Studies on Self-excited Oscillation of Traveling Wave Direct Energy Converter by Simulation Experiment

为实现核聚变发电的商业化，研究了行波直接能量转换器(TWDEC)的自激振荡问题。本课题针对TWDEC的自激振荡模拟工作，进行了实验和数值研究。在实验研究中，采用环形铁心和可变电容布置了TWDEC模拟器减速器的外部传输电路，并对调制束流产生的自激信号进行了检测。信号对调制电压的相对增益为-75dB，低于以往的实验结果。为了检验这种差异，特别是噪声分量的评估，在保持射频环境不变的情况下，解决了从流束到减速器的堤坝问题。信号是在不同条件下测量的，在这些条件下，通过估计没有束流的噪声分量来消除噪声分量。结果表明，由于依赖于等离子体的产生，存在着难以控制的不同工作模式。等离子体源的改进是必要的。在数值研究方面，扩展了先前构造的数值程序来检验TWDEC的工作。一种是对外部电路工作的补充，在简单的线性传输电路的情况下得到了适当的结果。其次，将空间结构扩展到二维空间。这使得可以根据电极几何形状的不同以及粒子与电极的碰撞来评估电场的差异。另一个扩展是由于粒子带电而引入的场。然而，在结果中，在光束的入口处进行了巨大的场。这是因为计算模型不充分。由于粒子带电产生的电场对于精确评估自激振荡是必不可少的，这一点计划加以改进。

The research project treats self-oscillation of traveling wave direct energy converter (TWDEC), which is desirable for commercialization of electric power generation by nuclear fusion. The project aims at simulating work of self-excited oscillation of TWDEC, and experimental and numerical studies were performed.In the experimental study, an external transmission circuit of decelerator of a TWDEC simulator was arranged by toroidal core and variable capacitor, and self-excited signals produced by modulated beam flowing were examined. Relative gain of the signal to modulation voltage was -75dB, which was lower than the previous experiments. To examine the difference, especially, evaluation of noise components, a dam for flowing beam to the decelerator was settled with keeping the RF environment the same. The signal was measured for various conditions in which the noise components were eliminated by estimating from those without beam flowing. The results revealed the existence of different working modes which was hard to control as it depended on plasma production. The improvement of plasma source is necessary.As for numerical study, a numerical code constructed previously was extended to examine the work of TWDEC. One is supplement of works of external circuit, and the suitable results were obtained in the case of a simple linear transmission circuit. In the next, the spatial structure was extended into two dimension. This enabled to evaluate difference of electric field according to difference of geometry of electrodes, and collision of particle to the electrodes. The other extension is introduction of field due to charge of particles. In the results, however, huge field was performed at the entrance of the beam. This was because of insufficient model of calculation. As field due to charge of particles is essential for precise evaluation of self-excited oscillation, this point is planned to be improved.