A study on asymmetric electrodes for pulsed plasma thrusters

There has recently been a significant increase in interest in small satellites in the kilogram weight range. Unfortunately, while the miniaturization of electronic systems has enabled these small satellites to have significant technological capabilities, there is still no propulsion system readily available for these small scales. More mature systems such as ion thrusters and Hall thrusters have been found to exhibit considerable losses when scaled down in size. The pulsed plasma thruster (PPT) may be a possible solution to the lack of a suitable micropropulsion system. PPTs are a structurally simple form of electric propulsion with a simplicity that lends itself well to scalability for small satellites. They have typically been used with symmetric electrode designs, with the historical assumption being that a slug of plasma is accelerated downstream between the electrodes by the self-induced magnetic field of the thruster. However, recent results have suggested that an asymmetric configuration can result in greater performance and efficiency. Here, we examine an asymmetric electrode configuration with the anode being shorter than the cathode. We show that the light emission from an asymmetric configuration is significantly greater than that from a symmetric configuration. Narrowband filters isolating light emission from C⁺ ions and molecular C2 also indicate significant light emission from the same band structure emitted from the anode, suggesting that significant collisions and recombination may be occurring within the plasma plume. High-speed imagery shows that the band is accelerated at a velocity significantly greater than the neutral gas diffusion velocity, further suggesting that neutral C2 emissions from the band must occur from the recombination of ions.