Characteristics Of The Hypervelocity Impact Generated Plasma

Space active is often suffered from hypervelocity impact by debris and meteoroids. Impactsfrom the millimeter-size debris are unavailable to avoid. Although the impacts will not leadto the fracture of the structure, the ionized gas generated by the impacts can disturb theexposed electronic equipment. This kind of multi-physical problem often contains complexmechanisms and comprehensive knowledge is needed for a better understanding of thephysical essence. And then the prediction and optimization of the protecting design can beconducted. For this purpose, depth theoretical analyses and numerical simulations of theplasma generated by hypervelocity impact were performed and this provided somebasements for optimizing protections from the plasma generated by hypervelocity impact.The innovative work of the paper has been listed as follows:(1) Based on the hypothesis of thermodynamic equilibrium between electrontemperature and gas temperature, an ionization equilibrium equation was derived todescribe the relationship between the ionization parameters and the temperature of real gas.Several hypervelocity impacts at different impact angles were numerically simulated byAUTODYN3D software and the gas temperature related to special internal energy anddensity given be numerical simulation was given by Thomas-Fermi equation. And then theelectron temperature and conductivity of the ionized gas at the fixed point were given bythe ionization equilibrium equation. The numerical predictions were compared with thecited experimental results and it was shown that the equilibrium model could be used topredict the ionization in hypervelocity impact but it was not enough in understanding theionization mechanisms. At the same time, the hypothesis was established under a certaincondition. Thus, some further discussions about the non-equilibrium between gastemperature and electron temperature were needed.(2) The thermodynamic non-equilibrium between gas temperature and electrontemperature was considered based on studies of thermodynamic equilibrium model ofimpact ionization. Electron temperature is considered as a function of gas temperature andelectron density and then the relationship between electron temperature, gas temperatureand electron density was derived as the thermodynamic condition. At the same time, theforward and backward reaction rates were equal for a balance reaction. By combining theenergy conservation in an isolated system, a group of equations were obtained to computethe characteristics of thermal ionized plasma. This group of equations was inserted into a self-developed SPH code to numerically simulate the plasma generated by hypervelocityimpact. The results of different impact velocities were compared with empirical formulasobtained by experiments in references. The numerical predictions fit to the empirical resultswell when the impact velocities are high while they are less than the empirical results whenthe impact velocities are relative low. For the low velocity is in a small range, generallyspeaking, the numerical predictions fit to the empirical results well.(3) Based on the conducted theoretical analyses and numerical simulations, the plasmacharges generated by different impact conditions were numerically simulated to discuss theinfluence of projecticle and target parameters. From the comparison between the numericalpredictions and empirical results of different velocity impacts, it is shown that the criticalvelocity of plasma generation that should exist is not considered in traditional empiricalformulas. Thus, the empirical formula is modified and the fitted parameters and criticalvelocity are given by numerical results. Numerical simulations of different impactconfigurations at the same velocity are conducted and effects to the plasma charges andcharge distribution are obtained. It is found that although the plasma charges and durationsare different, the integrals of charges with respect to time are similar. Then the influence oftarget parameters is numerically analyzed. It can be seen that target thickness has someeffects on the plasma charges but it becomes smaller when the target thickness is increased.When the projectile impacts on the double plates, the secondary impact of the debris cloudon the second plate generates much more charges than the first impact of the projectile onthe front plate. The thiner the front plate is and the larger the plate distance is, the morecharges the secondary impact will generate.(4) The single element ionization model was expanded to multi-element ionization andcombined with MMIC3D Euler fluid elastic-plastic code to simulate the plasma generatedby chemical explosion of explosive. The explosion was equivalently conversed tohypervelocity impact and then the generated electronic field and magnetic field werecomputed by the unchanged separated rate of charges. This numerical prediction wascompared with the cited experimental result and the reliability of the simulation wasverified. The developed multi-element model can be applied in hypervelocity impact.