Efficiency enhancement of thermal energy conversion and utilization is one of the critical issues in space exploitation and exploration. With the full consideration of material characteristics, space charge effect and Joule dissipation, thermionic conversion models were established based on Richardson's law. The models were coupled with a thermo-mechanical simulation code, developing the comprehensive simulation capability of the whole thermionic power system for the first time. This tool was validated by experiment data, and then used to conduct a parametric study for a space nuclear reactor named TOPAZ-II. The parametric study figured out key operating features and influencing factors of thermionic conversion. Based on the parametric study, the optimization for utilization efficiency enhancement was undertaken from the view of thermionic conversion performance improvement, electric circuit design optimization and radiation loss reduction. It was found that the conversion efficiency could be promoted from about 10% to over 15% and the utilization efficiency was increased from about 6% to over 8.5% by use of innovative materials or geometry designs, while ensure thermal parameters within the normal operating range. However, results also indicate that some efficiency enhancement strategies proposed without the consideration of the whole system in previous studies might to be useless.

提高热能转化和利用的效率是空间开发和探索中的关键问题之一。在充分考虑材料特性，空间电荷效应和焦耳耗散的基础上，根据理查森定律建立了热电子转换模型。这些模型与热机械仿真代码结合在一起，首次开发了整个热电子电源系统的综合仿真功能。该工具已通过实验数据验证，然后用于进行名为TOPAZ-II的空间核反应堆的参数研究。该参数研究指出了热离子转化的关键操作特征和影响因素。根据参数研究，从提高热电子转换性能，优化电路设计和减少辐射损失的角度出发，对提高利用效率进行了优化。发现通过使用创新的材料或几何设计，转换效率可以从大约10％提升到15％以上，利用效率从大约6％提高到8.5％以上，同时确保热参数在正常工作范围内。但是，结果还表明，在先前的研究中提出的一些未考虑整个系统的效率提高策略可能是无用的。发现通过使用创新的材料或几何设计，转换效率可以从大约10％提升到15％以上，利用效率从大约6％提高到8.5％以上，同时确保热参数在正常工作范围内。但是，结果还表明，在先前的研究中提出的一些未考虑整个系统的效率提高策略可能是无用的。发现通过使用创新的材料或几何设计，转换效率可以从大约10％提升到15％以上，利用效率从大约6％提高到8.5％以上，同时确保热参数在正常工作范围内。但是，结果还表明，在先前的研究中提出的一些未考虑整个系统的效率提高策略可能是无用的。