Abstract
To investigate the behavior of plasma generated in the shock tube, microwave reflectometry is proposed to extract the permittivity $\epsilon _{r}$ of plasma. To remove the influence of parasitic reflections caused by the surroundings, a calibration process is introduced and the unknown calibration coefficients are determined by utilizing microwave interferometry as the reference technique. The shock tube is modeled as a three-layered medium to calculate the reflection coefficient. A time-dependent reconstruction algorithm is applied and theoretically validated to eliminate the multiple solutions in the inverse problem. By comparing the permittivities extracted with microwave reflectometry and interferometry, the effects of plasma diffusion are demonstrated with a modified analytical model in the beginning time region of experiments. In addition, the nonuniform flow in the generated plasma located near the end time region is also observed. The determination of the effective time region for electron density $N_{e}$ and collision frequency $v_{e}$ extraction is discussed as well. Finally, the differences between microwave reflectometry and interferometry in terms of averaged $N_{e}$ $1{\times }10^{17} m^{-3}$ and averaged $v_{e}$ $1.5{\times }10^{9} s^{-1}$ are investigated in the effective time region
Highlights
During the atmosphere reentry of a spacecraft, the plasma or ionized gas layer surrounding the spacecraft forms a sheath [1]–[4] that intensively affects the radio frequency communication between spacecraft and ground station
Li et al.: Microwave Reflectometry to Characterize Time-Varying Plasma Generated in Shock Tube reflection in the monostatic setup leads to a significant deviation that certainly affects the characterization results
Li et al.: Microwave Reflectometry to Characterize Time-Varying Plasma Generated in Shock Tube TABLE 1
Summary
During the atmosphere reentry of a spacecraft, the plasma or ionized gas layer surrounding the spacecraft forms a sheath [1]–[4] that intensively affects the radio frequency communication between spacecraft and ground station. L. Li et al.: Microwave Reflectometry to Characterize Time-Varying Plasma Generated in Shock Tube. Microwave reflectometry operating at a single frequency is proposed to extract the permittivity of plasma generated in the shock tube. C. THE TIME-DEPENDENT RECONSTRUCTION ALGORITHM FOR THE EXTRACTION OF PERMITTIVITY As the dimensions and dielectric properties of shock tube are already known, r is expressed as a function of r , and r can be determined by matching the measured reflection coefficient rm with r ( r ).
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