Inversion method of two-dimensional distribution of electron density in hypersonic model wake

Abstract

The ballistic target uses a two-stage light gas gun to launch the model into a hypersonic state, and the model forms a plasma wake when flying at a hypersonic speed in the target chamber. In order to obtain the radial two-dimensional distribution of transient plasma electron density in the wake of hypervelocity model, a seven-channel Ka-band microwave interferometer measuring system is developed. In the transceiver system, a transmitting antenna achieves the plane wave irradiation plasma, and a seven-port array antenna is used to receive plane waves which are passing through the plasma: the antenna beam can completely cover the radial range of the wake. The shortest response time of measuring system is 1 s, and electron density measurement range of the interferometer measuring system is 10<sup>11</sup>–10<sup>13</sup>/cm<sup>3</sup> . The plasma is often treated as layered medium in data processing of multichannel microwave interferometer. Taking into consideration the effect of refraction on the stratified interface in this work, the ray tracing (RT) method is used to establish the electromagnetic propagation model. Combined with the measurement data to construct the objective function, the genetic algorithm (GA) is used to invert the radial two-dimensional distribution of the electron density under different test conditions. The result shows good agreement with the numerical simulation under the same test state, which proves the the data processing method reliable. Then, the influence of the layered model on the calculation result is analyzed, which shows that the seven-layer model is suitable for the wake modeling under given experimental conditions, and thus maximizing the number of receiving channels and ensuring the accuracy. The RT method is used for the first time to achieve the two-dimensional distribution of electron density in the wake of hypervelocity projectile, and some rules of two-dimensional electron density distribution of the hypersonic model under given experimental conditions are realized.