Precursor electrons formation before strong shock wave.

A series of probe measurements of low-temperature plasma parameters ahead of the front of the incident shock wave was carried out using a double-diaphragm shock tube DDST-M of the Institute of Mechanics of Moscow State University. Such investigations are needed for determining the electron concentration in front of the shock wave. This characteristic is important for the safety of the spacecraft flight since it's directly affects to communication problems during the descent and is necessary for adequate description of kinetic processes behind the shock wave. Nitrogen, oxygen, air, and argon were used as working gases. The results obtained make it possible to describe the processes of the photoelectric effect and photoionization of gas particles due to the hard radiation of a shock-heated medium, to evaluate the effect of these processes on the change in the probe potential, and to measure the electron concentration. The probe measurements were synchronized with the registration of the light flux, which was carried out using an avalanche photodiode and a 9-frame video camera located at the end of the shock tube. Data from the camera and piezoelectric sensors record the dynamics of the opening of the diaphragm, as well as the process of formation of a shock wave in the gas under study. • Electron emission due to the photoelectric effect. • Photoionization of the gas ahead of the shock front. • Estimation of electron concentration from the probe measurement. [ABSTRACT FROM AUTHOR]