Influence of magnetic fields on ionization and spatial distribution characteristics of RF plasma

The radio frequency （RF） plasma thruster utilizes RF antennas to ionize gases and generate plasma. It is an electrodeless plasma thruster and is considered the preferred thruster solution for ultra-low-orbit air-breathing electric propulsion systems. The ionization and spatial distribution characteristics of the plasma directly impact the performance and operational stability of the thruster. In this study， magnetic fields were applied separately to the discharge chamber and nozzle of an RF plasma thruster. Plasma parameters under various conditions of RF power， gas type， and flow rate were experimentally measured using diagnostic tools such as Langmuir probes and Mach probes. The influence of magnetic fields on plasma discharge and spatial distribution characteristics was analyzed. The results indicate that the magnetic field in the discharge chamber enhances plasma ionization and exerts confinement effects on the plasma. The plasma velocity distribution at the outlet cross-section transforms from a “V” shaped distribution to a “W” shaped distribution， with an average Mach number reduction of approximately 46%. Similarly， the magnetic field in the nozzle also significantly confines the plasma， causing the electron number density distribution at the outlet cross-section to shift from a “V” shaped distribution to a “Λ” shaped distribution. The average Mach number at the edge decreases by about 7.6%， while the central Mach number increases by approximately 4.7%. These findings evidence that the magnetic field exhibits a certain aggregation effect on the movement and distribution of the plasma.