Speculary reflected laser light component and its influence on indirect-drive fusion capsules

The laser light components specularly reflected by the inner wall of an X-ray confining cavity was experimentally investigated by means of time-resolved X-ray imaging and shock wave measurements. The experiments were made for two different cavity shapes (circular and decagonal cylinders) to confirm their geometrical effect on the reflected light. Time-resolved X-ray images for a gold coated surrogate sphere at the cavity center show that the reflected light shines strongly on the sphere. Shock wave measurements show that about one-third of the drive pressure of a shock wave propagating through an aluminum foil placed at the cavity center is due to the reflected light for the experimental conditions adopted in this study. The results were compared with calculations involving a simple illumination code and corresponded with the calculations. The code infers that the reflected light is intense enough to cause initial imprints on a capsule in the vacuum cavities conventionally used for indirect-drive implosions.