Experimental Investigation of a Very-high-frequency ALFVEN Plasma Thruster at 120 MHz

Kurzfassung

Electrodeless plasma thrusters offer an attractive solution for future electric propulsion by eliminating electrode erosion while enabling efficient operation with multiple propellants. The Advanced-Linear Field Vector Excitation Network (ALFVEN) plasma thruster employs a resonantly excited antenna to optimize wave-plasma coupling, demonstrating excellent ignition capability, enhanced plasma generation, and effective ion acceleration. Previous experimental investigations at around 40 MHz revealed promising plasma characteristics [1, 2]; however, comprehensive performance analyses identified wall losses as the dominant mechanism limiting thrust efficiency, indicating that improved plasma confinement is essential for further performance enhancement. [3] To address these limitations, this work presents the first experimental investigation of the ALFVEN thruster operating at 120 MHz. Increasing the operating frequency enables a shorter discharge chamber, thereby reducing plasma-wall interaction at thruster downstream, while improving the matching between the RF frequency and the magnetic field distribution to enhance wave-plasma coupling. The objective of this work is to experimentally characterize the plasma plume and evaluate the propulsion performance of the newly developed 120 MHz ALFVEN thruster, establishing the first performance assessment of the high-frequency configuration. The thruster was experimentally characterized over a range of propellant mass flow rates. Plasma diagnostics, including Langmuir probes, retarding potential analyzers, and a Faraday probe array, were employed to characterize the plasma plume, while thrust performance was evaluated using a calibrated double-inverted counter-weight sub-mN thrust balance. The experimental results provide new insight into the plasma plume characteristics and propulsion performance of the 120 MHz ALFVEN thruster. The findings establish an experimental basis for the further optimization of resonant RF plasma thrusters and contribute to the development of compact, high-performance electrodeless electric propulsion systems.