Measurement of transient electron density of a pulsed microwave argon plasma jet via microwave Rayleigh scattering

It is critical to measure the electron density and its transient variation in an atmospheric-pressure plasma jet. In the present study, the transient electron density of a pulsed microwave argon plasma jet at atmospheric gas pressure is measured using a homemade microwave Rayleigh scattering device. First, the high-speed photographs of the plasma jet are captured by an intensified charge-coupled device camera. Then, the radius and length of the plasma jet are determined from the high-speed photographs. Finally, the temporal scattering signal measurement is performed and the time-varying electron density is obtained. The electron density increases to a peak value of 4.55 × 1020 m−3 at 45 μs. Then, it decays monotonically until it reaches the detection limit. It is worth pointing out that there is no input microwave power after 40 μs, but the electron density still presents a sharp peak. This indicates that there is a change in the ionization process that further induces a variation in the discharge morphology. In addition, an electromagnetic simulation model is modulated to simulate the scattered electric field distributions produced by two different scatterers (air and plasma). The simulation results indicate that a higher electron density of scatterer leads to the acquisition of more intense scattering signals, which indicate that the microwave scattering process is similar to that associated with dipole radiation. These results verify the accuracy of the transient electron density measured using microwave Rayleigh scattering.