Studies on the Axial Position of the Decelerator in Traveling Wave Direct Energy Converter

In D-He-3 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. (C) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research