371 / 2019-02-28 11:23:37

Observation of the Tin ejecta entering into foam through high-energy X-ray radiograpy using high-intensity short-pulse laser

jetting,;spallation,;mixing,;instability

全体主题 > High Pressure Physics and Materials Science

Micron-scale fragment ejection (ejecta) of metals is a kind of surface dynamic fragmentation phenomenon upon laser shock loading. The study of ejecta is crucial in many fields, such as inertial confinement fusion and pyrotechnics. Due to the particular advantages of laser experiments, a lot of ejecta study by strong laser-induced shock loading have been conducted in recent years, including micro-spallation and micro-jetting. The shapes, size and mass of the particles can be obtained via static soft recovery technique with foam. However, the stagnation and succedent mixing of the ejecta with the foam could not be deduced by this technique. To study the mixing between the ejecta and foam, a radiography experiment has been performed by using the X-ray generated through irradiation of picosecond laser on the golden wire. This radiography technique not only has high spatial resolution but also has high temporal resolution. Two kind of mixing experiments have been designed and conducted. In the first one, the rear surface of the tin sample is flat and in the second one, the rear surface is machined with sinusoidal pertrubations .
The mixing of the ejecta entering into the foam has been observed by the X-ray radiography and analyzed with the determined areal density. The experimental results of the flat tin sample is similar to that of the results in vaccum case, suggesting that the micro-spallation particles has not underwent a secondary fragmentation upon collision with the foam. For the tin sample with initial perturbations, micro-jetting was generated like the spike in the Richtmyer-Meshkov (RM) instability experiments, as well as the bubble due to mutual penetration between the heavy and light medium. Later, curving density structure around the spike tip emerged as a result of nonlinear and asymmetrical growth of the spike and bubble. Furthermore, the growth rate of the spike and bubble with different foam density was deduced and compared.