Study of the Effect of Decrease in the Conductivity Ahead of a Shock Wave in a Glow-Discharge Plasma

Abstract

The electrical conductivity of a glow-discharge plasma ahead of a shock wave moving perpendicularly to the discharge axis has been investigated using a double electric probe. The obtained results have shown that the interaction of the shock wave with the glow-discharge plasma is accompanied by a change in its conductivity in the entire investigated volume simultaneously.Keywords: shock wave, glow discharge, plasma, double electric probe.Investigation of the interaction of various electric discharges with hypersonic fl ows of rarefi ed gases is a topical problem of modern plasma gasdynamics. Experiments and calculated-theoretical estimates [1-3] point to great prospects for using electric discharges in practice to control aerodynamic parameters of aircraft and to improve the effi ciency of propulsion systems.One line of these investigations is studying the interaction between shock waves and a glow discharge [3][4][5][6][7][8]. The infl uence of a shock wave on the plasma conductivity ahead of the front of this wave was reported even in the early studies [4,5]. However, for different reasons the accuracy of measurements in the indicated studies was low. In [4], the position of the shock wave relative to the probe signal was determined from the results of measurements performed in various experiments, which decreased the measurement accuracy. In [5], use was made of the microwave-interferometry method of low spatial resolution, as a result of which the accuracy of localization of the shock wave was low.The current study aims at investigating the effect of reduction in the conductivity of a glow-discharge plasma ahead of a shock wave by local measurements of its conductivity using a double electric probe with simultaneous recording of the position of the shock wave.Experiments were conducted on a plasma-gasdynamic setup whose diagram is shown in Fig. 1. In the working chamber of the setup of diameter 300 mm and height 400 mm in an air atmosphere at a pressure of 4 kPa, a steady-state gas discharge is set between two conic electrodes: anode 1 and cathode 2 disposed vertically at a distance of 100 mm from each other. Cathode 2 together with the working chamber is grounded, and the anode is connected to the external voltage source ensuring a discharge current of 1.1 A at an electrode voltage of 650 V. The discharge has the shape of a body of revolution with an increasing cross section in the direction to the cathode. A distinctive feature of this experimental setup is that in it, the discharge is implemented in the free space away from the chamber walls. The diameter of the cross section of the discharge midsection is less than 1/3 diameter of the working chamber.A shock wave is formed by electric-discharge shock tube 3 with an inside diameter of 30 mm and a length of 700 mm. The tube axis X intersects the discharge axis at a right angle in the middle of the discharge gap. Opposite the shock tube and coaxially with it is electric probe 4, which can move along the shock-tube axis. The coordinate X is reckoned from the c...