Study of the doubly-ionized argon in the RF-driven plasma source

Argon is the most common gas used in plasma sources, including RF-driven plasma thrusters [1]. Ion production and plasma dynamics have been studied extensively in the past using plasma probes, retarding potential analyzers and spectroscopic methods which assume that the plasma is composed of singly-ionized atoms and electrons. However, a semi-empirical model [2] predicts growing Ar²⁺ population in the discharge with the increase of power density. The spatial distribution and dynamics of double ions are studied in high-power helicon discharges using a combination of EUV vacuum and high-resolution Doppler spectroscopy methods [3].