Microwave Breakdown in High-Temperature Air

A review of investigations of microwave breakdown in high-temperature air reveals significant discrepancies between theoretical expectations and experimental observations. Experimental measurements obtained in shock-heated air are presented to confirm the temperature dependence of ionization frequency previously observed. The data are examined with regard to the nonequilibrium thermodynamic state of the gas behind the shock wave. An explanation is offered that attributes the temperature effect to the temperature dependence of the electron-molecule energy-transfer rate, and a method for modifying the conventional theory to take account of this is indicated. The relevance of these results to antenna breakdown on reentry vehicles is discussed.