Inert-material effects on ignition criteria and hot-layer volume ignition in high-gain room-temperature solid-fuel ICF targets

This work investigates how inert constituents modify ignition conditions in inertial confinement fusion (ICF) and, using idealized one-dimensional simulations, the ignition dynamics of massive room-temperature solid-fuel targets. We consider an ADT mixture in which equimolar DT is diluted by an inert species of atomic number Za and ion-number fraction xa. Reduced analytical models show that the inert component narrows the self-sustaining temperature window by decreasing the DT reaction rate through the dilution factor (1−xa)2 while increasing bremsstrahlung losses through Z⋆3=Z¯,Z2¯. Consequently, the Post condition, generalized Lawson criterion, ICF hot-spot areal-density threshold, and minimum kinetic-energy requirement become more restrictive as xa and Za increase, apart from a limited low-concentration regime for high-Za species. The numerical study uses the radiation-hydrodynamics code MULTI-IFE to investigate massive Carbon-DT (CDT) implosions as idealized ignition cases. A Monte Carlo pulse search yields a one-dimensional CDT target with a thermonuclear gain of approximately 22 for a laser energy of 411 MJ and a fuel mass of 164 mg. Homothetic scaling identifies the combustion threshold and compares targets on either side. Above this threshold, simulations reveal ignition in a fuel layer between a cold, dense, weakly reactive gap above the hot spot and the shock wave. The layer is formed and compressed hydrodynamically, then undergoes local volumetric self-heating when its thermodynamic trajectory crosses a local ignition condition. A reduced hot-layer ignition model linking areal density and temperature is derived and compared with simulations. Igniting this hot layer can compress the hot spot and ignite the remaining fuel.