Effect of high power microwave injection on tropospheric freon

Abstract

High power microwave injection into the troposphere is a feasible approach to the decomposition of chlorofluorocarbon (CFC). However, in existing researches, there are only basic principles which lack quantitative tests. Hence, in this article we introduce the finite-difference time-domain method to quantitatively analyze the decomposition of CFC under high power pulses. We first investigate the principal chemical reactions of CFC decomposition induced by high power microwave injection and find that dissociation attachment is a dominant process of the microwave discharge decomposition of CFC. We use an empirical formula to calculate the decomposition efficiency of CFC. The result shows that 20% of the initial content of CFC molecules will be dissociated over 100 microseconds where we assume the electron number density to be 1013 cm-3. Then according to Maxwell's equations and the current density equation, we adopt the finite difference time domain method to simulate the generation process of a large number of free electrons induced by injecting the high power microwaves into the troposphere. The ionized electron generated by the high power microwave in troposphere is in favor of CFC decomposition since the electron affinity of CFC is larger than dissociation energy of CFC molecules. The simulation results indicate that the number density of electrons grows up to 1017 cm-3 exponentially with the injection time and will grow faster at higher height (10 km) or by the larger field intensity. During the pulse, the higher electron energy corresponds to a smaller dissociative attachment coefficient. Thus, most of the CFC molecules are decomposed during the electron-decay phase. During the relaxation period, the electron energy will return to the natural state within 0.01 ns. The number density of electrons decreases slower than the electron energy and it will take 1 ms to reach the natural state. From the results we can also see that the decay rates of the electron energy and number density decrease with the increase of the height. In this paper, two methods of calculating the CFC decomposition rate are utilized. One method is from the chemical reaction and the other method is based on an empirical formula which is mentioned before. It is shown that the results of these two methods present obvious consistency. The simulation results demonstrate that the CFC decomposition rate will increase with larger microwave intensity or higher frequency and can approach up to 6%. In conclusion, this study gives the quantitative analyses of the CFC decomposition induced by high power microwave injection in the troposphere for the first time.