Traveling Wave Direct Energy Converter (TWDEC) was proposed to apply to D-3 He nuclear fusion power generation system, and is studied as an energy source of a spacecraft recently where miniaturization of the device is important. Not only the modulation process, but also the deceleration process are important to treat a trade-off between device size and efficiency. The suitable scheme of the constant deceleration, of which experimental investigation was insufficient, was studied. Based on the theory of the scheme, a decelerator for simulation experiments was assembled and deceleration experiments were performed. The efficiency of the highest record in simulation experiments and a fair agreement with the theory were obtained. The problem was also clarified that the improvement of the modulation process was necessary.
Traveling wave direct energy converter (TWDEC) was proposed as an efficient energy recovery device for fast protons produced by D-3 He fusion reaction. The application of TWDEC to fusion propulsion system was also studied, and its significant subject was miniaturization of the device. In TWDEC, there is a trade-off between device size and efficiency, and an employment of a decelerator of constant deceleration scheme is promising to realize miniaturization. The paper experimentally examines one of the working characteristics of the constant deceleration scheme by using a relative phase control method called active decelerator. The results of the experiment and corresponding numerical orbit calculation are consistent with the theory of the constant deceleration scheme.
In D-3 He fusion, most of fusion energy is carried by created protons as kinetic energy, so direct energy conversion can be applied. A traveling wave direct energy converter was proposed as an energy recovering system for these protons, which was composed of a modulator and a decelerator. The axial position of the decelerator is one of the important device parameters for both energy conversion efficiency and device size. The best position for conversion efficiency was considered to be the bunching position at which proton density is the highest, but it was not examined well. In this study, we investigated the dependence of deceleration efficiency on the axial position of the decelerator by using simulation experiments and numerical calculations. The results show that the bunching position is not necessarily the optimum one for conversion efficiency.
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