Experiment on Chaos Control of Plasma Wave

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Recently chaotic phenomena have been observed in plasma. Here, we tried to control wave chaos in unstable systems strongly related to plasma transport. Since chaos controlling was theoretically derived by Ott, Grebogi and York, many methods of controlling chaos were proposed. Now Time-Delay- Autosynchronization method (TDAS) is considered to be most observable chaos controlling theory. We carried out the experiments on both the ion beam plasma instability and the current driven ion acoustic instability using the double plasma. Main results are as follows :(1) Ion beam plasma instabilityWhen an ion beam was injected into plasma, the system developed to turbulent state, where chaotic phenomena were not observed. When a grid was installed as a boundary condition, intermittent behaviors were observed on time series. As a result of chaos analysis, the system was confirmed to be chaotic state. During chaos we propagated a test wave in the plasma to examine the detailed behavior of the system. When the amplitude of the test wave was increased, amplitude oscillation was observed, that is, particle trapping play an important role in nonlinear saturation of the instability.2. Current driven ion acoustic instabilityWe tried to control observed chaos by perturbing feed back system in the plasma and found that when DC voltage as well as pulsed voltage is applied, intermittent chaos caused by the current driven ion acoustic instability is controllable. Furthermore, a hysteresis was seen on I-V curve of the grid. Furthermore, we applied the TDAS method to the present system and found that chaos controlling is also achieved.These results contribute to nonlinear plasma wave physics. Future works is to control chaos caused by the instability in magnetized plasmas such as drift mode or flute mode which is closely related to transport phenomena in high temperature plasmas.