Crossed-microwave-beam air ionization laboratory experiments

Detailed laboratory measurements and theoretical modeling relevant to the production, geometrical description and decay of microwave-induced air ionization for an upper atmospheric RF reflecting layer are reported. It is found that breakdown thresholds are adequately predicted by fluid models and simplified scaling models with refinement by kinetic models being important at lower pressures. Repetitive pulse sustainment has been demonstrated to be straightforward with a commensurate reduction in sustainment power levels. However, establishment of a convenient breakdown geometry for specular RF reflections, other than a single layer in a crossed beam geometry, was not obtained. Detailed density decay measurements qualitatively support estimates of decay times and indicate ionization dwell times of tens of milliseconds. Chemistry studies indicate three N{sub x}O{sub x} species will be produced. Further study of these collateral reactions is required to establish whether adverse atmospheric consequences can result. However, large N{sub x}O{sub x} production does not appear as a concern for relatively small, low repetition rate, proof of concept atmospheric experiments. A realizable proof of concept experiment is found with simple optimization criteria which is corroborated by laboratory measurements and theoretical simulations. Tail-erosion appears as a potentially severe limitation in atmospheric experiments beyond the proof of concept level, more » suggesting use of multiple-beam systems. 20 refs., 18 figs. « less