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

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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.