Experiment on Chaos Control of Plasma Wave

最近，人们在等离子体中观察到了混沌现象。在这里，我们试图控制与等离子体输运密切相关的不稳定系统中的波混沌。自Ott，Grebogi和York从理论上推导出混沌控制以来，人们提出了许多控制混沌的方法。时延自同步法(TDAS)被认为是目前最具观测性的混沌控制理论。利用双等离子体对离子束等离子体不稳定性和电流驱动离子声不稳定性进行了实验研究。主要结果如下：(1)离子束等离子体不稳定性当离子束注入等离子体时，系统发展到湍流状态，没有观察到混沌现象。当设置网格作为边界条件时，在时间序列上观察到间歇性行为。混沌分析的结果表明，该系统处于混沌状态。在混乱期间，我们在等离子体中传播了一个测试波，以检查系统的详细行为。当测试波的振幅增大时，观察到振幅振荡，即粒子俘获在不稳定性的非线性饱和中起重要作用。电流驱动离子声不稳定性我们试图通过扰动等离子体中的反馈系统来控制观测到的混沌，发现当施加直流电压和脉冲电压时，电流驱动离子声不稳定性引起的间歇性混沌是可控的。此外，在栅极的I-V曲线上还观察到了滞后现象。此外，我们将TDAS方法应用到目前的系统中，发现混沌也能被控制，这些结果有助于非线性等离子体波物理。未来的工作是控制磁化等离子体中的漂移模或槽模等与高温等离子体输运现象密切相关的不稳定性引起的混沌。

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.