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

本课题研究的是行波直接能量转换器（TWDEC）的自振荡问题，这是核聚变发电商业化所需要的。本课题旨在模拟TWDEC的自激振荡工作，并进行了实验和数值研究。在实验研究中，采用环形铁芯和可变电容布置TWDEC模拟器的减速机外传动电路，对调制波束流动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，比以往的实验要低。为了检验两者之间的差异，特别是噪声成分的评估，在保持射频环境相同的情况下，解决了一个流束到减速机的大坝。在各种条件下，通过对无波束流动的噪声分量进行估计，消除了噪声分量，对信号进行了测量。结果表明，存在不同的工作模式，由于其依赖于等离子体的产生，难以控制。等离子体源的改进是必要的。在数值研究方面，扩展了先前构建的数值代码来检验TWDEC的工作。一是补充外部电路的功，并在简单的线性传输电路中得到了合适的结果。其次，将空间结构扩展到二维空间。这样就可以根据电极的几何形状和粒子与电极的碰撞来计算电场的差异。另一种引种是由于粒子的电荷而引入场。结果表明，在光束的入口处产生了巨大的场。这是由于计算模型不足造成的。由于粒子的电荷场是精确评价自激振荡的必要条件，因此计划对这一点进行改进。

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.