Caviton Induced Double Layr-Like Potential Structures in Plasmas

在高功率微波等离子体系统中，实验研究了在由强烈的局域电子等离子体振荡产生的密度腔的位置产生双层状势结构的新机制——空腔。空腔是被困在密度腔内的局域电子等离子体波，它是由与局域波本身相关的质动势产生的。众所周知，在处于强朗缪尔湍流状态的等离子体中，空腔起着重要的作用。在这项研究中，利用短微波脉冲（f=3GHz，峰值功率=60kW，脉冲持续时间-1 mus）的共振吸收，在非均匀等离子体中产生空腔。在共振层（n-10^<11>cm^<-3>）处，可以产生与空腔形成相关的双层状势结构。当空腔形成时，在空腔的位置出现负势阱。发现这种电位的下降排斥背景电子，导致低电位区域的膨胀发展成双层状的电位结构。离子分布函数的测量表明，在上述过程中产生了一个离子相空间空穴。数据表明，离子相空间空穴在空腔位置附近产生，并以近似于离子声速的速度移动。这个离子相空间空穴的作用将在我们未来的实验中进一步研究。注入微波束后，空腔诱导的双层势结构的高、低势区电位差在0.5 μ m时达到饱和，其值与入射微波脉冲的峰值功率成正比。一维细胞内粒子的计算机模拟结果与实验结果一致。进一步的模拟工作正在进行中。

A new mechanism for generating double layr-like potential structures at the location of a density cavity created by intense, localized electron plasma oscillation--caviton-- is experimentally investigated in a high-power microwave-plasma system.1. Cavitons are localized electron plasma waves trapped inside density cavities which are generated by the ponderomotive forces associated with the localized waves themselves. It has been known that cavitons play an important role in plasmas which are in the state of strong Langmuir turbulence.2. In this investigation, cavitons are created in an inhomogeneous plasma by utilizing the resonance absorption of a short microwave pulse (f=3GHz, peak power=60kW,pulse duration-1 mus). It has been found that a double layr-like potential structure can be generated associated with the formation of a caviton at the resonance layr (n-10^<11>cm^<-3>).3. As the caviton is formed, a negative potential well appears at the location of the caviton. It has been found that this potential dip repels background electrons, causing the expansion of the low potential region to develop into a double layr-like potential structure.4. The measurements of the ion distribution function suggest that an ion phase-space hole is generated during the above process. Data indicate that the ion phase-space hole is created near the location of the caviton and moves at approximately the ion acoustic speed. The role of this ion phase-space hole will be examined further in our future experiments.5. The potential difference between the high and low potential regions of the caviton induced double layr-like potential structure saturates at-0.5 mus after the injection of the microwave beam, and it's value is proportional to the peak power of the incident microwave pulse.6. The results of one-dimensional particle-in-cell computer simulations are consistent with our experimental results. Further simulation work is under way.