Characterisation of plasma thrusters for micro-satellites

The concept of radio frequency (RF) ambipolar thruster has gained significant interest in the electric propulsion sector over the last twenty years. The design of these devices, which lacks plasma-contacting electrodes, makes them durable and adaptable, ideal for use in space. However, despite their seemingly straightforward structure, the fundamental physics are intricate and not completely comprehended. Thus, ongoing research is crucial to improve their efficiency and allow them to rival other propulsion technologies. This thesis intends to explore how different operating conditions influence the performance of RF thrusters through both numerical and experimental approaches. The first phase of research investigated facility influences—particularly how background gas pressure affects plasma expansion within the magnetic nozzle. A combined global model and 2D3V fully kinetic particle-in-cell simulation were employed to evaluate a laboratory prototype thruster operating on xenon at power levels between 60 and 150 W and background pressures ranging from high vacuum to 10⁻² Pa. The findings indicated a key electron temperature threshold of 8 eV in the near-plume area, beyond which performance deterioration became notable. These observations guided further studies on propellants (xenon, krypton, iodine). At low power (approximately 20 W), iodine's performance was similar to that of xenon; however, it produced 50% less thrust at power levels exceeding 40 W due to molecular breakdown and increased collisional losses. Although krypton was effective in converting thermal energy to kinetic energy, it yielded the lowest thrust. An experimental campaign covering power ranges of 100 to 400 W revealed notable alterations in plasma behaviour, potentially indicating a transition between E–H modes. Simulated results aligned well with measured data, refining the assessment of source efficiency and associated losses.