Effects of seed electrons on the plasma bullet propagation

The effects of the seed electrons nseed of background gas of a plasma jet on the propagation of the plasma bullet are investigated. It is found out that the plasma bullet appears stable when the pulse repetition frequency is reduced from 10 kHz to 0.25 kHz. However, when the pulse frequency is further decreased to 0.2 kHz, the plasma bullet appears randomicity. Simulation results on the nseed for pulse frequency of 0.25 kHz immediately before the following pulse show that the nseed is on the order of 105 cm−3 near the nozzle, which is about five orders lower than the presumption of reported. Besides, the effect of the strong electric field in the detachment of O2− ions is investigated. It is found out that, whether the strong electric field considered or not in the detachment of O2− ions, there are no obvious differences of the spatial distribution of seed electrons nseed between them.