The problem of the interaction of a shock wave with plasma is a part of the fundamental problems that are directly related, in particular, with the development of modern aeronautics and space technology. An experimental study of the interaction of a shock wave with low temperature plasma of gas discharge was started in Ioffe Physico-Technical Institute at the end of the last century.
In this paper, investigation of shock wave interaction with plasma was conducted on the setup comprising a gas discharge and shock tube. Measurements were carried out in air at a pressure of 4 kPa.
In the working chamber (diameter of 300 mm and a height of 400 mm) stationary glow discharge was generated between two conical electrodes positioned vertically over a distance of 100 mm from each other. External source provides voltage on the electrodes 650 V and discharge current of 1.1 A. The discharge has a shape of body of revolution, with the increasing cross-section upward. The diameter of the cross section in which the measurements were made, is about 80 mm. Concentration of charged particles in the plasma of the glow discharge, as shown by the measurements, was ~ 1011 cm3 which corresponds to the degree of ionization ~ 10-6, the temperature of havy particals is 1200 - 1300 K. The gas surrounding the discharge has a room temperature.
The shock wave was formed in the electric shock tube with an inner diameter of 30 mm and a length of 700 mm and travels perpendicular to the axis of the discharge. Outlet section of the shock tube is located at a distance of 100 mm from the axis of the discharge. The shock wave velocity at the tube outlet corresponds to Mach 3. On the opposite side of plasma volume is located double electric probe. Double electric probe conducted studies of the distribution of concentration of charged particles behind the shock front in a gas discharge plasma in the presence of an electric field and without the electric field.
Double electric probe consists of two parallel platinum electrodes diameter 0.5 mm and length of 10 mm, distant at 8 mm away from each other and oriented parallel to the axis of discharge.
The experiments were performed at two operating modes: at first mode interaction shock wave with plasma occurs in the presence of an electric field between the electrodes, in the second case the interaction of a shock wave with plasma occurs without electric field.
The travel time of the shock wave through the plasma volume is approximately 0.5 ms. To implement the second mode shunting the discharge gap performed during not more than 10-5 s, motion of the shock wave through the plasma begins with time interval 1.5 ms after the shunting.
The results of the measurements led to the following conclusions.
Gas-dynamic plasma-shock wave interaction with electric field, results in deformation of the region occupied by the plasma, leads to rapid influx of external cold gas in the interelectrode space. The electric field holds the charged particles in the interelectrode space and prevents their entrainment by the shock wave. At the absence of an electric field, the plasma drifts over a distance comparable to the transverse size of the gas discharge. In this case, the effect of abnormal increase in the electrical conductivity of the medium was found. We have no now the satisfactory explanation of this effect.
