Thermal coupling analysis of an embedded bismuth reservoir—C12A7 hollow cathode

Abstract

The unique configuration of an embedded bismuth hollow cathode leads to a strong coupling between its discharge parameters and both internal temperatures and the mass flow rates. To elucidate this thermal coupling and achieve stable, self-sustaining operation without external heating, this study proposes an innovative cathode design that integrates an embedded bismuth reservoir with a low-work function C12A7 insert. The evolution of the temperature field during both the heating start-up and self-sustaining stages was systematically investigated through a combination of experiments and numerical simulations. The proposed design successfully demonstrated stable, self-sustaining discharge at currents from 2 to 5 A without external heat. The combined experimental and simulation results reveal the dominant role of discharge current: it directly governs the hollow cathode temperature, which, in turn, regulates the bismuth saturation vapor pressure and mass flow rate. The sensitivity of the cathode thermal state to power variations was quantified in different operating modes. The change in cathode-lid temperature per unit change in discharge power was approximately 6.35 °C/W in the keeper discharge mode and 4.15 °C/W in the anode discharge mode. These values are an order of magnitude higher than the 0.48 °C/W sensitivity observed from mass flow rate variations at a fixed current, underscoring the primary thermal influence of discharge current.