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

摘要

OPERATING RF antennas in a vacuum presents severalnchallenges that are relevant to the ground testing of plasmanpropulsion systems such as the Helicon Double Layer Thrustern(HDLT) prototype. Antennas immersed in vacuum can come intoncontact with the plasma and, if one end of the antenna is grounded,ndirect currents flow from the plasma to ground. To the authors’nknowledge, these issues have not been investigated previously in thencontext of plasma propulsion. However, in asymmetric plasmandischarges, which are used in materials processing, the RF biasednsubstrate or electrodes are frequently immersed in the vacuum (andnplasma) and biased negatively via a dc blocking capacitor. Thisnenables the energies of the ions impinging the substrate to bencontrolled independently of the current to the substrate, which isnimportant for various processing techniques [1]. Immersed RFnantennas have also been employed in plasma immersion ionnimplantation ( ) devices [2].