Plasma Characterization of an RF-Driven Magnetron Thruster

We present a characterization of an RF-driven magnetron discharge for potential space propulsion applications. The device is capacitively coupled in crossed E×B fields, with concentric magnets to create a strong radial field near the powered electrode. A downstream magnet supports a magnetic nozzle expansion. RF frequencies are swept from 50-120 MHz producing rectification in the partially magnetized regime. We characterize plasma properties using Langmuir probes and retarding potential analyzers across various operating conditions. Key findings include regimes of strong positive floating potentials (10-40V) at high background pressures suggesting polarization drift/collision-induced electron loss and positive space charge accumulation. At reduced pressures, ionization and collisions drop, electron confinement in the radial B region increases, and rectification effects are reduced, confirmed by a transition in floating potential from positive to negative values when below 130 mTorr. We examine resonance modes within the RF frequency range, speculating on the excitation of lower hybrid waves that are commonly observed in DC magnetrons at similar 40-60MHz frequencies. The lower hybrid frequency potentially contributes to enhanced plasma-wave coupling and improved thruster performance. This work provides fundamental insights into RF magnetron thruster physics, RF sheath rectification mechanisms, and wave-plasma interactions relevant for space propulsion applications.