Theoretical and experimental investigations on the interaction of wire-array Z-pinch with low density foam

The Z-pinch dynamic hohlraum is a possible concept to drive inertial confinement fusion, and has produced over 10¹¹ thermonuclear neutrons on the Z machine. A typical dynamic hohlraum is formed when a high speed wire-array Z-pinch plasma impacts on a low density converter. In this paper the interaction of the tungsten wire-array Z-pinch plasma with the low density foam on the 1.3MA “QiangGuang I” facility is investigated. Computational results show that this typical Z-pinch process can be divided into three stages: acceleration of the tungsten wire-array plasma, collision, and stagnation. The tungsten plasma is accelerated to a high speed by the J×B force and interacts weakly with the foam plasma in the first stage. Strong energy conversions take place in the second and third phases. When the high speed tungsten plasma impacts on the foam, the plasma is thermalized and a radial radiation peak is produced. Meanwhile, a shock wave is generated due to the collision, which plays the key role on the hohlraum formation. After the shock rebounds from the axis and meets the W/Foam boundary, the plasma stagnates and a second radial radiation peak appears. The collision and stagnation processes were observed and the two-peak radial radiation pulse was produced in experiments. Increasing the wire-array radius from 4mm to 6mm, the kinetic energy of the tungsten plasma is increased, which then causes a stronger thermalization and makes a higher first radiation peak. Experimental results also showed a higher ratio of the second peak to the first peak in the case of larger wire-array. If we just place a thin cover(C₈H₈) on the surface of the embedded foam converter, the first radiation peak will change less, because the acceleration of the tungsten plasma is not evidently affected by the cover. However, the second radial radiation peak decreases remarkably due to the heavier load and the corresponding weak compression.