Analysis of RF thrusters with TOPICA and a global system-level model

Recent advances in plasma-based propulsion systems have led to the development of electromagnetic (RF) generation and acceleration systems, capable of providing highly controllable and wide-ranging exhaust velocities, and potentially enabling a wide range of missions from KWs to MWs levels. In this paper we report the results obtained by the development of TOPICA 3D code for modelling the RF antennas in space thrusters. TOPICA is a self-consistent code, which was originally conceived for plasma facing antennas operating in tokamaks, and recently extended to handle cylindrically symmetric plasmas. TOPICA has been validated by analyzing the ICRH unit of a three-stage helicon plasma thruster composed of a helicon plasma source, a confining magnetic field structure enclosing a plasma heating section, and a magnetic nozzle. The simulations are aimed at improving the penetration and coupling of the RF waves with the magnetized plasma in order to enhance plasma heating and axial thrust. The results of TOPICA has been used as input of a system-level modelling. This combination enabled to optimize the design parameters: antenna shape, generators, matching circuits, as well as the ensuing required power, mass and other physical quantities, including magnetic field for confinement. We have divided the study into two different and linked parts: 1) RF system modelling, which provides an "interface" between the RF power generation and the power deposition into the plasma and relies on the TOPICA code, and 2) plasma device modelling of the sub-systems and of their connection, which yields the global, system-level description of the engine)