Examination of Efficiency Dependence on Deceleration Voltage in a Traveling Wave Direct Energy Converter Simulator

As for traveling wave direct energy converter (TWDEC), which was expected to be an efficient energy recovery device for fast protons created in D-3He fusion, efficiency dependence on deceleration voltage was examined. A decelerator was designed based on the theory of constant deceleration scheme, in which ions were trapped in a decelerated traveling wave potential, and a simulation experiment was performed. Over a certain deceleration voltage, deceleration efficiency degraded when deceleration voltage increased, which was contradictive to the theory. Numerical orbit calculation revealed that the trapped ion exhibited the expected bouncing motion for a very short period and exited the decelerator just after acceleration phase and this caused the degradation of the deceleration effect. In the design of the decelerator, bouncing motion as well as trapping should be considered.