Characterization of H2 plasma within RF-powered hollow cathode discharge equipped with hybrid multicusp magnetic field under varying inner-ring magnetic strength

This study investigates hydrogen plasma behavior in an RF-powered hollow cathode discharge system equipped with hybrid multicusp magnetic fields featuring varied inner-ring magnetic strengths. Two configurations—configuration A (moderate strength) and configuration B (enhanced strength)—were examined at hydrogen gas pressures of 0.7, 1, and 3 Pa. Plasma characteristics including magnetic field distribution, optical emission, discharge voltage, plasma density, and spatial uniformity were analyzed across three reactor regions: R1 (inner groove), R2 (transition zone), and R3 (downstream expansion). To evaluate performance more comprehensively, plasma uniformity factor (PUF) and relative plasma uniformity factor were introduced, integrating density and uniformity metrics. Configuration B exhibited superior plasma confinement at low pressures, achieving a 121% increase in plasma density and a 144% improvement in PUF in R3 at 0.7 Pa compared to configuration A. In contrast, at 1 Pa, configuration A provided 13% higher plasma density and higher PUF (11% more) in R2, despite both configurations sharing similar uniformity. These findings highlight the critical influence of inner-ring magnetic strength on confinement dynamics and establish PUF as robust, application-oriented metrics for optimizing plasma systems under low-pressure conditions.