.35.Ra The subject of order and chaos in dissipative physical systems has been the subject of intense research in recent years. 1 " 4 Universal characteristics of chaos such as period doubling have been observed both in numerical simulations 5 and in experiments. 6 " 9 In particular, experiments in optical bistability and nonlinear optics, 6 hydrodynamic flow systems, 7 nonlinear oscillator and electrical circuits, 8 the Belousov-Zhabotinskii reaction, 9 etc., have all demonstrated the transition from order to chaos in such systems and the various routes to chaos.In this Letter, we would like to present, to the best of our knowledge, the first experiment in plasmas which exhibits chaotic behavior and period doubling. In particular, two chaotic discharge routes, including period multiplication, have been observed in the presence of a large, unstable negative plasma potential. By following the period-doubling sequence, experimental measurements of the Feigenbaum constants have been obtained. 5 The study of chaotic behavior in plasma discharges enables us to understand the reproducibility of plasma conditions in laboratory plasma experiments and their sensitive dependence on initial conditions. The experiments were performed in a large, unmagnetized plasma device (d -L -1.8 m, where d and L are the diameter and length of the device). 10 The plasma discharge is initiated from ionization of background neutral gas, typically argon gas, by primary electrons emitted from hot tungsten filaments. The plasma discharge is pulsed as a negative voltage bias between the filaments and the chamber wall, the discharge voltage V D , is pulsed periodically to extract primary electrons into the chamber. The chamber wall is at ground potential. Both the discharge pulse duration and the discharge repetition rate are variable with a typical pulse duration of 2-3 ms and a repetition rate of 40-50 Hz. The wall of the device is aligned with small permanent magnets that serve to impede primary electrons emitted from the filaments from hitting the chamber wall, and thus help to create a denser and more uniform plasma in the device. H As will be discussed later, the fact that the mobility of the primary electrons is reduced by the permanent magnets causes the formation of negative plasma potential during the plasma discharge. 12,13 Typical plasma parameters are rto^lO 9 -10 10 cm" 3 , N n^= 10 12 -10 13 cm ~3, and T e -2-3 eV. «o and N n are the plasma electron density and neutral density, respectively.The rate of plasma formation is determined by the rate of neutral ionization by primary electrons and the plasma decay time: dnjdt = n p N n {av p ) -njr.(1) n p and v p are the primary electron density and velocity, respectively, a is the ion...
The transition to chaos through intermittency has been observed in a steady-state plasma system. Results from real-time signals, spectral analysis, and constructed Poincare sections are used to confirm the existence of intermittency. Low-frequency l//-type noise is also observed during the onset of chaos.
Large-scale density modification was optimally achieved by electromagnetic waves whose frequency matched the plasma frequency at a height where the ionospheric density profile was flat. The density in this region was dramatically clamped during the morning when it normally increases from solar ionization. Electromagnetic wave propagation in the polar magnetic field geometry and strongly resonantly enhanced electrostatic fields over a large region of constant density account for the observation.PACS 52.25.Sw, 52.70.Gw We report the observation of large-scale modification of the polar ionosphere by electromagnetic (EM) waves at modest power density (0.1
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