Operating Radio Frequency Antennas Immersed in Vacuum: Implications for Ground-Testing Plasma Thrusters

摘要

I. IntroductionrnOPERATING RF antennas in a vacuum presents several challenges that are relevant to the ground testing of plasma propulsion systems such as the Helicon Double Layer Thruster (HDLT) prototype. Antennas immersed in vacuum can come into contact with the plasma and, if one end of the antenna is grounded, direct currents flow from the plasma to ground. To the authors' knowledge, these issues have not been investigated previously in the context of plasma propulsion. However, in asymmetric plasma discharges, which are used in materials processing, the RF biased substrate or electrodes are frequently immersed in the vacuum (and plasma) and biased negatively via a dc blocking capacitor. This enables the energies of the ions impinging the substrate to be controlled independently of the current to the substrate, which is important for various processing techniques [1]. Immersed RF antennas have also been employed in plasma immersion ion implantation (PI3) devices [2].