Ion current collection by double flush-mounted probe in intermediate-pressure plasmas

A double flush-mounted probe method is proposed to analyze the characteristics of intermediate-pressure plasmas (10–100 Pa) by a sheath criterion. The analytical model mainly focuses on the effect of the ion drift velocity in the sheath edge and then provides a correction factor for the measured ion-collection current. The reduction of the ion current is attributed to ion–neutral collisions leading to the modified Bohm velocity. To validate this method, the ion density is calculated and compared with that measured by two types of cylindrical probes, and the results agree well with the data measured by other probes. On the basis of this work, the double flush-mounted probe can be adopted to diagnose plasma parameters accurately, without a reference electrode, in collisional and certain complex plasma environments, such as the reentry plasma sheath.