Increased neutron yield observed in indirect-drive double-shell experiments using high-energy x-ray preheat at the Shenguang laser facility

In traditional indirect-drive double-shell inertial confinement fusion, high-energy x-ray preheat has always been identified as a major source of degrading implosion performance. However, a significant increase of the neutron yield is observed in ignition-like double-shell implosion experiments performed at Shenguang laser facility by intentionally utilizing high-energy x-ray preheat, mostly from the $M$-band. Permission of more $M$-band x-ray absorption inside the inner shell can both significantly mitigate the mix between the fuel and shell with a more stable Awtood number at the fuel-shell interface during the shell deceleration and slightly improve the symmetry of the imploding shell with a high entropy state of the shell, and the contribution outweighs the potential detriment to destabilizing the inner shell from the $M$-band preheat, which is consistent with radiation-hydrodynamics simulations and theoretical analysis. This novel understanding of the favorable impact of high-energy x-ray preheat on double-shell implosion could facilitate to achieve volumetric ignition and burn with high-Z shells.