Beneficial and detrimental aspects of M-band preheating on one-dimensional ICF implosions

In indirect drive inertial confinement fusion, M-band radiation alters the implosion dynamics by preheating the capsule. It is well known that M-band preheat exacerbates hydrodynamic instabilities at the fuel–ablator interface, causing degradation from the ideal one-dimensional (1D) implosion performance. However, preheating also affects the 1D performance itself, about which there are few systematic investigations to date. We found it to be not a trivial issue, as 1D performance may be reduced or enhanced considerably by M-band preheat depending on the detailed target design. In this study, based on a large number of 1D capsule-only simulations of DT-layered targets, we identified two main mechanisms by which M-band preheat may degrade 1D performance: (1) If a significant portion of the remaining ablator is compressed to high density along with the DT fuel when the target stagnates, preheated ablator leads to reduced compression. (2) In other situations, M-band preheat reduces the opacity of the remaining ablator, making it inadequate to protect the DT fuel from being heated by the Planckian radiation. Otherwise, when both the degrading mechanisms are effectively avoided, M-band preheat tends to enhance 1D capsule performance. Especially, DT-layered targets designed for down-scaled non-igniting implosion experiments would very likely fall in this regime of 1D enhancement.