In direct-drive inertial confinement fusion (ICF), the lasers with the wavelength of 1053 nm act on the target after second or third harmonic generation because shorter wavelengths have higher energy coupling efficiency between the laser and the target, and the technology for generating the laser with the wavelength of 351 nm is relatively mature1-4. However, previous studies and engineering designs have not considered the effect of laser wavelength on growth of ablative Rayleigh-Taylor instability (ARTI)5,6. As we know, in direct-drive ICF, hydrodynamic instability is usually inevitable due to the nonuniformity of the irradiation (such as laser imprint) and the nonuniformity of the target (such as target roughness). Additionally, the validity of ARTI growth theory at short laser wavelengths has not been verified.
To better suppress and understand ARTI, we use 2D radiation hydrodynamic simulation to investigate the influence of laser wavelength on ARTI growth. We adjust the intensity to maintain a constant kinetic energy of the implosion fluid, thereby obtaining the relative coupling efficiency under a given intensity benchmark. Subsequently, we employ lasers of varying wavelengths and corresponding intensities to act on targets. We find that extreme ultraviolet lasers with specific wavelength ranges can better control the growth of hydrodynamic instability, thereby significantly reducing the laser energy required for fusion ignition and achieving higher fusion energy gain. In comparison, the ARTI growth rates are larger for both wavelengths longer and shorter for which the longer wavelength is traditionally used in direct-drive ICF and the shorter, used in indirect-drive. What's more, we verify the validity of the ARTI growth theory at shorter wavelengths for the first time and analyze the effects that cause deviations. This study and its achievements are beneficial for better understanding of the ICF process and perfecting the theory of ARTI growth, thereby, provide a valuable and meaningful reference for future design of inertial confinement fusion engineering.
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