Microwave breakdown on a symmetrically excited conical reentry vehicle

Predictions and measurements of microwave breakdown in air are compared for a conical reentry vehicle model with an overall length of approximately one wavelength. The vehicle is excited by means of a circumferential gap to form an asymmetric dipole with roll-symmetric radiation. Measurements performed in an evacuable chamber show breakdown occurring at either the nose tip or the feed gap, or simultaneously in both regions, depending upon the gas pressure. The electric fields are computed as functions of distance radially from the nose tip and normally from the feed gap by the use of moment methods. The breakdown calculation is based on a variational technique that can accommodate continuous wave or pulsed breakdown and can handle nonunifortuities in both gas properties and electric fields. Breakdown behavior is calculated at the nose tip and at the feed gap. Theory and experiment are shown to agree within the estimated accuracy of the experiment.