Investigation of discharge voltage characteristics of a lanthanum hexaboride heaterless hollow cathode

This study investigated the discharge voltage characteristics of an argon-fed lanthanum hexaboride heaterless hollow cathode to assess the influence of flow rate, discharge current, background pressure, and applied magnetic field strength. Decreasing the flow rate from 15 to 3 sccm led to a considerable increase in discharge voltage and peak-to-peak oscillation, particularly for flow rates below 5 sccm. Subsequently, variation in discharge current was tested at 4–7 A; this test revealed that the discharge voltage decreases from 53 to 48 V as the discharge current increases, while the peak-to-peak oscillation increases by approximately 2 V with the rise in discharge current. At high background pressures (8.1 × 10⁻⁴ Torr), the discharge voltage decreased by 15 V, and the peak-to-peak oscillation was maintained at 5 V. Furthermore, the spectral analysis of the discharge voltage indicated the occurrence of high-energy oscillations at 10–500 kHz owing to ionization instability. The discharge voltage decreased when the strength of an externally applied axial magnetic field increased from 0 to 118 G. Such a result can be attributed to increased ionization (caused by the applied magnetic field) in the emitter and cathode-keeper region, thereby decreasing sheath potential on the emitter surface.