Lanthanum hexaboride (${\mathrm{LaB}}_6$) hollow cathodes have demonstrated a capability for long life operation, which is critical to many space exploration missions. Thermal characterization of ${\mathrm{LaB}}_6$ hollow cathodes has revealed lower than expected electron emitter temperatures when the cathode reaches a steady state. This phenomenon is observed at discharge currents ranging from 5 to 35 A and xenon mass flow rates of 5–25 SCCM in cathodes with three different orifice diameters. Thus, the currently accepted value of the work function for polycrystalline ${\mathrm{LaB}}_6$, 2.67 eV, does not describe well the emission characteristics of ${\mathrm{LaB}}_6$ hollow cathodes operating with internal gas discharges at a steady state. We use empirically measured temperatures combined with a model of the hollow cathode emitter and xenon discharge to estimate the value of the work function, yielding a value ranging from 2.1 to 2.44 eV. This lower work function value implies that ${\mathrm{LaB}}_6$ hollow cathodes are expected to have even longer lifetimes than previously anticipated, further establishing them as a more suited alternative to other conventional cathode technologies for the task of long duration travel. Direct measurements of the work function as a function of depth on a hollow cathode emitter using x-ray photoelectron spectroscopy and ion beam milling indicate that the work function decreases with depth. We postulate several mechanisms that could explain the observed work function enhancement. Altogether, our results have important implications to the design, study approach, and operation of ${\mathrm{LaB}}_6$ cathodes and potentially other cathodes with hollow configuration. Finally, our work opens the question of why the work function is reduced upon interaction with Xe plasma.

中文翻译：

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多晶 LaB6 空心阴极的动态热行为

六硼化镧（${\mathrm{实验室}}_6$) 空心阴极已证明具有长寿命运行的能力，这对许多太空探索任务至关重要。热特性${\mathrm{实验室}}_6$当阴极达到稳定状态时，空心阴极显示出低于预期的电子发射器温度。在 5 至 35 A 的放电电流和 5 至 25 SCCM 的氙气质量流量下，在具有三种不同孔口直径的阴极中观察到这种现象。因此，目前公认的多晶功函数值${\mathrm{实验室}}_6$, 2.67 eV，不能很好地描述发射特性 ${\mathrm{实验室}}_6$空心阴极在稳定状态下内部气体放电。我们使用经验测量的温度结合空心阴极发射器和氙气放电的模型来估计功函数的值，产生的值范围为 2.1 到 2.44 eV。这个较低的功函数值意味着${\mathrm{实验室}}_6$预计空心阴极的寿命将比之前预期的更长，这进一步确立了它们作为其他传统阴极技术更适合用于长时旅行任务的替代品。使用 X 射线光电子能谱和离子束铣削对空心阴极发射器上作为深度函数的功函数的直接测量表明，功函数随深度降低。我们假设了几种可以解释观察到的功函数增强的机制。总之，我们的结果对设计、研究方法和操作具有重要意义。${\mathrm{实验室}}_6$阴极和潜在的其他具有中空结构的阴极。最后，我们的工作提出了为什么在与氙等离子体相互作用时功函数会降低的问题。