Nonlinear Waves in a Finite Plasma

我们从理论和实验上研究了无磁场的有限等离子体中的非线性现象，得到了以下结果。我们研究了边界反射的离子声波的特性。主要结果如下：(I)在负偏置网格周围形成的鞘层中的粒子对波的反射起着重要的作用。(Ii)当离子声波溶液传播到鞘层时，反射的波分别成为大振幅的解和小振幅的离子声波。(Iii)利用DP机进行了离子波的反射实验。发现离子在反射中起着重要的作用，对于束流模式，反射系数不依赖于频率，对于离子声波，反射系数是频率的递减函数。我们尝试用外场抑制离子-离子不稳定性，发现抑制不稳定性的阈值依赖于外场的频率。观察到了电子束-等离子体不稳定性的模式跃迁：从束流模式到束流朗缪尔模式。我们成功地激发了束流模式的次谐振子。倍频可以激发亚谐振子，这些结果将有助于等离子体中非线性现象的发展。

We have studied both theoretically and experimentally nonlinear phenomena in a finite plasma without magnetic fields, and the following results are obtained.1. We examined the characteristics of the ion acoustic wave reflected by the boundary. The main results are as follows :(i) The particles trapped in the sheath formed around a negatively biased grid play an important role in the wave reflection.(ii) When an ion acoustic solution propagates into the sheath, the reflected wave becomes a solution for the large amplitude, and an ion acoustic wave for the small amplitude, respectively.(iii) The experiments on the reflection of ion waves are carried out using the DP machine. It is found that ions play an important role in the reflection, and the reflection coefficient does not depend on the frequency for the beam modes and it is decreasing function of frequency for the ion acousti wave.2. We attempted the suppression of the ion-ion instability by an external field and found that the threshold value at which the instability is suppressed depends on the frequency of the external field.3. We observed the mode transition of the electron beam-plasma instability : from the beam mode to the beam Langmuir mode.4. We succeeded in the excitation of the subharmonics of the beam mode. The subharmonics may be excited by period doubling.These results will contribute to the development of nonlinear phenomena in plasmas.