Investigation on Direct Energy Conversion for Helium-3 Fuelled Nuclear Fusion

我们进行了行波直接能量转换器（TWDEC）的原理验证实验，该转换器是一种将D-^3-He燃料聚变反应堆产生的高能质子直接转化为电能的有效能量转换器。在TWDEC中，入射质子束经过速度调制，形成束状束，束状束通过射频波进行减速。行波电路中的感应电流为负载提供射频功率。我们使用几个keV的低能氦离子束，研究了束流与射频的调制和减速相互作用。实验装置由螺旋波离子源、调制器和减速器组成。在两个调制器栅格上施加7MHz的射频电场对氦离子束进行速度调制。减速器栅格（4到8）沿波束路径排列，每隔几厘米。它们连接到以匹配负载电阻端接的传输线。我们用相同的射频源驱动具有可变相位差的调制器的传输线。我们确认光束首先在调制器处进行速度调制，然后由于聚束而进行密度调制。比较了在输电线上有和没有驱动电压时光束的能量分布函数，发现在使用调制器和减速器射频后，光束的能量分布函数向能量较低的一侧偏移。当减速器RF相对于调制器RF的相位改变pi时，高能分量增加。这些结果表明，行波可以按照TWDEC的设想对离子束进行减速。梁的减速效率为14%，与仿真结果一致。

We perform a proof-of-principle experiment of a traveling wave direct energy converter (TWDEC), which was proposed as an efficient energy converter from high-energy protons produced by D-^3-He fueled fusion reactor directly into electricity. In TWDEC,the incident proton beam is velocity-modulated so as to form a bunched beam, which is to be decelerated by a traveling RF wave. The induced current in the traveling wave circuit provides RF power to the load.We use low-energy He-ion beam of a few keV and investigate the interaction of the beam with RF for modulation and deceleration. The experimental apparatus consists of a helicon-wave ion source, a modulator and a decelerator. The He-ion beam is velocity-modulated with RF electric fields at 7MHz applied to the two modulator grids. The decelerator grids (4 to 8) are aligned along the beam path with each separation of a few cm. They are connected to a transmission line terminated with a matched load resistor. We drive the transmission line by the same RF source for the modulator with a variable phase difference. We confirm that the beam is first velocity modulated at the modulator and then, density-modulated as a result of bunching. We compare the energy distribution functions of the beam with and without the driving voltage on the transmission line to find that the distribution function shifts toward lower energy side upon application of the modulator and decelerator RF.When the phase of the decelerator RF with respect to the modulator RF is changed by pi, the high energy component is increased. These results indicate that the ion beam can be decelerated by the traveling wave as planned in TWDEC concept. The efficiency of deceleration of the beam is measured to be 14%, which is consistent with simulation results.