Modifying ablator composition can reduce hot electron generation in laser-plasma interactions

In direct-drive inertial confinement fusion, laser beams irradiate a fusion fuel capsule to compress it to fusion conditions. However, this ignition process also generates hot, energetic electrons that are undesirable and must be suppressed. Solodov et al. studied the hot electrons in laser-plasma interactions to characterize their effects on ignition designs.

To observe the higher order effects of hot electron generation, the group studied laser-plasma interaction by irradiating disk-shaped targets at different incident angles. This ablates the target material and accelerates its imploded shell toward the center, compressing it into a very small volume with high density and pressure. However, some of the laser’s energy is lost to the heating of the electrons.

“The electrons generated are dangerous when we ramp up the intensity for ignition design,” said author Andrey Solodov. Therefore, strategies for mitigating the hot electrons’ impact on the target are necessary.

The authors demonstrated the ablation of a mid-Z material such as silicon can reduce the number of hot electrons generated. When they replaced a plastic ablator with silicon, it increased the threshold for hot electrons, thereby suppressing their production. This motivates the use of mid-Z layers in a multilayer ablator in direct-drive ignition designs.

According to Solodov, achieving plasma ignition with this scheme is important for a wide variety of applications. The ignition of hydrogen and its isotopes can be used in the development of future power plants, and the ability to study plasmas in extreme conditions has potential use in military design.

Source: “Hot-electron generation at direct-drive ignition-relevant plasma conditions at the National Ignition Facility,” by A. A. Solodov, M. J. Rosenberg, W. Seka, J. F. Myatt, M. Hohenberger, R. Epstein, C. Stoeckl, R. W. Short, S. P. Regan, P. Michel, T. Chapman, R. K. Follett, J. P. Palastro, D. H. Froula, P. B. Radha, J. D. Moody, and V. N. Goncharov, Physics of Plasmas (2020). The article can be accessed at https://doi.org/10.1063/1.5134044 .