Hydrodynamic Assessment of Direct Drive Inertial Confinement Fusion with Mixed $2ω-3ω$ Lasers

Abstract

Ablation with mixed $2ω$--$3ω$ lasers is investigated as a possible drive strategy for balancing drive efficiency and ablative stabilization in direct-drive inertial confinement fusion. One-dimensional radiation-hydrodynamic simulations are performed for planar CH targets using the FLASH code [B. Fryxell et al, The Astrophysical Journal Supplement Series \textbf{131}, 273 (2000)]. The total target-incident laser intensity is varied from 100 to $1600~\mathrm{TW}/\mathrm{cm}^{2}$, and the $3ω$ laser intensity fraction is scanned from 0 to 100\%. Thick-target simulations are used to determine quasi-steady ablation-pressure scalings, while thin-foil simulations are used to characterize the acceleration stage and to evaluate the linear ablative Rayleigh--Taylor instability (RTI) gain using a Takabe-type model. The simulations show that adding a $3ω$ component to a $2ω$-dominated drive increases the effective ablation pressure, enhances the ablation velocity, and reduces the maximum linear RTI gain. Within the present one-dimensional hydrodynamic model, the mixed drive also reduces the target-incident energy required to accelerate the foil to $300~\mathrm{km}/\mathrm{s}$, especially at high intensity. This improvement is attributed to the deeper penetration of $3ω$ light, which deposits energy closer to the dense ablation region and enhances conductive heat transport toward the ablation front. These results suggest that mixed-wavelength drive can recover much of the favorable hydrodynamic performance of $3ω$ irradiation while retaining part of the energy-accessibility advantage of $2ω$ operation, providing an additional design space of freedom for direct-drive target optimization.