Radiography of direct drive double shell targets with hard x-rays generated by a short pulse laser

Direct drive implosion experiments of a cone inserted double shell target were carried out at the SG-II Upgrade laser facility. Time-resolved radiographic images of the targets were obtained with hard x-rays generated by irradiating a short-pulse laser on a metal microwire embedded in a low-Z substrate. Since the SG-II Upgrade laser facility is mainly designed for indirect drive, it will lead to high direct illumination nonuniformity of the target surface. 2D nonuniformities of the inner shell were clearly shown by these images. Simple analytical estimations and radiation hydrodynamic simulations were also carried out, and calculations were consistent with the experimental results. Besides, areal density of the target was evaluated using the radiography images. Furthermore, it was found that the nanosecond laser had effects on hard x-ray generation, and the possibilities for improving the experimental results are discussed, which will be helpful to better understand the hydrodynamics of double shell or even triple shell target implosions. (paper)