X-ray flash photography of spark discharges in layers of liquid

When W.Schaaffs developed X-ray flash machines after World War II at Siemens in Germany, he used spark discharges in layers of liquid between solid plates as a nonmilitary test object W. Schaaffs discovered the so-called compression ring in 1947 during his experiments with spark discharges. This paper discusses the construction of triode X-ray flash tubes, the evolution of the discharge into the vacuum of the tube and the tubes characteristics depending on this mechanism. It will be found, that the special geometry of the tube shows an important influence on the discharge. The electrons will need a long time to reach the anode while positive ions are strongly accelerated near the anode. The duration of the x-ray flash is limited by the size and speed of the evaporated material from the anode. In the second part of this paper the spark discharge in a layer of liquid between solid plates is described. With this spark discharge it is possible to produce a shock wave in the liquid which finally moves to a vortex. Faster waves propagate in the plates at both sides of the layer. The plate waves induce a low pressure region in front of the ring and there it is possible to detect cavitation bubbles. The spatial arrangement of these bubbles in the layer of liquid between the solid plates depends on the excitation strength of the pulse waves in the plates. Their amplitude depends on the distance to the spark. Thus on a single X-ray flash picture it is possible to study the distribution of the cavitation bubbles for different excitation power. The spatial arrangement of the bubbles can show a periodic structure or it might be chaotic. X-ray flash experiments of this phenomenon will be presented. A model for the birth of cavitation bubbles will be shown. It explains how seeds of phase changes can be distributed in space under special conditions. This idea might also be valid for controlling the crystal growth.