Experimental verification of driving pressure enhancement and smoothing for hybrid driven inertial confinement fusion on a 100 kJ laser device

The research teams from the Laser Fusion Research Center of the Chinese Academy of Engineering Physics, the Beijing Institute of Applied Physics and Computational Mathematics, Peking University, and Shenzhen University of Technology reported experimental verification of the driving pressure enhancement and smoothing of hybrid driven inertial confinement fusion on a 100 kJ laser equipment.

The relevant research was published in the journal Nature Communications under the title of "Experimental confirmation of driving pressure boosting and smoothing for hybrid drive internal fusion at the 100 kJ laser facility".

The main purpose of laser driven inertial confinement fusion (ICF) is for fusion energy, defense applications, and high energy density physics research. The research on the ignition and combustion of deuterium tritium fuel has a history of decades, using two schemes: indirect drive (ID) and direct drive (DD), which use high-temperature ablation pressure to drive implosion.

Laser driven inertial confinement fusion (ICF) is an important way to convert laser energy into driving pressure implosion compressed fuel, ignite and burn under the support of fuel motion inertia, and obtain fusion energy.

Figure 1: Schematic diagram of ignition target, DD laser power (red) and ID laser conversion radiation temperature Tr (black).
Therefore, in laser driven inertial confinement fusion, improving and smoothing the driving pressure is a major challenge. Once such pressure is obtained, ignition targets can be designed to achieve stable implosion and ignition.

Figure 2: Schematic diagram of HD experiment.
The hybrid drive (HD) scheme proposed by the research team can provide ideal HD pressure, thereby achieving stable implosion and non stagnation ignition.

The article reports that a peak radiation temperature of 200 ± 6 eV was achieved in a semi cylindrical thermal cavity shrunk from the spherical thermal cavity of the designed ignition target in both hemispherical and planar ablation targets under an indirect driving (ID) laser energy of 43-50 kJ.

Figure 3: Radiation temperature and impact velocity.
Figure 4: one-dimensional simulation results under experimental parameters

And only using direct drive (DD) laser energy of 3.6-4.0 kJ and 1.8 ×  The laser intensity of 1015 W/cm2, the enhanced HD pressure of hemispherical and planar targets reached 3.8-4.0 and 3.5-3.6 times the radiation ablation pressure, respectively.

In all the experiments mentioned above, it has been demonstrated that the significant phenomena of HD pressure smoothing and symmetric strong HD impact suppress asymmetric ID impact compression of fuel. In addition, backscattering and hot electron energy fractions were measured, both of which were approximately one-third of the DD scheme.

Figure 5: Measurement of DD laser plasma interaction.
The experimental results well demonstrate that the high-density scheme can provide a smooth high-density pressure that is much greater than the radiation ablation pressure. By utilizing the fitting proportional relationship between HD pressure and laser energy, the proportional driving pressure for stable implosion and non stagnant ignition is very consistent, with an error of about 15%. This provides an important reference for the design of high gain ignition targets.

The experimental results confirm the key effects of the HD scheme, providing an effective way for ICF to stabilize implosion and high fusion energy.

Related paper links:
Yan, J., Li, J., He, X.T. et al. Experimental confirmation of driving pressure boosting and smoothing for hybrid drive imperial fusion at the 100-kJ laser facility Nat Commun 14, 5782 (2023) https://doi.org/10.1038/s41467-023-41477-2

Source: Yangtze River Delta Laser Alliance