The feasibility study of heavy ion-driven reactor-size double-shell target in inertial confinement fusion

In recent years, the design of double-shell targets has been investigated as an alternative approach to achieving ignition conditions at the National Ignition Facility. In this paper, we have numerically examined the parametric optimization of a double-shell spherical target in inertial confinement fusion driven by ion beams. Here, we have employed two deuterium-tritium (DT) fuel layers separated by low-density gas or foam. It facilitates the piston pressure on the central fuel at maximum compression, initiating the ignition there. The ignition and burn stage dynamics were studied numerically by the Deira-4 code, a one-dimensional, three-temperature code designed for heavy ion-driven fusion. We have assumed that Bi-209 ions were illuminated symmetrically on the outer surface of a reactor-sized target. The input power has a peak value of 175 TW and individual ion energies of 7 GeV (similar to 33.5 MeV/u). To attain proper hydrodynamics efficiency at the implosion stage, geometric optimization was performed on the two outermost layers, including the tamper and absorber layers. It was found that the released thermonuclear energy is sensitive to the outer DT fuel mass. More energetic ions result in a lower energy gain due to preheating. Finally, we compared the double-shell target with/without the density gradient effect. It was shown that the double-shell target with density gradient may manage the Rayleigh-Taylor instability during the implosion stage. In this case, the implosion velocity is reduced to 224 km/s. At stagnation, the ignition condition does not purely follow a volume ignition regime, and the average ion temperature over the fuel region arrives at 2.7 keV, and the optimized energy gain of 169 is achieved.