Electric field and plasma emission responses in a low pressure positive column discharge exposed to a low Mach number shock wave

Low Mach number shock waves propagating through a low pressure, nonequilibr ium positive column gas discharge have been observed to experience dispersi on and velocity changes. It is shown that these effects depend on discharge polarity. Optical and electrical measurements are described which show fur ther polarity-dependent effects in discharge light emission and changes in electrical properties. Using two types of probes, electrical measurements w ere made of both the global changes in discharge voltage and current and ti me resolved local electric field changes. The measured behaviors of dischar ge and shock wave point to very localized triple or quadruple layer electri c sheaths connected with the propagating shock wave, which provide local en hanced ionization at the shock front which can sustain the discharge, at le ast during the short shock propagation time. The postulated density gradien t driven large local recirculation current in the potential minimum near th is sheath [H. S. Maciel and J. E. Allen, J. Plasma Phys. 42, 321 (1989)] at the shock front will result in large local Joule heating, causing the shoc k dispersion and shock speed increase, which have been observed in many exp eriments. Thus, the conclusion is that the effects are due to highly locali zed gas heating which is facilitated by the response of the positive column plasma to the acoustic shock. (C) 2000 American Institute of Physics. [S10 70-664X(00)02509-X].