Nonequilibrium radio frequency discharge plasma effect on conical shock wave:: M=2.5 flow

An experimental study of shock modification in an M = 2.5 supersonic flow of nonequilibrium plasma over a cone is discussed. The experiments are conducted in a nonequilibrium plasma supersonic wind tunnel. Recent experiments at the Ohio State University using a supersonic plasma flow over a quasi-two-dimensional wedge showed that an oblique shock can be considerably weakened by a transverse rf discharge plasma. The previously observed shock weakening, however, has been found consistent with a temperature rise in the boundary layers heated by the discharge. In the present study, the boundary-layer effects on the shock wave are reduced by placing an entire cone model into a supersonic inviscid core flow. The electron density in the supersonic plasma flow in the test section is measured using microwave attenuation. The ionization fraction in the discharge is in the same range as in the previous plasma shock experiments, up to n(e)/N = (1.2-3.0) X 10(-7). The results do not show any detectable shock weakening by the plasma. This strongly suggests that the previously observed shock weakening and dispersion in nonequilibrium plasmas are entirely due to thermal effects.