Transient pressure effects in a pinch-compressed cylindrical metallic conductor.

For a cylindrical aluminum conductor, 0.2 cm in diameter and loaded by a current pulse from an overdamped discharge with an initial current rate of 490 kA/Mys, dynamic pinch compression and temperature rise have been calculated. The numerical solution for the azimuthal distribution of the pinch pressure, obtained by applying Picard's method of successive iteration, consists of the superposition of a quasi-stationary and a transient term. In the very initial phase of pinching a steep, narrow pressure pulse is created below the surface of the wire which converges at the center, thereby broadening in width, growing in strength, and increasing in propagation velocity. Already in the early stage of current flow at about 0.4 mys, well before reaching maximum current and pinch pressure, the quasi-stationary term becomes dominant. Then the conductor is compressed quite homogeneously with the exception of a narrow shell below the surface where maximum pressure gradients exist. For applications on dynamic materials research various experimental aspects of dynamic pinch compression and possible high-speed methods of sample diagnostics are reviewed.