Shock wave dispersion in weakly ionized gas

Electrodeless microwave (MW) discharge in two straight, circular cylindrical resonant cavities in TE_1,1,1 and TM_0,1,2 modes were introduced to perform additional experimental studies on shock wave modification in non-equilibrium weakly ionized gases and to clarify the physical mechanisms of the shock wave modification process. The discharge was generated in 99.99% Ar at a gas pressure between 20 and 100 Torr and at a discharge power density less than 10.0 Watts/cm3. Power density used for operating the discharge was rather low in the present work, which was determined by evaluating the power loss inside the resonant cavity. It was found that the shock wave deflection signal amplitude was decreased while the shock wave local velocity was increased in the presence of the discharge. However, there was no apparent evidence of the multiple shock structure or the widening of the shock wave deflection signal, as observed in the d.c. glow discharge [3,5]. The shock wave always retained a more compact structure even in the case of strong dispersion in both the TE and the TM mode. The shock wave propagated faster through the discharge in the TE mode than in the TM mode. Discharge characteristics and local parameters such as gas temperature T _g, electron density N_e, local electric field E, and average power density, were determined by using the MW discharge generated from an Argon gas mixture that contains 95% Ar, 5% H₂, and traces of N₂. The gas temperature was evaluated by using the amplitude reduction technique and the emission spectroscopy of Nitrogen. The gas temperature distribution was flat in the central region of the cavity. By comparing the gas temperature calculated from the shock wave local velocity and from the amplitude reduction technique, the present work was sufficiently accurate to indicate that the thermal effect is dominant. The electron density was obtained from measured line shapes of hydrogen Balmer lines by using the gas temperature and the well-tested approximate formula for deconvolution of Stark and Doppler broadening. The local electric field inside the MW discharge was evaluated by using a simplified kinetic model. Dispersion of a shock wave in a MW discharge will most likely be applied in future technical solutions in aircraft design, or rocket shock wave modification systems. We hope that the present study will contribute to a better understanding of the physical mechanism leading to shock wave dispersion in weakly ionized gas.