ELECTRON ATTACHMENT IN SEEDED AIR FOR HYPERVELOCITY MHD ACCELERATOR PROPULSION WIND TUNNEL APPLICATIONS

Magnetohydrodynamics (MHD) has been identified as one of only two technologies that is capable of producing hypervelocity, high flight dynamic pressure, clean-air wind tunnel simulations for development of air-breathing propulsion systems. An extensive study of MHD accelerator performance for application to a large-scale testing and evaluation (T&E) facilities was conducted for National Aeronautics and Space Administration (NASA). Several analytical and experimental studies were conducted during this project, including an analytical parametric and optimization study evaluating the performance of MHD accelerators for this application. An alkali metal seed material is generally used in MHD accelerators to enhance ionization. However, when ionization occurs in air, some of the free electrons can be lost through attachment to oxygen species, forming negative ions and reducing the electrical conductivity. Under some circumstances, this can be detrimental to MHD performance since MHD performance depends strongly on the electrical conductivity of the working gas. The results of an analysis to evaluate the effect of electron attachment to oxygen on the electrical conductivity of seeded air and on the performance of MHD accelerators is presented in this paper.