INVESTIGATION OF PRECURSOR IONIZATION IN FRONT OF THE SHOCK WAVES OF HYPERSONIC PROJECTILES
GM DEFENSE RESEARCH LABS SANTA BARBARA CA
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An experimental attempt was made to measure the precursor electron density as a function of distaoce ahead of the shock front of hypersonic projectiles in a ballistic range. The electron density just preceding the shock front was measured as a function of projectile velocity and of ambient pressure. For velocities up to 6,700 msec and pressures up to 30 mm Hg the measured density of electrons in the vicinity of the shock front is of the order of 10 to the 9th power e cubic cm. The maximum electron density of the precursor ionization increases almost exponentially with velocity. At a fixed pressure, the electron density increases about 30 times for an increase of velocity from 5,300 to 6,700 msec 18,000-22,000 ftsec. The electron density also increases with pressure, but this variation is not so explicit. An additional experiment showed that, at least in the considered region of velocities from 5,300 to 6,700 msec, photo-ionization is the dominant mechanism and electron diffusion plays only a secondary role.
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