Development of a Liquid-Fed Bismuth Lab6 Hollow Cathode for Hall Thrusters

Bismuth has attracted attention since the 1960s due to its high storage density ($\sim 9780 \mathrm{~kg} / \mathrm{m} 3$), large atomic mass (A=209 amu), and low ionization energy (7.3 eV) [1–3]. One significant drawback of bismuth, however, is its high evaporation temperature $\left(\sim 1000^{\circ} \mathrm{C}\right)$, which will consume a significant amount of power for reservoir and pipeline heating. Nonetheless, the lower melting temperature $\left(271.4^{\circ} \mathrm{C}\right)$ of bismuth provides a method to reduce heating power. Compared with thruster, the operating temperature of hollow cathode is higher and exceeds the evaporation temperature of bismuth under the corresponding pressure, making it more suitable for liquid feed without the involvement of vaporizers. The heat of cathode tube is sufficient to evaporate the liquid bismuth.