|关键词||激波管 等离子体 Langmuir 静电探针 微波透射技术|
In the study of the transmission mechanism of electromagnetic wave in plasma related to the "blackout" phenomenonin Φ800mm high temperature and low density shock tube in the Institute of Mechanics, CAS, under conditions of low density and strong shock, the experimental time at region 2 behind shock is significantly reduced due to the non-equilibrium processes such as gas dissociation and ionization. At the same time, the boundary layer effect leads to both the attenuation of the shock wave and the acceleration of the contact surface towards the shock front. Therefore, the experimental time at region 2 will further be reduced. These two effects lead to the reduction of the experimental observation time and the non-equilibrium state of test gas at region 2, resulting in the instability of data observation and the difficulty of data analysis.
In this dissertation, instead of air，two kinds of Ar+Air mixtures (95%Ar+5%Air and 90%Ar+10%Air) were used as the experimental test gas in the driven section in the Φ800mm high temperature and low density shock tube. Since Argon does not dissociate and is difficult to ionize, the density ratio across shock is reduced, thereby increasing the length of region 2 and the experimental time at region 2. The main research contents and conclusions in this dissertation are summarized as follows:
(1) The experimental time at region 2 of ideal flow in the Φ800mm shock tube was calculated and the factors that influence experimental times in the shock tube were analyzed. The Saha equation was used to calculate the equilibrium electron density behind the shock wave of Ar+Air mixtures. At the experimental Mach number range of 7-11,the equilibrium electron density increases first and then decreases with the increasing Mach number. Meanwhile, the equilibrium electron density increases with the initial pressure and the ratio of air to Argon.
(2) In the Φ800mm high temperature and low density shock tube, the electron density behind the shock wave of Ar+Air mixtures was measured with both the Langmuir electrostatic probe method and the microwave transmission attenuation method. The electron density behind the shock wave increases with the increasing Mach number, and reaches the order of 1012~1013cm-3. The electron densities obtained with the two measurement methods are consistent at the initial pressures of 0.4torr and 0.8torr. The electron densities measured with the microwave transmission attenuation method are higher than those with the electrostatic probe at the initial pressure of 0.2torr.
(3) In the Φ800mm high temperature and low density shock tube, the experimental times at region 2 were measured with the Langmuir electrostatic probe. The experimental times at region 2 of Ar and Air mixtures are about 300~800μs, and the lengths of region 2 are about 1 meter. At the same time, the probe signal showed that the gases at 2 region reached ionization equilibrium. Under the conditions of the same electron density and collision frequency, the experimental times at region 2 of Ar and Air mixtures are about 5 times than the pure air.
(4) When the 95%Ar+5%Air and 90%Ar+10%Air mixtures are used as the test gas in the Φ800mm high temperature and low density shock tube for electromagnetic wave transmission experiments, the experimental times at region 2 are about 5 times than the pure air and the equilibrium state of test gases at region 2 are reached. Under the condition of low collision frequency, the same electron density and collision frequency as the pure air can be obtained by using Ar+Air mixtures. Under the condition of high collision frequency, however, the same electron density as the pure air can be obtained by using Ar+Air mixtures, but the collision frequency value is less than the pure air.
|张勇勇. 氩气和空气混合气高温电离特性激波管研究[D]. 北京. 中国科学院大学,2018.|
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