Fixed‐Bias Probe Measurements Downstream of a Cesium‐Free Aluminum Plasma Grid System

This study employed a Langmuir probe to investigate charged particle production characteristics in a cesium‐free aluminum plasma grid (Al‐PG) system, wherein different electric voltage differences were applied across the control grid (CG), extraction grid (EX), and analyzer limiter plate (ALP). The probe enabled measurements of current at various spatial positions and bias voltages, providing direct insight into the behavior of electrons and ions under different electrode voltage conditions. The probe current results indicate that, when comparing different CG voltages, the probe current at V (positive ion extraction) is significantly larger than that at V (negative ion extraction). Probe measurements revealed that, when the ALP voltage is varied below the probe voltage, the probe current initially increases and subsequently decreases. Under the same conditions, the probe current gradually decreases with increasing EX voltage. When a negative voltage is applied to the probe, the floating potential corresponds to the probe current peak, and this peak shifts progressively with increasing EX voltage. These probe‐based observations clarify the influence of electrode potentials on charged particle transport and provide experimental guidance for optimizing cesium‐free negative ion sources for advanced plasma applications.