霍爾推進器做為電能推進器的一種，具有非常高的推力功率比，被世界各國廣泛的應用於衛星的軌道變換、高度維持和深空探索，如BUSEK公司的BHT系列、ESA的PPS-1350和俄羅斯的SPT系列。霍爾推進器的運作需要一穩定電子源提供足夠的電子來離子化燃料氣體和中和被加速的離子束，這使得中空陰極作為一電子源被應用於霍爾推進器上。傳統的中空陰極由陰極管、發射體、保持器和加熱器組成。加熱器被用於加熱發射體以達到陰極的工作溫度，讓發射體發射出電子。但多次的溫度變化過程會造成加熱器材料的熱疲乏，導致加熱器的損壞和短路。這個問題嚴重的影響了陰極的壽命，往往發射體還未蒸發殆盡，加熱器就已經損壞。無加熱器中空陰極的概念因此被提出，透過大流量和高電壓誘發的電弧放電來加熱發射體不僅避免了加熱器損壞的問題也帶來許多好處，包括重量減輕達到更緊湊的設計、減少能量需求和降低電源單元複雜度。
陰極的運作情況在文獻中被分為點模式和羽流模式。點模式為穩定運作的情況，外觀上為一明亮電漿球出現於保持器出口處。羽流模式為陰極不穩定運作的情況，外觀為大範圍電漿充滿陰極和陽極之間。羽流模式下放電電壓上升，電壓和電流大幅度振盪並產生高能粒子。高能粒子的產生對保持器和陰極的孔徑侵蝕增強，造成陰極的性能和壽命降低。針對陰極的模式轉換，多種以放電電流和電壓振盪幅度為測量值的半經驗公式被提出用以評估陰極的模式轉換。
本研究利用陽極放電壓和保持器浮動電壓的峰對峰值大於5伏特作為陰極發生模式轉換進入羽流模式的標準，對我們設計的陰極進行性能評估。在流量低於5 sccm時，放電電壓出現大幅振盪，說明陰極進入羽流模式。放電電流範圍4安培到7安培在流量 7 sccm下被測試，但低於振盪標準的峰對峰值說明運作仍然維持在點模式。陰極在兩個不同的背景壓力條件(8.1×10^(-4),3×10^(-4) torr)被測試以評估背景壓力對陰極性能的影響。結果顯示過高的背景壓力造成模式轉消失而無法利用電壓振盪標準來找出陰極的最佳工作流量和放電電流。軸向磁場的施加造成陽極放電電壓下降，推測原因為磁場降低電子的跨場傳輸能力，使得陽極接收電流的有效表面積增加。

Hall-effect thrusters, as a type of electric propulsion system, offer an exceptionally high thrust-to-power ratio, making them widely utilized in various space applications by countries around the world. They are commonly employed for satellite orbit changes, altitude maintenance, and deep space exploration. Examples include BUSEK's BHT series, ESA's PPS-1350, and Russia's SPT series. The operation of Hall-effect thrusters relies on a stable electron source to ionize propellant gas and neutralize accelerated ion beams. This has led to the utilization of hollow cathodes as electron sources in Hall-effect thrusters. Traditional hollow cathodes consist of a cathode tube, an emitter, a keeper, and a heater. The heater is used to raise the emitter's temperature to the working level, promoting electron emission. However, frequent temperature fluctuations can cause thermal fatigue in the heater material, resulting in damage and short circuits. This issue significantly impacts the cathode's lifespan, often leading to heater failure before the emitter is fully evaporated. The concept of a heaterless hollow cathode has thus been proposed. This approach involves inducing arc discharge through high flow rates and high voltages to heat the emitter. This approach not only avoids the issues related to heater damage but also brings forth several advantages. These include reduced weight, enabling a more compact design, decreased energy requirements, and lowered complexity of the power supply unit.
The operation of the cathode is categorized in the literature as either the "spot mode" or the "plume mode." In the spot mode, stable operation is observed, characterized by the appearance of a bright plasma ball at the cathode exit plane. In the plume mode, the cathode operates unstably, resulting in a wide-range plasma filling the region between the cathode and anode. In the plume mode, the discharge voltage increases, and both voltage and current exhibit significant oscillations, accompanied by the generation of high-energy particles. The production of high-energy particles enhances the erosion of the apertures in the keeper and cathode, leading to a degradation in cathode performance and lifespan. For the cathode mode transition, several semi-empirical formulas based on measurements of discharge current and voltage oscillations have been proposed to assess the cathode mode transition. In this study, we utilized a criterion of the peak-to-peak values of the anode discharge voltage and the keeper floating voltage exceeding 5 volts to indicate the cathode mode transition into the plume mode. This criterion was employed to evaluate the performance of the cathode design. When the flow rate was below 5 sccm, significant voltage oscillations were observed in the discharge voltage, indicating the transition of the cathode into the plume mode. Discharge currents ranging from 4 amperes to 7 amperes were tested at a flow rate of 7 sccm. However, the peak-to-peak voltage oscillations remained below the defined threshold, indicating that the operation was still maintained in the spot mode. The cathode was tested under two different background pressure conditions ("8.1×" 〖"10" 〗^"-4" and "3×" 〖"10" 〗^"-4" torr) to assess the impact of background pressure on cathode performance. The results indicated that excessively high background pressure led to the disappearance of the mode transition, making it impossible to utilize the voltage oscillation criterion to determine the optimal operating flow rate and discharge current for the cathode. The application of axial magnetic field resulted in a decrease in anode discharge voltage. The speculate is that the magnetic field diminish the electron mobility to traverse fields, thereby increasing the effective surface area of anode.

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